Structures and proton transfer processes of methionine effected by heavy metal cations (Pb2+, Hg2+, and As3+) in the gas phase and aqueous solution

Abstract

The interactions of methionine (Met) and heavy metal cations (Pb²⁺, Hg²⁺, and As³⁺) in both gas phase and aqueous solution were studied by theoretical calculations. The Met-Metal complex structures show that their most stable conformations in the gas phase are neutrals. In aqueous solution, Met-Pb²⁺ and Met-As³⁺ maintain neutrality, whereas Met-Hg²⁺ adopts a zwitterionic form. The proton transfer mechanism suggests that, for Met-Pb²⁺ and Met-Hg²⁺, the highest energy barrier of reaction is lower in aqueous solution compared to the gas phase, whereas for the Met-As³⁺ system, the opposite trend is observed. Additionally, the interaction energy, bond dissociation energy, atomic charge, interaction region indicator function, and atoms in molecules of key structures of the rate determining step in the proton transfer process were analyzed. The results will facilitate a deeper understanding of the mechanism underlying the complexation between amino acids and heavy metals.