La maladie d’Alzheimer est actuellement la forme de démence la plus courante. Les causes, les facteurs de risques ainsi que le(s) mécanisme(s) conduisant à l’apparition des symptômes ne sont pas encore clairement connus. Néanmoins, le rôle central du peptide amyloïde (Aβ) dans le développement de la maladie a été démontré au travers de nombreuses recherches et fait actuellement l’unanimité. L’espèce oligomérique d’Aβ est plus précisément pointée doigt comme l’espèce la plus toxique. La formation des oligomers, au cours du processus d’agrégation, conduit à une population hétérogène en termes de taille et morphologies limitant la compréhension actuelle de leur implication dans le processus pathologique ainsi que dans l’initiation de la maladie. <p>Notre étude structurale minutieuse du processus d’agrégation du peptide Aβ démontre la formation d’agrégats dont le degré d’assemblage augmente au cours du temps. Nous avons montré que les agrégats identifiés comme étant des oligomères adoptent une structure en feuillets β antiparallèles. Tandis que l’interconversion de la structure β d’antiparallèle à parallèle conduit à la formation de fibrilles. Sur base de l’interprétation des spectres infrarouges analysés par corrélation à 2 dimensions, nous suggérons que ce changement de conformation est rendu possible grâce aux modifications des liens hydrogènes. En effet, les liens hydrogènes intramoléculaires qui stabilisent la structure antiparallèle des brins β disparaissent en faveur de liens intermoléculaires conduisant à la formation de feuillets β parallèles. De plus, ce changement de conformation requière la rotation des brins β le long de leur axe respectif. <p>Notre travail a pu mettre en avant le rôle central des oligomères dans la pathologie d’une part par leur rôle d’intermédiaires transitoires nécessaires et obligatoires à la formation des fibrilles mais également par la relation étroite qui existe entre leur structure en feuillets β antiparallèles et leur toxicité cellulaire. La modulation et/ou suppression de cette conformation est requise spécifiquement pour réguler leur toxicité et empêcher le processus de mauvais reploiement du peptide conduisant au développement de la maladie. <p>Enfin, nous avons également apporté de nouvelles informations concernant l’implication des membranes biologiques dans le mécanisme de toxicité des oligomères. Nos résultats démontrent que l’interaction du peptide avec un modèle de la membrane biologique ne conduit pas à la déstabilisation de cette dernière. L’hypothèse suggérant la formation de pores et/ou de canaux ioniques comme mécanisme de cytotoxicité est de facto réfutée par notre travail. Néanmoins, nous suggérons que l’interaction du peptide avec les lipides modifie le processus d’agrégation décrit dans la première partie de notre travail. Elle accélère l’étape de nucléation permettant la formation rapide d’oligomères à la surface de la membrane et accentuant ainsi leur probabilité d’interaction avec les protéines membranaires neuronales telles que les récepteurs de neurotransmetteurs./<p>Aggregation of amyloid-β peptides (Aβ1-40 and Aβ1-42) leads to formation of heterogeneous<p>toxic species, oligomers and fibrils, implicated in Alzheimer’s disease. As oligomers were<p>identified as the most cytotoxic entities, our research did focus on their implications in<p>pathology and the Aβ aggregation process which are currently not fully understood.