Host−Guest Complexes of Carotenoids with β-Glycyrrhizic Acid

Abstract

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.

Glycyrrhizic Acid as a Novel Drug Delivery Vector: Synergy of Drug Transport and Efficacy

“…Application of inclusion complexes was first related to an attempt to minimize the aforementioned disadvantages of carotenoids when used in the food industry, cosmetology, and medicine [40]. Several attempts were made to prepare inclusion complexes of carotenoids with cyclodextrins, which are assumed to possess protective properties and to decrease the hydrophobic behavior of the included molecules [41][42][43][44][45]. Main imperfection of carotenoid-cyclodextrin complexes is their poor solubility.…”

Improvement of pharmacological values of the nifedipine by means of mechanochemical complexation with glycyrrhizic acid

“…Таким образом, по нашему мнению, при механической активации смеси твердых образцов ГК и НФ происходит их комплексообразование. Известно, что ГК в воде, этаноле и диметилформамиде существует в виде ассоциатов, состоящих из двух и более молекул, которые стабилизируются межмолекулярными водородными связями между карбоксильными группами агликона и углеводной цепи [7,[23][24][25][26]. Можно предположить, что при твёрдофазной реакции ГК и НФ даёт комплекс типа "host-guest", в котором связывание компонентов осуществляется как путём кислотно-основного взаимодействия карбоксильной цепи с NH-группой нифедипина, так и за счёт водородных связей между гидроксилами углеводной цепи с нитро-и карбометоксигруппами нифедипина.…”

“…Это обстоятельство демонстрирует ценность ГК как комплексообразователя, который не вызывает никаких изменений молекулы фармакона, известного своей способностью к необратимым превращениям [22,26].…”

Redox reactions of natural alkaloid lappaconitine

“…The stoichiometry of the complex was concluded from analysis of Job´s plot. 41, 42 The ob tained value indicates the extreme stability of the com plex. It should be mentioned for comparison that the stability constants of the cyclodextrin complexes 41, 43 widely used in pharmacology are 10 3 M -1 on the average.…”