@phdthesis{Flatken2022, author = {Flatken, Marion A.}, title = {The early stages of halide perovskites thin film formation}, doi = {10.25932/publishup-55259}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-552599}, school = {Universit{\"a}t Potsdam}, pages = {VI, 144}, year = {2022}, abstract = {As climate change worsens, there is a growing urgency to promote renewable energies and improve their accessibility to society. Here, solar energy harvesting is of particular importance. Currently, metal halide perovskite (MHP) solar cells are indispensable in future solar energy generation research. MHPs are crystalline semiconductors increasingly relevant as low-cost, high-performance materials for optoelectronics. Their processing from solution at low temperature enables easy fabrication of thin film elements, encompassing solar cells and light-emitting diodes or photodetectors. Understanding the coordination chemistry of MHPs in their precursor solution would allow control over the thin film crystallization, the material properties and the final device performance. In this work, we elaborate on the key parameters to manipulate the precursor solution with the long-term objective of enabling systematic process control. We focus on the nanostructural characterization of the initial arrangements of MHPs in the precursor solutions. Small-angle scattering is particularly well suited for measuring nanoparticles in solution. This technique proved to be valuable for the direct analyzes of perovskite precursor solutions in standard processing concentrations without causing radiation damage. We gain insights into the chemical nature of widely used precursor structures such as methylammonium lead iodide (MAPbI3), presenting first insights into the complex arrangements and interaction within this precursor state. Furthermore, we transfer the preceding results to other more complex perovskite precursors. The influence of compositional engineering is investigated using the addition of alkali cations as an example. As a result, we propose a detailed working mechanism on how the alkali cations suppress the formation of intermediate phases and improve the quality of the crystalline thin film. In addition, we investigate the crystallization process of a tin-based perovskite composition (FASnI3) under the influence of fluoride chemistry. We prove that the frequently used additive, tin fluoride (SnF2), selectively binds undesired oxidized tin (Sn(IV)) in the precursor solution. This prevents its incorporation into the actual crystal structure and thus reduces the defect density of the material. Furthermore, SnF2 leads to a more homogeneous crystal growth process, which results in improved crystal quality of the thin film material. In total, this study provides a detailed characterization of the complex system of perovskite precursor chemistry. We thereby cover relevant parameters for future MHP solar cell process control, such as (I) the environmental impact based on concentration and temperature (II) the addition of counter ions to reduce the diffuse layer surrounding the precursor nanostructures and (III) the targeted use of additives to eliminate unwanted components selectively and to ensure a more homogeneous crystal growth.}, language = {en} } @phdthesis{Bastian2022, author = {Bastian, Philipp U.}, title = {Core-shell upconversion nanoparticles - investigation of dopant intermixing and surface modification}, doi = {10.25932/publishup-55160}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-551607}, school = {Universit{\"a}t Potsdam}, pages = {XII, 108, xxiii}, year = {2022}, abstract = {Frequency upconversion nanoparticles (UCNPs) are inorganic nanocrystals capable to up-convert incident photons of the near-infrared electromagnetic spectrum (NIR) into higher energy photons. These photons are re-emitted in the range of the visible (Vis) and even ultraviolet (UV) light. The frequency upconversion process (UC) is realized with nanocrystals doped with trivalent lanthanoid ions (Ln(III)). The Ln(III) ions provide the electronic (excited) states forming a ladder-like electronic structure for the Ln(III) electrons in the nanocrystals. The absorption of at least two low energy photons by the nanoparticle and the subsequent energy transfer to one Ln(III) ion leads to the promotion of one Ln(III) electron into higher excited electronic states. One high energy photon will be emitted during the radiative relaxation of the electron in the excited state back into the electronic ground state of the Ln(III) ion. The excited state electron is the result of the previous absorption of at least two low energy photons. The UC process is very interesting in the biological/medical context. Biological samples (like organic tissue, blood, urine, and stool) absorb high-energy photons (UV and blue light) more strongly than low-energy photons (red and NIR light). Thanks to a naturally occurring optical window, NIR light can penetrate deeper than UV light into biological samples. Hence, UCNPs in bio-samples can be excited by NIR light. This possibility opens a pathway for in vitro as well as in vivo applications, like optical imaging by cell labeling or staining of specific organic tissue. Furthermore, early detection and diagnosis of diseases by predictive and diagnostic biomarkers can be realized with bio-recognition elements being labeled to the UCNPs. Additionally, "theranostic" becomes possible, in which the identification and the treatment of a disease are tackled simultaneously. For this to succeed, certain parameters for the UCNPs must be met: high upconversion efficiency, high photoluminescence quantum yield, dispersibility, and dispersion stability in aqueous media, as well as availability of functional groups to introduce fast and easy bio-recognition elements. The UCNPs used in this work were prepared with a solvothermal decomposition synthesis yielding in particles with NaYF4 or NaGdF4 as host lattice. They have been doped with the Ln(III) ions Yb3+ and Er3+, which is only one possible upconversion pair. Their upconversion efficiency and photoluminescence quantum yield were improved by adding a passivating shell to reduce surface quenching. However, the brightness of core-shell UCNPs stays behind the expectations compared to their bulk material (being at least μm-sized particles). The core-shell structures are not clearly separated from each other, which is a topic in literature. Instead, there is a transition layer between the core and the shell structure, which relates to the migration of the dopants within the host lattice during the synthesis. The ion migration has been examined by time-resolved laser spectroscopy and the interlanthanoid resonance energy transfer (LRET) in the two different host lattices from above. The results are presented in two publications, which dealt with core-shell-shell structured nanoparticles. The core is doped with the LRET-acceptor (either Nd3+ or Pr3+). The intermediate shell serves as an insulation shell of pure host lattice material, whose shell thickness has been varied within one set of samples having the same composition, so that the spatial separation of LRET-acceptor and -donor changes. The outer shell with the same host lattice is doped with the LRET-donor (Eu3+). The effect of the increasing insulation shell thickness is significant, although the LRET cannot be suppressed completely. Next to the Ln(III) migration within a host lattice, various phase transfer reactions were investigated in order to subsequently perform surface modifications for bioapplications. One result out of this research has been published using a promising ligand, that equips the UCNP with bio-modifiable groups and has good potential for bio-medical applications. This particular ligand mimics natural occurring mechanisms of mussel protein adhesion and of blood coagulation, which is why the UCNPs are encapsulated very effectively. At the same time, bio-functional groups are introduced. In a proof-of-concept, the encapsulated UCNP has been coupled successfully with a dye (which is representative for a biomarker) and the system's photoluminescence properties have been investigated.}, language = {en} } @phdthesis{Freyse2022, author = {Freyse, Daniel}, title = {Thioacetal-Bausteine f{\"u}r Fluoreszenzfarbstoffe und molekulare St{\"a}be}, doi = {10.25932/publishup-54925}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549252}, school = {Universit{\"a}t Potsdam}, pages = {292}, year = {2022}, abstract = {Im Rahmen dieser Dissertation wurde der Sauerstoff im Grundger{\"u}st der [1,3]-Dioxolo[4.5-f]benzodioxol-Fluoreszenzfarbstoffe (DBD-Fluoreszenzfarbstoffe) vollst{\"a}ndig mit Schwefel ausgetauscht und daraus eine neue Klasse von Fluoreszenzfarbstoffen entwickelt, die Benzo[1,2-d:4,5-d']bis([1,3]dithiol)-Fluorophore (S4-DBD-Fluorophore). Insgesamt neun der besonders interessanten, difunktionalisierten Vertreter konnten synthetisiert werden, die sich in ihren elektronenziehenden Gruppen und in ihrer Anordnung unterschieden. Durch den Austausch von Sauerstoff mit Schwefel kam es zu teilweise auff{\"a}lligen Ver{\"a}nderungen in den Fluoreszenzparametern, wie eine Abnahme der Fluoreszenzquantenausbeuten und -lebenszeiten aber auch eine deutliche Rotverschiebung in den Absorptions- und Emissionswellenl{\"a}ngen mit großen STOKES-Verschiebungen. Damit sind die S4-DBD-Fluorophore eine wertvolle Erg{\"a}nzung f{\"u}r die DBD-Farbstoffe. Die Ursachen f{\"u}r die Abnahme der Lebenszeiten und Quantenausbeuten konnte auf eine hohe Besetzung des Triplett-Zustandes zur{\"u}ckgef{\"u}hrt werden, welcher durch die verst{\"a}rkten Spin-Bahn-Kopplungen des Schwefels hervorgerufen wird. Zusammen mit dem Arbeitskreis physikalische Chemie der Universit{\"a}t Potsdam konnten auch die photophysikalischen Prozesse {\"u}ber die Transienten-Absorptionsspektroskopie (TAS) aufgekl{\"a}rt werden. Eine Strategie zur Funktionalisierung der S4-DBD-Farbstoffe am Thioacetalger{\"u}st konnte entwickelt werden. So gelang es Alkohol-, Propargyl-, Azid-, NHS-Ester-, Carbons{\"a}ure-, Maleimid- und Tosyl-Gruppen an S4-DBD-Dialdehyden anzubringen. Erweiternd wurden molekulare St{\"a}be auf Basis von Schwefel-Oligo-Spiro-Ketalen (SOSKs) untersucht, bei denen Sauerstoff durch Schwefel ersetzt wurde. Hier konnten die Synthesen der l{\"o}slichkeitsvermittelnden TER-Muffe und auch des Tetrathiapentaerythritols als Grundbaustein deutlich verbessert werden. Aus diesen konnte ein einfaches SOSK-Polymer hergestellt werden. Weitere Versuche zum Aufbau eines Stabes m{\"u}ssen aber noch untersucht werden. Um einen S-OSK-Stab aufzubauen hat sich dabei die Dithiocarbonat-Gruppe in ersten Versuchen als potenzielle geeignete Schutzgruppe f{\"u}r das Tetrathiapentaerythritol herausgestellt.}, language = {de} } @phdthesis{Luedecke2022, author = {L{\"u}decke, Nils}, title = {Bio-sourced adsorbing poly(2-oxazoline)s mimicking mussel glue proteins for antifouling applications}, doi = {10.25932/publishup-54983}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549836}, school = {Universit{\"a}t Potsdam}, pages = {iii, 224}, year = {2022}, abstract = {Nature developed countless systems for many applications. In maritime environments, several organisms established extra-ordinary mechanisms to attach to surfaces. Over the past years, the scientific interest to employ those mechanisms for coatings and long-lasting adhering materials gained significant attention. This work describes the synthesis of bio-inspired adsorbing copoly(2-oxazoline)s for surface coatings with protein repelling effects, mimicking mussel glue proteins. From a set of methoxy substituted phenyl, benzyl, and cinnamyl acids, 2-oxazoline monomers were synthesized. All synthesized 2-oxazolines were analyzed by FT-IR spectroscopy, NMR spectroscopy, and EI mass spectrometry. With those newly synthesized 2-oxazoline monomers and 2-ethyl-2-oxazoline, kinetic studies concerning homo- and copolymerization in a microwave reactor were conducted. The success of the polymerization reactions was demonstrated by FT-IR spectroscopy, NMR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography (SEC). The copolymerization of 2-ethyl-2-oxazoline with a selection of methoxy-substituted 2-oxazolines resulted in water-soluble copolymers. To release the adsorbing catechol and cationic units, the copoly(2-oxazoline)s were modified. The catechol units were (partially) released by a methyl aryl ether cleavage reaction. A subsequent partial acidic hydrolysis of the ethyl unit resulted in mussel glue protein-inspired catechol and cation-containing copolymers. The modified copolymers were analyzed by NMR spectroscopy, UV-VIS spectroscopy, and SEC. The catechol- and cation-containing copolymers and their precursors were examined by a Quartz Crystal Microbalance with Dissipation (QCM-D), so study the adsorption performance on gold, borosilicate, iron, and polystyrene surfaces. An exemplary study revealed that a catechol and cation-containing copoly(2-oxazoline)-coated gold surface exhibits strong protein repelling properties.}, language = {en} } @phdthesis{MathieuGaedke2021, author = {Mathieu-Gaedke, Maria}, title = {Grafting-to and grafting-from proteins - synthesis and characterization of protein-polymer conjugates on the way to biohybrid membrane materials}, doi = {10.25932/publishup-54292}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-542921}, school = {Universit{\"a}t Potsdam}, pages = {XVIII, 149}, year = {2021}, abstract = {The incorporation of proteins in artificial materials such as membranes offers great opportunities to avail oneself the miscellaneous qualities of proteins and enzymes perfected by nature over millions of years. One possibility to leverage proteins is the modification with artificial polymers. To obtain such protein-polymer conjugates, either a polymer can be grown from the protein surface (grafting-from) or a pre-synthesized polymer attached to the protein (grafting-to). Both techniques were used to synthesize conjugates of different proteins with thermo-responsive polymers in this thesis. First, conjugates were analyzed by protein NMR spectroscopy. Typical characterization techniques for conjugates can verify the successful conjugation and give hints on the secondary structure of the protein. However, the 3-dimensional structure, being highly important for the protein function, cannot be probed by standard techniques. NMR spectroscopy is a unique method allowing to follow even small alterations in the protein structure. A mutant of the carbohydrate binding module 3b (CBM3bN126W) was used as model protein and functionalized with poly(N-isopropylacrylamide). Analysis of conjugates prepared by grafting-to or grafting-from revealed a strong impact of conjugation type on protein folding. Whereas conjugates prepared by grafting a pre-formed polymer to the protein resulted in complete preservation of protein folding, grafting the polymer from the protein surface led to (partial) disruption of the protein structure. Next, conjugates of bovine serum albumin (BSA) as cheap and easily accessible protein were synthesized with PNIPAm and different oligoethylene glycol (meth)acrylates. The obtained protein-polymer conjugates were analyzed by an in-line combination of size exclusion chromatography and multi-angle laser light scattering (SEC-MALS). This technique is particular advantageous to determine molar masses, as no external calibration of the system is needed. Different SEC column materials and operation conditions were tested to evaluate the applicability of this system to determine absolute molar masses and hydrodynamic properties of heterogeneous conjugates prepared by grafting-from and grafting-to. Hydrophobic and non-covalent interactions of conjugates lead to error-prone values not in accordance to expected molar masses based on conversions and extents of modifications. As alternative to this method, conjugates were analyzed by sedimentation velocity analytical ultracentrifugation (SV-AUC) to gain insights in the hydrodynamic properties and how they change after conjugation. Within a centrifugal field, a sample moves and fractionates according to the mass, density, and shape of its individual components. Conjugates of BSA with PNIPAm were analyzed below and above the cloud point temperature of the thermo-responsive polymer component. It was identified that the polymer characteristics were transferred to the conjugate molecule which than showed a decreased ideality - defined as increased deviation from a perfect sphere model - below and increased ideality above the cloud point temperature. This effect can be attributed to an arrangement of the polymer chain pointing towards the solvent (expanded state) or snuggling around the protein surface depending on the applied temperature. The last project dealt with the synthesis of ferric hydroxamate uptake protein component A (FhuA)-polymer conjugates as building blocks for novel membrane materials. The shape of FhuA can be described as barrel and removal of a cork domain inside the protein results in a passive channel aimed to be utilized as pores in the membrane system. The polymer matrix surrounding the membrane protein is composed of a thermo-responsive and a UV-crosslinkable part. Therefore, an external trigger for covalent immobilization of these building blocks in the membrane and switchability of the membrane between different states was incorporated. The overall performance of membranes prepared by a drying-mediated self-assembly approach was evaluated by permeability and size exclusion experiments. The obtained membranes displayed an insufficiency in interchain crosslinking and therefore a lack in performance. Furthermore, the aimed switch between a hydrophilic and hydrophobic state of the polymer matrix did not occur. Correspondingly, size exclusion experiments did not result in a retention of analytes larger than the pores defined by the dimension of the used FhuA variant. Overall, different paths to generate protein-polymer conjugates by either grafting-from or grafting-to the protein surface were presented paving the way to the generation of new hybrid materials. Different analytical methods were utilized to describe the folding and hydrodynamic properties of conjugates providing a deeper insight in the overall characteristics of these seminal building blocks.}, language = {en} } @phdthesis{Saretia2021, author = {Saretia, Shivam}, title = {Modulating ultrathin films of semi-crystalline oligomers by Langmuir technique}, doi = {10.25932/publishup-54210}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-542108}, school = {Universit{\"a}t Potsdam}, pages = {XIII, 109}, year = {2021}, abstract = {Polymeric films and coatings derived from semi-crystalline oligomers are of relevance for medical and pharmaceutical applications. In this context, the material surface is of particular importance, as it mediates the interaction with the biological system. Two dimensional (2D) systems and ultrathin films are used to model this interface. However, conventional techniques for their preparation, such as spin coating or dip coating, have disadvantages, since the morphology and chain packing of the generated films can only be controlled to a limited extent and adsorption on the substrate used affects the behavior of the films. Detaching and transferring the films prepared by such techniques requires additional sacrificial or supporting layers, and free-standing or self supporting domains are usually of very limited lateral extension. The aim of this thesis is to study and modulate crystallization, melting, degradation and chemical reactions in ultrathin films of oligo(ε-caprolactone)s (OCL)s with different end-groups under ambient conditions. Here, oligomeric ultrathin films are assembled at the air-water interface using the Langmuir technique. The water surface allows lateral movement and aggregation of the oligomers, which, unlike solid substrates, enables dynamic physical and chemical interaction of the molecules. Parameters like surface pressure (π), temperature and mean molecular area (MMA) allow controlled assembly and manipulation of oligomer molecules when using the Langmuir technique. The π-MMA isotherms, Brewster angle microscopy (BAM), and interfacial infrared spectroscopy assist in detecting morphological and physicochemical changes in the film. Ultrathin films can be easily transferred to the solid silicon surface via Langmuir Schaefer (LS) method (horizontal substrate dipping). Here, the films transferred on silicon are investigated using atomic force microscopy (AFM) and optical microscopy and are compared to the films on the water surface. The semi-crystalline morphology (lamellar thicknesses, crystal number densities, and lateral crystal dimensions) is tuned by the chemical structure of the OCL end-groups (hydroxy or methacrylate) and by the crystallization temperature (Tc; 12 or 21 °C) or MMAs. Compression to lower MMA of ~2 {\AA}2, results in the formation of a highly crystalline film, which consists of tightly packed single crystals. Preparation of tightly packed single crystals on a cm2 scale is not possible by conventional techniques. Upon transfer to a solid surface, these films retain their crystalline morphology whereas amorphous films undergo dewetting. The melting temperature (Tm) of OCL single crystals at the water and the solid surface is found proportional to the inverse crystal thickness and is generally lower than the Tm of bulk PCL. The impact of OCL end-groups on melting behavior is most noticeable at the air-solid interface, where the methacrylate end-capped OCL (OCDME) melted at lower temperatures than the hydroxy end-capped OCL (OCDOL). When comparing the underlying substrate, melting/recrystallization of OCL ultrathin films is possible at lower temperatures at the air water interface than at the air-solid interface, where recrystallization is not visible. Recrystallization at the air-water interface usually occurs at a higher temperature than the initial Tc. Controlled degradation is crucial for the predictable performance of degradable polymeric biomaterials. Degradation of ultrathin films is carried out under acidic (pH ~ 1) or enzymatic catalysis (lipase from Pseudomonas cepcia) on the water surface or on a silicon surface as transferred films. A high crystallinity strongly reduces the hydrolytic but not the enzymatic degradation rate. As an influence of end-groups, the methacrylate end-capped linear oligomer, OCDME (~85 ± 2 \% end-group functionalization) hydrolytically degrades faster than the hydroxy end capped linear oligomer, OCDOL (~95 ± 3 \% end-group functionalization) at different temperatures. Differences in the acceleration of hydrolytic degradation of semi-crystalline films were observed upon complete melting, partial melting of the crystals, or by heating to temperatures close to Tm. Therefore, films of densely packed single crystals are suitable as barrier layers with thermally switchable degradation rates. Chemical modification in ultrathin films is an intricate process applicable to connect functionalized molecules, impart stability or create stimuli-sensitive cross-links. The reaction of end-groups is explored for transferred single crystals on a solid surface or amorphous monolayer at the air-water interface. Bulky methacrylate end-groups are expelled to the crystal surface during chain-folded crystallization. The density of end-groups is inversely proportional to molecular weight and hence very pronounced for oligomers. The methacrylate end-groups at the crystal surface, which are present at high concentration, can be used for further chemical functionalization. This is demonstrated by fluorescence microscopy after reaction with fluorescein dimethacrylate. The thermoswitching behavior (melting and recrystallization) of fluorescein functionalized single crystals shows the temperature-dependent distribution of the chemically linked fluorescein moieties, which are accumulated on the surfaces of crystals, and homogeneously dispersed when the crystals are molten. In amorphous monolayers at the air-water interface, reversible cross-linking of hydroxy-terminated oligo(ε-caprolactone) monolayers using dialdehyde (glyoxal) lead to the formation of 2D networks. Pronounced contraction in the area occurred for 2D OCL films in dependence of surface pressure and time indicating the reaction progress. Cross linking inhibited crystallization and retarded enzymatic degradation of the OCL film. Altering the subphase pH to ~2 led to cleavage of the covalent acetal cross-links. Besides as model systems, these reversibly cross-linked films are applicable for drug delivery systems or cell substrates modulating adhesion at biointerfaces.}, language = {en} } @phdthesis{Schutjajew2021, author = {Schutjajew, Konstantin}, title = {Electrochemical sodium storage in non-graphitizing carbons - insights into mechanisms and synthetic approaches towards high-energy density materials}, doi = {10.25932/publishup-54189}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-541894}, school = {Universit{\"a}t Potsdam}, pages = {v, 148}, year = {2021}, abstract = {To achieve a sustainable energy economy, it is necessary to turn back on the combustion of fossil fuels as a means of energy production and switch to renewable sources. However, their temporal availability does not match societal consumption needs, meaning that renewably generated energy must be stored in its main generation times and allocated during peak consumption periods. Electrochemical energy storage (EES) in general is well suited due to its infrastructural independence and scalability. The lithium ion battery (LIB) takes a special place, among EES systems due to its energy density and efficiency, but the scarcity and uneven geological occurrence of minerals and ores vital for many cell components, and hence the high and fluctuating costs will decelerate its further distribution. The sodium ion battery (SIB) is a promising successor to LIB technology, as the fundamental setup and cell chemistry is similar in the two systems. Yet, the most widespread negative electrode material in LIBs, graphite, cannot be used in SIBs, as it cannot store sufficient amounts of sodium at reasonable potentials. Hence, another carbon allotrope, non-graphitizing or hard carbon (HC) is used in SIBs. This material consists of turbostratically disordered, curved graphene layers, forming regions of graphitic stacking and zones of deviating layers, so-called internal or closed pores. The structural features of HC have a substantial impact of the charge-potential curve exhibited by the carbon when it is used as the negative electrode in an SIB. At defects and edges an adsorption-like mechanism of sodium storage is prevalent, causing a sloping voltage curve, ill-suited for the practical application in SIBs, whereas a constant voltage plateau of relatively high capacities is found immediately after the sloping region, which recent research attributed to the deposition of quasimetallic sodium into the closed pores of HC. Literature on the general mechanism of sodium storage in HCs and especially the role of the closed pore is abundant, but the influence of the pore geometry and chemical nature of the HC on the low-potential sodium deposition is yet in an early stage. Therefore, the scope of this thesis is to investigate these relationships using suitable synthetic and characterization methods. Materials of precisely known morphology, porosity, and chemical structure are prepared in clear distinction to commonly obtained ones and their impact on the sodium storage characteristics is observed. Electrochemical impedance spectroscopy in combination with distribution of relaxation times analysis is further established as a technique to study the sodium storage process, in addition to classical direct current techniques, and an equivalent circuit model is proposed to qualitatively describe the HC sodiation mechanism, based on the recorded data. The obtained knowledge is used to develop a method for the preparation of closed porous and non-porous materials from open porous ones, proving not only the necessity of closed pores for efficient sodium storage, but also providing a method for effective pore closure and hence the increase of the sodium storage capacity and efficiency of carbon materials. The insights obtained and methods developed within this work hence not only contribute to the better understanding of the sodium storage mechanism in carbon materials of SIBs, but can also serve as guidance for the design of efficient electrode materials.}, language = {en} } @phdthesis{Mazzanti2022, author = {Mazzanti, Stefano}, title = {Novel photocatalytic processes mediated by carbon nitride photocatalysis}, doi = {10.25932/publishup-54209}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-542099}, school = {Universit{\"a}t Potsdam}, pages = {418}, year = {2022}, abstract = {The key to reduce the energy required for specific transformations in a selective manner is the employment of a catalyst, a very small molecular platform that decides which type of energy to use. The field of photocatalysis exploits light energy to shape one type of molecules into others, more valuable and useful. However, many challenges arise in this field, for example, catalysts employed usually are based on metal derivatives, which abundance is limited, they cannot be recycled and are expensive. Therefore, carbon nitrides materials are used in this work to expand horizons in the field of photocatalysis. Carbon nitrides are organic materials, which can act as recyclable, cheap, non-toxic, heterogeneous photocatalysts. In this thesis, they have been exploited for the development of new catalytic methods, and shaped to develop new types of processes. Indeed, they enabled the creation of a new photocatalytic synthetic strategy, the dichloromethylation of enones by dichloromethyl radical generated in situ from chloroform, a novel route for the making of building blocks to be used for the productions of active pharmaceutical compounds. Then, the ductility of these materials allowed to shape carbon nitride into coating for lab vials, EPR capillaries, and a cell of a flow reactor showing the great potential of such flexible technology in photocatalysis. Afterwards, their ability to store charges has been exploited in the reduction of organic substrates under dark conditions, gaining new insights regarding multisite proton coupled electron transfer processes. Furthermore, the combination of carbon nitrides with flavins allowed the development of composite materials with improved photocatalytic activity in the CO2 photoreduction. Concluding, carbon nitrides are a versatile class of photoactive materials, which may help to unveil further scientific discoveries and to develop a more sustainable future.}, language = {en} } @phdthesis{Hechenbichler2021, author = {Hechenbichler, Michelle}, title = {New thermoresponsive amphiphilic block copolymers with unconventional chemical structure and architecture}, doi = {10.25932/publishup-54182}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-541822}, school = {Universit{\"a}t Potsdam}, pages = {XIX, 186}, year = {2021}, abstract = {Das Aggregationsverhalten von amphiphilen Blockcpoolymeren ist wichtig f{\"u}r zahlreiche Anwendungen, beispielsweise in der Waschmittelindustrie als Verdicker oder in der Pharmazie zur kontrollierten Freisetzung von Wirkstoffen. Wenn einer der Bl{\"o}cke thermoresponsiv ist, kann das Aggregationsverhalten zus{\"a}tzlich {\"u}ber die Temperatur gesteuert werden. W{\"a}hrend sich die bisherigen Untersuchungen solcher „intelligenten" Systeme zumeist auf einfache Diblockcopolymere beschr{\"a}nkt haben, wurde in der vorliegenden Arbeit die Komplexit{\"a}t der Polymere und damit die Vielseitigkeit dieser Systeme erh{\"o}ht. Dazu wurden spezifische Monomere, verschiedene Blockl{\"a}ngen, unterschiedliche Architekturen und zus{\"a}tzliche funktionelle Gruppen eingef{\"u}hrt. Durch systematische {\"A}nderungen wurde das Struktur-Wirkungsverhalten solcher thermoresponsiver amphiphiler Blockcopolymere untersucht. Dabei sind die Blockcopolymere typischerweise aus einem permanent hydrophoben „Sticker", einem permanent hydrophilen Block sowie einem thermoresponsiven Block, der ein Lower Critical Solution Temperature (LCST) Verhalten zeigt, aufgebaut. W{\"a}hrend der permanent hydrophile Block aus N,N Dimethylacrylamid (DMAm) bestand, wurden f{\"u}r den thermoresponsiven Block unterschiedliche Monomere, n{\"a}mlich N n Propylacrylamid (NPAm), N iso Propylacrylamid (NiPAm), N,N Diethylacrylamid (DEAm), N,N Bis(2 methoxyethyl)acrylamid (bMOEAm), oder N Acryloylpyrrolidin (NAP) mit entsprechend unterschiedlichen LCSTs von 25, 32, 33, 42 und 56 °C verwendet. Die Blockcopolymere wurden mittels aufeinanderfolgender reversibler Additions-Fragmentierungs-Ketten{\"u}bertragungspolymerisation (RAFT Polymerisation) hergestellt, um Polymere mit linearer, doppelt hydrophober sowie symmetrischer Quasi Miktoarm Architektur zu erhalten. Dabei wurden wohldefinierte Blockgr{\"o}ßen, Endgruppen und enge Molmassenverteilungen (Ɖ ≤ 1.3) erzielt. F{\"u}r komplexere Architekturen, wie die doppelt thermoresponsive und die nicht symmetrische Quasi Miktoarm Architekturen, wurde RAFT mit Atomtransfer-Radikalpolymerisation (ATRP) oder Single Unit Monomer Insertion (SUMI), kombiniert. Die dabei erhaltenen Blockcopolymere hatten ebenfalls wohldefinierte Blockl{\"a}ngen, allerdings war die Molmassenverteilung generell breiter (Ɖ ≤ 1.8) und Endgruppen gingen zum Teil verloren, da komplexere Syntheseschritte n{\"o}tig waren. Das thermoresponsive Verhalten in w{\"a}ssriger L{\"o}sung wurde mittels Tr{\"u}bungspunktmessung und Dynamischer Lichtstreuung (DLS) untersucht. Unterhalb der Phasen{\"u}berganstemperatur waren die Polymere l{\"o}slich in Wasser und mizellare Strukturen waren in der DLS sichtbar. Oberhalb der Phasen{\"u}bergangstemperatur war das Aggregationsverhalten dann stark abh{\"a}ngig von der Architektur und der chemischen Struktur des thermoresponsiven Blocks. Thermoresponsive Bl{\"o}cke aus PNAP und PbMOEAm mit einer Blockl{\"a}nge von DPn = 40 zeigten keinen Tr{\"u}bungspunkt (CP) bis hin zu 80 °C, da durch den angebrachten hydrophilen PDMAm Block die bereits hohe LCST der entsprechenden Homopolymere bei den Blockcopolymeren weiter erh{\"o}ht wurde. Blockcopolymere mit PNiPAm, PDEAm und PNPAm hinggeen zeigten abh{\"a}ngig von der Architektur und Blockgr{\"o}ße unterschiedliche CP's. Oberhalb der CP's waren gr{\"o}ßere Aggregate vor allem f{\"u}r die Blockcopolymere mit PNiPAm und PDEAm sichtbar, wohingegen der Phasen{\"u}bergang f{\"u}r Blockcopolymere mit PNPAm stark abh{\"a}ngig von der jeweiligen Architektur war und entsprechend kleinere oder gr{\"o}ßere Aggregate zeigte. Um das Aggregationsverhalten besser zu verstehen, wurden Fluoreszenzstudien an PDMAm und PNiPAm Homo und Blockcopolymeren mit linearer Architektur durchgef{\"u}hrt, welche mit komplement{\"a}ren Fluoreszenzfarbstoffen an den entgegengesetzten Kettenenden funktionalisiert wurden. Das thermoresponsive Verhalten wurde dabei sowohl in Wasser als auch in {\"O}l-in-Wasser Mikroemulsion untersucht. Die Ergebnisse zeigten, dass das Blockcopolymer sich, {\"a}hnlich wie die anderen hergestellten Architekturen, bei niedrigen Temperaturen wie ein Polymertensid verh{\"a}lt. Dabei bilden die hydrophoben Stickergruppen den Kern und die hydrophilen Arme die Corona der Mizelle. Oberhalb des Phasen{\"u}bergangs des PNiPAm Blocks verhielten sich die Blockcopolymere allerdings wie assoziative Telechele mit zwei nicht symmetrischen hydrophoben Endgruppen, die sich untereinander nicht mischten. Daher bildeten die Blockcopolymere anstatt aggregierter „Blumen"-Mizellen gr{\"o}ßere, dynamische Aggregate. Diese sind einerseits {\"u}ber die urspr{\"u}nglichen Mizellkerne bestehend aus den hydrophoben Sticker als auch {\"u}ber Cluster der kollabierten thermoresponsiven Bl{\"o}cke miteinander verkn{\"u}pft. In Mikroemulsion ist diese Art der Netzwerkbildung noch st{\"a}rker ausgepr{\"a}gt.