Heterocyclic amino acids-based green and sustainable corrosion inhibitors: Adsorption, bonding and corrosion control

The growing interest in green chemistry and sustainable development has led to immense research on biopolymers, plant extracts, polysaccharides, and other synthetic and natural green corrosion protection practices. Notable progress has also been made in using amino acids and their derivatives in corrosion prevention. In addition to being environmentally benign, AAs and their derivatives have the ability to adsorb and form strong chelating complexes with metallic substrates efficiently. Proline, histidine, tryptophan and their derivatives have been widely employed in corrosion prevention due to their capacity to bind to metal surfaces and create chelating complexes. Pristine Pro can form a bidentate chelating complex using -NH2 and -COOH groups. His and Trp can form tridentate chelating complexes with the extra nitrogen atoms of imidazole and indole moieties. Their adsorption primarily followed the Langmuir and Temkin adsorption isotherm, and they function as mixedtype inhibitors. Various surface analyses, such as FT-IR, SEM, EDX, and XPS, are extensively used to describe the adsorption mode and corrosion inhibition behavior of heterocycle AA -based inhibitors. GFN-xTB calculations indicate that heterocyclic amino acids adsorb via chemisorption, both with and without synergists. The Pro, His, and Trp's coordination ability is greatly improved using KI, metal ions (Zn2+), surfactants, and thiourea as synergists. The present article describes the adsorption, coordination binding and corrosion inhibition potential of heterocyclic AAs and their derivatives, along with their challenges and opportunities.