@phdthesis{Wattebled2006, author = {Wattebled, Laurent}, title = {Oligomeric surfactants as novel type of amphiphiles : structure - property relationships and behaviour with additives}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12855}, school = {Universit{\"a}t Potsdam}, year = {2006}, abstract = {The properties of a series of well-defined new surfactant oligomers (dimers to tetramers)were examined. From a molecular point of view, these oligomeric surfactants consist of simple monomeric cationic surfactant fragments coupled via the hydrophilic ammonium chloride head groups by spacer groups (different in nature and length). Properties of these cationic surfactant oligomers in aqueous solution such as solubility, micellization and surface activity, micellar size and aggregation number were discussed with respect to the two new molecular variables introduced, i.e. degree of oligomerization and spacer group, in order to establish structure - property relationships. Thus, increasing the degree of oligomerization results in a pronounced decrease of the critical micellization concentration (CMC). Both reduced spacer length and increased spacer hydrophobicity lead to a decrease of the CMC, but to a lesser extent. For these particular compounds, the formed micelles are relatively small and their aggregation number decreases with increasing the degree of oligomerization, increasing spacer length and sterical hindrance. In addition, pseudo-phase diagrams were established for the dimeric surfactants in more complex systems, namely inverse microemulsions, demonstrating again the important influence of the spacer group on the surfactant behaviour. Furthermore, the influence of additives on the property profile of the dimeric compounds was examined, in order to see if the solution properties can be improved while using less material. Strong synergistic effects were observed by adding special organic salts (e.g. sodium salicylate, sodium vinyl benzoate, etc.) to the surfactant dimers in stoichiometric amounts. For such mixtures, the critical aggregation concentration is strongly shifted to lower concentration, the effect being more pronounced for dimers than for analogous monomers. A sharp decrease of the surface tension can also be attained. Many of the organic anions produce viscoelastic solutions when added to the relatively short-chain dimers in aqueous solution, as evidenced by rheological measurements. This behaviour reflects the formation of entangled wormlike micelles due to strong interactions of the anions with the cationic surfactants, decreasing the curvature of the micellar aggregates. It is found that the associative behaviour is enhanced by dimerization. For a given counterion, the spacer group may also induce a stronger viscosifying effect depending on its length and hydrophobicity. Oppositely charged surfactants were combined with the cationic dimers, too. First, some mixtures with the conventional anionic surfactant SDS revealed vesicular aggregates in solution. Also, in view of these catanionic mixtures, a novel anionic dimeric surfactant based on EDTA was synthesized and studied. The synthesis route is relatively simple and the compound exhibits particularly appealing properties such as low CMC and σCMC values, good solubilization capacity of hydrophobic probes and high tolerance to hard water. Noteworthy, mixtures with particular cationic dimers gave rise to viscous solutions, reflecting the micelle growth.}, language = {en} } @phdthesis{Wang2019, author = {Wang, Xuepu}, title = {Polydimethylsiloxane wrinkles for surface patterns and assembly of metallic nanoparticles}, school = {Universit{\"a}t Potsdam}, pages = {131}, year = {2019}, language = {en} } @phdthesis{Wang2003, author = {Wang, Liying}, title = {Lipid monolayers coupled to polyelectrolyte multilayers : stability, dynamics and interactions}, pages = {133, II S.}, year = {2003}, language = {en} } @phdthesis{Wang2018, author = {Wang, Li}, title = {Reprogrammable, magnetically controlled polymer actuators}, school = {Universit{\"a}t Potsdam}, pages = {xxviii, 107}, year = {2018}, abstract = {Polymeric materials, which can perform reversible shape changes after programming, in response to a thermal or electrical stimulation, can serve as (soft) actuating components in devices like artificial muscles, photonics, robotics or sensors. Such polymeric actuators can be realized with hydrogels, liquid crystalline elastomers, electro-active polymers or shape-memory polymers by controlling with stumuli such as heat, light, electrostatic or magnetic field. If the application conditions do not allow the direct heating or electric stimulation of these smart devices, noncontact triggering will be required. Remotely controlled actuation have been reported for liquid crystalline elastomer composites or shape-memory polymer network composites, when a persistent external stress is applied during inductive heating in an alternating magnetic field. However such composites cannot meet the demands of applications requiring remotely controlled free-standing motions of the actuating components. The current thesis investigates, whether a reprogrammable remotely controlled soft actuator can be realized by magneto-sensitive multiphase shape-memory copolymer network composites containing magnetite nanoparticles as magneto-sensitive multivalent netpoints. A central hypothesis was that a magnetically controlled two-way (reversible bidirectional) shape-memory effect in such nanocomposites can be achieved without application of external stress (freestanding), when the required orientation of the crystallizable actuation domains (ADs) can be ensured by an internal skeleton like structure formed by a second crystallizable phase determing the samples´s geometry, while magneto-sensitive iron oxide nanoparticles covalently integrated in the ADs allow remote temperature control. The polymer matrix of these composites should exhibit a phase-segregated morphology mainly composed of cyrstallizable ADs, whereby a second set of higher melting crystallites can take a skeleton like, geometry determining function (geometry determining domains, GDs) after programming of the composite and in this way the orientation of the ADs is established and maintained during actuation. The working principle for the reversible bidirectional movements in the multiphase shape-memory polymer network composite is related to a melting-induced contraction (MIC) during inductive heating and the crystallization induced elongation (CIE) of the oriented ADs during cooling. Finally, the amount of multivalent magnetosensitive netpoints in such a material should be as low as possible to ensure an adequate overall elasticity of the nanocomposite and at the same time a complete melting of both ADs and GDs via inductive heating, which is mandatory for enabling reprogrammability. At first, surface decorated iron oxide nanoparticles were synthesized and investigated. The coprecipitation method was applied to synthesize magnetic nanoparticles (mNPs) based on magnetite with size of 12±3 nm and in a next step a ring-opening polymerization (ROP) was utilized for covalent surface modification of such mNPs with oligo(ϵ-caprolactone) (OCL) or oligo(ω-pentadecalactone) (OPDL) via the "grafting from" approach. A successful coating of mNPs with OCL and OPDL was confirmed by differential scanning calorimetry (DSC) experiments showing melting peaks at 52±1 °C for mNP-OCL and 89±1 °C for mNP-OPDL. It was further explored whether two-layered surface decorated mNPs, can be prepared via a second surface-initiated ROP of mNP-OCL or mNP-OPDL with ω-pentadecalactone or ϵ-caprolactone. The observation of two distinct melting transitions in DSC experiments as well as the increase in molecular weight of the detached coatings determined by GPC and 1H-NMR indicated a successful synthesis of the twolayered nanoparticles mNP-OCL-OPDL and mNP-OPDL-OCL. In contrast TEM micrographs revealed a reduction of the thickness of the polymeric coating on the nanoparticles after the second ROP, indicating that the applied synthesis and purification required further optimization. For evaluating the impact of the dispersion of mNPs within a polymer matrix on the resulting inductive heating capability of composites, plain mNPs as well as OCL coated magnetite nanoparticles (mNP-OCLs) were physically incorporated into crosslinked poly(ε-caprolactone) (PCL) networks. Inductive heating experiments were performed with both networks cPCL/mNP and cPCL/mNP-OCL in an alternating magnetic field (AMF) with a magnetic field strength of H = 30 kA·m-1. Here a bulk temperature of Tbulk = 74±2 °C was achieved for cPCL/mNP-OCL, which was almost 20 °C higher than the melting transition of the PCL-based polymer matrix. In contrast, the composite with plain mNPs could only reach a Tbulk of 48±2 °C, which is not sufficient for a complete melting of all PCL crystallites as required for actuation. The inductive heating capability of a multiphase copolymer nanocomposite network (designed as soft actuators) containing surface decorated mNPs as covalent netpoints was investigated. Such composite was synthesized from star-shaped OCL and OPDL precursors, as well as mNP-OCLs via reaction with HDI. The weight ratio of OPDL and OCL in the starting reaction mixture was 15/85 (wt\%/wt\%) and the amount of iron oxide in the nanocomposite was 4 wt\%. DSC experiments revealed two well separated melting and crystallization peaks confirming the required phase-segregated morphology in the nanocomposite NC-mNP-OCL. TEM images could illustrate a phase-segregated morphology of the polymer matrix on the microlevel with droplet shaped regions attributed to the OPDL domains dispersed in an OCL matrix. The TEM images could further demonstrate that the nanoparticulate netpoints in NC-mNP-OCL were almost homogeneously dispersed within the OCL domains. The tests of the inductive heating capability of the nanocomposites at a magnetic field strength of Hhigh = 11.2 kA·m-1 revealed a achievable plateau surface temperature of Tsurf = 57±1 °C for NC-mNP-OCL recorded by an infrared video camera. An effective heat generation constant (̅P) can be derived from a multi-scale model for the heat generation, which is proportional to the rate of heat generation per unit volume of the sample. NC-mNP-OCL with homogeneously dispersed mNP-OCLs exhibited a ̅P value of 1.04±0.01 K·s- 1 at Hhigh, while at Hreset = 30.0 kA·m-1 a Tsurf of 88±1 °C (where all OPDL related crystallite are molten) and a ̅P value of 1.93±0.02 K·s-1 was obtained indicating a high magnetic heating capability of the composite. The free-standing magnetically-controlled reversible shape-memory effect (mrSME) was explored with originally straight nanocomposite samples programmed by bending to an angle of 180°. By switching the magnetic field on and off the composite sample was allowed to repetitively heat to 60 °C and cool to the ambient temperature. A pronounced mrSME, characterized by changes in bending angle of Δϐrev = 20±3° could be obtained for a composite sample programmed by bending when a magnetic field strength of Hhigh = 11.2 kA·m-1 was applied in a multi-cyclic magnetic bending experiment with 600 heating-cooling cycles it could be shown that the actuation performance did not change with increasing number of test cycles, demonstrating the accuracy and reproducibility of this soft actuator. The degree of actuation as well as the kinetics of the shape changes during heating could be tuned by variation of the magnetic filed strength between Hlow and Hhigh or the magnetic field exposure time. When Hreset = 30.0 kA·m-1 was applied the programmed geometry was erased and the composite sample returned to it´s originally straight shape. The reprogrammability of the nanocomposite actuators was demonstrated by one and the same test specimen first exhibiting reversible angle changes when programmed by bending, secondly reprogrammed to a concertina, which expands upon inductive heating and contracts during cooling and finally reprogrammed to a clip like shape, which closes during cooling and opens when Hhigh was applied. In a next step the applicability of the presented remote controllable shape-memory polymer actuators was demonstrated by repetitive opening and closing of a multiring device prepared from NC-mNP-OCL, which repetitively opens and closes when a alternating magnetic field (Hhigh = 11.2 kA·m-1) was switched on and off. For investigation of the micro- and nanostructural changes related to the actuation of the developed nanocomposite, AFM and WAXS experiments were conducted with programmed nanocomposite samples under cyclic heating and cooling between 25 °C and 60 °C. In AFM experiments the change in the distance (D) between representative droplet-like structures related to the OPDL geometry determining domains was used to calculate the reversible change in D. Here Drev = 3.5±1\% was found for NC-mNP-OCL which was in good agreement with the results of the magneto-mechanical actuation experiments. Finally, the analysis of azimuthal (radial) WAXS scattering profiles could support the oriented crystallization of the OCL actuation domains at 25 °C. In conclusion, the results of this work successfully demonstrated that shape-memory polymer nanocomposites, containing mNPs as magneto-sensitive multifunctional netpoints in a covalently crosslinked multiphase polymer matrix, exhibit magnetically (remotely) controlled actuations upon repetitive exposure to an alternating magnetic field. Furthermore, the (shape) memory of such a nanocomposite can be erased by exposing it to temperatures above the melting temperature of the geometry forming domains, which allows a reprogramming of the actuator. These findings would be relevant for designing novel reprogrammable remotely controllable soft polymeric actuators.}, language = {en} } @phdthesis{Wandrey1997, author = {Wandrey, Christine}, title = {Polyelektrolyte : makromolekulare Parameter und Elektrolytverhalten}, publisher = {Cuvillier}, address = {G{\"o}ttingen}, isbn = {3-89588-814-1}, pages = {III, 190 S.: graph. Darst.}, year = {1997}, language = {de} } @phdthesis{Walther2018, author = {Walther, Sebastian}, title = {Funktionalisierung von {\"O}ls{\"a}uremethylester und Alkydharzen f{\"u}r die photoinduzierte radikalische Polymerisation im UV Bereich}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-421467}, school = {Universit{\"a}t Potsdam}, pages = {136}, year = {2018}, abstract = {Die vorliegende Arbeit behandelt die Synthese und Charakterisierung von funktionalisierten Alkydharzen und die photoinduzierte Polymerisation dieser unter Einsatz einer Quecksilberdampflampe oder einer UV LED mit unterschiedlicher Lichtintensit{\"a}t. Der Fokus dieser Arbeit bestand in der gezielten Substitution der internalen Doppelbindungen der Fetts{\"a}ureester durch reaktivere Gruppen, wie Acrylate oder Methacrylate, welche f{\"u}r Alkydharze in dieser Form so in der Literatur nicht beschrieben sind. Untersuchungen des Polymerisationsverhaltens dieser funktionalisierten Harze wurden mit der Photo DSC durchgef{\"u}hrt, wobei Bis - (4 - methoxybenzoyl) diethylgermanium als Photoinitiator diente. Die Ergebnisse haben gezeigt, dass die Harze radikalisch polymerisiert werden k{\"o}nnen und eine geringere Abh{\"a}ngigkeit von der Umgebungsatmosph{\"a}re (Luftsauerstoff bzw. Stickstoff) vorliegt. Dies ist so in der Literatur f{\"u}r funktionalisierte Alkydharze nicht bekannt. Abmischungen von unterschiedlichen Monomeren und funktionalisierten Harzen bewirkten eine Steigerung der Viskosit{\"a}t sowie eine Verringerung der Sauerstoffinhibierung im Zuge der photoinduzierten Polymerisation unter Luftsauerstoff f{\"u}r die Quecksilberdampflampe und der UV LED. Zur Untersuchung der sauerstoffinhibierenden Wirkung der Harze sind Synthesen unterschiedlicher, funktionalisierter {\"O}ls{\"a}uremethylester als Modellsubstanzen durchgef{\"u}hrt worden. Ein verbessertes Polymerisationsverhalten und eine geringe Abh{\"a}ngigkeit von der Umgebungsatmosph{\"a}re konnte f{\"u}r die Modelle nachgewiesen werden. Zur Aufkl{\"a}rung des verbesserten Polymerisationsverhaltens sind gezielt Substituenten (Imidazol, Brom, Alkohol, Acetat) in den funktionalisierten {\"O}ls{\"a}uremethylester eingebaut worden, um den Einfluss dieser aufzuzeigen. Im Rahmen dieser Synthesen sind neuartige Strukturen synthetisiert worden, welche so in der Literatur nicht beschrieben sind. Die Gegen{\"u}berstellung der Polymerisationszeit, der Umsatz der (Meth-)Acrylatgruppen sowie die Zeit zum Erreichen der maximalen Polymerisationsgeschwindigkeit unter Verwendung von unterschiedlichen UV Lichtquellen hat einen Einfluss der Substituenten auf das Polymerisationsverhalten gezeigt.}, 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} } @phdthesis{Wacker2008, author = {Wacker, Philipp}, title = {Konformationsanalyse meso-substituierter Porphyrine mittels NMR-Spektroskopie und quantenchemischer Berechnungen}, address = {Potsdam}, pages = {112, A36 : graph. Darst.}, year = {2008}, language = {de} } @phdthesis{Wacker2008, author = {Wacker, Philipp}, title = {Konformationsanalyse meso-substituierter Porphyrine mittels NMR-Spektroskopie und quantenchemischer Berechnungen}, address = {Potsdam}, pages = {112 S., A36: Ill., graph. Darst.}, year = {2008}, language = {de} } @phdthesis{Vukicevic2011, author = {Vukicevic, Radovan}, title = {Iodine- and azide-terminated poly(vinylidene fluoride) as a building block for the preparation of hybrid materials and block copolymers}, address = {Potsdam}, pages = {122 S.}, year = {2011}, 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{Voss2005, author = {Voß, Rebecca}, title = {Mesoporous organosilica materials with amine functions : surface characteristics and chirality}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5287}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {In this work mesoporous organisilica materials are synthesized through the silica sol-gel process. For this a new class of precursors which are also surfactant are synthesized and self-assembled. This leads to a high surface area functionality which is analysized with copper (II) and water adsorption.}, subject = {Silicate}, language = {en} } @phdthesis{Vorwerg1997, author = {Vorwerg, Lars}, title = {Elektrokinetische Untersuchungen an Modellkolloiden zur Beurteilung ihrer Stabilit{\"a}t}, address = {Teltow}, pages = {104 S. : graph. Darst.}, year = {1997}, language = {de} } @phdthesis{Vorndran2001, author = {Vorndran, Katja Marianne}, title = {Einfache Decarbonylierungen und stereoselektive Oxidationen von Cyclohexadienen und Cyclohexenen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0000331}, school = {Universit{\"a}t Potsdam}, year = {2001}, abstract = {Zusammenfassend konnte im Rahmen dieser Arbeit das Synthesepotential von Cyclohexadienen und Cyclohexenen deutlich erweitert werden. Die Darstellung der 1-Alkylcyclohexa-2,5-dien-1-carbons{\"a}uren erfolgte mittels Birch-Reduktion in fl{\"u}ssigem Ammoniak und anschließender Umsetzung der intermedi{\"a}r entstehenden Dianionen mit Alkylhalogeniden. So konnte ausgehend von verschiedenen Benzoes{\"a}urederivaten eine Reihe interessanter Cyclohexadiene in sehr guten Ausbeuten synthetisiert werden. Erstmals gelangen s{\"a}urekatalysierte Decarbonylierungen von Cyclohexadiencarbons{\"a}uren, was die einfache Synthese substituierter Aromaten in ausgezeichneten Ausbeuten erm{\"o}glichte. In dieser Arbeit wird der Reaktionsmechanismus vorgestellt, welcher durch den Nachweis von Kohlenmonoxid in der Gasphase der Reaktionsl{\"o}sung durch IR-Spektroskopie untermauert wird. Bei der s{\"a}urekatalysierten Umsetzung von 3-alkylsubstituierten Cyclohexadien-carbons{\"a}uren entstanden neben den erwarteten Aromaten Lactone in ca. 50\% Ausbeute. Schließlich zeigen die untersuchten Singulettsauerstoff-En-Reaktionen, der im ersten Teil dargestellten Cyclohexadiene und Lactone, durchweg hohe Regioselektivit{\"a}ten und lieferten durch elektrostatische Wechselwirkungen und konformative Effekte zum Teil sehr gute Diastereoselektivit{\"a}ten. Die auxiliarkontrollierte Photooxygenierungen von Cyclohexenon welches mit verschiedenen Weins{\"a}ureestern ketalisiert wurde, zeigten jedoch keine bevorzugte p-Facialit{\"a}t des Singulettsauerstoffs.}, subject = {Cyclohexadienderivate ; Chemische Synthese ; Birch-Reduktion ; Decarbonylierung | Cyclohexadienderivate ; Photooxidation ; Stereoselektive Reaktion ;}, language = {de} } @phdthesis{Vorberg1998, author = {Vorberg, Kerstin}, title = {Polyelektrolytadsorption an geladene Lipid-Monoschichten}, pages = {157 S. : graph. Darst.}, year = {1998}, language = {de} } @phdthesis{vonRuestenLange2012, author = {von R{\"u}sten-Lange, Maik}, title = {Improving Hemocompatibility of poly(ether imide) by surface functionalization with polyethers}, address = {Potsdam}, pages = {136, L S.