<p>Using ATR-FTIR spectroscopy, we demonstrated that Aβ oligomers adopt an antiparallel β-<p>sheet structure. β-sheet interconversion from antiparallel to parallel seems to be an important<p>step in the Aβ oligomers-to-fibrils transformation. Furthermore, 2-D correlation analysis of<p>infrared spectra recorded during aggregation showed that Aβ isoforms undergo different β-<p>sheet reorganizations explaining their distinct aggregation kinetics. Aβ1-40 misfolding seems<p>to be related to a greater extent of secondary structure changes (increase of β-sheet structure<p>while α-helices and random coil structures content decrease). On the contrary, the same<p>analysis for Aβ1-42 suggests that a possible β-strand ‘rotation’ triggering inter-H bonding<p>formation and stabilizing fibrils may probably explain the antiparallel to parallel β-sheet<p>conversion.<p>We also provided evidence that cytotoxicity is strongly related to the oligomeric antiparallel<p>β-sheet structure of Aβ. The concomitant absence of antiparallel β-sheet structure due to<p>incubation with whey protein-derived peptide hydrolysate strongly suggests that cytotoxicity<p>and β-sheets organization are related.<p>Formation of β-barrel spanning the lipid membrane has been proposed to explain this Aβ<p>structure-toxicity relationship. In the last part of our work, we demonstrated that the<p>interaction of Aβ1-42 with anionic lipid membranes creates and/or stabilizes specific-size<p>oligomers. These oligomers, especially the dodecamer, are known to be the most toxic.<p>Nevertheless, we could not show that these specific oligomers are implicated in membrane<p>destabilization. Further works are needed to separate and study the individual properties of<p>each oligomer. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Des oligonylons et des oligo(triazole-amide)s possédant des séquences contrôlées de comonomères ont été étudiés dans cette thèse. Ces polymères ont été synthétisés par des approches itératives ne nécessitant pas l’emploi de groupes protecteurs. Les oligonylons ont été préparés par une approche de type «AA+BB», c.à.d. par couplage alterné de monomères diacides (AA) et diamines (BB) utilisés en excès. Cette approche s’est avérée possible mais a conduit à des réactions non-souhaitées de pontage intermoléculaire. Une approche plus robuste de type «AB+CD» a été utilisée pour la synthèse des oligo(triazole-amide)s. Dans ce cas, les polymères ont été obtenus par couplage chimioséléctif de monomères bi-fonctionnels de type AB (A = acide carboxylique, B = alcyne) et CD (C = amine, D = azoture). Cette méthode a permis la synthèse d’oligomères monomoléculaires. De plus, un codage moléculaire de type binaire (0, 1) a pu être créé sur ces oligomères. Cependant, cette approche itérative reste lente et limitée à de courtes séquences. Afin de simplifier le processus, une stratégie basée sur des couplages de trimères a été étudiée. Cette nouvelle approche a permis la synthèse de longues séquences codées contenant un octet moléculaire. / In this thesis, iterative syntheses of sequence-controlled oligonylons and oligo(triazole-amide)s by protecting group-free approaches have been described. Oligonylons have been prepared by an «AA+BB» approach i.e. by stepwise couplings of a large excess of diacids (AA) and diamines (BB) monomers. This strategy was interesting but could not prevent the formation of bridged molecules. Therefore, an «AB+CD» strategy has been adopted for the synthesis of oligo(triazole-amide)s. In this case, the growth of oligomers was controlled by consecutive chemoselective couplings of AB (A = acid, B = alkyne) and CD (C = amine, D = azide) monomers. This approach was found to be efficient for the preparation of encoded monodisperse oligo(triazole-amide)s whose sequence is based on a binary code (0, 1). However, this iterative approach is slow and is not adapted to longer sequences. Consequently, a strategy based on trimers couplings has been developed in order to simplify the process. This new approach has enabled the synthesis of long code sequences containing a molecular byte.

No description available.

