Electrospray ionization mass spectrometric study of platinum(II) complexes with nucleobases and dimethyl sulfoxide

The electrospray ionization spectra of methanol solution containing adenine or guanine or cytosine (M) and PtCl2 and DMSO at a low cone voltage value, have shown the singly charged ions, namely [M + PtCl + 2DMSO]+. Analogous ions have been observed for adenosine, guanosine and cytidine. The data obtained from the mass spectra taken at a higher cone voltage and with the use of isotope labelled DMSO permit to discuss the fragmentation pathways of [M + PtCl + 2DMSO]+. On the grounds of the experimental results and respective literature data, the structures of [M + PtCl + 2DMSO]+ ions are proposed. In a methanol solution containing uracil or thymine (or their nucleosides), the ions containing deprotonated nucleobase (or nucleoside), namely [M − H + PtCl + 2DMSO + Na]+ and [M − H + PtCl + 2DMSO + K]+, have been detected. The higher acidity of uracil and thymine in relation to the other nucleobases may explain the existence of complexes containing deprotonated molecules. However, it has been difficult to propose their structures on the basis of the results obtained.