}, year = {2012}, language = {en} } @phdthesis{Volkmer1996, author = {Volkmer, Petra}, title = {Beitr{\"a}ge zu Stabilit{\"a}ts-Untersuchungen von Cephalosporin-Derivaten in L{\"o}sungen}, pages = {117 S.}, year = {1996}, 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{VillatoroLeal2018, author = {Villatoro Leal, Jos{\´e} Andr{\´e}s}, title = {A combined approach for the analysis of biomolecules using IR-MALDI ion mobility spectrometry and molecular dynamics simulations of peptide ions in the gas phase}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-419723}, school = {Universit{\"a}t Potsdam}, pages = {133}, year = {2018}, abstract = {The aim of this doctoral thesis was to establish a technique for the analysis of biomolecules with infrared matrix-assisted laser dispersion (IR-MALDI) ion mobility (IM) spectrometry. The main components of the work were the characterization of the IR-MALDI process, the development and characterization of different ion mobility spectrometers, the use of IR-MALDI-IM spectrometry as a robust, standalone spectrometer and the development of a collision cross-section estimation approach for peptides based on molecular dynamics and thermodynamic reweighting. First, the IR-MALDI source was studied with atmospheric pressure ion mobility spectrometry and shadowgraphy. It consisted of a metal capillary, at the tip of which a self-renewing droplet of analyte solution was met by an IR laser beam. A relationship between peak shape, ion desolvation, diffusion and extraction pulse delay time (pulse delay) was established. First order desolvation kinetics were observed and related to peak broadening by diffusion, both influenced by the pulse delay. The transport mechanisms in IR-MALDI were then studied by relating different laser impact positions on the droplet surface to the corresponding ion mobility spectra. Two different transport mechanisms were determined: phase explosion due to the laser pulse and electrical transport due to delayed ion extraction. The velocity of the ions stemming from the phase explosion was then measured by ion mobility and shadowgraphy at different time scales and distances from the source capillary, showing an initially very high but rapidly decaying velocity. Finally, the anatomy of the dispersion plume was observed in detail with shadowgraphy and general conclusions over the process were drawn. Understanding the IR-MALDI process enabled the optimization of the different IM spectrometers at atmospheric and reduced pressure (AP and RP, respectively). At reduced pressure, both an AP and an RP IR-MALDI source were used. The influence of the pulsed ion extraction parameters (pulse delay, width and amplitude) on peak shape, resolution and area was systematically studied in both AP and RP IM spectrometers and discussed in the context of the IR-MALDI process. Under RP conditions, the influence of the closing field and of the pressure was also examined for both AP and RP sources. For the AP ionization RP IM spectrometer, the influence of the inlet field (IF) in the source region was also examined. All of these studies led to the determination of the optimal analytical parameters as well as to a better understanding of the initial ion cloud anatomy. The analytical performance of the spectrometer was then studied. Limits of detection (LOD) and linear ranges were determined under static and pulsed ion injection conditions and interpreted in the context of the IR-MALDI mechanism. Applications in the separation of simple mixtures were also illustrated, demonstrating good isomer separation capabilities and the advantages of singly charged peaks. The possibility to couple high performance liquid chromatography (HPLC) to IR-MALDI-IM spectrometry was also demonstrated. Finally, the reduced pressure spectrometer was used to study the effect of high reduced field strength on the mobility of polyatomic ions in polyatomic gases. The last focus point was on the study of peptide ions. A dataset obtained with electrospray IM spectrometry was characterized and used for the calibration of a collision cross-section (CCS) determination method based on molecular dynamics (MD) simulations at high temperature. Instead of producing candidate structures which are evaluated one by one, this semi-automated method uses the simulation as a whole to determine a single average collision cross-section value by reweighting the CCS of a few representative structures. The method was compared to the intrinsic size parameter (ISP) method and to experimental results. Additional MD data obtained from the simulations was also used to further analyze the peptides and understand the experimental results, an advantage with regard to the ISP method. Finally, the CCS of peptide ions analyzed by IR-MALDI were also evaluated with both ISP and MD methods and the results compared to experiment, resulting in a first validation of the MD method. Thus, this thesis brings together the soft ionization technique that is IR-MALDI, which produces mostly singly charged peaks, with ion mobility spectrometry, which can distinguish between isomers, and a collision cross-section determination method which also provides structural information on the analyte at hand.}, language = {en} } @phdthesis{Vijayakrishnan2008, author = {Vijayakrishnan, Balakumar}, title = {Solution and solid phase synthesis of N,N'-diacetyl chitotetraoses}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18830}, school = {Universit{\"a}t Potsdam}, year = {2008}, abstract = {The three major biopolymers, proteins, nucleic acids and glycoconjugates are mainly responsible for the information transfer, which is a fundamental process of life. The biological importance of proteins and nucleic acids are well explored and oligosaccharides in the form of glycoconjugates have gained importance recently. The β-(1→4) linked N-acetylglucosamine (GlcNAc) moiety is a frequently occurring structural unit in various naturally and biologically important oligosaccharides and related conjugates. Chitin which is the most abundant polymer of GlcNAc is widely distributed in nature whereas the related polysaccharide chitosan (polymer of GlcN and GlcNAc) occurs in certain fungi. Chitooligosaccharides of mixed acetylation patterns are of interest for the determination of the substrate specificities and mechanism of chitinases. In this report, we describe the chemical synthesis of three chitotetraoses namely GlcNAc-GlcN-GlcNAc-GlcN, GlcN-GlcNAc-GlcNAc-GlcN and GlcN-GlcN-GlcNAc-GlcNAc. Benzyloxycarbonyl (Z) and p-nitrobenzyloxycarbonyl (PNZ) were used for the amino functionality due to their ability to form the β-linkage during the glycosylation reactions through neighboring group participation and the trichloroacetimidate approach was utilized for the donor. Monomeric, dimeric acceptors and donors have been prepared by utilizing the Z and PNZ groups and coupling between the appropriate donor and acceptors in the presence of Lewis acid yielded the protected tetrasaccharides. Finally cleavage of PNZ followed by reacetylation and the deblocking of other protecting groups afforded the N,N'-diacetyl chitotetraoses in good yield. Successful syntheses for the protected diacetyl chitotetraoses by solid phase synthesis have also been described.}, language = {en} } @phdthesis{Viala2002, author = {Viala, Sophie}, title = {Kontrollierte radikalische Heterophasenpolymerisaton mit Anwesenheit des Diphenylethylens}, pages = {130 S.}, year = {2002}, language = {de} } @phdthesis{Vergin2008, author = {Vergin, Annika}, title = {Charakterisierung von Metallosupramolekularen Polyelektrolyten mittels analytischer Ultrazentrifugation}, address = {Potsdam}, pages = {94 S.}, year = {2008}, language = {de} } @phdthesis{Verch2010, author = {Verch, Andreas}, title = {Pr{\"a}nukleationscluster und ihre Wechselwirkungen mit Additiven}, address = {Potsdam}, pages = {119 Bl. : Ill., graph. Darst.}, year = {2010}, language = {de} } @phdthesis{Vazhappilly2008, author = {Vazhappilly, Tijo Joseph}, title = {Vibrationally enhanced associative photodesorption of H2 (D2) from Ru(0001) : quantum and classical approaches}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19056}, school = {Universit{\"a}t Potsdam}, year = {2008}, abstract = {Nowadays, reactions on surfaces are attaining great scientific interest because of their diverse applications. Some well known examples are production of ammonia on metal surfaces for fertilizers and reduction of poisonous gases from automobiles using catalytic converters. More recently, also photoinduced reactions at surfaces, useful, \textit{e.g.}, for photocatalysis, were studied in detail. Often, very short laser pulses are used for this purpose. Some of these reactions are occurring on femtosecond (1 fs=\$10^{-15}\$ s) time scales since the motion of atoms (which leads to bond breaking and new bond formation) belongs to this time range. This thesis investigates the femtosecond laser induced associative photodesorption of hydrogen, H\$_2\$, and deuterium, D\$_2\$, from a ruthenium metal surface. Many interesting features of this reaction were explored by experimentalists: (i) a huge isotope effect in the desorption probability of H\$_2\$ and D\$_2\$, (ii) the desorption yield increases non-linearly with the applied visible (vis) laser fluence, and (iii) unequal energy partitioning to different degrees of freedom. These peculiarities are due to the fact that an ultrashort vis pulse creates hot electrons in the metal. These hot electrons then transfer energy to adsorbate vibrations which leads to desorption. In fact, adsorbate vibrations are strongly coupled to metal electrons, \textit{i.e.