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 f?? 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

Introduction

Metallic corrosion is a major global issue, costing over $2.5 trillion annually and causing significant environmental damage through resource depletion and pollution. Iron and its alloys, widely used in industry, are particularly prone to corrosion, necessitating effective protection methods. Traditional chemical inhibitors like chromates are now restricted due to toxicity, driving interest in eco-friendly alternatives.

Amino acids, especially aspartic acid, emerge as promising green corrosion inhibitors due to their biodegradability and ability to form protective films on metal surfaces. Aspartic acid’s molecular structure allows multiple binding sites to metals, and its oligomers (dimers, trimers) may enhance protection through cooperative adsorption.

Although experimental studies confirm their effectiveness, the detailed molecular mechanisms of aspartic acid’s corrosion inhibition are not fully understood. This study uses quantum chemical methods (density functional theory) to analyze aspartic acid and its oligomers, calculating electronic properties such as HOMO-LUMO energies, electronegativity, hardness, and Fukui indices that predict their reactivity and binding behavior.

Results indicate that larger oligomers have better electron-donating and accepting abilities, smaller energy gaps (indicating higher reactivity), and improved surface interaction properties like polar surface area and dipole moment. Fukui function analysis highlights oxygen atoms as key reactive sites for metal binding, supported by molecular electrostatic potential maps.

These findings suggest that aspartic acid oligomers could serve as efficient, environmentally friendly corrosion inhibitors, and computational insights can guide their optimization for real-world applications, promoting greener corrosion protection strategies.

Conclusion

This study elucidates the molecular-level mechanisms by which aspartic acid and its oligomers inhibit iron corrosion, combining quantum chemical calculations with reactivity analyses. Oligomerizationwould enhance performance through cooperative interactions between polymer chains and the iron surface, facilitating dense protective film formation. Future research should investigate synergistic combinations with other eco-friendly inhibitors and scalable synthesis methods for oligomers.This research advances corrosion science by linking molecular properties to inhibition performance, offering strategies to optimize green inhibitors. It also highlights the broader potential of bio-inspired molecules in sustainable materials engineering. From a practical application perspective, these findings offer valuable guidance for inhibitor design. The observed patterns suggest that optimal inhibitor design should maintain strong electron-accepting sites (like carbonyl oxygens) while a balanced distribution of reactive sites may be more effective than concentrated reactivity.

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Copyright

Copyright © 2025 Bababtunde T. Ogunyemi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.