Effect of 2-Hydroxypropyl-β-cyclodextrin on the diffusion behaviour of L-dopa in aqueous solutions

Ternary mutual diffusion coefficients (D11, D22, D12 and D21) measured by the Taylor dispersion method are reported for aqueous solutions of levodopa (L-dopa) (1) in the presence of 2-Hydroxypropyl-β-cyclodextrin (HP-β-CD) (2) at 25 °C and 37 °C and concentrations up to 0.005 mol · dm−3. The effects of HP-β-CD (HP-β-CD) on the transport of L-dopa are assessed by comparing the binary diffusion coefficient of aqueous L-dopa solutions with the main diffusion coefficient (D11) measured for ternary {L-dopa (1) + HP-β-CD (2)} solutions. 1H NMR spectroscopy suggests no significant complexation between HP-β-CD and L-dopa. However, coupled diffusion of L-dopa and HP-β-CD occurs, as indicated by non-zero values of the cross-diffusion coefficients, D12 and D21. HP-β-CD concentration gradients produce significant co-current coupled flows of L-dopa.