Chronocoulometry diffusion coefficients as a measure of cyclodextrin-estradiol complex association

Abstract

The formation of inclusion complexes between estradiol and p-cyclodextrin (CD), sulfobutyleter-beta-CD (SBCD) and hydroxypropil-beta-CD (HPCD) was studied by chronocoulometric and differential pulse voltammetry. In presence of CD there is a decrease of the cathodic peak current with the increase of the amount of CD. This decrease is due to the lower diffusion coefficient (D) of estradiol-cyclodextrin complex compared with the free guest. In absence of CD, an estradiol D value of 8.6 x 10(-6) +/- 0.1 x 10(-6) cm(2) s(-1) Was obtained. The addition of CDs produced a maximum decrease of 20%, 22% and 30% in the diffusion coefficient with CD, SBCD and HPCD, respectively. Using the variation in D, association constants of 132 +/- 18, 247 +/- 32 and 276 +/- 28 M-1 for CD, HPCD and SBCD were determined.