Assessment for the light-induced cis-trans isomerization of rhapontigenin and its glucoside rhaponticin by capillary electrophoresis and spectrometric methods

The light-induced cis-trans isomerization of rhapontigenin (RHA) and its glucoside rhaponticin (RHA-Glc) were evaluated under ultraviolet (UV) light irradiation. A simple and rapid capillary electrophoresis method was developed for the kinetic study of four stilbenes (both cis and trans format RHA and RNA-Glc). These analyses were achieved by using beta-cyclodextrin (beta-CD) modified capillary zone electrophoresis with diode array detector (CZE-DAD). The method provided reliable separations with a short analysis time of 3 min. The purity of individual compound was checked by UV spectral comparisons with known standards, and further confirmed by H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the UV absorbance and the molar absoptivity (epsilon) values were determined by UV-vis spectrophotometer to be 36824 L mol(-1) cm(-1) at lambda(max) 324.5 nm for trans-RHA and 43894 L mol(-1) cm(-1) at lambda(max) 325 nm for trans-RHA-Glc in methanol/water mixture solution (50%, v:v), respectively. CZE, UV-vis and NMR spectroscopy studies provided similar conclusions by considering the influence of irradiation time and the influence of irradiation wavelength. (C) 2011 Elsevier B.V. All rights reserved.