Kinetics and Mechanisms of Chlorine Dioxide Oxidation of Tryptophan

Permeation of photochemically-generated gaseous chlorine dioxide on Mars as a significant factor in destroying subsurface organic compounds

It has been shown that ultraviolet (UV) irradiation is responsible for the destruction of organic compounds on the surface of Mars. When combined with the photochemically-driven production of oxychlorines (ClOx) it can generate highly reactive species that can alter or destroy organic compounds. However, it has been assumed that since UV only penetrates the top few millimeters of the martian regolith, reactive ClOx oxidants are only produced on the surface. Of all the oxychlorine intermediates produced, gaseous chlorine dioxide [ClO2(g)] is of particular interest, being a highly reactive gas with the ability to oxidize organic compounds. Here we report on a set of experiments under Mars ambient conditions showing the production and permeation of ClO2(g) and its reaction with alanine as a test compound. Contrary to the accepted paradigm that UV irradiation on Mars only interacts with a thin layer of surface regolith, our results show that photochemically-generated ClO2(g) can permeate below the surface, depositing ClOx species (mainly Cl- and ClO 3 - ) and destroying organic compounds. With varying levels of humidity and abundant chloride and oxychlorines on Mars, our findings show that permeation of ClO2(g) must be considered as a significant contributing factor in altering, fragmenting, or potentially destroying buried organic compounds on Mars.

Virus on surfaces: Chemical mechanism, influence factors, disinfection strategies, and implications for virus repelling surface design

While SARS-CoV-2 is generally under control, the question of variants and infections still persists. Fundamental information on how the virus interacts with inanimate surfaces commonly found in our daily life and when in contact with the skin will be helpful in developing strategies to inhibit the spread of the virus. Here in, a critically important review of current understanding of the interaction between virus and surface is summarized from chemistry point-of-view. The Derjaguin-Landau-Verwey-Overbeek and extended Derjaguin-Landau-Verwey-Overbeek theories to model virus attachments on surfaces are introduced, along with the interaction type and strength, and quantification of each component. The virus survival and transfer are affected by a combination of biological, physical, and chemical parameters, as well as environmental parameters. The surface properties for virus and virus survival on typical surfaces such as metals, plastics, and glass are summarized. Attention is also paid to the transfer of virus to/from surfaces and skin. Typical virus disinfection strategies utilizing heat, light, chemicals, and ozone are discussed together with their disinfection mechanism. In the last section, design principles for virus repelling surface chemistry such as surperhydrophobic or surperhydrophilic surfaces are also introduced, to demonstrate how the integration of surface property control and advanced material fabrication can lead to the development of functional surfaces for mitigating the effect of viral infection upon contact.

Reaction of Polyamide Membrane Model Monomers with Chlorine Dioxide: Kinetics, Pathways, and Implications

Aromatic polyamide (PA) based membranes are widely used for reverse osmosis (RO), but they can be degraded by free chlorine used for controlling the biofouling prior to RO treatment. Kinetics and mechanisms for the reactions of PA membrane model monomers, i.e., benzanilide (BA), and acetanilide (AC), with chlorine dioxide (ClO₂) were investigated in this study. Rate constants for the reactions of ClO₂ with BA and AC at pH 8.3 and 21°C were determined to be (4.1±0.1) × 10^-1 M^-1.24 s^-1 and (6.0±0.1) × 10^-3 M^-1 s^-1, respectively. These reactions are base assisted with a strong pH dependence. The activation energies of BA and AC degradation by ClO₂ were 123.7 and 81.0 kJ mol^-1, respectively. This indicates a relatively strong temperature dependence in the studied temperature range of 21-35 °C. The presence of bromide and natural organic matter does not promote the degradation of model monomers by ClO₂. BA was degraded by ClO₂ via two pathways: (1) the attack on the anilide moiety with the formation of benzamide (major pathway) and (2) oxidative hydrolysis to benzoic acid (minor pathway). A kinetic model was developed to simulate the degradation of BA and formation of byproducts during ClO₂ pretreatment, and simulations agree well with the experimental data. Half-lives of BA treated by ClO₂ were 1-5 orders of magnitude longer than chlorine under typical seawater treatment conditions. These novel findings suggest the potential application of ClO₂ for controlling biofouling ahead of RO treatment at desalination treatments.

Overlooked Contribution of the Indole Moiety to the Formation of Haloacetonitrile Disinfection Byproducts

Haloacetonitriles (HANs) are a group of disinfection byproducts with high toxicity and frequent occurrence. Past studies have focused on the free amine groups, especially those in amino acids, as HAN precursors. This study reports, for the first time, that the indole moiety such as that in the tryptophan side chain is also a potent precursor for the most common HANs dichloroacetonitrile, bromochloroacetonitrile, and dibromoacetonitrile. 3-Indolepropionic acid, differing from tryptophan only in the absence of the free amine group, formed HANs at levels 57-76% of those by tryptophan at a halogen/nitrogen molar ratio of 10. Experiments with tryptophan-(amino-¹⁵N) showed that the indole contributed to 28-51% of the HANs formed by tryptophan. At low oxidant excess (e.g., halogen/precursor = 5), 3-indolepropionic acid even formed more HANs than Trp by 3.5-, 2.5-, and 1.8-fold during free chlorination, free bromination, and chlorination in the presence of bromide (0.6 mg/L), respectively. Indole's HAN formation pathway was investigated by exploring the chlorination/bromination products of 3-indolepropionic acid using liquid chromatography-orbitrap high-resolution mass spectrometry. A total of 22 intermediates were detected, including pyrrole ring-opening products with an N-formyl group, 2-substituted anilines with different hydroxyl/halogen substitutions, and an intermediate with a postulated non-aromatic ring structure.

Bacterial inactivation processes in water disinfection - mechanistic aspects of primary and secondary oxidants - A critical review

Water disinfection during drinking water production is one of the most important processes to ensure safe drinking water, which is gaining even more importance due to the increasing impact of climate change. With specific reaction partners, chemical oxidants can form secondary oxidants, which can cause additional damage to bacteria. Cases in point are chlorine dioxide which forms free available chlorine (e.g., in the reaction with phenol) and ozone which can form hydroxyl radicals (e.g., during the reaction with natural organic matter). The present work reviews the complex interplay of all these reactive species which can occur in disinfection processes and their potential to affect disinfection processes. A quantitative overview of their disinfection strength based on inactivation kinetics and typical exposures is provided. By unifying the current data for different oxidants it was observable that cultivated wild strains (e.g., from wastewater treatment plants) are in general more resistant towards chemical oxidants compared to lab-cultivated strains from the same bacterium. Furthermore, it could be shown that for selective strains chlorine dioxide is the strongest disinfectant (highest maximum inactivation), however as a broadband disinfectant ozone showed the highest strength (highest average inactivation). Details in inactivation mechanisms regarding possible target structures and reaction mechanisms are provided. Thereby the formation of secondary oxidants and their role in inactivation of pathogens is decently discussed. Eventually, possible defense responses of bacteria and additional effects which can occur in vivo are discussed.