}, through non-adiabatic couplings. This means that, surfaces introduce additional channels for energy exchange which makes the control of surface reactions more difficult than the control of reactions in the gas phase. In fact, the quantum yield of surface photochemical reactions is often notoriously small. One of the goals of the present thesis is to suggest, on the basis of theoretical simulations, strategies to control/enhance the photodesorption yield of H\$_2\$ and D\$_2\$ from Ru(0001). For this purpose, we suggest a \textit{hybrid scheme} to control the reaction, where the adsorbate vibrations are initially excited by an infrared (IR) pulse, prior to the vis pulse. Both \textit{adiabatic} and \textit{non-adiabatic} representations for photoinduced desorption problems are employed here. The \textit{adiabatic} representation is realized within the classical picture using Molecular Dynamics (MD) with electronic frictions. In a quantum mechanical description, \textit{non-adiabatic} representations are employed within open-system density matrix theory. The time evolution of the desorption process is studied using a two-mode reduced dimensionality model with one vibrational coordinate and one translational coordinate of the adsorbate. The ground and excited electronic state potentials, and dipole function for the IR excitation are taken from first principles. The IR driven vibrational excitation of adsorbate modes with moderate efficiency is achieved by (modified) \$\pi\$-pulses or/and optimal control theory. The fluence dependence of the desorption reaction is computed by including the electronic temperature of the metal calculated from the two-temperature model. Here, our theoretical results show a good agreement with experimental and previous theoretical findings. We then employed the IR+vis strategy in both models. Here, we found that vibrational excitation indeed promotes the desorption of hydrogen and deuterium. To summarize, we conclude that photocontrol of this surface reaction can be achieved by our IR+vis scheme.}, language = {en} } @phdthesis{ValverdeSerrano2011, author = {Valverde Serrano, Clara}, title = {Self-assembly behavior in hydrophilic block copolymers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54163}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Block copolymers are receiving increasing attention in the literature. Reports on amphiphilic block copolymers have now established the basis of their self-assembly behavior: aggregate sizes, morphologies and stability can be explained from the absolute and relative block lengths, the nature of the blocks, the architecture and also solvent selectiveness. In water, self-assembly of amphiphilic block copolymers is assumed to be driven by the hydrophobic. The motivation of this thesis is to study the influence on the self-assembly in water of A b B type block copolymers (with A hydrophilic) of the variation of the hydrophilicity of B from non-soluble (hydrophobic) to totally soluble (hydrophilic). Glucose-modified polybutadiene-block-poly(N-isopropylacrylamide) copolymers were prepared and their self-assembly behavior in water studied. The copolymers formed vesicles with an asymmetric membrane with a glycosylated exterior and poly(N-isopropylacrylamide) on the inside. Above the low critical solution temperature (LCST) of poly(N-isopropylacrylamide), the structure collapsed into micelles with a hydrophobic PNIPAM core and glycosylated exterior. This collapse was found to be reversible. As a result, the structures showed a temperature-dependent interaction with L-lectin proteins and were shown to be able to encapsulate organic molecules. Several families of double hydrophilic block copolymers (DHBC) were prepared. The blocks of these copolymers were biopolymers or polymer chimeras used in aqueous two-phase partition systems. Copolymers based on dextran and poly(ethylene glycol) blocks were able to form aggregates in water. Dex6500-b-PEG5500 copolymer spontaneously formed vesicles with PEG as the "less hydrophilic" barrier and dextran as the solubilizing block. The aggregates were found to be insensitive to the polymer's architecture and concentration (in the dilute range) and only mildly sensitive to temperature. Variation of the block length, yielded different morphologies. A longer PEG chain seemed to promote more curved aggregates following the inverse trend usually observed in amphiphilic block copolymers. A shorter dextran promoted vesicular structures as usually observed for the amphiphilic counterparts. The linking function was shown to have an influence of the morphology but not on the self-assembly capability in itself. The vesicles formed by dex6500-b-PEG5500 showed slow kinetics of clustering in the presence of Con A lectin. In addition both dex6500-b-PEG5500 and its crosslinked derivative were able to encapsulate fluorescent dyes. Two additional dextran-based copolymers were synthesized, dextran-b-poly(vinyl alcohol) and dextran-b-poly(vinyl pyrrolidone). The study of their self-assembly allowed to conclude that aqueous two-phase systems (ATPS) is a valid source of inspiration to conceive DHBCs capable of self-assembling. In the second part the principle was extended to polypeptide systems with the synthesis of a poly(N-hydroxyethylglutamine)-block-poly(ethylene glycol) copolymer. The copolymer that had been previously reported to have emulsifying properties was able to form vesicles by direct dissolution of the solid in water. Last, a series of thermoresponsive copolymers were prepared, dextran-b-PNIPAMm. These polymers formed aggregates below the LCST. Their structure could not be unambiguously elucidated but seemed to correspond to vesicles. Above the LCST, the collapse of the PNIPAM chains induced the formation of stable objects of several hundreds of nanometers in radius that evolved with increasing temperature. The cooling of these solution below LCST restored the initial aggregates. This self-assembly of DHBC outside any stimuli of pH, ionic strength, or temperature has only rarely been described in the literature. This work constituted the first formal attempt to frame the phenomenon. Two reasons were accounted for the self-assembly of such systems: incompatibility of the polymer pairs forming the two blocks (enthalpic) and a considerable solubility difference (enthalpic and entropic). The entropic contribution to the positive Gibbs free energy of mixing is believed to arise from the same loss of conformational entropy that is responsible for "the hydrophobic effect" but driven by a competition for water of the two blocks. In that sense this phenomenon should be described as the "hydrophilic effect".}, language = {en} } @phdthesis{Vacogne2016, author = {Vacogne, Charlotte D.}, title = {New synthetic routes towards well-defined polypeptides, morphologies and hydrogels}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396366}, school = {Universit{\"a}t Potsdam}, pages = {xii, 175}, year = {2016}, abstract = {Proteins are natural polypeptides produced by cells; they can be found in both animals and plants, and possess a variety of functions. One of these functions is to provide structural support to the surrounding cells and tissues. For example, collagen (which is found in skin, cartilage, tendons and bones) and keratin (which is found in hair and nails) are structural proteins. When a tissue is damaged, however, the supporting matrix formed by structural proteins cannot always spontaneously regenerate. Tailor-made synthetic polypeptides can be used to help heal and restore tissue formation. Synthetic polypeptides are typically synthesized by the so-called ring opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCA). Such synthetic polypeptides are generally non-sequence-controlled and thus less complex than proteins. As such, synthetic polypeptides are rarely as efficient as proteins in their ability to self-assemble and form hierarchical or structural supramolecular assemblies in water, and thus, often require rational designing. In this doctoral work, two types of amino acids, γ-benzyl-L/D-glutamate (BLG / BDG) and allylglycine (AG), were selected to synthesize a series of (co)polypeptides of different compositions and molar masses. A new and versatile synthetic route to prepare polypeptides was developed, and its mechanism and kinetics were investigated. The polypeptide properties were thoroughly studied and new materials were developed from them. In particular, these polypeptides were able to aggregate (or self-assemble) in solution into microscopic fibres, very similar to those formed by collagen. By doing so, they formed robust physical networks and organogels which could be processed into high water-content, pH-responsive hydrogels. Particles with highly regular and chiral spiral morphologies were also obtained by emulsifying these polypeptides. Such polypeptides and the materials derived from them are, therefore, promising candidates for biomedical applications.}, language = {en} } @phdthesis{Utecht2015, author = {Utecht, Manuel Martin}, title = {Zur Optimierung und dem Auslesen molekularer Schalter}, school = {Universit{\"a}t Potsdam}, pages = {143}, year = {2015}, language = {de} } @phdthesis{Unterlass2011, author = {Unterlass, Miriam Margarethe}, title = {From monomer salts and their tectonic crystals to aromatic polyimides : development of neoteric synthesis routes}, address = {Potsdam}, pages = {147 S.}, year = {2011}, language = {en} } @phdthesis{Ulaganathan2016, author = {Ulaganathan, Vamseekrishna}, title = {Molecular fundamentals of foam fractionation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-94263}, school = {Universit{\"a}t Potsdam}, pages = {ix, 136}, year = {2016}, abstract = {Foam fractionation of surfactant and protein solutions is a process dedicated to separate surface active molecules from each other due to their differences in surface activities. The process is based on forming bubbles in a certain mixed solution followed by detachment and rising of bubbles through a certain volume of this solution, and consequently on the formation of a foam layer on top of the solution column. Therefore, systematic analysis of this whole process comprises of at first investigations dedicated to the formation and growth of single bubbles in solutions, which is equivalent to the main principles of the well-known bubble pressure tensiometry. The second stage of the fractionation process includes the detachment of a single bubble from a pore or capillary tip and its rising in a respective aqueous solution. The third and final stage of the process is the formation and stabilization of the foam created by these bubbles, which contains the adsorption layers formed at the growing bubble surface, carried up and gets modified during the bubble rising and finally ends up as part of the foam layer. Bubble pressure tensiometry and bubble profile analysis tensiometry experiments were performed with protein solutions at different bulk concentrations, solution pH and ionic strength in order to describe the process of accumulation of protein and surfactant molecules at the bubble surface. The results obtained from the two complementary methods allow