A Kinetic Study of the Reaction of Aqueous Chlorine and Chlorine Dioxide with Amino Acids, Peptides and Proteins

Reactions involving aqueous chlorine and ClO₂ with amino acids in 0.1M sodium phosphate buffer at pH 3, 6, and 9 were studied using iodometric and spectrophotometric techniques. The N,N-diethyl-p-phenylene-diamine (DPD) titrimetric technique was used to differentiate the chlorinated species formed in the reaction mixture. Chlorinated derivatives of amino acids were readily formed and then decomposed. Except in the mixtures with proline, hydroxyproline and glycine, the rate of loss of available chlorine in the reaction mixtures followed first order kinetics and was found to be pH dependent. Only a few amino acids reacted with aqueous ClO₂. The reaction also followed pseudo-first order kinetics. Reactions of three peptides and two proteins with aqueous chlorine and ClO₂ at pH 6.0 were also studied. Except for aspartame, they reacted rapidly with both chlorine compounds.