Kinetics and mechanism of 2,3,5,4′-tetrahydroxystilbene-2-O-β-D-glycoside (THSG) degradation in aqueous solutions

The hydrolytic kinetics and degradation mechanism of 2,3,5,4'-tetrahydroxystilbene-2-O-beta-D-glycoside (THSG) extracted from Radix Polygoni Multiflori (a commonly used officinal Chinese herbal Heshouwu), were investigated using reversed-phase high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). The influences of pH (1.5-9.9), temperature (25-60 degrees C) and irradiation on the hydrolysis of THSG were studied in aqueous solutions. The results showed that the degradation of THSG was pH-, temperature- and irradiation-dependent and all followed first-order kinetics. The effect of temperature on the rate of THSG degradation was characterized using the Arrhenius equation. Maximum stability of THSG was found at pH 1.5 (t(0.5) = 47.57 d). THSG was unstable in alkaline and irradiation conditions. The active energy (E-a) of THSG degradation in aqueous solution at pH 6.8 (most frequently adopted extract solvent) under lucifugal and irradiation conditions was 47.7 kJ mol(-1) and 25.3 kJ mol(-1), respectively. Three hydrolytic products of THSG were identified by LC-MS. Cis-trans isomerism took place under irradiation, and hydrolysis took place in acid-base conditions. Moreover, further oxidation on aglycon occurred after hydrolytic cleavage of phenolic glycoside in acidic conditions. The possible hydrolytic pathways of THSG are proposed. (C) 2011 Elsevier B.V. All rights reserved.