Reactions of OH-radicals with procarbazine. A pulse radiolysis and computer simulation study.

Pulse radiolysis was applied to study the reactivity of *OH radicals with procarbazine (PC), a cytostatic agent widely used in radiation- and chemotherapy. An overall rate constant of k(*OH+PC) = 3.7 x 10(9) l.mol(-1).s(-1) was determined. The thereby formed transients had a strong absorption at 350 nm, epsilon350 = 4.46 x 10(3) l.mol(-1).cm(-1), and a weak absorption band around 530 nm. Computer simulation studies to elucidate the most probable sites of *OH attack on the PC molecule showed that *OH radical addition to the aromatic ring had the highest probability. These transients decayed by a first order reaction, k = 1.75 x 10(3) s(-1), whereby species having a maximum absorption at 300 nm and broad shoulder at 340-380 nm were formed. Similar absorptions were observed after gamma radiolysis of PC. A reaction mechanism is suggested. For the reaction of H-atoms with PC, a rate constant k(*H+PC) = 6.4 x 10(8) l.mol(-1).s(-1) was determined.