Equilibrium studies of thallium(I) complexes with cytidine 5′-monophosphate in different aqueous solutions of methanol

Abstract

The protonation equilibria of cytidine 5′-monophosphate (CMP) and its complex formation with Tl(I) ion were studied over a wide pH range (1.5 to 10.5), using a combination of spectrophotometric and potentiometric methods at constant temperature (25°C), different methanol–water mixtures (0 to 50% v/v), and constant ionic strength (0.1moldm−3 sodium perchlorate). Least squares regression calculations are consistent with the formation of TlHL and TlL− species, where L2− represents the fully dissociated ligand. The protonation of CMP and the formation constants of the formed complexes in different media were analyzed in terms of Kamlet, Abboud, and Taft (KAT) parameters. A single-parameter correlation of the formation constants versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity) and π* (dipolarity/polarizability) are relatively poor in all solutions, but dual and multi-parameter correlations represent significant improvements with regard to the single-parameter model. Linear correlation is observed when the experimental formation constant values (in logarithm scale) are plotted versus the calculated ones, while the KAT parameters are considered. Finally, the results are discussed in terms of the effect of solvent on protonation and complexation.