Chlorine Dioxide: Friend or Foe for Cell Biomolecules? A Chemical Approach

This review examines the role of chlorine dioxide (ClO₂) on inorganic compounds and cell biomolecules. As a disinfectant also present in drinking water, ClO₂ helps to destroy bacteria, viruses, and some parasites. The Environmental Protection Agency EPA regulates the maximum concentration of chlorine dioxide in drinking water to be no more than 0.8 ppm. In any case, human consumption must be strictly regulated since, given its highly reactive nature, it can react with and oxidize many of the inorganic compounds found in natural waters. Simultaneously, chlorine dioxide reacts with natural organic matter in water, including humic and fulvic acids, forming oxidized organic compounds such as aldehydes and carboxylic acids, and rapidly oxidizes phenolic compounds, amines, amino acids, peptides, and proteins, as well as the nicotinamide adenine dinucleotide NADH, responsible for electron and proton exchange and energy production in all cells. The influence of ClO₂ on biomolecules is derived from its interference with redox processes, modifying the electrochemical balances in mitochondrial and cell membranes. This discourages its use on an individual basis and without specialized monitoring by health professionals.

New Countermeasures Against Infections with/after COVID-19: Is Chlorine Dioxide a Useful and Safe Disinfectant?

Pandemics of microorganism are serious problem such as corona virus induced disease 2019(COVID-19), and the infectious diseases rapidly transmitted via airborne or aerosol among community space. To prevent aerosol infections, ozone and chlorine dioxide gases are practical methods in room air. However, ozone requires relatively high concentrations for this purpose, which might be toxic to humans present in the room. On the other hand, the low concentration of chlorine dioxide gas and aqueous solution are sufficiently effective against aerosol infection for the causative microorganism, and it is expected that when it is used in combination with a high-efficiency particulate air filter, it will be highly safe with high prevention effect and cost effectiveness.

Concerted and Stepwise Proton-Coupled Electron Transfer for Tryptophan-Derivative Oxidation with Water as the Primary Proton Acceptor: Clarifying a Controversy

Concerted electron-proton transfer (CEPT) reactions avoid charged intermediates and may be energetically favorable for redox and radical-transfer reactions in natural and synthetic systems. Tryptophan (W) often partakes in radical-transfer chains in nature but has been proposed to only undergo sequential electron transfer followed by proton transfer when water is the primary proton acceptor. Nevertheless, our group has shown that oxidation of freely solvated tyrosine and W often exhibit weakly pH-dependent proton-coupled electron transfer (PCET) rate constants with moderate kinetic isotope effects (KIE ≈ 2-5), which could be associated with a CEPT mechanism. These results and conclusions have been questioned. Here, we present PCET rate constants for W derivatives with oxidized Ru- and Zn-porphyrin photosensitizers, extracted from laser flash-quench studies. Alternative quenching/photo-oxidation methods were used to avoid complications of previous studies, and both the amine and carboxylic acid groups of W were protected to make the indole the only deprotonable group. With a suitably tuned oxidant strength, we found an ET-limited reaction at pH < 4 and weakly pH-dependent rates at pH > ∼5 that are intrinsic to the PCET of the indole group with water (H₂O) as the proton acceptor. The observed rate constants are up to more than 100 times higher than those measured for initial electron transfer, excluding the electron-first mechanism. Instead, the reaction can be attributed to CEPT. These conclusions are important for our view of CEPT in water and of PCET-mediated radical reactions with solvent-exposed tryptophan in natural systems.

Inactivation of Spores and Vegetative Forms of Clostridioides difficile by Chemical Biocides: Mechanisms of Biocidal Activity, Methods of Evaluation, and Environmental Aspects

Clostridioides difficile infections (CDIs) are the most common cause of acquired diseases in hospitalized patients. Effective surface disinfection, focused on the inactivation of the spores of this pathogen, is a decisive factor in reducing the number of nosocomial cases of CDI infections. An efficient disinfection procedure is the result of both the properties of the biocidal agent used and the technology of its implementation as well as a reliable, experimental methodology for assessing the activity of the biocidal active substance based on laboratory models that adequately represent real clinical conditions. This study reviews the state of knowledge regarding the properties and biochemical basis of the action mechanisms of sporicidal substances, with emphasis on chlorine dioxide (ClO₂). Among the analyzed biocides, in addition to ClO₂, active chlorine, hydrogen peroxide, peracetic acid, and glutaraldehyde were characterized. Due to the relatively high sporicidal effectiveness and effective control of bacterial biofilm, as well as safety in a health and environmental context, the use of ClO₂ is an attractive alternative in the control of nosocomial infections of CD etiology. In terms of the methods of assessing the biocidal effectiveness, suspension and carrier standards are discussed.

The occurrence and control of waterborne viruses in drinking water treatment: A review

As the coronavirus disease 2019 continues to spread globally, its culprit, the severe acute respiratory syndrome coronavirus 2 has been brought under scrutiny. In addition to inhalation transmission, the possible fecal-oral viral transmission via water/wastewater has also been brought under the spotlight, necessitating a timely global review on the current knowledge about waterborne viruses in drinking water treatment system - the very barrier that intercepts waterborne pathogens to terminal water users. In this article we reviewed the occurrence, concentration methods, and control strategies, also, treatment performance on waterborne viruses during drinking water treatment were summarized. Additionally, we emphasized the potential of applying the quantitative microbial risk assessment to guide drinking water treatment to mitigate the viral exposure risks, especially when the unregulated novel viral pathogens are of concern. This review paves road for better control of viruses at drinking water treatment plants to protect public health.

