Sulfhydrylgruppen

The sulfhydrylgruppen, also known as the thiol group, is a functional group in organic chemistry with the structure -SH. It consists of a sulfur atom bonded to a hydrogen atom and to the rest of the molecule (R-SH). Sulfur’s larger size and polarizability make thiols relatively nucleophilic and redox-active compared with alcohols, giving them characteristic chemical behavior.

In many thiols the hydrogen can be released, giving a thiolate anion RS−. The pKa of typical aliphatic thiols is around 8–9, but this value varies with the surrounding structure. Deprotonation yields a stronger nucleophile that is more readily oxidized. Thiols readily form disulfides through oxidation: 2 R-SH ⇌ R-S-S-R + 2 H+ + 2 e−. This redox chemistry is central to many biological and chemical processes.

Biological relevance is dominated by the thiol group of the amino acid cysteine. Cysteine residues in proteins can form disulfide bonds that help stabilize structure, or participate in catalytic processes. Methionine, another sulfur-containing amino acid, has a thioether rather than a thiol. In cells, the redox couple glutathione (GSH) / glutathione disulfide (GSSG) uses thiol chemistry to buffer oxidative stress and regulate cellular processes.

Detection and modification of thiols are common in chemistry and biochemistry. Free thiols can be quantified with Ellman’s reagent (DTNB), which yields a yellow chromophore. Thiols also undergo various post-translational modifications, such as S-nitrosylation, S-palmitoylation, and sulfenylation, reflecting their roles as reactive centers in enzymes and signaling pathways.