Chemical trapping and characterization of small oxoacids of sulfur (SOS) generated in aqueous oxidations of H2S

Abstract

Small oxoacids of sulfur (SOS) are elusive molecules like sulfenic acid, HSOH, and sulfinic acid, HS(O)OH, generated during the oxidation of hydrogen sulfide, H₂S, in aqueous solution. Unlike their alkyl homologs, there is a little data on their generation and speciation during H₂S oxidation. These SOS may exhibit both nucleophilic and electrophilic reactivity, which we attribute to interconversion between S(II) and S(IV) tautomers. We find that SOS may be trapped in situ by derivatization with nucleophilic and electrophilic trapping agents and then characterized by high resolution LC MS. In this report, we compare SOS formation from H₂S oxidation by a variety of biologically relevant oxidants. These SOS appear relatively long lived in aqueous solution, and thus may be involved in the observed physiological effects of H₂S.

Keywords: And bromobimane; Dimedone; Hydrogen sulfide; Sulfenic acid; Sulfinic acid.

Graphical abstract

Scheme 1

Small oxoacids of sulfur (SOS) species.

Fig. 1

Selective ion chromatogram and mass spectra of products 3, 4, 6 and 8, obtained in oxidation of H₂S (1 mM) with maleic peroxide (1.2 mM) in pH 7 iP buffer, trapped with a bolus of (5 mM) dimedone and iodoacetamide after 5 mins.

Scheme 2

Tautomeric forms of sulfenic acid.

Scheme 3

Sequential reaction mechanism of trapping of sulfenic acid tautomers.

Scheme 4

Reaction mechanism of sulfinyl trapping.

Fig. 2

Selective ion chromatograms and mass spectra of products 11, 12, 13 and 15, obtained in oxidation of H₂S (1 mM) with maleic peroxide (1.2 mM) in presence of mono- and dibromobimane (5 mM) in pH 7 IP buffer.

Scheme 5

Derivatized products of 1 and 2.

Scheme 6

Sketch of tautomeric forms sulfoxylic acid, H₂SO₂.

Fig. 3

Selective ion chromatogram and mass spectra of products 21 and 23, and 25 obtained in oxidation of H₂S (1 mM) with maleic peroxide (1.2 mM) in buffer, pH 7, trapped by a bolus of dimedone and acetamide (5 mM) after 5 min.

Scheme 7

Sequential reaction mechanism of trapping of sulfoxylic tautomers.

Fig. 4

Relative efficiency of HSOH and HOSOH generation in reactions of H₂S with various oxidants, based on the SIC peak areas for trapped species 4 and 21. All reactions done in the ratio of 1 mM H₂S, 1.2 mM oxidant in iP buffer pH 7, trapped by addition of 5 mM bolus of iodoacetamide and dimedone after 5 mins. The peak heights and error bars derive from an average of three experiments.

Fig. 5

Selective ion chromatogram and mass spectra of products 28 and 29, obtained in oxidation of H₂S (1 mM) with hydrogen peroxide-maleic anhydride mixture (1.2 mM) in pH 7 buffer, trapped by a bolus of dimedone and acetamide (5 mM) after 5 min.

Scheme 8

Sketch of tautomeric forms of H₂S₂O.

Fig. 6

Selective ion chromatogram and mass spectra of products 31 and 33, obtained in oxidation of H₂S (1 mM) with hydrogen peroxide-maleic anhydride mixture (1.2 mM) in pH 7 buffer, trapped by a bolus of dimedone and iodoacetamide (5 mM) after 5 min.

Scheme 9

Sketch of tautomeric forms of H₂S₂O₂.

Scheme 10

Derivatized products of 30 and 31.

Fig. 7

Selective ion chromatographs (top) and relative peak areas of those SICs (bottom) of HS_nOH generation in reactions of H₂S with H₂O₂ (black) and MP-11 (red). The reactions done in the ratio of 1 mM H₂S and 1.2 mM oxidant in iP buffer pH 7, trapped by a bolus of iodoacetamide and dimedone (5 mM) after 5 mins. The peak heights and error bars derive from an average of three experiments. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)