Journal of Molecular Liquids 180 (2013) 160–163 Contents lists available at SciVerse ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq Short Communication Solubility of daidzein in the binary system of ethanol and water Guang-De Yang, Yan-Ru Huang, Guan-Jun Nan, Hui-Juan Chen, Ai-Guo Zeng, Xiao-Li Bian ⁎ School of Medicine, Xi'an Jiaotong University, Shaanxi 710061, PR China article info abstract Article history: The solubility of daidzein in the binary system of ethanol and water was measured by UV spectrophotometric Received 29 November 2012 method from 288.2 K to 328.2 K. The solubility of daidzein increases with temperature and the ethanol con- Received in revised form 26 December 2012 tent of the mixture. The solubility data were correlated with a modified Apelblat equation. From solubilities Accepted 27 December 2012 of daidzein, the enthalpy and entropy of solution were evaluated using van't Hoff equation. Available online 19 January 2013 © 2013 Elsevier B.V. All rights reserved. Keywords: Daidzein Solubility 1. Introduction and entropy of daidzein were evaluated based on regression of the sol- ubility data by utilizing the van't Hoff equation. Daidzein (C15H10O4, CAS 486-66-8) of chemical name 7,4′-dihydroxy isoflavone is an isoflavone abundant in soybean and accordingly with a high intake in Asian populations. Fig. 1 shows the chemical structure of 2. Experimental section daidzein. It has been demonstrated to be a potent antioxidant and has been receiving much attention in relation to human health [1]. The con- 2.1. Materials centration of isoflavones in soybeans is much higher than those in other legumes. Therefore, soy and soy-based foods are regarded as the main The daidzein (melting point 320–323 °C) sample was supplied by sources of isoflavones in the human diet [2,3]. The most abundant Shanghai Tauto Biotech Co., Ltd (Shanghai, China) with a minimum pu- isoflavones are daidzein (7,4′-dihydroxy isoflavone) and genistein rity of 99.0%. The absolute ethanol was of analytical purity grade provid- (5,7,4′-trihydroxy isoflavone). ed by Tianjin Kermel Chemical Reagent Co., Ltd (Tianjin, China) and was Daidzein has been isolated from the traditional Chinese herbs such as used without any further purification. Redistilled deionized water was the root of Pueraria lobata (Willd.) Ohwi (Chinese herbal name Ye Ge), the used throughout. Table 1 shows the purity of chemicals. kudzu root (P. lobata)isusedasaningredientinkudzu-starchwhichisan important material for cooking as well as processed foods in Japan. The 2.2. Apparatus present study demonstrated that daidzein has potent antioxidant [4,5], antibacterial [6],andanti-inflammatory [7] activities. For pharmaceutical The absorbance measurements of daidzein samples were carried use, daidzein is usually extracted from the powdered kudzu root or soy out on a SP-752 UV–vis spectrophotometer (Shanghai Spectrum In- using solvents such as water, alcohols, or mixtures of those, followed by strument Co., Ltd., Shanghai, China). purification and crystallization from the solution [8–12]. Therefore, it is important to have the solubility data of daidzein in the binary system of ethanol and water mixed solvents. In the present study, the solubility of daidzein in the binary system of ethanol and water over the temperature range of (288.2 to 328.2) K OH was measured by ultraviolet spectrophotometry (UV). The enthalpy O ⁎ Corresponding author at: School of Medicine, Xi'an Jiaotong University, No. 76 Yanta HO O Westroad, Shaanxi Province, Xi'an 710061, P. R. China. Tel./fax: +86 29 82657833. E-mail address: [email protected] (X.-L. Bian). Fig 1. Molecular structure of daidzein. 0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molliq.2012.12.035 G.-D. Yang et al. / Journal of Molecular Liquids 180 (2013) 160–163 161 Table 1 equilibration time for the binary system of ethanol and water in the The purities of the chemicals. experiment. Substance Molecular weight Purity, mole fraction The mole fraction solubility of the solute (x1) in the binary system of ethanol and water solvents was calculated by the following Eq. (1). Absolute ethanol 46.07 0.999 fi Water 18.02 0.999 The composition of solvent mixtures x2 is de ned by Eq. (2): Daidzein 254.2 0.995 m1= M1 x ¼ ð1Þ 1 m1 = þ m2 = þ m3 = M1 M2 M3 Table 2 = Solubility of daidzein in the binary system of ethanol and water from 288.2 to 328.2 K. m2 M2 x ¼ ð2Þ 2 m2 = þ m3 = 6 6 calc 6 6 calc 5 5 calc M M T/K 10 x1 10 x1 10 x1 10 x1 10 x1 10 x1 2 3 x2 =0 x2 =0.0716 x2 =0.1707 where m1, m2, and m3 represent the mass of the daidzein, ethanol and 288.2 0.0564 0.0502 0.2346 0.1435 0.1934 0.1758 water, respectively; M1, M2, and M3 are the molecular weight of the 293.2 0.0608 0.0731 0.2416 0.2333 0.3154 0.2697 daidzein, ethanol and water, respectively. 