Theoretical Simulation of the Corrosion-inhibition Potentials of Triterpenoids on Aluminium Metal Surface

The mechanism of the corrosion-inhibition action of three selected triterpenoid compounds including α-amyrin, β-amyrin and Lupeol on Al(110) surface was studied using computational methods including molecular dynamic simulations and quantum chemical calculations. The relative corrosion-inhibition performance of the studied compounds was investigated. Quantum chemical parameters including fraction of electron transfer (ΔN) from the inhibitor molecule to the Al(110) surface, energy gap (ΔE), energy of the lowest unoccupied molecular orbital (ELUMO), energy of the highest occupied molecular orbital (EHOMO), global electrophilicity index (ω), global softness (σ), electronegativity (χ) and global hardness (η) were all computed. The local reactivity-indicating sites for electrophilic and nucleophilic attack were analyzed using Fukui indices, while molecular dynamic simulation was used to study their adsorption behavior on the surface of Al(110). Based on the interactions, the adsorption energy (Eads) values obtained, –49.533 kcal/mol for α-amyrin, –48.284 kcal/mol for β-amyrin and –37.654 kcal/mol for lupeol, are all negative with correspondingly low magnitudes (less than –100 kcal/mol). This shows weak and unstable adsorption structures and relatively low corrosion inhibition, suggesting a physical adsorption mechanism with the trend: α-amyrin > β-amyrin > lupeol.