Host-guest complexes of carotenoids with beta-glycyrrhizic acid.
The structure, stability, and reactivity of the host-guest complexes between a set of carotenoids and the triterpene glycoside, beta-glycyrrhizic acid (GA), were investigated by different physicochemical techniques: high-performance liquid chromatography, optical absorption, and fluorescence spectroscopy. It has been demonstrated recently that the molecular complexes of GA with a number of drugs are characterized by reduced toxicity and increased therapeutic activity of these drugs. In the present work it was found that carotenoids form 1:2 complexes with GA in aqueous solutions as well as in polar organic solvents, methanol, acetonitrile, and dimethylsulfoxide. We assume that the structure of the complex is a cycliclike dimer of GA encapsulating a carotenoid molecule. The stability constants in all solvents are near 10(4) M(-1). In addition, GA forms inclusion complexes with carotenoid radical cations, which results in their stabilization. Complex formation (a) decreases the rate of electron transfer from carotenoids to electron acceptors (Fe3+ or quinone) and (b) considerably increases the lifetime of the carotenoid-quinone charge-transfer complex and the yield of the major product (a carotenoid-quinone adduct). A thermodynamic study shows that hydrophobic interactions are the main driving force of the carotenoid-GA complex formation. These results are important for understanding both the nature of GA complexes and the influence of GA on the therapeutic activity of some drugs. Furthermore, carotenoid-GA complexes could be used for the design of artificial light-harvesting, photoredox, and catalytic systems.
Institute of Chemical Kinetics & Combustion, Institutskaya Str. 3, 630090 Novosibirsk, Russia.
Nikolay E
NE
Polyakov
Tatyana V
TV
Leshina
Nariman F
NF
Salakhutdinov
Lowell D
LD
Kispert
D016227:Benzoquinones / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry*; D002712:Chlorides; D002851:Chromatography, High Pressure Liquid; D005290:Ferric Compounds / Q000737:chemistry; D019695:Glycyrrhizic Acid / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D012996:Solutions; D013057:Spectrum Analysis
D016227:Benzoquinones; D002712:Chlorides; D005290:Ferric Compounds; D012996:Solutions; C000928:dichlorodicyanobenzoquinone; D002338:Carotenoids; D019695:Glycyrrhizic Acid; C024555:ferric chloride