@misc{TsukamotoHeabelValencaetal.2008,
  author    = {Tsukamoto, Junko and Heabel, Sophie and Valenca, Gustavo P. and Peter, Martin and Franco, Telma},
  title     = {Enzymatic direct synthesis of acrylic acid esters of mono- and disaccharides},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-42652},
  year      = {2008},
  abstract  = {BACKGROUND: There is an increased need to replace materials derived from fossil sources by renewables. Sugar-cane derived carbohydrates are very abundant in Brazil and are the cheapest sugars available in the market, with more than 400 million tons of sugarcane processed in the year 2007. The objective of this work was to study the preparation of sugar acrylates from free sugars and free acrylic acid, thus avoiding the previous preparation of protected sugar derivatives, such as glycosides, or activated acrylates, such as vinyl acrylate. RESULTS: Lipase catalyzed esterification of three mono- and two disaccharides with acrylic acid, in the presence or absence of molecular sieves was investigated. The reactions were monitored by high-performance liquid chromatography (HPLC) and the products were analyzed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. The main products are mono- and diacrylates, while higher esters are formed as minor products. The highest conversion to sugar acrylates was observed for the D-glucose and D-fructose, followed by D-xylose and D-maltose. Molecular sieves had no pronounced effect on the conversion CONCLUSIONS: A feasible method is described to produce and to characterize sugar acrylates, including those containing more than two acrylate groups. The process for production of these higher esters could potentially be optimized further to produce molecules for cross-linking in acrylate polymerization and other applications. The direct enzymatic esterification of free carbohydrates with acrylic acid is unprecedented.},
  language  = {en}
}
@misc{OliveiraJrGueddariMoerschbacheretal.2008,
  author    = {Oliveira Jr, E. N. and Gueddari, Nour E. El and Moerschbacher, Bruno M. and Peter, Martin and Franco, Telma},
  title     = {Growth of phytopathogenic fungi in the presence of partially acetylated chitooligosaccharides},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-42646},
  year      = {2008},
  abstract  = {Four phytopathogenic fungi were cultivated up to six days in media containing chitooligosaccharide mixtures differing in average DP and FA. The three different mixtures were named Q3 (which contained oligosaccharides ofDP2-DP10, withDP2-DP7 asmain components), Q2 (which contained oligosaccharides of DP2-DP12, with DP2-DP10 as main components) and Q1 (which derived from Q2 and contained oligomers of DP5-DP8 with hexamer and a heptamer as the main components). The novel aspect of this work is the description of the effect of mixtures of oligosaccharides with different and known composition on fungal growth rates. The growth rate of Alternaria alternata and Rhizopus stolonifer was initially inhibited by Q3 and Q2 at higher concentrations. Q1 had a growth stimulating effect on these two fungi. Growth of Botrytis cinerea was inhibited by Q3 and Q2, while Q1 had no effect on the growth of this fungus. Growth of Penicillium expansum was only slightly inhibited by higher concentrations of sample Q3, while Q2 and Q1 had no effect. The inhibition of growth rates or their resistance toward chitooligosaccharides correlated with the absence or presence of chitinolytic enzymes in the culture media, respectively.},
  language  = {en}
}
@misc{BringmannMutanyattaComarMaksimenkaetal.2008,
  author    = {Bringmann, Gerhard and Mutanyatta-Comar, Joan and Maksimenka, Katja and Wanjohi, John M. and Heydenreich, Matthias and Brun, Reto and M{\"u}ller, Werner E. G. and Peter, Martin and Midiwo, Jacob O. and Yenesew, Abiy},
  title     = {Joziknipholones A and B : the First Dimeric Phenylanthraquinones, from the Roots of Bulbine frutescens},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-42638},
  year      = {2008},
  abstract  = {From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-configuration (i.e., with the acetyl portions below the anthraquinone plane) at both axes in the case of joziknipholone A, whereas in joziknipholone B, the knipholone part was found to be M-configured. Joziknipholones A and B are active against the chloroquine resistant strain K1 of the malaria pathogen, Plasmodium falciparum, and show moderate activity against murine leukemic lymphoma L5178y cells.},
  language  = {en}
}
@misc{SchaeferBungNest2008,
  author    = {Sch{\"a}fer-Bung, Boris and Nest, Mathias},
  title     = {Correlated dynamics of electrons with reduced two-electron density matrices},
  issn      = {1866-8372},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41774},
  year      = {2008},
  abstract  = {We present an approach to the correlated dynamics of many-electron systems. We show, that the twoelectron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented.},
  language  = {en}
}
@phdthesis{Skrabania2008,
  author    = {Skrabania, Katja},
  title     = {The multifarious self-assembly of triblock copolymers : from multi-responsive polymers and multi-compartment micelles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-30764},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {New ABC triblock copolymers were synthesized by controlled free-radical polymerization via Reversible Addition-Fragmentation chain Transfer (RAFT). Compared to amphiphilic diblock copolymers, the prepared materials formed more complex self-assembled structures in water due to three different functional units. Two strategies were followed: The first approach relied on double-thermoresponsive triblock copolymers exhibiting Lower Critical Solution Temperature (LCST) behavior in water. While the first phase transition triggers the self-assembly of triblock copolymers upon heating, the second one allows to modify the self-assembled state. The stepwise self-assembly was followed by turbidimetry, dynamic light scattering (DLS) and 1H NMR spectroscopy as these methods reflect the behavior on the macroscopic, mesoscopic and molecular scale. Although the first phase transition could be easily monitored due to the onset of self-assembly, it was difficult to identify the second phase transition unambiguously as the changes