Solvent effects on complexation of thallium(I) with guanosine 5′-monophosphate in methanol-water mixtures

The interaction of guanosine 5'-monophosphate, GMP, with the thallium(I) ion was studied by UV-vis and potentiometric titration methods and P-31 NMR spectroscopy. Both NMR spectra and UV-vis titration data have shown that GMP coordinates via guanine to the thallium(I) ion in the pH range 1.5-10. Our study of the system Tl(I) + GMP was performed in water-methanol mixtures with different volume ratios of methanol. The complexation equilibrium in the pH range of study led to the following mononuclear species: TlH2(GMP)+, TlH(GMP) and Tl(GMP)(-), where (GMP)(2-) represents the fully dissociated ligand. The formation constants of the species were calculated in the various media at constant temperature (25 degrees C) and constant ionic strength of sodium perchlorate (0.1 mol dm(-3)) using a suitable computer program. The formation constants were analyzed in terms of Kamlet and Taft's parameters. A single-parameter correlation of the formation constants, beta(121), beta(111), and beta(101) vs alpha (hydrogen-bond donor acidity), beta (hydrogen-bond acceptor basicity) and for pi* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlations represent significant improvements with regard to the single-parameter model. In this work, we have also used the normalized polarity parameter, ET, alone and in combination with some of the Kamlet-Taft parameters to find a better correlation of the formation constants in different methanol-water mixtures. Copyright (c) 2007 John Wiley & Sons, Ltd.