The solubility of trehalose in a water + ethanol solvent system was measured with the mole fraction of water ranging from 0.000 to 1.000 at temperatures from (288.15 to 318.15) K using the gravimetric method. There was a minimum point on each solubility curve at the mole fraction of water ranging from 0.040 to 0.050. The differential scanning calorimetry measurement results show that anhydrous trehalose (a white flocculent precipitate) appeared in the suspension at water content lower than the critical point. While higher than that point, the crystals in the slurry were still hydrous polymorph which is apparently different from the anhydrous one. The solubility data at water content lower and higher than the critical points were nonlinear surface fitted separately using the combination version of the Jouyban-Acree and van't Hoff models which is a three-dimensional (3D) model. The average relative deviation (ARD) values for trehalose solubility at water content lower and higher than the critical point were 25.71 % and 11.62 %, respectively, which shows the model fitted the data well especially for the latter.

The solubility of trehalose in the water + methanol solvent system was measured with the mole fraction of water ranging from 0.000 to 0.700, at temperatures from (293.15 to 313.15) K, using the gravimetric method. Two kinds of crystals were collected and measured by differential scanning calorimetry and X-ray diffraction to prove the change of crystal habit for dihydrate trehalose from granular to powderlike at low water content. The turning points of every solubility curve were the critical points of crystal habit transition from the granular dihydrate trehalose (higher than the critical points) to the powderlike dihydrate trehalose (lower than the critical points). The mole fraction of the critical water content ranged from 0.160 to 0.250. The combination version of the Jouyban−Acree and van't Hoff models was used to separately correlate the solubility data lower and higher than the critical points by nonlinear surface fit. The root-mean-square deviation (rmsd) values for the powderlike and the granular dihydrate trehalose solubility data were 1.4900·10 −4 and 3.5919·10 −4 , respectively, which shows the model correlated the data well. ■ INTRODUCTIONTrehalose, a nonreducing disaccharide which is widespread in plants, animals and microbes, is formed by two glucose units linked in an α,α-1,1-glycosidic linkage. 1 Depending on the given thermodynamic conditions, trehalose mainly has two kinds of polymorphs: dihydrate and anhydrous forms. 2 The dihydrate trehalose can be easily obtained by crystallization from supersaturated solutions and is the most stable one. There are four different forms of anhydrous trehalose reported until now. 3 The β-form which is stable at room temperature and less hydroscopic has been obtained when keeping the dihydrate trehalose under vacuum at 130°C for 4 h, 4 or from the transformation of dihydrate trehalose to anhydrous trehalose using ethanol. 3,5,6 The α-form which could be easily rehydrated back to dihydrate trehalose has been observed when keeping the dihydrate trehalose under vacuum at 85°C for 4 h. 4 The γ-form, the mixture of dihydrate and β-form trehalose, has been shown by the shape of the calorimetric curve for the dihydrate trehalose at 5 K·min −1 to 20 K·min −1 . 4 The ε-form has been obtained still by thermal treatment according to Sussich's report. 7 The importance of observing polymorphic forms and solvated varieties has been recognized by most academic and industrial research groups. 8 In our previous work, we determined the solubility of trehalose in a water + ethanol solvent system, and a white flocculent suspension which is the anhydrous form was observed in low water content. Most researches simply involve water + methanol solvents and water + ethanol solvents to determine the solubility results. 9 So it is necessary to determine the solubility of trehalose in the water + methanol solvent system.In this work, the solubility of trehalose in the water + methanol solvent system was measured with the mole fraction of water ranging from 0.000 to 0.700, at temperatures ...

The solubility of the δ form of L-citrulline in the water + ethanol solvent system was measured at temperatures ranging from 293.15 to 333.15 K at atmospheric pressure using the gravimetric method. The crystal form of the solute is recognized as the δ form. It could be concluded that ethanol was an effective antisolvent in the crystallization process on the basis of the solubility behavior of the δ form of L-citrulline. The experimental solubility data were fitted by using the modified Apelblat equation, the simplified Combined Nearly Ideal Binary Solvent/Redich−Kister (CNIBS/R-K) model and the 3D Jouyban−Acree model (the combination version of the Jouyban− Acree and van't Hoff models). The corresponding relative absolute deviation values were 1.91, 1.71, and 5.13. The thermodynamic properties, including Gibbs energy, enthalpy, and entropy were obtained by using the van't Hoff analysis, which indicated that the dissolution of the δ form of L-citrulline is an endothermic and nonspontaneous process.

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