Abstract
Background: Fullerene-based compounds are being developed for an extensive range of biomedical applications, and may provide a completely new class of biologically useful reagents. In support of our continuing investigation and characterization of one such compound, e,e,e-fullerene(60)- 63-tris malonic acid (1) we optimized the conditions for obtaining mass spectra.
Methods: Both positive and negative ion mass spectra are obtained using electrospray ionization (ESI). However, the spectra are dramatically different in the different ionization modes. We studied the effect of solvent media, acid content as well as the concentration of the compound (1) on mass fragmentation pattern both in positive and negative mode. We also analyzed the ion current as function of capillary voltage for selected ion.
Results: The best mass spectra were obtained when 1 was sprayed from a solution containing a weak organic acid added to aqueous methanol (1:1) in positive mode. Fragment ions formed by the direct loss of carboxyl groups from the doubly-charged dimer occur for the loss of one, two and six carboxyl groups. Of these, the loss of one carboxyl is the most abundant. The dominant mechanism for the formation of singly-charged fragment ions arises from splitting of the doubly-charged dimers into singlycharged monomers with subsequent carboxyl losses.
Conclusion: In positive ion mode, the spectra are simple with minimal fragmentation and the molecular ion region increases linearly with analyte concentration over the range studied. In negative ion mode, the spectra are more complex with the formation of dimer and fragment ions and the molecular ion region increases in a non-linear way with concentration. Further, in negative ion mode, fragment ions are affected by nearly every instrumental parameter controlling the ionization process.
Keywords: Fullerene, ESI, positive ion, negative ion, doubly charged, dimer.
Graphical Abstract
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