Study of adduct ions of meso-phenyl-substituted tetrabenzoporphyrins by fast-atom bombardment mass spectrometry

Abstract

Mass spectra of meso-phenyl-substituted tetrabenzoporphyrins were investigated by fast-atom bombardment mass spectrometry and tandem mass spectrometry. A cluster of adduct ions with mass-to-charge ratio values higher than the corresponding molecular ions of the porphyrins has been observed. The mass number differences among the series of cluster ions are constant depending on the para-phenyl substituents. Under certain conditions, dimers or trimers of molecular ions with low abundances have been detected. To trace the origin of the adduct ions, a series of experiments based on mass spectrometry have been carried out. The mass spectrum of tetrabenzoporphyrin showed no adduct ions with mass number differences of 90 even with the addition of phenylacetic acid. The mass spectrum of meso-tetraphenylte-trabenzoporphyrin 13C-labeled at the meso carbons showed adduct ions with mass number differences of 91. Product spectra of [2M + H]+ or [3M + H]+ of porphyrins exhibited adduct ions. All these results suggest that fragmentations of [2M + H]+ or [3M + H]+ may be one of the many possible routes to form the adduct ions, and the mass number differences among the series of these cluster ions should correspond to the benzyl group from the meso positions of meso-phenyl-substituted tetrabenzoporphyrins.