N-Bromosuccinimide assisted oxidation of hydrophobic tetrapeptide sequences of elastin: A mechanistic study

The repeating sequences of elastin, glycyl–glycyl–alanyl–proline (GGAP) glycyl–glycyl–isoleucyl–proline (GGIP) and more hydrophobic glycyl–glycyl–phenylalanyl–proline (GGPP), were synthesized by classical solution phase methods and characterized. The kinetics of oxidation of tetrapeptides (TPs) and their constituent amino acids (AAs) by N-bromosuccinimide (NBS) was studied in the presence of perchlorate ions in acidic medium at 28 °C. The reaction was followed spectrophotometrically at λmax = 240 nm. The reactions follow identical kinetics, being first order each in [NBS], [AA] and [TP]. No effect on the rate of [H+], reduction product [succinimide] and ionic strength was observed. Effects of dielectric constant of the medium and the added anions such as chloride and perchlorate were studied. Activation parameters have been computed. The oxidation products of the reaction were isolated and characterized. The proposed mechanism is consistent with the experimental results. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of AAs and TPs.

Graphical abstractThe repeating sequences of elastin, glycyl–glycyl–alanyl–proline (GGAP), glycyl–glycyl–isoleucyl–proline (GGIP) and more hydrophobic glycyl–glycyl–phenylalanyl–proline (GGPP), were synthesized by classical solution phase methods and characterized. The kinetics of oxidation of tetrapeptides (TPs) and their constituent amino acids (AAs) by N-bromosuccinimide (NBS) was studied in the presence of perchlorate ions in acidic medium at 28 °C. The reaction was followed spectrophotometrically at λmax = 240 nm. The reactions follow identical kinetics, being first order each in [NBS], [AA] and [TP]. No effect on the rate of [H+], reduction product [succinimide] and ionic strength was observed. Effects of dielectric constant of the medium and the added anions such as chloride and perchlorate were studied. Activation parameters have been computed. The oxidation products of the reaction were isolated and characterized. The proposed mechanism is consistent with the experimental results. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of AAs and TPs.