Recognition mediated fabrication and tailoring of poymeric and colloidal microstructures

Abstract

Molecular self-assembly is the spontaneous and reversible organization of molecular units into ordered structures by non-covalent interactions. Due to specific non-covalent interactions, the building blocks such as molecules, macromolecules or colloidal particles with appropriate ligand shells recognize each other and result in formation of different structures such as micelles, vesicles, microspheres, colloidal microcapsules. In this thesis hydrogen bonding and hydrophobic interactions were employed to obtain self-assembled systems. Depending on the purpose, to supply more stable systems, some covalent crosslinking methods were applied to arrest dynamic systems. Study outlined in the thesis consists of three parts: (a) Using dendritic scaffolds to encapsulate polymeric chains via three point hydrogen bonding, (b)fabrication of robust polymersomes via molecular recognition and arresting these self-assembled structures, and (c) construction of colloidal microcapsules by the help of host-guest chemistry between appropriately functionalized gold and iron oxide nanoparticles. For the first study, monomeric flavin and polymeric flavin ( a styrene based polymer appended with flavin units) were synthesized. Three generations of polyaryl ether dendrons containing diaminopyridine (DAP) unit at their core were utilized to investigate the supramolecular encapsulation of monomeric and polymeric flavin units. Through the specific three point hydrogen bonding between the DAP moiety and flavin, the dendrons binds to monomeric and polymeric flavins to produce supramolecular structures. Monomeric flavins upon mixing with DAP containing dendrons, exhibit reversible, redoxmodulated behavior consistent with previous flavin model systems. Polymeric flavins, however, show diffusion limited redox behavior and site isolation when bound to increasing DAP dendrimer generations. For the second study, chloromethyl styrene/styrene copolymer was synthesized as a parent polymer. The parent polymer was functionalized with azide units and DAP units respectively to result in polymer I (PS-DAP-Az). After converting some chlorine units onparent poylmer into alkyne and thymine functionalities, polymer II (PS-THY-Alk) was obtained. Polymer I and polymer II selfassemble upon mixing in chloroform via three point hydrogen bonding held between DAP and Thy units. These microspheres are only stable in non-protic solvents such as chloroform and toluene. They disassemble upon addition of THF or methanol. To overcome the stability problem arising from the dynamic nature of these kind of systems, Cu(I) catalyzed Huisgen reaction occurring between azide and alkyne groups was utilized to arrest these selfassembled structures and build up stable polymersomes. Thus obtained stable polymersomes were converted to water dispersible systems by attaching PEG chains onto their surfaces. Amenability to further functionalization was demonstrated by attachment of fluorescent dye (BODIPY) and immobilization of an enzyme, streptavidin. In the last part, dynamic colloidal microcapsules or colloidosomes were fabricated by assembly of appropriately functionalized gold and ironoxide nanoparticles at the oil-water interface. For this purpose, -cyclodextrin coated gold nanoparticles and adamantly coated ironoxide nanoparticles were prepared. Due to the host guest interaction between - cyclodextrin and adamantane, fabrication of stimuli-responsive colloidal microcapsules at the oil-water interface was successfully accomplished.