Does Perthionitrite (SSNO<sup>–</sup>) Account
for Sustained Bioactivity of NO? A (Bio)chemical Characterization
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Abstract
Hydrogen sulfide (H<sub>2</sub>S)
and nitric oxide (NO) are important signaling molecules that regulate
several physiological functions. Understanding the chemistry behind
their interplay is important for explaining these functions. The reaction
of H<sub>2</sub>S with <i>S</i>-nitrosothiols to form the
smallest <i>S</i>-nitrosothiol, thionitrous acid (HSNO),
is one example of physiologically relevant cross-talk between H<sub>2</sub>S and nitrogen species. Perthionitrite (SSNO<sup>–</sup>) has recently been considered as an important biological source
of NO that is far more stable and longer living than HSNO. In order
to experimentally address this issue here, we prepared SSNO<sup>–</sup> by two different approaches, which lead to two distinct species:
SSNO<sup>–</sup> and dithionitric acid [HON(S)S/HSN(O)S]. (H)S<sub>2</sub>NO species and their reactivity were studied by <sup>15</sup>N NMR, IR, electron paramagnetic resonance and high-resolution electrospray
ionization time-of-flight mass spectrometry, as well as by X-ray structure
analysis and cyclic voltammetry. The obtained results pointed toward
the inherent instability of SSNO<sup>–</sup> in water solutions.
SSNO<sup>–</sup> decomposed readily in the presence of light,
water, or acid, with concomitant formation of elemental sulfur and
HNO. Furthermore, SSNO<sup>−</sup> reacted with H<sub>2</sub>S to generate HSNO. Computational studies on (H)SSNO provided additional
explanations for its instability. Thus, on the basis of our data,
it seems to be less probable that SSNO<sup>–</sup> can serve
as a signaling molecule and biological source of NO. SSNO<sup>–</sup> salts could, however, be used as fast generators of HNO in water
solutions