Photoelectron Circular Dichroism of Aqueous-Phase Alanine

TL;DR

This study demonstrates that photoelectron circular dichroism (PECD) can be effectively applied to aqueous-phase alanine, revealing molecule-specific and pH-sensitive chiral responses, thus opening new avenues for studying biological molecules in water.

Contribution

First demonstration of PECD measurements on aqueous-phase alanine, showing sensitivity to molecular structure and solution conditions, and highlighting its potential for biological studies.

Findings

PECD response varies for each carbon atom in alanine.

PECD magnitude in water is comparable to gas-phase measurements.

PECD can probe solvation shell chirality and structure.

Abstract

Amino acids and other small chiral molecules play key roles in biochemistry. However, in order to understand how these molecules behave in vivo, it is necessary to study them under aqueous-phase conditions. Photoelectron circular dichroism (PECD) has emerged as an extremely sensitive probe of chiral molecules, but its suitability for application to aqueous solutions had not yet been proven. Here, we report on our PECD measurements of aqueous-phase alanine, the simplest chiral amino acid. We demonstrate that the PECD response of alanine in water is different for each of alanine's carbon atoms, and is sensitive to molecular structure changes (protonation states) related to the solution pH. For C~1s photoionization of alanine's carboxylic acid group, we report PECD of comparable magnitude to that observed in valence-band photoelectron spectroscopy of gas-phase alanine. We identify key differences between PECD experiments from liquids and gases, discuss how PECD may provide information regarding solution-specific phenomena -- for example the nature and chirality of the solvation shell surrounding chiral molecules in water -- and highlight liquid-phase PECD as a powerful new tool for the study of aqueous-phase chiral molecules of biological relevance.