Photo-induced reactions of hemin(DMSO) n clusters (n = 0-3) produced with electrospray ionization

Photo-induced reaction of [Fe(III)-protoporphyrin]+ (hemin+) ions solvated with dimethylsulfoxide (DMSO) is investigated by using a tandem mass spectrometer with electrospray ionization. We measure the photodissociation yields of mass-selected hemin+(DMSO)n clusters for n = 0-3 in the energy region of 15 800-28 200 cm-1. The mass spectra of the fragment ions show the β-cleavage of carboxymethyl groups in addition to the evaporation of solvent molecules. Yield of the β-cleavage reaction is found to depend strongly on the excitation energy and the number of solvent molecules. We also examine the metastable decomposition of the clusters following primary mass selection and determine the incremental solvent binding energies and internal energies for the clusters using evaporative ensemble model. From these results, we investigate the reaction mechanism of β-cleavage of hemin+ ion.