Infrared Spectroscopy of Alanine and Its Water Cluster Isolated in Solid Parahydrogen

Abstract

High-resolution infrared spectra of β-alanine and its water clusters have been studied using solid para-H 2 FT-IR matrix-isolation spectroscopy. It is known that zwitterion forms of amino acids are more stable than neutral forms in water solutions and biological environments, but it is still under debate whether zwitterions are stable in small alaninewater clusters. We have investigated the stabilization effect of water molecules on the zwitterion form of β-alanine by codepositing H 2 O and β-alanine in solid para-H 2 . Through a comparison with theoretical calculations, as well as with crystalline β-alanine FT-IR spectra, the characteristic NH 3 N-H bending vibrational frequency for the zwitterionic form was identified. Analysis of the spectral peak temporal behavior shows that other proposed zwitterion peaks behave similarly to the characteristic NH 3 spectral peak. It has been shown that water can stabilize the zwitterionic form of gas phase amino acids, causing the zwitterion to form preferentially over the neutral form under certain conditions. The β-alanine zwitterion formation rate may be attributed to aggregation of small water clusters in the solid para-H 2 matrix. These findings provide insight into the behavior of amino acid zwitterion formation.