are either marginal or coincide with the slow response of the self-assembled system to relatively fast changes of temperature. The second approach towards advanced polymeric micelles exploited the thermodynamic incompatibility of "triphilic" block copolymers - namely polymers bearing a hydrophilic, a lipophilic and a fluorophilic block - as the driving force for self-assembly in water. The self-assembly of these polymers in water produced polymeric micelles comprising a hydrophilic corona and a microphase-separated micellar core with lipophilic and fluorophilic domains - so called multi-compartment micelles. The association of triblock copolymers in water was studied by 1H NMR spectroscopy, DLS and cryogenic transmission electron microscopy (cryo-TEM). Direct imaging of the polymeric micelles in solution by cryo-TEM revealed different morphologies depending on the block sequence and the preparation conditions. While polymers with the sequence hydrophilic-lipophilic-fluorophilic built core-shell-corona micelles with the core being the fluorinated compartment, block copolymers with the hydrophilic block in the middle formed spherical micelles where single or multiple fluorinated domains "float" as disks on the surface of the lipophilic core. Increasing the temperature during micelle preparation or annealing of the aqueous solutions after preparation at higher temperatures induced occasionally a change of the micelle morphology or the particle size distribution. By RAFT polymerization not only the desired polymeric architectures could be realized, but the technique provided in addition a precious tool for molar mass characterization. The thiocarbonylthio moieties, which are present at the chain ends of polymers prepared by RAFT, absorb light in the UV and visible range and were employed for end-group analysis by UV-vis spectroscopy. A variety of dithiobenzoate and trithiocarbonate RAFT agents with differently substituted initiating R groups were synthesized. The investigation of their absorption characteristics showed that the intensity of the absorptions depends sensitively on the substitution pattern next to the thiocarbonylthio moiety and on the solvent polarity. According to these results, the conditions for a reliable and convenient end-group analysis by UV-vis spectroscopy were optimized. As end-group analysis by UV-vis spectroscopy is insensitive to the potential association of polymers in solution, it was advantageously exploited for the molar mass characterization of the prepared amphiphilic block copolymers.},
  language  = {en}
}
@phdthesis{Beyvers2008,
  author    = {Beyvers, Stephanie},
  title     = {Selective excitation of adsorbate vibrations on dissipative surfaces},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-25516},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {The selective infrared (IR) excitation of molecular vibrations is a powerful tool to control the photoreactivity prior to electronic excitation in the ultraviolet / visible (UV/Vis) light regime ("vibrationally mediated chemistry"). For adsorbates on surfaces it has been theoretically predicted that IR preexcitation will lead to higher UV/Vis photodesorption yields and larger cross sections for other photoreactions. In a recent experiment, IR-mediated desorption of molecular hydrogen from a Si(111) surface on which atomic hydrogen and deuterium were co-adsorbed was achieved, following a vibrational mechanism as indicated by the isotope-selectivity. In the present work, selective vibrational IR excitation of adsorbate molecules, treated as multi-dimensional oscillators on dissipative surfaces, has been simulated within the framework of open-system density matrix theory. Not only potential-mediated, inter-mode coupling poses an obstacle to selective excitation but also the coupling of the adsorbate ("system") modes to the electronic and phononic degrees of freedom of the surface ("bath") does. Vibrational relaxation thereby takes place, depending on the availabilty of energetically fitting electron-hole (e/h) pairs and/or phonons (lattice vibrations) in the surface, on time-scales ranging from milliseconds to several hundreds of femtoseconds. On metal surfaces, where the relaxation process of the adsorbate via the e/h pair mechanism dominates, vibrational lifetimes are usually shorter than on insulator or semiconductor surfaces, in the range of picoseconds, being also the timescale of the IR pulses used here. Further inhibiting factors for selectivity can be the harmonicity of a mode and weak dipole activities ("dark modes") rendering vibrational excitation with moderate field intensities difficult. In addition to simple analytical pulses, optimal control theory (OCT) has been employed here to generate a suitable electric field to populate the target state/mode maximally. The complex OCT fields were analyzed by Husimi transformation, resolving the control field in time and energy. The adsorbate/surface systems investigated were CO/Cu(100), H/Si(100) and 2H/Ru(0001). These systems proved to be suitable models to study the above mentioned effects. Further, effects of temperature, pure dephasing (elastic scattering processes), pulse duration and dimensionality (up to four degrees of freedom) were studied. It was possible to selectively excite single vibrational modes, often even state-selective. Special processes like hot-band excitation, vibrationally mediated desorption and the excitation of "dark modes" were simulated. Finally, a novel OCT algorithm in density matrix representation has been developed which allows for time-dependent target operators and thus enables to control the excitation mechanism instead of only the final state. The algorithm is based on a combination of global (iterative) and local (non-iterative) OCT schemes, such that short, globally controlled time-intervals are coupled locally in time. Its numerical performance and accuracy were tested and verified and it was successfully applied to stabilize a two-state linear-combination and to enforce a successive "ladder climbing" in a rather harmonic system, where monochromatic, analytical pulses simultaneously excited several states, leading to a population loss in the target state.},
  language  = {en}
}
@phdthesis{HernandezGarcia2008,
  author    = {Hernandez Garcia, Hugo Fernando},
