Assessment of solubility of bioactive minor compounds of polyphenolic nature

The aim of the present study was to assess the thermodynamic solubility of minor bioactive compounds of polyphenolic nature. Polyphenols are represented by a huge number of biologically active substances belonging to classes of tannins, phenolic acids, stilbenes, flavonoids and others. A large proportion of these compounds exhibit pronounced pharmacological effects, including anti-inflammatory, antioxidant, antilipidemic, antihyperglycemic and anticancer effects. At the same time, the low solubility of many of these compounds is a barrier to the manifestation of their physiological effects in human systems. For this reason, the study of solubility properties of minor biologically active compounds of polyphenol nature is the basis for the prognostic evaluation of their pharmacological properties in general. Of particular interest is the comparative analysis of the structure of biologically active substances belonging to different classes of polyphenols with their solubility properties. For the present study, representatives of flavonoids and stilbenes were chosen as objects. Their solubility in distilled water at different temperatures (20, 35 and 50 °C) and dissolution times (20, 40 and 60 min) were evaluated. It was found that despite belonging to different classes of polyphenols, the biologically active substances under study were characterized by marked hydrophobicity, the highest solubility values not exceeding 2 %. Some correlations between the structure of the substances molecules and their solubility were determined. Mathematical models describing dissolution process of polyphenols depending on solvent temperature and dissolution time were obtained by two-factor regression analysis. The optimum combination of these factors for each substance has been established. The results obtained point to the need to search for ways to increase the solubility of the studied compounds, as well as to develop research, including the use of other types of solvents.