Electrospray ionization mass spectrometric study of thallium complexes with nucleosides

The complexes between Tl⁺, K⁺, and nucleosides were studied by using electrospray ionization mass spectrometry. It was found that for complexes of 1:1 stoichiometry, thallium complexes with cytidine were the most abundant and thallium complexes with guanosine were the second most abundant ones. The relative abundances of cytidine-Tl⁺ to cytidine-K⁺ complexes depended on stoichiometry (at higher stoichiometry the potassium complexes were more abundant). In other words, the relative affinity of Tl⁺ and K⁺ to form cytidine complexes depends on the stoichiometry of the formed complexes. Guanosine-Tl⁺ complexes were more abundant than guanosine-K⁺ complexes, irrespective of stoichiometry. Both guanosine tetramer and mixed cytidine/guanosine tetramer were more abundant when they were stabilized by thallium than potassium. Therefore, Tl⁺ may affect the K⁺ stabilization of these tetramers.