understanding the mechanism of adsorption, which is mainly governed by the diffusional transport of the adsorbing protein molecules to the bubble surface. This mechanism is the same as generally discussed for surfactant molecules. However, interesting peculiarities have been observed for protein adsorption kinetics at sufficiently short adsorption times. First of all, at short adsorption times the surface tension remains constant for a while before it decreases as expected due to the adsorption of proteins at the surface. This time interval is called induction time and it becomes shorter with increasing protein bulk concentration. Moreover, under special conditions, the surface tension does not stay constant but even increases over a certain period of time. This so-called negative surface pressure was observed for BCS and BLG and discussed for the first time in terms of changes in the surface conformation of the adsorbing protein molecules. Usually, a negative surface pressure would correspond to a negative adsorption, which is of course impossible for the studied protein solutions. The phenomenon, which amounts to some mN/m, was rather explained by simultaneous changes in the molar area required by the adsorbed proteins and the non-ideality of entropy of the interfacial layer. It is a transient phenomenon and exists only under dynamic conditions. The experiments dedicated to the local velocity of rising air bubbles in solutions were performed in a broad range of BLG concentration, pH and ionic strength. Additionally, rising bubble experiments were done for surfactant solutions in order to validate the functionality of the instrument. It turns out that the velocity of a rising bubble is much more sensitive to adsorbing molecules than classical dynamic surface tension measurements. At very low BLG or surfactant concentrations, for example, the measured local velocity profile of an air bubble is changing dramatically in time scales of seconds while dynamic surface tensions still do not show any measurable changes at this time scale. The solution's pH and ionic strength are important parameters that govern the measured rising velocity for protein solutions. A general theoretical description of rising bubbles in surfactant and protein solutions is not available at present due to the complex situation of the adsorption process at a bubble surface in a liquid flow field with simultaneous Marangoni effects. However, instead of modelling the complete velocity profile, new theoretical work has been started to evaluate the maximum values in the profile as characteristic parameter for dynamic adsorption layers at the bubble surface more quantitatively. The studies with protein-surfactant mixtures demonstrate in an impressive way that the complexes formed by the two compounds change the surface activity as compared to the original native protein molecules and therefore lead to a completely different retardation behavior of rising bubbles. Changes in the velocity profile can be interpreted qualitatively in terms of increased or decreased surface activity of the formed protein-surfactant complexes. It was also observed that the pH and ionic strength of a protein solution have strong effects on the surface activity of the protein molecules, which however, could be different on the rising bubble velocity and the equilibrium adsorption isotherms. These differences are not fully understood yet but give rise to discussions about the structure of protein adsorption layer under dynamic conditions or in the equilibrium state. The third main stage of the discussed process of fractionation is the formation and characterization of protein foams from BLG solutions at different pH and ionic strength. Of course a minimum BLG concentration is required to form foams. This minimum protein concentration is a function again of solution pH and ionic strength, i.e. of the surface activity of the protein molecules. Although at the isoelectric point, at about pH 5 for BLG, the hydrophobicity and hence the surface activity should be the highest, the concentration and ionic strength effects on the rising velocity profile as well as on the foamability and foam stability do not show a maximum. This is another remarkable argument for the fact that the interfacial structure and behavior of BLG layers under dynamic conditions and at equilibrium are rather different. These differences are probably caused by the time required for BLG molecules to adapt respective conformations once they are adsorbed at the surface. All bubble studies described in this work refer to stages of the foam fractionation process. Experiments with different systems, mainly surfactant and protein solutions, were performed in order to form foams and finally recover a solution representing the foamed material. As foam consists to a large extent of foam lamella - two adsorption layers with a liquid core - the concentration in a foamate taken from foaming experiments should be enriched in the stabilizing molecules. For determining the concentration of the foamate, again the very sensitive bubble rising velocity profile method was applied, which works for any type of surface active materials. This also includes technical surfactants or protein isolates for which an accurate composition is unknown.}, language = {en} } @phdthesis{Taeuber2016, author = {T{\"a}uber, Karoline}, title = {Porous Membranes from Imidazolium- and Pyridinium-based Poly(ionic liquid)s with Targeted Properties}, school = {Universit{\"a}t Potsdam}, pages = {115}, year = {2016}, language = {en} } @phdthesis{TzonevaVelinova2003, author = {Tzoneva-Velinova, Rumiana}, title = {The wettability of biomaterials determines the protein adsorption and the cellular responses}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001103}, school = {Universit{\"a}t Potsdam}, year = {2003}, abstract = {During the past several decades polymer materials become widely used as components of medical devices and implants such as hemodialysers, bioartificial organs as well as vascular and recombinant surgery. Most of the devices cannot avoid the blood contact in their use. When the polymer materials come in contact with blood they can cause different undesired host responses like thrombosis, inflammatory reactions and infections. Thus the materials must be hemocompatible in order to minimize these undesired body responses. The earliest and one of the main problems in the use of blood-contacting biomaterials is the surface induced thrombosis. The sequence of the thrombus formation on the artificial surfaces has been well established. The first event, which occurs, after exposure of biomaterials to blood, is the adsorption of blood proteins. Surface physicochemical properties of the materials as wettability greatly influence the amount and conformational changes of adsorbed proteins. In turn the type, amount and conformational state of the adsorbed protein layer determines whether platelets will adhere and become activated or not on the artificial surface and thus to complete the thrombus formation. The adsorption of fibrinogen (FNG), which is present in plasma, has been shown to be closely related to surface induced thrombosis by participating in all processes of the thrombus formation such as fibrin formation, platelet adhesion and aggregation. Therefore study the FNG adsorption to artificial surfaces could contribute to better understanding of the mechanisms of platelet adhesion and activation and thus to controlling the surface induced thrombosis. Endothelization of the polymer surfaces is one of the strategies for improving the materials hemocompatibility, which is believed to be the most ideal solution for making truly blood-compatible materials. Since at physiological conditions proteins such as FNG and fibronectin (FN) are the usual extracellular matrix (ECM) for endothelial cells (EC) adhesion, precoating of the materials with these proteins has been shown to improve EC adhesion and growth in vitro. ECM proteins play an essential role not only like a structural support for cell adhesion and spreading, but also they are important factor in transmitting signals for different cell functions. The ability of cells to remodel plasma proteins such as FNG and FN in matrix-like structures together with the classical cell parameters such as actin cytoskeleton and focal adhesion formation could be used as an criteria for proper cell functioning. The establishment and the maintaining of delicate balance between cell-cell and cell-substrate contacts is another important factor for better EC colonization of the implants. The functionality of newly established endothelium in order to produce antithromotic substances should be always considered when EC seeding is used for improving the hemocompatibility of the polymer materials. Controlling the polymer surface properties such as surface wettability represents a versatile approach to manipulate the above cellular responses and therefore can be used in biomaterial and tissue engineering applications for producing better hemocompatible materials.}, language = {en} } @phdthesis{TroegerMueller2018, author = {Tr{\"o}ger-M{\"u}ller, Steffen}, title = {Truly sustainable imidazolium ionics}, school = {Universit{\"a}t Potsdam}, pages = {158}, year = {2018}, language = {de} } @phdthesis{Travkova2010, author = {Travkova, Oksana G.}, title = {Interactions of the antimicrobial peptide Arenicin with amphiphiles at planar and curved interfaces}, address = {Potsdam}, pages = {122 S. : graph. Darst.