Les polyélectrolytes sont des polymères chargés, solubles dans l'eau, omniprésents dans les nature et capables d’interagir avec de nombreux composants cellulaires. Leur utilisation dans des essais cliniques est actuellement limitée par le manque de données fiables sur les relations entre leurs structures et leurs biopropriétés. Ce projet s'inscrit dans un programme plus vaste visant à obtenir une bibliothèque de polyélectrolytes multifonctionnalisés bien caractérisés pour le criblage de biopropriétés. Dans ce cadre, nous avons cherché à synthétiser des chaînes macromoléculaires contenant des unités maloniques C(COOH)2 situées à différentes positions le long du squelette du polymère. Ces unités peuvent être utilisées comme points de départ pour introduire plusieurs autres groupes fonctionnels en utilisant de nombreuses réactions de la chimie organique, conduisant à un grand nombre de structures à partir d'un squelette commun, y compris des copolymères. Cette thèse est schématiquement divisée en quatre parties : (a) une présentation bibliographique des relations existant entre structures et propriétés pour des polymères multifonctionnalisés, suivie d'une analyse plus spécifique de l'importance du positionnement d’esters carboxyliques le long d’une chaîne carbonée, (b) une description des efforts expérimentaux menés pour obtenir les poly(triméthylène-1,1-dicarboxylate)s, des intermédiaires clés dans la synthèse des polymères décrits dans les chapitres suivants, (c) une description de l'hydrolyse du précurseur ci-dessus, donnant l'acide poly(triméthylène-1,1-dicarboxylique), ainsi que des propriétés et de la réactivité de ce polyacide, (d) un rapport détaillé sur la synthèse de l’acide poly(triméthylène carboxylique) par décarboxylation quantitative du polyacide ci-dessus, ainsi que sur les propriétés et réactivité de ce polyacide. Dans les deux dernières sections, un accent particulier est mis sur la portée et les limites de diverses procédures de post-fonctionnalisation lorsque l'on tente d'obtenir une bibliothèque de polymères fonctionnels à partir de précurseurs polycarboxyliques / Polyelectrolytes are water-soluble charged polymers that are ubiquitous in life science and capable of interacting with many cellular constituents. Their use in clinical trials is currently limited by a lack of reliable data on the relationships linking their structures to bioproperties. This project is part of a larger program aimed at obtaining a library of well-characterized multifunctionalized polyelectrolytes for the screening of bioproperties. In this framework, we aimed at synthesizing macromolecular chains containing malonic units C(COOH)2 located at various positions alongside the polymer backbone. These units can be used as starting points to introduce several other functional groups using many reactions from organic chemistry, leading to a great number of structures from a common skeleton, including copolymers. This thesis is schematically divided into four parts: (a) a bibliographical presentation of the relationships existing between structures and properties for multifunctional polymers, followed by a more specific analysis on the importance of carboxylic esters positioning alongside a carbon chain backbone, (b) a description of experimental efforts aimed at obtaining poly(trimethylene-1,1-dicarboxylate)s, key intermediates in the synthesis of a large family of polymers described in the next chapters, (c) a depiction of the hydrolysis of the above precursor, yielding poly(trimethylene-1,1-dicarboxylic acid), as well as of the properties and reactivity of this polyacid, (d) a detailed report on the synthesis of poly(trimethylenecarboxylic acid) via the quantitative decarboxylation of the above polyacid, as well as of the properties and reactivity of this polyacid. A special focus is made in the last two sections on the scope and limitations of various post-functionalizing procedures when attempting to obtain a large library of functional polymers from polycarboxylic precursors

