Mn(III) oxidation of peptide polymers of elastin sequences: synthesis, kinetics and mechanistic study

Protein based‐polymers comprised of Ala‐, Val‐ and Ile‐containing tetrapeptide repeating sequences of elastin were synthesized based on the increasing order of hydrophobicity and subjected to metal‐catalyzed oxidation to identify the amino acid residues, which are sensitive to oxidation. These polytetrapeptides (PTP) were oxidized using Mn(OAc) 3 at 25°C and the kinetics of the reaction were monitored spectrophotometrically at λ max  = 400 nm. A first‐order rate dependence on the substrate concentration [PTP] and [Mn(III)] and an inverse order dependence on [H + ] has been observed. Further, the rate is independent of [Mn(OAc) 2 ]. The effect of the dielectric constant on the rate was studied by varying the percentage of AcOH. Activation parameters were evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. Based on the results obtained, a plausible mechanism involving [Mn(OAc) 4 ] − is proposed. It is noteworthy that the rate of oxidation of poly(GGIP) was higher than those of poly(GGVP) and poly(GGAP). This may be due to their increased hydrophobicity. The overall order of rate of oxidation of PTP is poly(GGIP) > poly(GGVP) > poly(GGAP). Copyright © 2005 John Wiley & Sons, Ltd.