  title     = {Multiscale simulation of heterophase polymerization : application to the synthesis of multicomponent colloidal polymer particles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-25036},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Heterophase polymerization is a technique widely used for the synthesis of high performance polymeric materials with applications including paints, inks, adhesives, synthetic rubber, biomedical applications and many others. Due to the heterogeneous nature of the process, many different relevant length and time scales can be identified. Each of these scales has a direct influence on the kinetics of polymerization and on the physicochemical and performance properties of the final product. Therefore, from the point of view of product and process design and optimization, the understanding of each of these relevant scales and their integration into one single model is a very promising route for reducing the time-to-market in the development of new products, for increasing the productivity and profitability of existing processes, and for designing products with improved performance or cost/performance ratio. The process considered is the synthesis of structured or composite polymer particles by multi-stage seeded emulsion polymerization. This type of process is used for the preparation of high performance materials where a synergistic behavior of two or more different types of polymers is obtained. Some examples include the synthesis of core-shell or multilayered particles for improved impact strength materials and for high resistance coatings and adhesives. The kinetics of the most relevant events taking place in an emulsion polymerization process has been investigated using suitable numerical simulation techniques at their corresponding time and length scales. These methods, which include Molecular Dynamics (MD) simulation, Brownian Dynamics (BD) simulation and kinetic Monte Carlo (kMC) simulation, have been found to be very powerful and highly useful for gaining a deeper insight and achieving a better understanding and a more accurate description of all phenomena involved in emulsion polymerization processes, and can be potentially extended to investigate any type of heterogeneous process. The novel approach of using these kinetic-based numerical simulation methods can be regarded as a complement to the traditional thermodynamic-based macroscopic description of emulsion polymerization. The particular events investigated include molecular diffusion, diffusion-controlled polymerization reactions, particle formation, absorption/desorption of radicals and monomer, and the colloidal aggregation of polymer particles. Using BD simulation it was possible to precisely determine the kinetics of absorption/desorption of molecular species by polymer particles, and to simulate the colloidal aggregation of polymer particles. For diluted systems, a very good agreement between BD simulation and the classical theory developed by Smoluchowski was obtained. However, for concentrated systems, significant deviations from the ideal behavior predicted by Smoluchowski were evidenced. BD simulation was found to be a very valuable tool for the investigation of emulsion polymerization processes especially when the spatial and geometrical complexity of the system cannot be neglected, as is the case of concentrated dispersions, non-spherical particles, structured polymer particles, particles with non-uniform monomer concentration, and so on. In addition, BD simulation was used to describe non-equilibrium monomer swelling kinetics, which is not possible using the traditional thermodynamic approach because it is only valid for systems at equilibrium. The description of diffusion-controlled polymerization reactions was successfully achieved using a new stochastic algorithm for the kMC simulation of imperfectly mixed systems (SSA-IM). In contrast to the traditional stochastic simulation algorithm (SSA) and the deterministic rate of reaction equations, instead of assuming perfect mixing in the whole reactor, the new SSA-IM determines the volume perfectly mixed between two consecutive reactions as a function of the diffusion coefficient of the reacting species. Using this approach it was possible to describe, using a single set of kinetic parameters, typical mass transfer limitations effects during a free radical batch polymerization such as the cage effect, the gel effect and the glass effect. Using multiscale integration it was possible to investigate the formation of secondary particles during the seeded emulsion polymerization of vinyl acetate over a polystyrene seed. Three different cases of radical generation were considered: generation of radicals by thermal decomposition of water-soluble initiating compounds, generation of radicals by a redox reaction at the surface of the particles, and generation of radicals by thermal decomposition of surface-active initiators "inisurfs" attached to the surface of the particles. The simulation results demonstrated the satisfactory reduction in secondary particles formation achieved when the locus of radical generation is controlled close to the particles surface.},
  language  = {en}
}
@phdthesis{Ide2008,
  author    = {Ide, Andreas Hans Peter},
  title     = {Self-Structuring of functionalized micro- and mesoporous organosilicas using boron-silane-precursors},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-23717},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {The structuring of porous silica materials at the nanometer scale and their surface functionalization are important issues of current materials research. Many innovations in chromatography, catalysis and electronic devices benefit from this knowledge. The work at hand is dedicated to the targeted design of functional organosilica materials. In this context a new precursor concept based on boron-silanes is presented. These precursors combine the properties of a structure directing group and a silica source by covalent borane linkage. Formation of the precursor is easily realized by a sequential two-step hydroboration, firstly on bis(triethoxysilyl)ethene, and secondly on an unsaturated structure directing moiety such as alkenes or polymers. The so prepared precursors self-organize when hydrolysis of their inorganic moiety takes place via an aggregation