Modeling the Interaction between Two- and Four-Ring Progestin Models and a Silicone-Based Polymer Model:  A Density Functional Theory Study

Abstract

In this paper, we introduce a relatively fast and reliable method for determining the feasibility of drug delivery from transdermal and implant materials. We are using density functional theory for modeling the interaction of progestins, that is, progesterone and six of its hydroxyl derivatives, with a silicone-based polymer. The silicone-based polymer model is a linear molecule, which consists of four dimethylsiloxane units. The progestin models are (1) complete progestin structures, which are called four-ring models, and (2) their two-ring models, which are comprised of the C and D rings of the basic steroid skeletons. We are investigating the interaction between the four- and two-ring models and the polymer model in three different interaction configurations. Altogether, 42 different equilibrium geometries of progestin-polymer model complexes and the corresponding interaction energies have been calculated. Our computational results are in very good agreement with the experimental findings reported previously in the literature, which state that the release rates and permeabilities of progestin pharmaceuticals in silicone-based drug delivery systems decrease when the number of hydroxyl groups is increased in the steroid skeleton. The four-ring models take the total interaction of the steroid into account slightly better than the two-ring models. However, the two-ring models are very good for predicting the local interactions between the steroid and the polymer model.