Peroxynitrite

The ion peroxynitrite and the acid peroxynitreux are known since the beginning of the 20th century. Since the middle of the years 1990, these two entities take an increasing importance in the comprehension of many cellular phenomena, and in particular in the explanation of the cellular suicide (Apoptose).

Synthesis - Description

At the laboratory, the sodium peroxynitrite is obtained by action of the Ozone O₃ on the Azoture of Sodium NaN₃

The synthesis in vivo of the ion peroxynitrite is done in intracellular medium by fast reaction of the Oxyde nitric with the ion superoxyde O₂^-.

The constant speed of this reaction lies, according to the authors, between 5.10⁹ and 2.10¹⁰ mol^-1.s^-1, whereas that of the opposite reaction is lower than 1 s^-1. Whereas the ion peroxynitrite is relatively stable, its combined acid, peroxynitreux acid HOONO, isomérise slowly in ion is nitrated. The constant speed of this isomerization is it of 1,2 s^-1.

This is why the time of half-life in vivo of the peroxynitrites is relatively high, namely 20 ms.

Potential diagram pH of the acid couple peroxynitreux/Dioxide nitrogen

The pKa of the peroxynitreux acid couple/ion peroxynitrite is of 6,8. the potential redox of the couple peroxynitreux ion/nitrogen dioxide is of 1,4 V with pH = 7.

It is possible to deduce following diagram potential-pH from it:

It is remarkable to note that the pKa of this couple is very close to the physiological pH (7,4). We can deduce from it that the acid form accounts for 20% of the totality of the species with this pH.

Diagram of Frost of nitrogen

with pH=0, the Diagramme of Frost of nitrogen eminently shows us the character oxidizing of the peroxynitreux acid.

This character mainly explains its properties of agent of nitration of the activated aromatic cycles, the such phenol S (Tyrosine), the Aniline S (Mifépristone), like its mutagen properties (cut of chains of DNA, oxidation of the déoxy Guanosine in 8-nitrodéoxy Guanosine and 8-oxodéoxy Guanosine).

Reactivity of the peroxynitrites

Here summarized principal reactions of the peroxynitrites and the peroxynitreux acid whose biological importance is remarkable.

The peroxynitrites are also known to oxidize sulfate thiols directly, to be one of the causes of the peroxidation of the lipids.

The replication of HIV is closely related to the presence of peroxynitrites, because the decomposition of those by MnTBAP (mn chloride (III) tetrakis (4-benzoi acid) porphrin) inhibits to 99% this replication during an acute infection and to 90% during a chronic infection.

References

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