Spectral and Acid-Base Properties of Hydroxyflavones in Micellar Solutions of Cationic Surfactants

Abstract

It has been shown that the spectral characteristics (intensity, position of the absorption band) and the acid-base properties in a series of structurally similar hydroxyfl avones depend on the concentration of the cationic surfactants miramistin and decamethoxin in aqueous solutions, and the extent of their changes is more pronounced for hydrophobic quercetin than for hydrophilic rutin. For the fi rst time, we have determined the apparent dissociation constants of quercetin and rutin in solutions of these cationic surfactants (pKa1) over a broad concentration range and we have established that they decrease in the series water-decamethoxin-miramistin. Introduction. The natural hydroxyfl avones (HFl) rutin (Rt) and its aglycone quercetin (Qu) are widely used in medicine (1-3), since they exhibit high antioxidant, anti-infl ammatory, antiviral activity and the ability to improve capillary resistance. It was shown earlier (4, 5) that in organized media of polyvinylpyrrolidone and serum albumins, a decrease occurs in the dissociation constants of hydroxyfl avones compared with aqueous solutions, as a result of formation of supramolecular complexes in these systems, evidence for which is also the bathochromic shifts of bands in the absorption spectra of quercetin and rutin over a broad solution pH range. As the object of this study, we selected self-organizing supramolecular micellar systems based on cationic surfactants, which are organized reaction media capable of affecting the solubility and other physicochemical properties of substances (spectral, acid-base, adsorption, etc.), the occurrence of chemical processes, and also can be promising systems for modeling biosystems (6, 7). Today some of the most effective broad-spectrum antiseptics are the cationic surfactants miramistin (MR) and decamethoxin (DCM) (1). No quantitative description of the effect of these cationic surfactants on the spectral and acid- base properties of hydroxyfl avones is available in the literature, even though taking into account protolytic interactions is of scientifi c and practical importance in medical practice for developing and using drugs based on such systems. The aim of this work was to study the effect of the cationic surfactants miramistin and decamethoxin over a broad concentration range on the spectral and acid-base properties of quercetin and rutin in the physiological pH range. The experiment. We used miramistin (Infamed), decamethoxin (pilot production of the Institute of Organic Chemistry, National Academy of Sciences of Ukraine), quercetin and rutin (Sichuan Xieli Pharmaceutical Co. Ltd., China), analytical grade. Stock solutions were prepared by dissolving exactly weighed amounts of the preparations. In all the experiments, the hydroxyfl avone concentration was 2·10 -5 M, ethanol 4%, μ = 0.2 (NaCl). The electronic absorption spectra of the solutions were measured on a Specord M-40 spectrophotometer (Carl Zeiss Jena, Germany) using a cuvet with l = 1 cm. Starting from the values given in the literature for the fi rst (pKa1) and second (pKa2) thermodynamic dissociation constants for quercetin: pKa1 = 6.74 (8), 7.03 (9), 7.3 (10), 6.62 (11), 8.21 (12); pKa2 = 9.02 (8), 9.15 (9), 9.7 (11) and for rutin: pKa1 = 7.40 (13), 8.96 (12); pKa2 = 8.70 (13), we see that in the physiological pH range (pH = 3-8) for the solution, dissociation of one hydroxyl group of the hydroxyfl avone occurs. For a quantitative estimate of the effect of cationic surfactants on this process, we determined the dissociation constants of the hydroxyfl avones (pKa1) by the standard spectrophotometric method (14) over a broad concentration range for miramistin and decamethoxin, with uncertainty ≤0.04.