sulfhydrylgrupper

Sulfhydrylgrupper, also called thiol groups, are functional groups consisting of a sulfur atom bonded to a hydrogen atom and to an organic moiety (R–SH). They are the sulfur analogs of hydroxyl groups and are widespread in organic chemistry and biochemistry. The sulfur atom is typically sp3-hybridized, and the S–H bond is relatively weak compared with O–H, giving thiols distinctive reactivity. In water, aliphatic thiols have pKa values around 8–9, so they can exist as thiolate anions (RS−) under modestly basic conditions.

Sulfhydrylgrupper are reactive due to the polarizable nature of sulfur. They readily participate in oxidation-reduction chemistry, most prominently forming disulfide bonds (R–S–S–R) when two thiol groups are oxidized. They can be deprotonated to thiolates (RS−), which are good nucleophiles and react with alkyl halides to produce thioether linkages (R–S–R′). Thiols also coordinate to soft metal centers in catalysis and metal biology.

Biological significance is dominated by cysteine residues in proteins. The thiol side chains can form reversible disulfide bonds that influence protein folding, stability, and redox signaling. Enzymes such as cysteine proteases and redox systems (for example, thioredoxin and glutaredoxin) rely on thiol chemistry for function. The redox state of protein thiols can modulate activity and interactions in cells.

Applications and detection methods include the use of reagents that specifically modify free thiols, such as iodoacetamide or N-ethylmaleimide in proteomics, and Ellman’s reagent (DTNB) for thiol quantification. Some sulfhydryl compounds, known as mercaptans, are notable for their strong odors.