Preparation and Charaterization of DAM-1 type Materials
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Preparation and Charaterization of DAM-1 type Materials Decio Coutinho, Ying Ma and Kenneth J. Balkus, Jr.* The University of Texas at Dallas, Department of Chemistry, Richardson, TX 75083-0688 ABSTRACT Vitamin E TPGS was found to be an effective structure-directing agent for the preparation of both hexagonal all silica DAM-1 and the alumina analog, Al-DAM-1. These free flowing powders offer many advantages in the handling and oral delivery of the sticky vitamin E TPGS. Upon exposure to simulated gastric fluid, the Al-DAM-1 host molecular sieve is dissolved releasing the vitamin E TPGS. As much as 0.6 grams of vitamin E TPGS can be immobilized into 1 gram of Al-DAM-1. Vitamin E TPGS also templates highly ordered mesoporous DAM-1 with tunable morphologies such as hexagons (various lengths), gyroids, rods, spheres and discoids depending upon the temperature and gel composition. Characterization of these composites as well as a preliminary evaluation of Al-DAM-1 as an oral drug delivery system under physiological conditions is presented. INTRODUCTION We recently reported the synthesis of the new hexagonal mesoporous silica DAM-1 (Dallas Amorphous Material no. 1) using Vitamin E TPGS (α-tocopheryl polyethylene glycol 1000 succinate) as a structure-directing agent [1,2]. This mesoporous composite was designed for the purpose of oral drug delivery, with a goal of improved stability as well as to achieve a free-flowing powder in order to facilitate handling and transportation. We have previously shown that mesoporous silica and transition metal oxide molecular sieves can effectively encapsulate biomolecules such as enzymes and proteins [3-5]. A natural extension of this work is the immobilization of bioactive molecules such as Vitamin E, a noted anti-oxidant [6-12]. Vitamin E TPGS is a water-soluble form developed for those with difficulty absorbing fatsoluble tocopherols [13-16]. This form of Vitamin E is a surfactant-like molecule that can generate micelles, which enhances solubility and protects the succinate linkage from hydrolysis in the stomach’s acidic environment. To retain this feature the Vitamin E TPGS must be immobilized as a micelle. This in turn is what lead us to explore the synthesis of silica DAM-1 around the Vitamin E micelles. We have also prepared an alumina version (Al-DAM-1) that completely dissolves in simulated gastric fluid. The all-silica DAM-1 is a highly ordered and thermally stable nanoporous material, which may have a variety of applications. For example, we have recently reported the preparation of oriented MCM-41 mesoporous silica membranes where the orientation of the film is partly dependent upon the morphology of the molecular sieve particles [17]. Therefore, we have explored the synthesis of DAM-1 under a variety of conditions in an effort to control morphology. Several recent reports describe the synthesis of mesoporous silica with controlled morphology using cationic surfactants [18-21] and neutral block copolymers as templates [22]. For example, Yang et al recently reported that hollo
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