Solubilization of Trans-Resveratrol in Some Mono-Solvents and Various Propylene Glycol + Water Mixtures.

This research deals with the determination of solubility, Hansen solubility parameters, dissolution properties, enthalpy-entropy compensation, and computational modeling of a naturally-derived bioactive compound trans-resveratrol (TRV) in water, methanol, ethanol, n-propanol, n-butanol, propylene glycol (PG), and various PG + water mixtures. The solubility of TRV in six different mono-solvents and various PG + water mixtures was determined at 298.2-318.2 K and 0.1 MPa. The measured experimental solubility values of TRV were regressed using six different computational/theoretical models, including van't Hoff, Apelblat, Buchowski-Ksiazczak λh, Yalkowsly-Roseman, Jouyban-Acree, and van't Hoff-Jouyban-Acree models, with average uncertainties of less than 3.0%. The maxima of TRV solubility in mole fraction was obtained in neat PG (2.62 × 10-2) at 318.2 K. However, the minima of TRV solubility in the mole fraction was recorded in neat water (3.12 × 10-6) at 298.2 K. Thermodynamic calculation of TRV dissolution properties suggested an endothermic and entropy-driven dissolution of TRV in all studied mono-solvents and various PG + water mixtures. Solvation behavior evaluation indicated an enthalpy-driven mechanism as the main mechanism for TRV solvation. Based on these data and observations, PG has been chosen as the best mono-solvent for TRV solubilization.

Solubility-physicochemical-thermodynamic theory of penetration enhancer mechanism of action.

The hypothesis for the investigation was that the overall mechanism of action of skin penetration enhancers is best explained by the Solubility-Physicochemical-Thermodynamic (SPT) theory. To our knowledge, this is the first report of the application of SPT theory in transdermal/topical/enhancer research. The SPT theory puts forward the concept that the mode of action of enhancers is related to solubility parameters, physicochemical interactions and thermodynamic activity. This paper discusses these concepts by using experimentally derived permeation data, various physicochemical and solubility parameters (ingredient active gap (IAG), ingredient skin gap (ISG), solubility of active in the formulation (SolV) and the formulation solubility in the skin (SolS)) generated by using FFE (Formulating for Efficacy™ - ACT Solutions Corp) software. These studies suggest that there is an inverse relationship between measured flux and IAG values given that there is an optimum ingredient skin gap, SolV and SolS ratio. The study demonstrated that the flux is actually proportional to a gradient of thermodynamic activity rather than the concentration and maximum skin penetration and deposition can be achieved when the drug is at its highest thermodynamic activity.