Determination of the Stability Constants of Supramolecular Complexes of Ester Derivatives of Betulin with Randomly Methylated β-Cyclodextrin by Affinity Capillary Electrophoresis

Using affinity capillary electrophoresis, the stability constants of inclusion complexes of a number of betulin ester derivatives with randomly methylated beta-cyclodextrin in 0.0100 M sodium tetraborate (pH 9.18, ionic strength 0.0200 M) at 25 degrees C were determined for the first time. The decimal logarithms of the stability constants of 1 : 1 complexes of betulin 3,28-diphthalate, betulin 3,28-disulfate, and betulin 3,28-disuccinate in a 95% confidence interval were 4.64 +/- 0.05, 4.78 +/- 0.02, and 4.94 +/- 0.02, respectively. The logarithms of the stability constants of 1 : 2 complexes of betulin 3,28-diphthalate and betulin 3,28-disulfate were 7.91 (6.66-8.19) and 8.02 (7.63-8.23), respectively. It was determined that betulin 3,28-disuccinate forms only 1 : 1 complex. The obtained stability constants of 1 : 1 complexes are generally higher than those of the complexes of the same compounds with beta-cyclodextrin (beta-CD) and lower than those for dimethyl-beta-CD, gamma-CD, and (2-hydroxypropyl)-gamma-CD complexes.