Nitrosation and nitrosylation

The biological functions of nitric oxide include S-nitrosylation, the conjugation of NO to cysteine thiols in proteins, which is an important part of cell signalling.

NO+ synthon transfer is catalyzed by a strong nucleophile, such as (in order of increasing efficacy) chloride, bromide, thiocyanate, or thiourea.

[6] Unusually for electrophilic aromatic substitution, proton release to the solvent is typically rate-limiting, and the reaction can be suppressed in superacidic conditions.

[8] S-nitrosothiols are typically prepared by condensation of a thiol and nitrous acid:[9] They are liable to disproportionate to the disulfide and nitrogen oxides.

The compounds are believed to nitrosate primary amines during the acid environment of the stomach, and the resulting diazonium ions alkylate DNA, leading to cancer.