Radical mechanisms of the decomposition of peroxynitrite and the peroxynitrite-CO2 adduct and of reactions with L-tyrosine and related compounds as studied by 15N chemically induced dynamic nuclear polarization

Enhanced absorption is observed in the N-15 NMR spectra of (NO3-)-N-15 during decomposition of peroxynitrite and the peroxynitrite-CO2 adduct at pH 5.25, indicating the formation of (NO3-)-N-15 in radical pairs [(NO2.)-N-15, HO.] and [(NO2.)-N-15, CO3.-]. During the reaction of peroxynitrite and the peroxynitrite-CO2 adduct with L-tyrosine, the N-15 NMR Signal of the nitration product 3-nitrotyrosine exhibits emission showing a radical pathway of its formation. The nuclear polarization is built up in radical pairs [(NO2.)-N-15, tyr(.)] generated by free radical encounters of nitrogen dioxide and tyrosinyl radicals, The N-15 NMR signal of (NO2-)-N-15 formed during reaction of peroxynitrite with L-tyrosine appears in emission, It is concluded that tyrosinyl radicals are generated by reaction of nitrogen dioxide with L-tyrosine, In contrast to this, (NO2-)-N-15 does not show N-15 chemically induced dynamic nuclear polarization (CIDNP) during reaction of the peroxynitrite-CO2 adduct with L-tyrosine, indicating a different reaction mechanism, which is assumed to be a hydrogen transfer between CO3.- and L-tyrosine. Emission is also observed in the N-15 NMR signals of 2-nitro-4-fluorophenol, 3-nitro-4-hydroxyphenylacetic acid, 2-nitrophenol, and 4-nitrophenol during reaction of 4-fluorophenol, 4-hydroxyphenylacetic acid, and phenol with peroxynitrite and the peroxynitrite-CO2 adduct, 3-Nitro-4-hydroxyphenylacetic acid is also observed in emission during reaction of phenylacetic acid with peroxynitrite, but is not formed with the peroxynitrite-CO2 adduct, The magnitude of the N-15 CIDNP effect during reaction of peroxynitrite with 4-fluorophenol and of the peroxynitrite-CO2 adduct with 4-fluorophenol and phenol is determined, It excludes the occurrence of nonradical reactions. Only weak emission signals are observed during the reaction of peroxynitrite with phenol in (NO2-)-N-15, 2-nitrophenol, and 4-nitrophenol. 2-Nitrophenol is only formed in traces, and 4-nitrophenol is only formed in higher yields, The latter might be generated in part via a nonradical pathway. (C) 1999 Academic Press.