Fast atom bombardment combined with tandem mass spectrometry for the study of dinucleotides

A study of mono- and dinucleotides by utilizing negative ion fast atom bombardment (FAB), metastable decomposition of (M-H)^- species, and collisionally activated decomposition (CAD) of (M-H)^- species is reported. Data were obtained for several complete series containing the standard nucleosides (guanosine, adenosine, cytidine, thymidine, and uridine): the 3′- and 5′-monophosphate mononucleotide series for both ribo- and 2′-deoxyribomononucleotides, all possible combinations for the 3′- → 5′-ribodinucleotides, and all possible combinations of the 3′- → 5′,2′-deoxyribodinucleotides. The metastable and CAD spectra provide more information than the FAB mass spectra. The (M-H)^- ions of all dinucleotides decompose either as metastable ions or upon collisional activation to eliminate BH (B = base) preferentially from the 3′- rather than the 5′-terminus. Isomeric dinucleotides can be distinguished on the basis of this fragmentation. To establish the identity of the base at the 5′-terminus, collisional activation is preferred. By comparing relative abundances of BH elimination observed, the inherent basicities of the nucleoside base anions can be inferred to be C^- > A^-, T^-, > G^-.