Aggregate Formation of Glycyrrhetic Acid 3‐O‐Glucuronide

Abstract

AbstractThe molecular structure of glycyrrhetic acid 3‐O‐glucuronide consists of an aglycone and glucuronic acid as hydrophobic and hydrophilic groups, respectively. In general, this amphiphile is obtained from glycyrrhizic acid (a major component of licorice root) by hydrolysis of the terminal glucuronic acid. Glycyrrhetic acid 3‐O‐glucuronide is used as a substitute for glycyrrhizic acids, which are potent sweeteners. In this work, the surface and aggregation properties of glycyrrhetic acid 3‐O‐glucuronide were studied using general surface chemistry techniques. The surface tension of a glycyrrhetic acid 3‐O‐glucuronide solution (pH 7) gradually decreased with increasing concentration and the critical micelle concentration (CMC) was determined to be 1.6 mmol L−1 (γCMC = 54 mN m−1). Similar values of CMC were further confirmed by the pyrene fluorescent probe method and light scattering measurements. According to the dynamic light scattering method, the average radius of aggregate was 200 nm over a concentration of 3 mmol L−1. Transmission electron microscopy showed that glycyrrhetic acid 3‐O‐glucuronide forms large spherical aggregates. These results suggested that its potential for surface activity is almost equivalent to that of glycyrrhizic acid, even though the two amphiphiles have a different number of hydrophilic groups in them. The removal of one glucuronic acid group significantly influenced the shape of the aggregate formed by glycyrrhetic acid 3‐O‐glucuronide. Furthermore, it was confirmed that glycyrrhetic acid 3‐O‐glucuronide can also be used as a plant‐derived surfactant, similar to glycyrrhetic acid.