engleski

Proton affinity of peroxynitrite and other N-O anions

Peroxynitrite (ONOO^–) is a biological toxin formed by the reaction of nitric oxide with superoxide (O_2^–). It forms in the body by protonation of peroxynitrous acid (ONOOH, pKa=6.8), which yields nitric acid in a fast isomerization reaction. It appears that neither peroxynitrite nor peroxynitrous acid have yet been obtained in the gas phase. We have been trying since 1995 to measure the gas phase proton affinity (PA) and other thermodynamic values for peroxynitrite in a Fourier transform mass spectrometer. Unfortunately, our attempts were so far unsuccessful because we were unable to generate gas phase ONOO^– in the spectrometer. However, we obtained an estimate for the PA of ONOO^– and ONOOH from good quality calculations using a standard G2 procedure. The recent experimental determination of PA for peroxynitric acid1, well supported by experimental results for nitric acid and by G2 calculations, makes it worthwhile to compare these results with our own estimates, in which we also use the results of calculations for nitrous acid (HONO) and its conjugate base (NO_2^–) as well as for a number of other established N-O anions. Thus, our focus will be on the PA of nitrous, nitric, peroxynitrous and peroxynitric acids and their conjugate bases (anions): ONO^–, NO_3^–, ONOO^– and O_2NOO^– as well as of O_2NNH^– (nitramide), O_2NNNO_2^– (dinitramide), ON:NO^2– (hyponitrite) and ON:NO_2^2– (oxyhyponitrite). The aim is to deduce the confidence limits for the calculated values.

nije evidentirano

nije evidentirano