Kinetic and Mechanistic Study of Oxidation of Protein-based Elastin Polymer with its Constituent Amino Acids and Peptides

Abstract Four peptides (Ps) with varying chain lengths, VP, GVP, VGVP, GVGVP, and a poly pentapeptide (PPP or poly(GVGVP) have been synthesized by a classical solution phase method and characterized. Oxidations of these peptides, including their constituent amino acids (AAs), V and P, have been studied using the oxidant, quinolinium dichromate (QDC), in perchloric acid medium at 25℃. Each reaction has been monitored spectrophotometrically at the λ max of 440 nm. The reactions follow an identical kinetics with the following general, experimental rate law: rate = k′ [QDC][substrate][H + ], where substrate = AA/P/PPP. Effects of dielectric constant of the medium and the added salts have been studied. The reaction stoichiometry has been determined and the products have been characterized. The dependence of the reaction rate on temperature has been determined and the activation parameters have been evaluated. A plausible mechanism has been envisaged based on the kinetic results. An apparent correlation has been noted between the rate of oxidation and the length of the peptide chain. The polymer, poly(GVGVP), has the slowest rate as compared to peptides, ranging from dipeptide to pentapeptide, which in turn have slow rates than their individual amino acid constituents. This is consistent with the dependence of the reaction rate on chain length.