Synthesis, spectral properties and use of thiodan, a new thiol-specific fluorescent reagent

A new fluorescent reagent, Thiodan, containing the -SO2-S- function, is described. It can be utilized in protein chemistry as a reversible fluorescent labeling agent of cysteine residues. Thiodan is also shown to be useful for titration of sulfhydryl groups, due to the intensely fluorescent sulfinate anion released during the reaction.