@phdthesis{Wattebled2006,
  author    = {Wattebled, Laurent},
  title     = {Oligomeric surfactants as novel type of amphiphiles : structure - property relationships and behaviour with additives},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12855},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {The properties of a series of well-defined new surfactant oligomers (dimers to tetramers)were examined. From a molecular point of view, these oligomeric surfactants consist of simple monomeric cationic surfactant fragments coupled via the hydrophilic ammonium chloride head groups by spacer groups (different in nature and length). Properties of these cationic surfactant oligomers in aqueous solution such as solubility, micellization and surface activity, micellar size and aggregation number were discussed with respect to the two new molecular variables introduced, i.e. degree of oligomerization and spacer group, in order to establish structure - property relationships. Thus, increasing the degree of oligomerization results in a pronounced decrease of the critical micellization concentration (CMC). Both reduced spacer length and increased spacer hydrophobicity lead to a decrease of the CMC, but to a lesser extent. For these particular compounds, the formed micelles are relatively small and their aggregation number decreases with increasing the degree of oligomerization, increasing spacer length and sterical hindrance. In addition, pseudo-phase diagrams were established for the dimeric surfactants in more complex systems, namely inverse microemulsions, demonstrating again the important influence of the spacer group on the surfactant behaviour. Furthermore, the influence of additives on the property profile of the dimeric compounds was examined, in order to see if the solution properties can be improved while using less material. Strong synergistic effects were observed by adding special organic salts (e.g. sodium salicylate, sodium vinyl benzoate, etc.) to the surfactant dimers in stoichiometric amounts. For such mixtures, the critical aggregation concentration is strongly shifted to lower concentration, the effect being more pronounced for dimers than for analogous monomers. A sharp decrease of the surface tension can also be attained. Many of the organic anions produce viscoelastic solutions when added to the relatively short-chain dimers in aqueous solution, as evidenced by rheological measurements. This behaviour reflects the formation of entangled wormlike micelles due to strong interactions of the anions with the cationic surfactants, decreasing the curvature of the micellar aggregates. It is found that the associative behaviour is enhanced by dimerization. For a given counterion, the spacer group may also induce a stronger viscosifying effect depending on its length and hydrophobicity. Oppositely charged surfactants were combined with the cationic dimers, too. First, some mixtures with the conventional anionic surfactant SDS revealed vesicular aggregates in solution. Also, in view of these catanionic mixtures, a novel anionic dimeric surfactant based on EDTA was synthesized and studied. The synthesis route is relatively simple and the compound exhibits particularly appealing properties such as low CMC and σCMC values, good solubilization capacity of hydrophobic probes and high tolerance to hard water. Noteworthy, mixtures with particular cationic dimers gave rise to viscous solutions, reflecting the micelle growth.},
  language  = {en}
}
@phdthesis{Hildebrandt2006,
  author    = {Hildebrandt, Niko},