Characteristics and transformation pathways of venlafaxine degradation during disinfection processes using free chlorine and chlorine dioxide

Venlafaxine, a representative antidepressant, has been detected frequently in aquatic environments. The treatment of venlafaxine by free chlorine (NaOCl) and chlorine dioxide (ClO₂) was investigated in this study. The effects of operational variables and the water matrix on venlafaxine degradation were evaluated. The transformation pathways of venlafaxine were also studied. The results indicated that venlafaxine was removed efficiently during disinfection processes, especially when reacted with ClO₂. A higher dosage of disinfectant and mildly alkaline conditions (pH 9) enhanced the degradation of venlafaxine. The reactions were impacted when the tests were conducted in real water matrices, especially in secondary effluent. The presence of chloride and low concentrations of fulvic acid enhanced venlafaxine decomposition. The presence of Br^- also accelerated the reaction between venlafaxine and NaOCl. However, NO₂^- inhibited venlafaxine removal in both disinfection processes. Six intermediates were identified during venlafaxine degradation by ultrahigh-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry, and the main reactions included dehydration and demethylation.

Kinetics and Mechanisms of Virus Inactivation by Chlorine Dioxide in Water Treatment: A Review

Chlorine dioxide (ClO₂), an alternative disinfectant to chlorine, has been widely applied in water and wastewater disinfection. This paper aims at presenting an overview of the inactivation kinetics and mechanisms of ClO₂ with viruses. The inactivation efficiencies vary greatly among different virus species. The inactivation rates for different serotypes within a family of viruses can differ by over 284%. Generally, to achieve a 4-log removal, the exposure doses, also being referred to as Ct values (mutiplying the concentration of ClO₂ and contact time) vary in the range of 0.06-10 mg L^-1 min. Inactivation kinetics of viruses show two phases: an initial rapid inactivation phase followed by a tailing phase. Inactivation rates of viruses increase as pH or temperature increases, but show different trends with increasing concentrations of dissolved organic matter (DOM). Both damages in viral proteins and in the 5' noncoding region within the genome contribute to virus inactivation upon ClO₂ disinfection.

Lignin-Derived Non-Heme Iron and Manganese Complexes: Catalysts for the On-Demand Production of Chlorine Dioxide in Water under Mild Conditions

A lignin-derived ligand, bis(2-hydroxy-3-methoxy-5-propylbenzyl)glycine (DHEG), was synthesized from 2-methoxy-4-propylphenol (dihydroeugenol (DHE)) and the amino acid glycine. Two mononuclear iron and manganese complexes of DHEG were prepared, characterized, and employed for the oxidation of chlorite to chlorine dioxide in aqueous solution. Peroxyacetic acid (PAA) was used as a "green" oxidant in the redox reactions to initiate the formation of high-valent Fe and Mn (IV)-OH intermediates. EPR studies verified the formation of a high-valent Mn^IV species. Both Fe and Mn complexes catalyzed chlorite oxidation with bimolecular rate constants of 32 and 144 M^-1 s^-1, respectively, at pH 4.0 and 25 °C. The Mn complex was found to be more efficient for chlorite oxidation with a turnover frequency of 17 h^-1 and remained active during subsequent additions of PAA. The rate of ClO₂ decomposition with PAA/Mn-DHEG was first order in PAA and increased significantly as pH increased. A mechanism that accounts for all observations is presented.

Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: Electron donating capacity and UV absorbance as surrogate parameters

Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO₂), ozone (O₃), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV₂₅₄) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV₂₅₄ abatement ranked in the order O₃ > Mn(VII) > Fe(VI)/ClO₂, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO₂ > Fe(VI) > O₃ and two phases were observed. At low specific ClO₂, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV₂₅₄ compared to the EDC was observed (~ 8% EDC abatement per 1% UV₂₅₄ abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV₂₅₄ and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV₂₅₄ (~ 0.9-1.2% EDC abatement per 1% UV₂₅₄ abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O₃ abated the relative UV₂₅₄ more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO₂ and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O₃ pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants_, trihalomethane formation was poorly correlated with both EDC and UV_254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV₂₅₄ measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.

ClO2 pre-oxidation impacts the formation and nitrogen origins of dichloroacetonitrile and dichloroacetamide during subsequent chloramination

Chlorine dioxide (ClO₂) can be used as a pre-oxidant when chloramination is performed in water treatment plants. However, the effects of ClO₂ pre-oxidation on the formation of nitrogenous disinfection by-products, such as dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm), during chloramination are not well understood. In this study, the effects of ClO₂ pre-oxidation on the formation of DCAN and DCAcAm during chloramination of 28 model compounds and seven real water samples were investigated. The sources of nitrogen for DCAN and DCAcAm formation were investigated using ¹⁵N-labeled monochloramine. ClO₂ pre-oxidation affected DCAN and DCAcAm formation during chloramination of model compounds in different ways. ClO₂ pre-oxidation increased unlabeled and ¹⁵N-labeled DCAN and DCAcAm formation during chloramination of six amino acids and peptides and five indoles and tertiary amines. ClO₂ pre-oxidation decreased DCAN formation but increased DCAcAm formation during chloramination of three hydroxybenzamide compounds, but had the opposite effects for four tetracyclines. ClO₂ pre-oxidation generally decreased DCAN and DCAcAm formation during chloramination of the phenolic compounds that are precursors not containing nitrogen. 2-Aminoacetophenone, formamid-trans-muconic acid, and unsaturated ketones were found to be transformation products of ClO₂ oxidation of 3-methylindole, salicylamide, and resorcinol, respectively. Possible DCAN and DCAcAm formation pathways during chloramination after ClO₂ oxidation were identified. For most of the water samples, ClO₂ pre-oxidation decreased the amounts of DCAN and DCAcAm formed during chloramination by 36%-70% and 11%-59%, respectively. This may have been caused by ClO₂ oxidation destroying phenolic precursors and macromolecular proteins rather than amino acids in the water samples.

Comparative study of hyperpure chlorine dioxide with two other irrigants regarding the viability of periodontal ligament stem cells

Objectives

Periodontal ligament stem cells (PDLSCs) have an underlined significance as their high proliferative capacity and multipotent differentiation provide an important therapeutic potential. The integrity of these cells is frequently disturbed by the routinely used irrigative compounds applied as periodontal or endodontic disinfectants (e.g., hydrogen peroxide (H₂O₂) and chlorhexidine (CHX)). Our objectives were (i) to monitor the cytotoxic effect of a novel dental irrigative compound, chlorine dioxide (ClO₂), compared to two traditional agents (H₂O₂, CHX) on PDLSCs and (ii) to test whether the aging factor of PDLSC cultures determines cellular responsiveness to the chemicals tested.

Methods

Impedimetry (concentration-response study), WST-1 assays (WST = water soluble tetrazolium salt), and morphology analysis were performed to measure changes in cell viability induced by the 3 disinfectants; immunocytochemistry of stem cell markers (STRO-1, CD90, and CD105) measured the induced mesenchymal characteristics.

