Interactions in binary mixed systems involving betablockers with different lipophilicity as a function of temperature and mixed ratios

Aqueous solution of the betablockers mixtures of propranolol hydrochloride and acebutolol hydrochloride have been studied by means of density and ultrasound measurements. The critical micelle concentration of the mixture was obtained at different drug molar ratios and over a wide range of temperatures from 288.15 to 313.15 K. The deviation from ideality has been analyzed by using different theoretical models (Rubingh, Motomura). Experimental data reflects an optimum correlation with theoretical models, showing slightly differences among them and indicating deviations from ideality. The interaction parameter for binary mixtures has been determined, which was found to be temperature and composition dependent. Apparent molal volumetric properties were also found for both betablockers mixtures over a wide concentration and temperature range. The nonexistence of dimers before cmc has been corroborated fitting experimental values to the Debye–Hückel limiting law equation. Changes in apparent molar volumes and compressibilities are all negatives confirming the predominant role of the increase of hydrophobic hydration in the association of the monomers of these drugs. From these data vertical stacking of the molecules in the aggregate with the polar groups and the side chains arranged around the periphery of the stack is suggested.