  title     = {Lanthanides and quantum dots : time-resolved laser spectroscopy of biochemical F{\"o}rster Resonance Energy Transfer (FRET) systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12686},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {F{\"o}rster Resonance Energy Transfer (FRET) plays an important role for biochemical applications such as DNA sequencing, intracellular protein-protein interactions, molecular binding studies, in vitro diagnostics and many others. For qualitative and quantitative analysis, FRET systems are usually assembled through molecular recognition of biomolecules conjugated with donor and acceptor luminophores. Lanthanide (Ln) complexes, as well as semiconductor quantum dot nanocrystals (QD), possess unique photophysical properties that make them especially suitable for applied FRET. In this work the possibility of using QD as very efficient FRET acceptors in combination with Ln complexes as donors in biochemical systems is demonstrated. The necessary theoretical and practical background of FRET, Ln complexes, QD and the applied biochemical models is outlined. In addition, scientific as well as commercial applications are presented. FRET can be used to measure structural changes or dynamics at distances ranging from approximately 1 to 10 nm. The very strong and well characterized binding process between streptavidin (Strep) and biotin (Biot) is used as a biomolecular model system. A FRET system is established by Strep conjugation with the Ln complexes and QD biotinylation. Three Ln complexes (one with Tb3+ and two with Eu3+ as central ion) are used as FRET donors. Besides the QD two further acceptors, the luminescent crosslinked protein allophycocyanin (APC) and a commercial fluorescence dye (DY633), are investigated for direct comparison. FRET is demonstrated for all donor-acceptor pairs by acceptor emission sensitization and a more than 1000-fold increase of the luminescence decay time in the case of QD reaching the hundred microsecond regime. Detailed photophysical characterization of donors and acceptors permits analysis of the bioconjugates and calculation of the FRET parameters. Extremely large F{\"o}rster radii of more than 100 {\AA} are achieved for QD as acceptors, considerably larger than for APC and DY633 (ca. 80 and 60 {\AA}). Special attention is paid to interactions with different additives in aqueous solutions, namely borate buffer, bovine serum albumin (BSA), sodium azide and potassium fluoride (KF). A more than 10-fold limit of detection (LOD) decrease compared to the extensively characterized and frequently used donor-acceptor pair of Europium tris(bipyridine) (Eu-TBP) and APC is demonstrated for the FRET system, consisting of the Tb complex and QD. A sub-picomolar LOD for QD is achieved with this system in azide free borate buffer (pH 8.3) containing 2 \% BSA and 0.5 M KF. In order to transfer the Strep-Biot model system to a real-life in vitro diagnostic application, two kinds of imunnoassays are investigated using human chorionic gonadotropin (HCG) as analyte. HCG itself, as well as two monoclonal anti-HCG mouse-IgG (immunoglobulin G) antibodies are labeled with the Tb complex and QD, respectively. Although no sufficient evidence for FRET can be found for a sandwich assay, FRET becomes obvious in a direct HCG-IgG assay showing the feasibility of using the Ln-QD donor-acceptor pair as highly sensitive analytical tool for in vitro diagnostics.},
  language  = {en}
}
@phdthesis{Mauser2006,
  author    = {Mauser, Tatjana},
  title     = {Multilayer capsules with stimuli-sensitive properties : pH-response and carbohydrate-sensing},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12529},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Polyelectrolyte microcapsules containing stimuli-responsive polymers have potential applications in the fields of sensors or actuators, stimulable microcontainers and controlled drug delivery. Such capsules were prepared, with the focus on pH-sensitivity and carbohydrate-sensing. First, pH-responsive polyelectrolyte capsules were produced by means of electrostatic layer-by-layer assembly of oppositely charged weak polyelectrolytes onto colloidal templates that were subsequently removed. The capsules were composed of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) or poly(4-vinylpyridine) (P4VP) and PMA and varied considerably in their hydrophobicity and the influence of secondary interactions. These polymers were assembled onto CaCO3 and SiO2 particles with diameters of ~ 5 µm, and a new method for the removal of the silica template under mild conditions was proposed. The pH-dependent