The dissociation constants of Adefovir ({[2-(6-amino-9H-purine-9-l)ethoxi]methyl}phosphoric acid) used in the treatment of hepatitis B and Cidofovir ({[2-(6-amino-9H-purine-9-l)ethoxi]methyl} phosphoric acid), used in the treatment of cytomegalovirus retinitis in AIDS patients, together with the stability constants of its Cu2+, Ni2+, Zn2+, Co2+, Ca2+, and Mg2+ complexes were studied by potentiometric titration. Adefovir and Cidofovir were abbreviated to PMEA and HPMPC. All measurements were obtained under two sets of conditions: at 298 K and ionic strength (I) of 0.1 mol dm(-3) (NaCl) and at 310 K and I of 0.16 mol dm(-3) (NaCl), corresponding to the conditions of human blood. Equilibrium constants in aqueous solution were calculated using the program SUPERQUAD. Also, solvent effects on the equilibrium constants of the ligands were examined. Moreover, all coordination studies were carried out with the hgand/metal molar ratios of 1:1. This ligand/metal stoichiometric ratio was spectrometrically determined using Job's method. (C) 2013 Elsevier B.V. All rights reserved.