Correlation Between Inhibition Efficiency and Chemical Structure of Some Amino Acids on the Corrosion of Armco Iron in Molar HCl

Weight loss measurement and various electrochemical AC and DC corrosion monitoring techniques are performed at 308 K using Armco iron specimens immersed in 1M HCl solution in the presence and absence of various amino acids (methionine, cysteine, cystine, glycine, leucine, arginine, serine, glutamic acid, ornithine, Lysine, aspartic acid, alanine, valine, asparagine, glutamine, and threonine). Polarisation curves indicated that theses amino acids act as cathodic inhibitors. Methionine, cysteine and cystine who have a sulphur atom in their molecular structure are the best inhibitors, and we suggested that theses three amino acids are adsorbed on the metal surface through the sulphur active centre and that the extent of inhibition is directly related to the formation of the adsorption layer which is sensitive function of the molecular structure. The corrosion inhibition of methionine is regarded by simple blocked fraction of the electrode surface related to the adsorption of inhibitor species according to Frumkin isotherm model on the Armco iron surface. It is clear that quantum descriptors are a better choice when predictivity is the main issue. Among the descriptors with major contribution we should point out that highest occupied molecular orbital energy (E-HOMO), total dipole moment, total energy and binding energy are important predictive descriptors.