Peroxynitrite Mediated Oxidations: Spin Trap Studies; Nitration and Hydroxylation of Phenol Result From Different Intermediates; CO(2) Catalyzes the Decomposition of Peroxynitrite.
Date of Award
Doctor of Philosophy (PhD)
William A. Pryor
In the first project the spin trap DMPO was used to probe for the production of hydroxyl radicals from peroxynitrite. Peroxynitrite reacts with DMPO to give $\sp\cdot$DMPO-OH, suggesting that $\sp\cdot$DMPO-OH results from a reaction between DMPO and HOONO or between DMPO and an activated intermediate of HOONO. Thiols produce a large increase in the $\sp\cdot$DMPO-OH signal intensity. Experiments employing SOD suggest that this increase results from the decomposition of $\sp\cdot$DMPO-OOH. These results are incompatible with the decomposition of peroxynitrite to form $\sp\cdot$OH but suggest that an intermediate of HOONO is produced that is less reactive and more selective than the hydroxyl radical. In the second project, we have examined the formation of hydroxyphenols, nitrophenols, and the minor products 4-nitrosophenol, benzoquinone, 2,2$\sp\prime$-biphenol, and 4,4$\sp\prime$-biphenol from the reaction of peroxynitrite with phenol with and without added carbonate. Without added carbonate, both the yields and rates of formation of nitrophenols and hydroxyphenols have different pH profiles. The sum of the rate constants for nitration and hydroxylation is identical to the rate constant for the spontaneous decomposition of peroxynitrite. When carbonate is added, hydroxylation is inhibited, whereas the rates of formation and yields of nitrophenols increase. The maximum yield of nitrophenols is 20 mol%, about 4-fold higher than without added carbonate. The o/p ratio of nitrophenols is independent of carbonate. These results suggest that hydroxylation and nitration occur via two different intermediates. We suggest that ONOOH$\sp*$ is the hydroxylating species, and that O = N-OO-CO$\sb2\sp-$, the product of the peroxynitrite/CO$\sb2$ reaction, or secondary products derived from it, is the nitrating agent. The third project is a study of the reaction of peroxynitrite with limiting concentrations of CO$\sb2.$ Peroxynitrite adds to CO$\sb2$ to give O = N-OO-CO$\sb2\sp-$ (1). The reformation of CO$\sb2$ (not CO$\sb3$ = or HCO$\sb3\sp-$) from O = N-OO-CO$\sb2\sp-$ is demonstrated. When the concentration of CO$\sb2$ is limiting, the reformation of CO$\sb2$ amplifies the fraction of peroxynitrite that reacts with CO$\sb2.$ Even low CO$\sb2$ concentrations dissolved from ambient air can cause deviations from predicted kinetic behavior. The reactions attributed to peroxynitrite depend on the availability of CO$\sb2,$ since O = N-OO-CO$\sb2\sp-,$ and intermediates derived from it, oxidize and nitrate.
Lemercier, Jean-noel, "Peroxynitrite Mediated Oxidations: Spin Trap Studies; Nitration and Hydroxylation of Phenol Result From Different Intermediates; CO(2) Catalyzes the Decomposition of Peroxynitrite." (1997). LSU Historical Dissertations and Theses. 6545.