Des oligomères de taille définie de chitosane ont été préparés et testés en tant qu'organocatalyseurs dans des réactions d'aldolisation énantiosélectives. Les précurseurs de ces catalyseurs sont obtenus en une seule étape par une réaction d'acétolyse contrôlée de la chitine, second polysaccharide le plus abondant. Une méthodologie reposant sur des réactions de glycosylation sous activation micro-ondes a été développée afin de fonctionnaliser la position anomérique de ces oligomères. Ainsi, le triflate de cuivre(II), utilisé en quantité catalytique, s’est révélé être le promoteur le plus efficace pour l’activation de la glucosamine ou du chitobiose peracétylés de configuration α. La sélectivité α des produits glycosylés résultent d’une isomérisation in situ des produits cinétiques β. Des organocatalyseurs se différenciant par leur partie aglycone et par leur degré de substitution ont été synthétisés en peu d’étapes. Les résultats les plus intéressants ont été obtenus avec un dérivé du chitobiose soluble en milieu aqueux. Nous avons montré, qu’en présence d’un co-catalyseur acide, l’acide 4-nitrobenzoïque, la réaction entre la cyclohexanone et le 4-nitrobenzaldéhyde, conduit à l’adduit anti avec un bon excès énantiomérique (89% ee). De plus, nous avons également montré que ce catalyseur pouvait être réutilisé dans plusieurs cycles catalytiques sans perte de sélectivité. / The catalytic behaviour of size-defined chitosan oligomers has been evaluated for asymmetric aldol reactions. These oligomers were obtained from chitin, which is one of the most abundant naturally occurring polymers, as a renewable starting biomolecule. Thus, controlled depolymerization of chitin was carried out by acetolysis providing per-O-acetylated N-acetyl-α-D-glucosamine oligomers with a polymerization degree from 2 to 4. To investigate the influence of the aglycon moiety, we developed a Lewis acid-promoted glycosylation reactions under microwave irradiation. Thus, a catalytic amount of copper(II) triflate proved to be the most effective promoter for the activation of α-per-O-acetylated glucosamine oligomers, which are considered as poorly reactive substrates, to selectively obtain α-glycosylated compounds. This selectivity results from in situ isomerization of kinetic β products. Chitosan-based catalysts, which differ in the distribution pattern, were synthesized in a few steps. The most promising results were obtained with a chitobiose derivative, which efficiently catalyzed the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde, in the presence of 4-nitrobenzoic acid as a co-catalyst, in water, providing the anti-adduct in high yield with good enantioselectivity (89% ee). In addition, this homogeneous organocatalyst can be reused in several cycles without loss of catalytic activity.

Chan, Wai Hon. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 134-141). / Abstracts in English and Chinese. / Acknowledgements --- p.2 / Abstract --- p.3 / 摘要 --- p.5 / Content --- p.6 / List of Abbreviations and symbols --- p.10 / Chapter Chapter 1 --- Introduction --- p.13 / Chapter 1.1 --- The Severity of Influenza A Virus --- p.14 / Chapter 1.2 --- Introduction to Influenza A Virus --- p.15 / Chapter 1.3 --- What is Nucleoprotein? --- p.17 / Chapter 1.4 --- Multifunctional role of Nucleoprotein --- p.19 / Chapter 1.4.1 --- Interaction of Nucleoprotein with Other Viral Components --- p.19 / Chapter 1.4.1 --- Interaction of Nucleoprotein with Cellular Components --- p.22 / Chapter 1.5 --- Aims of study --- p.23 / Chapter Chapter 2 --- Materials and Methods / Chapter 2.1 --- Materials --- p.25 / Chapter 2.1.1 --- Chemical reagents --- p.25 / Chapter 2.1.2 --- Buffers --- p.28 / Chapter 2.1.2.1 --- Preparation of Buffers --- p.28 / Chapter 2.1.2.2 --- Buffer for Common Use --- p.28 / Chapter 2.1.3 --- Plasmids and Strains --- p.31 / Chapter 2.2 --- Methods --- p.32 / Chapter 2.2.1 --- Molecular Cloning --- p.32 / Chapter 2.2.2 --- "Expression of the Recombinant NP-WT/ mutants and importin α1, 3and 5 in E.coli" --- p.46 / Chapter 2.2.3 --- Purification of the NP WT/ variants --- p.50 / Chapter 2.2.4 --- "Purification of importin αl, 3 and 5" --- p.53 / Chapter 2.2.5 --- In vitro interaction study between NP and importin α --- p.56 / Chapter 2.2.6 --- In vivo interaction study between NP and importin α --- p.59 / Chapter 2.2.7 --- In vivo analysis to study NP-NP homo-oligomerization --- p.64 / Chapter 2.2.8 --- In vitro static light scattering analysis to determine NP oligomeric state --- p.68 / Chapter 2.2.9 --- Control experiments to verify NP-polymerases and NP-RNA interaction --- p.69 / Chapter Chapter 3 --- Functional analysis of influenza H5N1 nucleoprotein tail loop for oligomerization and ribonucleoprotein activities / Chapter 3.1 --- Introduction --- p.72 / Chapter 3.2 --- Results --- p.75 / Chapter 3.2.1 --- Tail loop insertion is maintained by intra- and inter-molecular interactions --- p.75 / Chapter 3.2.2 --- NP mutants display defective transcription-replication activity --- p.77 / Chapter 3.2.3 --- Expression and purification of defective NP variants --- p.80 / Chapter 3.2.4 --- Defective NP variants interact with RNA and the polymerase complex --- p.85 / Chapter 3.2.5 --- Defective NP variants possess abnormal oligomeric states in vitro --- p.91 / Chapter 3.2.6 --- NP variants with impaired RNP activity cannot form homo-oligomers in vivo --- p.95 / Chapter 3.3 --- Discussion --- p.98 / Chapter Chapter 4 --- Biophysical characterization of the interaction between influenza nucleoprotein and importin α / Chapter 4.1 --- Introduction --- p.105 / Chapter 4.2 --- Results --- p.108 / Chapter 4.2.1 --- Expression and Purification of NP-WT/ NLS variants and Importin a --- p.108 / Chapter 4.2.2 --- Pull down Assay --- p.113 / Chapter 4.2.3 --- Light scattering analysis (NP-lmportin α5) --- p.114 / Chapter 4.2.4 --- Binding assay of NP NLS variants with importin α5 --- p.115 / Chapter 4.2.5 --- BIAcore 3000 Surface Plasmon Resonance (NP-lmportin α5) --- p.118 / Chapter 4.2.6 --- QRT-PCR (NP-lmportin a5) --- p.123 / Chapter 4.3 --- Discussion --- p.125 / References --- p.134

<p>The subject of this thesis was to develop and optimize delivery systems for plasmid DNA (pDNA) based on biocompatible polymers, in particular chitosan, suitable for non-viral gene therapy. At the onset of this thesis, studies had reported conflicting results on the efficiency of chitosan-based gene delivery systems. Therefore, structure-property relationships of chitosans as non-viral gene delivery systems <i>in vitro</i> and after lung administration <i>in vivo</i> were established for the first time.</p><p>Polymer-pDNA complexes (polyplexes) based on conventional high molecular weight chitosans transfected cells <i>in vitro</i> and after lung administration <i>in vivo</i>. The chitosan polyplexes were, in contrast to polyplexes formed with the "golden standard" polymer polyethylenimine (PEI), essentially non-toxic at escalating doses. However, a very high physical stability of the chitosan-pDNA complexes together with a low buffering capacity of chitosan at the slightly acidic endo/lysosomal pH resulted in a slow onset of the gene expression and also in a lower efficiency of gene expression compared to PEI polyplexes. A slow and biodegradation-dependent release of pDNA from the chitosan polyplexes was concluded to be a rate limiting step for the efficiency of high molecular weight chitosan. The optimized polyplexes of high molecular weight chitosan (around 1,000 monomer units) showed aggregated shapes and gave increased viscosity at concentrations used for <i>in vivo</i> gene delivery. To improve the pharmaceutical properties and the delivery properties of chitosan polyplexes, low molecular weight chitosans were studied. Chitosans of around 18 monomer units retained the ability to protect pDNA against DNase degradation, but were more easily dissociated than those of higher molecular weight and had an efficiency comparable to that of PEI <i>in vitro</i> and <i>in vivo</i>. The pharmaceutical advantages of low molecular weight chitosan polyplexes compared to higher molecular weights are that there is less aggregation and no increased viscosity at the concentrations used for <i>in vivo</i> gene delivery. Coupling of an oligosaccharide targeting ligand to chitosan further increased the efficiency of some oligomer polyplexes. In conclusion, biocompatible chitosan is an interesting alternative to other non-viral gene delivery systems such as PEI.</p>

