CHEMILUMINESCENCE OF CYPRIDINA LUCIFERIN ANALOGS .1. EFFECT OF PH ON RATES OF SPONTANEOUS AUTOXIDATION OF CLA IN AQUEOUS BUFFER SOLUTIONS

From the pH-rate profile of autoxidation of the Cypridina luciferin an alogue {2-methyl-6-phenylimidazo[1,2-a]pyrazin-3(7H)-one, CLA}, CLA wa s found not to react with ground-state molecular oxygen at a measurabl e rate, while the conjugate base of CLA was found to react with molecu lar oxygen with a second-order rate constant of 0.434 +/- 0.001 dm3 mo l-1 s-1 at 25-degrees-C. No chain reaction process contributed in the autoxidation of CLA. Superoxide dismutase (SOD) was observed to reduce the rate of the autoxidation to a small extent in the reaction with l ow-pH buffers, while SOD did not affect the reaction in buffers of pH higher than 7. The intimate radical pair (CLA.O2.-) is proposed to be the primary product of the reaction.