}, language = {en} } @phdthesis{Lood2021, author = {Lood, Kajsa}, title = {Stereoselective Construction of C-C Double Bonds via Olefin Metathesis: From Tethered Reactions to Water-Soluble Catalysts for Stereoretentive Metathesis}, doi = {10.25932/publishup-53914}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-539142}, school = {Universit{\"a}t Potsdam}, pages = {95}, year = {2021}, abstract = {Natural products have proved to be a major resource in the discovery and development of many pharmaceuticals that are in use today. There is a wide variety of biologically active natural products that contain conjugated polyenes or benzofuran structures. Therefore, new synthetic methods for the construction of such building blocks are of great interest to synthetic chemists. The recently developed one-pot tethered ring-closing metathesis approach allows for the formation of Z,E-dienoates in high stereoselectivity. The extension of this method with a Julia-Kocienski olefination protocol would allow for the formation of conjugated trienes in a stereoselective manner. This strategy was applied in the total synthesis of conjugated triene containing (+)-bretonin B. Additionally, investigations of cross metathesis using methyl substituted olefins were pursued. This methodology was applied, as a one-pot cross metathesis/ring-closing metathesis sequence, in the total synthesis of benzofuran containing 7-methoxywutaifuranal. Finally, the design and synthesis of a catalyst for stereoretentive metathesis in aqueous media was investigated.}, language = {en} } @phdthesis{Youk2022, author = {Youk, Sol}, title = {Molecular design of heteroatom-doped nanoporous carbons with controlled porosity and surface polarity for gas physisorption and energy storage}, doi = {10.25932/publishup-53909}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-539098}, school = {Universit{\"a}t Potsdam}, pages = {145}, year = {2022}, abstract = {The world energy consumption has constantly increased every year due to economic development and population growth. This inevitably caused vast amount of CO2 emission, and the CO2 concentration in the atmosphere keeps increasing with economic growth. To reduce CO2 emission, various methods have been developed but there are still many bottlenecks to be solved. Solvents easily absorbing CO2 such as monoethanol-amine (MEA) and diethanolamine, for example, have limitations of solvent loss, amine degradation, vulnerability to heat and toxicity, and the high cost of regeneration which is especially caused due to chemisorption process. Though some of these drawbacks can be compensated through physisorption with zeolites and metal-organic frameworks (MOFs) by displaying significant adsorption selectivity and capacity even in ambient conditions, limitations for these materials still exist. Zeolites demand relatively high regeneration energy and have limited adsorption kinetics due to the exceptionally narrow pore structure. MOFs have low stability against heat and moisture and high manufacturing cost. Nanoporous carbons have recently received attention as an attractive functional porous material due to their unique properties. These materials are crucial in many applications of modern science and industry such as water and air purification, catalysis, gas separation, and energy storage/conversion due to their high chemical and thermal stability, and in particular electronic conductivity in combination with high specific surface areas. Nanoporous carbons can be used to adsorb environmental pollutants or small gas molecules such as CO2 and to power electrochemical energy storage devices such as batteries and fuel cells. In all fields, their pore structure or electrical properties can be modified depending on their purposes. This thesis provides an in-depth look at novel nanoporous carbons from the synthetic and the application point of view. The interplay between pore structure, atomic construction, and the adsorption properties of nanoporous carbon materials are investigated. Novel nanoporous carbon materials are synthesized by using simple precursor molecules containing heteroatoms through a facile templating method. The affinity, and in turn the adsorption capacity, of carbon materials toward polar gas molecules (CO2 and H2O) is enhanced by the modification of their chemical construction. It is also shown that these properties are important in electrochemical energy storage, here especially for supercapacitors with aqueous electrolytes which are basically based on the physisorption of ions on carbon surfaces. This shows that nanoporous carbons can be a "functional" material with specific physical or chemical interactions with guest species just like zeolites and MOFs. The synthesis of sp2-conjugated materials with high heteroatom content from a mixture of citrazinic acid and melamine in which heteroatoms are already bonded in specific motives is illustrated. By controlling the removal procedure of the salt-template and the condensation temperature, the role of salts in the formation of porosity and as coordination sites for the stabilization of heteroatoms is proven. A high amount of nitrogen of up to 20 wt. \%, oxygen contents of up to 19 wt.\%, and a high CO2/N2 selectivity with maximum CO2 uptake at 273 K of 5.31 mmol g-1 are achieved. Besides, the further controlled thermal condensation of precursor molecules and advanced functional properties on applications of the synthesized porous carbons are described. The materials have different porosity and atomic construction exhibiting a high nitrogen content up to 25 wt. \% as well as a high porosity with a specific surface area of more than 1800 m2 g-1, and a high performance in selective CO2 gas adsorption of 62.7. These pore structure as well as properties of surface affect to water adsorption with a remarkably high Qst of over 100 kJ mol-1 even higher than that of zeolites or CaCl2 well known as adsorbents. In addition to that, the pore structure of HAT-CN-derived carbon materials during condensation in vacuum is fundamentally understood which is essential to maximize the utilization of porous system in materials showing significant difference in their pore volume of 0.5 cm3 g-1 and 0.25 cm3 g-1 without and with vacuum, respectively. The molecular designs of heteroatom containing porous carbon derived from abundant and simple molecules are introduced in the presented thesis. Abundant precursors that already containing high amount of nitrogen or oxygen are beneficial to achieve enhanced interaction with adsorptives. The physical and chemical properties of these heteroatom-doped porous carbons are affected by mainly two parameters, that is, the porosity from the pore structure and the polarity from the atomic composition on the surface. In other words, controlling the porosity as well as the polarity of the carbon materials is studied to understand interactions with different guest species which is a fundamental knowledge for the utilization on various applications.}, language = {en} } @phdthesis{Sand2021, author = {Sand, Patrick}, title = {{\"U}bergangsmetallkatalysierte Funktionalisierungsreaktionen an Vinylsulfonylverbindungen}, doi = {10.25932/publishup-53687}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-536879}, school = {Universit{\"a}t Potsdam}, pages = {ix, 169}, year = {2021}, abstract = {Innerhalb dieser Arbeit erfolgte die erstmalige systematische Untersuchung von Vinylsulfons{\"a}ureethylester (1a), Phenylvinylsulfon (1b), N-Benzyl-N-methylethensulfonamid (1c) in der FUJIWARA-MORITANI Reaktion (alternativ als DHR bezeichnet). Bei dieser {\"u}bergangsmetallkatalysierten Reaktion erfolgt der Aufbau einer neuen C-C-Bindung unter der doppelten Aktivierung einer C-H-Bindung. Somit kann ein atom{\"o}konomischer Aufbau von Molek{\"u}len realisiert werden, da keine Beiprodukte in Form von Salzen entstehen. Als aromatischer Reaktant wurden Acetanilide (2) verwendet, damit eine regiospezifische Kupplung durch die katalysatordirigierende Acetamid-Gruppe (CDG) erfolgt. F{\"u}r die Pd-katalysierte DHR wurde eine umfangreiche Optimierung durchgef{\"u}hrt und anschließend konnten neun verschieden, substituierte 2 mit 1a und sieben verschieden, substituierte 2 mit 1b funktionalisiert werden. Da eine Reaktion mit 1c ausblieb, erfolgte ein Wechsel auf eine Ru-katalysierte Methode f{\"u}r die DHR. Mit dieser Methode konnte 1c mit Acetaniliden funktionalisiert werden und das Spektrum der verwendeten 2, in Form von deaktivierenden Substituenten erweitert werden. Im Anschluss wurden die sulfalkenylierten Acetanilide in weiterf{\"u}hrenden Reaktionen untersucht. Hierf{\"u}r wurde eine Reaktionssequenz bestehend aus einer DeacetylierungDiazotierung-Kupplungsreaktion verwendet, um die Acetamid-Gruppe in eine Abgangsgruppe zu {\"u}berf{\"u}hren und danach in einer MATSUDA-HECK Reaktion zu kuppeln. Mit dieser Methode konnten mehrere 1,2-Dialkenylbenzole erhalten werden und die CDG ein weiteres Mal genutzt werden. Neben der {\"U}berf{\"u}hrung der CDG in eine Abgangsgruppe konnte diese auch in die Synthese verschiedener Heterozyklen integriert werden. Daf{\"u}r erfolgte zun{\"a}chst eine 1,3-Zykloaddition durch deprotonierten Tosylmethylisocanid an der elektronenarmen Sulfalkenylgruppe zur Synthese von Pyrrolen. Anschließend erfolgte eine Kupplung der PyrrolFunktion und der CDG durch Zyklokondensation, wodurch Quinoline dargestellt wurden. Durch diese Synthesen konnten Schwefelanaloga des Naturstoffes Marinoquionolin A erhalten werden. Ein weitere {\"u}bergangsmetallkatalysierte C-H-Aktivierungsreaktion, die MATSUDA-HECK Reaktion, wurde genutzt, um 1b zu mit verschieden, subtituierten Diazoniumsalzen zu arylieren. Hier konnten zahlreichen Styrenylsulfone erhalten werden. Der erfolgreiche Einsatz der Vinylsulfonylverbindungen in der Kreuzmetathese konnte innerhalb dieser Arbeit nicht erreicht werden. Daher erfolgte die Synthese verschiedener dialkenylierter Sulfonamide. Hierf{\"u}r wurde die Kettenl{\"a}nge der Alkenyl-Gruppe am Schwefel zwischen 2-3 und am Stickstoff zwischen 3-4 variiert. Der Einsatz der dialkenylierten Sulfonamide erfolgte in den zuvor untersuchten C-H-Aktivierungsmethoden. N-Allyl-N-phenylethensulfonamid (3) konnte erfolgreich in der DHR und HECK Reaktion funktionalisiert werden. Hierbei erfolgte eine methodenspezifische Kupplung in Abh{\"a}ngigkeit von der Elektronendichte der entsprechenden Alkenyl-Gruppe. Die DHR f{\"u}hrte zur selektiven Arylierung der Vinyl-Gruppe und die HECK Reaktion zur Arylierung an der Allyl-Gruppe. Gemischte Produkte wurden nicht erhalten. F{\"u}r die weiteren Diolefine wurde komplexe Produktgemische erhalten. Des Weiteren wurden die Diolefine in der Ringschlussmetathese untersucht und die entsprechenden Sultame in sehr guten Ausbeuten erhalten. Die Verwendung der Sultame in der C-H-Aktivierung war erfolglos. Es wird vermutet, dass f{\"u}r diese zweifachsubstituierten Sulfonamide die vorhandenen Reaktionsbedingungen optimiert werden m{\"u}ssen. Abschließend wurden verschiedene, enantiomerenreine Olefine ausgehend von Levoglucosenon dargestellt. Hierf{\"u}r wurde Levoglucosenon zun{\"a}chst mit einem Allyl- und 3-Butenylgrignard Reagenz umgesetzt. Die entsprechenden Produkte wurden in moderaten Ausbeuten erhalten. Eine weitere Methode begann mit der Reduktion von Levoglucosenon zum Levoglucosenol. Dieser Alkohol wurde mit Allylbromid erfolgreich verethert. Neben der Untersuchungen zur Ethersynthese, erfolgte die Veresterung von Levoglucosenol mit verschiedenen Sulfonylchloriden zu den entsprechenden Sulfons{\"a}ureestern. Diese Olefine wurden in einer Dominometathesereaktion untersucht. Ausgehend vom Allyllevoglucosenylether erfolgte die Darstellung eines Dihydrofurans.}, language = {de} } @phdthesis{Kossmann2021, author = {Kossmann, Janina}, title = {Controlled condensation to functional materials - synergetic effect of nitrogen content and pore structure}, doi = {10.25932/publishup-53693}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-536935}, school = {Universit{\"a}t Potsdam}, pages = {vi, 148}, year = {2021}, abstract = {The development and optimization of carbonaceous materials is of great interest for several applications including gas sorption, electrochemical storage and conversion, or heterogeneous catalysis. In this thesis, the exploration and optimization of nitrogen containing carbonaceous materials by direct condensation of smart chosen, molecular precursors will be presented. As suggested with the concept of noble carbons, the choice of a stable, nitrogen-containing precursor will lead to an even more stable, nitrogen doped carbonaceous material with a controlled structure and electronic properties. Molecules fulfilling this requirement are for example nucleobases. The direct condensation of nucleobases leads to highly nitrogen containing carbonaceous materials without any further post or pretreatment. By using salt melt templating, pore structure adjustment is possible without the use of hazardous or toxic reagents and the template can be reused. Using these simple tools, the synergetic effect of the pore structure and nitrogen content of the materials can be explored. Within this thesis, the influence of the condensation parameters will be correlated to the structure and performance of the materials. First, the influence of the condensation temperature to the porosity and nitrogen content of guanine will be discussed and the exploration of highly CO2 selective structural pores in C1N1 materials will be shown. Further tuning the pore structure of the materials by salt melt templating will be then explored, the potential of the prepared materials as heterogeneous catalysts and their basic catalytic strength will be correlated to their nitrogen content and pore morphology. A similar approach is used to explore the water sorption behavior of uric acid derived carbonaceous materials as potential sorbents for heat transformation applications. Changes in maximum water uptake and hydrophilicity of the prepared materials will be correlated to the nitrogen content and pore architecture. Due to the high thermal stability, porosity, and nitrogen content of ionic liquid derived nitrogen doped carbonaceous materials, a simple impregnation and calcination route can be conducted to obtain copper nano cluster decorated nitrogen-doped carbonaceous materials. The activity as catalyst for the oxygen reduction reaction of the obtained materials will be shown and structure performance relations are discussed. In conclusion, the versatility of nitrogen doped carbonaceous materials with a nitrogen to carbon ratio of up to one will be shown. The possibility to tune the pore structure as well as the nitrogen content by using a simple procedure including salt melt templating as well as the use of molecular precursors and their effect on the performance will be discussed.}, language = {en} } @phdthesis{Brandi2022, author = {Brandi, Francesco}, title = {Integrated biorefinery in continuous flow systems using sustainable heterogeneous catalysts}, doi = {10.25932/publishup-53766}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-537660}, school = {Universit{\"a}t Potsdam}, pages = {xii, 201}, year = {2022}, abstract = {The negative impact of crude oil on the environment has led to a necessary transition toward alternative, renewable, and sustainable resources. In this regard, lignocellulosic biomass (LCB) is a promising renewable and sustainable alternative to crude oil for the production of fine chemicals and fuels in a so-called biorefinery process. LCB is composed of polysaccharides (cellulose and hemicellulose), as well as aromatics (lignin). The development of a sustainable and economically advantageous biorefinery depends on the complete and efficient valorization of all components. Therefore, in the new generation of biorefinery, the so-called biorefinery of type III, the LCB feedstocks are selectively deconstructed and catalytically transformed into platform chemicals. For this purpose, the development of highly stable and efficient catalysts is crucial for progress toward viability in biorefinery. Furthermore, a modern and integrated biorefinery relies on process and reactor design, toward more efficient and cost-effective methodologies that minimize waste. In this context, the usage of continuous flow systems has the potential to provide safe, sustainable, and innovative transformations with simple process integration and scalability for biorefinery schemes. This thesis addresses three main challenges for future biorefinery: catalyst synthesis, waste feedstock valorization, and usage of continuous flow technology. Firstly, a cheap, scalable, and sustainable approach is presented for the synthesis of an efficient and stable 35 wt.-\% Ni catalyst on highly porous nitrogen-doped carbon support (35Ni/NDC) in pellet shape. Initially, the performance of this catalyst was evaluated for the aqueous phase hydrogenation of LCB-derived compounds such as glucose, xylose, and vanillin in continuous flow systems. The 35Ni/NDC catalyst exhibited high catalytic performances in three tested hydrogenation reactions, i.e., sorbitol, xylitol, and 2-methoxy-4-methylphenol with yields of 82 mol\%, 62 mol\%, and 100 mol\% respectively. In addition, the 35Ni/NDC catalyst exhibited remarkable stability over a long time on stream in continuous flow (40 h). Furthermore, the 35Ni/NDC catalyst was combined with commercially available Beta zeolite in a dual-column integrated process for isosorbide production from glucose (yield 83 mol\%). Finally, 35Ni/NDC was applied for the valorization of industrial waste products, namely sodium lignosulfonate (LS) and beech wood sawdust (BWS) in continuous flow systems. The LS depolymerization was conducted combining solvothermal fragmentation of water/alcohol mixtures (i.e.,methanol/water and ethanol/water) with catalytic hydrogenolysis/hydrogenation (SHF). The depolymerization was found to occur thermally in absence of catalyst with a tunable molecular weight according to temperature. Furthermore, the SHF generated an optimized cumulative yield of lignin-derived phenolic monomers of 42 mg gLS-1. Similarly, a solvothermal and reductive catalytic fragmentation (SF-RCF) of BWS was conducted using MeOH and MeTHF as a solvent. In this case, the optimized total lignin-derived phenolic monomers yield was found of 247 mg gKL-1.}, language = {en} } @phdthesis{Haubitz2021, author = {Haubitz, Toni}, title = {Transient absorption spectroscopy}, doi = {10.25932/publishup-53509}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-535092}, school = {Universit{\"a}t Potsdam}, pages = {xiii, 176}, year = {2021}, abstract = {The optical properties of chromophores, especially organic dyes and optically active inorganic molecules, are determined by their chemical structures, surrounding media, and excited state behaviors. The classical optical go-to techniques for spectroscopic investigations are absorption and luminescence spectroscopy. While both techniques are powerful and easy to apply spectroscopic methods, the limited time resolution of luminescence spectroscopy and its reliance on luminescent properties can make its application, in certain cases, complex, or even impossible. This can be the case when the investigated molecules do not luminesce anymore due to quenching effects, or when they were never luminescent in the first place. In those cases, transient absorption spectroscopy is an excellent and much more sophisticated technique to investigate such systems. This pump-probe laser-spectroscopic method is excellent for mechanistic investigations of luminescence quenching phenomena and photoreactions. This is due to its extremely high time resolution in the femto- and picosecond ranges, where many intermediate or transient species of a reaction can be identified and their kinetic evolution can be observed. Furthermore, it does not rely on the samples being luminescent, due to the active sample probing after excitation. In this work it is shown, that with transient absorption spectroscopy it was possible to identify the luminescence quenching mechanisms and thus luminescence quantum yield losses of the organic dye classes O4-DBD, S4-DBD, and pyridylanthracenes. Hence, the population of their triplet states could be identified as the competitive mechanism to their luminescence. While the good luminophores O4-DBD showed minor losses, the S4-DBD dye luminescence was almost entirely quenched by this process. However, for pyridylanthracenes, this phenomenon is present in both the protonated and unprotonated forms and moderately effects the luminescence quantum yield. Also, the majority of the quenching losses in the protonated forms are caused by additional non-radiative processes introduced by the protonation of the pyridyl rings. Furthermore, transient absorption spectroscopy can be applied to investigate the quenching mechanisms of uranyl(VI) luminescence by chloride and bromide. The reduction of the halides by excited uranyl(VI) leads to the formation of dihalide radicals X^(·-2). This excited state redox process is thus identified as the quenching mechanism for both halides, and this process, being diffusion-limited, can be suppressed by cryogenically freezing the samples or by observing these interactions in media with a lower dielectric constant, such as ACN and acetone.}, language = {en} } @phdthesis{Kluge2021, author = {Kluge, Steven}, title = {Integration anorganischer F{\"u}llstoffe in Polysulfonmembranen und Auswirkungen auf die Gastransporteigenschaften}, doi = {10.25932/publishup-53270}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-532700}, school = {Universit{\"a}t Potsdam}, pages = {110}, year = {2021}, abstract = {In der vorliegenden Arbeit wird die Herstellung und Charakterisierung von Mixed-Matrix-Membranen (MMM) f{\"u}r die Gastrennung thematisiert. Dazu wurden verschiedene F{\"u}llstoffe genutzt, um in Verbindung mit dem Membranmaterial Polysulfon MMMs herzustellen. Als F{\"u}llstoffe wurden 3 aktive und 2 passive F{\"u}llstoffe verwendet. Die aktiven F{\"u}llstoffe besaßen Poren{\"o}ffnungen, die in der Lage sind Gase in Abh{\"a}ngigkeit der Molek{\"u}lgr{\"o}ße zu trennen. Daraus folgt ein h{\"o}herer idealer Trennfaktor f{\"u}r bestimmte Gaspaare als in Polysulfon selbst. Aufgrund der durch die Poren gebildeten permanenten Kan{\"a}le in den aktiven F{\"u}llstoffen ergibt sich ein schnellerer Gastransport (Permeabilit{\"a}t) als in Polysulfon. Es handelte sich bei den aktiven F{\"u}llstoffen um den Zeolith SAPO-34 und 2 Chargen eines Zeolitic Imidazolate Framework (ZIF) ZIF-8. Die beiden Chargen ZIF-8 unterschieden sich in ihrer spezifischen Oberfl{\"a}che, was diesen Einfluss speziell in die Untersuchungen zum Gastransport einbeziehen sollte. Bei den passiven F{\"u}llstoffen handelte es sich um ein aminofunktionalisiertes Kieselgel und unpor{\"o}se (dichte) Glask{\"u}gelchen. Das Kieselgel besaß Poren, die zu groß waren, um Gase effektiv zu trennen. Die Glask{\"u}gelchen konnten keine Gastrennung erm{\"o}glichen, da sie keine Poren besaßen. Aus der Literatur ist bekannt, dass die Einbettung von F{\"u}llstoffen oft zu Defekten in MMMs f{\"u}hrt. Ein Ziel dieser Arbeit war es daher die Einbettung zu optimieren. Weiterhin sollte der Gastransport in MMMs dieser Arbeit mit dem in einer unbeladenen Polysulfonmembran verglichen werden. Aufgrund des selektiveren Trennverhaltens der aktiven F{\"u}llstoffe im Vergleich zum Membranmaterial, sollte mit der Einbettung aktiver F{\"u}llstoffe die Trennleistung der MMMs mit steigender F{\"u}llstoffbeladung immer weiter verbessert werden. Um die Eigenschaften der MMMs zu untersuchen, wurden diese mittels Rasterelektronenmikroskop (REM), Gaspermeationsmessungen (GP) und Thermogravimetrischer Analyse gekoppelt mit Massenspektrometrie (TGA-MS) charakterisiert. Untersuchungen am REM konnten eine Verbesserung der Einbettung zeigen, wenn ein polymerer Haftvermittler verwendet wurde. Verglichen wurde die optimierte Einbettung mit der Einbettung ohne Haftvermittler und Ergebnissen aus der Literatur, in der die Verwendung verschiedener Silane als Haftvermittler beschrieben wurde. Trotz der verbesserten Einbettung konnte lediglich bei geringen Beladungen an F{\"u}llstoff (10 und 20 Ma-\% bezogen auf das Membranmaterial) eine geringe Steigerung des idealen Trennfaktors in den MMMs gegen{\"u}ber der unbeladenen Polysulfonmembranen beobachtet werden. Bei h{\"o}heren F{\"u}llstoffbeladungen (30, 40 und 50 Ma-\%) war ein deutlicher Anstieg der Permeabilit{\"a}t bei stark sinkendem idealen Trennfaktor zu beobachten. Mit Hilfe von TGA-MS Messungen konnte dar{\"u}ber hinaus festgestellt werden, dass der verwendete Zeolith SAPO-34 durch Wassermolek{\"u}le blockierte Poren{\"o}ffnungen besaß. Das verhinderte den Gastransport im F{\"u}llstoff, wodurch die Trennleistung des F{\"u}llstoffes nicht ausgenutzt werden konnte. Die F{\"u}llstoffe ZIF-8 (chargenunabh{\"a}ngig) und aminofunktionalisiertes Kieselgel wiesen keine blockierten Poren auf. Dennoch zeigte sich in diesen MMMs keine Verbesserung der Gastrenn- oder Gastransporteigenschaften. MMMs mit dichten Glask{\"u}gelchen als F{\"u}llstoff zeigten dasselbe Gastrenn- und Gastransportverhalten, wie alle MMMs mit den zuvor genannten F{\"u}llstoffen. In dieser Arbeit konnte, trotz optimierter Einbettung anorganischer F{\"u}llstoffe, f{\"u}r MMMs keine Verbesserung der Gastrenn- oder Gastransporteigenschaften nachgewiesen werden. Vielmehr wurde ein Einfluss der F{\"u}llstoffmenge auf die Gastransporteigenschaften in MMMs festgestellt. Die {\"A}nderungen der MMMs gegen{\"u}ber Polysulfon stammen von den Folgen der Einbettung von F{\"u}llstoffen in das Matrixpolymer. Durch die Einbettung werden die Eigenschaften des Matrixpolymers {\"a}ndern, sodass auch der Gastransport beeinflusst wird. Des Weiteren wurde dokumentiert, dass in Abh{\"a}ngigkeit der F{\"u}llstoffbeladung die entstehende Membranstruktur beeinflusst wird. Die Beeinflussung war dabei unabh{\"a}ngig von der F{\"u}llstoffart. Es wurde eine Korrelation zwischen F{\"u}llstoffmenge und ver{\"a}nderter Membranstruktur gefunden.}, language = {de} } @phdthesis{ChandrakanthShetty2021, author = {Chandrakanth Shetty, Sunidhi}, title = {Directed chemical communication in artificial eukaryotic cells}, doi = {10.25932/publishup-53364}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-533642}, school = {Universit{\"a}t Potsdam}, year = {2021}, abstract = {Eukaryotic cells can be regarded as complex microreactors capable of performing various biochemical reactions in parallel which are necessary to sustain life. An essential prerequisite for these complex metabolic reactions to occur is the evolution of lipid membrane-bound organelles enabling compartmental- ization of reactions and biomolecules. This allows for a spatiotemporal control over the metabolic reactions within the cellular system. Intracellular organi- zation arising due to compartmentalization is a key feature of all living cells and has inspired synthetic biologists to engineer such systems with bottom-up approaches. Artificial cells provide an ideal platform to isolate and study specific re- actions without the interference from the complex network of biomolecules present in biological cells. To mimic the hierarchical architecture of eukaryotic cells, multi-compartment assemblies with nested liposomal structures also re- ferred to as multi-vesicular vesicles (MVVs) have been widely adopted. Most of the previously reported multi-compartment systems adopt bulk method- ologies which suffer from low yield and poor control over size. Microfluidic strategies help circumvent these issues and facilitate a high-throughput and robust technique to assemble MVVs of uniform size distribution. In this thesis, firstly, the bulk methodologies are explored to build MVVs and implement a synthetic signalling cascade. Next, a polydimethylsiloxane (PDMS)-based microfluidic platform is introduced to build MVVs and the significance of PEGylated lipids for the successful encapsulation of inner com- partments to generate stable multi-compartment systems is highlighted. Next, a novel two-inlet channel PDMS-based microfluidic device to create MVVs encompassing a three-step enzymatic reaction cascade is presented. A directed reaction pathway comprising of the enzymes α-glucosidase (α-Glc), glucose oxidase (GOx), and horseradish peroxidase (HRP) spanning across three compartments via reconstitution of size-selective membrane proteins is described. Furthermore, owing to the monodispersity of our MVVs due to microfluidic strategies, this platform is employed to study the effect of com- partmentalization on reaction kinetics. Further integration of cell-free expression module into the MVVs would allow for gene-mediated signal transduction within artificial eukaryotic cells. Therefore, the chemically inducible cell-free expression of a membrane protein alpha-hemolysin and its further reconstitution into liposomes is carried out. In conclusion, the present thesis aims to build artificial eukaryotic cells to achieve size-selective chemical communication that also show potential for applications as micro reactors and as vehicles for drug delivery.}, language = {en} } @phdthesis{Bagdahn2021, author = {Bagdahn, Christian}, title = {Synthese und Charakterisierung von Polymerionogelen basierend auf ionischen Fl{\"u}ssigkeiten und Polymethylmethacrylat}, doi = {10.25932/publishup-53287}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-532874}, school = {Universit{\"a}t Potsdam}, pages = {152}, year = {2021}, abstract = {Zentrales Element dieser Arbeit ist die Synthese und Charakterisierung praktisch nutzbarer Ionogele. Die Basis der Polymerionogele bildet das Modellpolymer Polymethylmethacrylat. Als Additive kommen ionische Fl{\"u}ssigkeiten zum Einsatz, deren Grundlage Derivate des vielfach verwendeten Imidazoliumkations sind. Die Eigenschaften der eingebetteten ionischen Fl{\"u}ssigkeiten sind f{\"u}r die Ionogele funktionsgebend. Die Funktionalit{\"a}t der jeweiligen Gele und damit der Transfer der Eigenschaften von ionischen Fl{\"u}ssigkeiten auf die Ionogele wurde in der vorliegenden Arbeit mittels zahlreicher Charakterisierungstechniken {\"u}berpr{\"u}ft und best{\"a}tigt. In dieser Arbeit wurden durch Ionogelbildung makroskopische Ionogelobjekte in Form von Folien und Vliesen erzeugt. Dabei kamen das Filmgießen und das Elektrospinnen als Methoden zur Erzeugung dieser Folien und Vliese zum Einsatz, woraus jeweils ein Modellsystem resultiert. Dadurch wird die vorliegende Arbeit in die Themenkomplexe „elektrisch halbleitende Ionogelfolien" und „antimikrobiell aktive Ionogelvliese" gegliedert. Der Einsatz von triiodidhaltigen ionischen Fl{\"u}ssigkeiten und einer Polymermatrix in einem diskontinuierlichen Gießprozess resultiert in elektrisch halbleitenden Ionogelfolien. Die flexiblen und transparenten Folien k{\"o}nnen Mittelpunkt zahlreicher neuer Anwendungsfelder im Bereich flexibler Elektronik sein. Das Elektrospinnen von Polymethylmethacrylat mit einer ionischen Fl{\"u}ssigkeit f{\"u}hrte zu einem homogen Ionogelvlies, welches ein Modell f{\"u}r die {\"U}bertragung antimikrobiell aktiver Eigenschaften ionischer Fl{\"u}ssigkeiten auf por{\"o}se Strukturen zur Filtration darstellt. Gleichzeitig ist es das erste Beispiel f{\"u}r ein kupferchloridhaltiges Ionogel. Ionogele sind attraktive Materialien mit zahlreichen Anwendungsm{\"o}glichkeiten. Mit der vorliegenden Arbeit wird das Spektrum der Ionogele um ein elektrisch halbleitendes und ein antimikrobiell aktives Ionogel erweitert. Gleichzeitig wurden durch diese Arbeit der Gruppe der ionischen Fl{\"u}ssigkeiten drei Beispiele f{\"u}r elektrisch halbleitende ionische Fl{\"u}ssigkeiten sowie zahlreiche kupfer(II)chloridbasierte ionische Fl{\"u}ssigkeiten hinzugef{\"u}gt.}, language = {de} } @phdthesis{Altabal2021, author = {Altabal, Osamah}, title = {Design and fabrication of geometry-assisted on-demand dosing systems}, doi = {10.25932/publishup-53244}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-532441}, school = {Universit{\"a}t Potsdam}, pages = {xxiv, 122}, year = {2021}, abstract = {The controlled dosage of substances from a device to its environment, such as a tissue or an organ in medical applications or a reactor, room, machinery or ecosystem in technical, should ideally match the requirements of the applications, e.g. in terms of the time point at which the cargo is released. On-demand dosage systems may enable such a desired release pattern, if the device contain suitable features that can translate external signals into a release function. This study is motivated by the opportunities arising from microsystems capable of an on-demand release and the contributions that geometrical design may have in realizing such features. The goals of this work included the design, fabrication, characterization and experimental proof-of-concept of geometry-assisted triggerable dosing effect (a) with a sequential dosing release and (b) in a self-sufficient dosage system. Structure-function relationships were addressed on the molecular, morphological and, with a particular attention, the device design level, which is on the micrometer scale. Models and/or computational tools were used to screen the parameter space and provide guidance for experiments.}, language = {en} } @phdthesis{Kirchhofer2021, author = {Kirchhofer, Tabea}, title = {The development of multi - compartmentalised systems for the directed organisation of artificial cells}, doi = {10.25932/publishup-52842}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-528428}, school = {Universit{\"a}t Potsdam}, pages = {II, 126}, year = {2021}, abstract = {Membrane contact sites are of particular interest in the field of synthetic biology and biophysics. They are involved in a great variety of cellular functions. They form in between two cellular organelles or an organelle and the plasma membrane in order to establish a communication path for molecule transport or signal transmission. The development of an artificial membrane system which can mimic membrane contact sites using bottom up synthetic biology was the goal of this research study. For this, a multi - compartmentalised giant unilamellar vesicle (GUV) system was created with the membrane of the outer vesicle mimicking the plasma membrane and the inner GUVs posing as cellular organelles. In the following steps, three different strategies were used to achieve an internal membrane - membrane adhesion.}, language = {en} } @misc{SchneiderFritzschePuciulMalinowskaetal.2020, author = {Schneider, Matthias and Fritzsche, Nora and Puciul-Malinowska, Agnieszka and Balis, Andrzej and Mostafa, Amr and Bald, Ilko and Zapotoczny, Szczepan and Taubert, Andreas}, title = {Surface etching of 3D printed poly(lactic acid) with NaOH: a systematic approach}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {8}, issn = {1866-8372}, doi = {10.25932/publishup-52508}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-525088}, pages = {18}, year = {2020}, abstract = {The article describes a systematic investigation of the effects of an aqueous NaOH treatment of 3D printed poly(lactic acid) (PLA) scaffolds for surface activation. The PLA surface undergoes several morphology changes and after an initial surface roughening, the surface becomes smoother again before the material dissolves. Erosion rates and surface morphologies can be controlled by the treatment. At the same time, the bulk mechanical properties of the treated materials remain unaltered. This indicates that NaOH treatment of 3D printed PLA scaffolds is a simple, yet viable strategy for surface activation without compromising the mechanical stability of PLA scaffolds.