Redox reactions of 3 '-azido-3 '-deoxythymidine (AZT) and interaction of its OH-derived radical with bilirubin and riboflavin: A pulse radiolysis study

Using the technique of pulse radiolysis, redox studies of 3'-azido-3'-deoxy thymidine (azidothymidine or AZT) with hydrated electron and hydroxyl radic als, generated in phosphate-buffered aqueous medium, are reported. The hydr ated electron reacts with AZT (k = 1.9 x 10(10) dm(3) mol(-1) s(-1)) to gen erate transients with absorption maxima at 300 and 340 nm. The hydroxyl rad ical adds to AZT to generate transients with absorption maxima at 310 and 3 65 nm, with formation rate constant of 9.0 x 10(9) dm(3) mol(-1) s(-1) as o bserved at 310 and 365 nm. The secondary radical 6-hydroxy-5-yl-azidothymid ine, formed in the reaction of AZT with hydroxyl radical, reacts with bilir ubin to give a transient of bilirubin with bimolecular rate constant of 1.8 x 10(8) dm(3) mol(-1) s(-1). In the reaction of hydroxyl radical with AZT/ riboflavin pair, an H-. atom transfer from riboflavin to the 6-hydroxy-5-yl -azidothymidine is observed. Reactions of (OH)-O-.-derived radicals of thym ine with bilirubin and riboflavin are similar to that of AZT. Possible mech anisms are proposed for the observed reactions.