<p>Alzheimer’s disease (AD) is a progressive neurodegenerative disorder, neuropathologically characterized by neurofibrillay tangles and deposition of amyloid-β (Aβ) peptides. Several mutations in the gene for amyloid precursor protein (APP) cause familial AD and affect APP processing leading to increased levels of Aβ42. However, the Arctic Alzheimer mutation (APP E693G) reduces Aβ levels. Instead, the increased tendency of Arctic Aβ peptides to form Aβ protofibrils is thought to contribute to the pathogenesis. </p><p>In this thesis, the pathogenic mechanisms of the Arctic mutation were further investigated, specifically addressing if and how the mutation affects APP processing. Evidence of a shift towards β-secretase cleavage of Arctic APP was demonstrated. Arctic APP did not appear to be an inferior substrate for α-secretase, but the availability of Arctic APP for α-secretase cleavage was reduced, with diminished levels of cell surface APP in Arctic cells. Interestingly, administration of the fatty acid docosahexaenoic acid (DHA) stimulated α-secretase cleavage and partly reversed the effects of the Arctic mutation on APP processing.</p><p>In contrast to previous findings, the Arctic mutation generated enhanced total Aβ levels suggesting increased Aβ production. Importantly, this thesis illustrates and explains why measures of both Arctic and wild type Aβ levels are highly dependent upon the Aβ assay used, with enzyme-linked immunosorbent assay (ELISA) and Western blot generating different results. It was shown that these differences were due to inefficient detection of Aβ oligomers by ELISA leading to an underestimation of total Aβ levels. </p><p>In conclusion, the Arctic APP mutation leads to AD by multiple mechanisms. It facilitates protofibril formation, but it also alters trafficking and processing of APP which leads to increased steady state levels of total Aβ, in particular at intracellular locations. Importantly, these studies highlight mechanisms, other than enhanced production of Aβ peptide monomers, which could be implicated in sporadic AD.</p>

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. / Die Eigenschaften einer Reihe gut definierter neuer oligomerer Tenside (von Dimeren bis zu Tetrameren) wurden untersucht. Strukturell bestehen diese oligomeren Tenside aus einfachen monomeren kationischen Tensidfragmenten, die über die hydrophile Kopfgruppe (Tetraalkyl-Ammoniumchlorid) durch „Spacer“-Gruppen unterschiedlicher Natur und Länge miteinander verbunden/gekoppelt sind. Die Eigenschaften dieser kationischen oligomeren Tenside in wässriger Lösung wie Löslichkeit, kritische Mizellbildungskonzentration und Oberflächenaktivität, Mizellgröße und Aggregationszahl werden in Bezug auf die zwei neuen molekularen Variabeln (d.h. dem Oligomerisationsgrad und der Spacer-Gruppe) untersucht, um Struktur-Eigenschafts-Beziehungen abzuleiten. Die Erhöhung des Oligomerizationsgrads verringert stark die kritische Mizellbildungskonzentration (CMC). Eine kurze Spacer-Länge oder ein erhöhte Hydrophobie des Spacers erniedrigt die CMC ebenfalls, aber in einem geringeren Umfang. Die gebildeten Mizellen sind relativ klein und ihre Aggregationszahl nimmt mit zunehmendem Oligomerisationsgrad ab, genau wie mit zunehmender Spacerlänge oder sterischer Behinderung. Außerdem wurden Pseudo-Phasendiagramme für die Gemini-Tenside in komplexen Systemen, nämlich in inversen Mikroemulsionen untersucht. Auch hier zeigt die Spacer-Gruppe einen großen Einfluß auf das Tensidverhalten. Weiterhin wurde der Einfluss von Zusätzen auf das Eigenschaftsprofil der dimeren Tenside untersucht. Starke Synergien wurden beobachtet, wenn man spezielle organische Anionen (z.B. Natriumsalicylat, Natriumvinylbenzoat, etc.) zu den dimeren Tensiden in stöchiometrischen Mengen hinzugibt. Für solche Mischungen wird die Mizellbildungskonzentration stark zu niedrigen Konzentrationen verschoben, wobei der Effekt für die Dimere ausgeprägter als für die analogen Monomere ist. Eine Verringerung der Oberflächenspannung wird ebenfalls erreicht. Gemini-Tenside mit geeigneten Spacer-Gruppen bilden nach Zugabe ausgewählter organischer Anionen viskoelastische Lösungen, selbst wenn die dimeren Tenside nur über relativ kurz Alkylketten verfügen. Dies wurde mittels rheologischer Messungen gezeigt. Dieses Verhalten resultiert aus der Bildung langer Zylinder-Mizellen aufgrund der starken Wechselwirkung der Anionen mit den kationischen Tensiden, die die Krümmung der mizellaren Strukturen verringern. Es wurde auch festgestellt, dass das assoziative Verhalten durch die Dimerisation erhöht wird. Für ein gegebenes Gegenion kann die Spacer-Gruppe den verdickenden Effekt verstärken, in Abhängichkeit von seiner Länge und Hydrophobie. Als weitere Zusätze wurden entgegengesetzt geladene Tenside wurden mit den kationischen Dimeren kombiniert. Einige Mischungen mit dem käuflichen anionischen Tensid SDS bilden Vesikel in Lösung. Mit Blick auf diese katanionischen Mischungen wurde ein neues anionisches Gemini-Tensid, das auf EDTA basiert ist, synthetisiert und charakterisiert. Der Syntheseweg ist relativ einfach und das Tensid zeigt interessante Eigenschaften wie niedrige CMC- und scmc-Werte, gute Solubilisierungskapazität von hydrophoben Substanzen und hohe Toleranz gegen hartes Wasser. Mischungen dieses anionischen Tensids mit bestimmten kationischen Dimeren bilden visköse Lösungen, was ein starkes Mizell-Wachstum widerspiegelt.

The subject of this thesis was to develop and optimize delivery systems for plasmid DNA (pDNA) based on biocompatible polymers, in particular chitosan, suitable for non-viral gene therapy. At the onset of this thesis, studies had reported conflicting results on the efficiency of chitosan-based gene delivery systems. Therefore, structure-property relationships of chitosans as non-viral gene delivery systems in vitro and after lung administration in vivo were established for the first time. Polymer-pDNA complexes (polyplexes) based on conventional high molecular weight chitosans transfected cells in vitro and after lung administration in vivo. The chitosan polyplexes were, in contrast to polyplexes formed with the "golden standard" polymer polyethylenimine (PEI), essentially non-toxic at escalating doses. However, a very high physical stability of the chitosan-pDNA complexes together with a low buffering capacity of chitosan at the slightly acidic endo/lysosomal pH resulted in a slow onset of the gene expression and also in a lower efficiency of gene expression compared to PEI polyplexes. A slow and biodegradation-dependent release of pDNA from the chitosan polyplexes was concluded to be a rate limiting step for the efficiency of high molecular weight chitosan. The optimized polyplexes of high molecular weight chitosan (around 1,000 monomer units) showed aggregated shapes and gave increased viscosity at concentrations used for in vivo gene delivery. To improve the pharmaceutical properties and the delivery properties of chitosan polyplexes, low molecular weight chitosans were studied. Chitosans of around 18 monomer units retained the ability to protect pDNA against DNase degradation, but were more easily dissociated than those of higher molecular weight and had an efficiency comparable to that of PEI in vitro and in vivo. The pharmaceutical advantages of low molecular weight chitosan polyplexes compared to higher molecular weights are that there is less aggregation and no increased viscosity at the concentrations used for in vivo gene delivery. Coupling of an oligosaccharide targeting ligand to chitosan further increased the efficiency of some oligomer polyplexes. In conclusion, biocompatible chitosan is an interesting alternative to other non-viral gene delivery systems such as PEI.