stability of PAH/PMA and P4VP/PMA capsules was studied by confocal laser scanning microscopy (CLSM). They were stable over a wide pH-range and exhibited a pronounced swelling at the edges of stability, which was attributed to uncompensated positive or negative charges within the multilayers. The swollen state could be stabilized when the electrostatic repulsion was counteracted by hydrogen-bonding, hydrophobic interactions or polymeric entanglement. This stabilization made it possible to reversibly swell and shrink the capsules by tuning the pH of the solution. The pH-dependent ionization degree of PMA was used to modulate the binding of calcium ions. In addition to the pH-sensitivity, the stability and the swelling degree of these capsules at a given pH could be modified, when the ionic strength of the medium was altered. The reversible swelling was accompanied by reversible permeability changes for low and high molecular weight substances. The permeability for glucose was evaluated by studying the time-dependence of the buckling of the capsule walls in glucose solutions and the reversible permeability modulation was used for the encapsulation of polymeric material. A theoretical model was proposed to explain the pH-dependent size variations that took into account an osmotic expanding force and an elastic restoring force to evaluate the pH-dependent size changes of weak polyelectrolyte capsules. Second, sugar-sensitive multilayers were assembled using the reversible covalent ester formation between the polysaccharide mannan and phenylboronic acid moieties that were grafted onto poly(acrylic acid) (PAA). The resulting multilayer films were sensitive to several carbohydrates, showing the highest sensitivity to fructose. The response to carbohydrates resulted from the competitive binding of small molecular weight sugars and mannan to the boronic acid groups within the film, and was observed as a fast dissolution of the multilayers, when they were brought into contact with the sugar-containing solution above a critical concentration. It was also possible to prepare carbohydrate-sensitive multilayer capsules, and their sugar-dependent stability was investigated by following the release of encapsulated rhodamine-labeled bovine serum albumin (TRITC-BSA).},
  language  = {en}
}
@phdthesis{Note2006,
  author    = {Note, Carine},
  title     = {Influence of hydrophobically modified polyelectrolytes on nanoparticle synthesis in self-organized systems and in water},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-11670},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {The formation of colloids by the controlled reduction, nucleation, and growth of inorganic precursor salts in different media has been investigated for more than a century. Recently, the preparation of ultrafine particles has received much attention since they can offer highly promising and novel options for a wide range of technical applications (nanotechnology, electrooptical devices, pharmaceutics, etc). The interest derives from the well-known fact that properties of advanced materials are critically dependent on the microstructure of the sample. Control of size, size distribution and morphology of the individual grains or crystallites is of the utmost importance in order to obtain the material characteristics desired. Several methods can be employed for the synthesis of nanoparticles. On the one hand, the reduction can occur in diluted aqueous or alcoholic solutions. On the other hand, the reduction process can be realized in a template phase, e.g. in well-defined microemulsion droplets. However, the stability of the nanoparticles formed mainly depends on their surface charge and it can be influenced with some added protective components. Quite different types of polymers, including polyelectrolytes and amphiphilic block copolymers, can for instance be used as protecting agents. The reduction and stabilization of metal colloids in aqueous solution by adding self-synthesized hydrophobically modified polyelectrolytes were studied in much more details. The polymers used are hydrophobically