of their organic side chains into hydrophobic domains. In this way, the additional use of a surfactant as a template is not necessary. Chemical cleavage of these moieties (e.g. by ammonolysis or oxidative saponification) yields an organosilica where all functionalities are exclusively located at the pore wall and therefore accessible. The accessibility of the functionalities is a vital point for applications and is not necessarily granted for common silica functionalization approaches. Further advantages of the boron-silane concept are the possibility to introduce a variety of surface functionalities by heterolytic cleavage of the boron linker and the control of the pore morphology. For that purpose the covalent linkage of different alkyl groups and polymers was studied. Another aspect is the access to chiral boron silane precursors yielding functionalized mesoporous organosilica with chiral functionalities exclusively located at the pore walls after condensation and removal of the structure directing moiety. These materials possess great potential for applications documented by preliminary investigations on chiral resolution of a racemic mixture by HPLC and asymmetric catalysis. In the course of this work valuable insights into the targeted structuring and surface functionalization of organosilicas were gained. A promising outlook for further investigations is the extension of this concept by altering the structure directing moieties of the precursor. That way the morphology of the final organosilica might be controlled by for example mesogens. Furthermore, the use of the boron linker enables the introduction of multiple functionalities into organosilicas, making the obtained material unique in its performance.},
  language  = {en}
}
@phdthesis{Bahrke2008,
  author    = {Bahrke, Sven},
  title     = {Mass spectrometric analysis of chitooligosaccharides and their interaction with proteins},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-20179},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Chitooligosaccharides are composed of glycosamin and N-acetylglycisamin residues. Gel permeations chromatography is employed for the separation of oligomers, cation exchange chromatography is used for the separation of homologes and isomers. Trideuterioacetylation of the chitooligosaccharides followed by MALDI-TOF mass spectrometry allowes for the quantitation of mixtures of homologes. vMALDI LTQ multiple-stage MS is employed for quantitative sequencing of complex mixtures of heterochitooligosaccharides. Pure homologes and isomers are applied to biological assays. Chitooligosaccahrides form high-affinity non-covalent complexes with HC gp-39 (human cartilage glycoprotein of 39 kDa). The affinity of the chitooligosaccharides depends on DP, FA and the sequence of glycosamin and N-acetylglycosamin moieties. (+)nanoESI Q TOF MS/MS is used for identification of a high-affinity binding chitooligosaccharide of a non-covalent chitinase B - chitooligosaccharide complex. DADAA is identified as the heterochitoisomer binding with highest affinity and biostability to HC gp-39. Fluorescence based enzyme assays confirm the results.},
  language  = {en}
}
@phdthesis{Gebauer2008,
  author    = {Gebauer, Denis},
  title     = {A novel view on the early stage of crystallization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19818},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {This thesis provides a novel view on the early stage of crystallization utilizing calcium carbonate as a model system. Calcium carbonate is of great economical, scientific and ecological importance, because it is a major part of water hardness, the most abundant Biomineral and forms huge amounts of geological sediments thus binding large amounts of carbon dioxide. The primary experiments base on the evolution of supersaturation via slow addition of dilute calcium chloride solution into dilute carbonate buffer. The time-dependent measurement of the Ca2+ potential and concurrent pH = constant titration facilitate the calculation of the amount of calcium and carbonate ions bound in pre-nucleation stage clusters, which have never been detected experimentally so far, and in the new phase after nucleation, respectively. Analytical Ultracentrifugation independently proves the existence of pre-nucleation stage clusters, and shows that the clusters forming at pH = 9.00 have a proximately time-averaged size of altogether 70 calcium and carbonate ions. Both experiments show that pre-nucleation stage cluster formation can be described by means of equilibrium thermodynamics. Effectively, the cluster formation equilibrium is physico-chemically characterized by means of a multiple-binding equilibrium of calcium ions to a 'lattice' of carbonate ions. The evaluation gives GIBBS standard energy for the formation of calcium/carbonate ion pairs in clusters, which exhibits a maximal value of approximately 17.2 kJ mol^-1 at pH = 9.75 and relates to a minimal binding strength in clusters at this pH-value. Nucleated calcium carbonate particles are amorphous at first and subsequently become crystalline. At high binding strength in clusters, only calcite (the thermodynamically stable polymorph) is finally obtained, while with decreasing binding strength in clusters, vaterite (the thermodynamically least stable polymorph) and presumably aragonite (the thermodynamically intermediate stable polymorph) are obtained additionally. Concurrently, two different solubility products of nucleated amorphous calcium carbonate (ACC) are detected at low binding strength and high binding strength in clusters (ACC I 3.1EE-8 M^2, ACC II 3.8EE-8 M^2), respectively, indicating the precipitation of at least two different ACC species, while the clusters provide the precursor species of ACC. It is proximate that ACC I may relate to calcitic ACC -i.e. ACC exhibiting short range order similar to the long range order of calcite and that ACC II may relate to vateritic ACC, which will subsequently transform into the particular crystalline polymorph as discussed in the literature, respectively. Detailed analysis of nucleated particles forming at minimal binding strength in clusters (pH = 9.75) by means of SEM, TEM, WAXS and light microscopy shows that predominantly vaterite with traces of calcite forms. The crystalline particles of early stages