@phdthesis{Doriti2017,
  author    = {Doriti, Afroditi},
  title     = {Sustainable bio-based poly-N-glycines and polyesters},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411286},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vi, 117},
  year      = {2017},
  abstract  = {Nowadays, the need to protect the environment becomes more urgent than ever. In the field of chemistry, this translates to practices such as waste prevention, use of renewable feedstocks, and catalysis; concepts based on the principles of green chemistry. Polymers are an important product in the chemical industry and are also in the focus of these changes. In this thesis, more sustainable approaches to make two classes of polymers, polypeptoids and polyesters, are described. Polypeptoids or poly(alkyl-N-glycines) are isomers of polypeptides and are biocompatible, as well as degradable under biologically relevant conditions. In addition to that, they can have interesting properties such as lower critical solution temperature (LCST) behavior. They are usually synthesized by the ring opening polymerization (ROP) of N-carboxy anhydrides (NCAs), which are produced with the use of toxic compounds (e.g. phosgene) and which are highly sensitive to humidity. In order to avoid the direct synthesis and isolation of the NCAs, N-phenoxycarbonyl-protected N-substituted glycines are prepared, which can yield the NCAs in situ. The conditions for the NCA synthesis and its direct polymerization are investigated and optimized for the simplest N-substituted glycine, sarcosine. The use of a tertiary amine in less than stoichiometric amounts compared to the N-phenoxycarbonyl--sarcosine seems to accelerate drastically the NCA formation and does not affect the efficiency of the polymerization. In fact, well defined polysarcosines that comply to the monomer to initiator ratio can be produced by this method. This approach was also applied to other N-substituted glycines. Dihydroxyacetone is a sustainable diol produced from glycerol, and has already been used for the synthesis of polycarbonates. Here, it was used as a comonomer for the synthesis of polyesters. However, the polymerization of dihydroxyacetone presented difficulties, probably due to the insolubility of the macromolecular chains. To circumvent the problem, the dimethyl acetal protected dihydroxyacetone was polymerized with terephthaloyl chloride to yield a soluble polymer. When the carbonyl was recovered after deprotection, the product was insoluble in all solvents, showing that the carbonyl in the main chain hinders the dissolution of the polymers. The solubility issue can be avoided, when a 1:1 mixture of dihydroxyacetone/ ethylene glycol is used to yield a soluble copolyester.},
  language  = {en}
}
@phdthesis{Braun2017,
  author    = {Braun, Max},
  title     = {Heterogeneous Catalysis for the Conversion of Fructose to Chemicals and Fuel in a Continuous Flow Process},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410370},
  school      = {Universit{\"a}t Potsdam},
  pages     = {151},
  year      = {2017},
  abstract  = {Die Umsetzung von Zucker (Kohlenhydrate) in einem kontinuierlichen Prozess er{\"o}ffnet M{\"o}glichkeiten der Synthese diverser Chemikalien und Treibstoff aus erneuerbaren Ressourcen, welche heute {\"u}berwiegend aus fossilen Quellen stammen. Passend zum Konzept der Bioraffinerie und der „gr{\"u}nen Chemie", liegt der Fokus dieser Arbeit auf der Umsetzung von in Ethanol gel{\"o}ster Fruktose in einem kontinuierlichen Verfahren, mit Hilfe eigens entwickelter heterogener Katalysatoren. Die Dehydratisierung von Fruktose wird mit einem heterogenen S{\"a}urekatalysator realisiert, w{\"a}hrend die Folgeprodukte mittels einer Hydrodesoxygenierung umgesetzt werden. F{\"u}r den zweiten Schritt kommen Metallkatalysatoren auf Basis von Nickel und Wolframcarbid (WC) zum Einsatz, wodurch der Einsatz teurer Edelmetalle vermieden werden kann. Hauptprodukte des zweistufigen Verfahrens sind 2,5-Dimethylfuran (DMF) und Ethyllevulinat (EL). Beide Molek{\"u}le sind vielversprechende alternative Treibstoffe, bzw. k{\"o}nnen gebr{\"a}uchlichen Treibstoffen beigemischt werden, um deren Einsatz zu reduzieren und schrittweise zu substituieren. Alternativ k{\"o}nnen die Zwischenprodukte der Dehydratisierung, sowie DMF und EL weiter zu Chemikalien umgesetzt werden, welche in der Polymersynthese, als L{\"o}sungsmittel oder als Grundchemikalien eingesetzt werden k{\"o}nnen. Die Entwicklung der jeweiligen Katalysatoren f{\"u}r Dehydratisierungs- und Hydrodesoxygenierungsreaktionen erfolgt auf Basis von karbonisierter Biomasse, sowie Wolframcarbid. Die jeweiligen Reaktivit{\"a}ten werden durch Standardreaktionen getestet, wobei sich Wolframcarbid in Nanopartikelform, in Kombination