Uncommon temperature effect on the interaction between levodopa and β-cyclodextrin seen by diffusometry and NMR spectroscopy

Experimental ternary mutual diffusion coefficients (D11, D22, D12 and D21, obtained by the Taylor dispersion method, are reported for aqueous solutions of levodopa (L-dopa) + β-cyclodextrin (β-CD) solutions at 310.15 K and concentrations up to 0.007 mol dm−3. Comparison of these experimental results with data predicted by a model of the diffusion that includes inclusion complexes, it is possible to conclude that the association equilibrium at 310.15 K has little effect on the diffusion properties. Support for this comes from 1H NMR spectroscopy, which shows that there are no interactions, which may be related to the reduced L-dopa/cavity interactions resulting from both the amine and carboxylate groups on L-dopa being charged.