Exchange of (18)O in the reaction of peroxynitrite with CO(2)

We have observed an exchange of (18)O in the reactions of CO(2) with peroxynitrite using membrane-inlet mass spectrometry and HPLC negative electrospray ionization mass spectrometry. The exchange appeared on addition of peroxynitrite to a solution containing (18)O-labeled CO(2) in equilibrium with bicarbonate. It was observed as a temporarily enhanced rate of depletion of (18)O from CO(2), a rate that was greater than the rate of (18)O depletion caused by the hydration/dehydration cycle of CO(2). In addition, we detected the appearance of mass peaks attributed to (18)O in product NO(3)(-). As a further measure of the (18)O exchange, there was a redistribution of (18)O such that the ratio of doubly to singly labeled CO(2) could not be described by the binomial expansion. This is not due to the hydration/dehydration cycle of CO(2) but most likely to recycling of CO(2) in the reaction with peroxynitrite. This (18)O exchange associated with the reactions of CO(2) and peroxynitrite may open a new methodology for studying this significant process.