mit Wasserstoff als sehr aktiv erwiesen hat. Der selbst entwickelte aktivierte Kohlenstoff, das kommerzielle Amberlyst 15, sowie Wolframcarbid mit zus{\"a}tzlichen Nickel-Nanopartikeln werden f{\"u}r weiterf{\"u}hrende Reaktionen in einem kontinuierlichen Prozess herangezogen und kombiniert. Um den Umsatz von Fruktose zu DMF in einer „zwei Reaktoren Anlage" zu erm{\"o}glichen, wird eine Erweiterung eines kommerziellen Reaktorsystems um einen weiteren Reaktor vorgenommen. Die Verweilzeit in der Reaktoranlage betr{\"a}gt somit ca. 14 Minuten, wobei 11 Minuten auf die erste S{\"a}ule (Dehydratisierung) und 3 Minuten auf die zweite S{\"a}ule (Hydrodesoxygenierung) entfallen. In diesem kontinuierlichen und zweistufigen System lassen sich Ausbeuten von 38.5 \% DMF und 47 \% EL erzielen. Ein kontinuierlicher Lauf von sieben Stunden zeigt die Stabilit{\"a}t der eingesetzten Katalysatoren, auch wenn eine geringe Deaktivierung des Dehydratisierungskatalysators beobachtet werden kann. Der Ni@WC Katalysator zeigte hingegen keine Abnahme der Nickel Konzentration und somit kommt es zu keiner Auswaschung des Metalls. Das gebildete EL wurde hingegen nicht umgesetzt und verbleibt unver{\"a}ndert in L{\"o}sung. Das zweistufige System wurde schließlich in einem Mischkatalysatorsystem kombiniert, wobei auf aktivierten und sulfonierten Kohlenstoff zur{\"u}ckgegriffen wurde. Dieser zeigte bereits eine Transferhydrodesoxygenierungsaktivit{\"a}t. Diese Beobachtung ist deshalb bemerkenswert, da erst seit kurzem bekannt ist, dass Graphenstrukturen an sich katalytisch aktiv sein k{\"o}nnen. Um diese Aktivit{\"a}t weiter zu steigern, wurde der aktivierte Kohlenstoff mit 10 wt\% Ni@WC gemischt, sodass beide Katalysatoren in einer S{\"a}ule vorliegen. Die urspr{\"u}nglichen 2 \% DMF Ausbeute mit reinem aktivierten Kohlenstoff k{\"o}nnen somit auf 12 \% gesteigert werden, da das Folgeprodukt EL hierbei vermieden wird und das Zwischenprodukt „HMF Derivat" direkt zu DMF weiter reagieren kann. Dieses Ergebnis zeigt das Potential der „ein Reaktor Umsetzung", weshalb eine kontinuierliche Durchflussreaktoranlage im Litermaßstab als Scale-Up des vorhergehenden Labormaßstabs realisiert wurde. Der 800 mm x 28.5 mm Reaktor bedient eine maximale Flussrate von 50 mL min-1, Dr{\"u}cke von 100 bar und Temperaturen bis zu 500 °C.},
  language  = {en}
}
@phdthesis{Meiling2017,
  author    = {Meiling, Till Thomas},
  title     = {Development of a reliable and environmentally friendly synthesis for fluorescence carbon nanodots},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410160},
  school      = {Universit{\"a}t Potsdam},
  pages     = {198},
  year      = {2017},
  abstract  = {Carbon nanodots (CNDs) have generated considerable attention due to their promising properties, e.g. high water solubility, chemical inertness, resistance to photobleaching, high biocompatibility and ease of functionalization. These properties render them ideal for a wide range of functions, e.g. electrochemical applications, waste water treatment, (photo)catalysis, bio-imaging and bio-technology, as well as chemical sensing, and optoelectronic devices like LEDs. In particular, the ability to prepare CNDs from a wide range of accessible organic materials makes them a potential alternative for conventional organic dyes and semiconductor quantum dots (QDs) in various applications. However, current synthesis methods are typically expensive and depend on complex and time-consuming processes or severe synthesis conditions and toxic chemicals. One way to reduce overall preparation costs is the use of biological waste as starting material. Hence, natural carbon sources such as pomelo peal, egg white and egg yolk, orange juice, and even eggshells, to name a few; have been used for the preparation of CNDs. While the use of waste is desirable, especially to avoid competition with essential food production, most starting-materials lack the essential purity and structural homogeneity to obtain homogeneous carbon dots. Furthermore, most synthesis approaches reported to date require extensive purification steps and have resulted in carbon dots with heterogeneous photoluminescent properties and indefinite composition. For this reason, among others, the relationship between CND structure (e.g. size, edge shape, functional groups and overall composition) and photophysical properties is yet not fully understood. This is particularly true for carbon dots displaying selective luminescence (one of their most intriguing properties), i.e. their PL emission wavelength can be tuned by varying the excitation wavelength. In this work, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain CNDs with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch, carboxylic acids and Tris-EDTA (TE) buffer as carbon- and nitrogen source, respectively. The presented microwave-assisted hydrothermal precursor carbonization (MW-hPC) is characterized by its cost-efficiency, simplicity, short reaction times, low environmental footprint, and high yields of approx. 