Structure of Biomolecules Adsorbed at the Hydrophobic Polymer-Solution Interface from Spectroscopic Experiments and Molecular Simulations
Date
2013-09-26
Authors
Hall, Shaun Andrew
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Abstract
The work herein describes efforts to improve the understanding of the structural and
optical properties of molecules adsorbed to polymeric surfaces. The main emphasis
was placed upon the determination of molecular orientation of adsorbed molecules by
developing methods for extracting structural information from vibrationally-resonant sum
frequency generation spectroscopy experiments. Through the comparison of electronic
structure calculations to the acquired spectra, orientation distributions were determined for
phenylalanine on polystyrene coated fused silica. The initial study was a single example of
a method that is applicable to any surface for which the adsorbing species has a completely
characterized infrared and Raman spectra. Predicted intensities for the symmetric and
antisymmetric CH2 stretches were compared to their corresponding amplitudes extracted
from the acquired spectra. In the second study, the method developed was more general,
incorporating the addition of molecular dynamics simulations, which were used to discover
various conformations present at the surface, allowing for fits to the acquired spectra to be
determined based on the relative populations of these species. This approach was chosen as
it is applicable to cases in which the adsorbing species has overlapping spectral features that
will not allow for characterization of specific modes. As an example of this, leucine, which
possesses highly coupled and overlapping absorptions in its infrared and Raman spectra,
adsorption to a polystyrene surface was studied. A high speed Stokes polarimeter based on
a dual photoelastic modulator was designed, assembled, and calibrated based on a novel
method, capable of measuring the adsorption kinetics of molecules adsorbing to surfaces.
The adsorption of bovine serum albumin (BSA) to a polystyrene coated fused silica surface
was studied. The configuration of the polarimeter was amenable to the determination of
Mueller matrices of equilibrated surfaces with minimal procedural modifications.
Description
Keywords
molecules, adsorbing, polystyrene