Theoretical and experimental studies of cationized uracil complexes in the gas phase.

Cationized uracil clusters were generated in the gas phase by electrospray ionization (ESI). Mass spectrometry experiments showed that with particular experimental conditions, decameric uracil clusters are magic number clusters. MS/MS experiments demonstrated that the structure of these decameric uracil clusters depends substantially on the size and the charge of the cation. On the basis of the ab initio and density functional theory (DFT) quantum chemistry calculations, structures for these decameric clusters were proposed. These structures are in agreement with the experimental mass spectra of modified nucleobases. Theoretical calculations showed that complexes experimentally observed using ESI-MS techniques, are not naturally the most stable in the gas phase.