EPR SPECTROSCOPIC STUDY OF THE RADICAL OXIDATION OF HYDROXYPURINES INAQUEOUS-SOLUTION - ACID-BASE PROPERTIES OF THE DERIVED RADICALS

EPR spectroscopy has been employed to study the reactions of SO4.- and OH. radicals with xanthine, 8-methylxanthine, hypoxanthine and 2-hydr oxypurine. Radicals obtained on the reaction of SO4.- with these hydro xypurines resulted, depending on the pH, from one-electron oxidation o f either the parent compound or its anion, followed by deprotonation. For xanthine and 8-methylxanthine the respective radical anion and rad ical dianion were observed, for hypoxanthine the species detected corr espond to the neutral radical and radical anion, whereas for 2-hydroxy purine only its radical anion was observed. The pK(a) values of the ra dical anion of xanthine and 8-methylxanthine were estimated as 12.0 +/ - 0.1 and 12.1 +/- 0.5, respectively, whereas the pK(a) value of the h ypoxanthine neutral radical was 7.7 +/- 0.1. In the reaction with OH., only the radical anion of xanthine was detected.