Results

Cell viability experiments demonstrated that the application of ClO₂ does not lead to a significant decrease in viability of PLDSCs in concentrations used to kill microbes. On the contrary, traditional irrigants, H₂O₂, and CHX are highly toxic on PDLSCs. Aging of PLDSC cultures (passages 3 vs. 7) has characteristic effects on their responsiveness to these agents as the increased expression of mesenchymal stem cell markers turns to decreased.

Conclusions and clinical relevance

While the active ingredients of mouthwash (H₂O₂, CHX) applied in endodontic or periodontitis management have a serious toxic effect on PDLSCs, the novel hyperpure ClO₂ is less toxic providing an environment favoring dental structure regenerations during disinfectant interventions.

Electronic supplementary material

The online version of this article (10.1007/s00784-020-03618-5) contains supplementary material, which is available to authorized users.

Oxidative degradation and mineralization of bentazone from water

Bentazone degradation efficiency and mineralization in water solutions using chlorine dioxide treatment were evaluated. Double distilled water and a river water sample spiked with bentazone were studied and compared after chlorine dioxide treatment. Degradation efficiency was determined using high-performance liquid chromatography (HPLC). Daphnia magna toxicity testing and total organic carbon (TOC) analysis were used to ascertain the toxicity of the degraded solutions and mineralization degree. Bentazone degradation products were identified using gas chromatography with a triple quadrupole mass detector (GC-MS-MS). A simple mechanistic scheme for oxidative degradation of bentazone was proposed based on the degradation products that were identified. Decrease in D. magna mortality, high degradation efficiency and partial bentazone mineralization were achieved by waters containing bentazone degradation products, which indicate the formation of less toxic compounds than the parent bentazone and effective removal of bentazone from the waters. Bentazone degraded into four main degradation products. Humic acid from Sava River water influenced bentazone degradation, resulting in a lower degradation efficiency in this matrix (about 10% lower than in distilled water). Chlorine dioxide treatment of water to degrade bentazone is efficient and offers a novel approach in the development of new technology for removal of this herbicide from contaminated water.

Exploration of reaction rates of chlorine dioxide with tryptophan residue in oligopeptides and proteins

Chlorine dioxide (ClO₂), an alternative disinfectant to chlorine, has a superior ability to inactivate microorganisms, in which protein damage has been considered as the main inactivation mechanism. However, the reactivity of ClO₂ with amino acid residues in oligopeptides and proteins remains poorly investigated. In this research, we studied the reaction rate constants of ClO₂ with tryptophan residues in five heptapeptides and four proteins using stopped-flow or competition kinetic method. Each heptapeptide and protein contain only one tryptophan residue and the reactivity of tryptophan residue with ClO₂ was lower than that of free tryptophan (3.88 × 10⁴ (mol/L)^-1sec^-1 at pH 7.0). The neighboring amino acid residues affected the reaction rates through promoting inter-peptide aggregation, changing electron density, shifting pK_a values or inducing electron transfer via redox reactions. A single amino acid residue difference in oligopeptides can make the reaction rate constants differ by over 60% (e.g. 3.01 × 10⁴ (mol/L)^-1sec^-1 for DDDWNDD and 1.85 × 10⁴ (mol/L)^-1sec^-1 for DDDWDDD at pH 7.0 (D: aspartic acid, W: tryptophan, N: asparagine)). The reaction rates of tryptophan-containing oligopeptides were also highly pH-dependent with higher reactivity for deprotonated tryptophan than the neutral specie. Tryptophan residues in proteins spanned a 4-fold range reactivity toward ClO₂ (i.e. 0.84 × 10⁴ (mol/L)^-1sec^-1 for ribonuclease T1 and 3.21 × 10⁴ (mol/L)^-1sec^-1 for melittin at pH 7.0) with accessibility to the oxidant as the determinating factor. The local environment surrounding the tryptophan residue in proteins can also accelerate the reaction rates by increasing the electron density of the indole ring of tryptophan or inhibit the reaction rates by inducing electron transfer reactions. The results are of significance in advancing understanding of ClO₂ oxidative reactions with proteins and microbial inactivation mechanisms.

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

Chlorine dioxide (ClO₂) degradation of the organophosphorus pesticides azamethiphos (AZA) and dimethoate (DM) (10 mg/L) in deionized water and in Sava River water was investigated for the first time. Pesticide degradation was studied in terms of ClO₂ level (5 and 10 mg/L), degradation duration (0.5, 1, 2, 3, 6, and 24 h), pH (3.00, 7.00, and 9.00), and under light/dark conditions in deionized water. Degradation was monitored using high-performance liquid chromatography. Gas chromatography coupled with triple quadrupole mass detector was used to identify degradation products of pesticides. Total organic carbon was measured to determine the extent of mineralization after pesticide degradation. Real river water was used under recommended conditions to study the influence of organic matter on pesticide degradation. High degradation efficiency (88-100% for AZA and 85-98% for DM) was achieved in deionized water under various conditions, proving the flexibility of ClO₂ degradation for the examined organophosphorus pesticides. In Sava River water, however, extended treatment duration achieved lower degradation efficiency, so ClO₂ oxidized both the pesticides and dissolved organic matter in parallel. After degradation, AZA produced four identified products (6-chlorooxazolo[4,5-b]pyridin-2(3H)-one; O,O,S-trimethyl phosphorothioate; 6-chloro-3-(hydroxymethyl)oxazolo[4,5-b]pyridin-2(3H)-one; O,O-dimethyl S-hydrogen phosphorothioate) and DM produced three (O,O-dimethyl S-(2-(methylamino)-2-oxoethyl) phosphorothioate; e.g., omethoate; S-(2-(methylamino)-2-oxoethyl) O,O-dihydrogen phosphorothioate; O,O,S-trimethyl phosphorodithioate). Simple pesticide degradation mechanisms were deduced. Daphnia magna toxicity tests showed degradation products were less toxic than parent compounds. These results contribute to our understanding of the multiple influences that organophosphorus pesticides and their degradation products have on environmental ecosystems and to improving pesticide removal processes from water.

