A B S T R A C TGlycyrrhizic acid is the main active component of Licorice root which has been known in traditional Chinese and Japanese medicine since ancient times. In these cultures glycyrrhizic acid (GA) is one of the most frequently used drugs. However, only in 21-st century a novel unusual property of the GA to enhance the activity of other drugs has been discovered. The review describes briefly the experimental evidences of wide spectrum of own biological activities of glycyrrhizic acid as well as discusses the possible mechanisms of the ability of GA to enhance the activity of other drugs. We have shown that due to its amphiphilic nature GA is able to form self-associates in aqueous and non-aqueous media, as well as water soluble complexes with a wide range of lipophilic drugs. The main purpose of our review is to focus reader's attention on physicochemical studies of the molecular mechanisms of GA activity as a drug delivery system (DDS). In our opinion, the most intriguing feature of glycyrrhizic acid which might be the key factor in its therapeutic activity is the ability of GA to incorporate into the lipid bilayer and to increase the membrane fluidity and permeability. The ability of biomolecules and their aggregates to change the properties of cell membranes is of great significance, from both fundamental and practical points of view. monstrated the ability of GA to interact with cell membrane and to https://doi.

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The carotenoid astaxanthin forms novel metal ion complexes with Ca2+, Zn2+ and Fe2+. MS and NMR measurements indicate that the two oxygen atoms on the terminal cyclohexene ring of astaxanthin chelate the metal to form 1:1 complexes with Ca2+ and Zn2+ at low salt concentrations < 0.2 mM. The stability constants of these complexes increased by a factor of 85 upon changing the solvent from acetonitrile to ethanol for Ca2+ and by a factor of 7 for Zn2+ as a consequence of acetonitrile being a part of the complex. Optical studies showed that at high concentrations (> 0.2 mM) of salt 2:1 metal:astaxanthin complexes were formed in ethanol. In the presence of Ca2+ and Zn2+ salts the lifetime of the radical cation and dication formed electrochemically decreased relative to that of the carotenoid neutral radical. DFT calculations showed that the deprotonation of the radical cation at the carbon C3 position resulted in the lowest energy neutral radical while proton loss at the C5, C9 or C13 methyl groups was less favorable. Pulsed EPR measurements were carried out on UV-produced radicals of astaxanthin supported on silica-alumina, MCM-41 or Ti-MCM-41. The pulsed EPR measurements detected the radical cation and neutral radicals formed by proton loss at 77 K from the C3, C5, C9, and C13-methyl groups and a radical anion formed by deprotonation of the neutral radical at C3. There was more than an order of magnitude increase in the concentration of radicals on Ti-MCM-41 relative to MCM-41, and the radical cation concentration exceeded that of the neutral radicals.

Xanthophyll carotenoids can self-assemble in aqueous solution to form J- and H-type aggregates. This feature significantly changes the photophysical and optical properties of these carotenoids, and has an impact on solar energy conversion and light induced oxidative damage. In this study we have applied EPR and optical absorption spectroscopy to investigate how complexation can affect the aggregation ability of the xanthophyll carotenoids zeaxanthin, lutein, and astaxanthin, their photostability, and antioxidant activity. It was shown that complexation with the polysaccharide arabinogalactan (AG) polymer matrix and the triterpene glycoside glycyrrhizin (GA) dimer reduced the aggregation rate but did not inhibit aggregation completely. Moreover, these complexants form inclusion complexes with both monomer and H-aggregates of carotenoids. H-aggregates of carotenoids exhibit higher photostability in aqueous solutions as compared with monomers, but much lower antioxidant activity. It was found that complexation increases the photostability of both monomers and the aggregates of xanthophyll carotenoids. Also their ability to trap hydroperoxyl radicals increases in the presence of GA as the GA forms a donutlike dimer in which the hydrophobic polyene chain of the xanthophylls and their H-aggregates lies protected within the donut hole, permitting the hydrophilic ends to be exposed to the surroundings.