80\% (w/w). Furthermore, only a single synthesis step is necessary to obtain homogeneous water-soluble CNDs with no need for further purification. Depending on starting materials and reaction conditions different types of CNDs have been prepared. The as-prepared CNDs exhibit reproducible, highly homogeneous and favourable PL properties with narrow emission bands (approx. 70nm FWHM), are non-blinking, and are ready to use without need for further purification, modification or surface passivation agents. Furthermore, the CNDs are comparatively small (approx. 2.0nm to 2.4nm) with narrow size distributions; are stable over a long period of time (at least one year), either in solution or as a dried solid; and maintain their PL properties when re-dispersed in solution. Depending on CND type, the PL quantum yield (PLQY) can be adjusted from as low as 1\% to as high as 90\%; one of the highest reported PLQY values (for CNDs) so far. An essential part of this work was the utilization of a microwave synthesis reactor, allowing various batch sizes and precise control over reaction temperature and -time, pressure, and heating- and cooling rate, while also being safe to operate at elevated reaction conditions (e.g. 230 ±C and 30 bar). The hereby-achieved high sample throughput allowed, for the first time, the thorough investigation of a wide range of synthesis parameters, providing valuable insight into the CND formation. The influence of carbon- and nitrogen source, precursor concentration and -combination, reaction time and -temperature, batch size, and post-synthesis purification steps were carefully investigated regarding their influence on the optical properties of as-synthesized CNDs. In addition, the change in photophysical properties resulting from the conversion of CND solution into solid and back into the solution was investigated. Remarkably, upon freeze-drying the initial brown CND-solution turns into a non-fluorescent white/slightly yellow to brown solid which recovers PL in aqueous solution. Selected CND samples were also subject to EDX, FTIR, NMR, PL lifetime (TCSPC), particle size (TEM), TGA and XRD analysis. Besides structural characterization, the pH- and excitation dependent PL characteristics (i.e. selective luminescence) were examined; giving inside into the origin of photophysical properties and excitation dependent behaviour of CNDs. The obtained results support the notion that for CNDs the nature of the surface states determines the PL properties and that excitation dependent behaviour is caused by the "Giant Red-Edge Excitation Shift" (GREES).},
  language  = {en}
}
@phdthesis{Heck2017,
  author    = {Heck, Christian},
  title     = {Gold and silver nanolenses self-assembled by DNA origami},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-409002},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 125},
  year      = {2017},
  abstract  = {Nanolenses are linear chains of differently-sized metal nanoparticles, which can theoretically provide extremely high field enhancements. The complex structure renders their synthesis challenging and has hampered closer analyses so far. Here, the technique of DNA origami was used to self-assemble DNA-coated 10 nm, 20 nm, and 60 nm gold or silver nanoparticles into gold or silver nanolenses. Three different geometrical arrangements of gold nanolenses were assembled, and for each of the three, sets of single gold nanolenses were investigated in detail by atomic force microscopy, scanning electron microscopy, dark-field scattering and Raman spectroscopy. The surface-enhanced Raman scattering (SERS) capabilities of the single nanolenses were assessed by labelling the 10 nm gold nanoparticle selectively with dye molecules. The experimental data was complemented by finite-difference time-domain simulations. For those gold nanolenses which showed the strongest field enhancement, SERS signals from the two different internal gaps were compared by selectively placing probe dyes on the 20 nm or 60 nm gold particles. The highest enhancement was found for the gap between the 20 nm and 10 nm nanoparticle, which is indicative of a cascaded field enhancement. The protein streptavidin was labelled with alkyne groups and served as a biological model analyte, bound between the 20 nm and 10 nm particle of silver nanolenses. Thereby, a SERS signal from a single streptavidin could be detected. Background peaks observed in SERS measurements on single silver nanolenses could be attributed to amorphous carbon. It was shown that the amorphous carbon is generated in situ.},