}, language = {en} } @misc{BreternitzLehmannBarnettetal.2019, author = {Breternitz, Joachim and Lehmann, Frederike and Barnett, Sarah A. and Nowell, Harriott and Schorr, Susan}, title = {Zur Rolle der Iodid-Methylammonium-Interaktion in der Ferroelektrizit{\"a}t in CH3NH3PbI3}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.1002/ange.201910599}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-525674}, pages = {7}, year = {2019}, abstract = {Ihre außergew{\"o}hnlich hohen Konversionseffizienzen von {\"u}ber 20 \% und die einfache Zellherstellung machen Hybridperowskite zu heißen Kandidaten f{\"u}r alternative Solarzellenmaterialien. CH3NH3PbI3 als Archetyp dieser Materialklasse besitzt außergew{\"o}hnliche Eigenschaften wie eine sehr effiziente Umwandlung von Solarenergie, wobei besonders Ferroelektrizit{\"a}t als m{\"o}gliche Erkl{\"a}rung in den Fokus ger{\"u}ckt ist. Diese erfordert allerdings eine nicht-zentrosymmetrische Kristallstruktur als notwendige Voraussetzung. Wir stellen hier eine Erkl{\"a}rung des Symmetriebruchs in diesem Material auf kristallographischem, d. h. fernordnungs-basiertem, Wege vor. W{\"a}hrend das Molek{\"u}lkation CH3NH3+ intrinsisch polar ist, ist es extrem fehlgeordnet und kann deshalb nicht die einzige Erkl{\"a}rung darstellen. Es verzerrt allerdings das umgebende Kristallgitter und ruft dadurch eine Verschiebung der Iod-Atome von den zentrosymmetrischen Positionen hervor.}, language = {de} } @misc{BreternitzLehmannBarnettetal.2019, author = {Breternitz, Joachim and Lehmann, Frederike and Barnett, Sarah A. and Nowell, Harriott and Schorr, Susan}, title = {Role of the Iodide-methylammonium interaction in the ferroelectricity of CH3NH3PbI3}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-51822}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-518227}, pages = {7}, year = {2019}, abstract = {Excellent conversion efficiencies of over 20\% and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long-range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions.}, language = {en} } @phdthesis{Dambowsky2021, author = {Dambowsky, Ina}, title = {Bioinspirierte Komposite - Strukturbildung durch Verkleben von Nano- oder Mesokristallen mit funktionalisierten Poly(2-oxazolin)en}, doi = {10.25932/publishup-52367}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-523671}, school = {Universit{\"a}t Potsdam}, pages = {XII, 220}, year = {2021}, abstract = {Die herausragenden mechanischen Eigenschaften nat{\"u}rlicher anorganisch-organischer Kompositmaterialien wie Knochen oder Muschelschalen entspringen ihrer hierarchischen Struktur, die von der nano- bis hinauf zur makroskopischen Ebene reicht, und einer kontrollierten Verbindung entlang der Grenzfl{\"a}chen der anorganischen und organischen Komponenten. Ausgehend von diesen Schl{\"u}sselprinzipien des biologischen Materialdesigns wurden in dieser Arbeit zwei Konzepte f{\"u}r die bioinspirierte Strukturbildung von Kompositen untersucht, die auf dem Verkleben von Nano- oder Mesokristallen mit funktionalisierten Poly(2-oxazolin)-Blockcopolymeren beruhen sowie deren Potenzial zur Herstellung bioinspirierter selbstorganisierter hierarchischer anorganisch-organischer Verbundstrukturen ohne {\"a}ußere Kr{\"a}fte beleuchtet. Die Konzepte unterschieden sich in den verwendeten anorganischen Partikeln und in der Art der Strukturbildung. {\"U}ber einen modularen Ansatz aus Polymersynthese und polymeranaloger Thiol-En-Funktionalisierung wurde erfolgreich eine Bibliothek von Poly(2-oxazolin)en mit unterschiedlichen Funktionalit{\"a}ten erstellt. Die Blockcopolymere bestehen aus einem kurzen partikelaffinen "Klebeblock", der aus Thiol-En-funktionalisiertem Poly(2-(3-butenyl)-2-oxazolin) besteht, und einem langen wasserl{\"o}slichen, strukturbildenden Block, der aus thermoresponsivem und kristallisierbarem Poly(2-isopropyl-2-oxazolin) besteht und hierarchische Morphologien ausbildet. Verschiedene analytische Untersuchungen wie Turbidimetrie, DLS, DSC, SEM oder XRD machten das thermoresponsive bzw. das Kristallisationsverhalten der Blockcopolymere in Abh{\"a}ngigkeit vom eingef{\"u}hrten Klebeblock zug{\"a}nglich. Es zeigte sich, dass diese Polymere ein komplexes temperatur- und pH-abh{\"a}ngiges Tr{\"u}bungsverhalten aufweisen. Hinsichtlich der Kristallisation {\"a}nderte der Klebeblock nicht die nanoskopische Kristallstruktur; er beeinflusste jedoch die Kristallisationszeit, den Kristallisationsgrad und die hierarchische Morphologie. Dieses Ergebnis wurde auf das unterschiedliche Aggregationsverhalten der Polymere in Wasser zur{\"u}ckgef{\"u}hrt. F{\"u}r die Herstellung von Kompositen nutzte Konzept 1 mikrometergroße Kupferoxalat-Mesokristalle, die eine innere Nanostruktur aufweisen. Die Strukturbildung {\"u}ber den anorganischen Teil wurde durch das Verkleben und Anordnen dieser Partikel erstrebt. Konzept 1 erm{\"o}glichte homogene freistehende stabile Kompositfilme mit einem hohen anorganischen Anteil. Die Partikel-Polymer-Kombination vereinte jedoch ung{\"u}nstige Eigenschaften in sich, d. h. ihre L{\"a}ngenskalen waren zu unterschiedlich, was die Selbstassemblierung der Partikel verhinderte. Aufgrund des geringen Aspektverh{\"a}ltnisses von Kupferoxalat blieb auch die gegenseitige Ausrichtung durch {\"a}ußere Kr{\"a}fte erfolglos. Im Ergebnis eignet sich das Kupferoxalat-Poly(2-oxazolin)-Modellsystem nicht f{\"u}r die Herstellung hierarchischer Kompositstrukturen. Im Gegensatz dazu verwendet Konzept 2 scheibenf{\"o}rmige Laponit®-Nanopartikel und kristallisierbare Blockcopolymere zur Strukturbildung {\"u}ber die organische Komponente durch polymervermittelte Selbstassemblierung. Komplement{\"a}re Analysemethoden (Zeta-Potenzial, DLS, SEM, XRD, DSC, TEM) zeigten sowohl eine kontrollierte Wechselwirkung zwischen den Komponenten in w{\"a}ssriger Umgebung als auch eine kontrollierte Strukturbildung, die in selbstassemblierten Nanokompositen resultiert, deren Struktur sich {\"u}ber mehrere L{\"a}ngenskalen erstreckt. Es wurde gezeigt, dass die negativ geladenen Klebebl{\"o}cke spezifisch und selektiv an den positiv geladenen R{\"a}ndern der Laponit®-Partikel binden und so Polymer-Laponit®-Nanohybridpartikel entstehen, die als Grundbausteine f{\"u}r die Kompositbildung dienen. Die Hybridpartikel sind bei Raumtemperatur elektrosterisch stabilisiert - sterisch durch ihre langen, mit Wasser wechselwirkenden Poly(2-isopropyl-2-oxazolin)-Bl{\"o}cke und elektrostatisch {\"u}ber die negativ geladenen Laponit®-Fl{\"a}chen. Im Ergebnis ließ sich Konzept 2 und damit die Strukturbildung {\"u}ber die organische Komponente erfolgreich umsetzten. Das Laponit®-Poly(2-oxazolin)-Modellsystem er{\"o}ffnete den Weg zu selbstassemblierten geschichteten quasi-hierarchischen Nanokompositstrukturen mit hohem anorganischen Anteil. Abh{\"a}ngig von der frei verf{\"u}gbaren Polymerkonzentration bei der Kompositbildung entstanden zwei unterschiedliche Komposit-Typen. Dar{\"u}ber hinaus entwarf die Arbeit einen Erkl{\"a}rungsansatz f{\"u}r den polymervermittelten Bildungsprozess der Komposit-Strukturen. Insgesamt legt diese Arbeit Struktur-Prozess-Eigenschafts-Beziehungen offen, um selbstassemblierte bioinspirierte Kompositstrukturen zu bilden und liefert neue Einsichten zu einer geeigneten Kombination an Komponenten und Herstellungsbedingungen, die eine kontrollierte selbstassemblierte Strukturbildung mithilfe funktionalisierter Poly(2-oxazolin)-Blockcopolymere erlauben.}, language = {de} } @misc{PerovicQinOschatz2020, author = {Perovic, Milena and Qin, Qing and Oschatz, Martin}, title = {From molecular precursors to nanoparticles}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, issn = {1866-8372}, doi = {10.25932/publishup-51614}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-516140}, pages = {23}, year = {2020}, abstract = {Nanoporous carbon materials (NCMs) provide the "function" of high specific surface area and thus have large interface area for interactions with surrounding species, which is of particular importance in applications related to adsorption processes. The strength and mechanism of adsorption depend on the pore architecture of the NCMs. In addition, chemical functionalization can be used to induce changes of electron density and/or electron density distribution in the pore walls, thus further modifying the interactions between carbons and guest species. Typical approaches for functionalization of nanoporous materials with regular atomic construction like porous silica, metal-organic frameworks, or zeolites, cannot be applied to NCMs due to their less defined local atomic construction and abundant defects. Therefore, synthetic strategies that offer a higher degree of control over the process of functionalization are needed. Synthetic approaches for covalent functionalization of NCMs, that is, for the incorporation of heteroatoms into the carbon backbone, are critically reviewed with a special focus on strategies following the concept "from molecules to materials." Approaches for coordinative functionalization with metallic species, and the functionalization by nanocomposite formation between pristine carbon materials and heteroatom-containing carbons, are introduced as well. Particular focus is given to the influences of these functionalizations in adsorption-related applications.}, language = {en} } @misc{SchoenemannKocAldredetal.2019, author = {Sch{\"o}nemann, Eric and Koc, Julian and Aldred, Nick and Clare, Anthony S. and Laschewsky, Andr{\´e} and Rosenhahn, Axel and Wischerhoff, Erik}, title = {Synthesis of novel sulfobetaine polymers with differing dipole orientations in their side chains, and their effects on the antifouling properties}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-52482}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-524820}, pages = {9}, year = {2019}, abstract = {The impact of the orientation of zwitterionic groups, with respect to the polymer backbone, on the antifouling performance of thin hydrogel films made of polyzwitterions is explored. In an extension of the recent discussion about differences in the behavior of polymeric phosphatidylcholines and choline phosphates, a quasi-isomeric set of three poly(sulfobetaine methacrylate)s is designed for this purpose. The design is based on the established monomer 3-[N-2-(methacryloyloxy)ethyl-N,N-dimethyl]ammonio-propane-1-sulfonate and two novel sulfobetaine methacrylates, in which the positions of the cationic and the ionic groups relative to the polymerizable group, and thus also to the polymer backbone, are altered. The effect of the varied segmental dipole orientation on their water solubility, wetting behavior by water, and fouling resistance is compared. As model systems, the adsorption of the model proteins bovine serum albumin (BSA), fibrinogen, and lysozyme onto films of the various polyzwitterion surfaces is studied, as well as the settlement of a diatom (Navicula perminuta) and barnacle cyprids (Balanus improvisus) as representatives of typical marine fouling communities. The results demonstrate the important role of the zwitterionic group's orientation on the polymer behavior and fouling resistance}, language = {en} } @misc{WalkowiakLuGradzielskietal.2020, author = {Walkowiak, Jacek and Lu, Yan and Gradzielski, Michael and Zauscher, Stefan and Ballauff, Matthias}, title = {Thermodynamic analysis of the uptake of a protein in a spherical polyelectrolyte brush}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-51730}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-517307}, pages = {10}, year = {2020}, abstract = {A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding Delta Gb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.}, language = {en} } @misc{NicolaiWeishauptBaesleretal.2021, author = {Nicolai, Merle Marie and Weishaupt, Ann-Kathrin and Baesler, Jessica and Brinkmann, Vanessa and Wellenberg, Anna and Winkelbeiner, Nicola Lisa and Gremme, Anna and Aschner, Michael and Fritz, Gerhard and Schwerdtle, Tanja and Bornhorst, Julia}, title = {Effects of manganese on genomic integrity in the multicellular model organism Caenorhabditis elegans}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1173}, issn = {1866-8372}, doi = {10.25932/publishup-52327}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-523275}, pages = {18}, year = {2021}, abstract = {Although manganese (Mn) is an essential trace element, overexposure is associated with Mn-induced toxicity and neurological dysfunction. Even though Mn-induced oxidative stress is discussed extensively, neither the underlying mechanisms of the potential consequences of Mn-induced oxidative stress on DNA damage and DNA repair, nor the possibly resulting toxicity are characterized yet. In this study, we use the model organism Caenorhabditis elegans to investigate the mode of action of Mn toxicity, focusing on genomic integrity by means of DNA damage and DNA damage response. Experiments were conducted to analyze Mn bioavailability, lethality, and induction of DNA damage. Different deletion mutant strains were then used to investigate the role of base excision repair (BER) and dePARylation (DNA damage response) proteins in Mn-induced toxicity. The results indicate a dose- and time-dependent uptake of Mn, resulting in increased lethality. Excessive exposure to Mn decreases genomic integrity and activates BER. Altogether, this study characterizes the consequences of Mn exposure on genomic integrity and therefore broadens the molecular understanding of pathways underlying Mn-induced toxicity. Additionally, studying the basal poly(ADP-ribosylation) (PARylation) of worms lacking poly(ADP-ribose) glycohydrolase (PARG) parg-1 or parg-2 (two orthologue of PARG), indicates that parg-1 accounts for most of the glycohydrolase activity in worms.}, language = {en} } @misc{KopyraWierzbickaTulwinetal.2021, author = {Kopyra, Janina and Wierzbicka, Paulina and Tulwin, Adrian and Thiam, Guillaume and Bald, Ilko and Rabilloud, Franck and Abdoul-Carime, Hassan}, title = {Experimental and theoretical studies of dissociative electron attachment to metabolites oxaloacetic and citric acids}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1156}, issn = {1866-8372}, doi = {10.25932/publishup-52182}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-521829}, pages = {16}, year = {2021}, abstract = {In this contribution the dissociative electron attachment to metabolites found in aerobic organisms, namely oxaloacetic and citric acids, was studied both experimentally by means of a crossed-beam setup and theoretically through density functional theory calculations. Prominent negative ion resonances from both compounds are observed peaking below 0.5 eV resulting in intense formation of fragment anions associated with a decomposition of the carboxyl groups. In addition, resonances at higher energies (3-9 eV) are observed exclusively from the decomposition of the oxaloacetic acid. These fragments are generated with considerably smaller intensities. The striking findings of our calculations indicate the different mechanism by which the near 0 eV electron is trapped by the precursor molecule to form the transitory negative ion prior to dissociation. For the oxaloacetic acid, the transitory anion arises from the capture of the electron directly into some valence states, while, for the citric acid, dipole- or multipole-bound states mediate the transition into the valence states. What is also of high importance is that both compounds while undergoing DEA reactions generate highly reactive neutral species that can lead to severe cell damage in a biological environment.}, language = {en} } @misc{BlockGuenterRodriguesetal.2021, author = {Block, Inga and G{\"u}nter, Christina and Rodrigues, Alysson Duarte and Paasch, Silvia and Hesemann, Peter and Taubert, Andreas}, title = {Carbon Adsorbents from Spent Coffee for Removal of Methylene Blue and Methyl Orange from Water}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {14}, issn = {1866-8372}, doi = {10.25932/publishup-52165}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-521653}, pages = {20}, year = {2021}, abstract = {Activated carbons (ACs) were prepared from dried spent coffee (SCD), a biological waste product, to produce adsorbents for methylene blue (MB) and methyl orange (MO) from aqueous solution. Pre-pyrolysis activation of SCD was achieved via treatment of the SCD with aqueous sodium hydroxide solutions at 90 °C. Pyrolysis of the pretreated SCD at 500 °C for 1 h produced powders with typical characteristics of AC suitable and effective for dye adsorption. As an alternative to the rather harsh base treatment, calcium carbonate powder, a very common and abundant resource, was also studied as an activator. Mixtures of SCD and CaCO3 (1:1 w/w) yielded effective ACs for MO and MB removal upon pyrolysis needing only small amounts of AC to clear the solutions. A selectivity of the adsorption process toward anionic (MO) or cationic (MB) dyes was not observed.}, language = {en} } @phdthesis{Sanay2021, author = {Sanay, Berran}, title = {Monomers and polymers based on renewable resources for new photopolymer coating}, doi = {10.25932/publishup-51868}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-518684}, school = {Universit{\"a}t Potsdam}, pages = {XXXIII, 124}, year = {2021}, abstract = {The present work focuses on minimising the usage of toxic chemicals by integration of the biobased monomers, derived from fatty acid esters, to photopolymerization processes, which are known to be nature friendly. Internal double bond present in the oleic acid was converted to more reactive (meth)acrylate or epoxy group. Biobased starting materials, functionalized by different pendant groups, were used for photopolymerizing formulations to design of new polymeric structures by using ultraviolet light emitting diode (UV-LED) (395 nm) via free radical polymerization or cationic polymerization. New (meth)acrylates (2,3 and 4) consisting of two isomers, methyl 9-((meth)acryloyloxy)-10-hydroxyoctadecanoate / methyl 9-hydroxy-10-((meth)acryloyloxy)octadecanoate (2 and 3) and methyl 9-(1H-imidazol-1-yl)-10-(methacryloyloxy)octadecanoate / methyl 9-(methacryloyloxy)-10-(1H-imidazol-1-yl)octadecanoate (4), modified from oleic acid mix, and ionic liquid monomers (1a and 1b) bearing long alkyl chain were polymerized photochemically. New (meth)acrylates are based on vegetable oil, and ionic liquids (ILs) have nonvolatile behaviour. Therefore, both monomer types have green approach. Photoinitiated polymerization of new (meth)acrylates and ionic liquids was investigated in the presence of ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate (Irgacure® TPO-L) or di(4-methoxybenzoyl)diethylgermane (Ivocerin®) as photoinitiator (PI). Additionally, the results were discussed in comparison with those obtained from commercial 1,6-hexanediol di(meth)acrylate (5 and 6) for deeper investigation of biobased monomer's potential to substitute petroleum derived materials with renewable resources for possible coating applications. Kinetic study shows that methyl 9-(1H-imidazol-1-yl)-10-(methacryloyloxy)octadecanoate / methyl 9-(methacryloyloxy)-10-(1H-imidazol-1-yl)octadecanoate (4) and ionic liquids (1a and 1b) have quantitative conversion after irradiation process which is important for practical applications. On the other hand, heat generation occurs in a longer time during the polymerization of biobased systems or ILs. The poly(meth)acrylates modified from (meth)acrylated fatty acid methyl ester monomers generally show a low glass transition temperature because of the presence of long aliphatic chain in the polymer structure. However, poly(meth)acrylates containing aromatic group have higher glass transition temperature. Therefore, new 4-(4-methacryloyloxyphenyl)-butan-2-one (7) was synthesized which can be a promising candidate for the green techniques, such as light induced polymerization. Photokinetic investigation of the new monomer, 4-(4-methacryloyloxyphenyl)-butan-2-one (7), was discussed using Irgacure® TPO-L or Ivocerin® as photoinitiator. The reactivity of that monomer was compared to commercial 2-phenoxyethyl methacrylate (8) and phenyl methacrylate (9) basis of the differences on monomer structures. The photopolymer of 4-(4-methacryloyloxyphenyl)-butan-2-one (7) might be an interesting candidate for the coating application with the properties of quantitative conversion and high molecular weight. It also shows higher glass transition temperature. In addition to the linear systems based on renewable materials, new crosslinked polymers were also designed in this thesis. Therefore, isomer mixture consisting of ethane-1,2-diyl bis(9-methacryloyloxy-10-hydroxy octadecanoate), ethane-1,2-diyl 9-hydroxy-10-methacryloyloxy-9'-methacryloyloxy10'-hydroxy octadecanoate and ethane-1,2-diyl bis(9-hydroxy-10-methacryloyloxy octadecanoate) (10) was synthesized by derivation of the oleic acid which has not been previously described in the literature. Crosslinked material based on this biobased monomer was produced by photoinitiated free radical polymerization using Irgacure® TPO-L or Ivocerin® as photoinitiator. Furthermore, material properties were diversified by copolymerization of 10 with 4-(4-methacryloyloxyphenyl)-butan-2-one (7) or methyl 9-(1H-imidazol-1-yl)-10-(methacryloyloxy)octadecanoate / methyl 9-(methacryloyloxy)-10-(1H-imidazol-1-yl)octadecanoate (4). In addition to this, influence of comonomer with different chemical structure on the network system was investigated by analysis of thermo-mechanical properties, crosslink density and molecular weight between two crosslink junctions. An increase in the glass transition temperature caused by copolymerization of biobased monomer 10 with the excess amount of 4-(4-methacryloyloxyphenyl)-butan-2-one (7) was confirmed by both techniques, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). On the other hand, crosslink density decreased as a result of copolymerization reactions due to the reduction in the mean functionality of the system. Furthermore, surface characterization has been tested by contact angle measurements using solvents with different polarity. This work also contributes to the limited data reported about cationic photopolymerization of the epoxidized vegetable oils in the literature in contrast to the widely investigation of thermal curing of the biorenewable epoxy monomers. In addition to the 9,10-epoxystearic acid methyl ester (11), a new monomer of bis-(9,10-epoxystearic acid) 1,2-ethanediyl ester (12) has been synthesized from oleic acid. These two biobased epoxies have been polymerized via cationic photoinitiated polymerization in the presence of bis(t-butyl)-iodonium-tetrakis(perfluoro-t-butoxy)aluminate ([Al(O-t-C4F9)4]-) and isopropylthioxanthone (ITX) as photinitiating system. Polymerization kinetic of 9,10-epoxystearic acid methyl ester (11) and bis-(9,10-epoxystearic acid) 1,2-ethanediyl ester (12) was investigated and compared with the kinetic of commercial monomers being 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate (13), 1,4-butanediol diglycidyl ether (14), and diglycidylether of bisphenol-A (15). Both biobased epoxies (11 and 12) showed higher conversion than cycloaliphatic epoxy (13), and lower reactivity than 1,4-butanediol diglycidyl ether (14). Additional network systems were designed by copolymerization of bis-(9,10-epoxystearic acid) 1,2-ethanediyl ester (12) and diglycidylether of bisphenol-A (15) in different molar ratios (1:1; 1:5; 1:9). It addresses that, final conversion is dependent on polymerization rate as well as physical processes such as vitrification during polymerization. Moreover, low glass transition temperature of homopolymer derived from bis-(9,10-epoxystearic acid) 1,2-ethanediyl ester (12) was successfully increased by copolymerization with diglycidylether bisphenol-A (15). On the other hand, the surface produced from bis-(9,10-epoxystearic acid) 1,2-ethanediyl ester (12) shows hydrophobic character. Higher concentration of biobased diepoxy (12) in the copolymerizing mixture decreases surface free energy. Network systems were also investigated according to the rubber elasticity theory. Crosslinked polymer derived from the mixture of bis-(9,10-epoxystearic acid) 1,2-ethanediyl ester (12) and diglycidylether of bisphenol-A (15) (molar ratio=1:5) exhibits almost ideal polymer network.}, language = {en} } @phdthesis{Izraylit2021, author = {Izraylit, Victor}, title = {Reprogrammable and tunable actuation in multiblock copolymer blends}, doi = {10.25932/publishup-51843}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-518434}, school = {Universit{\"a}t Potsdam}, pages = {104}, year = {2021}, abstract = {Soft actuators have drawn significant attention due to their relevance for applications, such as artificial muscles in devices developed for medicine and robotics. Tuning their performance and expanding their functionality are frequently done by means of chemical modification. The introduction of structural elements rendering non-synthetic modification of the performance possible, as well as control over physical appearance and facilitating their recycling is a subject of a great interest in the field of smart materials. The primary aim of this thesis was to create a shape-memory polymeric actuator, where the capability for non-synthetic tuning of the actuation performance is combined with reprocessability. Physically cross-linked polymeric matrices provide a solid material platform, where the in situ processing methods can be employed for modification of the composition and morphology, resulting in the fine tuning of the related mechanical properties and shape-memory actuation capability. The morphological features, required for shape-memory polymeric actuators, namely two crystallisable domains and anchoring points for physical cross-links, were embedded into a multiblock copolymer with poly(ε-caprolactone) and poly(L-lactide) segments (PLLA-PCL). Here, the melting transition of PCL was bisected into the actuating and skeleton-forming units, while the cross-linking was introduced via PLA stereocomplexation in blends with oligomeric poly(D-lactide) (ODLA). PLLA segment number average length of 12-15 repeating units was experimentally defined to be capable of the PLA stereocomplexes formation, but not sufficient for the isotactic crystallisation. Multiblock structure and phase dilution broaden the PCL melting transition, facilitating its separation into two conditionally independent crystalline domains. Low molar mass of the PLA stereocomplex components and a multiblock structure enables processing and reprocessing of the PLLA-PCL / ODLA blends with common non-destructive techniques. The modularity of the PLLA-PCL structure and synthetic approach allows for independent tuning of the properties of its components. The designed material establishes a solid platform for non-synthetic tuning of thermomechanical and structural properties of thermoplastic elastomers. To evaluate the thermomechanical stability of the formed physical network, three criteria were appraised. As physical cross-links, PLA stereocomplexes have to be evenly distributed within the material matrix, their melting temperature shall not overlap with the thermal transitions of the PCL domains and they have to maintain the structural integrity within the strain ε ranges further applied in the shape-memory actuation experiments. Assigning PCL the function of the skeleton-forming and actuating units, and PLA stereocomplexes the role of physical netpoints, shape-memory actuation was realised in the PLLA-PCL / ODLA blends. Reversible strain of shape-memory actuation was found to be a function of PLA stereocomplex crystallinity, i.e. physical cross-linking density, with a maximum of 13.4 ± 1.5\% at PLA stereocomplex content of 3.1 ± 0.3 wt\%. In this way, shape-memory actuation can be tuned via adjusting the composition of the PLLA-PCL / ODLA blend. This makes the developed material a valuable asset in the production of cost-effective tunable soft polymeric actuators for the applications in medicine and soft robotics.}, language = {en} } @misc{BaldKeller2014, author = {Bald, Ilko and Keller, Adrian}, title = {Molecular processes studied at a single-molecule level using DNA origami nanostructures and atomic force microscopy}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {9}, issn = {1866-8372}, doi = {10.25932/publishup-47584}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475843}, pages = {13803 -- 13823}, year = {2014}, abstract = {DNA origami nanostructures allow for the arrangement of different functionalities such as proteins, specific DNA structures, nanoparticles, and various chemical modifications with unprecedented precision. The arranged functional entities can be visualized by atomic force microscopy (AFM) which enables the study of molecular processes at a single-molecular level. Examples comprise the investigation of chemical reactions, electron-induced bond breaking, enzymatic binding and cleavage events, and conformational transitions in DNA. In this paper, we provide an overview of the advances achieved in the field of single-molecule investigations by applying atomic force microscopy to functionalized DNA origami substrates.}, language = {en} } @phdthesis{John2021, author = {John, Leonard}, title = {Neuartige DBD-Fluoreszenzfarbstoffe}, doi = {10.25932/publishup-51048}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-510487}, school = {Universit{\"a}t Potsdam}, pages = {257}, year = {2021}, abstract = {Zusammenfassung zur Dissertation „Neuartige DBD-Fluoreszenzfarbstoffe: Synthese, Untersuchungen und Anwendungen" von Leonard John In dieser Arbeit konnten auf Basis der etablierten [1,3]-Dioxolo[4,5-f][1,3]benzodioxol (DBD) Fluoreszenzfarbstoffe zwei neue Konzepte zur Darstellung unsymmetrisch funktionalisierter DBD-Fluorophore entwickelt werden. Die Variation der elektronenziehenden Reste f{\"u}hrte zu einer Erweiterung des Farbspektrums an DBD-Fluorophoren, wobei alle weiteren spektroskopischen Parameter (Fluoreszenzlebenszeit, -quantenausbeute und STOKES-Verschiebung) unver{\"a}ndert hohe Werte aufweisen. Neben der Variation der elektronenziehenden Reste wurde das "pi"-System des DBD-Farbstoffs mit der Einf{\"u}hrung von Stilben-, und Tolan-Derivaten vergr{\"o}ßert. Stilben-Derivate zeigten {\"a}hnlich gute spektroskopische Eigenschaften wie die bereits etablierten DBD-Farbstoffe. Fluorophore mit langwelliger Emission sind auf Grund der großen Gewebe-Eindringtiefe besonders interessant f{\"u}r biologische Anwendungen. Da der langwelligste Vertreter der O4-DBD-Farbstoffe in polaren Medien nur schwer l{\"o}slich ist, wurde ein Weg zur Einf{\"u}hrung l{\"o}slichkeitsvermittelnder Gruppen gesucht. Hierbei fiel die Wahl auf eine Carbons{\"a}ure-Gruppe zur Steigerung der Hydrophilie. Eine von vier untersuchten Methoden erwies sich als zielf{\"u}hrend, sodass das gew{\"u}nschte Molek{\"u}l isoliert werden konnte. Eine erh{\"o}hte Wasserl{\"o}slichkeit wurde allerdings nicht beobachtet. Zur Erforschung von Fettstoffwechselkrankheiten wie der ALZHEIMER-Krankheit werden fluoreszenzmarkierte Lipide ben{\"o}tigt. Um unterschiedliche Bereiche einer Membran zu untersuchen, war das Ziel, den Fluorophor an unterschiedlichen Stellen innerhalb der Fetts{\"a}ure zu lokalisieren. Hierbei sollte die Gesamtkettenl{\"a}nge des DBD-Lipids einer C18-Kette, analog der Stearins{\"a}ure, entsprechen. Durch die stufenweise Einf{\"u}hrung der Reste gelang es, drei DBD-Lipide herzustellen, wobei sich der Fluorophor an unterschiedlichen Positionen innerhalb der Kette befindet. Die photophysikalischen Eigenschaften der Lipide weichen nur marginal von denen der reinen Fluorophore ab. Eine Einlagerung in giant unilamellar vesicles (GUVs) konnte f{\"u}r zwei Derivate beobachtet werden, wobei keine dom{\"a}nenspezifisch war. Ein weiteres Ziel dieser Arbeit war es, die vier Sauerstoffatome im DBD-Grundk{\"o}rper stufenweise durch Schwefelatome zu ersetzen und die Ringgr{\"o}ßen des DBD-Fluorophors zu variieren. F{\"u}r die Ringgr{\"o}ße zeigte der 1,2-S2-DBD mit jeweils zwei F{\"u}nfringen die besten spektroskopischen Eigenschaften. Durch die Synthese von zwei weiteren schwefelhaltigen DBD-Grundk{\"o}rpern (S1- und 1,4-S2-DBD) konnten insgesamt drei neue Farbstoffklassen zug{\"a}nglich gemacht werden. F{\"u}r alle neuen Chromophore wurden elektronenziehende Reste (Aldehyd, Acyl, Ester, Carboxy) eingef{\"u}hrt und die jeweiligen Derivate spektroskopisch untersucht. Mit steigender Anzahl an Schwefel-Atomen im Grundk{\"o}rper zeigt sich eine bathochrome Verschiebung der Emission, wobei die Werte f{\"u}r die Fluoreszenzlebenszeit- und -quantenausbeute abnehmen. Die optimalen spektroskopischen Eigenschaften aus langwelliger Emission, hoher Fluoreszenzlebenszeit und -quantenausbeute zeigt das 1,4-S2-Dialdehyd-Derivat. F{\"u}r die S1- und 1,2-S2-Dialdehyd- Derivate wurden Konzepte entwickelt, um bioreaktive Reste (Alkin, HOSu, Maleimid) einzuf{\"u}hren und die Fluorophore in biologischen Systemen anwenden zu k{\"o}nnen.}, language = {de} } @phdthesis{Kaestner2021, author = {Kaestner, Pia Isabel}, title = {Neue Polymermaterialien auf der Basis von funktionalisierten ionischen Fl{\"u}ssigkeiten zur potentiellen Anwendung in Membranen}, doi = {10.25932/publishup-50940}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-509403}, school = {Universit{\"a}t Potsdam}, pages = {VI, 164}, year = {2021}, abstract = {Die vorliegende Arbeit thematisiert die Synthese und Charakterisierung von neuen funktionalisierten ionischen Fl{\"u}ssigkeiten und deren Polymerisation. Die ionischen Fl{\"u}ssigkeiten wurden dabei sowohl mit polymerisierbaren Kationen als auch Anionen hergestellt. Zum einen wurden bei thermisch initiierten Polymerisationen Azobis(isobutyronitril) (AIBN) verwendet und zum anderen dienten bei photochemisch initiierten Polymerisationen Bis-4-(methoxybenzoyl)diethylgermanium (Ivocerin®) als Radikalstarter. Mittels Gelpermeationschromatographie konnte das Homopolymer Polydimethylaminoethylmethacrylat untersucht werden, welches erst im Anschluss an die GPC-Messungen polymeranalog modifiziert wurde. Dabei wurden nach einer Quaternisierung und anschließender Anionenmetathese bei diesen Polymeren die Grenzviskosit{\"a}ten bestimmt und mit den Grenzviskosit{\"a}ten der direkt polymerisierten ionischen Fl{\"u}ssigkeiten verglichen. Bei der direkten Polymerisation von Poly(N-[2-(Methacryloyloxy)ethyl]-N-butyl-N,N-dimethyl-ammoniumbis(trifluormethylsulfonyl)imid) lag [η_Huggins] bei 100 mL/g und bei dem polymeranalog hergestellten Polymer betrug [η_Huggins] = 40 mL/g. Die ionischen Fl{\"u}ssigkeiten mit polymerisierbaren funktionellen Gruppen wurden mittels Photo-DSC hinsichtlich der maximalen Polymerisationsgeschwindigkeit (Rpmax), der Zeit, in der dieses Maximum erreicht wurde, tmax, ihrer Glas{\"u}berganstemperatur (Tg) und des Umsatzes an Vinylprotonen untersucht. Bei diesen Messungen wurde zum einen der Einfluss der unterschiedlichen Alkylkettenl{\"a}nge am Ammoniumion und der Einfluss von verschiedenen Anionen bei gleichbleibender Kationenstruktur analysiert. So polymerisierte das ethylsubstituierte Kation mit einer tmax von 21 Sekunden am langsamsten. Die maximale Polymerisationsgeschwindigkeit (Rpmax) betrug 3.3∙10-2 s-1. Die tmax Werte der {\"u}brigen alkylsubstituierten ionischen Fl{\"u}ssigkeiten mit einer polymerisierbaren funktionellen Gruppe hingegen lagen zwischen 10 und 15 Sekunden. Die Glas{\"u}bergangstemperaturen der mittels photoinduzierter Polymerisation hergestellten Polymere lagen mit 44 bis 55 °C nahe beieinander. Alle Monomere zeigten einen hohen Umsatz der Vinylprotonen; er betrug zwischen 93 und 100\%. Mithilfe einer Bandanlage, ausger{\"u}stet mit einer LED (λ = 395 nm), konnten Polymerfilme hergestellt werden. Der Umsatz an Doppelbindungs{\"a}quivalenten dieser Filme wurde anhand der 1H-NMR Spektroskopie bestimmt. Bei der dynamisch-mechanischen Analyse wurden die Polymerfilme mit einer konstanten Heizrate und Frequenz periodisch wechselnden Beanspruchungen ausgesetzt, um die Glas{\"u}bergangstemperaturen zu bestimmen. Die niedrigste Tg mit 26 °C besaß das butylsubstituierte N-[2-(Methacryloyloxy)ethyl]-N-butyl-N,N-dimethyl-ammoniumbis(trifluormethylsulfonyl)imid, welches als Polymerfilm mit Ivocerin® als Initiator hergestellt wurde, wohingegen die h{\"o}chste Tg bei dem gleichen Polymer, welches direkt durch freie radikalische Polymerisation der ionischen Fl{\"u}ssigkeit in Masse mit AIBN hergestellt wurde, 51 °C betrug. Zus{\"a}tzlich wurden die Filme unter dem Aspekt der Topographie mit einem Rasterkraftmikroskop untersucht, welches eine Dom{\"a}nenstruktur des Polymers N-[2-(methacryloyloxy)ethyl]-N-butyl-N,N-dimethyl-ammonium tris(pentafluorethyl)trifluorphosphat offenbarte.