Kinetics and Mechanisms of Chlorine Dioxide Oxidation of Tryptophan

Abstract

The reactions of aqueous ClO2 (*) and tryptophan (Trp) are investigated by stopped-flow kinetics, and the products are identified by high-performance liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry and by ion chromatography. The rates of ClO2 (*) loss increase from pH 3 to 5, are essentially constant from pH 5 to 7, and increase from pH 7 to 10. The reactions are first-order in Trp with variable order in ClO2 (*). Below pH 5.0, the reactions are second- or mixed-order in [ClO2 (*)], depending on the chlorite concentration. Above pH 5.0, the reactions are first-order in [ClO2 (*)] in the absence of added chlorite. At pH 7.0, the Trp reaction with ClO2 (*) is first-order in each reactant with a second-order rate constant of 3.4 x 10(4) M(-1) s(-1) at 25.0 degrees C. In the proposed mechanism, the initial reaction is a one-electron oxidation to form a tryptophyl radical cation and chlorite ion. The radical cation deprotonates to form a neutral tryptophyl radical that combines rapidly with a second ClO 2 (*) to give an observable, short-lived adduct ( k obs = 48 s(-1)) with proposed C(H)-OClO bonding. This adduct decays to give HOCl in a three-electron oxidation. The overall reaction consumes two ClO2 (*) per Trp and forms ClO2- and HOCl. This corresponds to a four-electron oxidation. Decay of the tryptophyl-OClO adduct at pH 6.4 gives five initial products that are observed after 2 min and are separated by HPLC with elution times that vary from 4 to 17 min (with an eluent of 6.3% CH 3OH and 0.1% CH 3COOH). Each of these products is characterized by mass spectrometry and UV-vis spectroscopy. One initial product with a molecular weight of 236 decays within 47 min to yield the most stable product, N-formylkynurenine (NFK), which also has a molecular weight of 236. Other products also are observed and examined.

Subtle Differences in Virus Composition Affect Disinfection Kinetics and Mechanisms

“…Interestingly, not all of the peptides in this region contained amino acids susceptible to ClO 2 (see Table S7 in the supplemental material). Their degradation can be explained by the fact that ClO 2 is a one-electron acceptor that can create radicals upon reaction (41). This can trigger radical chain reactions that damage adjacent parts of the protein, as has been observed previously with hydroxyl radicals (42).…”

“…The lack of genome damage is surprising given that the rather small size of the chlorine dioxide molecule should allow it to penetrate the virus capsid by way of the 1-to 2-nm pores in the capsid and to access the genome. The absence of genome damage may be explained by the fact that chlorine dioxide reacts more rapidly with some amino acids than with nucleotides (e.g., tryptophan reacts at least 75 times faster than the most susceptible nucleotide, G [11,41]) (see Table S7 in the supplemental material). Hence, by the time detectable genome damage has accumulated, the virus may have already been inactivated as a result of protein damage.…”

Inactivation Kinetics and Mechanism of a Human Norovirus Surrogate on Stainless Steel Coupons via Chlorine Dioxide Gas

“…We found that the mechanism of MNV-1 inactivation by ClO 2 involved damage to the integrity of the viral capsid structure and degradation of the viral capsid protein and viral genomic RNA. ClO 2 reacts with amino acids with electron-rich side chains, such as tryptophan, tyrosine, cysteine, and histidine (56)(57)(58)(59)(60), which leads to the disruption of primary and secondary structures, which ultimately results in the degradation of the viral capsid protein, VP1. Hauchman and others (61) found that naked viral RNA was more susceptible to degradation than RNA extracted from treated virus particles, suggesting that genomic RNA inside intact viral particles was partially protected from ClO 2 treatment.…”

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

“…However, in some cases, the decay of ClO 2 might follow the mixed-order or second-order kinetics [35,36]. Initially, the experiments were conducted at pH 7.0 and 298 K to determine the rate law of the reaction between ClO 2 and DCF.…”