Theoretical investigation on corrosion inhibition efficiency of some amino acid compounds

The DFT approach was used to do quantum chemical calculations of amino acids energy, geometrical shape, and optoelectronic properties. The investigation of the optoelectronic properties of the substance under consideration is focused on its UV-vis spectra. The calculation of dipole moment, polarizability, hardness, softness, ionization potential, electronegativity, electrophilicity, nucleophilicity, electron transfer, back-donation energy, and firstorder static hyperpolarizability at the DFT/B3LYP/6-311++G(d,p) level of theory revealed the underlying molecule's nonlinear optical behavior. To further elucidate the compound's molecular properties, frontier molecular orbitals, and molecular electrostatic potential maps were provided. At different temperatures, the chemical reactivity and thermodynamic characteristics of amino acids were determined. The computed HOMO and LUMO energies demonstrated that the charge transfer takes place within the molecule. Studies have shown that higher EHOMO values result in higher electron donation, and ELUMO values determine the ability to receive electrons. The order of corrosion inhibition efficiency is determined by the band gap energy of the inhibitor, and a larger band gap results in the poorest corrosion inhibitor. The heteroatoms such as nitrogen, oxygen, sulfur, and phosphorus in an inhibitor structure leads to stronger inhibition when adsorbed onto a metal surface. The selected molecules studied in this work have charge transfer properties towards mild steel, and their inhibition efficiency increases as the electron-donating ability increases. The maximum amount of negative-adsorption energy indicates the best inhibitor for corrosion, with the ranking of identified substances being 3-(((2methyl-4-nitrophenyl)amino)methyl)phenol(D) > 2-((2-hydroxy-5-methoxybenzylidene)amino) pyridine(C) > 3-(((2,4-dinitrophenyl)imino)methyl)phenol (F) > 2-[(methylamino)methyl]pyridine (E) > L-Tryptophan(B) > LHistidine(A).