}, language = {de} } @phdthesis{Czarnecki2021, author = {Czarnecki, Maciej}, title = {Untersuchungen zur Synthese von (1,7)-Naphthalenophanen {\"u}ber eine Dehydro-DIELS-ALDER-Reaktion als Schl{\"u}sselschritt}, doi = {10.25932/publishup-50867}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-508670}, school = {Universit{\"a}t Potsdam}, pages = {vii, 227, XXX}, year = {2021}, abstract = {Die vorliegende Dissertation behandelt drei thematische Schwerpunkte. Im Ergebnisteil steht die chemische Synthese von sogenannten (1,7)-Naphthalenophanen im Vordergrund, die zur Substanzklasse von Cyclophanen geh{\"o}ren. W{\"a}hrend zahlreiche Synthesemethoden Strategien zum Aufbau von Ringsystemen (wie z. B. von Naphthalenophanen) verfolgen, die Teil einer bereits existierenden aromatischen Struktur der Ausgangsverbindung sind, nutzen nur wenige Ans{\"a}tze Reaktionen, die einen Ringschluss zum gew{\"u}nschten Produkt erst im Zuge der Synthese etablieren. Eine Benzanellierung, die eine besondere Aufmerksamkeit im Arbeitskreis erfahren hat, ist die Dehydro-DIELS-ALDER-Reaktion (DDA-Reaktion). Im Rahmen dieser Arbeit konnte gezeigt werden, dass zw{\"o}lf ausgew{\"a}hlte (1,7)-Naphthalenophane, die teilweise ringgespannt und makrozyklisch aufgebaut waren, mithilfe einer photochemischen Variante der DDA-Reaktion (PDDA-Reaktion) zug{\"a}nglich gemacht werden k{\"o}nnen. Die Versuche, auf thermischem Wege (TDDA-Reaktion) (1,7)-Naphthalenophane herzustellen, misslangen. Die außergew{\"o}hnliche Reaktivit{\"a}t der Photoreaktanten konnte mithilfe quantenchemischer Berechnungen durch eine gefaltete Grundzustandsgeometrie erkl{\"a}rt werden. Dar{\"u}ber hinaus wurden Ringspannungen und strukturelle Spannungsindikatoren der relevanten Photoprodukte ermittelt und Trends in Abh{\"a}ngigkeit der Linkerl{\"a}nge in den NMR-Spektren der Zielverbindungen ermittelt sowie diskutiert. Zudem zeigte eine Variation am Chromophor (Acyl-, Carbons{\"a}ure- und Carbons{\"a}ureester) der Photoreaktanten bei der Bestrahlung in Dichlormethan eine vergleichbare Photokinetik und -reaktivit{\"a}t. Der zweite Abschnitt dieser Dissertation ist dem Design und der Entwicklung zweier Photoreaktoren f{\"u}r UV-Anwendungen im kontinuierlichen Durchfluss gewidmet, da photochemische Transformationen bekanntermaßen in ihrer Skalierbarkeit limitiert sind. Im ersten Prototyp konnten mittels effizienter Parallelschaltung mit bis zu drei UV-Lampen (𝜆𝜆 = 254, 310 und 355 nm) Produktmaterialmengen von bis zu n = 188 mmol anhand eines ausgew{\"a}hlten Fallbeispiels erreicht werden. Im konstruktionstechnisch stark vereinfachten zweiten Photoreaktor wurden alle quarzhaltigen Elemente gegen g{\"u}nstigeres PLEXIGLAS® ersetzt. Das Resultat waren identische Raum-Zeit-Ausbeuten in Bezug auf das zuvor gew{\"a}hlte Synthesebeispiel. Demnach bietet die UV-Photochemie im kontinuierlichen Durchfluss Vorteile gegen{\"u}ber der traditionellen Bestrahlung im Tauchreaktor. Hinsichtlich Reaktionszeit, Produktausbeuten und L{\"o}semittelverbrauch ist sie synthetisch weit {\"u}berlegen. Im letzten Abschnitt der Arbeit wurden diese Erkenntnisse genutzt, um biomedizinisch und pharmakologisch vielversprechende 1-Arylnaphthalen-Lignane mittels einer intramolekularen PDDA-Reaktion (IMPDDA-Reaktion) als Schl{\"u}sselschritt herzustellen. Hierzu wurden drei Konzepte erarbeitet und in der Totalsynthese von drei ausgew{\"a}hlten Zielstrukturen auf Basis des 1-Arylnaphthalengrundger{\"u}sts realisiert.}, language = {de} } @phdthesis{Ebel2021, author = {Ebel, Kenny}, title = {Quantification of low-energy electron induced single and double strand breaks in well-defined DNA sequences using DNA origami nanostructures}, doi = {10.25932/publishup-50449}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-504499}, school = {Universit{\"a}t Potsdam}, pages = {111}, year = {2021}, abstract = {Ionizing radiation is used in cancer radiation therapy to effectively damage the DNA of tumors leading to cell death and reduction of the tumor tissue. The main damage is due to generation of highly reactive secondary species such as low-energy electrons (LEE) with the most probable energy around 10 eV through ionization of water molecules in the cells. A simulation of the dose distribution in the patient is required to optimize the irradiation modality in cancer radiation therapy, which must be based on the fundamental physical processes of high-energy radiation with the tissue. In the present work the accurate quantification of DNA radiation damage in the form of absolute cross sections for LEE-induced DNA strand breaks (SBs) between 5 and 20 eV is done by using the DNA origami technique. This method is based on the analysis of well-defined DNA target sequences attached to DNA origami triangles with atomic force microscopy (AFM) on the single molecule level. The present work focuses on poly-adenine sequences (5'-d(A4), 5'-d(A8), 5'-d(A12), 5'-d(A16), and 5'- d(A20)) irradiated with 5.0, 7.0, 8.4, and 10 eV electrons. Independent of the DNA length, the strand break cross section shows a maximum around 7.0 eV electron energy for all investigated oligonucleotides confirming that strand breakage occurs through the initial formation of negative ion resonances. Additionally, DNA double strand breaks from a DNA hairpin 5'-d(CAC)4T(Bt-dT)T2(GTG)4 are examined for the first time and are compared with those of DNA single strands 5'-d(CAC)4 and 5'- d(GTG)4. The irradiation is made in the most likely energy range of 5 to 20 eV with an anionic resonance maximum around 10 eV independently of the DNA sequence. There is a clear difference between σSSB and σDSB of DNA single and double strands, where the strand break for ssDNA are always higher in all electron energies compared to dsDNA by the factor 3. A further part of this work deals with the characterization and analysis of new types of radiosensitizers used in chemoradiotherapy, which selectively increases the DNA damage upon radiation. Fluorinated DNA sequences with 2'-fluoro-2'-deoxycytidine (dFC) show an increased sensitivity at 7 and 10 eV compared to the unmodified DNA sequences by an enhancement factor between 2.1 and 2.5. In addition, light-induced oxidative damage of 5'-d(GTG)4 and 5'-d((CAC)4T(Bt-dT)T2(GTG)4) modified DNA origami triangles by singlet oxygen 1O2 generated from three photoexcited DNA groove binders [ANT994], [ANT1083] and [Cr(ddpd)2][BF4]3 illuminated in different experiments with UV-Vis light at 430, 435 and 530 nm wavelength is demonstrated. The singlet oxygen induced generation of DNA damage could be detected in both aqueous and dry environments for [ANT1083] and [Cr(ddpd)2][BF4]3.}, language = {en} } @misc{SchwarzeRiemerMuelleretal.2019, author = {Schwarze, Thomas and Riemer, Janine and M{\"u}ller, Holger and John, Leonard and Holdt, Hans-J{\"u}rgen and Wessig, Pablo}, title = {Na+ Selective Fluorescent Tools Based on Fluorescence Intensity Enhancements, Lifetime Changes, and on a Ratiometric Response}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1136}, issn = {1866-8372}, doi = {10.25932/publishup-43748}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-437482}, pages = {13}, year = {2019}, abstract = {Over the years, we developed highly selective fluorescent probes for K+ in water, which show K+-induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1-K4). In this paper, we introduce selective fluorescent probes for Na+ in water, which also show Na+ induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent probes 2, 4, 5, 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na+ responsive ionophore unit and the fluorophore moiety to adjust different K-d values for an intra- or extracellular Na+ analysis. Thus, we found that 2, 4 and 5 are Na+ selective fluorescent tools, which are able to measure physiologically important Na+ levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na+ levels by fluorescence lifetime changes. Herein, only 8 (K-d=106 mm) is a capable fluorescent tool to measure Na+ levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na+ induced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 (K-d=78 mm) showed a ratiometric fluorescence response towards Na+ ions and is a suitable tool to measure physiologically relevant Na+ levels by the intensity change of two emission wavelengths at 404 nm and 492 nm.}, language = {en} } @misc{BauchFudickarLinker2021, author = {Bauch, Marcel and Fudickar, Werner and Linker, Torsten}, title = {Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1116}, issn = {1866-8372}, doi = {10.25932/publishup-49336}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-493361}, pages = {19}, year = {2021}, abstract = {Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.}, language = {en} } @misc{MachatschekSchoeneRaschdorfetal.2019, author = {Machatschek, Rainhard Gabriel and Sch{\"o}ne, Anne-Christin and Raschdorf, Elisa and Ihlenburg, Ramona and Schulz, Burkhard and Lendlein, Andreas}, title = {Interfacial properties of morpholine-2,5-dione-based oligodepsipeptides and multiblock copolymers}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1106}, issn = {1866-8372}, doi = {10.25932/publishup-46975}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469755}, pages = {170 -- 180}, year = {2019}, abstract = {Oligodepsipeptides (ODPs) with alternating amide and ester bonds prepared by ring-opening polymerization of morpholine-2,5-dione derivatives are promising matrices for drug delivery systems and building blocks for multifunctional biomaterials. Here, we elucidate the behavior of three telechelic ODPs and one multiblock copolymer containing ODP blocks at the air-water interface. Surprisingly, whereas the oligomers and multiblock copolymers crystallize in bulk, no crystallization is observed at the air-water interface. Furthermore, polarization modulation infrared reflection absorption spectroscopy is used to elucidate hydrogen bonding and secondary structures in ODP monolayers. The results will direct the development of the next ODP-based biomaterial generation with tailored properties for highly sophisticated applications.}, language = {en} } @misc{JiangMansfeldKratzetal.2019, author = {Jiang, Yi and Mansfeld, Ulrich and Kratz, Karl and Lendlein, Andreas}, title = {Programmable microscale stiffness pattern of flat polymeric substrates by temperature-memory technology}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, volume = {9}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-46974}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469745}, pages = {181 -- 188}, year = {2019}, abstract = {Temperature-memory technology was utilized to generate flat substrates with a programmable stiffness pattern from cross-linked poly(ethylene-co-vinyl acetate) substrates with cylindrical microstructures. Programmed substrates were obtained by vertical compression at temperatures in the range from 60 to 100 degrees C and subsequent cooling, whereby a flat substrate was achieved by compression at 72 degrees C, as documented by scanning electron microscopy and atomic force microscopy (AFM). AFM nanoindentation experiments revealed that all programmed substrates exhibited the targeted stiffness pattern. The presented technology for generating polymeric substrates with programmable stiffness pattern should be attractive for applications such as touchpads. optical storage, or cell instructive substrates.}, language = {en} } @misc{IhlenburgLehnenKoetzetal.2021, author = {Ihlenburg, Ramona and Lehnen, Anne-Catherine and Koetz, Joachim and Taubert, Andreas}, title = {Sulfobetaine Cryogels for Preferential Adsorption of Methyl Orange from Mixed Dye Solutions}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1093}, issn = {1866-8372}, doi = {10.25932/publishup-48898}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-488987}, pages = {13}, year = {2021}, abstract = {New cryogels for selective dye removal from aqueous solution were prepared by free radical polymerization from the highly water-soluble crosslinker N,N,N',N'-tetramethyl-N,N'-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The resulting white and opaque cryogels have micrometer sized pores with a smaller substructure. They adsorb methyl orange (MO) but not methylene blue (MB) from aqueous solution. Mixtures of MO and MB can be separated through selective adsorption of the MO to the cryogels while the MB remains in solution. The resulting cryogels are thus candidates for the removal of hazardous organic substances, as exemplified by MO and MB, from water. Clearly, it is possible that the cryogels are also potentially interesting for removal of other compounds such as pharmaceuticals or pesticides, but this must be investigated further.}, language = {en} } @misc{SchoenemannLaschewskyRosenhahn2018, author = {Sch{\"o}nemann, Eric and Laschewsky, Andr{\´e} and Rosenhahn, Axel}, title = {Exploring the long-term hydrolytic behavior of zwitterionic polymethacrylates and polymethacrylamides}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1091}, issn = {1866-8372}, doi = {10.25932/publishup-47305}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473052}, pages = {25}, year = {2018}, abstract = {The hydrolytic stability of polymers to be used for coatings in aqueous environments, for example, to confer anti-fouling properties, is crucial. However, long-term exposure studies on such polymers are virtually missing. In this context, we synthesized a set of nine polymers that are typically used for low-fouling coatings, comprising the well-established poly(oligoethylene glycol methylether methacrylate), poly(3-(N-2-methacryloylethyl-N,N-dimethyl) ammoniopropanesulfonate) ("sulfobetaine methacrylate"), and poly(3-(N-3-methacryamidopropyl-N,N-dimethyl)ammoniopropanesulfonate) ("sulfobetaine methacrylamide") as well as a series of hitherto rarely studied polysulfabetaines, which had been suggested to be particularly hydrolysis-stable. Hydrolysis resistance upon extended storage in aqueous solution is followed by ¹H NMR at ambient temperature in various pH regimes. Whereas the monomers suffered slow (in PBS) to very fast hydrolysis (in 1 M NaOH), the polymers, including the polymethacrylates, proved to be highly stable. No degradation of the carboxyl ester or amide was observed after one year in PBS, 1 M HCl, or in sodium carbonate buffer of pH 10. This demonstrates their basic suitability for anti-fouling applications. Poly(sulfobetaine methacrylamide) proved even to be stable for one year in 1 M NaOH without any signs of degradation. The stability is ascribed to a steric shielding effect. The hemisulfate group in the polysulfabetaines, however, was found to be partially labile.}, language = {en} } @misc{EichSchmaelzlinLoehmannsroeben2013, author = {Eich, Susanne and Schm{\"a}lzlin, Elmar and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Distributed fiber optical sensing of oxygen with optical time domain reflectometry}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1085}, issn = {1866-8372}, doi = {10.25932/publishup-47665}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476659}, pages = {16}, year = {2013}, abstract = {In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical oxygen sensor dye, triangular-[4] phenylene (TP), immobilized in a polymer matrix. The TP luminescence decay time is 86 ns. The short decay time of the sensor dye is suitable to achieve a spatial resolution of some meters. In this paper we present the development and characterization of a reflectometer in the UV range of the electromagnetic spectrum as well as optical oxygen sensing with different fiber arrangements.}, language = {en} } @misc{SchulzeWehrholdHille2018, author = {Schulze, Sven and Wehrhold, Michel and Hille, Carsten}, title = {Femtosecond-pulsed laser written and etched fiber bragg gratings for fiber-optical biosensing}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1073}, issn = {1866-8372}, doi = {10.25932/publishup-47269}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-472692}, pages = {22}, year = {2018}, abstract = {We present the development of a label-free, highly sensitive fiber-optical biosensor for online detection and quantification of biomolecules. Here, the advantages of etched fiber Bragg gratings (eFBG) were used, since they induce a narrowband Bragg wavelength peak in the reflection operation mode. The gratings were fabricated point-by-point via a nonlinear absorption process of a highly focused femtosecond-pulsed laser, without the need of prior coating removal or specific fiber doping. The sensitivity of the Bragg wavelength peak to the surrounding refractive index (SRI), as needed for biochemical sensing, was realized by fiber cladding removal using hydrofluoric acid etching. For evaluation of biosensing capabilities, eFBG fibers were biofunctionalized with a single-stranded DNA aptamer specific for binding the C-reactive protein (CRP). Thus, the CRP-sensitive eFBG fiber-optical biosensor showed a very low limit of detection of 0.82 pg/L, with a dynamic range of CRP detection from approximately 0.8 pg/L to 1.2 µg/L. The biosensor showed a high specificity to CRP even in the presence of interfering substances. These results suggest that the proposed biosensor is capable for quantification of CRP from trace amounts of clinical samples. In addition, the adaption of this eFBG fiber-optical biosensor for detection of other relevant analytes can be easily realized.}, language = {en} } @misc{TaoLiuWuetal.2020, author = {Tao, Lumi and Liu, Yuchuan and Wu, Dan and Wei, Qiao-Hua and Taubert, Andreas and Xie, Zailai}, title = {Luminescent Ionogels with Excellent Transparency, High Mechanical Strength, and High Conductivity}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1058}, issn = {1866-8372}, doi = {10.25932/publishup-48733}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-487334}, pages = {13}, year = {2020}, abstract = {The paper describes a new kind of ionogel with both good mechanical strength and high conductivity synthesized by confining the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([Bmim][NTf₂]) within an organic-inorganic hybrid host. The organic-inorganic host network was synthesized by the reaction of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), and methyl methacrylate (MMA) in the presence of a coupling agent, offering the good mechanical strength and rapid shape recovery of the final products. The silane coupling agent 3-methacryloxypropyltrimethoxysilane (KH-570) plays an important role in improving the mechanical strength of the inorganic-organic hybrid, because it covalently connected the organic component MMA and the inorganic component SiO₂. Both the thermal stability and mechanical strength of the ionogel significantly increased by the addition of IL. The immobilization of [Bmim][NTf₂] within the ionogel provided the final ionogel with an ionic conductivity as high as ca. 0.04 S cm⁻¹ at 50 °C. Moreover, the hybrid ionogel can be modified with organosilica-modified carbon dots within the network to yield a transparent and flexible ionogel with strong excitation-dependent emission between 400 and 800 nm. The approach is, therefore, a blueprint for the construction of next-generation multifunctional ionogels.}, language = {en} } @misc{SchneiderGuenterTaubert2018, author = {Schneider, Matthias and G{\"u}nter, Christina and Taubert, Andreas}, title = {Co-deposition of a hydrogel/calcium phosphate hybrid layer on 3D printed poly(lactic acid) scaffolds via dip coating}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1057}, issn = {1866-8372}, doi = {10.25932/publishup-47442}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-474427}, pages = {21}, year = {2018}, abstract = {The article describes the surface modification of 3D printed poly(lactic acid) (PLA) scaffolds with calcium phosphate (CP)/gelatin and CP/chitosan hybrid coating layers. The presence of gelatin or chitosan significantly enhances CP co-deposition and adhesion of the mineral layer on the PLA scaffolds. The hydrogel/CP coating layers are fairly thick and the mineral is a mixture of brushite, octacalcium phosphate, and hydroxyapatite. Mineral formation is uniform throughout the printed architectures and all steps (printing, hydrogel deposition, and mineralization) are in principle amenable to automatization. Overall, the process reported here therefore has a high application potential for the controlled synthesis of biomimetic coatings on polymeric biomaterials.}, language = {en} } @misc{ViouxTaubert2014, author = {Vioux, Andr{\´e} and Taubert, Andreas}, title = {Ionic liquids 2014 and selected papers from ILMAT 2013}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1055}, issn = {1866-8372}, doi = {10.25932/publishup-47506}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475062}, pages = {6}, year = {2014}, language = {en} } @phdthesis{Perovic2020, author = {Perovic, Milena}, title = {Functionalization of nanoporous carbon materials for chiral separation and heterogeneous oxidation catalysis}, doi = {10.25932/publishup-48659}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-486594}, school = {Universit{\"a}t Potsdam}, pages = {140}, year = {2020}, abstract = {The impact that catalysis has on global economy and environment is substantial, since 85\% of all chemical industrial processes are catalytic. Among those, 80\% of the processes are heterogeneously catalyzed, 17\% make use of homogeneous catalysts, and 3\% are biocatalytic processes. Especially in the pharmaceutical and agrochemical industry, a significant part of these processes involves chiral compounds. Obtaining enantiomerically pure compounds is necessary and it is usually accomplished by asymmetric synthesis and catalysis, as well as chiral separation. The efficiency of these processes may be vastly improved if the chiral selectors are positioned on a porous solid support, thereby increasing the available surface area for chiral recognition. Similarly, the majority of commercial catalysts are also supported, usually comprising of metal nanoparticles (NPs) dispersed on highly porous oxide or nanoporous carbon material. Materials that have exceptional thermal and chemical stability, and are electrically conductive are porous carbons. Their stability in extreme pH regions and temperatures, the possibility to tailor their pore architecture and chemical functionalization, and their electric conductivity have already established these materials in the fields of separation and catalysis. However, their heterogeneous chemical structure with abundant defects make it challenging to develop reliable models for the investigation of structure-performance relationships. Therefore, there is a necessity for expanding the fundamental understanding of these robust materials under experimental conditions to allow for their further optimization for particular applications. This thesis gives a contribution to our knowledge about carbons, through different aspects, and in different applications. On the one hand, a rather exotic novel application was investigated by attempts in synthesizing porous carbon materials with an enantioselective surface. Chapter 4.1 described an approach for obtaining mesoporous carbons with an enantioselective surface by direct carbonization of a chiral precursor. Two enantiomers of chiral ionic liquids (CIL) based on amino acid tyrosine were used as carbon precursors and ordered mesoporous silica SBA-15 served as a hard template for obtaining porosity. The chiral recognition of the prepared carbons has been tested in the solution by isothermal titration calorimetry with enantiomers of Phenylalanine as probes, as well as chiral vapor adsorption with 2-butanol enantiomers. Measurements in both solution and the gas phase revealed the differences in the affinity of carbons towards two enantiomers. The atomic efficiency of the CIL precursors was increased in Chapter 4.2, and the porosity was developed independently from the development of chiral carbons, through the formation of stable composites of pristine carbon and CIL-derived coating. After the same set of experiments for the investigation of chirality, the enantiomeric ratios of the composites reported herein were even higher than in the previous chapter. On the other hand, the structure‒activity relationship of carbons as supports for gold nanoparticles in a rather traditional catalytic model reaction, on the interface between gas, liquid, and solid, was studied. In Chapter 5.1 it was shown on the series of catalysts with different porosities that the kinetics of ᴅ-glucose oxidation reaction can be enhanced by increasing the local concentration of the reactants around the active phase of the catalyst. A large amount of uniform narrow mesopores connected to the surface of the Au catalyst supported on ordered mesoporous carbon led to the water confinement, which increased the solubility of the oxygen in the proximity of the catalyst and thereby increased the apparent catalytic activity of this catalyst. After increasing the oxygen concentration in the internal area of the catalyst, in Chapter 5.2 the concentration of oxygen was increased in the external environment of the catalyst, by the introduction of less cohesive liquids that serve as efficient solvent for oxygen, perfluorinated compounds, near the active phase of the catalyst. This was achieved by a formation of catalyst particle-stabilized emulsions of perfluorocarbon in aqueous ᴅ-glucose solution, that further promoted the catalytic activity of gold-on-carbon catalyst. The findings reported within this thesis are an important step in the understanding of the structure-related properties of carbon materials.}, language = {en} } @misc{Laschewsky2014, author = {Laschewsky, Andr{\´e}}, title = {Structures and synthesis of zwitterionic polymers}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1043}, issn = {1866-8372}, doi = {10.25932/publishup-47616}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476167}, pages = {60}, year = {2014}, abstract = {The structures and synthesis of polyzwitterions ("polybetaines") are reviewed, emphasizing the literature of the past decade. Particular attention is given to the general challenges faced, and to successful strategies to obtain polymers with a true balance of permanent cationic and anionic groups, thus resulting in an overall zero charge. Also, the progress due to applying new methodologies from general polymer synthesis, such as controlled polymerization methods or the use of "click" chemical reactions is presented. Furthermore, the emerging topic of responsive ("smart") polyzwitterions is addressed. The considerations and critical discussions are illustrated by typical examples.}, language = {en} } @misc{WessigMatthes2013, author = {Wessig, Pablo and Matthes, Annika}, title = {Photochemical synthesis and properties of 1,6- and 1,8-Naphthalenophanes}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1042}, issn = {1866-8372}, doi = {10.25932/publishup-47667}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476675}, pages = {13}, year = {2013}, abstract = {Various 1,6- and 1,8-naphthalenophanes were synthesized by using the Photo-Dehydro-Diels-Alder (PDDA) reaction of bis-ynones. These compounds are easily accessible from omega-(3-iodophenyl)carboxylic acids in three steps. The obtained naphthalenophanes are axially chiral and the activation barrier for the atropisomerization could be determined in some cases by means of dynamic NMR (DNMR) and/or dynamic HPLC (DHPLC) experiments.}, language = {en} } @phdthesis{Schmidt2020, author = {Schmidt, Bernhard V. K. J.}, title = {Polymers, self-assembly and materials}, doi = {10.25932/publishup-48481}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-484819}, school = {Universit{\"a}t Potsdam}, pages = {VI, 350}, year = {2020}, abstract = {In der vorliegenden Arbeit wurden die Selbstorganisation von hydrophilen Polymeren, verst{\"a}rkte Hydrogele, sowie anorganische/Polymer Hybridmaterialien untersucht. Dabei beschreibt die Arbeit den Weg von Polymersynthese mittels verschiedener Methoden {\"u}ber Polymerselbstanordnung bis zur Herstellung von Polymermaterialien mit vielversprechenden Eigenschaften f{\"u}r zuk{\"u}nftige Anwendungen. Hydrophile Polymere wurden verwendet, um Mehrphasensysteme herzustellen, Wasser-in-Wasser Emulsionen zu bilden und selbstangeordneten Strukturen zu erzeugen, z. B. Partikel/Aggregate oder hohle Strukturen aus komplett wasserl{\"o}slichen Bausteinen. Die Strukturbildung in w{\"a}ssriger Umgebung wurde ferner f{\"u}r supramolekulare Hydrogele mit definierter Unterstruktur und reversiblem Gelierungsverhalten eingesetzt. Auf dem Gebiet der Hydrogele wurde das anorganische Material graphitisches Kohlenstoffnitrid (g-CN) als Photoinitiator f{\"u}r die Hydrogelsynthese und als Verst{\"a}rker der Gelstruktur beschrieben. Hierbei konnten Hydrogele mit herausragenden Eigenschaften generiert werden, z. B. hohe Kompressibilit{\"a}t, hohe Speichermodule oder Gleitf{\"a}higkeit. Die Kombinationen von g-CN mit verschiedenen Polymeren erlaubte es zudem neue Materialien f{\"u}r die Photokatalyse bereitzustellen. Als weiteres anorganisches Material wurden Metall-organische Ger{\"u}ste (MOFs) mit Polymeren kombiniert. Es konnte gezeigt werden, dass die Verwendung von MOFs in der Polymersynthese einen starken Einfluss auf die erzeugte Polymerstruktur hat und MOFs als Katalysator f{\"u}r Polymerisationen verwendet werden k{\"o}nnen. Zuletzt wurde die MOF Synthese an sich untersucht, wobei Polymeradditive oder L{\"o}sungsmittel eingesetzt wurden um die kristalline Struktur der MOFs zu modulieren. Insgesamt wurden hier verschiedene Errungenschaften f{\"u}r die Polymerchemie beschrieben, z.B. neuartige hydrophile Polymere und Hydrogele, die zur Zeit wichtige Materialien im Polymerbereich durch ihre vielversprechenden Anwendungen im biomedizinischen Sektor darstellen. Außerdem ergab die Kombination von Polymeren mit Materialien aus anderen Bereichen der Chemie, z. B. g-CN und MOFs, neue Materialien mit bemerkenswerten Eigenschaften, die ebenfalls von Interesse f{\"u}r zuk{\"u}nftige Anwendungen sind, z. B. Beschichtungen, Partikeltechnologie und Katalyse.}, language = {en} } @misc{HeyneArltGessneretal.2020, author = {Heyne, Benjamin and Arlt, Kristin and Geßner, Andr{\´e} and Richter, Alexander F. and D{\"o}blinger, Markus and Feldmann, Jochen and Taubert, Andreas and Wedel, Armin}, title = {Mixed Mercaptocarboxylic Acid Shells Provide Stable Dispersions of InPZnS/ZnSe/ZnS Multishell Quantum Dots in Aqueous Media}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1026}, issn = {1866-8372}, doi = {10.25932/publishup-48603}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-486032}, pages = {26}, year = {2020}, abstract = {Highly luminescent indium phosphide zinc sulfide (InPZnS) quantum dots (QDs), with zinc selenide/zinc sulfide (ZnSe/ZnS) shells, were synthesized. The QDs were modified via a post-synthetic ligand exchange reaction with 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) in different MPA:MUA ratios, making this study the first investigation into the effects of mixed ligand shells on InPZnS QDs. Moreover, this article also describes an optimized method for the correlation of the QD size vs. optical absorption of the QDs. Upon ligand exchange, the QDs can be dispersed in water. Longer ligands (MUA) provide more stable dispersions than short-chain ligands. Thicker ZnSe/ZnS shells provide a better photoluminescence quantum yield (PLQY) and higher emission stability upon ligand exchange. Both the ligand exchange and the optical properties are highly reproducible between different QD batches. Before dialysis, QDs with a ZnS shell thickness of ~4.9 monolayers (ML), stabilized with a mixed MPA:MUA (mixing ratio of 1:10), showed the highest PLQY, at ~45\%. After dialysis, QDs with a ZnS shell thickness of ~4.9 ML, stabilized with a mixed MPA:MUA and a ratio of 1:10 and 1:100, showed the highest PLQYs, of ~41\%. The dispersions were stable up to 44 days at ambient conditions and in the dark. After 44 days, QDs with a ZnS shell thickness of ~4.9 ML, stabilized with only MUA, showed the highest PLQY, of ~34\%.}, language = {en} } @misc{Koetz2020, author = {Koetz, Joachim}, title = {The Effect of Surface Modification of Gold Nanotriangles for Surface-Enhanced Raman Scattering Performance}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1022}, issn = {1866-8372}, doi = {10.25932/publishup-48517}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-485172}, pages = {15}, year = {2020}, abstract = {A surface modification of ultraflat gold nanotriangles (AuNTs) with different shaped nanoparticles is of special relevance for surface-enhanced Raman scattering (SERS) and the photo-catalytic activity of plasmonic substrates. Therefore, different approaches are used to verify the flat platelet morphology of the AuNTs by oriented overgrowth with metal nanoparticles. The most important part for the morphological transformation of the AuNTs is the coating layer, containing surfactants or polymers. By using well established AuNTs stabilized by a dioctyl sodium sulfosuccinate (AOT) bilayer, different strategies of surface modification with noble metal nanoparticles are possible. On the one hand undulated superstructures were synthesized by in situ growth of hemispherical gold nanoparticles in the polyethyleneimine (PEI)-coated AOT bilayer of the AuNTs. On the other hand spiked AuNTs were obtained by a direct reduction of Au³⁺ ions in the AOT double layer in presence of silver ions and ascorbic acid as reducing agent. Additionally, crumble topping of the smooth AuNTs can be realized after an exchange of the AOT bilayer by hyaluronic acid, followed by a silver-ion mediated reduction with ascorbic acid. Furthermore, a decoration with silver nanoparticles after coating the AOT bilayer with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC) can be realized. In that case the ultraviolet (UV)-absorption of the undulated Au@Ag nanoplatelets can be tuned depending on the degree of decoration with silver nanoparticles. Comparing the Raman scattering data for the plasmon driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4′-dimercaptoazobenzene (DMAB) one can conclude that the most important effect of surface modification with a 75 times higher enhancement factor in SERS experiments becomes available by decoration with gold spikes.