modified derivatives of poly(sodium acrylate) and of maleamic acid copolymers as well as the commercially available branched poly(ethyleneimine). The first notable result is that the polyelectrolytes used can act alone as both reducing and stabilizing agent for the preparation of gold nanoparticles. The investigation was then focused on the influence of the hydrophobic substitution of the polymer backbone on the reduction and stabilization processes. First of all, the polymers were added at room temperature and the reduction process was investigated over a longer time period (up to 8 days). In comparison, the reduction process was realized faster at higher temperature, i.e. 100°C. In both cases metal nanoparticles of colloidal dimensions can be produced. However, the size and shape of the individual nanoparticles mainly depends on the polymer added and the temperature procedure used. In a second part, the influence of the prior mentioned polyelectrolytes was investigated on the phase behaviour as well as on the properties of the inverse micellar region (L2 phase) of quaternary systems consisting of a surfactant, toluene-pentanol (1:1) and water. The majority of the present work has been made with the anionic surfactant sodium dodecylsulfate (SDS) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) since they can interact with the oppositely charged polyelectrolytes and the microemulsions formed using these surfactants present a large water-in-oil region. Subsequently, the polymer-modified microemulsions were used as new templates for the synthesis of inorganic particles, ranging from metals to complex crystallites, of very small size. The water droplets can indeed act as nanoreactors for the nucleation and growth of the particles, and the added polymer can influence the droplet size, the droplet-droplet interactions, as well as the stability of the surfactant film by the formation of polymer-surfactant complexes. One further advantage of the polymer-modified microemulsions is the possibility to stabilize the primary formed nanoparticles via a polymer adsorption (steric and/or electrostatic stabilization). Thus, the polyelectrolyte-modified nanoparticles formed can be redispersed without flocculation after solvent evaporation.},
  subject      = {Mikroemulsion},
  language  = {en}
}
@phdthesis{Peikow2006,
  author    = {Peikow, Dirk},
  title     = {Synthese und Glycosidasehemmung von Thio-analogen Kohlenhydraten},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-11192},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Chitin ist ein Polysaccharid, welches aus N-Acetylglucosamin (GlcNAc) aufgebaut ist. Das Biopolymer kommt in der Natur in Invertebraten, Algen, Pilzen und Einzellern vor. Chitinasen hydrolysieren Chitin. Diese Enzyme sind essentiell f{\"u}r die Regulierung und Entwicklung von Arthropoden und Mikroorganismen. Sie fungieren in Pflanzen als Phytoalexine. Das verst{\"a}rkt das Interesse am Design neuer nat{\"u}rlicher und synthetischer Chitinase-inhibitoren, die als potentielle Insektizide, Fungizide, Antimalaria bzw. Antiasthmatika eingesetzt werden k{\"o}nnen. Ziel dieser Arbeit war die Synthese von neuen Thioglycosidanaloga von N-Acetyl-chitooligosacchariden und deren Untersuchung als Enzyminhibitoren. Die gesch{\"u}tzten 4-O-Tf-galactopyranosylthioglycoside wurden aus den korrespondierenden p-Methoxyphenylglycosiden von GlcNAc nach einer neuen Methode in einer Stufe hergestellt. Die Reaktion der galacto-Triflate mit 2-Acetamido-3,4,6-tri-O-acetyl-2-desoxy-1-thio-ß-D-glucopyranose in Gegenwart von Natriumhydrid und 15-Krone-5 in THF lieferte die Pseudo-Trisaccharide. Die Herstellung der Glycosyl-Thiazoline aus den entsprechenden p-Methoxyphenyl-glycosiden mit Lawesson's Reagenz ist nach einem neuen Reaktionsweg beschrieben wie auch die Synthese der Thioacetamide von GlcNAc-Oligomeren. Die Pseudo-Oligosaccharide wurden als Inhibitoren der Chitinasen von Serratia marcescens, Chironomus tentans, Acanthocheilonema viteae und Hevaea brasiliensis sowie der N-Acetyl-glucosaminidase von Chironomus tentans getestet. In einigen F{\"a}llen ergab sich eine Hemmung (IC50) im µM-Bereich.},
