Determination of sulfite radical (SO 3 ? ?) reaction rate constants by means of competition kinetics

Abstract
The sulfite radical anion (SO 3 ⋅ −) was found to react rapidly with the flavonoid quercetin (k = 2.5 × 108 dm3mol−1 s−1) and the carotenoids crocin (k = 1.0 × 109 dm3mol−1 s1−) and crocetin (k = 1.5 × 109 dm3mol1− s1−). The reactions can easily be monitored due to the strong absorptions of the substrates and, in the case of quercetin, the formation of a strongly absorbing transient species. Using these substances, we determined by means of competition kinetics rate constants of SO 3 ⋅ − reactions with nucleic acid components, polyunsaturated fatty acids, and glutathione.