}, language = {en} } @phdthesis{Harmanli2020, author = {Harmanli, İpek}, title = {Towards catalytic activation of nitrogen in ionic liquid/nanoporous carbon interfaces for electrochemical ammonia synthesis}, doi = {10.25932/publishup-48359}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483591}, school = {Universit{\"a}t Potsdam}, pages = {v, 126}, year = {2020}, abstract = {Ammonia is a chemical of fundamental importance for nature`s vital nitrogen cycle. It is crucial for the growth of living organisms as well as food and energy source. Traditionally, industrial ammonia production is predominated by Haber- Bosch process (HBP) which is based on direct conversion of N2 and H2 gas under high temperature and high pressure (~500oC, 150-300 bar). However, it is not the favorite route because of its thermodynamic and kinetic limitations, and the need for the energy intense production of hydrogen gas by reforming processes. All these disfavors of HBP open a target to search for an alternative technique to perform efficient ammonia synthesis via electrochemical catalytic processes, in particular via water electrolysis, using water as the hydrogen source to save the process from gas reforming. In this study, the investigation of the interface effects between imidazolium-based ionic liquids and the surface of porous carbon materials with a special interest in the nitrogen absorption capability. As the further step, the possibility to establish this interface as the catalytically active area for the electrochemical N2 reduction to NH3 has been evaluated. This particular combination has been chosen because the porous carbon materials and ionic liquids (IL) have a significant importance in many scientific fields including catalysis and electrocatalysis due to their special structural and physicochemical properties. Primarily, the effects of the confinement of ionic liquid (EmimOAc, 1-Ethyl-3-methylimidazolium acetate) into carbon pores have been investigated. The salt-templated porous carbons, which have different porosity (microporous and mesoporous) and nitrogen species, were used as model structures for the comparison of the IL confinement at different loadings. The nitrogen uptake of EmimOAc can be increased by about 10 times by the confinement in the pores of carbon materials compared to the bulk form. In addition, the most improved nitrogen absorption was observed by IL confinement in micropores and in nitrogen-doped carbon materials as a consequence of the maximized structural changes of IL. Furthermore, the possible use of such interfaces between EmimOAc and porous carbon for the catalytic activation of dinitrogen during the kinetically challenging NRR due to the limited gas absorption in the electrolyte, was examined. An electrocatalytic NRR system based on the conversion of water and nitrogen gas to ammonia at ambient operation conditions (1 bar, 25 °C) was performed in a setup under an applied electric potential with a single chamber electrochemical cell, which consists of the combination of EmimOAc electrolyte with the porous carbon-working electrode and without a traditional electrocatalyst. Under a potential of -3 V vs. SCE for 45 minutes, a NH3 production rate of 498.37 μg h-1 cm-2 and FE of 12.14\% were achieved. The experimental observations show that an electric double-layer, which serves the catalytically active area, occurs between a microporous carbon material and ions of the EmimOAc electrolyte in the presence of sufficiently high provided electric potential. Comparing with the typical NRR systems which have been reported in the literature, the presented electrochemical ammonia synthesis approach provides a significantly higher ammonia production rate with a chance to avoid the possible kinetic limitations of NRR. In terms of operating conditions, ammonia production rate and the faradic efficiency without the need for any synthetic electrocatalyst can be resulted of electrocatalytic activation of nitrogen in the double-layer formed between carbon and IL ions.}, language = {en} } @phdthesis{Buechele2020, author = {B{\"u}chele, Dominique}, title = {Entwicklung einer robusten Online-Methode zur Bestimmung von N{\"a}hrelementen in Ackerb{\"o}den mit einem Energie-dispersiven RFA-Sensor}, doi = {10.25932/publishup-48373}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483735}, school = {Universit{\"a}t Potsdam}, pages = {IX, 106, XLV}, year = {2020}, abstract = {Im Rahmen der vom Bundesministerium f{\"u}r Bildung und -forschung gef{\"o}rderten Forschungsinitiative „BonaRes - Boden als nachhaltige Ressource der Bio{\"o}konomie" soll sich das Teilprojekt „I4S - integrated system for site-specific soil fertility management" der Entwicklung eines integrierten Systems zum ortsspezifischen Management der Bodenfruchtbarkeit widmen. Hierf{\"u}r ist eine Messplattform zur Bestimmung relevanter Bodeneigenschaften und der quantitativen Analyse ausgew{\"a}hlter Makro- und Mikron{\"a}hrstoffe geplant. In der ersten Phase dieses Projekts liegt das Hauptaugenmerk auf der Kalibrierung und Validierung der verschiedenen Sensoren auf die Matrix Boden, der Probennahme auf dem Acker und der Planung sowie dem Aufbau der Messplattform. Auf dieser Plattform sollen in der zweiten Phase des Projektes die verschiedenen Bodensensoren installiert, sowie Modelle und Entscheidungsalgorithmen zur Steuerung der D{\"u}ngung und dementsprechend Verbesserung der Bodenfunktionen erstellt werden. Ziel der vorliegenden Arbeit ist die Grundlagenuntersuchung und Entwicklung einer robusten Online-Analyse mittels Energie-dispersiver R{\"o}ntgenfluoreszenzspektroskopie (EDRFA) zur Quantifizierung ausgew{\"a}hlter Makro- und Mikron{\"a}hrstoffe in B{\"o}den f{\"u}r eine kosteng{\"u}nstige und fl{\"a}chendeckende Kartierung von Ackerfl{\"a}chen. F{\"u}r die Entwicklung eines Online-Verfahrens wurde ein dem Stand der Technik entsprechender R{\"o}ntgenfluoreszenzmesskopf in Betrieb genommen und die dazugeh{\"o}rigen Ger{\"a}teparameter auf die Matrix Boden optimiert. Die Bestimmung der analytischen Qualit{\"a}ts-merkmale wie Pr{\"a}zision und Nachweisgrenzen fand f{\"u}r eine Auswahl an N{\"a}hrelementen von Aluminium bis Zink statt. Um eine m{\"o}glichst Matrix-angepasste Kalibrierung zu erhalten, wurde sowohl mit zertifizierten Referenzmaterialien (CRM), als auch mit Ackerb{\"o}den kalibriert. Da einer der gr{\"o}ßten Nachteile der R{\"o}ntgenfluoreszenzanalyse die Beeinflussung durch Matrixeffekte ist, wurde neben der klassischen univariaten Datenauswertung auch die chemometrische multivariate Methode der Partial Least Squares Regression (PLSR) eingesetzt. Die PLSR bietet dabei den Vorteil, Matrixeffekte auszugleichen, wodurch robustere Kalibriermodelle erhalten werden k{\"o}nnen. Zus{\"a}tzlich wurde eine Hauptkomponentenanalyse (PCA) durchgef{\"u}hrt, um Gemeinsamkeiten und Ausreißer innerhalb des Probensets zu identifizieren. Es zeigte sich, dass eine Klassifizierung der B{\"o}den anhand ihrer Textur Sand, Schluff, Lehm und Ton m{\"o}glich ist. Aufbauend auf den Ergebnissen idealer Bodenproben (zu Tabletten gepresste luftgetrocknete Proben mit Korngr{\"o}ßen < 0,5 mm) wurde im Verlauf dieser Arbeit die Probenvorbereitung immer weiter reduziert und der Einfluss verschiedener Kenngr{\"o}ßen untersucht. Diese Einflussfaktoren k{\"o}nnen die Dichte und die Homogenit{\"a}t der Probe, sowie Korngr{\"o}ßeneffekte und die Feuchtigkeit sein. Anhand des RMSE (Wurzel der mittleren Fehlerquadratsumme) und unter Ber{\"u}cksichtigung der Residuen werden die jeweils erstellten Kalibriermodelle miteinander verglichen. Um die G{\"u}te der Modelle zu bewerten, wurden diese mit einem Testset validiert. Hierf{\"u}r standen 662 Bodenproben von 15 verschiedenen Standorten in Deutschland zur Verf{\"u}gung. Da die Ergebnisse an gepressten Tabletten f{\"u}r die Elemente Al, Si, K, Ca, Ti, Mn, Fe und Zn den Anforderungen f{\"u}r eine sp{\"a}tere Online-Analyse entsprechen, wurden im weiteren Verlauf dieser Arbeit Kalibriermodelle mit losen Bodenproben erstellt. Auch hier konnten gute Ergebnisse durch ausreichende Nachweisgrenzen und eine niedrige gemittelte Messabweichung bei der Vorhersage unbekannter Testproben erzielt werden. Es zeigte sich, dass die Vorhersagef{\"a}higkeit mit der multivariaten PLSR besser ist als mit der univariaten Datenauswertung, insbesondere f{\"u}r die Elemente Mn und Zn. Der untersuchte Einfluss der Feuchtigkeit und der Korngr{\"o}ßen auf die Quantifizierung der Elementgehalte war vor allem bei leichteren Elementen deutlich zu sehen. Es konnte schließlich eine multivariate Kalibrierung unter Ber{\"u}cksichtigung dieser Faktoren f{\"u}r die Elemente Al bis Zn erstellt werden, so dass ein Einsatz an B{\"o}den auf dem Acker m{\"o}glich sein sollte. Eine h{\"o}here Messunsicherheit muss dabei einkalkuliert werden. F{\"u}r eine sp{\"a}tere Probennahme auf dem Feld wurde zudem der Unterschied zwischen statischen und dynamischen Messungen betrachtet, wobei sich zeigte, dass beide Varianten genutzt werden k{\"o}nnen. Zum Abschluss wurde der hier eingesetzte Sensor mit einem kommerziell erh{\"a}ltlichen Hand-Ger{\"a}t auf sein Quantifizierungspotential hin verglichen. Der Sensor weist anhand seiner Ergebnisse ein großes Potential als Online-Sensor f{\"u}r die Messplattform auf. Die Ergebnisse unter Laborbedingungen zeigen, dass eine robuste Analyse Ackerb{\"o}den unter Ber{\"u}cksichtigung der Einflussfaktoren m{\"o}glich ist.}, language = {de} } @phdthesis{Ilic2020, author = {Ilic, Ivan}, title = {Design of sustainable cathodes for Li-ion batteries}, doi = {10.25932/publishup-48368}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483689}, school = {Universit{\"a}t Potsdam}, pages = {iv, 154}, year = {2020}, abstract = {In recent years people have realised non-renewability of our modern society which relays on spending huge amounts of energy mostly produced from fosil fuels, such as oil and coal, and the shift towards more sustainable energy sources has started. However, sustainable sources of energy, such as wind-, solar- and hydro-energy, produce primarily electrical energy and can not just be poured in canister like many fosil fuels, creating necessity for rechragable batteries. However, modern Li-ion batteries are made from toxic heavy metals and sustainable alternatives are needed. Here we show that naturally abundant catecholic and guaiacyl groups can be utilised to replace heavy metals in Li-ion batteries. Foremost vanillin, a naturally occurring food additive that can be sustainably synthesised from industrial biowaste, lignin, was utilised to synthesise materials that showed extraordinary performance as cathodes in Li-ion batteries. Furthermore, behaviour of catecholic and guiacyl groups in Li-ion system was compared, confirming usability of guiacayl containing biopolymers as cathodes in Li-ion batteries. Lastly, naturally occurring polyphenol, tannic acid, was incorporated in fully bioderived hybrid material that shows performance comparable to commercial Li-ion batteries and good stability. This thesis presents an important advancement in understanding of biowaste derived cathode materials for Li-ion batteries. Further research should be conducted to better understand behaviour of guaiacyl groups during Li-ion battery cycling. Lastly, challenges of incorporation of lignin, an industrial biowaste, have to be addressed and lignin should be incorporated as a cathode material in Li-ion batteries.}, language = {en} } @phdthesis{Markushyna2020, author = {Markushyna, Yevheniia}, title = {Modern photoredox transformations applied to the needs of organic synthesis}, doi = {10.25932/publishup-47766}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-477661}, school = {Universit{\"a}t Potsdam}, pages = {275}, year = {2020}, abstract = {Abstract. Catalysis is one of the most effective tools for the highly efficient assembly of complex molecular structures. Nevertheless, it is mainly represented by transition metal-based catalysts and typically is an energy consuming process. Therefore, photocatalysis utilizing solar energy is one of the appealing approaches to overcome these problems. A great alternative to classic transition metal-based photocatalysts, carbon nitrides, a group of organic polymeric semiconductors, have already shown their efficiency in water splitting, CO2 reduction, and organic pollutants degradation. However, these materials have also a great potential for the use in functionalization of complex organic molecules for synthetic needs as it was shown in recent years. This work addresses the challenge to develop efficient system for heterogeneous organic photocatalysis, employing cheap and environmentally benign photocatalysts - carbon nitrides. Herein, fundamental properties of semiconductors are studied from the organic chemistry standpoint; the inherent properties of carbon nitrides, such as ability to accumulate electrons, are deeply investigated and their effect on the reaction outcome is established. Thus, understanding of the electron charging processes allowed for the synthesis of otherwise hardly-achieved diazetidines-1,3 by tetramerization of benzylamines. Furthermore, the high electron capacity of Potassium Poly(heptazine imide)s (K-PHI) made possible a multi-electron reduction of aromatic nitro compounds to bare or formylated anilines. Additionally, two deep eutectic solvents (DES) were designed as a sustainable reaction media and reducing reagent for this reaction. Eventually, the high oxidation ability of carbon nitride K-PHI is employed in a challenging reaction of halide anion oxidation (Cl―, Br―) to accomplish electrophilic substitution in aromatic ring. The possibility to utilize NaCl solution (seawater mimetic) for the chlorination of electron rich arenes was shown. Eventually, light itself is used as a tool in a chromoselective photocatalytic oxidation of aromatic thiols and thioacetatas to three different compounds, using UV, blue, and red LEDs. All in all, the work enhances understanding the mechanism of heterogeneous photocatalysis in synthetic organic reactions and therefore, is a step forward to the sustainable methods of synthesis in organic chemistry.}, language = {en} } @phdthesis{Chao2020, author = {Chao, Madlen}, title = {Entwicklung und Validierung eines Online-LIBS-Verfahrens f{\"u}r die Bestimmung von N{\"a}hrelementen in B{\"o}den}, doi = {10.25932/publishup-47677}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476772}, school = {Universit{\"a}t Potsdam}, pages = {XII, 130}, year = {2020}, abstract = {In den letzten Jahrzehnten ist die Nachfrage nach kosteng{\"u}nstigen und fl{\"a}chendeckenden Kartierungsm{\"o}glichkeiten im Hinblick auf eine ertragssteigernde und umweltfreundlichere Bewirtschaftung von landwirtschaftlichen Nutzfl{\"a}chen stark gestiegen. Hierf{\"u}r eignen sich spektroskopische Methoden wie die R{\"o}ntgenfluoreszenzanalyse (RFA), Raman- und Gammaspektroskopie sowie die laserinduzierte Plasmaspektroskopie (LIBS). In Abh{\"a}ngigkeit von der Funktionsweise der jeweiligen Methoden werden Informationen zu verschiedensten Bodeneigenschaften wie N{\"a}hrelementgehalt, Textur und pH-Wert erhalten. Ziel dieser Arbeit ist die Entwicklung eines Online-LIBS-Verfahrens zur N{\"a}hrelementbestimmmung und Kartierung von Ackerfl{\"a}chen. Die LIBS ist eine schnelle und simultane Multielementanalyse bei der durch das Fokussieren eines hochenergetischen Laserpulses Probenmaterial von der Probenoberfl{\"a}che ablatiert wird und in ein Plasma {\"u}berf{\"u}hrt wird. Beim Abk{\"u}hlen des Plasmas wird Strahlung emittiert, welche R{\"u}ckschl{\"u}sse {\"u}ber die elementare Zusammensetzung der Probe gibt. Diese Arbeit ist im Teilprojekt I4S (Intelligenz f{\"u}r B{\"o}den) im Forschungsprogramm BonaRes (Boden als nachhaltige Ressource f{\"u}r die Bio{\"o}konomie) des Bundesministerium f{\"u}r Bildung und Forschung (BMBF) entstanden. Es wurden insgesamt 651 Bodenproben von verschiedenen Test-Agrarfl{\"a}chen unterschiedlichster Standorte Deutschlands gemessen, ausgewertet und zu Validierungszwecken mit entsprechender Referenzanalytik wie die Optische Emissionsspektroskopie mittels induktiv gekoppeltem Plasma (ICP-OES) und die wellenl{\"a}ngendispersive R{\"o}ntgenfluoreszenzanalyse (WDRFA) charakterisiert. F{\"u}r die Quantifizierung wurden zun{\"a}chst die Messparameter des LIBS-Systems auf die Bodenmatrix optimiert und f{\"u}r die Elemente geeignete Linien ausgew{\"a}hlt sowie deren Nachweisgrenzen bestimmt. Es hat sich gezeigt, dass eine absolute Quantifizierung basierend auf einem univariaten Ansatz aufgrund der starken Matrixeffekte und der schlechten Reproduzierbarkeit des Plasmas nur eingeschr{\"a}nkt m{\"o}glich ist. Bei Verwendung eines multivariaten Ansatz wie der Partial Least Squares Regression (PLSR) f{\"u}r die Kalibrierung konnten f{\"u}r die N{\"a}hrelemente im Vergleich zur univariaten Variante Analyseergebnisse mit h{\"o}herer G{\"u}te und geringeren Messunsicherheiten ermittelt werden. Die Untersuchungen haben gezeigt, dass das multivariate Modell weiter verbessert werden kann, indem mit einer Vielzahl von gut analysierten B{\"o}den verschiedener Standorte, Bodenarten und einem breiten Gehaltsbereich kalibriert wird. Mithilfe der Hauptkomponentenanalyse (PCA) wurde eine Klassifizierung der B{\"o}den nach der Textur realisiert. Weiterhin wurde auch eine Kalibrierung mit losem Bodenmaterial erstellt. Trotz der Signalabnahme konnten f{\"u}r die verschiedenen N{\"a}hrelemente Kalibriergeraden mit ausreichender, analytischer G{\"u}te erstellt werden. F{\"u}r den Einsatz auf dem Acker wurde außerdem der Einfluss von Korngr{\"o}ße und Feuchtigkeit auf das LIBS-Signal untersucht. Die unterschiedlichen Korngr{\"o}ßen haben nur einen geringen Einfluss auf das LIBS-Signal und das Kalibriermodell l{\"a}sst sich durch entsprechende Proben leicht anpassen. Dagegen ist der Einfluss der Feuchtigkeit deutlich st{\"a}rker und h{\"a}ngt stark von der Bodenart ab, sodass f{\"u}r jede Bodenart ein separates Kalibriermodell f{\"u}r verschiedene Feuchtigkeitsgehalte erstellt werden muss. Mithilfe der PCA kann der Feuchtigkeitsgehalt im Boden grob abgesch{\"a}tzt werden und die entsprechende Kalibrierung ausgew{\"a}hlt werden. Diese Arbeit liefert essentielle Informationen f{\"u}r eine Echtzeit-Analyse von N{\"a}hrelementen auf dem Acker mittels LIBS und leistet einen wichtigen Beitrag zu einer fortschrittlichen und zukunftsf{\"a}higen Nutzung von Ackerfl{\"a}chen.}, language = {de} } @phdthesis{Phung2020, author = {Phung, Thi Thuy Nga}, title = {Defect chemistry in halide perovskites}, doi = {10.25932/publishup-47652}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476529}, school = {Universit{\"a}t Potsdam}, pages = {vi, 231}, year = {2020}, abstract = {Metallhalogenid-Perowskite haben sich aufgrund ihrer hervorragenden optoelektronischen Eigenschaften zu einer attraktiven Materialklasse f{\"u}r die Photovoltaikindustrie entwickelt. Die Langzeitstabilit{\"a}t ist jedoch noch immer ein Hindernis f{\"u}r die industrielle Realisierung dieser Materialklasse. Zunehmend zeigen sich Hinweise daf{\"u}r, dass intrinsische Defekte im Perowskit die Material-Degradation f{\"o}rdern. Das Verst{\"a}ndnis der Defekte im Perowskit ist wichtig, um seine Stabilit{\"a}t und optoelektronische Qualit{\"a}t weiter zu verbessern. Diese Dissertation konzentriert sich daher auf das Thema Defektchemie im Perowskit. Der erste Teil der Dissertation gibt einen kurzen {\"U}berblick {\"u}ber die Defekteigenschaften von Halogenid-Perowskiten. Anschließend zeigt der zweite Teil, dass das Dotieren von Methylammoniumbleiiodid mit einer kleinen Menge von Erdalkalimetallen (Sr und Mg) ein h{\"o}herwertiges, weniger fehlerhaftes Material erzeugt, was zu hohen Leerlaufspannungen sowohl in der n-i-p als auch in der p-i-n Architektur von Solarzellen f{\"u}hrt. Es wurde beobachtet, dass die Dotierung in zwei Dom{\"a}nen stattfindet: eine niedrige Dotierungskonzentration f{\"u}hrt zum Einschluss der entsprechenden Elemente in das Kristallgitter erm{\"o}glicht, w{\"a}hrend eine hohe Dotierungskonzentration zu einer Phasentrennung f{\"u}hrt. Das Material kann im Niedrigdotierungsbereich mehr n-dotiert sein, w{\"a}hrend es im Hochdotierungsbereich weniger n-dotiert ist. Die Schwelle dieser beiden Regime h{\"a}ngt von der Atomgr{\"o}ße der Dotierelemente ab. Der n{\"a}chste Teil der Dissertation untersucht die photoinduzierte Degradation von Methylammonium-Bleiiodid. Dieser Abbaumechanismus h{\"a}ngt eng mit der Bildung und Migration von defekten zusammen. Nach der Bildung k{\"o}nnen sich diese in Abh{\"a}ngigkeit von der Defektdichte und ihrer Verteilung bewegen. Demnach kann eine hohe Defektdichte wie an den Korngrenzen eines Perowskitfilms die Beweglichkeit von ionischen Punktdefekten hemmen. Diese Erkenntnis ließe sich auf das zuk{\"u}nftige Materialdesign in der Photovoltaikindustrie anwenden, da die Perowskit-Solarzellen normalerweise einen polykristallinen D{\"u}nnfilm mit hoher Korngrenzendichte verwenden. Die abschließende Studie, die in dieser Dissertation vorgestellt wird, konzentriert sich auf die Stabilit{\"a}t der neuesten „dreifach-kationen" Perowskit-basierten Solarzellen unter dem Einfluss einer permanent angelegten elektrischen Spannung. Eine l{\"a}ngere Betriebsdauer (mehr als drei Stunden permanente Spannung) f{\"o}rdert die Amorphisierung im Halogenid-Perowskiten. Es wird hierbei vermutet, dass sich eine amorphe Phase an den Grenzfl{\"a}chen bildet, insbesondere zwischen der lochselektiven Schicht und dem Perowskit. Diese amorphe Phase hemmt den Ladungstransport und beeintr{\"a}chtigt die Leistung der Perowskit-Solarzelle erheblich. Sobald jedoch keine Spannung mehr anliegt k{\"o}nnen sich die Perowskitschichten im Dunkeln bereits nach einer kurzen Pause regenerieren. Die Amorphisierung wird auf die Migration von ionischen Fehlordnungen zur{\"u}ckgef{\"u}hrt, h{\"o}chstwahrscheinlich auf die Migration von Halogeniden. Dieser Ansatz zeigt ein neues Verst{\"a}ndnis des Abbau-Mechanismus in Perowskit-Solarzellen unter Betriebsbedingungen.}, language = {en} } @phdthesis{LopezdeGuerenu2020, author = {L{\´o}pez de Guere{\~n}u, Anna}, title = {Tm3+-doped NaYF4 nanoparticles}, doi = {10.25932/publishup-47559}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475593}, school = {Universit{\"a}t Potsdam}, pages = {119}, year = {2020}, abstract = {Lately, the integration of upconverting nanoparticles (UCNP) in industrial, biomedical and scientific applications has been increasingly accelerating, owing to the exceptional photophysical properties that UCNP offer. Some of the most promising applications lie in the field of medicine and bioimaging due to such advantages as, among others, deeper tissue penetration, reduced optical background, possibility for multicolor imaging, and lower toxicity, compared to many known luminophores. However, some questions regarding not only the fundamental photophysical processes, but also the interaction of the UCNP with other luminescent reporters frequently used for bioimaging and the interaction with biological media remain unanswered. These issues were the primary motivation for the presented work. This PhD thesis investigated several aspects of various properties and possibilities for bioapplications of Yb3+,Tm3+-doped NaYF4 upconverting nanoparticles. First, the effect of Gd3+ doping on the structure and upconverting behaviour of the nanocrystals was assessed. The ageing process of the UCNP in cyclohexane was studied over 24 months on the samples with different Gd3+ doping concentrations. Structural information was gathered by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and discussed in relation to spectroscopic results, obtained through multiparameter upconversion luminescence studies at various temperatures (from 4 K to 295 K). Time-resolved and steady-state emission spectra recorded over this ample temperature range allowed for a deeper understanding of photophysical processes and their dependence on structural changes of UCNP. A new protocol using a commercially available high boiling solvent allowed for faster and more controlled production of very small and homogeneous UCNP with better photophysical properties, and the advantages of a passivating NaYF4 shell were shown. F{\"o}rster resonance energy transfer (FRET) between four different species of NaYF4: Yb3+, Tm3+ UCNP (synthesized using the improved protocol) and a small organic dye was studied. The influence of UCNP composition and the proximity of Tm3+ ions (donors in the process of FRET) to acceptor dye molecules have been assessed. The brightest upconversion luminescence was observed in the UCNP with a protective inert shell. UCNP with Tm3+ ions only in the shell were the least bright, but showed the most efficient energy transfer. In the final part, two surface modification strategies were applied to make UCNP soluble in water, which simultaneously allowed for linking them via a non-toxic copper-free click reaction to the liposomes, which served as models for further cell experiments. The results were assessed on a confocal microscope system, which was made possible by lesser known downshifting properties of Yb3+, Tm3+-doped UCNP. Preliminary antibody-staining tests using two primary and one dye-labelled secondary antibodies were performed on MDCK-II cells.}, language = {en} } @phdthesis{Kaergell2020, author = {K{\"a}rgell, Martin}, title = {Layer formation from perovskite nanoparticles with tunable optical and electronic properties}, doi = {10.25932/publishup-47566}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475667}, school = {Universit{\"a}t Potsdam}, pages = {ix, 233}, year = {2020}, abstract = {Hybrid organic-inorganic perovskites have attracted attention in recent years, caused by the incomparable increase in efficiency in energy convergence, which implies the application as an absorber material for solar cells. A disadvantage of these materials is, among others, the instability to moisture and UV-radiation. One possible solution for these problems is the reduction of the size towards the nano world. With that nanosized perovskites are showing superior stability in comparison to e.g. perovskite layers. Additionally to this the nanosize even enables stable perovskite structures, which could not be achieved otherwise at room temperature. This thesis is separated into two major parts. The separation is done by the composition and the band gap of the material and at the same time the shape and size of the nanoparticles. Here the division is made by the methylammonium lead tribromide nanoplatelets and the caesium lead triiodide nanocubes. The first part is focusing on the hybrid organic-inorganic perovskite (methylammonium lead tribromide) nanoplatelets with a band gap of 2.35 eV and their thermal behaviour. Due to the challenging character of this material, several analysis methods are used to investigate the sub nano and nanostructures under the influence of temperature. As a result, a shift of phase-transition temperatures towards higher temperatures is observed. This unusual behaviour can be explained by the ligand, which is incorporated in the perovskite outer structure and adds phase-stability into the system. The second part of this thesis is focusing on the inorganic caesium lead triiodide nanocubes with a band gap of 1.83 eV. These nanocrystals are first investigated and compared by TEM, XRD and other optical methods. Within these methods, a cuboid and orthorhombic structure are revealed instead of the in literature described cubic shape and structure. Furthermore, these cuboids are investigated towards their self-assembly on a substrate. Here a high degree in self-assembly is shown. As a next step, the ligands of the nanocuboids are exchanged against other ligands to increase the charge carrier mobility. This is further investigated by the above-mentioned methods. The last section is dealing with the enhancement of the CsPbI3 structure, by incorporating potassium in the crystal structure. The results are suggesting here an increase in stability.}, language = {en} } @phdthesis{Knauf2020, author = {Knauf, Jan}, title = {Synthesis of highly fluorinated precursors and their deposition conditions for self-assembled monolayers with defined small-scale surface structures as templates for the manipulation of wetting behavior}, doi = {10.25932/publishup-47380}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473804}, school = {Universit{\"a}t Potsdam}, pages = {X, 204}, year = {2020}, abstract = {"How Wenzel and Cassie were wrong" - this was the eye-catching title of an article published by Lichao Gao and Thomas McCarthy in 2007, in which fundamental interpretations of wetting behavior were put into question. The authors initiated a discussion on a subject, which had been generally accepted a long time ago and they showed that wetting phenomena were not as fully understood as imagined. Similarly, this thesis tries to put a focus on certain aspects of liquid wetting, which so far have been widely neglected in terms of interpretation and experimental proof. While the effect of surface roughness on the macroscopically observed wetting behavior is commonly and reliably interpreted according to the well-known models of Wenzel and Cassie/Baxter, the size-scale of the structures responsible for the surface's rough texture has not been of further interest. Analogously, the limits of these models have not been described and exploited. Thus, the question arises, what will happen when the size of surface structures is reduced to the size of the contacting liquid molecules itself? Are common methods still valid or can deviations from macroscopic behavior be observed? This thesis wants to create a starting point regarding these questions. In order to investigate the effect of smallest-scale surface structures on liquid wetting, a suitable model system is developed by means of self-assembled monolayer (SAM) formation from (fluoro)organic thiols of differing lengths of the alkyl chain. Surface topographies are created which rely on size differences of several {\AA}ngstr{\"o}ms and exhibit surprising wetting behavior depending on the choice of the individual precursor system. Thus, contact angles are experimentally detected, which deviate considerably from theoretical calculations based on Wenzel and Cassie/Baxter models and confirm that sub-nm surface topographies affect wetting. Moreover, experimentally determined wetting properties are found to correlate well to an assumed scale-dependent surface tension of the contacting liquid. This behavior has already been described for scattering experiments taking into account capillary waves on the liquid surface induced by temperature and had been predicted earlier by theoretical calculations. However, the investigation of model surfaces requires the provision of suitable precursor molecules, which are not commercially available and opens up a door to the exotic chemistry of fluoro-organic materials. During the course of this work, the synthesis of long-chain precursors is examined with a particular focus put on oligomerically pure semi-fluorinated n-alkyl thiols and n-alkyl trichlorosilanes. For this, general protocols for the syntheses of the desired compounds are developed and product mixtures are assayed to be separated into fractions of individual chain lengths by fluorous-phase high-performance liquid chromatography (F-HPLC). The transition from model systems to technically more relevant surfaces and applications is initiated through the deposition of SAMs from long-chain fluorinated n-alkyl trichlorosilanes. Depositions are accomplished by a vapor-phase deposition process conducted on a pilot-scale set-up, which enables the exact control of relevant process parameters. Thus, the influence of varying deposition conditions on the properties of the final coating is examined and analyzed for the most important parameters. The strongest effect is observed for the partial pressure of reactive water vapor, which directly controls the extent of precursor hydrolysis during the deposition process. Experimental results propose that the formation of ordered monolayers rely on the amount of hydrolyzed silanol species present in the deposition system irrespective of the exact grade of hydrolysis. However, at increased amounts of species which are able to form cross-linked molecules due to condensation reactions, films deteriorate in quality. This effect is assumed to be caused by the introduction of defects within the film and the adsorption of cross linked agglomerates. Deposition conditions are also investigated for chain extended precursor species and reveal distinct differences caused by chain elongation.}, language = {en} } @phdthesis{Erler2020, author = {Erler, Alexander}, title = {Entwicklung von online-Detektionsverfahren f{\"u}r landwirtschaftlich relevante Analyten}, doi = {10.25932/publishup-47340}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473406}, school = {Universit{\"a}t Potsdam}, pages = {viii, 123}, year = {2020}, abstract = {Die Entwicklung nachhaltiger Bewirtschaftungs- und Produktionsmethoden ist eine der zentralen Fragestellungen der modernen Agrarwirtschaft. Die vorliegende Arbeit besch{\"a}ftigt sich mit zwei Forschungsthemen, die das Konzept Nachhaltigkeit beinhalten. In beiden F{\"a}llen werden analytische Grundlagen f{\"u}r die Entwicklung entsprechender landwirtschaftlicher Arbeitsmethoden gelegt. Das erste Thema ist an den sogenannten Pr{\"a}zisionsackerbau angelehnt. Bei diesem wird die Bearbeitung von Agrarfl{\"a}chen ortsabh{\"a}ngig ausgef{\"u}hrt. Das heißt, die Ausbringung von Saatgut, D{\"u}nger, Bew{\"a}sserung usw. richtet sich nach den Eigenschaften des jeweiligen Standortes und wird nicht pauschal gleichm{\"a}ßig {\"u}ber ein ganzes Feld verteilt. Voraussetzung hierf{\"u}r ist eine genaue Kenntnis der Bodeneigenschaften. In der vorliegenden Arbeit sollten diese Parameter mittels der analytischen Technik der Laser-induzierten Breakdown Spektroskopie (LIBS), die eine Form der Elementaranalyse darstellt, bestimmt werden. Bei den hier gesuchten Bodeneigenschaften handelte es sich um die Gehalte von N{\"a}hrstoffen sowie einige sekund{\"a}re Parameter wie den Humusanteil, den pH-Wert und den pflanzenverf{\"u}gbaren Anteil einzelner N{\"a}hrstoffe. Diese Eigenschaften wurden durch etablierte Referenzanalysen bestimmt. Darauf aufbauend wurden die Messergebnissen der LIBS-Untersuchungen durch verschiedene Methoden der sogenannten multivariaten Datenanalyse (MVA) ausgewertet. Daraus sollten Modelle zur Vorhersage der Bodenparameter in zuk{\"u}nftigen LIBS-Messungen erarbeitet werden. Die Ergebnisse dieser Arbeit zeigten, dass mit der Kombination von LIBS und MVA s{\"a}mtliche Bodenparameter erfolgreich vorhergesagt werden konnten. Dies beinhaltete sowohl die tats{\"a}chlich messbaren Elemente als auch die sekund{\"a}ren Eigenschaften, welche durch die MVA mit den Elementgehalten in Zusammenhang gebracht wurden. Das zweite Thema besch{\"a}ftigt sich mit der Vermeidung von Verlusten durch Sch{\"a}dlingsbefall bei der Getreidelagerung. Hier sollten mittels der Ionenmobilit{\"a}tsspektrometrie (IMS) Schimmelpilzkontaminationen detektiert werden. Dabei wurde nach den fl{\"u}chtigen Stoffwechselprodukten der Pilze gesucht. Die durch Referenzmessungen mit Massenspektrometern identifizierten Substanzen konnten durch IMS im Gasvolumen {\"u}ber den Proben, dem sogenannten Headspace, nachgewiesen werden. Dabei wurde nicht nur die Anwesenheit einer Kontamination festgestellt, sondern diese auch charakterisiert. Die freigesetzten Substanzen bildeten spezifische Muster, anhand derer die Pilze identifiziert werden konnten. Hier wurden sowohl verschiedene Gattungen als auch einzelne Arten unterschieden. Die Messungen fanden auf verschiedenen N{\"a}hrb{\"o}den statt um den Einfluss dieser auf die Stoffwechselprodukte zu beobachten. Auch die sekund{\"a}ren Stoffwechselprodukte der Schimmelpilze, die Mykotoxine, konnten durch IMS detektiert werden. Beide in dieser Arbeit vorgestellten Forschungsthemen konnten erfolgreich abgeschlossen werden. Sowohl LIBS als auch IMS erwiesen sich f{\"u}r den Nachweis der jeweiligen Analyten als geeignet, und der Einsatz moderner computergest{\"u}tzter Auswertemethoden erm{\"o}glichte die genaue Charakterisierung der gesuchten Parameter. Beide Techniken k{\"o}nnen in Form von mobilen Ger{\"a}ten verwendet werden und zeichnen sich durch eine schnelle und sichere Analyse aus. In Kombination mit entsprechenden Modellen der MVA sind damit alle Voraussetzungen f{\"u}r Vor-Ort-Untersuchungen und damit f{\"u}r den Einsatz in der Landwirtschaft erf{\"u}llt.