  language  = {de}
}
@phdthesis{Meyer2006,
  author    = {Meyer, Matthias},
  title     = {PIPOX-PEP : kontrollierte Synthese und Aggregationsverhalten von Blockcopolymeren mit schaltbarer Hydrophilie},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10832},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Es wurden Poly(2-isopropyl-2-oxazolin)-Makroinitiatoren mit terminaler Ammoniumtrifluoracetat-Endgruppe synthetisiert, die anschließend f{\"u}r die Ammonium vermittelte NCA Polymerisation in NMP eingesetzt wurden. Die hierbei synthetisierten Poly(2-isopropyl-2-oxazolin)-block-poly(L-glutamat) (PIPOX-PEP) Blockcopolymere hatten eine Molekulargewichtsverteilung von 1,2 (UZ). Es wurde beobachtet, dass Poly(2-isopropyl-2-oxazolin) bei langen Zeiten oberhalb der LCST irreversibel sph{\"a}rische Strukturen bildet, die eine hierarchische Struktur besitzen und bei denen es sich m{\"o}glicherweise um "large compound micelles" handelt. PIPOX-PEP kann in w{\"a}sseriger L{\"o}sung bei langen Zeiten oberhalb der LCST "cottonball" Strukturen bilden. Die Aggregate wurden mittels Lichtstreuung, NMR und TEM charakterisiert. Im Rahmen der Arbeit wurden Strukturbildungsmodelle entwickelt.},
  subject      = {Polymer},
  language  = {de}
}
@phdthesis{Rettig2006,
  author    = {Rettig, Hartmut Arnim},
  title     = {Methoden zur Synthese von definierten bioorganisch-synthetischen Blockcopolymeren},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10293},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Bioorganisch-synthetische Blockcopolymere sind sowohl f{\"u}r die Materialwissenschaft als auch f{\"u}r die Medizin hochinteressant. Diese Arbeit besch{\"a}ftigte sich mit neuen Synthesewegen f{\"u}r die Herstellung dieser Blockcopolymere. Zun{\"a}chst wurde der klassische Ansatz zur Herstellung eines Blockcopolymers {\"u}ber die Kupplung der beiden Segmente aufgegriffen. Hierzu wurde eine Methode zur Synthese von selektiv s{\"a}ureendfunktionalisierten Polyacrylaten mittels einer terminalen Benzylesterschutzgruppe vorgestellt. F{\"u}r die Herstellung von bioorganisch-synthetischen Blockcopolymeren mit einem gr{\"o}ßeren Polymersegment wurde daher ein anderer Syntheseansatz entwickelt. Dieser geht von einem funktionalisierten Oligopeptid aus, an dem durch Polymerisation das synthetische Segment aufgebaut wird. Der Aufbau erfolgte durch kontrolliert radikalische Polymerisation, um ein m{\"o}glichst definiertes Segment zu erhalten. Zun{\"a}chst wurde eine Synthese von Oligopeptid-Makroinitiatoren f{\"u}r die ATRP-Polymerisation durchgef{\"u}hrt. Es konnte gezeigt werden, dass in geeigneten polaren L{\"o}sungsmitteln (DMSO, DMF) eine Polymerisation mit dem ATRP-Oligopeptid-Makroinitiator erfolgreich ist. Allerdings treten w{\"a}hrend der Polymerisation Wechselwirkungen zwischen dem Katalysator und dem Oligopeptid auf. Eine Alternative bietet die RAFT-Polymerisation, da sie ohne einen Katalysator durchgef{\"u}hrt wird. Es gelang ausgehend von dem Oligopeptid-ATRP-Makroinitiator den {\"U}bertr{\"a}ger herzustellen. Die RAFT-Polymerisation mit einem Oligopeptid{\"u}bertr{\"a}ger stellt eine wichtige Methode f{\"u}r die Herstellung von bioorganisch-synthetischen Blockcopolymeren dar. Sie besitzt eine hohe Toleranz gegen{\"u}ber funktionellen Gruppen. Die so hergestellten Blockcopolymere sind frei von Verunreinigungen, wie z.B. {\"U}bergangsmetallen. Dabei l{\"a}ßt sich das Molekulargewicht des synthetischen Blocks bei einer Polydispersit{\"a}t um 1,2 gut kontrollieren.},
  subject      = {ATRP},
  language  = {de}
}
@phdthesis{Ba2006,
  author    = {Ba, Jianhua},
