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Infrared Reflection Absorption Spectroscopy Studies of Thin Organic Films Adsorbed at Gold (111) Electrode Surfaces

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Title: Infrared Reflection Absorption Spectroscopy Studies of Thin Organic Films Adsorbed at Gold (111) Electrode Surfaces
Author: Leitch, J. Jay
Department: Department of Chemistry
Program: Chemistry
Advisor: Lipkowski, Jacek
Abstract: This thesis is an infrared reflection absorption spectroscopy (IRRAS) investigation of the structure, conformation and orientation of organic films adsorbed at the surface of gold (111) electrodes. The first study employed subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) to examine the adsorption behaviour of sodium dodecyl sulfate (SDS) as a function of applied voltage. The SNIFTIRS data confirmed that adsorbed SDS molecules adopt a hemicylindrical film structure at potentials ranging from −250 to 450 mV. Conversely, the calculated average angle of the transition dipole contradicted existing models of interdigitated SDS films at potentials greater than 450 mV. With this new IR data, the structure of the adsorbed SDS film could be more accurately described as a disordered, tilted bilayer. The second study examined the effects of cholera toxin B (CTB) protein bound to the outer surface of a model bilayer lipid membrane supported on the surface of a gold electrode. The binding of CTB to the membrane surface resulted in ~15o increase in the average tilt angle of the phospholipid tails with no change in the membrane capacitance. This increase in lipid disorder suggests that CTB may be forming lipid rafts on the membrane surface. The orientation of the CTB α-helices showed significant voltage-dependent changes. These changes may correspond to voltage-gated opening and closing of the central pore, supporting the translocation mechanism for cholera toxin infection. The final work examined the physical properties of self-assembled 2,3-di-O-phytanyl-sn-glycerol-1-tetraethylene glycol-D,L-α-lipoic acid ester lipid (DPTL) monolayers. The goal was to evaluate the candidacy of this molecule in creating tethered phospholipid bilayers for mimicking biological cell membranes. Polarization modulation infrared reflection spectroscopy (PM-IRRAS) spectra of the DPTL monolayer showed that the film is very stable over a wide range of potentials. In addition, the IR spectra showed that the tetraethylene glycol chains were coiled, disordered and poorly hydrated, contradicting the original tBLM design.
Description: Infrared Studies of the Structure, Orientation and Conformation of Adsorbed Thin Organic Films at a Gold (111) Electrode-Solution Interface
Date: 2014-11
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