Quantum Chemical and Reactivity-Based Evaluation of Aspartic Acid and its Oligomers as Eco-Friendly Corrosion Inhibitors for Iron Surfaces

Abstract

This study investigates the corrosion inhibition potential of aspartic acid (ASP) and oligomers on iron surfaces through quantum chemical calculations. Aspartic acid monomer (ASP), dimer (DASP), and trimer (TASP) were analyzed using density functional theory at the B3LYP/6-31G(d) level to determine their electronic properties and reactivity patterns. Quantum chemical parameters including HOMO-LUMO energies, energy gap, dipole moment, softness, hardness, and electrophilicity were calculated to elucidate structure-activity relationships. Results revealed a progressive decrease in energy gap values (ASP: 7.12 eV → DASP: 6.12 eV → TASP: 6.05 eV), indicating enhanced chemical reactivity with increasing molecular size. HOMO energies demonstrated an increasing trend from ASP (-6.89 eV) to TASP (-6.48 eV), suggesting improved electron-donating capability in larger molecules. Fukui function analysis identified specific reactive sites, with oxygen atoms exhibiting strong electrophilic character as evidenced by significant negative fₖ⁻ values, particularly at carbonyl groups. The distribution of reactive sites became more dispersed with increasing molecular size, potentially enabling multiple points of interaction with metal surfaces. These findings suggest that larger PASP oligomers may provide superior corrosion inhibition through enhanced electron transfer capabilities, stronger dipole interactions, and more distributed reactive sites for surface adsorption. This computational study provides valuable insights for the rational design of environmentally friendly corrosion inhibitors based on aspartic acid and oligomers.