The Properties of Biologically Significant Chloramine Oxidants: Reactivity and Its Dependence on the Structure of the Functional Atom Group

Resumo

A procedure for the direct photometric determination of rate constants for the oxidation of dithiothreitol (a thiol-compound example) by N-chlorotaurine and N-chloroglycine and their analogues that have a different structure of the reaction center was developed. The time dependences of the sum of the chloramine oxidant absorbance and the absorbance of dithiane (the product of the dithiothreitol conversion) were calculated for different values of the bimolecular rate constant. The value of the rate constant was considered as established when the best agreement between the calculated curve and the measured kinetic curve of absorbance was observed. The oxidative activities of monochloramine oxidants showed little difference: the rate constants for N-chlorotaurine, N-chloroglycine, and N-chloro-2,2-dimethyltaurine were equal to 170 ± 4, 235 ± 9.8, and 145 ± 4.3 M^–1 s^–1, respectively. When the reaction center structure was modified by introducing the substituents of the hydrogen atom into the chloramine group, the activities of the compounds changed dramatically: the rate constants for N-isopropyl-N-chlorotaurine, N,N-dichloro-2,2-dimethyltaurine and N-acetyl-N-chloro- 2,2-dimethyltaurine determined using the competitive kinetics method were 9 ± 0.5, 12 000 ± 950 and 25 300 ± 3000 M^–1 s^–1, respectively. The reactivity of N-chloroglycine and the structural analogues of taurine chloramine with respect to thiol-compounds correlates with the magnitude of the active chlorine charge. Predictions about the reactivity of unknown structural analogues of N-chloramino acids and N-chlorotaurine were obtained.