are composed of nano-crystallites of approximately 5 to 10 nm size, respectively, which are aligned in high mutual order as in mesocrystals. The analyses of precipitation at pH = 9.75 in presence of additives -polyacrylic acid (pAA) as a model compound for scale inhibitors and peptides exhibiting calcium carbonate binding affinity as model compounds for crystal modifiers- shows that ACC I and ACC II are precipitated in parallel: pAA stabilizes ACC II particles against crystallization leading to their dissolution for the benefit of crystals that form from ACC I and exclusively calcite is finally obtained. Concurrently, the peptide additives analogously inhibit the formation of calcite and exclusively vaterite is finally obtained in case of one of the peptide additives. These findings show that classical nucleation theory is hardly applicable for the nucleation of calcium carbonate. The metastable system is stabilized remarkably due to cluster formation, while clusters forming by means of equilibrium thermodynamics are the nucleation relevant species and not ions. Most likely, the concept of cluster formation is a common phenomenon occurring during the precipitation of hardly soluble compounds as qualitatively shown for calcium oxalate and calcium phosphate. This finding is important for the fundamental understanding of crystallization and nucleation-inhibition and modification by additives with impact on materials of huge scientific and industrial importance as well as for better understanding of the mass transport in crystallization. It can provide a novel basis for simulation and modelling approaches. New mechanisms of scale formation in Bio- and Geomineralization and also in scale inhibition on the basis of the newly reported reaction channel need to be considered.},
  language  = {en}
}
@phdthesis{Fischer2008,
  author    = {Fischer, Anna},
  title     = {"Reactive hard templating" : from carbon nitrides to metal nitrides},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19777},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Nanostructured inorganic materials are routinely synthesized by the use of templates. Depending on the synthesis conditions of the product material, either "soft" or "hard" templates can be applied. For sol-gel processes, usually "soft" templating techniques are employed, while "hard" templates are used for high temperature synthesis pathways. In classical templating approaches, the template has the unique role of structure directing agent, in the sense that it is not participating to the chemical formation of the resulting material. This work investigates a new templating pathway to nanostructured materials, where the template is also a reagent in the formation of the final material. This concept is described as "reactive templating" and opens a synthetic path toward materials which cannot be synthesised on a nanometre scale by classical templating approaches. Metal nitrides are such kind of materials. They are usually produced by the conversion of metals or metal oxides in ammonia flow at high temperature (T > 1000°C), which make the application of classical templating techniques difficult. Graphitic carbon nitride, g-C3N4, despite its fundamental and theoretical importance, is probably one of the most promising materials to complement carbon in material science and many efforts are put in the synthesis of this material. A simple polyaddition/elimination reaction path at high temperature (T = 550°C) allows the polymerisation of cyanamide toward graphitic carbon nitride solids. By hard templating, using nanostructured silica or aluminium oxide as nanotemplates, a variety of nanostructured graphitic carbon nitrides such as nanorods, nanotubes, meso- and macroporous powders could be obtained by nanocasting or nanocoating. Due to the special semi-conducting properties of the graphitic carbon nitride matrix, the nanostructured graphitic carbon nitrides show unexpected catalytic activity for the activation of benzene in Friedel-Crafts type reactions, making this material an interesting metal free catalyst. Furthermore, due to the chemical composition of g-C3N4 and the fact that it is totally decomposed at temperatures between 600°C and 800°C even under inert atmosphere, g-C3N4 was shown to be a good nitrogen donor for the synthesis of early transition metal nitrides at high temperatures. Thus using the nanostructured carbon nitrides as "reactive templates" or "nanoreactors", various metal nitride nanostructures, such as nanoparticles and porous frameworks could be obtained at high temperature. In this approach the carbon nitride nanostructure played both the role of the nitrogen source and of the exotemplate, imprinting its size and shape to the resulting metal nitride nanostructure.},
  language  = {en}
}
@phdthesis{Hentschel2008,
  author    = {Hentschel, Jens},
  title     = {Synthese und kontrollierte Mikrostrukturbildung funktionaler Peptid-Polymerkonjugate in organischen L{\"o}sungsmitteln},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19840},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {In der vorliegenden Arbeit wurde ein Ansatz verfolgt, die besonderen Eigenschaften der Strukturbildung sequenzdefinierter Peptide mit den vielseitigen Materialeigenschaften synthetischer Blockcopolymere zu kombinieren. Dazu wurde ein synthetisches Polymer kovalent mit einer definierten Peptidsequenz verkn{\"u}pft. Der Peptidblock (die Organisationseinheit) wurde speziell designt, um sp{\"a}ter die Strukturbildung des Peptid-Polymerkonjugates induzieren und leiten zu k{\"o}nnen. Als Organisationsmotiv diente hierbei das aus der Natur bekannte β-Faltblatt Strukturmotiv. Das Peptidsegment wurde in einer festphasengebundenen Synthese aufgebaut. Dabei wurden tempor{\"a}re St{\"o}r-Segmente (Switch-Segmente) in die Peptidsequenz integriert. Diese Segmente unterdr{\"u}cken die Aggregationstendenz w{\"a}hrend der Synthese und k{\"o}nnen durch einen pH-abh{\"a}ngigen Schaltvorgang in das nat{\"u}rliche Peptidr{\"u}ckgrat {\"u}berf{\"u}hrt werden. Zus{\"a}tzlich zu der verbesserten Ausbeute und Reinheit der entsprechenden Peptide war auf diese Weise eine kontrollierte Aktivierung der Mikrostrukturbildung m{\"o}glich. Mit Hilfe zwei verschiedener Synthesestrategien (Kupplungs- bzw. Polymerisationsstrategie) wurde ein Satz von definierten Peptid-Polymerkonjugaten mit unterschiedlich großen Polymersegmenten synthetisiert. Diese wurden anschließend im Hinblick auf ihre Strukturbildungseigenschaften in organischen L{\"o}sungsmitteln untersucht. Durch mikroskopische Verfahren (AFM, TEM), konnte f{\"u}r alle Konjugate, die Bildung faserartiger Aggregate mit Dimensionen im Nano- bis Mikrometerbereich beobachtet werden. Genauere Untersuchungen zeigten, dass die Peptidsegmente in diesen Faserstrukturen ein β-Faltblatt ausbilden. Dies ist ein deutlicher Hinweis darauf, dass die Strukturbildung der Konjugate tats{\"a}chlich durch den Peptidblock gesteuert und kontrolliert wurde.},
