Limiting diffusion coefficients of sodium octanoate, and octanoic acid in aqueous solutions without and with α-cyclodextrin

• Limiting diffusion coefficients of sodium octanoate and octanoic acid in aqueous solutions.
• Limiting diffusion coefficients of the molecular and dissociated forms of the octanoic acid.
• Estimation of the equilibrium constant, K, for a supramolecular host–guest complex between octanoic acid and α-CD.

The Taylor dispersion technique has been used for measuring limiting binary mutual diffusion coefficients of octanoic acid and sodium octanoate at T = 298.15 K (D0), respectively, using water as carrier solution, and different injections solutions from (0.75 to 100) · 10−3 mol ⋅ dm−3. These D0 values, together with the Stokes–Einstein equation, were used to determine the equivalent hydrodynamic radii, Rh, at infinitesimal concentration of these species (octanoic acid and sodium octanoate). In addition, the limiting diffusion coefficients of the molecular (D0m) and dissociated (D0±) forms of the octanoic acid were estimated.We have also investigated the diffusion properties for a system containing octanoic acid, α-cyclodextrin (α-CD) and water. From these results, we have estimated the percentages of free (C7COOH) and associated forms of octanoic acid (α-CD/C7COOH) and the equilibrium constant, K, for a supramolecular host–guest complex between octanoic acid and α-CD.