Preparation And Applications Of Organic Silsesquioxane In Chiral Stationary Phases And Single-handed Helical Carbonaceous Nanofiber Fabrication

Enantioselective separation on chiral stationary phases (CSPs) in high performance liquidchromatography (HPLC) is known as the most effective and convenient method for analysis of manyracemic compounds. Peptide CSPs have made a progress in recent years. Recent reports are focused onthe changing the number of amino acid units, linker length and end-capping groups to design diffrentCSPs and explore the chiral recognition mechanisms. Organic bridged polysilsesquioxanes is a class ofhybrid materials with special properties and bridging organic units covalently linked to the inorganicmoieties through Si-C bonds. The polysilsesquioxanes combine the advantages both of inorganic andorganic compounds and have a wide variety of tunable properties through changing the bridging organicunits. These advantages make them ideal materials for applications in catalysis, chiral separation andadsorbent. Moreover, these materials could be used as precursors for carbonaceous materials. The mainworks are as following:First, five CSPs based on L-phenylalanine were prepared and evaluated using racemates. Theeffects of the number of L-phenylalanine units, end-capping groups and linkage length on separationperformance were studied. The separation results indicated that with the increase of L-phenylalanineunits and linkage length, the separation performance became better and the end-capping groups also hada influence on the enantioselective separation.Second, single-handed helical biphenylene-bridged polysilsesquioxanes were prepared through aself-templating approach and evaluated its adsorption performance using aromatic compounds. Thestudy found that the morphology of polysilsesquioxanes was affected by the reaction conditions. Thescanning electron microscopy (SEM) indicated that the LL-2monomers polymerized into right-handedhelical fibers and the DD-2monomers polymerized into left-handed helical fibers in the solventdimethyl sulfoxide. The circular dichroism (CD) spectrum indicated that the aromatic rings stacked inchiral within the skeleton of the polysilsesquioxanes. The adsorption test indicated that this materialcould adsorb aromatic compounds and may have potential as adsorbents. Third, single-handed helical polybissilsesquioxanes bundles were also prepared through aself-templating approach. After carbonization and removal of silica, left-handed helical carbonaceousbundles were obtained. The SEM indicated that both the morphology and handedness did not changemuch after carbonization and removal of silica. The Raman spectra and X-ray diffraction (XRD) patternindicated that the carbon was amorphous. The diffuse reflectance circular dichroism (DRCD) spectrumindicated that they exhibited optical chirality. The BET surface area is211m2g-1indicated that thismaterial may have potential as catalyst supports, chirality sensors and adsorbents.