Abstract
The encapsulation of tetracaine hydrochloride (TTAC...HCl) by β-cyclodextrin (β-CD) andhydroxypropyl-β-cyclodextrin (HPBCD) has been analyzedfrom a thermodynamic point of view, by means of conductometric studies at different temperatures. Conductivity measurements of aqueous solutions of the drug were performed: (i) in the absence of CD, as a function of drug concentration; and (ii) in the presence of CD, as a function of CD concentration, both studies at different temperatures ranging from 15 to 40 °C. The stoichiometry of the complexes, the association constants, and the ionic molar conductivities at infinite dilution ofthe free (λDRUG0) and complexed(λCD:DRUG0) drug were obtained from these conductivitydata. From the dependency of the association constants with temperature (van't Hoff analysis), the inclusion complexes formed by β-CD and/or HPBCD and the drug were found to be enthalpy driven, with a favorable enthalpic term dominant over an unfavorable entropic term. This pattern could be revealing the contribution of van der Waals interactions, hydrophobic effect and solvent reorganization as the main driven forces promoting the interaction.
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