Activity and activity coefficient studies of aqueous binary solutions of procaine, lidocaine and tetracaine hydrochloride at 298.15 K
Vasim R. Shaikh, Dilip H. Dagade, Santosh S. Terdale, Dilip G. Hundiwale, Kesharsingh J. Patil
School of Chemical Sciences, North Maharashtra University, Jalgaon-425001, (M.S.) India
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Osmotic coefficient and density measurements are reported for the aqueous solutions of three hydrochloride salts of local anesthetical drug compounds, procaine (PC∙HCl), lidocaine (LC∙HCl) and tetracaine (TC∙HC) at 298.15 K and at ambient pressure. The experimental osmotic coefficient data are used to determine the activity and mean ionic activity coefficients of solute and solvent, respectively. The activity data have been processed to obtain the mixing and excess thermodynamic property, such as Gibbs free energy (which has been studied as a function of drug concentration) as well as to obtain the osmotic pressure and osmotic virial coefficients of the drug compounds. The mean ionic activity coefficients of the ions decrease with increase in drug concentration. The results of mixing and excess free energy changes do not show abrupt changes. These results are examined from the point of view of pre-miceller (associative) equilibria and occurrence of critical micelle concentration (cmc). A discussion is presented on the basis of aggregation of cations and the aggregation numbers of 2, 1.56 and 6 are obtained or PC∙HCl, LC∙HCl and TC∙HCl respectively in solution phase applying pseudo-phase separation model.1,2 Application of McMillan-Mayer theory of solutions to the data is made. It is noted that overall second virial coefficient are small negative for the drug molecular salt, whereas it is positive for non-electrolyte contribution. All these are examined on the basis of structural characteristic of molecules, electrostatic and hydrophobic interactions.
Keywords: Osmotic coefficient,Osmotic pressure, Mean molal activity coefficient, Second virial coefficient, Hydrophobic and stacking interactions.
1. Attwood, D.; Boitard, E.; Dubes, J. P.; Tachoire, H. J. Phys. Chem. 1992, 96, 11018-11021.
2. Desnoyers, J. E.; Caron, G.; Delisi. R.; Roberts, D.; Roux, A.; Perron. G. J. Phys. Chem. 1983, 87, 1397-1406.