Novel Composite Materials for Chiral Separation from Cellulose and Barium Sulfate

Cellulose was dissolved in an aqueous solution of sodium hydroxide (NaOH) and urea followed by the addition of barium sulfate (BaSO4) to yield the BaSO4/cellulose composite particles. The morphology, particle size, and BaSO4 content of the composite particles were adjusted by controlling the feed ratio of cellulose and BaSO4. The cellulose within the composite particles then reacted with 3,5-dimethylphenyl isocyanate. The resulting materials were utilized as the chiral stationary phases (CSPs) whose enantioseparation capabilities were evaluated by various chiral analytes. Due to the mechanical enhancement effect of BaSO4, the composite particles could be applied to the chromatographic packing materials. 1. Introduction Cellulose is one of the most abundant polysaccharides in nature and consists of glucose units linked with 1, 4-β-glucans [1, 2]. Because of strong intra- and intermolecular interactions between hydroxyl groups, cellulose is insoluble in water and common organic solvents [3]. However, Zhang et al. [4] reported that cellulose could be dissolved in a precooled sodium hydroxide (NaOH)/urea solution rapidly. Moreover, the chiral complexation between organic molecules and the substituents attached to the skeleton of the cellulose derivatives can take place due to the helical cavity of cellulose. Till now, the cellulose derivatives have been employed as the adsorbents for chromatographic separation of organic compounds, in particular, for the enantioseparation of chiral compounds [5–8]. In general, cellulose has been first functionalized by aryl carbamoylation or acylation, and the as-synthesized derivatives have been then coated or covalently immobilized on the silica gel to obtain the chiral separation materials [9, 10]. However, chromatographic-grade porous silica gel is very expensive. Luo and Zhang [11] prepared the cellulose microspheres in a pre-cooled NaOH/urea solution and then employed them as the packing materials to fractionate polyethylene oxide. It was usually necessary for the cellulose microspheres to be cross-linked in order to enhance the mechanical and structural stability before use [12]. However, the cross-linking of the cellulose derivatives affects their enantioseparation capabilities because the superstructure of cellulose is altered [13]. Therefore, it is highly desirable to prepare a cellulosic material showing both sufficient mechanical strength and satisfactory chromatographic separation ability. Organic/inorganic composites generally combine the functions of two components with the mechanical enhancement effect of