}, year = {2010}, language = {en} } @phdthesis{Trautmann2016, author = {Trautmann, Michael}, title = {Neue Polystyrolharze mit Sulfoxid-Ankergruppen f{\"u}r die Festphasenextraktion von Platin und Ruthenium aus salzsauren L{\"o}sungen}, school = {Universit{\"a}t Potsdam}, pages = {191}, year = {2016}, language = {de} } @phdthesis{Traeger2012, author = {Traeger, Juliane}, title = {Unges{\"a}ttigte Dithioetherliganden : selektive Extraktionsmittel f{\"u}r die Gewinnung von Palladium(II) aus Sekund{\"a}rrohstoffen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-64753}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {Die Entwicklung neuer Verfahren f{\"u}r die R{\"u}ckf{\"u}hrung von Palladium aus Altmaterialien, wie gebrauchten Autoabgaskatalysatoren, in den Stoffstromkreislauf ist sowohl aus {\"o}kologischer als auch {\"o}konomischer Sicht erstrebenswert. In dieser Arbeit wurden neue Fl{\"u}ssig-Fl{\"u}ssig- und Fest-Fl{\"u}ssig-Extraktionsmittel entwickelt, mit denen Palladium(II) aus einer oxidierenden, salzsauren Laugungsl{\"o}sung, die neben Palladium auch Platin und Rhodium sowie zahlreiche unedle Metalle enth{\"a}lt, zur{\"u}ckgewonnen werden kann. Die neuen Extraktionsmittel unges{\"a}ttigte monomere 1,2-Dithioether und oligomere Ligandenmischungen mit vicinalen Dithioether-Einheiten - sind im Gegensatz zu vielen in der Literatur aufgef{\"u}hrten Extraktionsmitteln hochselektiv. Aufgrund ihrer geometrischen und elektronischen Pr{\"a}organisation bilden sie mit Palladium(II) stabile quadratisch-planare Chelatkomplexe. F{\"u}r die Entwicklung des Fl{\"u}ssig-Fl{\"u}ssig-Extraktionsmittels wurde eine Reihe von unges{\"a}ttigten 1,2-Dithioetherliganden dargestellt, welche auf einer starren 1,2-Dithioethen-Einheit, die in ein variierendes elektronenziehendes Grundger{\"u}st eingebettet ist, basieren und polare Seitenketten besitzen. Neben der Bestimmung der Kristallstrukturen der Liganden und ihrer Palladiumdichlorid-Komplexe wurden die elektro- und photochemischen Eigenschaften, die Komplexstabilit{\"a}t und das Verhalten in L{\"o}sung untersucht. In Fl{\"u}ssig-Fl{\"u}ssig-Extraktionsuntersuchungen konnte gezeigt werden, dass einige der neuen Liganden industriell genutzten Extraktionsmitteln durch eine schnellere Einstellung des Extraktionsgleichgewichts {\"u}berlegen sind. Anhand von Kriterien, die f{\"u}r eine industrielle Nutzbarkeit entscheidend sind, wie: guter Oxidationsbest{\"a}ndigkeit, einer hohen Extraktionsausbeute (auch bei hohen Salzs{\"a}urekonzentrationen der Speisel{\"o}sung), schneller Extraktionskinetik und einer hohen Selektivit{\"a}t f{\"u}r Palladium(II) wurde aus der Reihe der sechs Liganden ein geeignetes Fl{\"u}ssig-Fl{\"u}ssig-Extraktionsmittel ausgew{\"a}hlt: 1,2-Bis(2-methoxyethylthio)benzen. Mit diesem wurde ein praxisnahes Fl{\"u}ssig-Fl{\"u}ssig-Extraktionssystem entwickelt. Nach der schrittweisen Adaption der w{\"a}ssrigen Phase von einer Modelll{\"o}sung hin zu der oxidierenden, salzsauren Laugungsl{\"o}sung erfolgte die Auswahl eines geeigneten großtechnisch, einsetzbaren L{\"o}semittels (1,2-Dichlorbenzen) und eines effizienten Reextraktionsmittels (0,5 M Thioharnstoff in 0,1 M HCl). Die hohe Palladium(II)-Selektivit{\"a}t dieses Fl{\"u}ssig-Fl{\"u}ssig-Extraktionssystems konnte verifiziert und seine Wiederverwendbarkeit und Praxistauglichkeit unter Beweis gestellt werden. Weiterhin wurde gezeigt, dass sich beim Kontakt mit oxidierenden Medien aus dem Dithioether 1,2-Bis(2-methoxyethylthio)benzen geringe Mengen des Thioethersulfoxids 1-(2-Methoxyethylsulfinyl)-2-(2-methoxyethylthio)benzen bilden. Dieses wird im sauren Milieu protoniert und beschleunigt die Extraktion wie ein Phasentransferkatalysator, ohne jedoch die Palladium(II)-Selektivit{\"a}t herabzusetzen. Die Kristallstruktur des Palladiumdichlorid-Komplexes des Tioethersulfoxids zeigt, dass der unprotonierte Ligand Palladium(II), analog zum Dithioether, {\"u}ber die chelatisierenden Schwefelatome koordiniert. Verschiedene Mischungen von Oligo(dithioether)-Liganden und der monomere Ligand 1,2-Bis(2-methoxyethylthio)benzen dienten als Extraktionsmittel f{\"u}r Fest-Fl{\"u}ssig-Extraktionsversuche mit SIRs (solvent impregnated resins) und wurden zu diesem Zweck auf hydrophilem Kieselgel und organophilem Amberlite® XAD 2 adsorbiert. Die Oligo(dithioether)-Liganden basieren auf 1,2-Dithiobenzen oder 1,2-Dithiomaleonitril-Einheiten, welche {\"u}ber Tris(oxyethylen)ethylen- oder Trimethylen-Br{\"u}cken miteinander verkn{\"u}pft sind. Mit Hilfe von Batch-Versuchen konnte gezeigt werden, dass sich strukturelle Unterschiede - wie die Art der chelatisierenden Einheit, die Art der verbr{\"u}ckenden Ketten und das Tr{\"a}germaterial - auf die Extraktionsausbeuten, die Extraktionskinetik und die Beladungskapazit{\"a}t auswirken. Die kieselgelhaltigen SIRs stellen das Extraktionsgleichgewicht viel schneller ein als die Amberlite® XAD 2-haltigen. Jedoch bleiben die Extraktionsmittel auf Amberlite® XAD 2, im Gegensatz zu Kieselgel, dauerhaft haften. Im salzsauren Milieu sind die 1,2-Dithiobenzen-derivate besser als Extraktionsmittel geeignet als die 1,2-Dithiomaleonitrilderivate. In S{\"a}ulenversuchen mit der oxidierenden, salzsauren Laugungsl{\"o}sung und wiederverwendbaren, mit 1,2-Dithiobenzenderivaten impr{\"a}gnierten, Amberlite® XAD 2-haltigen SIRs zeigte sich, dass f{\"u}r die Realisierung hoher Beladungskapazit{\"a}ten sehr geringe Pumpraten ben{\"o}tigt werden. Trotzdem konnte die gute Palladium(II)-Selektivit{\"a}t dieser Festphasenmaterialien demonstriert werden. Allerdings wurden in den Eluaten im Gegensatz zu den Eluaten, die aus Fl{\"u}ssig-Fl{\"u}ssig-Extraktion resultierten neben dem Palladium auch geringe Mengen an Platin, Aluminium, Eisen und Blei gefunden.}, language = {de} } @phdthesis{Tomczyk2013, author = {Tomczyk, Jaroslaw}, title = {Photoinduced optical anisotropy in films of photochromic star-shaped liquid crystals}, address = {Potsdam}, pages = {121 S.}, year = {2013}, language = {en} } @phdthesis{TocaHerrara1999, author = {Toca-Herrara, Jos{\´e} Luis = Herrera}, title = {Wechselwirkungskr{\"a}fte und Struktur in Phospholipid-Schaumfilmen}, address = {Potsdam}, pages = {104 Bl. : graph. Darst.}, year = {1999}, language = {de} } @phdthesis{Titov2017, author = {Titov, Evgenii}, title = {Quantum chemistry and surface hopping dynamics of azobenzenes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394610}, school = {Universit{\"a}t Potsdam}, pages = {205}, year = {2017}, abstract = {This cumulative doctoral dissertation, based on three publications, is devoted to the investigation of several aspects of azobenzene molecular switches, with the aid of computational chemistry. In the first paper, the isomerization rates of a thermal cis → trans isomerization of azobenzenes for species formed upon an integer electron transfer, i.e., with added or removed electron, are calculated from Eyring's transition state theory and activation energy barriers, computed by means of density functional theory. The obtained results are discussed in connection with an experimental study of the thermal cis → trans isomerization of azobenzene derivatives in the presence of gold nanoparticles, which is demonstrated to be greatly accelerated in comparison to the same isomerization reaction in the absence of nanoparticles. The second paper is concerned with electronically excited states of (i) dimers, composed of two photoswitchable units placed closely side-by-side, as well as (ii) monomers and dimers adsorbed on a silicon cluster. A variety of quantum chemistry methods, capable of calculating molecular electronic absorption spectra, based on density functional and wave function theories, is employed to quantify changes in optical absorption upon dimerization and covalent grafting to a surface. Specifically, the exciton (Davydov) splitting between states of interest is determined from first-principles calculations with the help of natural transition orbital analysis, allowing for insight into the nature of excited states. In the third paper, nonadiabatic molecular dynamics with trajectory surface hopping is applied to model the photoisomerization of azobenzene dimers, (i) for the isolated case (exhibiting the exciton coupling between two molecules) as well as (ii) for the constrained case (providing the van der Waals interaction with environment in addition to the exciton coupling between two monomers). For the latter, the additional azobenzene molecules, surrounding the dimer, are introduced, mimicking a densely packed self-assembled monolayer. From obtained results it is concluded that the isolated dimer is capable of isomerization likewise the monomer, whereas the steric hindrance considerably suppresses trans → cis photoisomerization. Furthermore, the present dissertation comprises the general introduction describing the main features of the azobenzene photoswitch and objectives of this work, theoretical basis of the employed methods, and discussion of gained findings in the light of existing literature. Also, additional results on (i) activation parameters of the thermal cis → trans isomerization of azobenzenes, (ii) an approximate scheme to account for anharmonicity of molecular vibrations in calculation of the activation entropy, as well as (iii) absorption spectra of photoswitch-silicon composites obtained from time-demanding wave function-based methods are presented.}, language = {en} } @phdthesis{Tiarks2001, author = {Tiarks, Franca}, title = {Neue Strukturen und Synthesen durch die Miniemulsionspolymerisation: Polyaddition, Nanokapseln und Hybridpartikel}, publisher = {Shaker}, address = {Aachen}, isbn = {3-8265-8997-1}, issn = {0945-070X}, pages = {158 S.}, year = {2001}, language = {de} } @phdthesis{Tian2019, author = {Tian, Zhihong}, title = {Oxygen-, Sulfur-doped Novel Porous Carbon-Nitrogen Frameworks by Salt Melt Method}, school = {Universit{\"a}t Potsdam}, pages = {101}, year = {2019}, language = {en} } @phdthesis{Thuermer2013, author = {Th{\"u}rmer, Stephan}, title = {Inquiring photoelectrons about the dynamics in liquid water}, publisher = {Mensch \& Buch Verl.}, address = {Berlin}, isbn = {978-3-86387-336-3}, pages = {X, 106 S.}, year = {2013}, language = {en} } @phdthesis{Thuenemann2000, author = {Th{\"u}nemann, Andreas F.}, title = {Self-assembly, ordered nanostructures and functionality of polyelectrolyte-amphiphile complexes}, pages = {188 S.}, year = {2000}, language = {en} } @phdthesis{Thomas1995, author = {Thomas, Steffen}, title = {Anwendung von Substituenteneffekten und quantenchemischer Daten zur Zuordnung von 13C-NMR Spektren aromatischer und heteroaromatischer Verbindungen}, pages = {[4] Bl., 99 S., [7] Bl.}, year = {1995}, language = {de} } @phdthesis{Thomas2003, author = {Thomas, Arne Christian}, title = {Por{\"o}se Silikate durch Nanocasting : von chiralen Templaten zu neuer Chemie in Poren}, pages = {112 S.