Electrospray Ionization Mass Spectral Characterization of Transient Iron Species of Bioinorganic Relevance

Strategies have been developed to obtain electrospray ionization mass spectral data on short-lived intermediates derived from the reactions of non-heme iron complexes with peroxides. The molecular composition of a transient green intermediate generated from Fe(2)O(5-Me(3)-TPA)(2)(OH)(H(2)O)](ClO(4))(3) with H(2)O(2) in CH(3)CN at -40 degrees C was determined by introducing the solution via a precooled syringe to the inlet of the mass spectrometer. The observation of prominent ion clusters in both positive and negative mass regions, together with isotope distribution patterns characteristic of the number of associated ClO(4) ions, allows its formulation as Fe(2)(O)(2)(5-Me(3)-TPA)(2)](ClO(4))(3). The molecular composition of a transient blue species derived from the reaction of Fe(2)O(TPA)(2)(H(2)O)(ClO(4))](ClO(4))(3) with excess benzyl alcohol and (t)BuOOH at -40 degrees C was also determined. Due to its limited stability even at -40 degrees C, the blue intermediate was generated in a cooled mixing tee from its precursor components and directly introduced into the mass spectrometer. Its formulation as {Fe(TPA)(OO(t)Bu)(ROH)](ClO(4))}(+) (R = H or CH(2)Ph) is based on the masses observed, isotope distribution patterns, the observation of expected shifts in the mass values by appropriate substitutions, and tandem mass spectral data. These transient species relate to possible intermediates of non-heme iron enzymes.