Inhibition of Flash Rusting of HY80 By a Mussel Adhesive Protein: Characterizing the Interaction of MAP-5 with a High Strength Low Alloy Steel

Abstract

A proteinaceous biopolymer, mussel adhesive protein #5, isolated from the common blue mussel (Mytilus edulis L) has been investigated as a model for designing an aqueously soluble candidate corrosion inhibitor system that is non-toxic and environmentally friendly and that could inhibit the flash rusting of exposed high strength low alloy steel surfaces during the paint removal process. It was found that a significant amount of corrosion inhibition is possible (100% inhibition after 7 days) on HY80 steel in a 100% relative humidity environment at 95°F. Indeed, these results were shown to surpass the performance of a commercially available flash rust inhibitor (90% inhibition after 7 days) currently in use on maritime vessels. These results indicated that it is possible to utilize the biochemistry of a naturally occurring biopolymer isolated from the marine mussel, Mytilus edulis (L), to develop a non-toxic and environmentally friendly corrosion inhibitor. This protein is unique in containing 27% L-Dopa and 20% lysine, two unique amino acids containing catecholic and primary amine functional groups, respectively. Currently, characterization of the interaction of the MAP-5 biopolymer on the steel substrate is underway to better understand its mechanism of corrosion inhibition. Energy dispersive spectroscopy (EDS) findings indicate that iron content is highest where the MAP-5 biopolymer is adsorbed onto the steel substrate at pH 5.5, twice the content of the iron on the steel surface alone. When the biopolymer is enzymatically cross-linked on the steel surface at pH 5.5, the iron content is decreased by 1/3 of that of the adsorbed biopolymer. These results suggest that the iron at the steel surface is undergoing complexation and possible metal-mediated cross-linking, whereas the enzyme cross-linked protein on the steel surface complexes less of the iron. Further EDS analysis indicates that when the biopolymer is first dissolved in acetic acid and then phosphate buffer added and placed on the HY80 surface, the same amount of iron is present for all conditions indicating that the presence of acetate or a more acidic pH inhibits any complexation of the iron by the biopolymer as well as any enzymatic cross-linking. Fourier transform infrared (FTIR) spectroscopy using attenuated total reflectance (ATR) and nanoscale IR spectroscopy of the MAP-5 adsorbed onto the steel substrate indicates that the peaks associated with the L-Dopa catecholic hydroxyl groups (-OH) present are very much diminished on the HY80 substrate vs on glass, whereas the aromatic benzene ring peak assignment of the catechol is present on both substrates, confirming the complexation of the surface iron atoms. However, the primary amine (NH3+) functional group present in the amino acid lysine is present in numerous peak assignments on both substrates, with deformation and scissoring, indicating their orientation at the metal surface. It has been suggested that the primary amine may allow for displacement of hydroxyl groups on a metal hydroxide surface, thus allowing the formation of a bi-dentate catechol complex by the L-Dopa amino acids present within the proteinaceous polymer.