Coordination interaction of biologically important macromolecules with metals and alloys for corrosion protection: An extensive study

Tetrapyrrole and phthalocyanine are significant groups of naturally occurring nitrogenous macromolecules which protects surface of metal by exhibiting strong anticorrosive property. Due to their association with extremely conjugated π-system and heteroatoms with non-bonded electrons, tetrapyrroles and phthalocyanines exhibit a reassuringly good level of efficiency against metallic degradation both in coating and aqueous phase. These chemical substances are effective ligands. Compounds and their derivatives produce chelating complexes with metals, which protect metallic species from harsh environments. The current review article aims to compile research findings on the use of tetrapyrroles, phthalocyanine, and their green and non- green derivatives as anti-corrosion agents from both the recent and historical studies. Additionally, this study intends to provide insight into the anti-corrosion characteristics of these macromolecules compounds by discussing their unique coordination and bonding properties and correlating these with theoretical observations. Observed data clearly shows that such macromolecules and their derivatives function mainly as mixed-kind inhibiting agents, effectively delaying both oxidation and reduction processes and adsorb according to the Langmuir adsorption isotherm in most cases. It is evident from the observations that the preventive effect is further improved by combining these macromolecules with additional compounds or groups that are highly efficient toward corrosion. Such molecules provide a broad area for further research.