Volatile organic chloramines formation during ClO2 treatment

Volatile organic chloramines are reported as the disinfection byproducts during chlorination or chloramination. However, ClO₂, as an important alternative disinfectant for chlorine, was not considered to produce halogenated amines. In the present work, volatile organic chloramines including (CH₃)₂NCl and CH₃NCl₂ were found to be generated during the reaction of ClO₂ and the dye pollutants. (CH₃)₂NCl was the dominant volatile DBP to result from ClO₂ treated all four dye pollutants including Methyl Orange, Methyl Red, Methylene Blue and Malachite Green, with molar yields ranging from 2.6% to 38.5% at a ClO₂ to precursor (ClO₂/P) molar ratio of 10. HOCl was identified and proved to be the reactive species for the formation of (CH₃)₂NCl, which implied (CH₃)₂NCl was transformed by a combined oxidation of ClO₂ and hypochlorous acid. (CH₃)₂NCl concentrations in the ppb range were observed when real water samples were treated by ClO₂ in the presence of the dye pollutants. The results suggest that these azo dyes are one of the significant precursors for the formation of HOCl during ClO₂ treatment and that organic chloramines should be considered in ClO₂ disinfection chemistry and water treatment.

Can chlorine dioxide prevent the spreading of coronavirus or other viral infections? Medical hypotheses

Motivation

Viruses have caused many epidemics throughout human history. The novel coronavirus [10] is just the latest example. A new viral outbreak can be unpredictable, and development of specific defense tools and countermeasures against the new virus remains time-consuming even in today's era of modern medical science and technology. In the lack of effective and specific medication or vaccination, it would be desirable to have a nonspecific protocol or substance to render the virus inactive, a substance/protocol, which could be applied whenever a new viral outbreak occurs. This is especially important in cases when the emerging new virus is as infectious as SARS-CoV-2 [4].

Aims and structure of the present communication

In this editorial, we propose to consider the possibility of developing and implementing antiviral protocols by applying high purity aqueous chlorine dioxide (ClO2) solutions. The aim of this proposal is to initiate research that could lead to the introduction of practical and effective antiviral protocols. To this end, we first discuss some important properties of the ClO2 molecule, which make it an advantageous antiviral agent, then some earlier results of ClO2 gas application against viruses will be reviewed. Finally, we hypothesize on methods to control the spread of viral infections using aqueous ClO2 solutions.

Chlorite formation during ClO2 oxidation of model compounds having various functional groups and humic substances

Chlorine dioxide (ClO₂) has been used as an alternative to chlorine in water purification to reduce the formation of halogenated by-products and give superior inactivation of microorganisms. However, the formation of chlorite (ClO₂^-) is a major consideration in the application of ClO₂. In order to improve understanding in ClO₂^- formation kinetics and mechanisms, this study investigated the reactions of ClO₂ with 30 model compounds, 10 humic substances and 2 surface waters. ClO₂^- yields were found to be dependent on the distribution of functional groups. ClO₂ oxidation of amines, di- and tri-hydroxybenzenes at pH 7.0 had ClO₂^- yields >50%, while oxidation of olefins, thiols and benzoquinones had ClO₂^- yields <50%. ClO₂^- yields from humic substances depended on the ClO₂ dose, pH and varied with different reaction intervals, which mirrored the behavior of the model compounds. Phenolic moieties served as dominant fast-reacting precursors (during the first 5 min of disinfection). Aromatic precursors (e.g., non-phenolic lignins or benzoquinones) contributed to ClO₂^- formation over longer reaction time (up to 24  h). The total antioxidant capacity (indication of the amount of electron-donating moieties) determined by the Folin-Ciocalteu method was a good indicator of ClO₂-reactive precursors in waters, which correlated with the ClO₂ demand of waters. Waters bearing high total antioxidant capacity tended to generate more ClO₂^- at equivalent ClO₂ exposure, but the prediction in natural water should be conservative.

In Situ Formation of Free Chlorine During ClO2 Treatment: Implications on the Formation of Disinfection Byproducts

Chlorine dioxide (ClO₂) is commonly used as an alternative disinfectant to chlorine in drinking water treatment because it produces limited concentrations of halogenated organic disinfection byproducts. During drinking water treatment, the primary ClO₂ byproducts are the chlorite (50-70%) and the chlorate ions (0-30%). However, a significant portion of the ClO₂ remains unaccounted for. This study demonstrates that when ClO₂ was reacting with phenol, one mole of free available chlorine (FAC) was produced per two moles of consumed ClO₂. The in situ formed FAC completed the mass balance on Cl for inorganic ClO₂ byproducts (FAC + ClO₂^- + ClO₃^-). When reacting with organic matter extracts at near neutral conditions (pH 6.5-8.1), ClO₂ also yielded a significant amount of FAC (up to 25%). Up to 27% of this in situ formed FAC was incorporated in organic matter forming adsorbable organic chlorine, which accounted for up to 7% of the initial ClO₂ dose. Only low concentrations of regulated trihalomethanes were produced because of an efficient mitigation of their precursors by ClO₂ oxidation. Conversely, dichloroacetonitrile formation from ClO₂-induced generation of FAC was higher than from addition of FAC in absence of ClO₂. Overall, these findings provide important information on the formation of FAC and disinfection byproducts during drinking water treatment with ClO₂.

Chlorine Dioxide-Pollutant Transformation and Formation of Hypochlorous Acid as a Secondary Oxidant

Chlorine dioxide (ClO₂) has been used as a disinfectant in water treatment for a long time, and its use for micropollutant abatement in wastewater has recently been suggested. Surprisingly, a mechanistic understanding of ClO₂ reactions in (waste)water matrices is largely lacking. The present study contributes to this mechanistic understanding by performing a detailed investigation of ClO₂ reactions with organic matter using phenol as a surrogate for reactive phenolic moieties. A concept for indirectly determining HOCl using 2- and 4-bromophenol was developed. The reaction of phenol with ClO₂ formed chlorite (62 ± 4% per ClO₂ consumed) and hypochlorous acid (HOCl) (42 ± 3% per ClO₂ consumed). The addition of ClO₂ to wastewater (5 × 10^-5 M ClO₂) resulted in 40% atenolol and 47% metoprolol transformation. The presence of the selective HOCl scavenger glycine largely diminished their transformation, indicating that atenolol and metoprolol were transformed by a fast reaction with HOCl (e.g., k (atenolol + HOCl) = 3.5 × 10⁴ M^-1 s^-1) that formed in ClO₂ reactions with the wastewater matrix. The formation of HOCl may thus increase the number of transformable micropollutants in ClO₂ applications. However, chlorine related byproducts may also be formed.

