Charge transfer reactions from tryptophan and tyrosine to sulfur‐centered dimer radical cation in aqueous –sulfuric acid medium: a pulse radiolysis study

Kinetics and mechanism of one‐electron oxidation of N‐acetyl methionine (NAM), tryptophan (TrpH), tyrosine (TyrOH), and phenylalanine (Phe) have been studied in 33% v/v H 2 SO 4 solution. The solvent radical (SO 4 •¯ ) oxidized NAM, TrpH, TyrOH, and Phe to produce NAM 2 •+ (480 nm), TrpH •+ (330, 580 nm), TyrO • (350, 410 nm), and Phe(H) • (320 nm), with rate constants (10 9  M −1  s −1 ) 0.6, 2.7, 3.9, 1.6, respectively. Time resolved radical transformation from NAM 2 •+ to TrpH •+ and TyrO • have been observed to occur with k(10 8  M −1  s −1 ) = 3.60 and 0.35, respectively. However, NAM 2 •+ to Phe(H) • and TrpH •+ to TyrO • radical transformations have not been observed in this medium. The study shows the kinetics and mechanism of oxidation of some amino acids in strong acidic solutions. To the best of our knowledge, radical cations of amino acids and electron transfer reactions between them could be studied in strong acidic solutions for the first time. Copyright © 2016 John Wiley & Sons, Ltd.