}, year = {2003}, language = {de} } @phdthesis{Thesen2010, author = {Thesen, Manuel Wolfram}, title = {Synthese und Charakterisierung von phosphoreszenten Terpolymeren und nichtkonjugierten Matrixpolymeren f{\"u}r effiziente polymere Leuchtdioden}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51709}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Mit Seitenkettenpolystyrenen wurde ein neues Synthesekonzept f{\"u}r phosphoreszente polymere LED-Materialien aufgestellt und experimentell verifiziert. Zun{\"a}chst erfolgten auf Grundlage strukturell einfacher Verbindungen Untersuchungen zum Einfluss von Spacern zwischen aktiven Seitengruppen und dem Polystyrenr{\"u}ckgrat. Es wurden Synthesemethoden f{\"u}r die Monomere etabliert, durch die aktive Elemente - Elektronen- und Lochleiter - mit und ohne diesen Spacer zug{\"a}nglich sind. Durch Kombination dieser Monomere waren unter Hinzunahme von polymerisierbaren Iridium-Komplexen in unterschiedlicher Emissionswellenl{\"a}nge statistische Terpolymere darstellbar. Es wurde gezeigt, dass die Realisierung bestimmter Verh{\"a}ltnisse zwischen Loch-, Elektronenleiter und Triplettemitter in ausreichender Molmasse m{\"o}glich ist. Die Glasstufen der Polymere zeigten eine deutliche Strukturabh{\"a}ngigkeit. Auf die Lage der Grenzorbitale {\"u}bten die Spacer nahezu keinen Einfluss aus. Die unterschiedlichen Makromolek{\"u}le kamen in polymeren Licht emittierenden Dioden (PLEDs) zum Einsatz, wobei ein deutlicher Einfluss der Spacereinheiten auf die Leistungscharakteristik der PLEDs festzustellen war: Sowohl Effizienz, Leuchtdichte wie auch Stromdichte waren durch den Einsatz der kompakten Makromolek{\"u}le ohne Spacer deutlich h{\"o}her. Diese Beobachtungen begr{\"u}ndeten sich haupts{\"a}chlich in der Verwendung der aliphatischen Spacer, die den Anteil im Polymer erh{\"o}hten, der keine Konjugation und damit elektrisch isolierende Eigenschaften besaß. Diese Schlussfolgerungen waren mit allen drei realisierten Emissionsfarben gr{\"u}n, rot und blau verifizierbar. Die besten Messergebnisse erzielte eine PLED aus einem gr{\"u}n emittierenden und spacerlosen Terpolymer mit einer Stromeffizienz von etwa 28 cd A-1 (bei 6 V) und einer Leuchtdichte von 3200 cd m-2 (bei 8 V). Ausgehend von obigen Ergebnissen konnten neue Matrixmaterialien aus dem Bereich verdampfbarer Molek{\"u}le geringer Molmasse in das Polystyrenseitenkettenkonzept integriert werden. Es wurden Strukturvariationen sowohl von loch- wie auch von elektronenleitenden Verbindungen als Homopolymere dargestellt und als molekular dotierte Systeme in PLEDs untersucht. Sieben verschiedene lochleitende Polymere mit Triarylamin-Grundk{\"o}rper und drei elektronendefizit{\"a}re Polymere auf der Basis von Phenylbenzimidazol konnten erfolgreich in den Polymeransatz integriert werden. Spektroskopische und elektrochemische Untersuchungen zeigten kaum eine Ver{\"a}nderung der Charakteristika zwischen verdampfbaren Molek{\"u}len und den dargestellten Makromolek{\"u}len. Diese ladungstransportierenden Makro-molek{\"u}le wurden als polymere Matrizes molekular dotiert und l{\"o}sungsbasiert zu Einschicht-PLEDs verarbeitet. Als aussichtsreichstes Lochleiterpolymer dieser Reihe, mit einer Strom-effizenz von etwa 33 cd A-1 (bei 8 V) und einer Leuchtdichte von 6700 cd m-2 (bei 10 V), stellte sich ein Triarylaminderivat mit Carbazolsubstituenten heraus. Als geeignetstes Matrixmaterial f{\"u}r die Elektronenleitung wurde ein meta-verkn{\"u}pftes Di-Phenylbenzimidazol ausfindig gemacht, das in der PLED eine Stromeffizienz von etwa 20 cd A-1 (bei 8 V) und eine Leuchtdichte von 7100 cd m-2 (bei 10 V) erzielte. Anschließend wurden die geeignetsten Monomere zu Copolymeren kombiniert: Die lochleitende Einheit bildete ein carbazolylsubstituiertes Triarylamin und die elektronen-leitende Einheit war ein disubstituiertes Phenylbenzimidazol. Dieses Copolymer diente im Folgenden dazu, PLEDs zu realisieren und die Leistungsdaten mit denen eines Homopolymer-blends zu vergleichen, wobei der Blend die bessere Leistungscharakteristik zeigte. Mit dem Homopolymerblend waren Bauteileffizienzen von ann{\"a}hernd 30 cd A-1 (bei 10 V) und Leuchtdichten von 6800 cd m-2 neben einer Verringerung der Einsatzspannung realisierbar. F{\"u}r die abschließende Darstellung bipolarer Blockcopolymere wurde auf die Nitroxid-vermittelte Polymerisation zur{\"u}ckgegriffen. Mit dieser Technik waren kontrollierte radikalische Polymersiationen mit ausgew{\"a}hlten Monomeren in unterschiedlichen Block-l{\"a}ngen durchf{\"u}hrbar. Diese Blockcopolymere kamen als molekular dotierte Matrizes in phosphoreszenten gr{\"u}n emittierenden PLEDs zum Einsatz. Die Bauteile wurden sowohl mit statistischen Copolymeren, wie auch mit Homopolymerblends in gleicher Zusammensetzung aber unterschiedlichem Polymerisationsgrad hinsichtlich der Leistungscharakteristik verglichen. Kernaussage dieser Untersuchungen ist, dass hochmolekulare Systeme eine bessere Leistungscharakteristik aufweisen als niedermolekulare Matrizes. {\"U}ber Rasterkraft-mikroskopie konnte eine Phasenseparation in einem Gr{\"o}ßenbereich von etwa 10 nm f{\"u}r den hochmolekularen Homopolymerblend nachgewiesen werden. F{\"u}r die Blockcopolymere war es nicht m{\"o}glich eine Phasenseparation zu beobachten, was vorwiegend auf deren zu geringe Blockl{\"a}nge zur{\"u}ckgef{\"u}hrt wurde.}, language = {de} } @phdthesis{tenBrummelhuis2011, author = {ten Brummelhuis, Niels}, title = {Self-assembly of cross-linked polymer micelles into complex higher-order aggregates}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52320}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The creation of complex polymer structures has been one of the major research topics over the last couple of decades. This work deals with the synthesis of (block co-)polymers, the creation of complex and stimuli-responsive aggregates by self-assembly, and the cross-linking of these structures. Also the higher-order self-assembly of the aggregates is investigated. The formation of poly-2-oxazoline based micelles in aqueous solution and their simultaneous functionalization and cross-linking using thiol-yne chemistry is e.g. presented. By introducing pH responsive thiols in the core of the micelles the influence of charged groups in the core of micelles on the entire structure can be studied. The charging of these groups leads to a swelling of the core and a decrease in the local concentration of the corona forming block (poly(2-ethyl-2-oxazoline)). This decrease in concentration yields a shift in the cloud point temperature to higher temperatures for this Type I thermoresponsive polymer. When the swelling of the core is prohibited, e.g. by the introduction of sufficient amounts of salt, this behavior disappears. Similar structures can be prepared using complex coacervate core micelles (C3Ms) built through the interaction of weakly acidic and basic polymer blocks. The advantage of these structures is that two different stabilizing blocks can be incorporated, which allows for more diverse and complex structures and behavior of the micelles. Using block copolymers with either a polyanionic or a polycationic block C3Ms could be created with a corona which contains two different soluble nonionic polymers, which either have a mixed corona or a Janus type corona, depending on the polymers that were chosen. Using NHS and EDC the micelles could easily be cross-linked by the formation of amide bonds in the core of the micelles. The higher-order self-assembly behavior of these core cross-linked complex coacervate core micelles (C5Ms) was studied. Due to the cross-linking the micelles are stabilized towards changes in pH and ionic strength, but polymer chains are also no longer able to rearrange. For C5Ms with a mixed corona likely network structures were formed upon the collapse of the thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm), whereas for Janus type C5Ms well defined spherical aggregates of micelles could be obtained, depending on the pH of the solution. Furthermore it could be shown that Janus micelles can adsorb onto inorganic nanoparticles such as colloidal silica (through a selective interaction between PEO and the silica surface) or gold nanoparticles (by the binding of thiol end-groups). Asymmetric aggregates were also formed using the streptavidin-biotin binding motive. This is achieved by using three out of the four binding sites of streptavidin for the binding of one three-arm star polymer, end-functionalized with biotin groups. A homopolymer with one biotin end-group can be used to occupy the last position. This binding of two different polymers makes it possible to create asymmetric complexes. This phase separation is theoretically independent of the kind of polymer since the structure of the protein is the driving force, not the intrinsic phase separation between polymers. Besides Janus structures also specific cross-linking can be achieved by using other mixing ratios.}, language = {en} } @phdthesis{Techen2012, author = {Techen, Anne}, title = {Fluoreszenzspektroskopische Untersuchungen von Arzneimittel-Tr{\"a}ger-Wechselwirkungen am Beispiel von Xanthenfarbstoff-markierten CTAB-Mizellen}, address = {Potsdam}, pages = {II, 114, XLIV S.}, year = {2012}, language = {de} } @phdthesis{Tassler2015, author = {Taßler, Stephanie}, title = {Physical-Chemical Investigation of newly-synthesised Lysine-Based Amino-Functionalised Lipids for gene transfection in 2D and 3D model systems}, school = {Universit{\"a}t Potsdam}, pages = {142}, year = {2015}, language = {en} } @phdthesis{Tang2022, author = {Tang, Jo Sing Julia}, title = {Biofunctional polymers for medical applications}, doi = {10.25932/publishup-56363}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-563639}, school = {Universit{\"a}t Potsdam}, pages = {III, 150, V}, year = {2022}, abstract = {Carbohydrates are found in every living organism, where they are responsible for numerous, essential biological functions and processes. Synthetic polymers with pendant saccharides, called glycopolymers, mimic natural glycoconjugates in their special properties and functions. Employing such biomimetics furthers the understanding and controlling of biological processes. Hence, glycopolymers are valuable and interesting for applications in the medical and biological field. However, the synthesis of carbohydrate-based materials can be very challenging. In this thesis, the synthesis of biofunctional glycopolymers is presented, with the focus on aqueous-based, protecting group free and short synthesis routes to further advance in the field of glycopolymer synthesis. A practical and versatile precursor for glycopolymers are glycosylamines. To maintain biofunctionality of the saccharides after their amination, regioselective functionalization was performed. This frequently performed synthesis was optimized for different sugars. The optimization was facilitated using a design