Degradation of triclosan by chlorine dioxide: Reaction mechanism,2,4-dichlorophenol accumulation and toxicity evaluation

The mechanism and toxicity of TCS degradation by ClO₂ was investigated. Intermediate products during the oxidation process were identified by GC/MS and LC/MS. A microtox bioassay and a SOS/umu assay were employed to evaluate the acute toxicity and genotoxicity of the resulting solutions during the chlorination process. The results showed that the reaction between TCS and ClO₂ was of second-order overall. The pseudo first-order rate constants (k_obs) exhibited significant dependence on solution pH and chlorine dioxide concentration, with the apparent second-order rate constant, k_app, being 7.07 × 10⁴ M^-1s^-1 in the pH range of 6.80-7.02. TCS decomposition was accompanied by the accumulation of 2,4-dichlorophenol (2,4-DCP), and the maximum molar yield ratios of 2,4-DCP/TCS were in the range of 31.71%-35.43%. The major intermediates identified were 2,7/2,8-dichlorodibenzop-dioxin (2,7/2.8-Cl₂DD), 2,4-DCP, 2,4,6-trichlorophenol (2,4,6-TCP), tetraclosan and pentaclosan. The proposed mechanism for TCS oxidation involved the cleavage of the ether link in TCS, chlorination of the phenolic ring and ring closure of a single TCS molecule. The transformation and degradation of TCS led to reduction of the acute toxicity and genotoxicity. However, irregular fluctuations in the toxicity changes indicated that the oxidation of TCS was not a simultaneous detoxification process.

Correlation of Conformational Changes and Protein Degradation with Loss of Lysozyme Activity Due to Chlorine Dioxide Treatment

Chlorine dioxide (ClO₂) is a potent oxidizing agent used for the treatment of drinking water and decontamination of facilities and equipment. The purpose of this research is to elucidate the manner in which ClO₂ destroys proteins by studying the effects of ClO₂ on lysozyme. The degree of enzyme activity lost can be correlated to the treatment time and levels of the ClO₂ used. Lysozyme activity was drastically reduced to 45.3% of original enzyme activity when exposed to 4.3 mM ClO₂ in the sample after 3 h. Almost all activities were lost in 3 h after exposure to higher ClO₂ concentrations of up to 16.8 and 21.9 mM. Changes in protein conformation and amount as a result of ClO₂ treatment were determined using the Raman spectroscopy and gel electrophoresis. Raman shifts and the alteration of spectral features observed in the ClO₂-treated lysozyme samples are associated with loss of the α-helix secondary structure, tertiary structure, and disulfide bond. Progressive degradation of the denatured lysozyme by increasing levels of chlorine dioxide was also observed in gel electrophoresis. Hence, ClO₂ can effectively cause protein denaturation and degradation resulting in loss of enzyme activity.

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

Acute gastroenteritis caused by human norovirus is a significant public health issue. Fresh produce and seafood are examples of high-risk foods associated with norovirus outbreaks. Food contact surfaces also have the potential to harbor noroviruses if exposed to fecal contamination, aerosolized vomitus, or infected food handlers. Currently, there is no effective measure to decontaminate norovirus on food contact surfaces. Chlorine dioxide (ClO2) gas is a strong oxidizer and is used as a decontaminating agent in food processing plants. The objective of this study was to determine the kinetics and mechanism of ClO2 gas inactivation of a norovirus surrogate, murine norovirus 1 (MNV-1), on stainless steel (SS) coupons. MNV-1 was inoculated on SS coupons at the concentration of 10(7) PFU/coupon. The samples were treated with ClO2 gas at 1, 1.5, 2, 2.5, and 4 mg/liter for up to 5 min at 25°C and a relative humidity of 85%, and virus survival was determined by plaque assay. Treatment of the SS coupons with ClO2 gas at 2 mg/liter for 5 min and 2.5 mg/liter for 2 min resulted in at least a 3-log reduction in MNV-1, while no infectious virus was recovered at a concentration of 4 mg/liter even within 1 min of treatment. Furthermore, it was found that the mechanism of ClO2 gas inactivation included degradation of viral protein, disruption of viral structure, and degradation of viral genomic RNA. In conclusion, treatment with ClO2 gas can serve as an effective method to inactivate a human norovirus surrogate on SS contact surfaces.

The kinetics and mechanism of the oxidation of pyruvate ion by hypochlorous acid

Kinetic experiments and DFT calculations confirm a concerted oxygen atom transfer mechanism for the oxidation of pyruvic acid by HOCl.

Fluorescence quenching of (dimethylamino)naphthalene dyes Badan and Prodan by tryptophan in cytochromes P450 and micelles

Fluorescence of 2-(N,N-dimethylamino)-6-propionylnaphthalene dyes Badan and Prodan is quenched by tryptophan in Brij 58 micelles as well as in two cytochrome P450 proteins (CYP102, CYP119) with Badan covalently attached to a cysteine residue. Formation of nonemissive complexes between a dye molecule and tryptophan accounts for about 76% of the fluorescence intensity quenching in micelles, the rest is due to diffusive encounters. In the absence of tryptophan, fluorescence of Badan-labeled cytochromes decays with triexponential kinetics characterized by lifetimes of about 100 ps, 700–800 ps, and 3 ns. Site mutation of a histidine residue in the vicinity of the Badan label by tryptophan results in shortening of all three decay lifetimes. The relative amplitude of the fastest component increases at the expense of the two slower ones. The average quenching rate constants are 4.5 × 10⁸ s^–1 (CYP102) and 3.7 × 10⁸ s^–1 (CYP119), at 288 K. Cyclic voltammetry of Prodan in MeCN shows a reversible reduction peak at −1.85 V vs NHE that becomes chemically irreversible and shifts positively upon addition of water. A quasireversible reduction at −0.88 V was observed in an aqueous buffer (pH 7.3). The excited-state reduction potential of Prodan (and Badan) is estimated to vary from about +0.6 V (vs NHE) in polar aprotic media (MeCN) to approximately +1.6 V in water. Tryptophan quenching of Badan/Prodan fluorescence in CYPs and Brij 58 micelles is exergonic by ≤0.5 V and involves tryptophan oxidation by excited Badan/Prodan, coupled with a fast reaction between the reduced dye and water. Photoreduction is a new quenching mechanism for 2-(N,N-dimethylamino)-6-propionylnaphthalene dyes that are often used as solvatochromic polarity probes, FRET donors and acceptors, as well as reporters of solvation dynamics.

Chlorine dioxide is a size-selective antimicrobial agent

Background / Aims

ClO₂, the so-called “ideal biocide”, could also be applied as an antiseptic if it was understood why the solution killing microbes rapidly does not cause any harm to humans or to animals. Our aim was to find the source of that selectivity by studying its reaction-diffusion mechanism both theoretically and experimentally.

