Thermodynamic parameters for the complexation of water-soluble betulin derivatives with (2-hydroxypropyl)-β-cyclodextrin determined by affinity capillary electrophoresis.

The interaction between (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and water-soluble betulin derivatives, betulin 3,28-disulfate (DSB) and betulin 3-acetate-28-sulfate (ASB), belonging to the class of pentacyclic lupane triterpenoids, was studied using affinity capillary electrophoresis. It was found that 1:1 and 1:2 complexes were formed. The stability constants of the complexes in the temperature range of 293.15–318.15 K were determined. The values obtained are sufficiently large; log K (1:1) and log K (1:2) are 4.25–5.02 and 6.08–7.59, respectively. This phenomenon can be explained by the presence of broad hydrophobic regions in the molecules of the compound studied. The stability constants decrease with increasing temperature. The stability constants for ASB complexes are slightly higher as compared to the constants for DSB complexes. The thermodynamic parameters for the complexation were calculated from the van't Hoff plots. The complexation was found to be controlled by the enthalpy change. The obtained values of stability constants at 298 K were compared with values for the β-CD complexes of the compounds under study and for the HP-β-CD and β-CD complexes of water-insoluble betulin derivatives. It was found that water-soluble betulin derivatives form more stable complexes with CDs as compared to water-insoluble derivatives (betulonic and betulinic acids), and the HP-β-CD complexes are more stable than the β-CD complexes. • Betulin 3,28-disulfate and betulin 3-acetate-28-sulfate form 1:1 and 1:2 complexes with (2-hydroxypropyl)-β-cyclodextrin • Logarithms of stability constants are >4 • The complexation is controlled by the enthalpy change • Water-soluble betulin derivatives form more stable complexes with CDs as compared to water-insoluble derivatives • The HP-β-CD complexes are more stable than the β-CD complexes [ABSTRACT FROM AUTHOR]