Mn(III) oxidation of peptides: A mechanistic investigation of kinetic variations in hydrophobic-induced oxidation of tetrapeptides of elastin sequences

✍ Scribed by G. R. Srinivasa; K. Abiraj; A. Ramesha Baba; D. Channe Gowda

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 125 KB
• Volume: 38
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20144

✦ Synopsis

Abstract

Four tetrapeptide analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐valyl‐proline (GGVP), glycyl‐glycyl‐isoleucyl‐proline (GGIP), and glycyl‐glycyl‐phenylalanyl‐proline (GGFP) were synthesized, based on their increasing order of hydrophobicity, by a classical solution phase method and were characterized. These tetrapeptides (TETPs) were oxidized using Mn(OAc)~3~ in 25% acetic acid at 298 K, and the kinetics of the reaction was monitored spectrophotometrically at λ~max~ = 400 nm. A first‐order dependence of rate on each of [Mn(OAc)~3~], [OAc^−^], and substrate [TETP], an inverse order dependence on [H^+^], has been observed. The rate is independent of [Mn(II)]. However, an inverse order dependence on varying the dielectric constant using various percentages (v/v) of acetic acid has also been observed, and but addition of anions such as Cl^−^ and ClO~4~^−^ has insignificant effect on the rate. Activation parameters have been evaluated using the Arrhenius and Erying plots. The oxidation products were isolated and characterized. Based on the results obtained, a plausible mechanism involving [Mn(OAc)~4~]^−^ has been proposed. An apparent correlation was noted between the rate of oxidation of these TETPs by Mn(III) in the presence of sulfate ions in sulfuric acid medium and Mn(OAc)~3~ in the acetic acid medium. The rate of oxidation with Mn(OAc)~3~ was observed to be slower than with the former. The rate of oxidation of GGFP was found to be higher than GGIP, GGVP, and GGAP. This may be due to the presence of an aromatic side chain and/or because of the increased hydrophobicity. The overall order of rate of oxidation of TETPs is GGFP > GGIP > GGVP > GGAP, which also represents an increasing order of their hydrophobicity. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 115–123, 2006