Determination of the solubility, dissolution enthalpy and entropy of icariin in water, ethanol, and methanol
Highlights
► The solubility of icariin was measured the first time. ► The solubility of icariin in the three solvents increased with temperature. ► Solubility data correlated with a modified Apelblat equation. ► The viscosity and the surface tension of solvents affect the solubility behaviour.
Introduction
Icariin, a natural flavonoid, was isolated from Epimedium Herba and is considered to be the major bioactive component of Epimedium Herba [1], [2]. The chemical name of this compound is 3-[(6-deoxy-alpha-l-mannopyranosyl)oxy]-7-(beta-d-glucopyranosyloxy)-5-hydroxy-2-(4-methoxyphenyl)-8-(3-methyl-2-buten-1-yl)-4H-1-benzopyran-4-one. Fig. 1 shows the chemical structure of icariin.
Icariin has a broad range of therapeutic applications in cardiovascular, endocrine, bronchial, urinary and immune systems [1], [2]. For pharmaceutical use, icariin is usually extracted from the Epimedium grandiflorum Morr using solvents such as water, alcohols, or mixtures of these, followed by purification and crystallization from the solution. Therefore, it is important to have thermodynamic data for the solubility of icariin in different solvents. However, only equilibrium solubility of icariin and its apparent oil/water partition coefficient have been reported in the literature. Solubility of icariin in different solvents at different temperatures has not been reported until now. So it is necessary to determine systematically the solubility of icariin since the solubility data are important for its extraction and purification. The temperature dependence of the solubility allows a thermodynamic analysis that permits insight into the molecular mechanisms involved in the solution processes [3].
In this work, the solubility of icariin in water, ethanol and methanol from 288.2 K to 328.2 K was measured by ultraviolet spectrophotometry (UV). The enthalpy and entropy of dissolution of icariin were estimated based on regression of the solubility data by utilizing the van’t Hoff equation.
Section snippets
Materials and apparatus
Icariin (C33H40O15, CAS: 489-32-7, purity higher than 0.990 in mass fraction) was purchased from the National Institute for the Control of Pharmaceuticals and Biological Products (Beijing, China). The ethanol and methanol used were of analytical purity grade with mass fraction purity higher than 0.990 and 0.995 respectively and were provided by Tianjin Kermel Chemical Reagent Co., Ltd (Tianjin, China). Redistilled deionized water (conductivity <2 μS cm−1) was used throughout the study. The
Results and discussion
Solubility data for icariin in water, ethanol and methanol at different temperatures are presented in Table 2. The temperature dependence of icariin solubility in solvents can be described by the modified semi-empirical Apelblat equation [6], [7], [8], [9] (2).where x1 is the mole solubility of icariin, T is the absolute temperature, and A, B and C are the parameters determined by least square analysis. Calculated solubility values for icariin are provided in Table 2. The
Conclusion
Solubility of icariin in water, ethanol and methanol was measured by UV spectrophotometry from 288.2 K to 328.2 K. The solubility of icariin in the three solvents was a function of temperature, with solubility increasing with temperature. The experimental data were correlated with the modified Apelblat equation. The calculated results show good agreement with the experimental values. Based on the solubility data, the dissolution enthalpy and entropy of icariin were calculated using van’t Hoff
List of symbols
- x1
mole fraction solubility
- m1
mass of the solute
- m2
mass of the solvent
- M1
molar mass of the solute
- M2
molar mass of the solvent
- xi
experimental solubility value
calculated solubility value
- R
gas constant
- T
absolute temperature
- ΔHd
enthalpy of dissolution
- ΔSd
entropy of dissolution
- ΔGd
Gibbs energy of solution
- r
correlation coefficient
- ρ
density of solvent
- nD
refractive index of solvent
Acknowledgement
This research was financially supported in part by National Natural Science Foundations of China (No. 81173024) to Q. Fu.
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