Multicomponent diffusion in (cyclodextrin-drug + salt + water) systems: {2-Hydroxypropyl-β-cyclodextrin (HP-βCD) + KCl + theophylline + water}, and {β-cyclodextrin (βCD) + KCl + theophylline + water}

The Taylor dispersion technique was used to measure values of mutual diffusion coefficient in aqueous solutions of {2-hydroxypropyl-β-cyclodextrin (HP-βCD)  + KCl + theophylline (THP)  + water}, and {β-cyclodextrin (βCD)  + KCl + theophylline (THP)  + water} at T = 298.15 K at equimolar carrier concentrations of (0.002, 0.005, and 0.010) mol · dm−3, for each solute. We determined the nine multicomponent diffusion coefficients for these systems, 123D11, 123D22, 123D33, 123D12, 123D13, 123D21, 123D23, 123D31, and 123D32, and compared them with those previously obtained for the corresponding ternary and binary systems.Coupled diffusion of those components, as indicated by cross-diffusion coefficients, 123D12, 123D13, 123D21, 123D23, 123D31, and 123D32, are discussed in terms of salting-out effects, as well as the possible formation of both theophylline–metal ion or cyclodextrins–metal ion complexes.

► Quaternary diffusion coefficients for the systems containing potassium chloride, theophylline, and some cyclodextrins.
► Diffusion of potassium chloride and theophylline driven by HP-βCD gradients.
► Coupled diffusion as indicated by cross-diffusion coefficients.