}, language = {de} } @phdthesis{Melani2019, author = {Melani, Giacomo}, title = {From structural fluctuations to vibrational spectroscopy of adsorbates on surfaces}, doi = {10.25932/publishup-44182}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441826}, school = {Universit{\"a}t Potsdam}, pages = {119}, year = {2019}, abstract = {Aluminum oxide is an Earth-abundant geological material, and its interaction with water is of crucial importance for geochemical and environmental processes. Some aluminum oxide surfaces are also known to be useful in heterogeneous catalysis, while the surface chemistry of aqueous oxide interfaces determines the corrosion, growth and dissolution of such materials. In this doctoral work, we looked mainly at the (0001) surface of α-Al 2 O 3 and its reactivity towards water. In particular, a great focus of this work is dedicated to simulate and address the vibrational spectra of water adsorbed on the α-alumina(0001) surface in various conditions and at different coverages. In fact, the main source of comparison and inspiration for this work comes from the collaboration with the "Interfacial Molecular Spectroscopy" group led by Dr. R. Kramer Campen at the Fritz-Haber Institute of the MPG in Berlin. The expertise of our project partners in surface-sensitive Vibrational Sum Frequency (VSF) generation spectroscopy was crucial to develop and adapt specific simulation schemes used in this work. Methodologically, the main approach employed in this thesis is Ab Initio Molecular Dynamics (AIMD) based on periodic Density Functional Theory (DFT) using the PBE functional with D2 dispersion correction. The analysis of vibrational frequencies from both a static and a dynamic, finite-temperature perspective offers the ability to investigate the water / aluminum oxide interface in close connection to experiment. The first project presented in this work considers the characterization of dissociatively adsorbed deuterated water on the Al-terminated (0001) surface. This particular structure is known from both experiment and theory to be the thermodynamically most stable surface termination of α-alumina in Ultra-High Vacuum (UHV) conditions. Based on experiments performed by our colleagues at FHI, different adsorption sites and products have been proposed and identified for D 2 O. While previous theoretical investigations only looked at vibrational frequencies of dissociated OD groups by staticNormal Modes Analysis (NMA), we rather employed a more sophisticated approach to directly assess vibrational spectra (like IR and VSF) at finite temperature from AIMD. In this work, we have employed a recent implementation which makes use of velocity-velocity autocorrelation functions to simulate such spectral responses of O-H(D) bonds. This approach allows for an efficient and qualitatively accurate estimation of Vibrational Densities of States (VDOS) as well as IR and VSF spectra, which are then tested against experimental spectra from our collaborators. In order to extend previous work on unimolecularly dissociated water on α-Al 2 O 3 , we then considered a different system, namely, a fully hydroxylated (0001) surface, which results from the reconstruction of the UHV-stable Al-terminated surface at high water contents. This model is then further extended by considering a hydroxylated surface with additional water molecules, forming a two-dimensional layer which serves as a potential template to simulate an aqueous interface in environmental conditions. Again, employing finite-temperature AIMD trajectories at the PBE+D2 level, we investigated the behaviour of both hydroxylated surface (HS) and the water-covered structure derived from it (known as HS+2ML). A full range of spectra, from VDOS to IR and VSF, is then calculated using the same methodology, as described above. This is the main focus of the second project, reported in Chapter 5. In this case, comparison between theoretical spectra and experimental data is definitely good. In particular, we underline the nature of high-frequency resonances observed above 3700 cm -1 in VSF experiments to be associated with surface OH-groups, known as "aluminols" which are a key fingerprint of the fully hydroxylated surface. In the third and last project, which is presented in Chapter 6, the extension of VSF spectroscopy experiments to the time-resolved regime offered us the opportunity to investigate vibrational energy relaxation at the α-alumina / water interface. Specifically, using again DFT-based AIMD simulations, we simulated vibrational lifetimes for surface aluminols as experimentally detected via pump-probe VSF. We considered the water-covered HS model as a potential candidate to address this problem. The vibrational (IR) excitation and subsequent relaxation is performed by means of a non-equilibrium molecular dynamics scheme. In such a scheme, we specifically looked at the O-H stretching mode of surface aluminols. Afterwards, the analysis of non-equilibrium trajectories allows for an estimation of relaxation times in the order of 2-4 ps which are in overall agreement with measured ones. The aim of this work has been to provide, within a consistent theoretical framework, a better understanding of vibrational spectroscopy and dynamics for water on the α-alumina(0001) surface,ranging from very low water coverage (similar to the UHV case) up to medium-high coverages, resembling the hydroxylated oxide in environmental moist conditions.}, language = {en} } @phdthesis{Vranic2019, author = {Vranic, Marija}, title = {3D Structure of the biomarker hepcidin-25 in its native state}, doi = {10.25932/publishup-45929}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-459295}, school = {Universit{\"a}t Potsdam}, pages = {xii, 135}, year = {2019}, abstract = {Hepcidin-25 (Hep-25) plays a crucial role in the control of iron homeostasis. Since the dysfunction of the hepcidin pathway leads to multiple diseases as a result of iron imbalance, hepcidin represents a potential target for the diagnosis and treatment of disorders of iron metabolism. Despite intense research in the last decade targeted at developing a selective immunoassay for iron disorder diagnosis and treatment and better understanding the ferroportin-hepcidin interaction, questions remain. The key to resolving these underlying questions is acquiring exact knowledge of the 3D structure of native Hep-25. Since it was determined that the N-terminus, which is responsible for the bioactivity of Hep-25, contains a small Cu(II)-binding site known as the ATCUN motif, it was assumed that the Hep-25-Cu(II) complex is the native, bioactive form of the hepcidin. This structure has thus far not been elucidated in detail. Owing to the lack of structural information on metal-bound Hep-25, little is known about its possible biological role in iron metabolism. Therefore, this work is focused on structurally characterizing the metal-bound Hep-25 by NMR spectroscopy and molecular dynamics simulations. For the present work, a protocol was developed to prepare and purify properly folded Hep-25 in high quantities. In order to overcome the low solubility of Hep-25 at neutral pH, we introduced the C-terminal DEDEDE solubility tag. The metal binding was investigated through a series of NMR spectroscopic experiments to identify the most affected amino acids that mediate metal coordination. Based on the obtained NMR data, a structural calculation was performed in order to generate a model structure of the Hep-25-Ni(II) complex. The DEDEDE tag was excluded from the structural calculation due to a lack of NMR restraints. The dynamic nature and fast exchange of some of the amide protons with solvent reduced the overall number of NMR restraints needed for a high-quality structure. The NMR data revealed that the 20 Cterminal Hep-25 amino acids experienced no significant conformational changes, compared to published results, as a result of a pH change from pH 3 to pH 7 and metal binding. A 3D model of the Hep-25-Ni(II) complex was constructed from NMR data recorded for the hexapeptideNi(II) complex and Hep-25-DEDEDE-Ni(II) complex in combination with the fixed conformation of 19 C-terminal amino acids. The NMR data of the Hep-25-DEDEDE-Ni(II) complex indicates that the ATCUN motif moves independently from the rest of the structure. The 3D model structure of the metal-bound Hep-25 allows for future works to elucidate hepcidin's interaction with its receptor ferroportin and should serve as a starting point for the development of antibodies with improved selectivity.}, language = {en} } @phdthesis{Rietze2020, author = {Rietze, Clemens}, title = {Optimierung und Analyse von molekularen Schaltern in komplexen Umgebungen: thermische Stabilit{\"a}t, Auslesbarkeit und Schaltbarkeit}, doi = {10.25932/publishup-45959}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-459594}, school = {Universit{\"a}t Potsdam}, pages = {131}, year = {2020}, abstract = {Seit Jahrzehnten stellen die molekularen Schalter ein wachsendes Forschungsgebiet dar. Im Rahmen dieser Dissertation stand die Verbesserung der thermischen Stabilit{\"a}t, der Auslesbarkeit und Schaltbarkeit dieser molekularen Schalter in komplexen Umgebungen mithilfe computergest{\"u}tzter Chemie im Vordergrund. Im ersten Projekt wurde die Kinetik der thermischen E → Z-Isomerisierung und die damit verbundene thermische Stabilit{\"a}t eines Azobenzol-Derivats untersucht. Daf{\"u}r wurde Dichtefunktionaltheorie (DFT) in Verbindung mit der Eyring-Theorie des {\"U}bergangszustandes (TST) angewendet. Das Azobenzol-Derivat diente als vereinfachtes Modell f{\"u}r das Schalten in einer komplexen Umgebung (hier in metallorganischen Ger{\"u}sten). Es wurden thermodynamische und kinetische Gr{\"o}ßen unter verschiedenen Einfl{\"u}ssen berechnet, wobei gute {\"U}bereinstimmungen mit dem Experiment gefunden wurden. Die hier verwendete Methode stellte einen geeigneten Ansatz dar, um diese Gr{\"o}ßen mit angemessener Genauigkeit vorherzusagen. Im zweiten Projekt wurde die Auslesbarkeit der Schaltzust{\"a}nde in Form des nichtlinearen optischen (NLO) Kontrastes f{\"u}r die Molek{\"u}lklasse der Fulgimide untersucht. Die daf{\"u}r ben{\"o}tigten dynamischen Hyperpolarisierbarkeiten unter Ber{\"u}cksichtigung der Elektronenkorrelation wurden mittels einer etablierten Skalierungsmethode berechnet. Es wurden verschiedene Fulgimide analysiert, wobei viele experimentelle Befunde best{\"a}tigt werden konnten. Dar{\"u}ber hinaus legte die theoretische Vorhersage f{\"u}r ein weiteres System nahe, dass insbesondere die Erweiterung des π-Elektronensystems ein vielversprechender Ansatz zur Verbesserung von NLO-Kontrasten darstellt. Die Fulgimide verf{\"u}gen somit {\"u}ber n{\"u}tzliche Eigenschaften, sodass diese in Zukunft als Bauelemente in photonischen und optoelektronischen Bereichen Anwendungen finden k{\"o}nnten. Im dritten Projekt wurde die E → Z-Isomerisierung auf ein quantenmechanisch (QM) behandeltes Dimer mit molekularmechanischer (MM) Umgebung und zwei Fluorazobenzol-Monomeren durch Molek{\"u}ldynamik simuliert. Dadurch wurde die Schaltbarkeit in komplexer Umgebung (hier selbstorgansierte Einzelschichten = SAMs) bzw. von Azobenzolderivaten analysiert. Mit dem QM/MM Modell wurden sowohl Van-der-Waals-Interaktionen mit der Umgebung als auch elektronische Kopplung (nur zwischen QM-Molek{\"u}len) ber{\"u}cksichtigt. Dabei wurden systematische Untersuchungen zur Packungsdichte durchgef{\"u}hrt. Es zeigte sich, dass bereits bei einem Molek{\"u}labstand von 4.5 {\AA} die Quantenausbeute (prozentuale Anzahl erfolgreicher Schaltprozesse) des Monomers erreicht wird. Die gr{\"o}ßten Quantenausbeuten wurden f{\"u}r die beiden untersuchten Fluorazobenzole erzielt. Es wurden die Effekte des Molek{\"u}labstandes und der Einfluss von Fluorsubstituenten auf die Dynamik eingehend untersucht, sodass der Weg f{\"u}r darauf aufbauende Studien geebnet ist.}, language = {de} } @misc{Linker2020, author = {Linker, Torsten}, title = {Addition of Heteroatom Radicals to endo-Glycals}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {873}, issn = {1866-8372}, doi = {10.25932/publishup-45997}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-459970}, pages = {15}, year = {2020}, abstract = {Radical reactions have found many applications in carbohydrate chemistry, especially in the construction of carbon-carbon bonds. The formation of carbon-heteroatom bonds has been less intensively studied. This mini-review will summarize the efforts to add heteroatom radicals to unsaturated carbohydrates like endo-glycals. Starting from early examples, developed more than 50 years ago, the importance of such reactions for carbohydrate chemistry and recent applications will be discussed. After a short introduction, the mini-review is divided in sub-chapters according to the heteroatoms halogen, nitrogen, phosphorus, and sulfur. The mechanisms of radical generation by chemical or photochemical processes and the subsequent reactions of the radicals at the 1-position will be discussed. This mini-review cannot cover all aspects of heteroatom-centered radicals in carbohydrate chemistry, but should provide an overview of the various strategies and future perspectives}, language = {en} } @phdthesis{Latza2020, author = {Latza, Victoria Maria}, title = {Interactions involving lipid-based surfaces}, doi = {10.25932/publishup-44559}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-445593}, school = {Universit{\"a}t Potsdam}, pages = {217}, year = {2020}, abstract = {Interactions involving biological interfaces such as lipid-based membranes are of paramount importance for all life processes. The same also applies to artificial interfaces to which biological matter is exposed, for example the surfaces of drug delivery systems or implants. This thesis deals with the two main types of interface interactions, namely (i) interactions between a single interface and the molecular components of the surrounding aqueous medium and (ii) interactions between two interfaces. Each type is investigated with regard to an important scientific problem in the fields of biotechnology and biology: 1.) The adsorption of proteins to surfaces functionalized with hydrophilic polymer brushes; a process of great biomedical relevance in context with harmful foreign-body-response to implants and drug delivery systems. 2.) The influence of glycolipids on the interaction between lipid membranes; a hitherto largely unexplored phenomenon with potentially great biological relevance. Both problems are addressed with the help of (quasi-)planar, lipid-based model surfaces in combination with x-ray and neutron scattering techniques which yield detailed structural insights into the interaction processes. Regarding the adsorption of proteins to brush-functionalized surfaces, the first scenario considered is the exposure of the surfaces to human blood serum containing a multitude of protein species. Significant blood protein adsorption was observed despite the functionalization, which is commonly believed to act as a protein repellent. The adsorption consists of two distinct modes, namely strong adsorption to the brush grafting surface and weak adsorption to the brush itself. The second aspect investigated was the fate of the brush-functionalized surfaces when exposed to aqueous media containing immune proteins (antibodies) against the brush polymer, an emerging problem in current biomedical applications. To this end, it was found that antibody binding cannot be prevented by variation of the brush grafting density or the polymer length. This result motivates the search for alternative, strictly non-antigenic brush chemistries. With respect to the influence of glycolipids on the interaction between lipid membranes, this thesis focused on the glycolipids' ability to crosslink and thereby to tightly attract adjacent membranes. This adherence is due to preferential saccharide-saccharide interactions occurring among the glycolipid headgroups. This phenomenon had previously been described for lipids with special oligo-saccharide motifs. Here, it was investigated how common this phenomenon is among glycolipids with a variety of more abundant saccharide-headgroups. It was found that glycolipid-induced membrane crosslinking is equally observed for some of these abundant glycolipid types, strongly suggesting that this under-explored phenomenon is potentially of great biological relevance.}, language = {en} } @misc{ErlerRiebeBeitzetal.2019, author = {Erler, Alexander and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Gebbers, Robin}, title = {Soil Nutrient Detection for Precision Agriculture Using Handheld Laser-Induced Breakdown Spectroscopy (LIBS) and Multivariate Regression Methods (PLSR, Lasso and GPR)}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {815}, issn = {1866-8372}, doi = {10.25932/publishup-44418}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-444183}, pages = {19}, year = {2019}, abstract = {Precision agriculture (PA) strongly relies on spatially differentiated sensor information. Handheld instruments based on laser-induced breakdown spectroscopy (LIBS) are a promising sensor technique for the in-field determination of various soil parameters. In this work, the potential of handheld LIBS for the determination of the total mass fractions of the major nutrients Ca, K, Mg, N, P and the trace nutrients Mn, Fe was evaluated. Additionally, other soil parameters, such as humus content, soil pH value and plant available P content, were determined. Since the quantification of nutrients by LIBS depends strongly on the soil matrix, various multivariate regression methods were used for calibration and prediction. These include partial least squares regression (PLSR), least absolute shrinkage and selection operator regression (Lasso), and Gaussian process regression (GPR). The best prediction results were obtained for Ca, K, Mg and Fe. The coefficients of determination obtained for other nutrients were smaller. This is due to much lower concentrations in the case of Mn, while the low number of lines and very weak intensities are the reason for the deviation of N and P. Soil parameters that are not directly related to one element, such as pH, could also be predicted. Lasso and GPR yielded slightly better results than PLSR. Additionally, several methods of data pretreatment were investigated.}, language = {en} } @misc{EbelBald2020, author = {Ebel, Kenny and Bald, Ilko}, title = {Length and Energy Dependence of Low-Energy Electron-Induced Strand Breaks in Poly(A) DNA}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {814}, issn = {1866-8372}, doi = {10.25932/publishup-44412}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-444125}, pages = {13}, year = {2020}, abstract = {The DNA in living cells can be effectively damaged by high-energy radiation, which can lead to cell death. Through the ionization of water molecules, highly reactive secondary species such as low-energy electrons (LEEs) with the most probable energy around 10 eV are generated, which are able to induce DNA strand breaks via dissociative electron attachment. Absolute DNA strand break cross sections of specific DNA sequences can be efficiently determined using DNA origami nanostructures as platforms exposing the target sequences towards LEEs. In this paper, we systematically study the effect of the oligonucleotide length on the strand break cross section at various irradiation energies. The present work focuses on poly-adenine sequences (d(A₄), d(A₈), d(A₁₂), d(A₁₆), and d(A₂₀)) irradiated with 5.0, 7.0, 8.4, and 10 eV electrons. Independent of the DNA length, the strand break cross section shows a maximum around 7.0 eV electron energy for all investigated oligonucleotides confirming that strand breakage occurs through the initial formation of negative ion resonances. When going from d(A₄) to d(A₁₆), the strand break cross section increases with oligonucleotide length, but only at 7.0 and 8.4 eV, i.e., close to the maximum of the negative ion resonance, the increase in the strand break cross section with the length is similar to the increase of an estimated geometrical cross section. For d(A₂₀), a markedly lower DNA strand break cross section is observed for all electron energies, which is tentatively ascribed to a conformational change of the dA₂₀ sequence. The results indicate that, although there is a general length dependence of strand break cross sections, individual nucleotides do not contribute independently of the absolute strand break cross section of the whole DNA strand. The absolute quantification of sequence specific strand breaks will help develop a more accurate molecular level understanding of radiation induced DNA damage, which can then be used for optimized risk estimates in cancer radiation therapy.}, language = {en} } @phdthesis{Qin2019, author = {Qin, Qing}, title = {Chemical functionalization of porous carbon-based materials to enable novel modes for efficient electrochemical N2 fixation}, doi = {10.25932/publishup-44339}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-443397}, school = {Universit{\"a}t Potsdam}, pages = {146}, year = {2019}, abstract = {The central motivation of the thesis was to provide possible solutions and concepts to improve the performance (e.g. activity and selectivity) of electrochemical N2 reduction reaction (NRR). Given that porous carbon-based materials usually exhibit a broad range of structural properties, they could be promising NRR catalysts. Therefore, the advanced design of novel porous carbon-based materials and the investigation of their application in electrocatalytic NRR including the particular reaction mechanisms are the most crucial points to be addressed. In this regard, three main topics were investigated. All of them are related to the functionalization of porous carbon for electrochemical NRR or other electrocatalytic reactions. In chapter 3, a novel C-TixOy/C nanocomposite has been described that has been obtained via simple pyrolysis of MIL-125(Ti). A novel mode for N2 activation is achieved by doping carbon atoms from nearby porous carbon into the anion lattice of TixOy. By comparing the NRR performance of M-Ts and by carrying out DFT calculations, it is found that the existence of (O-)Ti-C bonds in C-doped TixOy can largely improve the ability to activate and reduce N2 as compared to unoccupied OVs in TiO2. The strategy of rationally doping heteroatoms into the anion lattice of transition metal oxides to create active centers may open many new opportunities beyond the use of noble metal-based catalysts also for other reactions that require the activation of small molecules as well. In chapter 4, a novel catalyst construction composed of Au single atoms decorated on the surface of NDPCs was reported. The introduction of Au single atoms leads to active reaction sites, which are stabilized by the N species present in NDPCs. Thus, the interaction within as-prepared AuSAs-NDPCs catalysts enabled promising performance for electrochemical NRR. For the reaction mechanism, Au single sites and N or C species can act as Frustrated Lewis pairs (FLPs) to enhance the electron donation and back-donation process to activate N2 molecules. This work provides new opportunities for catalyst design in order to achieve efficient N2 fixation at ambient conditions by utilizing recycled electric energy. The last topic described in chapter 5 mainly focused on the synthesis of dual heteroatom-doped porous carbon from simple precursors. The introduction of N and B heteroatoms leads to the construction of N-B motives and Frustrated Lewis pairs in a microporous architecture which is also rich in point defects. This can improve the strength of adsorption of different reactants (N2 and HMF) and thus their activation. As a result, BNC-2 exhibits a desirable electrochemical NRR and HMF oxidation performance. Gas adsorption experiments have been used as a simple tool to elucidate the relationship between the structure and catalytic activity. This work provides novel and deep insights into the rational design and the origin of activity in metal-free electrocatalysts and enables a physically viable discussion of the active motives, as well as the search for their further applications. Throughout this thesis, the ubiquitous problems of low selectivity and activity of electrochemical NRR are tackled by designing porous carbon-based catalysts with high efficiency and exploring their catalytic mechanisms. The structure-performance relationships and mechanisms of activation of the relatively inert N2 molecules are revealed by either experimental results or DFT calculations. These fundamental understandings pave way for a future optimal design and targeted promotion of NRR catalysts with porous carbon-based structure, as well as study of new N2 activation modes.}, language = {en} } @misc{BurekDenglerEmmerlingetal.2019, author = {Burek, Katja and Dengler, Joachim and Emmerling, Franziska and Feldmann, Ines and Kumke, Michael Uwe and Stroh, Julia}, title = {Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {808}, issn = {1866-8372}, doi = {10.25932/publishup-44243}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442433}, pages = {14}, year = {2019}, abstract = {The hydration process of Portland cement in a cementitious system is crucial for development of the high-quality cement-based construction material. Complementary experiments of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time-resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time-dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium-silicate-hydrates (C-S-H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C-S-H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.}, language = {en} } @phdthesis{Riemer2019, author = {Riemer, Janine}, title = {Synthese und Charakterisierung selektiver Fluoroionophore f{\"u}r intra- und extrazellul{\"a}re Bestimmungen von Kalium- und Natrium-Ionen}, doi = {10.25932/publishup-44193}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441932}, school = {Universit{\"a}t Potsdam}, pages = {IV, 165}, year = {2019}, abstract = {Im Rahmen dieser Dissertation konnten neue Kalium- und Natrium-Ionen Fluoreszenzfarbstoffe von der Klasse der Fluoroionophore synthetisiert und charakterisiert werden. Sie bestehen aus einem N Phenylazakronenether als Ionophor und unterschiedlichen Fluorophoren und sind {\"u}ber einen π-konjugierten 1,2,3-Triazol-1,4-diyl Spacer verbunden. Dabei lag der Fokus w{\"a}hrend ihrer Entwicklung darauf, diese in ihrer Sensitivit{\"a}t, Selektivit{\"a}t und in ihren photophysikalischen Eigenschaften so zu funktionalisieren, dass sie f{\"u}r intra- bzw. extrazellul{\"a}re Konzentrationsbestimmungen geeignet sind. Durch Variation der in ortho Position der N-Phenylazakronenether befindlichen Alkoxy-Gruppen und der fluorophoren Gruppe der Fluoroionophore konnte festgestellt werden, dass die Sensitivit{\"a}t und Selektivit{\"a}t f{\"u}r Kalium- bzw. Natrium-Ionen jeweils durch eine bestimmte Isomerie der 1,2,3-Triazol-1,4-diyl-Einheit erh{\"o}ht wird. Des Weiteren wurde gezeigt, dass durch eine erh{\"o}hte Einschr{\"a}nkung der N,N-Diethylamino-Gruppe des Fluorophors eine Steigerung der Fluoreszenzquantenausbeute und eine Verschiebung des Emissionsmaximums auf {\"u}ber 500 nm erreicht werden konnte. Die Einf{\"u}hrung einer Isopropoxy-Gruppe an einem N-Phenylaza-[18]krone-6-ethers resultierte dabei in einem hoch selektiven Kalium-Ionen Fluoroionophor und erm{\"o}glichte eine in vitro {\"U}berwachung von 10 - 80 mM Kalium-Ionen. Die Substitution einer Methoxy-Gruppe an einem N-Phenylaza-[15]krone-5-ether kombiniert mit unterschiedlich N,N-Diethylamino-Coumarinen lieferte hingegen zwei Natrium-Ionen Fluoroionophore, die f{\"u}r die {\"U}berwachung von intra- bzw. extrazellul{\"a}ren Natrium-Ionen Konzentrationen geeignet sind. In einem weiteren Schritt wurden N-Phenylaza-[18]krone-6-ether mit einem Fluorophor, basierend auf einem [1,3]-Dioxolo[4,5-f][1,3]benzodioxol-(DBD)-Grundger{\"u}st, funktionalisiert. Die im Anschluss durchgef{\"u}hrten spektroskopischen Untersuchungen ergaben, dass die Isopropoxy-Gruppe in ortho Position des N-Phenylaza-[18]krone-6-ether in einen f{\"u}r extrazellul{\"a}re Kalium-Ionen Konzentrationen selektiven Fluoroionophor resultierte, der die Konzentrationsbestimmungen {\"u}ber die Fluoreszenzintensit{\"a}t und -lebensdauer erm{\"o}glicht. In einem abschließenden Schritt konnte unter Verwendung eines Pyrens als fluorophore Gruppe ein weiterer f{\"u}r extrazellul{\"a}re Kalium-Ionen Konzentrationen geeigneter Fluoroionophor entwickelt werden. Die Bestimmung der Kalium-Ionen Konzentration erfolgte hierbei anhand der Fluoreszenzintensit{\"a}tsverh{\"a}ltnisse bei zwei Emissionswellenl{\"a}ngen. Insgesamt konnten 17 verschiedene neue Fluoroionophore f{\"u}r die Bestimmung von Kalium- bzw. Natrium-Ionen synthetisiert und charakterisiert werden. Sechs dieser neuen Molek{\"u}le erm{\"o}glichen in vitro Messungen der intra- oder extrazellul{\"a}ren Kalium- und Natrium-Ionen Konzentrationen und k{\"o}nnten zuk{\"u}nftig f{\"u}r in vivo Konzentrationsmessungen verwendet werden.}, language = {de} } @phdthesis{Debsharma2019, author = {Debsharma, Tapas}, title = {Cellulose derived polymers}, doi = {10.25932/publishup-44131}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-441312}, school = {Universit{\"a}t Potsdam}, pages = {x, 103}, year = {2019}, abstract = {Plastics, such as polyethylene, polypropylene, and polyethylene terephthalate are part of our everyday lives in the form of packaging, household goods, electrical insulation, etc. These polymers are non-degradable and create many environmental problems and public health concerns. Additionally, these polymers are produced from finite fossils resources. With the continuous utilization of these limited resources, it is important to look towards renewable sources along with biodegradation of the produced polymers, ideally. Although many bio-based polymers are known, such as polylactic acid, polybutylene succinate adipate or polybutylene succinate, none have yet shown the promise of replacing conventional polymers like polyethylene, polypropylene and polyethylene terephthalate. Cellulose is one of the most abundant renewable resources produced in nature. It can be transformed into various small molecules, such as sugars, furans, and levoglucosenone. The aim of this research is to use the cellulose derived molecules for the synthesis of polymers. Acid-treated cellulose was subjected to thermal pyrolysis to obtain levoglucosenone, which was reduced to levoglucosenol. Levoglucosenol was polymerized, for the first time, by ring-opening metathesis polymerization (ROMP) yielding high molar mass polymers of up to ~150 kg/mol. The poly(levoglucosenol) is thermally stable up to ~220 ℃, amorphous, and is exhibiting a relatively high glass transition temperature of ~100 ℃. The poly(levoglucosenol) can be converted to a transparent film, resembling common plastic, and was found to degrade in a moist acidic environment. This means that poly(levoglucosenol) may find its use as an alternative to conventional plastic, for instance, polystyrene. Levoglucosenol was also converted into levoglucosenyl methyl ether, which was polymerized by cationic ring-opening metathesis polymerization (CROP). Polymers were obtained with molar masses up to ~36 kg/mol. These polymers are thermally stable up to ~220 ℃ and are semi-crystalline thermoplastics, having a glass transition temperature of ~35 ℃ and melting transition of 70-100 ℃. Additionally, the polymers underwent cross-linking, hydrogenation and thiol-ene click chemistry.}, language = {en} } @phdthesis{Schuerings2019, author = {Sch{\"u}rings, Marco Philipp Hermann}, title = {Synthesis of 1D microgel strands and their motion analysis in solution}, doi = {10.25932/publishup-43953}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439532}, school = {Universit{\"a}t Potsdam}, pages = {167}, year = {2019}, abstract = {The fabrication of 1D nanostrands composed of stimuli responsive microgels has been shown in this work. Microgels are well known materials able to respond to various stimuli from outer environment. Since these microgels respond via a volume change to an external stimulus, a targeted mechanical response can be achieved. Through carefully choosing the right composition of the polymer matrix, microgels can be designed to react precisely to the targeted stimuli (e.g. drug delivery via pH and temperature changes, or selective contractions through changes in electrical current125). In this work, it was aimed to create flexible nano-filaments which are capable of fast anisotropic contractions similar to muscle filaments. For the fabrication of such filaments or strands, nanostructured templates (PDMS wrinkles) were chosen due to a facile and low-cost fabrication and versatile tunability of their dimensions. Additionally, wrinkling is a well-known lithography-free method which enables the fabrication of nanostructures in a reproducible manner and with a high long-range periodicity. In Chapter 2.1, it was shown for the first time that microgels as soft matter particles can be aligned to densely packed microgel arrays of various lateral dimensions. The alignment of microgels with different compositions (e.g. VCL/AAEM, NIPAAm, NIPAAm/VCL and charged microgels) was shown by using different assembly techniques (e.g. spin-coating, template confined molding). It was chosen to set one experimental parameter constant which was the SiOx surface composition of the templates and substrates (e.g. oxidized PDMS wrinkles, Si-wafers and glass slides). It was shown that the fabrication of nanoarrays was feasible with all tested microgel types. Although the microgels exhibited different deformability when aligned on a flat surface, they retained their thermo-responsivity and swelling behavior. Towards the fabrication of 1D microgel strands interparticle connectivity was aspired. This was achieved via different cross-linking methods (i.e. cross-linking via UV-irradiation and host-guest complexation) discussed in Chapter 2.2. The microgel arrays created by different assembly methods and microgel types were tested for their cross-linking suitability. It was observed that NIPAAm based microgels cannot be cross-linked with UV light. Furthermore, it was found that these microgels exhibit a strong surface-particle-interaction and therefore could not be detached from the given substrates. In contrast to the latter, with VCL/AAEM based microgels it was possible to both UV cross-link them based on the keto-enol tautomerism of the AAEM copolymer, and to detach them from the substrate due to the lower adhesion energy towards SiOx surfaces. With VCL/AAEM microgels long, one-dimensional microgel strands could be re-dispersed in water for further analysis. It has also been shown that at least one lateral dimension of the free dispersed 1D microgel strands is easily controllable by adjusting the wavelength of the wrinkled template. For further work, only VCL/AAEM based microgels were used to focus on the main aim of this work, i.e. the fabrication of 1D microgel nanostrands. As an alternative to the unspecific and harsh UV cross-linking, the host-guest complexation via diazobenzene cross-linkers and cyclodextrin hosts was explored. The idea behind this approach was to give means to a future construction kit-like approach by incorporation of cyclodextrin comonomers in a broad variety of particle systems (e.g. microgels, nanoparticles). For this purpose, VCL/AAEM microgels were copolymerized with different amounts of mono-acrylate functionalized β-cyclodextrin (CD). After successfully testing the cross-linking capability in solution, the cross-linking of aligned VCL/AAEM/CD microgels was tried. Although the cross-linking worked well, once the single arrays came into contact to each other, they agglomerated. As a reason for this behavior residual amounts of mono-complexed diazobenzene linkers were suspected. Thus, end-capping strategies were tried out (e.g. excess amounts of β-cyclodextrin and coverage with azobenzene functionalized AuNPs) but were unsuccessful. With deeper thought, entropy effects were taken into consideration which favor the release of complexed diazobenzene linker leading to agglomerations. To circumvent this entropy driven effect, a multifunctional polymer with 50\% azobenzene groups (Harada polymer) was used. First experiments with this polymer showed promising results regarding a less pronounced agglomeration (Figure 77). Thus, this approach could be pursued in the future. In this chapter it was found out that in contrast to pearl necklace and ribbon like formations, particle alignment in zigzag formation provided the best compromise in terms of stability in dispersion (see Figure 44a and Figure 51) while maintaining sufficient flexibility. For this reason, microgel strands in zigzag formation were used for the motion analysis described in Chapter 2.3. The aim was to observe the properties of unrestrained microgel strands in solution (e.g. diffusion behavior, rotational properties and ideally, anisotropic contraction after temperature increase). Initially, 1D microgel strands were manipulated via AFM in a liquid cell setup. It could be observed that the strands required a higher load force compared to single microgels to be detached from the surface. However, with the AFM it was not possible to detach the strands in a controllable manner but resulted in a complete removal of single microgel particles and a tearing off the strands from the surface, respectively. For this reason, to observe the motion behavior of unrestrained microgel strands in solution, confocal microscopy was used. Furthermore, to hinder an adsorption of the strands, it was found out that coating the surface of the substrates with a repulsive polymer film was beneficial. Confocal and wide-field microscopy videos showed that the microgel strands exhibit translational and rotational diffusive motion in solution without perceptible bending. Unfortunately, with these methods the detection of the anisotropic stimuli responsive contraction of the free moving microgel strands was not possible. To summarize, the flexibility of microgel strands is more comparable to the mechanical behavior of a semi flexible cable than to a yarn. The strands studied here consist of dozens or even hundreds of discrete submicron units strung together by cross-linking, having few parallels in nanotechnology. With the insights gained in this work on microgel-surface interactions, in the future, a targeted functionalization of the template and substrate surfaces can be conducted to actively prevent unwanted microgel adsorption for a given microgel system (e.g. PVCL and polystyrene coating235). This measure would make the discussed alignment methods more diverse. As shown herein, the assembly methods enable a versatile microgel alignment (e.g. microgel meshes, double and triple strands). To go further, one could use more complex templates (e.g. ceramic rhombs and star shaped wrinkles (Figure 14) to expand the possibilities of microgel alignment and to precisely control their aspect ratios (e.g. microgel rods with homogeneous size distributions).