2479-49-4

The kinetics of the photooxidation of aromatic amino acids histidine (His), tyrosine (Tyr), and tryptophan (Trp) by Benzophenonetetracarboxylic acid has been investigated in aqueous solutions using time-resolved laser flash photolysis and time-resolved chemically induced dynamic nuclear polarization. The pH dependence of quenching rate constants is measured within a large pH range. The chemical reactivities of free His, Trp, and Tyr and of their acetylated derivatives, N-AcHis, N-AcTyr, and N-AcTrp, toward Benzophenonetetracarboxylic acid triplets are compared to reveal the influence of amino group charge on the oxidation of aromatic amino acids. Thus, it has been established that the presence of charged amino group changes oxidation rates by a significant factor; i.e., His with a positively charged amino group quenches the Benzophenonetetracarboxylic acid triplets 5 times more effectively than N-AcHis and His with a neutral amino group. The efficiency of quenching reaction between the Benzophenonetetracarboxylic acid triplets and Tyr and Trp with a positively charged amino group is about 3 times as high as that of both Tyr and Trp with a neutral amino group, N-AcTyr and N-AcTrp.