Abstract
The lag-time method of diffusion has been used to investigate permeation of hydrocortisone, dexamethasone, testosterone and progesterone across cellulose acetate membranes between 10 degrees and 40 degrees. The process depended mainly on membrane-water partition coefficients of the steroids so that the least polar compound permeated the fastest. Permeation generally increased with increasing temperature and from the temperature dependance of the diffusion coefficient, energies of activation were derived. The varied from 2.4 kcal mol(-1) for the least polar steroid, progesterone, to 7.4 kcal mol(-1) for the most polar, hydrocortisone. n-C16 Polyoxyethylene surfactants when present below and above the cmc increased the steroids permeation rates. Varying the polyoxyethylene chain length (OE equals 17-63) did not significantly affect permeation rates, suggesting that the enhancing effect of surfactants arises from their hydrophobic group.
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