  title     = {Nonaqueous synthesis of metal oxide nanoparticles and their assembly into mesoporous materials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10173},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {This thesis mainly consist of two parts, the synthesis of several kinds of technologically interesting crystalline metal oxide nanoparticles via nonaqueous sol-gel process and the formation of mesoporous metal oxides using some of these nanoparticles as building blocks via evaporation induced self-assembly (EISA) technique. In the first part, the experimental procedures and characterization results of successful syntheses of crystalline tin oxide and tin doped indium oxide (ITO) nanoparticles are reported. SnO2 nanoparticles exhibit monodisperse particle size (3.5 nm in average), high crystallinity and particularly high dispersibility in THF, which enable them to become the ideal particulate precursor for the formation of mesoporous SnO2. ITO nanoparticles possess uniform particle morphology, narrow particle size distribution (5-10 nm), high crystallinity as well as high electrical conductivity. The synthesis approaches and characterization of various mesoporous metal oxides, including TiO2, SnO2, mixture of CeO2 and TiO2, mixture of BaTiO3 and SnO2, are reported in the second part of this thesis. Mesoporous TiO2 and SnO2 are presented as highlights of this part. Mesoporous TiO2 was produced in the forms of both films and bulk material. In the case of mesoporous SnO2, the study was focused on the high order of the porous structure. All these mesoporous metal oxides show high crystallinity, high surface area and rather monodisperse pore sizes, which demonstrate the validity of EISA process and the usage of preformed crystalline nanoparticles as nanobuilding blocks (NBBs) to produce mesoporous metal oxides.},
  subject      = {Nanopartikel},
  language  = {en}
}
@phdthesis{Bhattacharryya2006,
  author    = {Bhattacharryya, Saroj Kumar},
  title     = {Development of detector for analytical ultracentrifuge. - [korr. Fassung]},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-8215},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {In this work approaches for new detection system development for an Analytical Ultracentrifuge (AUC) were explored. Unlike its counterpart in chromatography fractionation techniques, the use of a Multidetection system for AUC has not yet been implemented to full extent despite its potential benefit. In this study we tried to couple existing fundamental spectroscopic and scattering techniques that are used in day to day science as tool for extracting analyte information. Trials were performed for adapting Raman, Light scattering and UV/Vis (with possibility to work with the whole range of wavelengths) to AUC. Conclusions were drawn for Raman and Light scattering to be a possible detection system for AUC, while the development for a fast fiber optics based multiwavelength detector was completed. The multiwavelength detector demonstrated the capability of data generation matching the literature and reference measurement data and faster data collection than that of the commercial instrument. It became obvious that with the generation of data in 3-D space in the UV/Vis detection system, the user can select the wavelength for the evaluation of experimental results as the data set contains the whole range of information from UV/Vis wavelength. The detector showed the data generation with much faster speed unlike the commercial instruments. The advantage of fast data generation was exemplified with the evaluation of data for a mixture of three colloids. These data were in conformity with measurement results from normal radial experiments and without significant diffusion broadening. Thus conclusions were drawn that with our designed Multiwavelength detector, meaningful data in 3-D space can be collected with much faster speed of data generation.},
  subject      = {Ultrazentrifuge},
  language  = {en}
}
@phdthesis{Gehrke2006,
  author    = {Gehrke, Nicole},
