engleski

Gas-phase organometallation in the mass spectrometer

One can argue that mass spectrometry (MS) has evolved through three developmental phases: i), mass and composition determinations ; ii), structure determination either by fragmentation or exact mass determination ; and, recently, iii), synthesis and reaction mechanism determinations. For realization phase iii), it was necessary to develop vacuum, magnet and computer technology that would permit reactants and products to remain for sufficiently long periods in the instrument. Such a state of affairs exists, for example, in a Fourier transform mass spectrometer (FTMS), in which measurements can be carried out over several minutes of reaction time. We report here metallation reactions of polycyclic aromatic hydrocarbons (PAH's) and their heteroanalogs, as ligands (L) with metal monocations produced by laser desorption ionization (LDI) in a 3T FTMS instrument (FT/MS 2001 DD, Finnigan, Madison, WI, USA). Four types of reactions are observed: i), charge exchange (M+ + L → M + L+) ; ii), simple addition (M+ L → ML+) ; iii), addition accompanied by a loss of part of a ligand (M+ + L → M(L-X)+ + X) ; and iv), consequtive n-merization (ML+ + L → ML2+ ; L+ + L → L2+ ; M(L-X)+ + L → ML(L-X)+ ; M(L-X)+ + L → (M(L-X)(L-Y))+ + Y ; ML2+ + L → ML3+ ; etc.).Such reactions generate new products, they provide insights into the reactivity of bare metal ions void of solvation and neighboring effects (intrinsic reactivity), and they permit records of time-delayed mass spectra so that reaction rate constants may be determined and reaction mechanisms may be postulated. The reactions of various metal monocations with PAH's (pyrene, phenanthrene) and their heteroanalogs (9-azaphenanthrene, 4, 9-diazapyrene) and three porphyrins will be discussed.

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