Hydrophobicity dependence of oxidation of tetrapeptides of elastin sequences with Mn(III): Synthesis, characterization, kinetics, and mechanistic study

The analogues of elastin sequences, glycyl-glycyl-alanyl-proline (GGAP), glycyl-glycyl-phenylalanyl-proline (GGFP), and glycyl-glycyl-isoleucyl-proline (GGIP) were synthesized by classical solution phase method and characterized, The kinetics of oxidation of these tetrapeptides (TETP) by Mn(III) has been studied in the presence of sulphate ions in acidic solution at 25degreesC. The reaction was followed spectrophotometrically at lambda(max) = 500 nm, A first-order dependence of rate on both [Mn(Ill)] and [TETP] was observed. The rate is independent of the concentration of the reduction product, Mn(II), and hydrogen ions, The effects of varying the dielectric constant of the medium and addition of anions such as sulphate, chloride, or perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Erying plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of TETP with Mn(III) in the rate-limiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these sequences, where increased hydrophobicity results in increased rate of oxidation. (C) 2001 John Wiley Sons, Inc.