  title     = {Retrosynthese von Perlmutt},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7971},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {In dieser Arbeit ist es gelungen, die Bedeutung physikalisch-chemischer Mechanismen in der Biomineralisation gegen{\"u}ber der bisher angenommenen Dominanz spezifischer biomolekularer Erkennungsmechanismen aufzuzeigen. Dazu wurden drei Ans{\"a}tze verfolgt: Zum einen wurden Studien zur Calciumcarbonatkristallisation durchgef{\"u}hrt. Zum anderen wurde das Biomineral Perlmutt intensiv untersucht. Als drittes wurde ein Modellsystem entwickelt, mit dem k{\"u}nstliches Perlmutt synthetisiert und ein Mechanismus f{\"u}r die Perlmuttmineralisation vorgeschlagen werden konnte. Im ersten Schritt wurden in einem simplen Kristallisationsansatz komplexe Calciumcarbonat{\"u}berstrukturen ohne die Verwendung von Additiven synthetisiert. Es wurde gezeigt, daß diese durch orientierte Anlagerung von Nanopartikeln gebildet werden, bei der dipolare Felder eine wichtige Rolle zu spielen scheinen. Dieser Mechansimus war bislang f{\"u}r Calciumcarbonat unbekannt und erm{\"o}glicht die Synthese komplexer Kristallmorphologien, wodurch die Frage aufgeworfen wird, ob er bei der Biomineralbildung von Bedeutung sein kann. Durch Einsatz minimaler Mengen eines einfachen, synthetischen Additivs bei der Kristallisation wurden zu {\"U}berstrukturen angeordnete Aragonitpl{\"a}ttchen synthetisiert, die von einer wenige nm dicken Schicht aus amorphen Calciumcarbonat umgeben sind. Eine solche Schicht wurde auch bei den Aragonitpl{\"a}ttchen Perlmutts entdeckt (s.u.) und bietet m{\"o}glicherweise in verschiedenen Systemen eine Erkl{\"a}rung f{\"u}r die Stabilisierung der sonst metastabilen Aragonitphase. Im zweiten Schritt wurden bei der Untersuchung von nat{\"u}rlichem Perlmutt zwei bislang unbekannte Strukturmerkmale entdeckt: Es gibt Bereiche, die nicht aus den charakteristischen Pl{\"a}ttchen bestehen, sondern wesentlich weniger stark mineralisert sind. Die Mineralphase besteht in diesen Bereichen aus Nanopartikeln. Es wurde weiterhin gezeigt, daß die Aragonitpl{\"a}ttchen von einer wenige nm dicken Schicht aus amorphem Calciumcarbonat umgeben ist. Die g{\"a}ngigen Modelle der Perlmuttbildung sind mit diesen Beobachtungen nicht zu vereinbaren und somit zu hinterfragen. Dagegen deuten diese Ergebnisse ein Wachstum von Perlmutt {\"u}ber ACC-Nanopartikel an. Unter der Annahme der Bedeutung physikalisch-chemischer Mechanismen in der Biomineralisation wurde schließlich als dritter Schritt ein Ansatz zur in vitro-Retrosynthese von Biomineralien ausgehend von ihrer unl{\"o}slichen Matrix entwickelt. Mit diesem Ansatz ist es erstmals gelungen, k{\"u}nstliches Perlmutt auf synthetischem Wege herzustellen, das morphologisch nicht vom Original zu unterscheiden ist. Die existierenden Unterschiede konnten zeigen, daß der Mineralisationsprozeß nicht auf ein spezifisches Mikroumgebungssystem beschr{\"a}nkt, sondern "allgemeiner g{\"u}ltig"' sein muß. Bei der Retrosynthese gibt es zwei Schl{\"u}sselfaktoren: Zum einen die demineralisierte unl{\"o}sliche Perlmuttmatrix als dreidimensionales Ger{\"u}st f{\"u}r das k{\"u}nstliche Perlmutt, zum anderen amorphe Precursorpartikel, die die Mineralphase bilden. Es werden keinerlei Proteine oder andere Biomolek{\"u}le verwendet. Dieser Ansatz bietet die M{\"o}glichkeit, den Mineralisationsprozeß an einem in vitro-Modellsystem zu verfolgen, was f{\"u}r das in vivo-System, wenn {\"u}berhaupt, nur unter starken Einschr{\"a}nkungen m{\"o}glich ist. Es wurde gezeigt, daß das k{\"u}nstliche Perlmutt {\"u}ber die Mesoskalentransformation von ACC-Precursorn innerhalb der Matrix gebildet wird und als m{\"o}glicher Mechanismus bei der Biomineralisation von nat{\"u}rlichem Perlmutt diskutiert. Es konnte in der vorliegenden Arbeit konsequent gezeigt werden, daß die Imitation von Biomineralisationsprozessen in in vitro-Ans{\"a}tzen m{\"o}glich ist, wobei chemisch-physikalische Parameter dominieren. In zuk{\"u}nftigen Studien sollten einerseits die mechanischen Eigenschaften des k{\"u}nstlichen Perlmutts untersucht werden, wof{\"u}r sich in Vorversuchen im Rahmen dieser Arbeit die Nanoindentierung als geeignet herausgestellt hat. Es sollte gepr{\"u}ft werden, ob das hier ermittelte Prinzip zur Mineralisierung in der Materialentwicklung angewendet werden kann. Andererseits sollte die Retrosynthese auf andere Systeme ausgeweitet und in vivo-Studien durchgef{\"u}hrt werden, um die G{\"u}ltigkeit der vorgeschlagenen Mechanismen zu {\"u}berpr{\"u}fen.},
  subject      = {Biomineralisation},
  language  = {de}
}