Issue 8, 2002

Absolute rate constants for the formation of nitrogen-centred radicals from chloramines/amides and their reactions with antioxidants

Abstract

Pulse radiolysis techniques have been employed to investigate the one-electron reduction of a variety of chloramines and chloramides. These include models for the side-chain of Lys (6-aminohexanoic acid chloramine and α-N-acetyl-Lys chloramine), Gly chloramine, β-alanine chloramine and two models of protein backbone amides, the chloramides of cyclo-(Gly)2 and cyclo-(Ala)2. The molar absorption coefficients and stabilities of these chloramines/amides have been determined. The one-electron reduction of these chloramine/amide species by hydrated electrons occurs with second-order rate constants of the order of 109–1010 M−1 s−1, and results in cleavage of the N–Cl bonds to yield nitrogen-centred radicals and chloride ions (as measured by high performance ion chromatography). The reactivities of the nitrogen-centred radicals have been investigated with the readily oxidisable quenchers, hydroquinone and Trolox. These quenchers were used as models of the in vivo antioxidants, ubiquinol-10 and α-tocopherol, and react with second-order rate constants between 2 × 107 and 1 × 108 M−1 s−1. No evidence was obtained in these pulse radiolysis experiments for a rapid rearrangement of the oxidising nitrogen-centred radicals to reducing carbon-centred radicals, though such reactions have been indicated in previous EPR studies.

Graphical abstract: Absolute rate constants for the formation of nitrogen-centred radicals from chloramines/amides and their reactions with antioxidants

Article information

Article type
Paper
Submitted
12 Mar 2002
Accepted
29 May 2002
First published
20 Jun 2002

J. Chem. Soc., Perkin Trans. 2, 2002, 1461-1467

Absolute rate constants for the formation of nitrogen-centred radicals from chloramines/amides and their reactions with antioxidants

D. I. Pattison, M. J. Davies and K. Asmus, J. Chem. Soc., Perkin Trans. 2, 2002, 1461 DOI: 10.1039/B202526D

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