Hydration-dependent interaction of Na+, K+ with glycine: A comparative study of neutral and zwitterionic forms via DFT calculations

Abstract

This study employs ab initio calculations to probe glycine-Na⁺/K⁺ interactions in water clusters. The results reveal that Na⁺-glycine complexes transition from neutral to zwitterionic configurations at six water molecules, while K⁺ systems achieve this shift at four. Proton transfer analysis shows that hydration can reduce zwitterion formation energy barriers. Multimethod analyses (IGMH, AIM) reveal that the binding strength of glycine-Na⁺/K⁺ initially decreases with hydration, with the weakest interactions occurring at the structural pre-transition stage from the neutral to the zwitterionic form. Energy decomposition analysis quantifies the dominan of electrostatic interactions. These results elucidate hydration-modulated amino acid-ion coordination dynamics critical for biological transport processes.