人髓过氧化物酶(MPO)在中性pH值下使用氯化物和硫氰酸盐作为生理底物。由氧化还原中间体化合物I介导的硫氰酸盐氧化为次硫氰酸盐迅速还原了MPO的三价态。在低硫氰酸盐浓度和过氧化氢存在下,观察到的反应顺序为化合物I→铁MPO→化合物II→MPO-氰化物络合物,而在高硫氰酸盐浓度且没有H 2 O 2时唯一观察到的转变是化合物I→MPO铁。MPO铁与次硫氰酸盐的反应直接形成了MPO-氰化物配合物,而由次硫氰酸盐与过氧化氢之间的反应产生的瞬时产物被证明可介导MPO铁向化合物II的转化。讨论并提出了这些反应的机制。
Thiocyanogen as an Intermediate in the Oxidation of Thiocyanate by Hydrogen Peroxide in Acidic Aqueous Solution
摘要:
The kinetics of the reaction of H2O2 With excess SCN- in acidic media was studied by use of TI(IV) as an indicator for the concentration of H2O2. Pseudo-first-order behavior was realized by this method, and these data confirm the acid-catalyzed rate law and rate constant reported some 40 years ago for this reaction under conditions of excess H2O2 Under the same conditions except without Ti(IV), repetitive-scan spectra reveal the formation and decay of an intermediate that absorbs in the UV. In the proposed mechanism, HOSCN is produced in the first step and it is converted rapidly to (SCN)(2) through its equilibrium reaction with SCN-. The observed intermediate is believed to be (SCN)2, which decays on a longer time scale. Excellent global fits of this mechanism to the repetitive-scan data are obtained with rate constants constrained by the Ti(IV) data and published previously in our study of the ClO2/SCN- reaction. These fits yield a spectrum for (SCN)2 that is characterized by lambda (max) = 297 nm and epsilon (297) = 147 M-1 cm(-1) in fine agreement with our prior report.