298.2 0.0958 0.1120 0.2724 0.3590 0.4509 0.3957 303.2 0.1695 0.1534 0.4768 0.5251 0.5359 0.5569 308.2 0.2132 0.1992 0.8150 0.7318 0.6220 0.7534 2.4. Sample analysis 313.2 0.2467 0.2462 0.9847 0.9750 0.9383 0.9823 318.2 0.2800 0.2904 1.1695 1.2449 1.3444 1.2368 To determine the daidzein concentration in the solution, the ab- 323.2 0.3076 0.3279 1.5999 1.5271 1.5578 1.5070 328.2 0.3659 0.3551 1.7784 1.8039 1.7281 1.7803 sorbencies of the standard and sample were measured at the daidzein a maximum absorption wavelength of 256 nm. The calibration curve 4 4 calc 4 4 calc 4 4 calc 2 T/K 10 x1 10 x1 10 x1 10 x1 10 x1 10 x1 (y=33,190×−0.0659, R =0.9996) for the estimating of daidzein x2 =0.3166 x2 =0.5527 x2 =1 was prepared using standard solutions in the appropriate concentra- tion range (5.11×10−6 −3.06×10−5 mol/L). 288.2 0.4052 0.4137 1.2427 1.2861 2.3948 2.3710 293.2 0.4318 0.4514 1.4243 1.4402 2.7015 2.6273 The saturated solubility of the solute (x1) in the binary system of 298.2 0.5348 0.5011 1.6393 1.6226 2.8781 2.9300 ethanol and water solvent mixtures was measured three times. The 303.2 0.5834 0.5653 1.9179 1.8386 3.2375 3.2871 uncertainty of the experimental solubility values was estimated to 308.2 0.6319 0.6474 2.0966 2.0941 3.5968 3.7080 be less than 1.0%. 313.2 0.7384 0.7519 2.4447 2.3967 4.1926 4.2041 318.2 0.9165 0.8846 2.7293 2.7553 4.9110 4.7889 323.2 1.0079 1.0536 3.0196 3.1806 5.5768 5.4790 3. Results and discussion 328.2 1.2893 1.2692 3.7852 3.6854 6.1987 6.2937 The solubility data of daidzein in the binary system of the ethanol and water at different temperatures are presented in Table 2. The ex- perimental data show that the solubility of daidzein in the binary sys- tem increases with an increase in ethanol concentration and with an 2.3. Sample preparation increase in temperature. The temperature dependence of daidzein solubility in solvents can be described by the modified Apelblat – An excess amount of daidzein was added to the solvents (water, ab- Eq. (3) [14 17]: solute ethanol, ethanol and water mixed solvents) in a specially designed B sealed 10-mL dual-wall flask. Between the outer and inner walls of the lnðÞ¼x A þ þ ClnðÞT ð3Þ 1 T flask, the flask was maintained at a constant temperature by circulated water. The temperature of the water was controlled using a thermostat where x1is the mole fraction solubility of daidzein; T is the absolute (uncertainty of ±0.1 K). The solubility of daidzein in different solutions temperature; and A, B and C are the parameters. The calculated solu- was measured using a method described in literature [13].Thesolution calc bility values of daidzein (xi ) are also provided in Table 2. The values was constantly stirred using a magnetic stirrer for 2.5 h. After attaining of parameters A, B, and C are listed in Table 3 together with the the equilibrium, the stirring was turned off and the solution was settled root-mean-square deviations (rmsd) Eq. (4): for2h.Thentheupperportionwastaken,filtered, and poured into a vol- vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi umetric flask and diluted to an appropriate concentration for UV u uXN u 2 analysis. u xcalc−x t i i The concentration of daidzein in water after 0.5, 1.0 h, 1.5 h, 2.0 h, ¼ rmsd ¼ i 1 ð4Þ 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, 5.5 h and 6.0 h was determined N at 288.2 K. The 2.0 h equilibration time was deduced from the pre- calc liminary experiments carried out in water, which to be the longest where N is the number of experimental points, xi represents the equilibration time among the water. So we choose the 2.5 h as the solubility calculated, and xi represents the experimental solubility Table 3 Parameters of Apelblat equation for daidzein in the binary system of ethanol and water.