Methods

ClO₂ permeation measurements through protein membranes were performed and the time delay of ClO₂ transport due to reaction and diffusion was determined. To calculate ClO₂ penetration depths and estimate bacterial killing times, approximate solutions of the reaction-diffusion equation were derived. In these calculations evaporation rates of ClO₂ were also measured and taken into account.

Results

The rate law of the reaction-diffusion model predicts that the killing time is proportional to the square of the characteristic size (e.g. diameter) of a body, thus, small ones will be killed extremely fast. For example, the killing time for a bacterium is on the order of milliseconds in a 300 ppm ClO₂ solution. Thus, a few minutes of contact time (limited by the volatility of ClO₂) is quite enough to kill all bacteria, but short enough to keep ClO₂ penetration into the living tissues of a greater organism safely below 0.1 mm, minimizing cytotoxic effects when applying it as an antiseptic. Additional properties of ClO₂, advantageous for an antiseptic, are also discussed. Most importantly, that bacteria are not able to develop resistance against ClO₂ as it reacts with biological thiols which play a vital role in all living organisms.

Conclusion

Selectivity of ClO₂ between humans and bacteria is based not on their different biochemistry, but on their different size. We hope initiating clinical applications of this promising local antiseptic.

Kinetics and mechanism of oxidation of tryptophan by ferrate(VI)

Kinetics of the oxidation of tryptophan (Trp) and kynurenine (Kyn), precursors of nitrogenous disinfection byproducts (N-DBP), by ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) were investigated over the acidic to basic pH range. The second-order rate constants decreased with increase in pH, which could be described by the speciation of Fe(VI) and Trp (or Kyn). The trend of pH dependence of rates for Trp (i.e., aromatic α-amino acid) differs from that for glycine (i.e., aliphatic α-amino acid). A nonlinear relationship between transformation of Trp and the added amount of Fe(VI) was found. This suggests that the formed intermediate oxidized products (OPs), identified by LC-PDA and LC-MS techniques, could possibly compete with Trp to react with Fe(VI). N-Formylkynurenine (NFK) at pH 7.0 and 4-hydroxyquinoline (4-OH Q) and kynurenic acid (Kyn-A) at pH 9.0 were the major OPs. Tryptophan radical formation during the reaction was confirmed by the rapid-freeze quench EPR experiments. The oxygen atom transfer from Fe(VI) to NFK was demonstrated by reacting Fe(18)O4(2-) ion with Trp. A proposed mechanism explains the identified OPs at both neutral and alkaline pH. Kinetics and OPs by Fe(VI) were compared with other oxidants (chlorine, ClO2(•), O3, and (•)OH).

Subtle differences in virus composition affect disinfection kinetics and mechanisms

Viral disinfection kinetics have been studied in depth, but the molecular-level inactivation mechanisms are not understood. Consequently, it is difficult to predict the disinfection behavior of nonculturable viruses, even when related, culturable viruses are available. The objective of this work was to determine how small differences in the composition of the viral genome and proteins impact disinfection. To this end, we investigated the inactivation of three related bacteriophages (MS2, fr, and GA) by UV254, singlet oxygen ((1)O2), free chlorine (FC), and chlorine dioxide (ClO2). Genome damage was quantified by PCR, and protein damage was assessed by quantitative matrix-assisted laser desorption ionization (MALDI) mass spectrometry. ClO2 caused great variability in the inactivation kinetics between viruses and was the only treatment that did not induce genome damage. The inactivation kinetics were similar for all viruses when treated with disinfectants possessing a genome-damaging component (FC, (1)O2, and UV254). On the protein level, UV254 subtly damaged MS2 and fr capsid proteins, whereas GA's capsid remained intact. (1)O2 oxidized a methionine residue in MS2 but did not affect the other two viruses. In contrast, FC and ClO2 rapidly degraded the capsid proteins of all three viruses. Protein composition alone could not explain the observed degradation trends; instead, molecular dynamics simulations indicated that degradation is dictated by the solvent-accessible surface area of individual amino acids. Finally, despite the similarities of the three viruses investigated, their mode of inactivation by a single disinfectant varied. This explains why closely related viruses can exhibit drastically different inactivation kinetics.

A Much-Needed Mechanism and Reaction Rate for the Oxidation of Phenols with ClO2: A Joint Experimental and Computational Study

The oxidation of phenols with chlorine dioxide, a powerful means to eliminate phenol pollutants from drinking water, is explored. Kinetic experiments reveal that 2,4,6-trichlorophenol exhibits a lower oxidation rate than other phenols because the chlorine atoms (σ = 0.22) at ortho and para-positions decrease the benzene’s electron density, in agreement with the Hammett plot. The oxidation of phenol was found to be second order with respect to phenol and first order with respect to ClO2 and a possible mechanism is proposed. The phenol/ClO2 oxidation was found to be pH-dependent since the reaction rate constant increases with increasing pH. The oxidation rate was also significantly enhanced with an increasing methanol ratio in water. The oxidation products, such as benzoquinones, were analysed and confirmed by liquid chromatography and gas chromatography–mass spectrometry. Density functional theory computations at both the B3LYP/6-311+G(d,p) and M06-2X.6-311+G(d,p) levels with the SCRF-PCM solvation model (i.e. with water) further supported the proposed mechanisms in which activation barriers predicted the right reactivity trend as shown by the kinetic experiments.

Virus inactivation mechanisms: impact of disinfectants on virus function and structural integrity

Oxidative processes are often harnessed as tools for pathogen disinfection. Although the pathways responsible for bacterial inactivation with various biocides are fairly well understood, virus inactivation mechanisms are often contradictory or equivocal. In this study, we provide a quantitative analysis of the total damage incurred by a model virus (bacteriophage MS2) upon inactivation induced by five common virucidal agents (heat, UV, hypochlorous acid, singlet oxygen, and chlorine dioxide). Each treatment targets one or more virus functions to achieve inactivation: UV, singlet oxygen, and hypochlorous acid treatments generally render the genome nonreplicable, whereas chlorine dioxide and heat inhibit host-cell recognition/binding. Using a combination of quantitative analytical tools, we identified unique patterns of molecular level modifications in the virus proteins or genome that lead to the inhibition of these functions and eventually inactivation. UV and chlorine treatments, for example, cause site-specific capsid protein backbone cleavage that inhibits viral genome injection into the host cell. Combined, these results will aid in developing better methods for combating waterborne and foodborne viral pathogens and further our understanding of the adaptive changes viruses undergo in response to natural and anthropogenic stressors.