  language  = {en}
}
@phdthesis{Willersinn2017,
  author    = {Willersinn, Jochen},
  title     = {Self-Assembly of double hydrophilic block copolymers},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-408578},
  school      = {Universit{\"a}t Potsdam},
  pages     = {119, clxxiv},
  year      = {2017},
  abstract  = {The motivation of this work was to investigate the self-assembly of a block copolymer species that attended little attraction before, double hydrophilic block copolymers (DHBCs). DHBCs consist of two linear hydrophilic polymer blocks. The self-assembly of DHBCs towards suprastructures such as particles and vesicles is determined via a strong difference in hydrophilicity between the corresponding blocks leading to a microphase separation due to immiscibility. The benefits of DHBCs and the corresponding particles and vesicles, such as biocompatibility, high permeability towards water and hydrophilic compounds as well as the large amount of possible functionalizations that can be addressed to the block copolymers make the application of DHBC based structures a viable choice in biomedicine. In order to assess a route towards self-assembled structures from DHBCs that display the potential to act as cargos for future applications, several block copolymers containing two hydrophilic polymer blocks were synthesized. Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone) (PEO-b-PVP) and Poly(ethylene oxide)-b-poly(N-vinylpyrrolidone-co-N-vinylimidazole) (PEO-b-P(VP-co-VIm) block copolymers were synthesized via reversible deactivation radical polymerization (RDRP) techniques starting from a PEO-macro chain transfer agent. The block copolymers displayed a concentration dependent self-assembly behavior in water which was determined via dynamic light scattering (DLS). It was possible to observe spherical particles via laser scanning confocal microscopy (LSCM) and cryogenic scanning electron microscopy (cryo SEM) at highly concentrated solutions of PEO-b-PVP. Furthermore, a crosslinking strategy with (PEO-b-P(VP-co-VIm) was developed applying a diiodo derived crosslinker diethylene glycol bis(2-iodoethyl) ether to form quaternary amines at the VIm units. The formed crosslinked structures proved stability upon dilution and transfer into organic solvents. Moreover, self-assembly and crosslinking in DMF proved to be more advantageous and the crosslinked structures could be successfully transferred to aqueous solution. The afforded spherical submicron particles could be visualized via LSCM, cryo SEM and Cryo TEM. Double hydrophilic pullulan-b-poly(acrylamide) block copolymers were synthesized via copper catalyzed alkyne azide cycloaddition (CuAAC) starting from suitable pullulan alkyne and azide functionalized poly(N,N-dimethylacrylamide) (PDMA) and poly(N-ethylacrylamide) (PEA) homopolymers. The conjugation reaction was confirmed via SEC and 1H-NMR measurements. The self-assembly of the block copolymers was monitored with DLS and static light scattering (SLS) measurements indicating the presence of hollow spherical structures. Cryo SEM measurements could confirm the presence of vesicular structures for Pull-b-PEA block copolymers. Solutions of Pull-b-PDMA displayed particles in cryo SEM. Moreover, an end group functionalization of Pull-b-PDMA with Rhodamine B allowed assessing the structure via LSCM and hollow spherical structures were observed indicating the presence of vesicles, too. An exemplified pathway towards a DHBC based drug delivery vehicle was demonstrated with the block copolymer Pull-b-PVP. The block copolymer was synthesized via RAFT/MADIX techniques starting from a pullulan chain transfer agent. Pull-b-PVP displayed a concentration dependent self-assembly in water with an efficiency superior to the PEO-b-PVP system, which could be observed via DLS. Cryo SEM and LSCM microscopy displayed the presence of spherical structures. In order to apply a reversible crosslinking strategy on the synthesized block copolymer, the pullulan block was selectively oxidized to dialdehydes with NaIO4. The oxidation of the block copolymer was confirmed via SEC and 1H-NMR measurements. The self-assembled and oxidized structures were subsequently crosslinked with cystamine dihiydrochloride, a pH and redox responsive crosslinker resulting in crosslinked vesicles which were observed via cryo SEM. The vesicular structures of crosslinked Pull-b-PVP could be disassembled by acid treatment or the application of the redox agent tris(2-carboxyethyl)-phosphin-hydrochloride. The successful disassembly was monitored with DLS measurements. To conclude, self-assembled structures from DHBCs such as particles and vesicles display a strong potential to generate an impact on biomedicine and nanotechnologies. The variety of DHBC compositions and functionalities are very promising features for future applications.},
