Publikationsserver der RWTH Aachen University
Multifunctional chitosans obtained via polymer-analogous reaction with functional five-membered cyclic carbonates
Abstract
dc:descriptionThis thesis deals with the preparation and characterisation of multi-functional chitosan derivatives. The resulting materials can be used as surfactants and as biocides. In the preparation of these compounds carbonate couplers play an important role. Therfore different carbonate couplers were developed and evaluated by reaction with amines. Chitosan is a biocompatible natural polyamine, which is obtained from chitin - the second most abundant polysaccharide in nature - by deacetylation with sodium hydroxide. It is composed of glucosamine and N-acetyl-glucosamine units and is available in different molecular weights and degrees of deacetylation (DD). The solubility is influenced by these two properties; however, the majority of chitosan derivatives are only soluble at low pH values in aqueous solution. Only low-molecular weight chitosans, so-called chitosan oligosaccharides and modified chitosans like glycol chitosan are soluble in water at any pH. Chitosan surfactants, amphiphilic derivatives bearing hydrophilic and hydrophobic (alkylic) branches were prepared from glycol chitosan (GC) and chitosan oligosaccharides (COS) in a three-step synthesis. In the case of GC water-insoluble products were obtained, the functionalisation of which was proven via IR spectroscopy. With the oligomers a broad variety of products were obtained using a short (C3) or a long (C6) carbonate linker. The products vary in the degree of functionalisation, hydrophobic to hydrophilic ratio and length of the hydrophobic side group (C8, C12 and C14) and were characterised by NMR spectroscopy and partially by IR spectroscopy. Thermogravimetric analysis showed a higher thermal stability for the derivatives investigated and measurement of surface tensions resulted in a critical micelle concentration (cmc) being 0.01 mg/mL for a hydrophilic to hydrophobic ratio of 1:1 and a C12 alkyl chain. The antibacterial activity of these chitosan surfactants was tested against B. subtilis and E. coli. Highest activity was determined for derivatives prepared with the C6 linker, dodecyl-(A12) branches and moderate (1:1, 2:3) ratios of cationic to A12 side chains. The hemocompatibility of the more potent antibacterial compounds was assessed based on their haemolytic action on human red blood cells (RBCs). All samples investigated were found harmless for blood cells. Moreover, direct functionalisation of chitosan with ethylene carbonate or functional ethylene carbonates was studied. The results show that due to the low reactivity of the amino group in glucosamine repeating units this procedure is not viable. The carbonate coupler is a bifunctional molecule bearing two amino-reactive groups, which can be addressed selectively: The linear carbonate unit reacts at low temperatures; the five-membered cyclic carbonate moiety reacts at elevated temperatures (> 40°C). On the basis of glycerol carbonate, four coupling reagents were prepared: (2-oxo-1,3-dioxolan-4-yl)methyl phenyl carbonate (I), (2-oxo-1,3-dioxolan-4-yl)methyl 4-nitrophenyl carbonate (II), (2-oxo-1,3-dioxolan-4-yl)methyl 1-imidazole carbonate (III) and (2-oxo-1,3-dioxolan-4-yl)methyl 4-(propan-2-ylideneaminooxy) carbonate (IV). Their synthesis and characterization, starting from glycerol carbonate is described. To evaluate the differences in reactivity these couplers were reacted with valine methyl ester and the results were compared with the already known coupler I. Reaction conditions influenced the conversion of the couplers I-IV containing -phenyl, -4-nitrophenyl, -imidazolyl and acetone oxime leaving groups; highest conversion and fastest reaction rates were obtained with 2-oxo-1,3-dioxolan-4-yl)methyl 4-nitrophenyl carbonate (II). The coupling reagents I, and II were used for the synthesis of functional carbonate building blocks from amino acid methyl esters and glucosamine. In an additional study amino acids were reacted with (2-oxo-1,3-dioxolan-4-yl)methyl 4-nitrophenyl carbonate (II) and with glycerol carbonate chloroformiate. It could be shown that the desired products were formed; however the isolation of these amino acid couplers failed.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2009
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Fricke, Nicole
- Contributors dc:contributor
-
- Möller, Martin
Subjects
dc:subject × 12Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng