| Peroxynitrtite plays an important role in biological and physical chemistry. One hand, in biological systems peroxynitrite has been proposed as a potential pathogenic agent in human diseases and as an important microbicidal agent generated by phagocytic cells associated with the host defence system. On the other hand, the photoisomerization of nitrate to peroxynitrite with UV radiation must be also considered in those chemical changes that occur in the Earth's atmosphere.; In this work, an experimental kinetic study of peroxynitrite decomposition reaction in absence and presence of iron and molybdenum cyanocomplexes has been described. Moreover, these reactions have been studied in presence of CO2, a very important process in biological systems where the physiological conditions favour the catalytic effect.; The half time of peroxynitrous acid is very short (1 s), therefore the kinetic measurements have been carried out using an Applied Photophysics Instruments Stopped-Flow Apparatus, to be able to measure reaction times bigger than 2 ms. The variations of the observed rate constant with peroxynitrite and substrate concentration, pH, ionic strength and temperature have been investigated in a wide range of the experimental conditions. The reactions products have been also determined.; A reaction mechanism that justifies our experimental data has been proposed, which involves homolytic cleavage of the O--O bond of the peroxy nitrous acid to form HO· and ·NO2 radicals. The cyanocomplex is oxidized in competitive paths by HOONO (direct oxidation) and by both radicals (indirect oxidation). The rate constants for both HOONO homolysis (k1) and direct oxidation (k2) have been determined, as well as the activation parameters for these elemental steps.; Peroxynitrite decomposition, in absence or presence of substrate, is catalysed by CO2. This effect is more important around pH = 6.2. In this case ONOO- reacts with CO2 forming an adduct ONO2CO2-, which decomposes by homolysis forming ·NO2 and ·CO3 2-. Both radicals oxidize the substrate rapidly. The determining-rate constant of adduct formation between ONOO- and CO 2 has been determined. |
