PhD Thesis
Surface Modification of Spherical Particles with Bioactive Glycopolymers
André Pfaff (05/2011-07/2011)
Support: Axel H. E. Müller
Summary
Glycopolymers containing different kinds of carbohydrates were grafted from various spherical templates, whereby the glycopolymer chains were prepared via controlled radical polymerization techniques, namely ATRP and RAFT. A library of carbohydrate-displaying spheres and their interaction with lectins is presented. Glucose- or acetylglucosamine-displaying nanospheres were prepared via the combination of emulsion polymerization and photo-induced conventional polymerization or ATRP, respectively. The particles were able to stabilize gold nanoparticles to form catalytically active hybrid particles that were capable of reducing p-nitrophenol in the presence of NaBH4. Investigation of the interactions between acetylglucosamine-displaying polymers and a series of lectins revealed a selective binding towards the lectin wheat germ agglutinin (WGA) whereby the binding affinity of the protein to the polymer brushes was found to be magnitudes higher than to acetylglucosamine unimers. Lectin precipitation experiments revealed that 1 mg of glycopolymer brush was able to precipitate 0.5 mg of WGA. Surface modification of poly(divinylbenzene) microspheres was performed using two different glycomonomers and various types of grafting techniques. Grafting through of a mannose-displaying glycomonomer yielded core-shell particles with densely grafted glycopolymer arms that were found to show no binding affinity towards a series of lectins. The nexus of the carbohydrate moiety to the polymer backbone seemed to hamper the key-lock interaction of the sugar and protein. Grafting experiments of a galactose-displaying glycomonomer yielded particles with grafting densities ranging from 0.20 to 0.35 chains per nm2 depending on the utilized grafting approach. These particles showed a selective binding towards the lectin Ricinus communis agglutinin (RCA120), whereby each grafted glycopolymer chain was capable of binding to 0.7 molecules of RCA120. Furthermore, the particles were found to have a superior binding affinity towards RCA120 in comparison to microspheres covered with galactose unimers. The preparation of core-shell particles consisting of a poly(divinylbenzene) micro-sphere core and a shell of highly branched glycopolymers was achieved via self-condensing vinyl copolymerization of an initiator-monomer and acetylglucosamine-displaying glycomonomer. It was found that an increase in incorporated inimer, which results in more compact and branched structures, directly led to an increase in particle coverage (1.6 2.4 wt.-%). Carbohydrate-lectin binding studies revealed that the incorporation of approximately 50% of the hydrophobic inimer led to an increase in adsorption of 26% compared to a less branched glycopolymer and 16% compared to linear glycopolymer grafted particles. These results indicated that the three-dimensional glycopolymer architecture directly affects the strength of the key-lock interaction of sugar and sugar-binding protein. Studies on the interactions between glycopolymers and lectins were extended towards the cellular uptake of fluorescent, magnetic galactose-displaying core-shell nanospheres. These particles were prepared by grafting a galactose-displaying glycocopolymer onto silica-encapsulated iron oxide particles via thiol-ene chemistry. Due to the carbohydrate-containing shell, these particles could be localized not only in the cytoplasm but also in the nucleus of human lung cancer cells. This cell line expresses a galactose-binding protein which indicates that carbohydrate-lectin interactions are responsible for the uptake of the functionalized particles. In general, these studies show the capability of utilizing carbohydrate-lectin interactions for potential applications like lectin precipitation and cellular imaging.