  language  = {de}
}
@phdthesis{Imranulhaq2008,
  author    = {Imran ul-haq, Muhammad},
  title     = {Synthesis of fluorinated polymers in supercritical carbon dioxide (scCO₂)},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19868},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {For the first time stabilizer-free vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical CO₂. Polymerizations were carried out at 140°C, 1500 bar and were initiated with di-tert-butyl peroxide (DTBP). In-line FT-NIR (Fourier Transform- Near Infrared) spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography (SEC) and polymer end group analysis by 1H-NMR spectroscopy. The number average molecular weights were below 104 g∙mol-1 and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. To allow for isothermal reactions high CO₂ contents ranging from 61 to 83 wt.\% were used. The high-temperature, high-pressure conditions were required for homogeneous phase polymerization. These conditions did not alter the amount of defects in VDF chaining. Scanning electron microscopy (SEM) indicated that regular stack-type particles were obtained upon expansion of the homogeneous polymerization mixture. To reduce the required amount of initiator, further VDF polymerizations using chain transfer agents (CTAs) to control molecular weights were carried out in homogeneous phase with supercritical carbon dioxide (scCO₂) at 120 °C and 1500 bar. Using perfluorinated hexyl iodide as CTA, polymers of low polydispersity ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol·L-1 were obtained. Electrospray ionization- mass spectroscopy (ESI-MS) indicates the absence of initiator derived end groups, supporting livingness of the system. The "livingness" is based on the labile C-I bond. However, due to the weakness of the C-I bond perfluorinated hexyl iodide also contributes to initiation. To allow for kinetic analyses of VDF polymerizations the CTA should not contribute to initiation. Therefore, additional CTAs were applied: BrCCl3, C6F13Br and C6F13H. It was found that C6F13H does not contribute to initiation. At 120°C and 1500 bar kp/kt0.5~ 0.64 (L·mol-1·s-1)0.5 was derived. The chain transfer constant (CT) at 120°C has been determined to be 8·10-1, 9·10-2 and 2·10-4 for C6F13I, C6F13Br and C6F13H, respectively. These CT values are associated with the bond energy of the C-X bond. Moreover, the labile C-I bond allows for functionalization of the polymer to triazole end groups applying click reactions. After substitution of the iodide end group by an azide group 1,3 dipolar cycloadditions with alkynes yield polymers with 1,2,3 triazole end groups. Using symmetrical alkynes the reactions may be carried out in the absence of any catalyst. This end-functionalized poly (vinylidene fluoride) (PVDF) has higher thermal stability as compared to the normal PVDF. PVDF samples from homogeneous phase polymerizations in supercritical CO₂ and subsequent expansion to ambient conditions were analyzed with respect to polymer end groups, crystallinity, type of polymorphs and morphology. Upon expansion the polymer was obtained as white powder. Scanning electron microscopy (SEM) showed that DTBP derived polymer end groups led to stack-type particles whereas sponge- or rose-type particles were obtained in case of CTA fragments as end groups. Fourier-Transform Infrared spectroscopy and wide angle X-ray diffraction indicated that the type of polymorph, α or β crystal phase was significantly affected by the type of end group. The content of β-phase material, which is responsible for piezoelectricity of PVDF, is the highest for polymer with DTBP-derived end groups. In addition, the crystallinity of the material, as determined via differential scanning calorimetry is affected by the end groups and polymer molecular weights. For example, crystallinity ranges from around 26 \% for DTBP-derived end groups to a maximum of 62 \% for end groups originating from perfluorinated hexyl iodide for polymers with Mn ~2200 g·mol-1. Expansion of the homogeneous polymerization mixture results in particle formation by a non-optimized RESS (Rapid Expansion from Supercritical Solution) process. Thus, it was tested how polymer end groups affect the particles size distribution obtained from RESS process under controlled conditions (T = 50°C and P = 200 bar). In all RESS experiments, small primary PVDF with diameters less than 100 nm without the use of liquid solvents, surfactants, or other additives were produced. A strong correlation between particle size and particle size distribution with polymer end groups and molecular weight of the original material was observed. The smallest particles were found for RESS of PVDF with Mn~ 4000 g·mol-1 and PFHI (C6F13I) - derived end groups.},
  language  = {en}
}
@phdthesis{Kessel2008,
  author    = {Kessel, Stefanie},
