QSAR, Experimental and Computational Chemistry Simulation Studies on the Inhibition Potentials of Some Amino Acids for the Corrosion of Mild Steel in 0.1 M HCl

Inhibition and adsorption potentials of cysteine, glycine, leucine and alanine for the corrosion of mild steel in hydrochloric acid (HCl) solution were investigated using experimental and quantum chemical approaches. The experimental study was carried out using gravimetric, gasometric, thermometric and Fourier transformed infra red (FTIR) methods while the quantum chemical study was carried out using semi-empirical, ab-initio and quantitative structure activity relation (QSAR) methods. The results obtained indicated that various concentrations of the studied amino acids inhibited the corrosion of mild steel in HCl solution through physiosorption. The inhibition potentials of the inhibitors decreased in the order, cysteine > leucine > alanine > glycine. The adsorption of the inhibitors on mild steel surface was found to be exothermic, spontaneous and supported the Langmuir adsorption model. Results obtained from quantum chemical studies showed excellent correlations between quantum chemical parameters and experimental inhibition efficiencies (for gas and aqueous phases using density functional theory (DFT) and Moller-Plesset (MP2) perturbations). Correlations between the experimental inhibition efficiencies and theoretical inhibition efficiencies (obtained from QSAR) were also excellent.