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Sequence dependence of oxidation of some repeating pentapeptide sequences of elastin with electrolytically generated Mn(III): synthesis, kinetics and mechanistic study
Author(s) -
Gowda D. Channe,
Gowda B. K. Kempe,
Rangappa K. S.
Publication year - 2001
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.417
Subject(s) - chemistry , pentamer , kinetics , reaction rate constant , chloride , arrhenius equation , redox , perchlorate , polymer chemistry , inorganic chemistry , ion , medicinal chemistry , organic chemistry , activation energy , biochemistry , physics , quantum mechanics
The repeating sequence of elastin, valylprolylglycylvalylglycine (VPGVG), its permutation pentamer glycylvalylglycylvalylproline (GVGVP), and its more hydrophobic pentamer glycylphenylalanylglycylvalylproline (GFGVP) were synthesized by classical solution‐phase methods and characterized. The kinetics of the oxidation of these pentapeptides (PP) by Mn(III) was studied in the presence of sulphate ions in acidic medium at 25 °C. The reaction was followed spectrophotometrically at λ max = 500 nm. A first‐order dependence of rate on both [Mn(III)] and [PP] was observed. The rate is independent of concentration of the reduction product, Mn(II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulphate, chloride and perchlorate were studied. Activation parameters were evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of PP 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 an increased rate of oxidation. Further, it was observed that the pentamers with Pro as C‐terminus are more susceptible to oxidation than the pentamer with Gly as C‐terminus. Copyright © 2001 John Wiley & Sons, Ltd.