Orientational Behavior and Vibrational Response of Glycine at Aqueous Interfaces

Abstract

Aqueous glycine plays many different roles in living systems, from being a building block for proteins to being a neurotransmitter. To better understand its fundamental behavior, we study glycine's orientational behavior near model aqueous interfaces, in the absence and presence of electric fields and biorelevant ions. To this purpose, we use a surfacespecific technique called heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). Using HD-VSFG, we directly probe the symmetric and antisymmetric stretching vibrations of the carboxylate group of zwitterionic glycine. From their relative amplitudes, we infer the zwitterion's orientation near surfactant-covered interfaces and find that it is governed by both electrostatic and surfactant-specific interactions. By introducing additional ions, we observe that the net orientation is altered by the enhanced ionic strength, indicating a change in the balance of the electrostatic and surfactant-specific interactions.

Observation of Electrostatically Driven Surface Adsorption in Mixed Surfactant Systems

“…A more detailed explanation of the fitting procedure can be found elsewhere. 42 The amplitudes resulting from the fit are shown in Figure 4 . A selection of fitted spectra is shown in the Supporting Information .…”