}, language = {en} } @misc{RiebeErlerBrinkmannetal.2019, author = {Riebe, Daniel and Erler, Alexander and Brinkmann, Pia and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Gebbers, Robin}, title = {Comparison of Calibration Approaches in Laser-Induced Breakdown Spectroscopy for Proximal Soil Sensing in Precision Agriculture}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {786}, issn = {1866-8372}, doi = {10.25932/publishup-44007}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-440079}, pages = {16}, year = {2019}, abstract = {The lack of soil data, which are relevant, reliable, affordable, immediately available, and sufficiently detailed, is still a significant challenge in precision agriculture. A promising technology for the spatial assessment of the distribution of chemical elements within fields, without sample preparation is laser-induced breakdown spectroscopy (LIBS). Its advantages are contrasted by a strong matrix dependence of the LIBS signal which necessitates careful data evaluation. In this work, different calibration approaches for soil LIBS data are presented. The data were obtained from 139 soil samples collected on two neighboring agricultural fields in a quaternary landscape of northeast Germany with very variable soils. Reference analysis was carried out by inductively coupled plasma optical emission spectroscopy after wet digestion. The major nutrients Ca and Mg and the minor nutrient Fe were investigated. Three calibration strategies were compared. The first method was based on univariate calibration by standard addition using just one soil sample and applying the derived calibration model to the LIBS data of both fields. The second univariate model derived the calibration from the reference analytics of all samples from one field. The prediction is validated by LIBS data of the second field. The third method is a multivariate calibration approach based on partial least squares regression (PLSR). The LIBS spectra of the first field are used for training. Validation was carried out by 20-fold cross-validation using the LIBS data of the first field and independently on the second field data. The second univariate method yielded better calibration and prediction results compared to the first method, since matrix effects were better accounted for. PLSR did not strongly improve the prediction in comparison to the second univariate method.}, language = {en} } @misc{BuecheleChaoOstermannetal.2019, author = {B{\"u}chele, Dominique and Chao, Madlen and Ostermann, Markus and Leenen, Matthias and Bald, Ilko}, title = {Multivariate chemometrics as a key tool for prediction of K and Fe in a diverse German agricultural soil-set using EDXRF}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {784}, issn = {1866-8372}, doi = {10.25932/publishup-43998}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439988}, pages = {11}, year = {2019}, abstract = {Within the framework of precision agriculture, the determination of various soil properties is moving into focus, especially the demand for sensors suitable for in-situ measurements. Energy-dispersive X-ray fluorescence (EDXRF) can be a powerful tool for this purpose. In this study a huge diverse soil set (n = 598) from 12 different study sites in Germany was analysed with EDXRF. First, a principal component analysis (PCA) was performed to identify possible similarities among the sample set. Clustering was observed within the four texture classes clay, loam, silt and sand, as clay samples contain high and sandy soils low iron mass fractions. Furthermore, the potential of uni- and multivariate data evaluation with partial least squares regression (PLSR) was assessed for accurate determination of nutrients in German agricultural samples using two calibration sample sets. Potassium and iron were chosen for testing the performance of both models. Prediction of these nutrients in 598 German soil samples with EDXRF was more accurate using PLSR which is confirmed by a better overall averaged deviation and PLSR should therefore be preferred.}, language = {en} } @misc{LiebigHenningSarhanetal.2019, author = {Liebig, Ferenc and Henning, Ricky and Sarhan, Radwan Mohamed and Prietzel, Claudia Christina and Schmitt, Clemens Nikolaus Zeno and Bargheer, Matias and Koetz, Joachim}, title = {A simple one-step procedure to synthesise gold nanostars in concentrated aqueous surfactant solutions}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {769}, issn = {1866-8372}, doi = {10.25932/publishup-43874}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-438743}, pages = {23633 -- 23641}, year = {2019}, abstract = {Due to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in the presence of Ag⁺ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption.}, language = {en} } @phdthesis{Noack2019, author = {Noack, Sebastian}, title = {Poly(lactide)-based amphiphilic block copolymers}, doi = {10.25932/publishup-43616}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436168}, school = {Universit{\"a}t Potsdam}, pages = {xvii, 148}, year = {2019}, abstract = {Due to its bioavailability and (bio)degradability, poly(lactide) (PLA) is an interesting polymer that is already being used as packaging material, surgical seam, and drug delivery system. Dependent on various parameters such as polymer composition, amphiphilicity, sample preparation, and the enantiomeric purity of lactide, PLA in an amphiphilic block copolymer can affect the self-assembly behavior dramatically. However, sizes and shapes of aggregates have a critical effect on the interactions between biological and drug delivery systems, where the general understanding of these polymers and their ability to influence self-assembly is of significant interest in science. The first part of this thesis describes the synthesis and study of a series of linear poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA)-based amphiphilic block copolymers with varying PLA (hydrophobic), and poly(ethylene glycol) (PEG) (hydrophilic) chain lengths and different block copolymer sequences (PEG-PLA and PLA-PEG). The PEG-PLA block copolymers were synthesized by ring-opening polymerization of lactide initiated by a PEG-OH macroinitiator. In contrast, the PLA-PEG block copolymers were produced by a Steglich-esterification of modified PLA with PEG-OH. The aqueous self-assembly at room temperature of the enantiomerically pure PLLA-based block copolymers and their stereocomplexed mixtures was investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). Spherical micelles and worm-like structures were produced, whereby the obtained self-assembled morphologies were affected by the lactide weight fraction in the block copolymer and self-assembly time. The formation of worm-like structures increases with decreasing PLA-chain length and arises from spherical micelles, which become colloidally unstable and undergo an epitaxial fusion with other micelles. As shown by DSC experiments, the crystallinity of the corresponding PLA blocks increases within the self-assembly time. However, the stereocomplexed self-assembled structures behave differently from the parent polymers and result in irregular-shaped clusters of spherical micelles. Additionally, time-dependent self-assembly experiments showed a transformation, from already self-assembled morphologies of different shapes to more compact micelles upon stereocomplexation. In the second part of this thesis, with the objective to influence the self-assembly of PLA-based block copolymers and its stereocomplexes, poly(methyl phosphonate) (PMeP) and poly(isopropyl phosphonate) (PiPrP) were produced by ring-opening polymerization to implement an alternative to the hydrophilic block PEG. Although, the 1,8 diazabicyclo[5.4.0]unde 7 ene (DBU) or 1,5,7 triazabicyclo[4.4.0]dec-5-ene (TBD) mediated synthesis of the corresponding poly(alkyl phosphonate)s was successful, however, not so the polymerization of copolymers with PLA-based precursors (PLA-homo polymers, and PEG-PLA block copolymers). Transesterification, obtained by 1H-NMR spectroscopy, between the poly(phosphonate)- and PLA block caused a high-field shifted peak split of the methine proton in the PLA polymer chain, with split intensities depending on the used catalyst (DBU for PMeP, and TBD for PiPrP polymerization). An additional prepared block copolymer PiPrP-PLLA that wasn't affected in its polymer sequence was finally used for self-assembly experiments with PLA-PEG and PEG-PLA mixing. This work provides a comprehensive study of the self-assembly behavior of PLA-based block copolymers influenced by various parameters such as polymer block lengths, self-assembly time, and stereocomplexation of block copolymer mixtures.}, language = {en} } @misc{KirsteBrietzkeHoldtetal.2019, author = {Kirste, Matthias and Brietzke, Thomas Martin and Holdt, Hans-J{\"u}rgen and Schilde, Uwe}, title = {The crystal structure of 1,12-diazaperylene, C₁₈H₁₀N₂}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {752}, issn = {1866-8372}, doi = {10.25932/publishup-43650}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436501}, pages = {3}, year = {2019}, abstract = {C₁₈H₁₀N₂, monoclinic, P2₁/c (no. 14), a=7.9297(9) {\AA}, b=11.4021(14) {\AA}, c=13.3572(15) {\AA}, β=105.363(8)°, V =1164.5(2) {\AA}³, Z =4, Rgt(F)=0.0325, wRref(F²)=0.0774, T =210(2) K.}, language = {en} } @misc{RajuLiebigHessetal.2019, author = {Raju, Rajarshi Roy and Liebig, Ferenc and Hess, Andreas and Schlaad, Helmut and Koetz, Joachim}, title = {Temperature-triggered reversible breakdown of polymer-stabilized olive}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {751}, issn = {1866-8372}, doi = {10.25932/publishup-43646}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436461}, pages = {19271 -- 19277}, year = {2019}, abstract = {A one-step moderate energy vibrational emulsification method was successfully employed to produce thermo-responsive olive/silicone-based Janus emulsions stabilized by poly(N,N-diethylacrylamide) carrying 0.7 mol\% oleoyl side chains. Completely engulfed emulsion droplets remained stable at room temperature and could be destabilized on demand upon heating to the transition temperature of the polymeric stabilizer. Time-dependent light micrographs demonstrate the temperature-induced breakdown of the Janus droplets, which opens new aspects of application, for instance in biocatalysis.}, language = {en} } @phdthesis{Otte2019, author = {Otte, Fabian}, title = {C-Arylglykoside und Chalkone}, doi = {10.25932/publishup-43430}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-434305}, school = {Universit{\"a}t Potsdam}, pages = {XI, 201}, year = {2019}, abstract = {Im bis heute andauernden Zeitalter der wissenschaftlichen Medizin, konnte ein breites Spektrum von Wirkstoffen zur Behandlung diverser Krankheiten zusammengetragen werden. Dennoch hat es sich die organische Synthesechemie zur Aufgabe gemacht, dieses Spektrum auf neuen oder bekannten Wegen und aus verschiedenen Gr{\"u}nden zu erweitern. Zum einen ist das Vorkommen bestimmter Verbindungen in der Natur h{\"a}ufig limitiert, sodass synthetische Methoden immer {\"o}fter an Stelle eines weniger nachhaltigen Abbaus treten. Zum anderen kann durch Derivatisierung und Wirkstoffanpassung die physiologische Wirkung oder die Bioverf{\"u}gbarkeit eines Wirkstoffes erh{\"o}ht werden. In dieser Arbeit konnten einige Vertreter der bekannten Wirkstoffklassen C-Arylglykoside und Chalkone durch den Schl{\"u}sselschritt der Palladium-katalysierten MATSUDA-HECK-Reaktion synthetisiert werden. Dazu wurden im Fall der C-Arylglykoside zun{\"a}chst unges{\"a}ttigte Kohlenhydrate (Glykale) {\"u}ber eine Ruthenium-katalysierte Zyklisierungsreaktion dargestellt. Diese wurden im Anschluss mit unterschiedlich substituierten Diazoniumsalzen in der oben erw{\"a}hnten Palladium-katalysierten Kupplungsreaktion zur Reaktion gebracht. Bei der Auswertung der analytischen Daten konnte festgestellt werden, dass stets die trans-Diastereomere gebildet wurden. Im Anschluss konnte gezeigt werden, dass die Doppelbindungen dieser Verbindungen durch Hydrierung, Dihydroxylierung oder Epoxidierung funktionalisiert werden k{\"o}nnen. Auf diesem Wege konnte u. a. eine dem Diabetesmedikament Dapagliflozin {\"a}hnliche Verbindung hergestellt werden. Im zweiten Teil der Arbeit wurden Arylallylchromanone durch die MATSUDA-HECK-Reaktion von verschiedenen 8-Allylchromanonen mit Diazoniumsalzen dargestellt. Dabei konnte beobachtet werden, dass eine MOM-Schutzgruppe in 7-Position der Molek{\"u}le die Darstellung von Produktgemischen unterdr{\"u}ckt und jeweils nur eine der m{\"o}glichen Verbindungen gebildet wird. Die Lage der Doppelbindung konnte mittels 2D-NMR-Untersuchungen lokalisiert werden. In Kooperation mit der theoretischen Chemie sollte durch Berechnungen untersucht werden, wie die beobachteten Verbindungen entstehen. Durch eine auftretende Wechselwirkung innerhalb des Molek{\"u}ls konnte allerdings keine explizite Aussage getroffen werden. Im Anschluss sollten die erhaltenen Verbindungen in einer allylischen Oxidation zu Chalkonen umgesetzt werden. Die Ruthenium-katalysierten Methoden zeigten u. a. keine Eignung. Es konnte allerdings eine metallfreie, Mikrowellen-unterst{\"u}tzte Methode erfolgreich erprobt werden, sodass die Darstellung einiger Vertreter dieser physiologisch aktiven Stoffklasse gelang.}, language = {de} } @phdthesis{Walczak2019, author = {Walczak, Ralf}, title = {Molecular design of nitrogen-doped nanoporous noble carbon materials for gas adsorption}, doi = {10.25932/publishup-43524}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-435241}, school = {Universit{\"a}t Potsdam}, pages = {II, 155}, year = {2019}, abstract = {In den modernen Gesellschaften f{\"u}hrt ein stetig steigender Energiebedarf zu dem zunehmenden Verbrauch fossiler Brennstoffe wie Kohle, {\"O}l, und Gas. Die Verbrennung dieser kohlenstoffbasierten Brennstoffe f{\"u}hrt unweigerlich zur Freisetzung von Treibhausgasen, vor allem von CO2. Die CO2 Aufnahme unmittelbar bei den Verbrennungsanlagen oder direkt aus der Luft, zusammen mit Regulierung von CO2 produzierenden Energiesektoren (z.B. K{\"u}hlanlagen), k{\"o}nnen den CO2 Ausstoß reduzieren. Allerdings f{\"u}hren insbesondere bei der CO2 Aufnahme die geringen CO2 Konzentrationen und die Aufnahme konkurrierender Gase zu niedrigen CO2 Kapazit{\"a}ten und Selektivit{\"a}ten. Das Zusammenspiel der Gastmolek{\"u}le mit por{\"o}sen Materialien ist dabei essentiell. Por{\"o}se Kohlenstoffmaterialien besitzen attraktive Eigenschaften, unter anderem elektrische Leitf{\"a}higkeit, einstellbare Porosit{\"a}t, als auch chemische und thermische Stabilit{\"a}t. Allerdings f{\"u}hrt die zu geringe Polarisierbarkeit dieser Materialien zu einer geringen Affinit{\"a}t zu polaren Molek{\"u}len (z.B. CO2, H2O, oder NH3). Diese Affinit{\"a}t kann durch den Einbau von Stickstoff erh{\"o}ht werden. Solche Materialien sind oft „edler" als reine Kohlenstoffe, dies bedeutet, dass sie eher oxidierend wirken, als selbst oxidiert zu werden. Die Problematik besteht darin, einen hohen und gleichm{\"a}ßig verteilten Stickstoffgehalt in das Kohlenstoffger{\"u}st einzubauen. Die Zielsetzung dieser Dissertation ist die Erforschung neuer Synthesewege f{\"u}r stickstoffdotierte edle Kohlenstoffmaterialien und die Entwicklung eines grundlegenden Verst{\"a}ndnisses f{\"u}r deren Anwendung in Gasadsorption und elektrochemischer Energiespeicherung. Es wurde eine templatfreie Synthese f{\"u}r stickstoffreiche, edle, und mikropor{\"o}se Kohlenstoffmaterialien durch direkte Kondensation eines stickstoffreichen organischen Molek{\"u}ls als Vorl{\"a}ufer erarbeitet. Dadurch konnten Materialien mit hohen Adsorptionskapazit{\"a}ten f{\"u}r H2O und CO2 bei niedrigen Konzentrationen und moderate CO2/N2 Selektivit{\"a}ten erzielt werden. Um die CO2/N2 Selektivit{\"a}ten zu verbessern, wurden mittels der Einstellung des Kondensationsgrades die molekulare Struktur und Porosit{\"a}t der Kohlenstoffmaterialien kontrolliert. Diese Materialien besitzen die Eigenschaften eines molekularen Siebs f{\"u}r CO2 {\"u}ber N2, das zu herausragenden CO2/N2 Selektivit{\"a}ten f{\"u}hrt. Der ultrahydrophile Charakter der Porenoberfl{\"a}chen und die kleinen Mikroporen dieser Kohlenstoffmaterialien erm{\"o}glichen grundlegende Untersuchungen f{\"u}r die Wechselwirkungen mit Molek{\"u}len die polarer sind als CO2, n{\"a}mlich H2O und NH3. Eine weitere Reihe stickstoffdotierter Kohlenstoffmaterialien wurde durch Kondensation eines konjugierten mikropor{\"o}sen Polymers synthetisiert und deren strukturelle Besonderheiten als Anodenmaterial f{\"u}r die Natriumionen Batterie untersucht. Diese Dissertation leistet einen Beitrag zur Erforschung stickstoffdotierter Kohlenstoffmaterialien und deren Wechselwirkungen mit verschiedenen Gastmolek{\"u}len.}, language = {en} } @misc{KruegerKellingLinkeretal.2019, author = {Krueger, Tobias and Kelling, Alexandra and Linker, Torsten and Schilde, Uwe}, title = {Crystal structures of three cyclohexane‑based γ‑spirolactams}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {738}, doi = {10.25932/publishup-43491}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-434911}, pages = {9}, year = {2019}, abstract = {The title compounds, 2-azaspiro[4.5]deca-1-one, C₉H₁₅NO, (1a), cis-8-methyl-2-azaspiro[4.5]deca-1-one, C₁₀H₁₇NO, (1b), and trans-8-methyl-2-azaspiro[4.5]deca-1-one, C₁₀H₁₇NO, (1c), were synthesized from benzoic acids 2 in only 3 steps in high yields. Crystallization from n-hexane afforded single crystals, suitable for X-ray diffraction. Thus, the configurations, conformations, and interesting crystal packing effects have been determined unequivocally. The bicyclic skeleton consists of a lactam ring, attached by a spiro junction to a cyclohexane ring. The lactam ring adopts an envelope conformation and the cyclohexane ring has a chair conformation. The main difference between compound 1b and compound 1c is the position of the carbonyl group on the 2-pyrrolidine ring with respect to the methyl group on the 8-position of the cyclohexane ring, which is cis (1b) or trans (1c). A remarkable feature of all three compounds is the existence of a mirror plane within the molecule. Given that all compounds crystallize in centrosymmetric space groups, the packing always contains interesting enantiomer-like pairs. Finally, the structures are stabilized by intermolecular N-H···O hydrogen bonds.}, language = {en} } @phdthesis{Sarhan2019, author = {Sarhan, Radwan Mohamed}, title = {Plasmon-driven photocatalytic reactions monitored by surface-enhanced Raman spectroscopy}, doi = {10.25932/publishup-43330}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-433304}, school = {Universit{\"a}t Potsdam}, year = {2019}, abstract = {Plasmonic metal nanostructures can be tuned to efficiently interact with light, converting the photons into energetic charge carriers and heat. Therefore, the plasmonic nanoparticles such as gold and silver nanoparticles act as nano-reactors, where the molecules attached to their surfaces benefit from the enhanced electromagnetic field along with the generated energetic charge carriers and heat for possible chemical transformations. Hence, plasmonic chemistry presents metal nanoparticles as a unique playground for chemical reactions on the nanoscale remotely controlled by light. However, defining the elementary concepts behind these reactions represents the main challenge for understanding their mechanism in the context of the plasmonically assisted chemistry. Surface-enhanced Raman scattering (SERS) is a powerful technique employing the plasmon-enhanced electromagnetic field, which can be used for probing the vibrational modes of molecules adsorbed on plasmonic nanoparticles. In this cumulative dissertation, I use SERS to probe the dimerization reaction of 4-nitrothiophenol (4-NTP) as a model example of plasmonic chemistry. I first demonstrate that plasmonic nanostructures such as gold nanotriangles and nanoflowers have a high SERS efficiency, as evidenced by probing the vibrations of the rhodamine dye R6G and the 4-nitrothiophenol 4-NTP. The high signal enhancement enabled the measurements of SERS spectra with a short acquisition time, which allows monitoring the kinetics of chemical reactions in real time. To get insight into the reaction mechanism, several time-dependent SERS measurements of the 4-NTP have been performed under different laser and temperature conditions. Analysis of the results within a mechanistic framework has shown that the plasmonic heating significantly enhances the reaction rate, while the reaction is probably initiated by the energetic electrons. The reaction was shown to be intensity-dependent, where a certain light intensity is required to drive the reaction. Finally, first attempts to scale up the plasmonic catalysis have been performed showing the necessity to achieve the reaction threshold intensity. Meanwhile, the induced heat needs to quickly dissipate from the reaction substrate, since otherwise the reactants and the reaction platform melt. This study might open the way for further work seeking the possibilities to quickly dissipate the plasmonic heat generated during the reaction and therefore, scaling up the plasmonic catalysis.}, language = {en} } @phdthesis{Gabriel2019, author = {Gabriel, Christina}, title = {Entwicklung neuer St{\"a}rkederivate f{\"u}r die Anwendung als wasserbasierte Filmbildner in Farben und Lacken}, doi = {10.25932/publishup-43294}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-432942}, school = {Universit{\"a}t Potsdam}, pages = {XVIII, 160, xxxix, x1}, year = {2019}, abstract = {In den letzten Jahrzehnten fand auch in der Beschichtungsindustrie ein Umdenken hin zu umweltfreundlicheren Farben und Lacken statt. Allerdings basieren auch neue L{\"o}sungen meist nicht auf Biopolymeren und in einem noch geringeren Anteil auf wasserbasierten Beschichtungssystemen aus nachwachsenden Rohstoffen. Dies stellt den Ankn{\"u}pfungspunkt dieser Arbeit dar, in der untersucht wurde, ob das Biopolymer St{\"a}rke das Potenzial zum wasserbasierten Filmbildner f{\"u}r Farben und Lacke besitzt. Dabei m{\"u}ssen angelehnt an etablierte synthetische Marktprodukte die folgenden Kriterien erf{\"u}llt werden: Die w{\"a}ssrige Dispersion muss mindestens einen 30\%igen Feststoffgehalt haben, bei Raumtemperatur verarbeitet werden k{\"o}nnen und Viskosit{\"a}ten zwischen 10^2-10^3 mPa·s aufweisen. Die finale Beschichtung muss einen geschlossenen Film bilden und sehr gute Haftfestigkeiten zu einer spezifischen Oberfl{\"a}che, in dieser Arbeit Glas, besitzen. Als Grundlage f{\"u}r die Modifizierung der St{\"a}rke wurde eine Kombination von molekularem Abbau und chemischer Funktionalisierung ausgew{\"a}hlt. Da nicht bekannt war, welchen Einfluss die St{\"a}rkeart, die gew{\"a}hlte Abbaureaktion als auch verschiedene Substituenten auf die Dispersionsherstellung und deren Eigenschaften sowie die Beschichtungseigenschaften aus{\"u}ben k{\"o}nnten, wurden die strukturellen Parameter getrennt voneinander untersucht. Das erste Themengebiet beinhaltete den oxidativen Abbau von Kartoffel- und Palerbsenst{\"a}rke mittels des Hypochlorit-Abbaus (OCl-) und des ManOx-Abbaus (H2O2, KMnO4). Mit beiden Abbaureaktionen konnten vergleichbare gewichtsmittlere Molmassen (Mw) von 2·10^5-10^6 g/mol (GPC-MALS) hergestellt werden. Allerdings f{\"u}hrten die gew{\"a}hlten Reaktionsbedingungen beim ManOx-Abbau zur Bildung von Gelpartikeln. Diese lagen im µm-Bereich (DLS und Kryo-REM-Messungen) und hatten zur Folge, dass die ManOx-Proben deutlich erh{\"o}hte Viskosit{\"a}ten (c: 7,5 \%; 9-260 mPa·s) im Vergleich zu den OCl--Proben (4-10 mPa·s) bei scherverd{\"u}nnendem Verhalten besaßen und die Eigenschaften von viskoelastischen Gelen (G' > G'') zeigten. Des Weiteren wiesen sie reduzierte Heißwasserl{\"o}slichkeiten (95 °C, vorrangig: 70-99 \%) auf. Der OCl--Abbau f{\"u}hrte zu hydrophileren (Carboxylgruppengehalt bis zu 6,1 \%; ManOx: bis zu 3,1 \%), nach 95 °C-Behandlung vollst{\"a}ndig wasserl{\"o}slichen abgebauten St{\"a}rken, die ein Newtonsches Fließverhalten mit Eigenschaften einer viskoelastischen Fl{\"u}ssigkeit (G'' > G') hatten. Die OCl--Proben konnten im Vergleich zu den ManOx-Produkten (10-20 \%) zu konzentrierteren Dispersionen (20-40 \%) verarbeitet werden, die gleichzeitig die Einschr{\"a}nkung von anwendungsrelevanten Mw auf < 7·10^5 g/mol zuließen (Konzentration sollte > 30 \% sein). Außerdem f{\"u}hrten nur die OCl--Proben der Kartoffelst{\"a}rke zu transparenten (alle anderen waren opak) geschlossenen Beschichtungsfilmen. Somit hebt sich die Kombination von OCl--Abbau und Kartoffelst{\"a}rke mit Hinblick auf die Endanwendung ab. Das zweite Themengebiet umfasste Untersuchungen zum Einfluss von Ester- und Hydroxyalkylether-Substituenten auf Basis einer industriell abgebauten Kartoffelst{\"a}rke (Mw: 1,2·10^5 g/mol) vor allem auf die Dispersionsherstellung, die rheologischen Eigenschaften der Dispersionen und die Beschichtungseigenschaften in Kombination mit Glassubstraten. Dazu wurden Ester und Ether mit DS/MS-Werten von 0,07-0,91 synthetisiert. Die Derivate konnten zu wasserbasierten Dispersionen mit Konzentrationen von 30-45 \% verarbeitet werden, wobei bei hydrophoberen Modifikaten ein Co-L{\"o}semittel, Diethylenglycolmonobutylether (DEGBE), eingesetzt werden musste. Die Feststoffgehalte sanken dabei f{\"u}r beide Derivatklassen vor allem mit zunehmender Alkylkettenl{\"a}nge. Die anwendungsrelevanten Viskosit{\"a}ten (323-1240 mPa·s) stiegen auf Grund von Wechselwirkungen tendenziell mit DS/MS und Alkylkettenl{\"a}nge an. Hinsichtlich der Beschichtungseigenschaften erwiesen sich die Ester vergleichend zu den Ethern als die bevorzugte Substituentenklasse, da nur die Ester geschlossene, defektfreie und mehrheitlich transparente Beschichtungsfilme bildeten, die exzellente bis sehr gute Haftfestigkeiten (ISO Klasse: 0 und 1) auf Glas besaßen. Die Ether bildeten mehrheitlich br{\"u}chige Filme. Basierend auf der Kombination der Ergebnisse aus L{\"o}semittelaustausch, den rheologischen Untersuchungen und zus{\"a}tzlichen Oberfl{\"a}chenspannungsmessungen (30-61 mN/m) konnte geschlossen werden, dass wahrscheinlich fehlende oder schlechte Haftfestigkeiten vorrangig akkumuliertem Wasser in den Beschichtungsfilmen (visuell: tr{\"u}b oder weiß) geschuldet sind, w{\"a}hrend die Br{\"u}chigkeit vermutlich auf Wechselwirkungen (H-Br{\"u}cken Wechselwirkungen, hydrophobe Wechselwirkungen) zwischen den Polymeren zur{\"u}ckgef{\"u}hrt werden kann. Insgesamt scheint die Kombination aus Kartoffelst{\"a}rke basierend auf dem OCl--Abbau mit Mw < 7·10^5 g/mol und einem Estersubstituenten eine gute Wahl f{\"u}r wasserbasierte Dispersionen mit hohen Feststoffkonzentrationen (> 30 \%), guter Filmbildung und exzellenten Haftungen auf Glas zu sein.}, language = {de} } @phdthesis{SchulteOsseili2019, author = {Schulte-Osseili, Christine}, title = {Vom Monomer zum Glykopolymer}, doi = {10.25932/publishup-43216}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-432169}, school = {Universit{\"a}t Potsdam}, pages = {xiii, 149}, year = {2019}, abstract = {Glykopolymere sind synthetische und nat{\"u}rlich vorkommende Polymere, die eine Glykaneinheit in der Seitenkette des Polymers tragen. Glykane sind durch die Glykan-Protein-Wechselwirkung verantwortlich f{\"u}r viele biologische Prozesse. Die Beteiligung der Glykanen in diesen biologischen Prozessen erm{\"o}glicht das Imitieren und Analysieren der Wechselwirkungen durch geeignete Modellverbindungen, z.B. der Glykopolymere. Dieses System der Glykan-Protein-Wechselwirkung soll durch die Glykopolymere untersucht und studiert werden, um die spezifische und selektive Bindung der Proteine an die Glykopolymere nachzuweisen. Die Proteine, die in der Lage sind, Kohlenhydratstrukturen selektiv zu binden, werden Lektine genannt. In dieser Dissertationsarbeit wurden verschiedene Glykopolymere synthetisiert. Dabei sollte auf einen effizienten und kosteng{\"u}nstigen Syntheseweg geachtet werden. Verschiedene Glykopolymere wurden durch funktionalisierte Monomere mit verschiedenen Zuckern, wie z.B. Mannose, Laktose, Galaktose oder N-Acetyl-Glukosamin als funktionelle Gruppe, hergestellt. Aus diesen funktionalisierten Glykomonomeren wurden {\"u}ber ATRP und RAFT-Polymerisation Glykopolymere synthetisiert. Die erhaltenen Glykopolymere wurden in Diblockcopolymeren als hydrophiler Block angewendet und die Selbstassemblierung in w{\"a}ssriger L{\"o}sung untersucht. Die Polymere formten in w{\"a}ssriger L{\"o}sung Mizellen, bei denen der Zuckerblock an der Oberfl{\"a}che der Mizellen sitzt. Die Mizellen wurden mit einem hydrophoben Fluoreszenzfarbstoff beladen, wodurch die CMC der Mizellenbildung bestimmt werden konnte. Außerdem wurden die Glykopolymere als Oberfl{\"a}chenbeschichtung {\"u}ber „Grafting from" mit SI-ATRP oder {\"u}ber „Grafting to" auf verschiedene Oberfl{\"a}chen gebunden. Durch die glykopolymerbschichteten Oberfl{\"a}chen konnte die Glykan Protein Wechselwirkung {\"u}ber spektroskopische Messmethoden, wie SPR- und Mikroring Resonatoren untersucht werden. Hierbei wurde die spezifische und selektive Bindung der Lektine an die Glykopolymere nachgewiesen und die Bindungsst{\"a}rke untersucht. Die synthetisierten Glykopolymere k{\"o}nnten durch Austausch der Glykaneinheit f{\"u}r andere Lektine adressierbar werden und damit ein weites Feld an anderen Proteinen erschließen. Die biovertr{\"a}glichen Glykopolymere w{\"a}ren alternativen f{\"u}r den Einsatz in biologischen Prozessen als Transporter von Medikamenten oder Farbstoffe in den K{\"o}rper. Außerdem k{\"o}nnten die funktionalisierten Oberfl{\"a}chen in der Diagnostik zum Erkennen von Lektinen eingesetzt werden. Die Glykane, die keine selektive und spezifische Bindung zu Proteinen eingehen, k{\"o}nnten als antiadsorptive Oberfl{\"a}chenbeschichtung z.B. in der Zellbiologie eingesetzt werden.}, language = {de} } @phdthesis{Yan2019, author = {Yan, Runyu}, title = {Nitrogen-doped and porous carbons towards new energy storage mechanisms for supercapacitors with high energy density}, doi = {10.25932/publishup-43141}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-431413}, school = {Universit{\"a}t Potsdam}, pages = {152}, year = {2019}, abstract = {Supercapacitors are electrochemical energy storage devices with rapid charge/discharge rate and long cycle life. Their biggest challenge is the inferior energy density compared to other electrochemical energy storage devices such as batteries. Being the most widely spread type of supercapacitors, electrochemical double-layer capacitors (EDLCs) store energy by electrosorption of electrolyte ions on the surface of charged electrodes. As a more recent development, Na-ion capacitors (NICs) are expected to be a more promising tactic to tackle the inferior energy density due to their higher-capacity electrodes and larger operating voltage. The charges are simultaneously stored by ion adsorption on the capacitive-type cathode surface and via faradic process in the battery-type anode, respectively. Porous carbon electrodes are of great importance in these devices, but the paramount problems are the facile synthetic routes for high-performance carbons and the lack of fundamental understanding of the energy storage mechanisms. Therefore, the aim of the present dissertation is to develop novel synthetic methods for (nitrogen-doped) porous carbon materials with superior performance, and to reveal a deeper understanding energy storage mechanisms of EDLCs and NICs. The first part introduces a novel synthetic method towards hierarchical ordered meso-microporous carbon electrode materials for EDLCs. The large amount of micropores and highly ordered mesopores endow abundant sites for charge storage and efficient electrolyte transport, respectively, giving rise to superior EDLC performance in different electrolytes. More importantly, the controversial energy storage mechanism of EDLCs employing ionic liquid (IL) electrolytes is investigated by employing a series of porous model carbons as electrodes. The results not only allow to conclude on the relations between the porosity and ion transport dynamics, but also deliver deeper insights into the energy storage mechanism of IL-based EDLCs which is different from the one usually dominating in solvent-based electrolytes leading to compression double-layers. The other part focuses on anodes of NICs, where novel synthesis of nitrogen-rich porous carbon electrodes and their sodium storage mechanism are investigated. Free-standing fibrous nitrogen-doped carbon materials are synthesized by electrospinning using the nitrogen-rich monomer (hexaazatriphenylene-hexacarbonitrile, C18N12) as the precursor followed by condensation at high temperature. These fibers provide superior capacity and desirable charge/discharge rate for sodium storage. This work also allows insights into the sodium storage mechanism in nitrogen-doped carbons. Based on this mechanism, further optimization is done by designing a composite material composed of nitrogen-rich carbon nanoparticles embedded in conductive carbon matrix for a better charge/discharge rate. The energy density of the assembled NICs significantly prevails that of common EDLCs while maintaining the high power density and long cycle life.