Thiol - Thiyl Radicals

Thiyl Radicals

For the chemistry of the SH radical, see Sulfanyl.

Free radicals derived from mercaptans, called thiyl or thiol radical or mercapto radical, are commonly invoked to explain reactions in organic chemistry and biochemistry. They have the formula RS where R is an organic substituent such as alkyl or aryl. They arise from or can be generated by a number of routes, but the principal method is H-atom abstraction from thiols. Another method involves homolysis of organic disulfides. In biology thiyl radicals are responsible for the formation of the deoxyribonucleic acids, building blocks for DNA. This conversion is catalysed by ribonucleotide reductase (see figure). Thiyl intermediates also are produced by the oxidation of glutathione, an antioxidant in biology. Thiyl radicals are also intermediates in the vulcanization process. For example, the vulcanization of polyisoprene results when mercapto radicals couple forming disulfide and polysulfide crosslinks. Thiyl radicals (sulfur-centred) can transform to carbon-centred radicals via hydrogen atom exchange equilibria. The formation of carbon-centred radicals could lead to protein damage via the formation of C—C bonds or backbone fragmentation.