Drug delivery systems: Study of inclusion complex formation for ternary caffeine–β-cyclodextrin–water mixtures from apparent molar volume values at 298.15 K and 310.15 K

Abstract

The aim of this paper is to provide insight into the molecular mechanisms of inclusion complex formation along with the structural understanding of drug–carrier molecule interactions in aqueous ternary systems including caffeine and β-cyclodextrin.Apparent partial molar volumes (Vφ) were determined from density experimental measurements for the binary aqueous solutions of both β-cyclodextrin and caffeine, as well as for the ternary aqueous solutions in the low concentration range (i.e., corresponding to the therapeutic applications in the drug-releasing field).Mathematical modelling of this apparent molar property, assuming inclusion complexes of 1:1 stoichiometry, allowed the estimation of the corresponding equilibrium constant. Information about the driving forces for the insertion of the caffeine into the β-cyclodextrin molecule was derived from the volume changes.Interactions between aqueous solutes and/or solute–solvent interactions taking place in the solutions were evaluated from the volumes of transfer, Δ Vφ,c , and the viscosity B coefficients of transfer, ΔB, for the caffeine from water to the different aqueous solutions of β-cyclodextrin.The measurements were carried out at the standard (298.15±0.01) K and the physiological (310.15±0.01) K temperatures.