Spontaneous and Selective Formation of HSNO, a Crucial Intermediate Linking H

Abstract

Thionitrous acid (HSNO), a potential key intermediate in biological signaling pathways, has been proposed to link NO and H[superscript 2]S biochemistries, but its existence and stability in vivo remain controversial. We establish that HSNO is spontaneously formed in high concentration when NO and H[subscript 2]S gases are mixed at room temperature in the presence of metallic surfaces. Our measurements reveal that HSNO is formed by the reaction H[superscript 2]S + N[subscript 2]O[subscript 3] → HSNO + HNO[subscript 2], where N[superscript 2]O[superscript 3] is a product of NO disproportionation. These studies also suggest that further reaction of HSNO with H[subscript 2]S may form HNO and HSSH. The length of the S–N bond has been derived to high precision and is found to be unusually long: 1.84 Å, the longest S–N bond reported to date for an R-SNO compound. The present structural and, particularly, reactivity investigations of this elusive molecule provide a firm foundation to better understand its potential physiological chemistry and propensity to undergo S–N bond cleavage in vivo.