Aromatic amino acid–metal ion interactions: comparative effects of alkali and Zn2+ on acidity and coordination behavior via QM studies

Among the 20 standard amino acids, aromatic amino acids hold particular importance due to their crucial roles in protein-protein interactions. These residues, including phenylalanine, tyrosine, tryptophan, and histidine, contribute significantly to protein structure and function through their ability to engage in non-covalent interactions, such as π-π stacking and cation-π interactions. In addition, the acid-base duality of aromatic amino acids makes their interactions with metal ions particularly valuable. These interactions are implicated in several essential biological processes, including protein biosynthesis, enzyme catalysis, and molecular recognition. While the interactions between transition metal ions and amino acids have been extensively studied and well-documented, the role of alkali metal ions in similar contexts has received comparatively less attention. However, their influence on amino acid coordination and stability cannot be overlooked, especially given their biological relevance in processes such as ionic regulation, enzyme activation, and membrane transport. The results of this study demonstrate that the complexation of aromatic amino acids with alkali metal ions enhances their acidity. Additionally, we examined the detailed interactions of these metals with the aromatic amino acids.