The Redox Chemistry of Sulfenic Acids

A persistent triptycenyl sulfenic acid is used as a model for cysteine-derived and other biologically relevant sulfenic acids in experiments which define their redox chemistry. EPR spectroscopy reveals that sulfinyl radicals are persistent and unreactive toward O-2, allowing the O-H bonding dissociation enthalpy (BDE) of the sulfenic acid to be readily determined by equilibration with TEMPO as 71.9 kcal/mol. The E degrees (RSO center dot/RSO-) and pK(a) of this sulfenic acid are also reported.