Evaluation of the reduction of imidazophenazine dye derivatives under fast-atom-bombardment mass-spectrometric conditions

Satellite [M + 2]^+• and [M + 3]⁺ peaks accompanying the common peak of the protonated molecule [M + H]⁺ that are known to indicate the occurrence of a reduction process were observed in the fast atom bombardment (FAB) mass spectra of imidazophenazine dye derivatives in glycerol matrix. The distribution of the abundances in the [M + nH] ⁺ peak group varied noticeably for different derivatives. This indicated different levels of the reduction depending on the different structure variations of the studied molecules. In the search for correlations between the mass spectral pattern and the structural features of the dyes, ab initio HF/6-31++G** quantum chemical calculations were performed. They revealed that the abundances of the [M + 2]^+• and [M + 3] ⁺ ions show growth proportional to the decrease of the energy of the lowest unoccupied molecular orbital, i.e. proportional to the increase of the electron affinity of the dye molecule. A method for rapid screening of reductive properties of sets of dye derivatives on the basis of the FAB mass spectral data is discussed.