On the NO/H2S ?crosstalk? reactions. Role of thionitrites (SNO-) and perthionitrites (SSNO-)

JUAN P. MARCOLONGO; MATEUS VENANCIO; WILLIAN ROCHA; FABIO DOCTOROVICH; JOSÉ A. OLABE

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2019

0020-1669

The redox chemistry of H2S with NO and other oxidants containing the NO-group isdiscussed on a mechanistic basis, due to the expanding interest in their biological relevance,with an eye open to the chemical differences of H2S and thiols RSH. We focus on the properties of two ?crosstalk? intermediates, SNO- (thionitrite) and SSNO- (perthionitrite, nitrosodisulfide) based in the largely controversial status on their identity and chemistry in aqueous/nonaqueous media, in the route to final products N2O, NO2-, NH2OH/NH3 and S8.Thionitrous acid, generated either in the direct reaction of NO + H2S, or through the transnitrosation of RSNO?s (nitrosothiols) with H2S at pH 7.4, is best described as a mixture of rapidly interconverting isomers, {(H)SNO}. It is reactive in different competitive modes, with a half-life of a few seconds at pH 7.4 for the homolytic cleavage of the N-S bond andcould be deprotonated at pHs up to ca. 10 giving SNO-, a less reactive species than {(H)SNO}. The latter mixture can also react with HS- giving HNO and HS2-(hydrogen disulfide), a So(sulfane)-transfer reagent toward {(H)SNO}, leading to SSNO-, a moderately stable species that slowly decomposes in aqueous sulfide-containing solutions in the minutehour time scale, depending on [O2]. The previous characterization of HSNO/SNO- andSSNO- is critically discussed based on the available chemical and spectroscopic evidence (MS, UV-vis, 15N NMR, FTIR), together with computational studies including molecular dynamics QM-MM simulations that provide a structural and UV-vis description of the solvatochromic properties of cis-SSNO- acting as an electron-donor in water, alcohols and aprotic acceptor solvents. In this way SSNO- is confirmed as the elusive ?yellow intermediate? (I412) emerging in the aqueous crosstalk reactions, in contrast with its assignment to polysulfides, HSn-. The analysis extends to the coordination abilities of {(H)SNO}, SNO- andSSNO- into heme- and nonheme iron centers, providing a basis for best unraveling their putative specific signaling roles.