LIQUID SECONDARY-ION MASS-SPECTRA OF 2-IMINOTHIOLANE DERIVATIVES

The derivatization reaction of 2-iminothiolane with several small pept ides has been studied using Liquid secondary ion mass spectrometry. Th e 2-iminothiolane reagent reacts with side-chain amino groups and with N-terminal amines in peptides. Addition of 2-iminothiolane introduces a free sulfhydryl group and an immonium group into the peptide. The s ignal intensity for the derivative of a small peptide is approximately the same as that of the [M + H](+) ion of the same underivatized pept ide from a glycerol solution. The pattern of dissociation observed in the product ion MS/MS spectrum is altered to reflect the derivative. T he sulfhydryl group introduced via 2-iminothiolane reaction further al lows for the incorporation of maleimide fluorophores into the peptide for sensitive detection by ultraviolet/visible absorption or fluoresce nce. This work also reports a previously unrecognized recyclization si de-reaction that involves loss of the immonium group during the deriva tization reaction.