  language  = {en}
}
@phdthesis{MbayaMani2017,
  author    = {Mbaya Mani, Christian},
  title     = {Functional nanoporous carbon-based materials derived from oxocarbon-metal coordination complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407866},
  school      = {Universit{\"a}t Potsdam},
  pages     = {IV, 135},
  year      = {2017},
  abstract  = {Nanoporous carbon based materials are of particular interest for both science and industry due to their exceptional properties such as a large surface area, high pore volume, high electroconductivity as well as high chemical and thermal stability. Benefiting from these advantageous properties, nanoporous carbons proved to be useful in various energy and environment related applications including energy storage and conversion, catalysis, gas sorption and separation technologies. The synthesis of nanoporous carbons classically involves thermal carbonization of the carbon precursors (e.g. phenolic resins, polyacrylonitrile, poly(vinyl alcohol) etc.) followed by an activation step and/or it makes use of classical hard or soft templates to obtain well-defined porous structures. However, these synthesis strategies are complicated and costly; and make use of hazardous chemicals, hindering their application for large-scale production. Furthermore, control over the carbon materials properties is challenging owing to the relatively unpredictable processes at the high carbonization temperatures. In the present thesis, nanoporous carbon based materials are prepared by the direct heat treatment of crystalline precursor materials with pre-defined properties. This synthesis strategy does not require any additional carbon sources or classical hard- or soft templates. The highly stable and porous crystalline precursors are based on coordination compounds of the squarate and croconate ions with various divalent metal ions including Zn2+, Cu2+, Ni2+, and Co2+, respectively. Here, the structural properties of the crystals can be controlled by the choice of appropriate synthesis conditions such as the crystal aging temperature, the ligand/metal molar ratio, the metal ion, and the organic ligand system. In this context, the coordination of the squarate ions to Zn2+ yields porous 3D cube crystalline particles. The morphology of the cubes can be tuned from densely packed cubes with a smooth surface to cubes with intriguing micrometer-sized openings and voids which evolve on the centers of the low index faces as the crystal aging temperature is raised. By varying the molar ratio, the particle shape can be changed from truncated cubes to perfect cubes with right-angled edges. These crystalline precursors can be easily transformed into the respective carbon based materials by heat treatment at elevated temperatures in a nitrogen atmosphere followed by a facile washing step. The resulting carbons are obtained in good yields and possess a hierarchical pore structure with well-organized and interconnected micro-, meso- and macropores. Moreover, high surface areas and large pore volumes of up to 1957 m2 g-1 and 2.31 cm3 g-1 are achieved, respectively, whereby the macroscopic structure of the precursors is preserved throughout the whole synthesis procedure. Owing to these advantageous properties, the resulting carbon based materials represent promising supercapacitor electrode materials for energy storage applications. This is exemplarily demonstrated by employing the 3D hierarchical porous carbon cubes derived from squarate-zinc coordination compounds as electrode material showing a specific capacitance of 133 F g-1 in H2SO4 at a scan rate of 5 mV s-1 and retaining 67\% of this specific capacitance when the scan rate is increased to 200 mV s-1. In a further application, the porous carbon cubes derived from squarate-zinc coordination compounds are used as high surface area support material and decorated with nickel nanoparticles via an incipient wetness impregnation. The resulting composite material combines a high surface area, a hierarchical pore structure with high functionality and well-accessible pores. Moreover, owing to their regular micro-cube shape, they allow for a good packing of a fixed-bed flow reactor along with high column efficiency and a minimized pressure drop throughout the packed reactor. Therefore, the composite is employed as heterogeneous catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran showing good catalytic performance and overcoming the conventional problem of column blocking. Thinking about the rational design of 3D carbon geometries, the functions and properties of the resulting carbon-based materials can be further expanded by the rational introduction of heteroatoms (e.g. N, B, S, P, etc.) into the carbon structures in order to alter properties such as wettability, surface polarity as well as the electrochemical landscape. In this context, the use of crystalline materials based on oxocarbon-metal ion complexes can open a platform of highly functional materials for all processes that involve surface processes.},
