Peroxynitrous acid formation

The plot of In A, versus time gives k = 3.76 s 1. The pattern may seem to suggest that the reaction occurs with fast formation of the peroxynitrous acid intermediate (k = 3.76 s-1) and slower consumption of it (k = 0.0854 s-1). This is not necessarily so, however, as will be considered in Section 4.2. Rather than committing oneself as to... 

It should be noted that Reaction (4) is not a one-stage process.) Both free radical N02 and highly reactive peroxynitrite are the initiators of lipid peroxidation although the elementary stages of initiation by these compounds are not fully understood. (Crow et al. [45] suggested that trans-ONOO is protonated into trans peroxynitrous acid, which is isomerized into the unstable cis form. The latter is easily decomposed to form hydroxyl radical.) Another possible mechanism of prooxidant activity of nitric oxide is the modification of unsaturated fatty acids and lipids through the formation of active nitrated lipid derivatives. 

Zhu and co-workers (1993) observed the formation of HONO in an environmental chamber during the decay of peroxynitric acid, H02N02, and suggested that H02N02, formed in the H02 + N02 reaction,... 

Figure 7.9, for example, shows the decay of H02N02 and the formation of HONO and HN03 in their chamber. The peroxynitric acid was generated by reaction (27), where the H02 was formed by the bromine atom initiated oxidation of formaldehyde in air. Zhu et al. 

Zhu, T., G. Yarwood, J. Chen, and H. Niki, Evidence for the Heterogeneous Formation of Nitrous Acid from Peroxynitric Acid in Environmental Chambers, Environ. Sci. TechnoL, 27, 982-983 (1993). 

The nearly constant peroxynitrite concentration observed in neutral solution changes dramatically when [Ft] of the solution is increased. Fig. 2 compares the transient absorption of aqueous nitrate at [Ft ] = 10-7 M and [Ft] = 0.140 M. The peroxynitrite concentration drops rapidly as protonation leads to the formation of peronitrous acid (peroxynitrous acids absorbs relatively weakly around 240 nm and is not observable in Fig. 2.). In Fig. 3 the peroxynitrite concentration is represented by the transient absorption at 310 nm as a function of [it]. As expected the formation of peroxynitrous acid increases with the concentration of protons. The protonation of peroxynitrite can be viewed as a prototypical diffusion limited bimolecular reaction and thus constitutes an excellent test bed for diffusion models. 

Coddington JW, Hurst JK, Lymar SV (1999) Flydroxyl radical formation during peroxynitrous acid decomposition. J Am Chem Soc 1999 2438-2443... 

Logager T, Sehested K (1993) Formation and decay of peroxynitric acid a pulse radiolysis study. J Phys Chem 97 10047-10052... 

The upper wavelength range in which reaction 9 has been studied is relatively near the lower end of solar UVB radiation, but at present very little information is available on the real environmental role of such a process, if it has any. However, since the occurrence of reaction 9 under UVB irradiation cannot be excluded, Mack and Bolton discussed the need to revisit the reaction pathways proposed for the transformation of organic molecules in the presence of irradiated nitrate and nitrite in the light of the findings concerning the possible formation of HOONO/ONOCT [24], Since new data concerning the transformation reactions of phenol in the presence of N03 + hv, N02 + hv and HOONO are now available, the possible role of peroxynitrous acid in that particular case will be discussed later (Sect. 3.2.3). 

Another pathway that can lead to the formation of peroxynitrous acid is the reaction between OH and NO2, provided that no hydroxyl scavengers are present in solution. Another unstable species, peroxynitrate (02N00-), can also form upon reaction between 0(3P) and nitrate [22-24,27,29,33,34] ... 

In the presence of organic compounds, peroxynitrous acid induces oxidation and nitration processes [72,74,76,77]. Oxidation reactions are due to the generation of hydroxyl (reaction 28). In the case of phenol, nitration is most likely to be electrophilic as evidenced by the very steep pH trend of nitrophenol initial formation rates ( Rate oc [H+] [57]). 

The pH trend of nitrophenol formation is interesting also because with this datum, it is possible to discuss the role of peroxynitrous acid in a transformation process induced by nitrate photolysis, thus giving a first answer to the observation made by Mack and Bolton [24], HOONO forms upon irradiation of nitrate (reactions 9 and 10), although its formation at k > 280 nm is uncertain. In the presence of HOONO phenol undergoes various transformation reactions, among which nitration [57]. The pH trend of nitrophenol formation in the presence of HOONO is of the kind Rate a [H+], as discussed in... 

M15. Merenyi, G., and Lind, J., Free radical formation in the peroxynitrous acid (ONOOH)/ peroxynitrite (ONOO-) system. Chem. Res. Toxicol. 11, 243-246 (1998). 

The protonated form of peroxynitrite anion, peroxynitrous acid, is highly reactive with biologic molecnles. Hence, the production of nitric oxide from nitric oxide synthase (a complex enzyme containing several cofactors, and a heme group that is part of the catalytic site), which catalyzes the formation of NO from oxygen and arginine, can render ceUnlar components such as DNA susceptible to superoxide-mediated damage (1). 

Benton, D. J., and P. Moore (1970). Kinetics and mechanism of the formation and decay of peroxynitrous acid in perchloric solutions. J. Chem. Soc. A, 3179-3182. 

Logager, T., and Sehested, K. (1993). Formation and decay of peroxynitrous acid A pulse radiolysis study. J. Fhys. Chem. 97, 6664-6669. 

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