Experimental and theoretical investigation towards anti-corrosive property of glutamic acid and poly-γ-glutamic acid for mild steel in 1 M HCl: intramolecular synergism due to copolymerization

The potentiality of poly-gamma-glutamic acid (PGA), a naturally occurring polypeptide, towards inhibiting corrosion of mild steel in 1 M HCl is hereby assessed through electrochemical and gravimetric analysis, evaluation of adsorption and activation parameters, coupled with theoretical calculations. Inhibition efficiency of PGA is compared with that of its monomeric unit, glutamic acid (GA, a non-essential amino acid). While GA does not show any anti-corrosive effect, PGA is found to be a good corrosion inhibitor for the studied system with inhibition efficiency more than 90% within the temperature range of 293-303 K and up to an exposure time of 24 h. Experimental result has been explained in terms of decreased energy gap between the frontier molecular orbitals, increased dipole moment, and molecular chain length, as well as availability of interacting amide groups resulting due to co-polymerization. Occurrence of intramolecular synergism towards corrosion inhibition due to co-polymerization is further supported by molecular dynamics simulation results.