REACTIONS OF NITRATE RADICAL WITH AMINO-ACIDS IN ACIDIC AQUEOUS-MEDIUM - A FLASH-PHOTOLYSIS INVESTIGATION

The reactions of nitrate radical (photochemically generated by the fla sh photolysis of a mixture of eerie ammonium nitrate and nitric acid) with amino acids are reported. An electron transfer reaction pathway i s proposed for phenylalanine and histidine, whereas a hydrogen abstrac tion pathway is invoked for the other amino acids, based on the magnit udes of the second- order rate constants and the observation of cation radicals. The reactivity of the nitrate radical is compared with that of other oxidizing radicals, such as Cl-2(.-), CO3.- and SO4.-. The n itrate radical is expected to show a higher reactivity than SO4.- base d on their redox couples, but an inverse reactivity relationship is ob served and is suggested to be due to the difference in solvation in th e transition state.