Deformation and ordering of molecular assemblies in high magnetic fields

Abstract

In this thesis the synthesis and physical properties of polymers of isocyanides containing thiophene and other functional groups are described. Polyisocyanides are ideal frameworks for the incorporation of such groups, because they possess a high degree of structural regularity as a result of the helical arrangement of the polymer backbone. A new type of isocyanide, viz. L-isocyanoalanine(2-thiophen-3-yl-ethyl)amide (IAT), was synthesized and polymerized using Ni(II) catalysts to give the corresponding polymer PIAT. The use of an amino-terminated polystyrene as the initiator in the polymerization of IAT resulted in the formation of a diblock copolymer (PS-PIAT), which displayed amphiphilic character. On dispersal in THF/water, aggregates with morphologies that depended on the ratio between the PS and PIAT block lengths could be obtained. Interestingly, PS-PIAT diblock copolymers also formed well-defined aggregates in organic solvents. In aqueous solution typically polymersomes were obtained, which were found to fuse upon standing, thereby increasing their average diameter by a factor of 20. The thiophene groups present in the polymersomes of PS-PIAT could be polymerized both electrochemically and chemically. Chemical polymerization proved to be the most suitable procedure, because it left the morphology of the polymersomes unaltered, in contrast to electrochemical polymerization, which led to destruction of the aggregates. Nanoreactors were constructed by encapsulating enzymes within the aqueous compartment of the PS-PIAT polymersomes. Three different enzymes, viz. lipase B from Candida antarctica, horseradish peroxidase, and glucose oxidase, were successfully compartmentalized. With the help of enzyme activity assays it was possible to prove that the enzymes inside the polymersomes remained active. Externally added substrates were found to diffuse through the polymersome membrane into the inner aqueous compartment of the nanoreactors where they were converted by the enzymes present. The resulting products were capable of diffusing out of the polymersomes, while the enzymes remained entrapped.