  title     = {Induktion und Kontrolle hierarchischer Ordnung durch selbstorganisierte, funktionale Polymer-Peptid-Nanostrukturen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-19835},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Im Rahmen der Arbeit werden hierarchisch strukturierte Silikakompositfasern pr{\"a}sentiert, deren Bildung {\"a}hnlich zu nat{\"u}rlichen Silifizierungsreaktionen verl{\"a}uft. Als Analoga zu Proteinfilamenten in Silika Morphogeneseorganismen werden selbstorganisierte, funktionale Polyethylenoxid-Peptid-Nanob{\"a}nder eingesetzt. Mit der Isolierung einheitlicher Nanokompositfasern wird gezeigt, dass die PEO-Peptid-Nanob{\"a}nder eine starke Bindungsaffinit{\"a}t gegen{\"u}ber Kiesels{\"a}ure besitzen, diese aus sehr stark verd{\"u}nnten L{\"o}sungen anreichern und deren Kondensation zu Silikanetzwerken kontrollieren k{\"o}nnen. In h{\"o}heren Konzentrationen entstehen durch die peptidgeleitete Silifizierung der PEO-Peptid-Nanob{\"a}nder spontan makroskopische Kompositfasern mit sechs Hierarchieebenen. Diese verbinden L{\"a}ngen von bis zu 3 cm und Durchmesser von 1-2 mm mit einer definierten Feinstruktur im Submikrometerbereich. Als Resultat der komplexen inneren Struktur und der Kontrolle der Grenzfl{\"a}chen zwischen Nanob{\"a}ndern und Silika wird eine Nanoh{\"a}rte erreicht, die schon ~1/3 der H{\"a}rte von Bioglasfasern darstellt. F{\"u}r die Elastizit{\"a}t (reduziertes Eindr{\"u}ckmodul) dagegen konnte durch den relativ hohen Anteil (~40\%) an verformbaren, organischen Komponenten ein ~4-mal gr{\"o}ßer Wert im Vergleich mit Bioglasfasern bestimmt werden. Des Weiteren wird die Prozessierung der makroskopischen Kompositfasern in einem 2D-Plotprozess vorgestellt. Mit Verwendung der PEO-Peptid-Nanob{\"a}nder als „Tinte" k{\"o}nnen Kompositobjekte in beliebigen Formen geplottet werden, deren Linienbreite sowie anisotrope Ausrichtung der Nano- und Submikrometerstrukturelemente direkt mit der Plotgeschwindigkeit korrelieren. Außerdem k{\"o}nnen die Kompositobjekte als Vorstufen f{\"u}r orientierte, mesopor{\"o}se Silikaobjekte verwendet werden. Nachdem Calcinieren werden Silikastrukturen mit einer hohen spezifischen Oberfl{\"a}che und in Plotrichtung ausgerichteten zylindrischen Poren erhalten. Im Kontrast zu den anorganisch-bioorganischen Kompositfasern sollten unter Ausnutzung ionischer Wechselwirkungen oder Metallkoordination Kompositmaterialien mit anderen mechanischen Eigenschaften dargestellt werden. Es wird gezeigt, dass durch Variationen in der Aminos{\"a}uresequenz des Peptidkerns, die Oberfl{\"a}chen der PEO-Peptid-Nanob{\"a}nder gezielt mit funktionellen Gruppen versehen werden k{\"o}nnen. Eine gerichtete Vernetzung dieser modifizierten Nanob{\"a}nder wurde nicht erreicht, daf{\"u}r k{\"o}nnten die imidazolfunktionalisierten Nanob{\"a}nder als eindimensionale Protonenleiter, die mit photochromen Gruppen (Spiropyran) funktionalisierten Nanob{\"a}nder f{\"u}r die Modifizierung von Oberfl{\"a}chenpolarit{\"a}ten oder f{\"u}r gerichtete Kristallisationsprozesse eingesetzt werden.},
  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{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{Gress2008,
  author    = {Greß, Anja},
  title     = {Funktionalisierte Poly(2-oxazoline) : kontrollierte Synthese, bioinspirierte Strukturbildung und Anwendungen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18646},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Funktionalisierte Poly(2-oxazoline) als neue Materialien stellen sowohl unter strukturellen Gesichtspunkten als auch im Hinblick auf potentielle Anwendungen eine interessante Polymerklasse dar. Die Ausbildung von hierarchischen Strukturen mit Poly(2-oxazolinen) {\"u}ber intermolekulare Wasserstoffbr{\"u}ckenbindungen ist hierbei ein bisher nicht beachteter Aspekt. {\"U}ber einen bioinspirierten Ansatz sollten gezielt funktionelle Gruppen, die f{\"u}r einen hierarchischen Aufbau, z.B. in Proteinen, verantwortlich sind, in vereinfachter Weise auf die synthetische Substanzklasse der Poly(2-oxazoline) {\"u}bertragen werden. Die vorliegende Arbeit besch{\"a}ftigt sich mit der modularen Synthese neuer, funktionalisierter Poly(2-oxazolin) Homo- und Copolymere. Ausgehend von der Synthese von 2-(3-Butenyl)-2-oxazolin wurden definierte Pr{\"a}polymere in einer kationischen Isomerisierungspolymerisation unter kontrolliert/„lebenden" Bedingungen hergestellt. In einer anschließenden „Thio-Click" (Thiol-En-Reaktion) Modifizierungsreaktion wurden die gew{\"u}nschten funktionellen Gruppen quantitativ eingef{\"u}hrt. Hydroxylierte Poly(2-oxazoline) wurden hinsichtlich ihres Aggregationsverhaltens in Wasser untersucht. Bereits die jeweiligen Homopolymere bildeten aufgrund von intermolekularen Wasserstoffbr{\"u}ckenbindungen supramolekulare tubul{\"a}re Nanofasern aus. Durch Einsatz verschiedener analytischer Methoden konnte die innere Struktur der Nanor{\"o}hren beschrieben und ein entsprechendes Modell aufgestellt werden. Die dargestellten funktionellen Poly(2-oxazoline) wurden hinsichtlich ihrer Anwendung als potentielle, synthetische „antifreeze additives" untersucht. Alle Polymere besitzen eine ausgepr{\"a}gte Tendenz zur Nukleierung von Wasser und f{\"u}hren daher zu signifikanten {\"A}nderungen der Eismorphologie. Des weiteren wurde ein carboxyliertes Derivat zur biomimetischen Mineralisation von Kalziumcarbonat eingesetzt und nach ph{\"a}nomenologischen Gesichtspunkten untersucht.},
  language  = {de}
}
@phdthesis{Buha2008,
  author    = {Buha, Jelena},
  title     = {Nonaqueous syntheses of metal oxide and metal nitride nanoparticles},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18368},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Nanostructured materials are materials consisting of nanoparticulate building blocks on the scale of nanometers (i.e. 10-9 m). Composition, crystallinity and morphology can enhance or even induce new properties of the materials, which are desirable for todays and future technological applications. In this work, we have shown new strategies to synthesise metal oxide and metal nitride nanomaterials. The first part of the work deals with the study of nonaqueous synthesis of metal oxide nanoparticles. We succeeded in the synthesis of In2O3 nanopartcles where we could clearly influence the morphology by varying the type of the precursors and the solvents; of ZnO mesocrystals by using acetonitrile as a solvent; of transition metal oxides (Nb2O5, Ta2O5 and HfO2) that are particularly hard to obtain on the nanoscale and other technologically important materials. Solvothermal synthesis however is not restricted to formation of oxide materials only. In the second part we show examples of nonaqueous, solvothermal reactions of metal nitrides, but the main focus lies on the investigation of the influence of different morphologies of metal oxide precursors on the formation of the metal nitride nanoparticles. In spite of various reports, the number and variety of nanocrystalline metal nitrides is marginally small by comparison to metal oxides; hence preformed metal oxides as precursors for the preparation of metal nitrides are a logical choice. By reacting oxide nanoparticles with cyanamide, urea or melamine, at temperatures of 800 to 900 °C under nitrogen flow metal nitrides could be obtained. We studied in detail the influence of the starting material and realized that size, crystallinity, type of nitrogen source and temperature play the most important role. We have managed to propose and verify a dissolution-recrystallisation model as the formation mechanism. Furthermore we could show that the initial morphology of the oxides could be retained when ammonia flow was used instead.},
  language  = {en}
}
@misc{Klaumuenzer2008,
  type      = {Master Thesis},
  author    = {Klaum{\"u}nzer, Bastian},
  title     = {Stickstoffinversion in Azacyclen : Modellsimulationen f{\"u}r einen molekularen Schalter},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17482},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {In dieser Arbeit wird durch Modellrechnungen gezeigt, wie die Stickstoffinversion in Azacyclen als molekularer Schalter genutzt werden k{\"o}nnte. Hierzu werden ein Fluorazetidin- und ein Fluorazacyclopentanderviat quantenchemisch untersucht. Das letztere Molek{\"u}l wird auch quantendynamisch untersucht. Jedes der beiden Molek{\"u}le besitzt zwei stabile Konformationen. Es wird gezeigt, dass das Azabicyclopentanderivat von der einen Konformation mittels zweier linear polarisierter IR-Laserpulse durch sogenanntes "ladder climbing" in die andere {\"u}berf{\"u}hrt werden kann.},
  language  = {de}
}
@phdthesis{Nazaran2008,
  author    = {Nazaran, Pantea},
  title     = {Nucleation in emulsion polymerization : steps towards a non-micellar nucleation theory},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17521},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {For more than 70 years, understanding of the mechanism of particle nucleation in emulsion polymerization has been one of the most challenging issues in heterophase polymerization research. Within this work a comprehensive experimental study of particle nucleation in emulsion polymerization of styrene at 70 °C and variety of conditions has been performed. To follow the onset of nucleation, on-line conductivity measurements were applied. This technique is highly sensitive to the mobility of conducting species and hence, it can be employed to follow aggregation processes leading to particle formation. On the other hand, by recording the optical transmission (turbidity) of the reaction mixture particle growth was followed. Complementary to the on-line investigations, off-line characterizations of the particle morphology and the molecular weight have been performed. The aim was to achieve a better insight in the processes taking place after starting the reaction via particle nucleation until formation of colloidally stable latex particles. With this experimental protocol the initial period of styrene emulsion polymerization in the absence as well as in the presence of various surfactants (concentrations above and below the critical micellization concentration) and also in the presence of seed particles has been investigated. Ionic and non-ionic initiators (hydrophilic and hydrophobic types) have been applied to start the polymerizations. Following the above algorithm, experimental evidence has been obtained showing the possibility of performing surfactant-free emulsion polymerization of styrene with oil-soluble initiators. The duration of the pre-nucleation period (that is the time between starting the polymerization and nucleation) can be precisely adjusted with the initiator hydrophobicity, the equilibration time of styrene in water, and the surfactant concentration. Spontaneous emulsification of monomer in water, as soon as both phases are brought into contact, is a key factor to explain the experimental results. The equilibration time of monomer in water as well as the type and concentration of other materials in water (surfactants, seed particles, etc.) control the formation rate and the size of the emulsified droplets and thus, have a strong influence on the particle nucleation and the particle morphology. One of the main tasks was to investigate the effect of surfactant molecules and especially micelles on the nucleation mechanism. Experimental results revealed that in the presence of emulsifier micelles the conductivity pattern does not change essentially. This means that the presence of emulsifiers does not change the mechanism of particle formation qualitatively. However, surfactants assist in the nucleation process as they lower the activation free energy of particle formation. Contrary, seed particles influence particle nucleation, substantially. In the presence of seed particles above a critical volume fraction the formation of new particles can be suppressed. However, micelles and seed particles as absorbers exhibit a common behavior under conditions where monomer equilibration is not allowed. Results prove that the nucleation mechanism comprises the initiation of water soluble oligomers in the aqueous phase followed by their aggregation. The process is heterogeneous in nature due to the presence of monomer droplets.},
  language  = {en}
}
@phdthesis{Issaree2008,
  author    = {Issaree, Arisara},
  title     = {Synthesis of Hetero-chitooligosaccharides},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17069},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Chitooligosaccharides are composed of linear β-(1→4)-linked 2-acetamido-2-deoxy-β-D-glucopyranose (GlcNAc) and/or 2-amino-2-deoxy-β-D-glucopyranose (GlcN). They are of interest due to their remarkable biological properties including antibacterial, antitumor, antifungal and elicitor activities. They can be obtained from the aminoglucan chitosan by chemical or enzymatic degradation which obviously affords rather heterogenous mixtures. On the other hand, chemical synthesis provides pure compounds with defined sequences of GlcNAc and GlcN monomers. The synthesis of homo- and hetero-chitobioses and hetero-chitotetraoses is described in this thesis. Dimethylmaleoyl and phthaloyl groups were used for protection of the amines. The donor was activated as the trichloroacetimidate in order to form the β-linkages. Glycosylation in the presence of trimethylsilyl trifluoromethanesulfonate, followed by N- and O-deprotection furnished chitobioses and chitotetraoses in good yields.},
  language  = {en}
}