  language  = {en}
}
@phdthesis{Muzdalo2017,
  author    = {Muzdalo, Anja},
  title     = {Thermal cis-trans isomerization of azobenzene studied by path sampling and QM/MM stochastic dynamics},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-405814},
  school      = {Universit{\"a}t Potsdam},
  pages     = {144},
  year      = {2017},
  abstract  = {Azobenzene-based molecular photoswitches have extensively been applied to biological systems, involving photo-control of peptides, lipids and nucleic acids. The isomerization between the stable trans and the metastable cis state of the azo moieties leads to pronounced changes in shape and other physico-chemical properties of the molecules into which they are incorporated. Fast switching can be induced via transitions to excited electronic states and fine-tuned by a large number of different substituents at the phenyl rings. But a rational design of tailor-made azo groups also requires control of their stability in the dark, the half-lifetime of the cis isomer. In computational chemistry, thermally activated barrier crossing on the ground state Born-Oppenheimer surface can efficiently be estimated with Eyring's transition state theory (TST) approach; the growing complexity of the azo moiety and a rather heterogeneous environment, however, may render some of the underlying simplifying assumptions problematic. In this dissertation, a computational approach is established to remove two restrictions at once: the environment is modeled explicitly by employing a quantum mechanical/molecular mechanics (QM/MM) description; and the isomerization process is tracked by analyzing complete dynamical pathways between stable states. The suitability of this description is validated by using two test systems, pure azo benzene and a derivative with electron donating and electron withdrawing substituents ("push-pull" azobenzene). Each system is studied in the gas phase, in toluene and in polar DMSO solvent. The azo molecules are treated at the QM level using a very recent, semi-empirical approximation to density functional theory (density functional tight binding approximation). Reactive pathways are sampled by implementing a version of the so-called transition path sampling method (TPS), without introducing any bias into the system dynamics. By analyzing ensembles of reactive trajectories, the change in isomerization pathway from linear inversion to rotation in going from apolar to polar solvent, predicted by the TST approach, could be verified for the push-pull derivative. At the same time, the mere presence of explicit solvation is seen to broaden the distribution of isomerization pathways, an effect TST cannot account for. Using likelihood maximization based on the TPS shooting history, an improved reaction coordinate was identified as a sine-cosine combination of the central bend angles and the rotation dihedral, r (ω,α,α′). The computational van't Hoff analysis for the activation entropies was performed to gain further insight into the differential role of solvent for the case of the unsubstituted and the push-pull azobenzene. In agreement with the experiment, it yielded positive activation entropies for azobenzene in the DMSO solvent while negative for the push-pull derivative, reflecting the induced ordering of solvent around the more dipolar transition state associated to the latter compound. Also, the dynamically corrected rate constants were evaluated using the reactive flux approach where an increase comparable to the experimental one was observed for a high polarity medium for both azobenzene derivatives.},
  language  = {en}
}
@phdthesis{Charan2017,
  author    = {Charan, Himanshu},
  title     = {Self assembled transmembrane protein polymer conjugates for the generation of nano thin membranes and micro compartments},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402060},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 138},
  year      = {2017},
