Conductometry, spectrophotometry and mass spectrometric investigation of Mg(II) and Ca(II) complexes with an antiretroviral drug, zidovudine

Metal ions play a key role in living systems and are used to perform different physiological activities in our body. Complexation of drugs with metal ions is known to influence the bioavailability and other pharmacokinetic properties of drugs. In the present work, complexation of two essential cations, Mg2+ and Ca2+ with zidovudine (AZT), the first approved antiretroviral drug for human immunodeficiency virus (HIV) has been studied by conductometry and spectrophotometry. The plots of molar conductance versus the mole ratio of [AZT]/[M2+], Job’s method of continuous variation and mole ratio method showed the stoichiometry to be 1:1 (M2+:AZT) for both the cations. The metal ion-AZT complexes formed through the nitrogen of the azide group were further ascertained by liquid chromatography-mass spectrometric analysis. The formation constants of the complexes as evaluated by the conductance method and the Rose-Drago method were in good agreement. The values of thermodynamic parameters (∆H and ∆S) for the formation of complexes were obtained from the Van’t Hoff plots. The results revealed that both the complexation reactions were spontaneous, endothermic and entropy stabilized.