Selective oxidation of tyrosine-oxidation by NO₂ and ClO₂ at basic pH

This study, using chlorine dioxide and nitrogen dioxide as oxidants, was carried out in basic aqueous solutions of the free amino acids, purged of oxygen and saturated with N//2O to convert hydrated electrons to hydroxyl radicals. The solutions were irradiated with 5 ns electron pulses from an ARCO LP-7 linear accelerator. Chlorine dioxide was produced by using solutions of NaClO//2, and nitrogen dioxide was produced similarly from NaNO//2 solutions. ClO//2 radicals were found to oxidize both tryptophan and tyrosine. The rates for the reaction of ClO//2 plus amino acid were studied from the first-order build-up of these spectra over a four- to five-fold concentration range of the amino acid. The rates were found to be proportional to the amino acid concentration. From these dependencies the rate constants for the reaction of ClO//2 with tyrosine and tryptophan are found.