Editing Thiol (section)

== Thiyl radicals ==
{{main|Thiyl radical}}[[Free radical]]s derived from mercaptans, called [[thiyl radical]]s, are commonly invoked to explain reactions in [[organic chemistry]] and [[biochemistry]]. They have the formula RS<sup>•</sup> where R is an organic substituent such as [[alkyl]] or [[aryl]].<ref name="CremlynAn" /> 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 (chemistry)|homolysis]] of organic disulfides.<ref name=Ullmann>{{Ullmann|first=Kathrin-Maria |last=Roy |title=Thiols and Organic Sulphides |year=2005|doi=10.1002/14356007.a26_767}}</ref> 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).<ref>{{cite journal|first1=JoAnne |last1=Stubbe |first2=Daniel G. |last2=Nocera |first3=Cyril S. |last3=Yee |first4=Michelle C. Y. |last4=Chang |title=Radical Initiation in the Class I Ribonucleotide Reductase: Long-Range Proton-Coupled Electron Transfer? |journal=Chem. Rev. |date=2003 |volume=103 |issue=6 |pages=2167–2202 |doi=10.1021/cr020421u|pmid=12797828 }}</ref> Thiyl intermediates also are produced by the oxidation of [[glutathione]], an antioxidant in biology. Thiyl radicals (sulfur-centred) can transform to carbon-centred radicals via [[hydrogen]] atom exchange [[chemical equilibrium|equilibria]]. The formation of [[carbon]]-centred radicals could lead to protein damage via the formation of [[Carbon|C]]−C bonds or backbone fragmentation.<ref name=Hofstetter>{{cite journal | last1 = Hofstetter | first1 = Dustin | last2 = Nauser | first2 = Thomas | last3 = Koppenol | first3 = Willem H. | year = 2010 | title = Hydrogen Exchange Equilibria in Glutathione Radicals: Rate Constants | journal = Chem. Res. Toxicol. | volume = 23 | issue = 10| pages = 1596–1600 | doi = 10.1021/tx100185k | pmc = 2956374 | pmid = 20882988 }}</ref>

Because of the weakness of the S−H bond, thiols can function as [[scavenger (chemistry)|scavenger]]s of [[free radical]]s.<ref name="Koch Parliament Brown Urtasun 2010 pp. 55–68">{{cite book | last1=Koch | first1=Cameron J. | last2=Parliament | first2=Matthew B. | last3=Brown | first3=J. Martin | last4=Urtasun | first4=Raul C. | title=Leibel and Phillips Textbook of Radiation Oncology | chapter=Chemical Modifiers of Radiation Response | publisher=Elsevier | year=2010 | isbn=978-1-4160-5897-7 | doi=10.1016/b978-1-4160-5897-7.00004-4 | pages=55–68 | quote=Sulfhydryls are scavengers of free radicals, protecting chemical damage induced by either ionizing radiation or alkylating agents.}}</ref>