Synthesis and characterization of chiral periodic mesoporous organosilicas.
Synthesis and characterization of chiral periodic mesoporous organosilicas.
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DOI：
10.1002/anie.200702666
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发表时间：
2007-10
影响因子：
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通讯作者：
Xiangju Meng;T. Yokoi;D. Lu;T. Tatsumi
中科院分区：
文献类型：
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作者：
Xiangju Meng;T. Yokoi;D. Lu;T. Tatsumi
手性在生物学、功能材料、精细化学和药学等领域的基础研究和实际应用中都是一个重要课题。最近报道了一些具有手性纳米通道的无机材料的开创性工作。[1-5]第一个实例是通过四乙氧基硅烷（TEOS）在胆固醇和二氨基环己烷基有机凝胶体系中的溶胶-凝胶缩聚获得的手性螺旋二氧化硅。[1，2]另一个成功的例子是通过使用手性阴离子表面活性剂作为模板制备的有序手性介孔二氧化硅。[3]此外，在不存在此类手性添加剂的情况下合成手性介孔二氧化硅也已报道，从而为使用非手性模板剂制备手性介孔材料打开了一扇门。[4，5]周期性介孔有机硅（PMO）是一类特殊的杂化材料，其中手性在基本方面和可能的应用方面都具有特别重要的意义。[6-10]然而，迄今为止，还没有关于PMO材料中手性通道的报道。在这里，我们报告的非手性氟化的表面修饰模板的PMO含有手性通道。这种手性PMO包括使用1，2-双（三乙氧基甲硅烷基）乙烯（BTEE）作为混合二氧化硅前体合成的扭曲六角棒，和使用1，4-双（三乙氧基甲硅烷基）苯（BTEB）制备的螺旋六角棒。用BTEB合成的螺旋样品具有结构周期性，在晶体状介孔壁中的间距为0.85 nm。因此，我们期望我们的手性PMO导致新的应用，例如，在开发对映选择性催化剂，吸附剂，传感器，虽然目前-螺旋通道的对映纯度不高。为了制备手性PMO材料，使用非手性阳离子氟化表面活性剂[CF 3（CF 2）3SO 2NH（CH 2）3 N+（CH 3）3 I]（FC-4911）和阳离子烃表面活性剂十六烷基三甲基溴化铵（CTAB）作为结构导向剂，而使用BTEE或BTEB作为杂化二氧化硅前体。FC-4911与CTAB的比例是影响手性产物生成的关键因素。低反应物浓度和相对较短的反应时间也是重要因素。最终产物-通过溶剂萃取除去模板后-显示出棒状形态（见图1）。使用BTEE制备的样品（指定为样品A）表现出扭曲的棒状形态，具有明显的弯曲晶面，外径为120-150 nm，长度为1-2 μm（见图1a和支持信息）。沿着棒的轴观察到周期性条纹（长度L= 300-450 nm），螺旋节距（即6 L）估计为1.8-3 μm（图1 B）。[3，11]另一方面，使用BTE B制备的样品（指定为样品B）表现出螺旋棒状形态，具有显著的扭曲晶体小面，其具有100-120 nm的外径和1-3 μm的长度（参见图1c）。还观察到沿这些棒的轴的沿着周期性条纹（长度L= 100-200 nm），并且螺旋节距估计为约0.5-1.2 μm（图1 d）。两个样品的条纹似乎是沿着轴移动或弯曲，
Chirality is an important topic both in fundamental research and for practical applications in fields as diverse as biology, functional materials, fine chemistry, and pharmacy. Some pioneering work on inorganic materials with chiral nanochannels has recently been reported.[1–5] The first example is chiral spiral silica obtained by sol–gel polycondensation of tetraethoxysilane (TEOS) in cholesterol and diaminocyclohexane-based organogel systems.[1, 2] Another successful example is well-ordered chiral mesoporous silica prepared by using chiral anionic surfactants as templates.[3] Moreover, the synthesis of chiral mesostructured silica in the absence of such chiral additives has also been reported, thus opening a door for the preparation of chiral mesoporous materials using achiral templates.[4, 5] Periodic mesoporous organosilicas (PMOs) are a special class of hybrid materials, in which chirality assumes a particular importance both with regard to fundamental aspects and in relation to possible applications.[6–10] However, there are no reports on chiral channels in PMO materials up to now. Herein, we report on achiralfluorinated surfactant-templated PMOs that contain chiral channels. Such chiral PMOs include twisted hexagonal rods synthesized using 1, 2-bis (triethoxysilyl) ethene (BTEE), as hybrid silica precursors, and spiral hexagonal rods prepared using 1, 4-bis (triethoxysilyl) benzene (BTEB). The spiral samples synthesized with BTEB exhibit structural periodicity, with a spacing of 0.85 nm in the crystal-like mesoporous wall. Thus, we expect our chiral PMOs to lead to new applications, for example, in the development of enantioselective catalysts, adsorbents, sensors, although—currently—the enantiopurity of the helical channels is not high. To produce the chiral PMO materials, the achiral cationic fluorinated surfactant [CF3 (CF2) 3SO2NH (CH2) 3N+(CH3) 3IÀ](FC-4911) and the cationic hydrocarbon surfactant cetyltrimethylammonium bromide (CTAB) were employed as structure-directing agents, while BTEE or BTEB were used as hybrid silica precursors. The ratio of FC-4911 to CTAB was the key factor for the formation of chiral products. Low reactant concentrations and relatively short reaction times were also important factors. The final products—after removal of the templates by means of solvent extraction—showed a rodlike morphology (see Figure1). The sample prepared using BTEE (designated as sample A) exhibited a twisted rodlike morphology with distinguished bent crystal facets that had an outer diameter of 120–150 nm and a length of 1–2 μm (see Figure 1a and the Supporting Information). Periodic fringes were observed along the axes of the rods (with a length L= 300–450 nm) and the helical pitches (that is, 6L) were estimated to be 1.8–3 μm (Figure 1 b).[3, 11] On the other hand, the sample prepared using BTEB (designated as sample B) exhibited a spiral rodlike morphology with distinguished twisted crystal facets that had an outer diameter of 100–120 nm and a length of 1–3 μm (see Figure 1c). Periodic fringes were also observed along the axes of these rods (with a length L= 100–200 nm) and the helical pitches were estimated to be about 0.5–1.2 μm (Figure 1 d). The fringes of both samples appeared to be moving along the axis or curved when