Enhanced Understanding of Amphipathic Peptide Adsorbed Structure by Modeling of the Nonlinear Vibrational Response

Abstract

We have used molecular dynamics simulations to study the structure and nonlinear vibrational spectra of a face-wise amphipathic α-helical peptide when adsorbed onto hydrophobic, neutral, and charged hydrophilic surfaces from the solution state. Visible-infrared sum-frequency spectroscopy is a powerful probe of interfacial structure, and is unmatched in its sensitivity and specificity for molecules at the buried solid–liquid interface. However, although the resulting experimental spectra serve as fingerprints for the adsorbed-state structure, there is currently limited understanding in how to extract quantitative structural information. We compare our structural results and simulated spectroscopic response with the results of several experimental studies in the literature. We are able to reproduce all of the main features in the experimental observations, and thereby provide some additional fundamental insight into the interaction of this important class of molecules with surfaces of varying hydrophobicity and charge.