of experiment (DoE) approach to enable a reduced number of necessary experiments and efficient procedure. Here, the utility of using DoE for optimizing the synthesis of glycosylamines is discussed. The glycosylamines were converted to glycomonomers which were then polymerized to yield biofunctional glycopolymers. Here, the glycopolymers were aimed to be applicable as layer-by-layer (LbL) thin film coatings for drug delivery systems. To enable the LbL technique, complimentary glycopolymer electrolytes were synthesized by polymerization of the glycomonomers and subsequent modification or by post-polymerization modification. For drug delivery, liposomes were embedded into the glycopolymer coating as potential cargo carriers. The stability as well as the integrity of the glycopolymer layers and liposomes were investigated at physiological pH range. Different glycopolymers were also synthesized to be applicable as anti-adhesion therapeutics by providing advanced architectures with multivalent presentations of saccharides, which can inhibit the binding of pathogene lectins. Here, the synthesis of glycopolymer hydrogel particles based on biocompatible poly(N-isopropylacrylamide) (NiPAm) was established using the free-radical precipitation polymerization technique. The influence of synthesis parameters on the sugar content in the gels and on the hydrogel morphology is discussed. The accessibility of the saccharides to model lectins and their enhanced, multivalent interaction were investigated. At the end of this work, the synthesis strategies for the glycopolymers are generally discussed as well as their potential application in medicine.}, language = {en} } @phdthesis{Tan2018, author = {Tan, Li}, title = {Synthesis, assembly and thermo-responsivity of polymer-functionalized magnetic cobalt nanoparticles}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418153}, school = {Universit{\"a}t Potsdam}, pages = {X, 111}, year = {2018}, abstract = {This thesis mainly covers the synthesis, surface modification, magnetic-field-induced assembly and thermo-responsive functionalization of superparamagnetic Co NPs initially stabilized by hydrophobic small molecules oleic acid (OA) and trioctylphosphine oxide (TOPO), as well as the synthesis of both superparamagnetic and ferromagnetic Co NPs by using end-functionalized-polystyrene as stabilizer. Co NPs, due to their excellent magnetic and catalytic properties, have great potential application in various fields, such as ferrofluids, catalysis, and magnetic resonance imaging (MRI). Superparamagnetic Co NPs are especially interesting, since they exhibit zero coercivity. They get magnetized in an external magnetic field and reach their saturation magnetization rapidly, but no magnetic moment remains after removal of the applied magnetic field. Therefore, they do not agglomerate in the body when they are used in biomedical applications. Normally, decomposition of metallic precursors at high temperature is one of the most important methods in preparation of monodisperse magnetic NPs, providing tunability in size and shape. Hydrophobic ligands like OA, TOPO and oleylamine are often used to both control the growth of NPs and protect them from agglomeration. The as-prepared magnetic NPs can be used in biological applications as long as they are transferred into water. Moreover, their supercrystal assemblies have the potential for high density data storage and electronic devices. In addition to small molecules, polymers can also be used as surfactants for the synthesis of ferromagnetic and superparamagnetic NPs by changing the reaction conditions. Therefore, chapter 2 gives an overview on the basic concept of synthesis, surface modification and self-assembly of magnetic nanoparticles. Various examples were used to illustrate the recent work. The hydrophobic Co NPs synthesized with small molecules as surfactants limit their biological applications, which require a hydrophilic or aqueous environment. Surface modification (e.g., ligand exchange) is a general idea for either phase transition or surface-functionalization. Therefore, in chapter 3, a ligand exchange process was conducted to functionalize the surface of Co NPs. PNIPAM is one of the most popular smart polymers and its lower critical solution temperature (LCST) is around 32 °C, with a reversible change in the conformation structure between hydrophobic and hydrophilic. The novel nanocomposites of superparamagnetic Co NPs and thermo-responsive PNIPAM are of great interest. Thus, well-defined superparamagnetic Co NPs were firstly synthesized through the thermolysis of cobalt carbonyl by using OA and TOPO as surfactants. A functional ATRP initiator, containing an amine (as anchoring group) and a 2-bromopropionate group (SI-ATRP initiator), was used to replace the original ligands. This process is rapid and facial for efficient surface functionalization and afterwards the Co NPs can be dispersed into polar solvent DMF without aggregation. FT-IR spectroscopy showed that the TOPO was completely replaced, but a small amount of OA remained on the surface. A TGA measurement allowed the calculation of the grafting density of the initiator as around 3.2 initiator/nm2. Then, the surface-initiated ATRP was conducted for the polymerization of NIPAM on the surface of Co NPs and rendered the nanocomposites water-dispersible. A temperature-dependent dynamic light scattering study showed the aggregation behavior of PNIPAM-coated Co NPs upon heating and this process was proven to be reversible. The combination of superparamagnetic and thermo-responsive properties in these hybrid nanoparticles is promising for future applications e.g. in biomedicine. In chapter 4, the magnetic-field-induced assembly of superparamagnetic cobalt nanoparticles both on solid substrates and at liquid-air interface was investigated. OA- and TOPO-coated Co NPs were synthesized via the thermolysis of cobalt carbonyl and dispersed into either hexane or toluene. The Co NP dispersion was dropped onto substrates (e.g., TEM grid, silicon wafer) and at liquid-air (water-air or ethylene glycol-air) interface. Due to the attractive dipolar interaction, 1-D chains formed in the presence of an external magnetic field. It is known that the concentration and the strength of the magnetic field can affect the assembly behavior of superparamagnetic Co NPs. Therefore, the influence of these two parameters on the morphology of the assemblies was studied. The formed 1-D chains were shorter and flexible at either lower concentration of the Co NP dispersion or lower strength of the external magnetic field due to thermal fluctuation. However, by increasing either the concentration of the NP dispersion or the strength of the applied magnetic field, these chains became longer, thicker and straighter. The reason could be that a high concentration led to a high fraction of short dipolar chains, and their interaction resulted in longer and thicker chains under applied magnetic field. On the other hand, when the magnetic field increased, the induced moments of the magnetic nanoparticles became larger, which dominated over the thermal fluctuation. Thus, the formed short chains connected to each other and grew in length. Thicker chains were also observed through chain-chain interaction. Furthermore, the induced moments of the NPs tended to direct into one direction with increased magnetic field, thus the chains were straighter. In comparison between the assembly on substrates, at water-air interface and at ethylene glycol-air interface, the assembly of Co NPs in hexane dispersion at ethylene glycol-air interface showed the most regular and homogeneous chain structures due to the better spreading of the dispersion on ethylene glycol subphase than on water subphase and substrates. The magnetic-field-induced assembly of superparamagnetic nanoparticles could provide a powerful approach for applications in data storage and electronic devices. Chapter 5 presented the synthesis of superparamagnetic and ferromagnetic cobalt nanoparticles through a dual-stage thermolysis of cobalt carbonyl (Co2(CO)8) by using polystyrene as surfactant. The amine end-functionalized polystyrene surfactants with different molecular weight were prepared via atom transfer radical polymerization technique. The molecular weight determination of polystyrene was conducted by gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry techniques. The results showed that, when the molecular weight distribution is low (Mw/Mn < 1.2), the measurement by GPC and MALDI-ToF MS provided nearly similar results. For example, the molecular weight of 10600 Da was obtained by MALDI-ToF MS, while GPC gave 10500 g/mol (Mw/Mn = 1.17). However, if the polymer is poly distributed, MALDI-ToF MS cannot provide an accurate value. This was exemplified for a polymer with a molecular weight of 3130 Da measured by MALDI-TOF MS, while GPC showed 2300 g/mol (Mw/Mn = 1.38). The size, size distribution and magnetic properties of the hybrid particles were different by changing either the molecular weight or concentration of the polymer surfactants. The analysis from TEM characterization showed that the size of cobalt nanoparticles stabilized with polystyrene of lower molecular weight (Mn = 2300 g/mol) varied from 12-22 nm, while the size with middle (Mn = 4500 g/mol) and higher molecular weight (Mn = 10500 g/mol) of polystyrene-coated cobalt nanoparticles showed little change. Magnetic measurements exhibited that the small cobalt particles (12 nm) were superparamagnetic, while larger particles (21 nm) were ferromagnetic and assembled into 1-D chains. The grafting density calculated from thermogravimetric analysis showed that a higher grafting density of polystyrene was obtained with lower molecular weight (Mn = 2300 g/mol) than those with higher molecular weight (Mn = 10500 g/mol). Due to the larger steric hindrance, polystyrene with higher molecular weight cannot form a dense shell on the surface of the nanoparticles, which resulted in a lower grafting density. Wide angle X-ray scattering measurements revealed the epsilon cobalt crystalline phases of both superparamagnetic Co NPs coated with polystyrene (Mn = 2300 g/mol) and ferromagnetic Co NPs coated with polystyrene (Mn = 10500 g/mol). Furthermore, a stability study showed that PS-Co NPs prepared with higher polymer concentration and polymer molecular weight exhibited a better stability.}, language = {en} }