178 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS QH ,co ¸ CH30 c'•_ 1•8••• O ,'•••-•¾' ' •',•/•• 17 •'H3 COOH • CH3 CH3 Osj_ O TANS H H / i OOH OM OM O CMa .' a •• o dh, COOH • V ¸ U H I I OH OH HOOL•co0 H H O•'Sb cH3 cIs Figure 1. Chemical structures of o•- and [•-Gs. cording to the method reported by Miyashita eta/. (6). o•-G had a purity determined by HPLC analysis (7) of not less than 93.7%. [3-G was commercially available (Maruzen Kasei Co., Ltd. purity 98.5%) and used without further purification. Since both Gs were only slightly soluble in water, their monoammonium salts were used in our experiments unless otherwise noted. a- and [•-glycyrrhetins. Both o•- and [3-glycyrrhetins, which are aglycones corresponding to respective Gs (glycosides), were commercial products (Maruzen Kasei Co., Ltd.) and subjected to the experiments with no refinement. The minimal purity of both com- pounds exceeded 97%. &lethy/ •-g/ycyrrhizinate. Reaction of dipotassium salt of •-G with a large excess of ethereal diazomethane at room temperature yielded the dipotassium salt of methyl •- glycyrrhizinate as colorless crystals IR: 1740 cm-z O/C = 0) z3C-NMR(D20): 8 52.3 (-OCH3), 177.9 (-CO2CH3). Anal. Calc. for C43H62Oz6K2: C, 56.56 H, 6.84. Found: C, 56.46 H, 6.98. Methyl •-glycyrrhizinate was obtained by dissolving the above salt in water, subsequent acidification with acetic acid, and addition of acetone. A white precipitate was collected, washed with acetone, and dried in vacuo, mp 268.0- 268.5øC (dec). [•-g/ycyrrhizin pentaacetate. •-G was subjected to the esterification with eight equivalents of acetic anhydride at 40øC. Methanol was added to the reaction mixture to decompose an excess of acetic anhydride. After evacuating the volatiles and washing the residue with ether, colorless crystals were obtained mp 225-227øC IR: 1740 cm-• O/C = O)

PROPERTIES OF o•- AND [B-GLYCYRRHIZINS 179 o • 40 .•_ 30 lO I I I I -5 -4 -3 -2 log C ( mol/I ) Figure 2. Interfacial tension of Gs at water-liquid paraffin interface (25øC). 13C-N. MR(CD3OD + CDC13): 8 20.7, 20.9 (•H3COO-), 170.8, 171.0, 171.1 (CH3COO-). Anal. Calc. for C52H72017: C, 60.45 H, 7.02. Found: C, 60.59 H, 7.12. Other chemicals used in the present study were all of reagent grade. INTERFACIAL TENSION Measurements were carried out with a Rigosha Auto Tensionmeter, Model 6801 ESD, at 25øC by the ring method. The inner diameter of the ring and the diameter of the platinum wire were 1.909 and 0.060 cm, respectively. NUCLEAR MAGNETIC RESONANCE (NMR) •C-NMR spectra were recorded on a JEOL JNM-FX 100 Spectrometer with tetra- methylsilane as the external standard. Pulse width: 10 •sec (45ø). Pulse repetition: 1.0 sec. Spectral width: 6024 Hz. SCANNING ELECTRON MICROSCOPY (SEM) A Hitachi Scanning Electron Miscroscope, Model S-450, equipped with a cryosystem