Physical chemistry of solvation interactions in the system: a biocomposite matrix of marine macrophytes – a deep eutectic solvent

The aim of this study is the physicochemical characterization of solvation interactions during the extraction of biologically active compounds from arctic brown algae of the species Ascophyllum nodosum using deep eutectic solvents (DES) based on choline chloride and carboxylic acids (formic, acetic, lactic, oxalic, malonic, malic) of various compositions. A significant effect of the functional nature of the hydrogen bond donor and the water content on the total biomass solubility and the yield of individual fractions of bioactive components (polyphenols and easily hydrolysable polysaccharides) was established. The relationship between the extraction efficiency and the solvatochromic parameters of the solvents was studied, and a positive correlation was found between the total dissolving ability and the Kamlet-Taft parameter π*. High selectivity of the DES based on choline chloride and formic acid (molar ratio 1:2) towards polyphenols was established. Extraction conditions were optimized for this solvent (temperature of 85 °C, duration of 130 min and water content of 30% mass ) using response surface methodology, and the mechanism of solvation interactions was investigated: according to IR-spectroscopy data, the extracted components form hydrogen bonds with the carboxyl groups of acids; the introduction of solutes into the structure of the solvent is accompanied by a decrease in the free molar volume.