Quantum chemical exploration on the inhibition performance of indole and some of its derivatives against copper corrosion

Abstract

The inhibitory behavior of indole and some of its derivatives and their conformers against copper corrosion was studied by density functional theory (DFT) and molecular dynamics simulations. The calculated reactivity parameters based on the values of EHOMO, ELUMO, energy gap (ΔEgap), hardness (η), softness (σ), electronegativity (χ), electrophilicity (ω), Fukui indices (fk), fraction of electron transferred (ΔN) and back-donation of electrons (ΔEback-d) between the inhibitors and the copper surface have been scrutinized. DFT-molecular dynamics simulations have been used to investigate the adsorption mechanism for neutral and deprotonated forms of inhibitors. It was established that the carbonyl and carboxylic groups of the indole derivatives have a great effect on the inhibition efficiency. The results of molecular reactivity indicate that the inhibition efficiency is ranked as follows: indole < IND3-C2 < IND3-C1 < IND5-C1 < IND2-C2 < IND2-C1 < IND5-C2 < isatin. Neutral inhibitors physisorb to the copper surface except for isatin, which is chemisorbed due to its higher binding energy and its increased amount of charge transfer. The deprotonated inhibitors are chemisorbed on Cu(111) surface by establishing strong covalent CuN bonds, as supported by charge density difference analysis.