}, language = {en} } @misc{HeckKanehiraKneippetal.2019, author = {Heck, Christian and Kanehira, Yuya and Kneipp, Janina and Bald, Ilko}, title = {Amorphous Carbon Generation as a Photocatalytic Reaction on DNA-Assembled Gold and Silver Nanostructures}, series = {Mathematisch-Naturwissenschaftliche Reihe}, journal = {Mathematisch-Naturwissenschaftliche Reihe}, number = {732}, issn = {1866-8372}, doi = {10.25932/publishup-43081}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-430812}, pages = {10}, year = {2019}, abstract = {Background signals from in situ-formed amorphous carbon, despite not being fully understood, are known to be a common issue in few-molecule surface-enhanced Raman scattering (SERS). Here, discrete gold and silver nanoparticle aggregates assembled by DNA origami were used to study the conditions for the formation of amorphous carbon during SERS measurements. Gold and silver dimers were exposed to laser light of varied power densities and wavelengths. Amorphous carbon prevalently formed on silver aggregates and at high power densities. Time-resolved measurements enabled us to follow the formation of amorphous carbon. Silver nanolenses consisting of three differently-sized silver nanoparticles were used to follow the generation of amorphous carbon at the single-nanostructure level. This allowed observation of the many sharp peaks that constitute the broad amorphous carbon signal found in ensemble measurements. In conclusion, we highlight strategies to prevent amorphous carbon formation, especially for DNA-assembled SERS substrates.}, language = {en} } @phdthesis{Zimmermann2018, author = {Zimmermann, Marc}, title = {Multifunctional patchy silica particles via microcontact printing}, doi = {10.25932/publishup-42773}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427731}, school = {Universit{\"a}t Potsdam}, pages = {IX, 121, xiii}, year = {2018}, abstract = {This research addressed the question, if it is possible to simplify current microcontact printing systems for the production of anisotropic building blocks or patchy particles, by using common chemicals while still maintaining reproducibility, high precision and tunability of the Janus-balance Chapter 2 introduced the microcontact printing materials as well as their defined electrostatic interactions. In particular polydimethylsiloxane stamps, silica particles and high molecular weight polyethylenimine ink were mainly used in this research. All of these components are commercially available in large quantities and affordable, which gives this approach a huge potential for further up-scaling developments. The benefits of polymeric over molecular inks was described including its flexible influence on the printing pressure. With this alteration of the µCP concept, a new method of solvent assisted particle release mechanism enabled the switch from two-dimensional surface modification to three-dimensional structure printing on colloidal silica particles, without changing printing parameters or starting materials. This effect opened the way to use the internal volume of the achieved patches for incorporation of nano additives, introducing additional physical properties into the patches without alteration of the surface chemistry. The success of this system and its achievable range was further investigated in chapter 3 by giving detailed information about patch geometry parameters including diameter, thickness and yield. For this purpose, silica particles in a size range between 1µm and 5µm were printed with different ink concentrations to change the Janus-balance of these single patched particles. A necessary intermediate step, consisting of air-plasma treatment, for the production of trivalent particles using "sandwich" printing was discovered and comparative studies concerning the patch geometry of single and double patched particles were conducted. Additionally, the usage of structured PDMS stamps during printing was described. These results demonstrate the excellent precision of this approach and opens the pathway for even greater accuracy as further parameters can be finely tuned and investigated, e.g. humidity and temperature during stamp loading. The performance of these synthesized anisotropic colloids was further investigated in chapter 4, starting with behaviour studies in alcoholic and aqueous dispersions. Here, the stability of the applied patches was studied in a broad pH range, discovering a release mechanism by disabling the electrostatic bonding between particle surface and polyelectrolyte ink. Furthermore, the absence of strong attractive forces between divalent particles in water was investigated using XPS measurements. These results lead to the conclusion that the transfer of small PDMS oligomers onto the patch surface is shielding charges, preventing colloidal agglomeration. However, based on this knowledge, further patch modifications for particle self-assembly were introduced including physical approaches using magnetic nano additives, chemical patch functionalization with avidin-biotin or the light responsive cyclodextrin-arylazopyrazoles coupling as well as particle surface modification for the synthesis of highly amphiphilic colloids. The successful coupling, its efficiency, stability and behaviour in different solvents were evaluated to find a suitable coupling system for future assembly experiments. Based on these results the possibility of more sophisticated structures by colloidal self-assembly is given. Certain findings needed further analysis to understand their underlying mechanics, including the relatively broad patch diameter distribution and the decreasing patch thickness for smaller silica particles. Mathematical assumptions for both effects are introduced in chapter 5. First, they demonstrate the connection between the naturally occurring particle size distribution and the broadening of the patch diameter, indicating an even higher precision for this µCP approach. Second, explaining the increase of contact area between particle and ink surface due to higher particle packaging, leading to a decrease in printing pressure for smaller particles. These calculations ultimately lead to the development of a new mechanical microcontact printing approach, using centrifugal forces for high pressure control and excellent parallel alignment of printing substrates. First results with this device and the comparison with previously conducted by-hand experiments conclude this research. It furthermore displays the advantages of such a device for future applications using a mechanical printing approach, especially for accessing even smaller nano particles with great precision and excellent yield. In conclusion, this work demonstrates the successful adjustment of the µCP approach using commercially available and affordable silica particles and polyelectrolytes for high flexibility, reduced costs and higher scale-up value. Furthermore, its was possible to increase the modification potential by introducing three-dimensional patches for additional functionalization volume. While keeping a high colloidal stability, different coupling systems showed the self-assembly capabilities of this toolbox for anisotropic particles.}, language = {en} } @misc{AbbasVranicHoffmannetal.2019, author = {Abbas, Ioana M. and Vranic, Marija and Hoffmann, Holger and El-Khatib, Ahmed H. and Montes-Bay{\´o}n, Mar{\´i}a and M{\"o}ller, Heiko Michael and Weller, Michael G.}, title = {Investigations of the Copper Peptide Hepcidin-25 by LC-MS/MS and NMR⁺}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {701}, issn = {1866-8372}, doi = {10.25932/publishup-42792}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427926}, year = {2019}, abstract = {Hepcidin-25 was identified as themain iron regulator in the human body, and it by binds to the sole iron-exporter ferroportin. Studies showed that the N-terminus of hepcidin is responsible for this interaction, the same N-terminus that encompasses a small copper(II) binding site known as the ATCUN (amino-terminal Cu(II)- and Ni(II)-binding) motif. Interestingly, this copper-binding property is largely ignored in most papers dealing with hepcidin-25. In this context, detailed investigations of the complex formed between hepcidin-25 and copper could reveal insight into its biological role. The present work focuses on metal-bound hepcidin-25 that can be considered the biologically active form. The first part is devoted to the reversed-phase chromatographic separation of copper-bound and copper-free hepcidin-25 achieved by applying basic mobile phases containing 0.1\% ammonia. Further, mass spectrometry (tandemmass spectrometry (MS/MS), high-resolutionmass spectrometry (HRMS)) and nuclear magnetic resonance (NMR) spectroscopy were employed to characterize the copper-peptide. Lastly, a three-dimensional (3D)model of hepcidin-25with bound copper(II) is presented. The identification of metal complexes and potential isoforms and isomers, from which the latter usually are left undetected by mass spectrometry, led to the conclusion that complementary analytical methods are needed to characterize a peptide calibrant or referencematerial comprehensively. Quantitative nuclear magnetic resonance (qNMR), inductively-coupled plasma mass spectrometry (ICP-MS), ion-mobility spectrometry (IMS) and chiral amino acid analysis (AAA) should be considered among others.}, language = {en} } @phdthesis{Kumru2018, author = {Kumru, Baris}, title = {Utilization of graphitic carbon nitride in dispersed media}, doi = {10.25932/publishup-42733}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427339}, school = {Universit{\"a}t Potsdam}, pages = {III, 190}, year = {2018}, abstract = {Utilization of sunlight for energy harvesting has been foreseen as sustainable replacement for fossil fuels, which would also eliminate side effects arising from fossil fuel consumption such as drastic increase of CO2 in Earth atmosphere. Semiconductor materials can be implemented for energy harvesting, and design of ideal energy harvesting devices relies on effective semiconductor with low recombination rate, ease of processing, stability over long period, non-toxicity and synthesis from abundant sources. Aforementioned criteria have attracted broad interest for graphitic carbon nitride (g-CN) materials, metal-free semiconductor which can be synthesized from low cost and abundant precursors. Furthermore, physical properties such as band gap, surface area and absorption can be tuned. g-CN was investigated as heterogeneous catalyst, with diversified applications from water splitting to CO2 reduction and organic coupling reactions. However, low dispersibility of g-CN in water and organic solvents was an obstacle for future improvements. Tissue engineering aims to mimic natural tissues mechanically and biologically, so that synthetic materials can replace natural ones in future. Hydrogels are crosslinked networks with high water content, therefore are prime candidates for tissue engineering. However, the first requirement is synthesis of hydrogels with mechanical properties that are matching to natural tissues. Among different approaches for reinforcement, nanocomposite reinforcement is highly promising. This thesis aims to investigate aqueous and organic dispersions of g-CN materials. Aqueous g-CN dispersions were utilized for visible light induced hydrogel synthesis, where g-CN acts as reinforcer and photoinitiator. Varieties of methodologies were presented for enhancing g-CN dispersibility, from co-solvent method to prepolymer formation, and it was shown that hydrogels with diversified mechanical properties (from skin-like to cartilage-like) are accessible via g-CN utilization. One pot photografting method was introduced for functionalization of g-CN surface which provides functional groups towards enhanced dispersibility in aqueous and organic media. Grafting vinyl thiazole groups yields stable additive-free organodispersions of g-CN which are electrostatically stabilized with increased photophysical properties. Colloidal stability of organic systems provides transparent g-CN coatings and printing g-CN from commercial inkjet printers. Overall, application of g-CN in dispersed media is highly promising, and variety of materials can be accessible via utilization of g-CN and visible light with simple chemicals and synthetic conditions. g-CN in dispersed media will bridge emerging research areas from tissue engineering to energy harvesting in near future.}, language = {en} } @phdthesis{Menski2019, author = {Menski, Antonia Isabell}, title = {Europium als strukturelle Sonde zur Analyse neuartiger Materialien}, doi = {10.25932/publishup-42714}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427141}, school = {Universit{\"a}t Potsdam}, pages = {181}, year = {2019}, abstract = {Im Rahmen dieser Arbeit wird anhand von neuartigen Materialien das Potential der Europium-Lumineszenz f{\"u}r die strukturelle Analyse dargestellt. Bei diesen Materialien handelt es sich zum einen um Nanopartikel mit Matrizes aus mehreren Metall-Mischoxiden und Dotierungen durch die Sonde Europium und zum anderen um Metallorganische Netzwerke (MOFs), die mit Neodym , Samarium- und Europium-Ionen beladen sind. Die Synthese der aus der Kombination von Metalloxiden enthaltenen Nanopartikel ist unter milden Bedingungen mithilfe von speziell daf{\"u}r hergestellten Reagenzien erfolgt und hat zu sehr kleinen, amorphen Nanopartikeln gef{\"u}hrt. Durch eine nachfolgende Temperaturbehandlung hat sich die Kristallinit{\"a}t erh{\"o}ht. Damit verbunden haben sich auch die Kristallstruktur sowie die Position des Dotanden Europium ver{\"a}ndert. W{\"a}hrend die etablierte Methode der R{\"o}ntgendiffraktometrie einen Blick auf das Kristallgitter als Gesamtes erm{\"o}glicht, so trifft die Lumineszenz des Europiums durch die Sichtbarkeit einzelner Stark-Aufspaltungen Aussagen {\"u}ber dessen lokale Symmetrien. Die Symmetrie wird durch Sauerstofffehlstellen ver{\"a}ndert, welche die Sauerstoffleitf{\"a}higkeit der Nanopartikel beeinflussen. Diese ist f{\"u}r die Anwendung als Katalysatoren in industriellen Prozessen und ebenso als Sensoren und Therapeutika in biologischen Systemen von Bedeutung. Zur ersten katalytischen Charakterisierung werden die Proben mittels Temperatur-programmierter Reduktion untersucht. Des Weiteren werden die Mischoxid-Nanopartikel auch hinsichtlich ihrer Verwendbarkeit als Matrix in Aufkonversionsprozessen untersucht. Die Metallorganischen Netzwerke eignen sich aufgrund ihrer mikropor{\"o}sen Struktur f{\"u}r Anwendungen in der Speicherung gleichermaßen von Nutzgasen wie auch von Schadstoffen. Ebenfalls ist eine biologische Anwendung denkbar, die insbesondere den Bereich der drug delivery-Reagenzien betrifft. Erfolgt in die mikropor{\"o}sen Strukturen der Metallorganischen Netzwerke die Einlagerung von Lanthanoid-Ionen, so k{\"o}nnen diese bei der entsprechenden Kombination als Weißlicht-Emittierer fungieren. Dabei ist neben den Verh{\"a}ltnissen zwischen den Lanthanoid-Ionen auch die genaue Position innerhalb des Netzwerks sowie die Distanz zu anderen Ionen von Interesse. Zur Untersuchung dieser Fragestellungen wird die Umgebungssensitivit{\"a}t der Europium-Lumineszenz ausgenutzt. Die auf diese Weise festgestellte Formiat-Bildung h{\"a}ngt von zahlreichen Parametern ab. Insgesamt stellt sich die im Rahmen dieser Arbeit verwendete Methodik des Einsatzes von Europium als strukturelle Sonde in h{\"o}chstem Maße vielseitig dar und zeigt seine gr{\"o}ßte St{\"a}rke in der Kombination mit weiteren Methoden der Strukturanalytik. Die auf diese Weise genauestens charakterisierten neuartigen Materialien k{\"o}nnen nun gezielt und anwendungsfokussiert weiterentwickelt werden.}, language = {de} } @phdthesis{Heiden2018, author = {Heiden, Sophia L.}, title = {Water at α-alumina surfaces}, doi = {10.25932/publishup-42636}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426366}, school = {Universit{\"a}t Potsdam}, pages = {124}, year = {2018}, abstract = {The (0001) surface of α-Al₂O₃ is the most stable surface cut under UHV conditions and was studied by many groups both theoretically and experimentally. Reaction barriers computed with GGA functionals are known to be underestimated. Based on an example reaction at the (0001) surface, this work seeks to improve this rate by applying a hybrid functional method and perturbation theory (LMP2) with an atomic orbital basis, rather than a plane wave basis. In addition to activation barriers, we calculate the stability and vibrational frequencies of water on the surface. Adsorption energies were compared to PW calculations and confirmed PBE+D2/PW stability results. Especially the vibrational frequencies with the B3LYP hybrid functional that have been calculated for the (0001) surface are in good agreement with experimental findings. Concerning the barriers and the reaction rate constant, the expectations are fully met. It could be shown that recalculation of the transition state leads to an increased barrier, and a decreased rate constant when hybrid functionals or LMP2 are applied. Furthermore, the molecular beam scattering of water on (0001) surface was studied. In a previous work by Hass the dissociation was studied by AIMD of molecularly adsorbed water, referring to an equilibrium situation. The experimental method to obtaining this is pinhole dosing. In contrast to this earlier work, the dissociation process of heavy water that is brought onto the surface from a molecular beam source was modeled in this work by periodic ab initio molecular dynamics simulations. This experimental method results in a non-equilibrium situation. The calculations with different surface and beam models allow us to understand the results of the non-equilibrium situation better. In contrast to a more equilibrium situation with pinhole dosing, this gives an increase in the dissociation probability, which could be explained and also understood mechanistically by those calculations. In this work good progress was made in understanding the (1120) surface of α-Al₂O₃ in contact with water in the low-coverage regime. This surface cut is the third most stable one under UHV conditions and has not been studied to a great extent yet. After optimization of the clean, defect free surface, the stability of different adsorbed species could be classified. One molecular minimum and several dissociated species could be detected. Starting from these, reaction rates for various surface reactions were evaluated. A dissociation reaction was shown to be very fast because the molecular minimum is relatively unstable, whereas diffusion reactions cover a wider range from fast to slow. In general, the (112‾0) surface appears to be much more reactive against water than the (0001) surface. In addition to reactivity, harmonic vibrational frequencies were determined for comparison with the findings of the experimental "Interfacial Molecular Spectroscopy" group from Fritz-Haber institute in Berlin. Especially the vibrational frequencies of OD species could be assigned to vibrations from experimental SFG spectra with very good agreement. Also, lattice vibrations were studied in close collaboration with the experimental partners. They perform SFG spectra at very low frequencies to get deep into the lattice vibration region. Correspondingly, a bigger slab model with greater expansion perpendicular to the surface was applied, considering more layers in the bulk. Also with the lattice vibrations we could obtain reasonably good agreement in terms of energy differences between the peaks.}, language = {en} } @phdthesis{Bauch2019, author = {Bauch, Marcel}, title = {Untersuchungen an neuartigen sauerstoffsubstituierten Donoren und Akzeptoren f{\"u}r Singulettsauerstoff}, doi = {10.25932/publishup-42514}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-425140}, school = {Universit{\"a}t Potsdam}, pages = {VI, 196, xiv, A-27}, year = {2019}, abstract = {Im Verlauf dieser Arbeit wurden Aromaten wie Naphthaline und Anthracene mit Singulettsauerstoff, einer reaktiven Form des gew{\"o}hnlichen Sauerstoffs, zu sogenannten Endoperoxiden umgesetzt. Die hier eingesetzten Systeme wurden mit funktionellen Gruppen modifiziert, die {\"u}ber eine Sauerstoffbr{\"u}cke mit dem Aromaten verkn{\"u}pft sind. Die daraus entstandenen Endoperoxide sind meist besonders labil und konnten in dieser Arbeit isoliert und umfassend untersucht werden. Hierbei wurde zum einen das Reaktionsverhalten untersucht. Es konnte gezeigt werden, dass die Aromaten in Abh{\"a}ngigkeit ihrer funktionellen Gruppen unterschiedlich schnell mit Singulettsauerstoff reagieren. Die so ermittelten Reaktivit{\"a}ten wurden zus{\"a}tzlich durch theoretische Berechnungen gest{\"u}tzt. Die resultierenden Endoperoxide wurden unter verschiedenen Bedingungen wie erh{\"o}hter Temperatur oder einem sauren bzw. basischen Milieu auf ihre Stabilit{\"a}t hin untersucht. Dabei konnte gezeigt werden, dass die auf Naphthalinen basierenden Endoperoxiden den gebundenen Singulettsauerstoff in guten Ausbeuten oft schon bei sehr niedrigen Temperaturen (-40 bis 0 °C) freisetzen. Diese Verbindungen k{\"o}nnen daher als milde Quellen dieser reaktiven Sauerstoffspezies eingesetzt werden. Weiterhin konnten bei den Anthracenendoperoxiden Zerfallsmechanismen aufgekl{\"a}rt und andere reaktive Sauerstoffspezies wie Wasserstoffperoxid oder Pers{\"a}uren nachgewiesen werden. Zu den Modifikationen der Aromaten geh{\"o}ren auch Glucosereste. Dadurch k{\"o}nnten sich die hier hergestellten Endoperoxide als vielversprechende Verbindungen in der Krebstherapie herausstellen, da Krebszellen deutlich st{\"a}rker als gesunde Zellen kohlenhydratreiche Verbindungen f{\"u}r ihren Stoffwechsel ben{\"o}tigen. Bei der Spaltung von Endoperoxiden mit Glucosesubstituenten werden ebenfalls reaktive Sauerstoffspezies frei, die so zum Zelltod f{\"u}hren k{\"o}nnten.}, language = {de} } @phdthesis{Cheng2018, author = {Cheng, Xiao}, title = {Controlled solvent vapor annealing of block copolymer films}, doi = {10.25932/publishup-42417}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-424179}, school = {Universit{\"a}t Potsdam}, pages = {X, 166}, year = {2018}, abstract = {This project was focused on exploring the phase behavior of poly(styrene)187000-block-poly(2-vinylpyridine)203000 (SV390) with high molecular weight (390 kg/mol) in thin films, in which the self-assembly of block copolymers (BCPs) was realized via thermo-solvent annealing. The advanced processing technique of solvent vapor treatment provides controlled and stable conditions. In Chapter 3, the factors to influence the annealing process and the swelling behavior of homopolymers are presented and discussed. The swelling behavior of BCP in films is controlled by the temperature of the vapor and of the substrate, on one hand, and variation of the saturation of the solvent vapor atmosphere (different solvents), on the other hand. Additional factors like the geometry and material of the chamber, the type of flow inside the chamber etc. also influence the reproducibility and stability of the processing. The slightly selective solvent vapor of chloroform gives 10\% more swelling of P2VP than PS in films with thickness of ~40 nm. The tunable morphology in ultrathin films of high molecular weight BCP (SV390) was investigated in Chapter 4. First, the swelling behavior can be precisely tuned by temperature and/or vapor flow separately, which provided information for exploring the multiple-parameter-influenced segmental chain mobility of polymer films. The equilibrium state of SV390 in thin films influenced by temperature was realized at various temperatures with the same degree of swelling. Various methods including characterization with SFM, metallization and RIE were used to identify the morphology of films as porous half-layer with PS dots and P2VP matrix. The kinetic investigations demonstrate that on substrates with either weak or strong interaction the original morphology of the BCP with high molecular weight is changed very fast within 5 min, and the further annealing serves for annihilation of defects. The morphological development of symmetric BCP in films with thickness increasing from half-layer to one-layer influenced by confinement factors of gradient film thicknesses and various surface properties of substrates was studied in Chapter 5. SV390 and SV99 films show bulk lamella-forming morphology after slightly selective solvent vapor (chloroform) treatment. SV99 films show cylinder-forming morphology under strongly selective solvent vapor (toluene) treatment since the asymmetric structure (caused by toluene uptake in PS blocks only) of SV99 block copolymer during annealing. Both kinds of morphology (lamella and cylinder) are influenced by the film thickness. The annealed morphology of SV390 and SV99 influenced by the combination of confined film and substrate property is similar to the morphology on flat silicon wafers. In this chapter the gradients in the film thickness and surface properties of the substrates with regard to their influence on the morphological development in thin BCP films are presented. Directed self-assembly (graphoepitaxy) of this SV390 was also investigated to compare with systematically reported SV99. In Chapter 6 an approach to induced oriented microphase separation in thick block copolymer films via treatment with the oriented vapor flow using mini-extruder is envisaged to be an alternative to existing methodologies, e.g. via non-solvent-induced phase separation. The preliminary tests performed in this study confirm potential perspective of this method, which alters the structure through the bulk of the film (as revealed by SAXS measurements), but more detailed studies have to be conducted in order to optimize the preparation.}, language = {en} } @phdthesis{Grunert2018, author = {Grunert, Bianca}, title = {Entwicklung von Markierungsreagenzien f{\"u}r die bildgebende Diagnostik}, doi = {10.25932/publishup-42283}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-422830}, school = {Universit{\"a}t Potsdam}, pages = {155}, year = {2018}, abstract = {Die intrazellul{\"a}re Markierung mit geeigneten Reagenzien erm{\"o}glicht ihre bildgebende Darstellung in lebenden Organismen. Dieses Verfahren (auch „Zell-Tracking" genannt) wird in der Grundlagenforschung zur Entwicklung zellul{\"a}rer Therapien, f{\"u}r die Erforschung pathologischer Prozesse, wie der Metastasierung, sowie f{\"u}r Therapiekontrollen eingesetzt. Besondere Bedeutung haben in den letzten Jahren zellul{\"a}re Therapien mit Stammzellen erlangt, da sie großes Potential bei der Regeneration von Geweben bei Krankheiten wie Morbus Parkinson oder Typ-1-Diabetes versprechen. F{\"u}r die Entwicklung einer zellul{\"a}ren Therapie sind Informationen {\"u}ber den Verbleib der applizierten Zellen in vivo (Homing-Potential), {\"u}ber ihre Zellphysiologie sowie {\"u}ber die Entstehung m{\"o}glicher Entz{\"u}ndungen notwendig. Das Ziel der vorliegenden Arbeit war daher die Synthese von Markierungsreagenzien, die nicht nur eine effiziente Zellmarkierung erm{\"o}glichen, sondern einen synergistischen Effekt hinsichtlich des modalit{\"a}ts{\"u}bergreifenden Einsatzes in den bildgebenden Verfahren MRT und Laser-Ablation(LA)-ICP-MS erlauben. Die MRT-Bildgebung erm{\"o}glicht die nicht invasive Nachverfolgung markierter Zellen in vivo und die LA-ICP-MS die anschließende ex vivo Analytik zur Darstellung der Elementverteilung (Bioimaging) in einer Biopsieprobe oder in einem Gewebeschnitt. F{\"u}r diese Zwecke wurden zwei verschiedene Markierungsreagenzien mit dem kontrastgebenden Element Gadolinium synthetisiert. Gadolinium eignet sich aufgrund seines hohen magnetischen Moments hervorragend f{\"u}r die MRT-Bildgebung und da es in Biomolek{\"u}len nicht nat{\"u}rlich vorkommt, konnten die Reagenzien gleichermaßen f{\"u}r die Zellmarkierung und das Bioimaging mit der LA-ICP-MS untersucht werden. F{\"u}r die Synthese eines makromolekularen Reagenzes wurde das kommerziell verf{\"u}gbare Dendrimer G5-PAMAM {\"u}ber bifunktionelle Linker mit dem Chelator DOTA funktionalisiert, um anschließend Gadolinium zu komplexieren. Ein zweites, nanopartikul{\"a}res Reagenz wurde {\"u}ber eine Solvothermal-Synthese erhalten, bei der Ln:GdVO4-Nanokristalle mit einer funktionellen Polyacryls{\"a}ure(PAA)-H{\"u}lle dargestellt wurden. Die Dotierung der Ln:GdVO4-PAA Nanokristalle mit verschiedenen Lanthanoiden (Ln=Eu, Tb) zeigte ihre prinzipielle Multiplexf{\"a}higkeit in der LA-ICP-MS. Beide Markierungsreagenzien zeichneten sich durch gute Biovertr{\"a}glichkeiten und r1-Relaxivit{\"a}ten aus, was zudem ihr Potential f{\"u}r Anwendungen als pr{\"a}klinische „blood-pool" MRT-Kontrastmittel belegte. Die Untersuchung der Zellmarkierung erfolgte anhand einer Tumorzelllinie und einer Stammzelllinie, wobei beide Zellarten erfolgreich intrazellul{\"a}r mit beiden Reagenzien markiert wurden. Nach der Zellmarkierung veranschaulichte die in vitro MRT-Bildgebung von Zell-Phantomen eine deutlichere Kontrastverst{\"a}rkung der Zellen nach der Markierung mit den Nanokristallen im Vergleich zum kommerziellen Kontrastmittel Magnevist®. Die hohe Effizienz der Zellmarkierung mit den Nanokristallen und die damit verbundenen hohen Signalintensit{\"a}ten in einer einzelnen Zelle erlaubten beim Bioimaging mit der LA-ICP-MS, Messungen bis zu einer Aufl{\"o}sung von 4 µm Laser Spot Size. Nach der Zellmarkierung mit den DOTA(Gd3+)-funktionalisierten G5-PAMAM Dendrimeren waren hingegen Aufnahmen mit der LA-ICP-MS nur bis zu einer Aufl{\"o}sung von 12 µm Laser Spot Size m{\"o}glich. Insgesamt waren die Ln:GdVO4-PAA Nanokristalle mit gr{\"o}ßerer Ausbeute und kosteng{\"u}nstiger herstellbar als die DOTA(Gd3+)-funktionalisierten G5-PAMAM Dendrimere und zeigten zudem eine effizientere Zellmarkierung. Die Ln:GdVO4-PAA Nanokristalle erscheinen somit f{\"u}r das Zell-Tracking als besonders vielversprechend. Darauf aufbauend wurden die Nanokristalle zur Etablierung der Antik{\"o}rper-Konjugation ausgew{\"a}hlt, was sie f{\"u}r die molekulare in vivo Bildgebung sowie f{\"u}r die Immuno-Bildgebung von Gewebeschnitten oder Biopsie-Proben mit der LA-ICP-MS anwendbar macht.}, language = {de} } @phdthesis{Vogel2018, author = {Vogel, Stefanie}, title = {Sequence dependency of photon and electron induced DNA strand breaks}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-419669}, school = {Universit{\"a}t Potsdam}, pages = {xii, 117}, year = {2018}, abstract = {Deoxyribonucleic acid (DNA) is the carrier of human genetic information and is exposed to environmental influences such as the ultraviolet (UV) fraction of sunlight every day. The photostability of the DNA against UV light is astonishing. Even if the DNA bases have a strong absorption maximum at around 260 nm/4.77 eV, their quantum yield of photoproducts remains very low 1. If the photon energies exceed the ionization energy (IE) of the nucleobases ( ̴ 8-9 eV) 2, the DNA can be severely damaged. Photoexcitation and -ionization reactions occur, which can induce strand breaks in the DNA. The efficiency of the excitation and ionization induced strand breaks in the target DNA sequences are represented by cross sections. If Si as a substrate material is used in the VUV irradiation experiments, secondary electrons with an energy below 3.6 eV are generated from the substrate. This low energy electrons (LEE) are known to induce dissociative electron attachment (DEA) in DNA and with it DNA strand breakage very efficiently. LEEs play an important role in cancer radiation therapy, since they are generated secondarily along the radiation track of ionizing radiation. In the framework of this thesis, different single stranded DNA sequences were irradiated with 8.44 eV vacuum UV (VUV) light and cross sections for single strand breaks (SSB) were determined. Several sequences were also exposed to secondary LEEs, which additionally contributed to the SSBs. First, the cross sections for SSBs depending on the type of nucleobases were determined. Both types of DNA sequences, mono-nucleobase and mixed sequences showed very similar results upon VUV radiation. The additional influence of secondarily generated LEEs resulted in contrast in a clear trend for the SSB cross sections. In this, the polythymine sequence had the highest cross section for SSBs, which can be explained by strong anionic resonances in this energy range. Furthermore, SSB cross sections were determined as a function of sequence length. This resulted in an increase in the strand breaks to the same extent as the increase in the geometrical cross section. The longest DNA sequence (20 nucleotides) investigated in this series, however, showed smaller cross section values for SSBs, which can be explained by conformational changes in the DNA. Moreover, several DNA sequences that included the radiosensitizers 5-Bromouracil (5BrU) and 8-Bromoadenine (8BrA) were investigated and the corresponding SSB cross sections were determined. It was shown that 5BrU reacts very strongly to VUV radiation leading to high strand break yields, which showed in turn a strong sequence-dependency. 8BrA, on the other hand, showed no sensitization to the applied VUV radiation, since almost no increase in strand breakage yield was observed in comparison to non-modified DNA sequences. In order to be able to identify the mechanisms of radiation damage by photons, the IEs of certain DNA sequences were further explored using photoionization tandem mass spectrometry. By varying the DNA sequence, both the IEs depending on the type of nucleobase as well as on the DNA strand length could be identified and correlated to the SSB cross sections. The influence of the IE on the photoinduced reaction in the brominated DNA sequences could be excluded.}, language = {en} } @phdthesis{Choi2018, author = {Choi, Youngeun}, title = {DNA origami structures as versatile platforms for nanophotonics}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-421483}, school = {Universit{\"a}t Potsdam}, pages = {125}, year = {2018}, abstract = {Nanophotonics is the field of science and engineering aimed at studying the light-matter interactions on the nanoscale. One of the key aspects in studying such optics at the nanoscale is the ability to assemble the material components in a spatially controlled manner. In this work, DNA origami nanostructures were used to self-assemble dye molecules and DNA coated plasmonic nanoparticles. Optical properties of dye nanoarrays, where the dyes were arranged at distances where they can interact by F{\"o}rster resonance energy transfer (FRET), were systematically studied according to the size and arrangement of the dyes using fluorescein (FAM) as the donor and cyanine 3 (Cy 3) as the acceptor. The optimized design, based on steady-state and time-resolved fluorometry, was utilized in developing a ratiometric pH sensor with pH-inert coumarin 343 (C343) as the donor and pH-sensitive FAM as the acceptor. This design was further applied in developing a ratiometric toxin sensor, where the donor C343 is unresponsive and FAM is responsive to thioacetamide (TAA) which is a well-known hepatotoxin. The results indicate that the sensitivity of the ratiometric sensor can be improved by simply arranging the dyes into a well-defined array. The ability to assemble multiple fluorophores without dye-dye aggregation also provides a strategy to amplify the signal measured from a fluorescent reporter, and was utilized here to develop a reporter for sensing oligonucleotides. By incorporating target capturing sequences and multiple fluorophores (ATTO 647N dye molecules), a reporter for microbead-based assay for non-amplified target oligonucleotide sensing was developed. Analysis of the assay using VideoScan, a fluorescence microscope-based technology capable of conducting multiplex analysis, showed the DNA origami nanostructure based reporter to have a lower limit of detection than a single stranded DNA reporter. Lastly, plasmonic nanostructures were assembled on DNA origami nanostructures as substrates to study interesting optical behaviors of molecules in the near-field. Specifically, DNA coated gold nanoparticles, silver nanoparticles, and gold nanorods, were placed on the DNA origami nanostructure aiming to study surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS) of molecules placed in the hotspot of coupled plasmonic structures.}, language = {en} }