Quantum chemical analysis of amino acids as anti-corrosion agents

Abstract Anti-corrosion properties of L-lysine (Lys), S-methyl (S-Met), L-cysteine (Cys), L-glycine (Gly), valinin (Val), and L-glutamine (Glu), all of which are amino acids, were evaluated on the surfaces of iron, copper, and aluminum in both the protonated and non-protonated states in both the gas and aqueous phases at their optimal symmetry. Analysis was performed based on density functional theory (DFT) calculation at 6-311++G(d,p) and B3LYP level. Monte Carlo simulation generated top and side views of the most energetically stable configuration for the adsorption of all selected amino acids on Al (110), Fe (110), and Cu (110). This suggests that the Monte Carlo simulation was able to accurately predict the adsorption properties of the amino acids on the selected metal surfaces. Glu was found to be the strongest inhibitor amongst the six molecules tested, as it had the lowest energy difference and the highest reactivity, according to the decreasing sequence of ∆E values. Electronegativity difference of the compounds investigated from highest to lowest is Lys, S-Met, Cyst, Gly, Val, and Glu. This order is also reflected in the polarizability of the compounds, with Lys having the highest polarizability and Glu having the lowest, suggesting that Glu may have the highest inhibitory efficacy.