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 surface-specific 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.

European Research Council (ERC) , NWO-I
J. Phys. Chem. Lett.
Ultrafast Spectroscopy

Antalicz, B., Sengupta, S., Vilangottunjalil, A., Versluis, J., & Bakker, H. (2024). Orientational Behavior and Vibrational Response of Glycine at Aqueous Interfaces. J. Phys. Chem. Lett., 15(7), 2075–2081. doi:10.1021/acs.jpclett.3c02930