Light emission from tryptophan oxidation by hypobromous acid

The emission of ultraweak light from cells is a phenomenon associated with the oxidation of biomolecules by reactive oxygen species. The indole moiety present in tryptophan, serotonin and melatonin is frequently associated with the emission of light during the oxidation of these metabolites. This study presents results for hypobromous acid (HOBr) oxidation of tryptophan as a putative endogenous source of ultraweak light emission. We found that chemiluminescence elicited by the oxidation of tryptophan by HOBr was significantly higher than by hypochlorous acid (HOCl). This difference was related to secondary oxidation reactions, which were more intense using HOBr. The products identified during oxidation by HOCl, but depleted by using HOBr, were N-formylkynurenine, kynurenine, 1,2,3,3a,8,8a-hexahydro-3a-hydroxypyrrolo[2,3-b]-indole-2-carboxylic acid, oxindolylalanine and dioxindolylalanine. The emission of light is dependent on the free α-amino group of tryptophan, and hence, the indole of serotonin and melatonin, although efficiently oxidized, did not produce chemiluminescence. The emission of light was even greater using taurine monobromamine and dibromamine as the oxidant compared to HOBr. A mechanism based on bromine radical intermediates is suggested for the higher efficiency in light emission. Altogether, the experimental evidence described in the present study indicates that the oxidation of free tryptophan or tryptophan residues in proteins is an important source of ultraweak cellular emission of light. This light emission is increased in the presence of taurine, an amino acid present in large amounts in leukocytes, where this putative source of ultraweak light emission is even more relevant.

Inactivation of influenza virus haemagglutinin by chlorine dioxide: oxidation of the conserved tryptophan 153 residue in the receptor-binding site

Airborne influenza virus infection of mice can be prevented by gaseous chlorine dioxide (ClO(2)). This study demonstrated that ClO(2) abolished the function of the haemagglutinin (HA) of influenza A virus (H1N1) in a concentration-, time- and temperature-dependent manner. The IC(50) during a 2 min reaction with ClO(2) at 25 °C was 13.7 µM, and the half-life time of HA with 100 µM ClO(2) at 25 °C was 19.5 s. Peptides generated from a tryptic digest of ClO(2)-treated virus were analysed by mass spectrometry. An HA fragment, (150)NLLWLTGK(157) was identified in which the tryptophan residue (W153) was 32 mass units greater than expected. The W153 residue of this peptide, which is derived from the central region of the receptor-binding site of HA, is highly conserved. It was shown that W153 was oxidized to N-formylkynurenine in ClO(2)-treated virus. It was concluded that the inactivation of influenza virus by ClO(2) is caused by oxidation of W153 in HA, thereby abolishing its receptor-binding ability.

Cell-based detection of electrochemical oxidative stress by a fluorescent tryptophan intermediate

The present study suggests a sensitive and rapid cell analysis method to evaluate the oxidative stress produced in a physiological culture medium, by anodic electrochemical products. The detection of these oxidizing agents, probably involving hypochlorite, is carried out by measuring the presence of an oxidized tryptophan intermediate, entrapped and stabilized in the cell cytoplasm. The formation of this tryptophan intermediate depends solely on the presence of a free tryptophan in the extracellular medium near the anode. This intermediate possesses a characteristic emission maximum at λ~560 nm, which can be abolished by the presence of anti-oxidants in the media during the cells' exposure to electric current. However, this intermediate's emission is unaffected by increased concentrations of intracellular anti-oxidants. This suggests that the anodic produced unstable tryptophan intermediate permeates the cell plasma membrane and becomes stabilized by cytoplasmic proteins. Tryptophan oxidative intermediates with similar spectra could also be formed by the chemical reaction of hypochlorite with tryptophan in solution. The analysis of the intracellularly stabilized tryptophan intermediate by flow cytometry can be used for measuring external oxidation stress without the disturbance of intracellular anti-oxidative capacity.

Kinetics and mechanism for methiocarb degradation by chlorine dioxide in aqueous solution

The kinetics and mechanism for methiocarb (MC) degradation by aqueous ClO2 were investigated under simulated water treatment conditions. Experimental results indicate that the reaction between MC and ClO2 was of second-order overall, and the rate constant rapidly increased from 0.56 to 4.5 M(-1) s(-1) as the solution pH increased from 6.0 to 9.1 at 23 degrees C. The activation energy was determined to be 75 kJ mol(-1) in the studied temperature range of 7-35 degrees C. Methiocarb sulfoxide (MCX) and methiocarb sulfone (MCN) were quantified to be the major byproducts from MC degradation. Unlike the sequential formation of sulfoxide and sulfone during the oxidation of many thioethers, the two byproducts were formed simultaneously during MC degradation by ClO2. The solution pH significantly affected the type and quantity of the degradation byproducts. For example, at pH 6.5 MCX and MCN accumulated as the reaction proceeded and finally accounted for 71% and 28% of MC degraded, respectively; while at pH 8.6 three more minor byproducts were identified. Though ClO2 can effectively oxidize MC in water, the significant increase in toxicity raises a potential risk to consumers.

Oxidation of nitrogen-containing pollutants by novel ferrate(VI) technology: a review

Nitrogen-containing pollutants have been found in surface waters and industrial wastewaters due to their presence in pesticides, dyes, proteins, and humic substances. Treatment of these compounds by conventional oxidants produces disinfection by-products (DBP). Ferrate(VI) (Fe(VI)O(4)(2-), Fe(VI)) is a strong oxidizing agent and produces a non-toxic by-product Fe(III), which acts as a coagulant. Ferrate(VI) is also an efficient disinfectant and can inactivate chlorine resistant microorganisms. A novel ferrate(VI) technology can thus treat a wide range of pollutants and microorganisms in water and wastewater. The aim of this paper is to review the kinetics and products of the oxidation of nitrogen-containing inorganic (ammonia, hydroxylamine, hydrazine, and azide) and organic (amines, amino acids, anilines, sulfonamides, macrolides, and dyes) compounds by ferrate(VI) in order to demonstrate the feasibility of ferrate(VI) treatment of polluted waters of various origins. Several of the compounds can degraded in seconds to minutes by ferrate(VI) with the formation of non-hazardous products. The mechanism of oxidation involves either one-electron or two-electrons processes to yield oxidation products. Future research directions critical for the implementation of the ferrate(VI)-based technology for wastewater and industrial effluents treatment are recommended.