Molecular level interfacial structures of proteins and antifouling polymers studied by sum frequency generation vibrational spectroscopy.

Abstract

The overall purpose of the research in this thesis was to investigate the interfacial conformational behavior of polymers and proteins in order to provide insight into the biofouling process and acquire information that might contribute to the design of new kinds of antifouling polymers. A nonlinear optical spectroscopic technique, sum frequency generation (SFG) vibrational spectroscopy, was used in the research. SFG can detect vibrational spectra of surfaces and interfaces with a submonolayer surface specificity, providing molecular level structural information of these surfaces and interfaces in situ in real time. In Chapter 2, SFG was used to elucidate molecular structures of buried solid/liquid interfaces. Poly(ethylene glycol)s (PEGS) with different end groups were found to adopt interfacial structures that changed in response to contact with different solid polymers. With increasing hydrophobicity of solid contacting polymers, the hydrophobic end groups of the PEGS segregated to the interface and/or became more strongly ordered. In Chapter 3, SFG was used for the first time to detect ordered CF₃ groups on trifluoromethylbenzyl alcohol. Strong correlations between SFG, IR, Raman and DFT data allowed reliable peak assignments to be made for all available spectral information, demonstrating the feasibility of detecting CF₃ groups at an interface. In Chapter 4, SFG was used to observe the conformational behavior of Mefp-3, a 'primer' mussel adhesive protein, when solutions were placed in contact with solid polymers. Unlike PEGs in Chapter 2, specific functional group interactions, rather than polymer hydrophobicity, were found to govern the interfacial conformational behavior of the protein. In Chapter 5, SFG conformational changes in response to exposure to water were monitored by SFG for surfaces of two commercial PDMS materials and were correlated to their fouling release performance with barnacles and <italic> ulva</italic> sporelings. The surface of Sylgard 184 exhibited greater restructuring, which may explain sporeling adhesive attaching more strongly to Sylgard 184 than to Silastic T2. This research demonstrates that SFG is a powerful tool to elucidate molecular structures of polymer and biological molecules at interfaces in situ, leading to a more in-depth understanding of the biofouling process.