Adsorbents with Chemically Bonded Saccharide Surfaces: Synthesis and Application for Stereoisomer Separation And The Synthesis of Chiral Porous Silicas using Templates Chiral Surfactant.

摘要

Stereoisomeric separation is a common and at times difficult problem. Using chiral materials as stationary phases for stereoisomeric separations is a common practice. Saccharides have many stereocenters making them ideal for stereoselective recognition. They are natural products that are relatively inexpensive. They typically contain numerous functional groups which are mainly hydroxyl groups. Some saccharides have at least one amino group. Our research has focused mainly on the design and synthesis of materials with defined surface structures containing saccharides and the subsequent study of their use in separating stereoisomers such as derivatized monosaccharides, Pirkle's alcohol, and cis- and trans-stilbene oxide. In addition, we have attempted pseudomorphic transformations of Prodigy and SBA-15 silica to helical silica forms using chiral surfactants.;It is known that carbon-sulfur bonding is hydrolytically stable 1-2 and carbohydrates linked to silica in this fashion have not been reported in the literature. For this reason, we have prepared a series of peracetylated-1-thiol-saccharide analogs (1, 3, 7 and 13 glucose units). The synthesis of peracetylated-1-thiol-saccharides is demonstrated in Chapter 1. These ligands were characterized by high pressure liquid chromatography (HPLC), mass spectrometry (MS), ultraviolet (UV), circular dichroism (CD), matrix-assisted laser desorption/ionization (MALDI) and nuclear magnetic resonance (NMR).;Peracetylated-1-thiol-saccharides were used as ligands on our new class of adsorbents in which a thiol group links peracetylated saccharides to silica through an epoxy-silane linker, glycido-oxypropyl trimethoxysilane. The preparation of these trimethoxysilylated saccharides are also described in Chapter 1. The saccharide stationary phases were prepared using two methods: (1) the direct incorporation of derivatized saccharides onto the silica structure in a process known as co-condensation and, (2) post-synthesis grafting-direct immobization methods.;Chapter 2 discusses the synthesis of mesoporous silica with a well-ordered network of porous materials. These materials were prepared using co-condensation of tetraethyl orthosilicate (TEOS) with trimethoxy-silylated derivatives of peracetylated glucose, maltotriose, and maltoheptaose affording ordered mesoporous SBA-15 type silicas. The post synthesis grafting method was performed by modifying Prodigy silica with analogs (1, 3, 7 and 13 glucose units) following direct immobilization and surface chemical assembly approaches. The post synthesis grafting of the saccharide Prodigy silica materials is described in detail in Chapter 3. The resulting materials from saccharide SBA-15 type and Prodigy silicas were characterized by FTIR, nitrogen isotherms, TGA, elemental analysis and TEM (for SBA-15 type silica). The saccharide silica stationary phases prepared have been evaluated in normal phase and reverse phase HPLC stereoisomeric separations.;Chapter 4 focuses on the synthesis of chiral mesoporous silicas using the anionic chiral surfactant, N-myristoyl-L-alanine, and the cationic oligosaccharide, chitosan. In order to synthesize these silicas, co-condensation and pseudomorphic transformation techniques were used. These materials were prepared using different temperatures, aging and pH. The resulting materials were characterized by nitrogen isotherms and TEM. TEM data suggests that the new silica forms could have an ordered helical porous structure.