Molecular-Level Assessment of Adsorptive Interaction and Corrosion Inhibition Potential of Some Green Compounds with Caffeine Scaffold on Fe(110) Surface

ABSTRACT: Five compounds, namely, caffeine, theobromine, theophylline, paraxanthine, and xanthine, that exhibit the caffeine-based scaffolds, were assessed using density functional theory (DFT) and molecular dynamics (MD) simulations to elucidate their adsorption behaviour on Fe(110) surface. The potential adsorption sites in the compounds were probed in terms of quantum chemical descriptors, frontier molecular orbitals, Fukui functions, and Mulliken charges, while MD simulations provided insight into adsorption energies, binding, and deformation configurations. Results reveal that theobromine exhibited the highest reactivity and strongest adsorption as a result of favourable electronic properties and potential of interaction with the metal surface through two active sites. Caffeine followed closely, but exhibited slight steric limitations. Paraxanthine and theophylline exhibited moderate behaviour, while xanthine displayed the weakest surface interaction as a result of relatively poor donor-acceptor potential. The results also demonstrate the essential role of N-methyl substitution and electronic softness in optimizing caffeine-derived molecules for application as corrosion inhibitors for steel. The findings from this study offer insights into sustainable adsorption corrosion inhibitors derived from naturally occurring scaffolds before engaging in rigorous experiments on trial and error basis, which often consumes time, energy, and resources.