| L-arabinose has taken interest in researches hotpot in food, medicine, bio-engineering, and other fields as it is a novel low-caloric functional sweeting agent. L-arabinose can be used in the treatment of obesity, hypertension, hyperlipidemia and intestine disease due to its selectively inhibit the absorption of sucrose and the accumulation of fat. However, up to now, the factory production of L-arabinose is low as a result of the lack of L-arabinose crystallization mechanism. Therefore, it is imperative to carry out research on the crystallization process and mechanism of L-arabinose crystallization. The main content and results of this paper are listed as follows:(1) Crystal morphology and structure analysis of L-arabinose. The L-arabinose crystal cultivated by evaporation was analyzed by single crystal X-ray diffraction and its structure being determined. The β-L-arabinose is in the Orthorhombic system, P21212 space group with a = 4.8331(10), b = 6.5149(13), c = 19.440(4) ?, and α = β = γ= 90.00°. X-ray powder diffraction showed that crystals prepared by cooling and anti-solvent crystallization were of the same structure, namely β-L-arabinose. Based on the analysis of DSC, the melting point of L-arabinose was being determined by polarizing melting point apparatus and found the melting point of commercial L-arabinose, L-arabinose obtained by cooling crystallization, and by anti-solvent crystallization is 156.6~158.5 oC, 158.2~159.8 oC, and 158.2~159.9 oC, respectively.The crystal morphology of L-arabinose in vacuum was calculated based on BFDH, growth morphology and equilibrium morphology methods by Material Studio 6.0 software. The morphology of L-arabinose obtained by those three methods is nearly rectangular, cuboid, and sphere, respectively. The morphology simulated by growth Morphology is consistent with the real one obtained by cooling crystallization. Factors that may affect the crystal morphology were been discussed.(2) Thermodynamic study of L-arabinose. The solubility and metastable zone width(MSZW) of L-arabinose in aqueous solution were determined. Solubility in 20~68 °C was measured by a conventional equilibrium method and quantitation was determined using the ion chromatography technique. Seeded MSZW was determined by the automatictemperature logging device(ATLD) in solution concentration 51~73%. Results show that the MSZW of L-arabinose was not a constant but a range, namely(27.11± 2.34 oC). It is also found that the nucleation temperature is significantly affected by solution concentration, stirring rate, however cooling rate had no significant influence on the nucleation temperature. The effect of impurities on the solubility and MSZW of L-arabinose were also evaluated.(3) Growth kinetics of L-arabinose by cooling crystallization. Focus beam reflectance measurement(FBRM) and microscope was used to observe the nucleation and growth phenomenon of L-arabinose during the crystallization process. FBRM was been used to study the kinetic parameter of L-arabinose by cooling crystallization. The effect of operating factors on the supersatureation of solution, yields of L-arabinose crystals, mean chord length, nucleation kinetics, growth kinetics, etc. was being studied. The empirical kinetic equations of cooling crystallization were established based on the size independent model.(4) Growth kinetics of L-arabinose by anti-solvent crystallization. Solubility of L-arabinose in ethanol- water system is been determined from 20~65 oC by equilibrium method, and empirical equation been established. FBRM and microscope was used to observe the nucleation, growth, aggregation and breakage of L-arabinose during the anti-solvent crystallization process, and empirical kinetic equations of anti-solvent crystallization of L-arabinose been established based on the size independent model.(5) Preparation and characterization of calcium-L-arabinose complex. The crystal of the metal-organic frame Ca(C5H9O5)2·CH3OH·2H2O(1) has been synthesized and structure characterized. In complex 1, the sugar moiety shows a beta-L configuration of pyranose form. The calcium(II) is eight-coordinated, binding to four such sugar moieties, via O(1), O(2) of two molecules and O(3), O(4) of the other two, with the 4-hydroxy group being deprotonated. The water and methanol molecules are not coordinated with the calcium ion. |
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