Kinetics and Mechanisms of Chlorine Dioxide and Chlorite Oxidations of Cysteine and Glutathione

Abstract

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.

Oxidative removal of diclofenac by chlorine dioxide: Reaction kinetics and mechanism

“…The kinetic experiments were designed under the condition of ClO 2 in excess of DCF ([DCF] 0 =3.00 μM, and [ClO 2 ] 0 =18.9~42.6 μM). When the initial ClO 2 concentration was added from 18.9 μM to 42.6 μM, the removal rate of DCF was increased from 81.9% to 98.0% after 60 s of reaction time, while the ClO 2 consumed during the kinetic investigation was varied correspondingly from 7.29% to 4.08% as observed at 359 nm on an UV-Vis spectrophotometer[33], confirming the negligible amount of ClO 2 loss throughout the experiments. Eq.…”

“…The high concentration of ClO 2 stock solution was standardized just prior to application by idometric titration with a standard sodium thiosulfate solution [32] and the low concentrations of ClO 2 reaction solutions were determined spectrophotometrically based on the molar absorption coefficient of ClO 2 , ε 359 nm =1230 M −1 cm −1 at 359 nm [33]. The pH of the solution was measured using a Mettler Toledo Delta 320 pH, whereas, the reaction temperatures were simultaneously controlled by a HX-08 Cryostat (Shanghai Bilon Instruments Co. Ltd., China).…”

“…HClO species is a much stronger electrophile than ClO 2 − and ClO − [33], thus it may promote the oxidation of DCF by increasing the fraction of deprotonated DCF and HClO in the reaction system. Above pH 7.0, the reaction rates gradually slowed down, as the pH was increased from 7.0 to 10.0, although the fraction of DCF − and ClO − increased, which maybe due to the unfavorable repulsion between ClO − and DCF − anions.…”

“…(2) During the direct oxidization of DCF· by ClO 2 , the oxidant is initially reduced to ClO, then to HClO, and subsequently to Cl − [33]. Therefore, four tentative routes may contribute to the direct oxidization, and occur through oxygen transfer process [31,46] …”

Virus Inactivation Mechanisms: Impact of Disinfectants on Virus Function and Structural Integrity

“…This is consistent with previous studies that demonstrated ClO 2 reacts more readily with amino acids than with nucleotides. 27,50,51 On the protein level, ClO 2 is a selective oxidant, which reacts mainly with Cys, Trp and Tyr. 27 Similar to 1 O 2 , CP degradation was specific and affected mainly peptide Ser84-Lys106 ( Figure 3, SI Table S5).…”