KINETICS AND SPECTRAL CHARACTERISTICS OF TRANSIENT SPECIES FORMED ON ONE-ELECTRON OXIDATION OF ACRIDINE-1,8-DIONE IN AQUEOUS-SOLUTION - PULSE-RADIOLYSIS STUDY

The (OH)-O-. radicals in a neutral aqueous solution of acridine-1,8-di one (AD) have been shown to react with a bimolecular rate constant of 6.1 x 10(9) dm(3) mol(-1) s(-1) and form two transient absorption band s with lambda(max) = 320 and 650 nm. The 650 nm band is observed to de cay by first-order kinetics with k = 2.2 x 10(3) s(-1) and the 320 nm band showed mixed kinetics. Both H-. and O-.- react with AD to form tr ansient absorption bands with lambda(max) = 330 and 680 nm, and are as signed to a radical species formed on H atom abstraction from a CH3 gr oup. One-electron oxidants such as Br-.-, N-3(.) and I-2(.-) react wit h AD and form transient absorption, bands with lambda(max) = 310 and 6 50 nm. They are assigned to a radical species formed on deprotonation of solute radical cations at neutral pH. Based on these studies, (OH)- O-. radicals at neutral pH are inferred to react with AD by H atom abs traction from two different sites: 38% from a CH3 group and 62% from a CH2 group which on protonation results in a solute radical cation. Th e 320 nm band formed on reaction of (OH)-O-. radicals is resolved into two bands with lambda(max) = 310 nm (radical species formed on deprot onation of solute radical cation) and 330 nm (radical formed on H atom abstraction from CH3 group). Cl-2(.-) is able to oxidize AD and form transient absorption bands with lambda(max) = 305 and 560 nm which are assigned to the solute radical cation AD(.+) in acidic solutions. The pK value for the deprotonation of the solute radical cation is found to be 2.3. The I-2(.-)/2I(-) redox couple established an equilibrium w ith AD/AD(.+), and the oxidation potential for the AD/AD(.+) couple wa s determined to be 1.02 +/- 0.03 V close to the half-wave potential, E (1/2), value obtained electrochemically (1.17 V).