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The solubility, dissolution rate, dipolar moment and conformational properties of flavone in ethanol have been investigated using dielectric and UV spectroscopic procedures and the AM1 method. It was determined that flavone presents a high saturation solubility in ethanol. This fact is due mainly to the hydrogen-bond-donor capability of ethanol, which facilitates the formation of intermolecular hydrogen bonds. It was also determined that the dissolution rate of flavone tablets in ethanol is 14.8 mg of drug/min, and that this phenomenon occurs according to the kinetic model of Noyes–Whitney and Nernst. Furthermore, it was proved that in an alcoholic medium, flavone behaves as a true non-electrolyte. By means of Buckingham's equation it was observed that the polarity of the compound increased notably in ethanol. Thus, it was determined that its dipolar moment is 5.83 D. On the other hand, by applying the AM1 method it was determined that the two symmetrical conformers of flavone in ethanol have non-planar structures and also that their dipolar moments, 5.81 and 5.82 D, respectively, are very similar to the experimental value. It was proposed that the drug interacts with the solvent by means of two intermolecular hydrogen bonds and two electrostatic interactions, forming a solvent–solute association complex of 2:1 stoichiometry. The principal molecular region implied in these interactions comprises the carbonyl group of flavone. It was concluded that the (EtOH)2–flavone association complex, whose dipolar moment is 5.81 D, is the predominant form in alcoholic solutions of flavone, which determines the magnitude of the analyzed properties. |
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