Reactivity of chlorine dioxide with amino acids, peptides, and proteins

Abstract

Amino acids, proteins, and peptides are found ubiquitously in waters. They can form harmful byproducts during water treatment by reaction with disinfectants. Chlorination and chloramination of water containing natural organic matter is known to result in the production of toxic substances, often referred to as disinfection byproducts. The main advantage of using chlorine dioxide (ClO2) over other known chlorine-containing disinfectants is the minimization of the formation of harmful trihalomethanes. Because ClO2 is a promising alternative to other chlorine-containing disinfectants, the chemistry of ClO2 interactions with amino acids, proteins, and peptides should be understood to ensure the safety of potable water supplies. Here, we present an overview of the aqueous chemistry of ClO2 and its reactivity with amino acids, peptides, and proteins. The kinetics and products of the reactions are reviewed. Only a few amino acids have been reported to be reactive with ClO2, and they have been found to follow second-order kinetics for the overall reaction. The rate constants vary from 10−2 to 107 M−1 s−1 and follow an order of reactivity: cysteine > tyrosine > tryptophan > histidine > proline. For reactions of histidine, tryptophan, and tyrosine with ClO2, products vary depending largely on the molar ratios of ClO2 with the specific amino acid. Products of ClO2 oxidation differ with the presence or absence of oxygen in the reaction mixture. Excess molar amounts of ClO2 relative to amino acids are associated with the production of low molecular weight compounds. The oxidation of the biochemically important compounds bovine serum albumin and glucose-6-phosphate dehydrogenase by ClO2 suggests a denaturing of proteins by ClO2 by an attack on tryptophan and tyrosine residues and relates to the inactivation of microbes by ClO2.