  abstract  = {This project was focused on generating ultra thin stimuli responsive membranes with an embedded transmembrane protein to act as the pore. The membranes were formed by crosslinking of transmembrane protein polymer conjugates. The conjugates were self assembled on air water interface and the polymer chains crosslinked using a UV crosslinkable comonomer to engender the membrane. The protein used for the studies reported herein was one of the largest transmembrane channel proteins, ferric hydroxamate uptake protein component A (FhuA), found in the outer membrane of Escherichia coli (E. coli). The wild type protein and three genetic variants of FhuA were provided by the group of Prof. Schwaneberg in Aachen. The well known thermo responsive poly(N isopropylacrylamide) (PNIPAAm) and the pH and thermo responsive polymer poly((2-dimethylamino)ethyl methacrylate) (PDMAEMA) were conjugated to FhuA and the genetic variants via controlled radical polymerization (CRP) using grafting from technique. These polymers were chosen because they would provide stimuli handles in the resulting membranes. The reported polymerization was the first ever attempt to attach polymer chains onto a membrane protein using site specific modification. The conjugate synthesis was carried out in two steps - a) FhuA was first converted into a macroinitiator by covalently linking a water soluble functional CRP initiator to the lysine residues. b) Copper mediated CRP was then carried out in pure buffer conditions with and without sacrificial initiator to generate the conjugates. The challenge was carrying out the modifications on FhuA without denaturing it. FhuA, being a transmembrane protein, requires amphiphilic species to stabilize its highly hydrophobic transmembrane region. For the experiments reported in this thesis, the stabilizing agent was 2 methyl 2,4-pentanediol (MPD). Since the buffer containing MPD cannot be considered a purely aqueous system, and also because MPD might interfere with the polymerization procedure, the reaction conditions were first optimized using a model globular protein, bovine serum albumin (BSA). The optimum conditions were then used for the generation of conjugates with FhuA. The generated conjugates were shown to be highly interfacially active and this property was exploited to let them self assemble onto polar apolar interfaces. The emulsions stabilized by particles or conjugates are referred to as Pickering emulsions. Crosslinking conjugates with a UV crosslinkable co monomer afforded nano thin micro compartments. Interfacial self assembly at the air water interface and subsequent UV crosslinking also yielded nano thin, stimuli responsive membranes which were shown to be mechanically robust. Initial characterization of the flux and permeation of water through these membranes is also reported herein. The generated nano thin membranes with PNIPAAm showed reduced permeation at elevated temperatures owing to the resistance by the hydrophobic and thus water-impermeable polymer matrix, hence confirming the stimulus responsivity. Additionally, as a part of collaborative work with Dr. Changzhu Wu, TU Dresden, conjugates of three enzymes with current/potential industrial relevance (candida antarctica lipase B, benzaldehyde lyase and glucose oxidase) with stimuli responsive polymers were synthesized. This work aims at carrying out cascade reactions in the Pickering emulsions generated by self assembled enzyme polymer conjugate.},
  language  = {en}
}
@misc{GrunwaldKellingHoldtetal.2017,
  author    = {Grunwald, Nicolas and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen and Schilde, Uwe},
  title     = {The crystal structure of 1,1′-bisisoquinoline, C18H12N2},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-401952},
  pages     = {3},
  year      = {2017},
  abstract  = {C18H12N2, tetragonal, I41/a (no. 88), a=13.8885(6) {\AA}, c=13.6718(6) {\AA}, V =2637.2(3) {\AA}3, Z =8, Rgt(F)=0.0295, wRref(F2)=0.0854, T =210 K. CCDC no.: 631823},
  language  = {en}
}
@misc{SchildePazOrtiz2017,
  author    = {Schilde, Uwe and Paz, Christian and Ortiz, Leandro},
  title     = {Crystal structure of erioflorin isolated from Podanthus mitiqui (L.)},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-401832},
  pages     = {4},
  year      = {2017},
  abstract  = {The title compound, erioflorin, C19H24O6 [systematic name: (1aR,3S,4Z,5aR,8aR,9R,10aR)-1a, 2,3,5a, 7,8,8a, 9,10,10a-decahydro-3-hydroxy-4,10a-dimethyl-8-methylidene-7-oxooxireno[5,6] cyclodeca[1,2-b]furan-9-yl methacrylate], is a tricyclic germacrane sesquiterpene lactone, which was isolated from Podanthus mitiqui (L.). The compound crystallizes in the space group P2(1)2(1)2(1), and its molecular structure consists of a methacrylic ester of a ten-membered ring sesquiterpenoid annelated with an epoxide and a butyrolactone. The structure is stabilized by one intramolecular C-H center dot center dot center dot O hydrogen bond. An O-H center dot center dot center dot O hydrogen bond and further C-H center dot center dot center dot O interactions can be observed in the packing.},
  language  = {en}
}