Theoretical Evaluation of Zn(II) Binding Affinities and Structural Properties With L ‐Arginine and L‐Canavanine in Aqueous Complexes

Abstract

ABSTRACT The experimental study of the complexation of the amino acids (glycine, alanine, L‐canavanine, and L‐arginine) with the zinc ion Zn(II) was completed, and a computational study employing density functional theory (DFT) with implicit solvation was conducted to investigate the protonation behavior and complexation of these amino acids. The analysis of proton affinities (PA) and charges identifies the carboxyl group as the primary deprotonation and metal‐binding site. For glycine and alanine, stable bidentate complexes are formed via the carboxyl oxygen and amine nitrogen. A key finding is the distinct behavior of L‐canavanine compared to L‐arginine. The existence of a supplementary oxygen atom in L‐canavanine's guanidyl group reduces its PA, allowing for tridentate coordination with Zn(II). Structural optimizations reveal that Zn(II) complexes exhibit shorter, more rigid metal–ligand bonds and higher formation enthalpies than Hg(II) complexes, indicating greater thermodynamic stability. The observed geometric distortions in octahedral complexes are rationalized by ligand denticity and coordination sphere homogeneity. These theoretical results on binding energetics, bond lengths, and coordination modes are in strong agreement with available experimental data, validating our approach for predicting the environmental reactivity of these biomolecules with toxic metal pollutants.