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Ionization constants of some flavanols (catechin and epicatechin) and flavonols (kaempherol, fisetin, morin, and quercetin) are determined by capillary zone electrophoresis (CZE). This technique allows the determination of pK(a) values until about 12. The pK(a) values obtained are compared with those calculated by the SPARC computational program. This program predicts the microscopic and macroscopic pK(a) values and the order of deprotonation of the different -OH groups. While for catechin and epicatechin the first ionizable OH group occurs in ring 1 and the second ionizable group in ring 2, in flavonols the first deprotonation occurs in ring 2 and the second in ring 1.

A preferential solvation model that takes into account the enhancement of the structure of water when small amounts of alcohol are added was applied to solvatochromic data for binary mixtures of water with 2-methylpropan-2-ol, propan-2-ol, ethanol and methanol. Application of the model allows the calculation of the effect of the enhancement of the water structure on solvatochromic solvent properties. It is demonstrated that the enhancement of water structure increases the solvent dipolarity/polarizability and hydrogen-bond donor acidity and decreases the solvent hydrogen-bond acceptor basicity. The effect decreases in the order 2-methylpropan-2-ol-water, propan-2-ol-water, ethanol-water and methanol-water.

Static dielectric constants of acetonitrile/water mixtures in the whole composition range and within the temperature range from (15 to 60) °C have been measured. The values were fitted to a unique equation as a simultaneous function of temperature and acetonitrile composition. Densities of these mixtures at temperatures from (5 to 55) °C and different compositions have been collected from the literature. The complete data set was critically analyzed, the outliers were excluded, and the remaining values were also fitted to a unique equation as a function of temperature and acetonitrile composition. From the dielectric constants and densities, the activity coefficients of ions can be calculated by means of the Debye−Hückel approach, allowing the study of the ionic equilibria and determination of reference pH values or acidity constants in any acetonitrile/water mixture at any temperature within the studied range.