Self-assembled porous materials from cyclic ureas

有机和大分子化学项目支持南卡罗来纳大学Linda Shimizu教授的工作，她将开发具有合理可调腔的均匀微孔材料。这些将被用作在反应中诱导选择性的受限环境，用于主/客体化学和分离。已经证明，双尿素大环可预测地自组装成多孔晶体，其中包含空心管状通道。这种组装由非共价相互作用指导，主要是尿素-尿素氢键和芳基堆叠相互作用。最初的结构，苯醚双尿素，证明了这种方法是有效的，因为它按照设计组装成晶体，其中含有充满乙酸客体的管状通道。来访者可以从这些晶体中去除，形成一个多孔主体，显示出与开放框架微孔材料一致的1型气体吸附等温线。最近有研究表明，结晶苯醚双尿素结合客体分子，这些客体分子可以像沸石一样被移除并可逆地反弹。事实上，结晶苯醚双脲可以作为反应的容器，在高转化率下促进2-环己酮的高度立体选择性的头对尾[2+2]光二聚化。重点将放在从刚性间隔片和尿素合成双尿素大环上，通过调节间隔片的大小和形状，自组装后将显示更大范围的腔尺寸和内部特性。然后可以在内部添加官能团来调节反应环境，并将导致“可调”腔，旨在结合特定的客体并催化反应。此外，这些多孔材料将被研究作为选择性光化学反应的环境和作为醇脱水的催化剂。由有机和大分子化学计划资助的这项工作将产生新的分子构建块，可预测地自组装成管状超分子组件和多孔固体，已被用作传感器，定向反应模板，分离和催化剂载体以及金属隔离剂。在这个项目中训练的研究生将获得广泛的多学科背景，这将使他们能够从事广泛的科学事业。该奖项将支持本科生和高中生的首次研究经历。该奖项还将支持加强和延续化学推广计划，促进K-12学生、教师和熟练的科学研究人员之间的互动。将纳入满足教师要求并与科学标准相关的新实验。

The Organic and Macromolecular Chemistry Program supports the work of Professor Linda Shimizu of the University of South Carolina who will develop homogeneous microporous materials with rationally tunable cavities. These will be used as confined environments for inducing selectivity in reactions, for host/guest chemistry, and for separations. It has been demonstrated that bis-urea macrocycles predictably self-assemble into porous crystals, which contain hollow tubular channels. The assembly is directed by non-covalent interactions, primarily urea-urea hydrogen bonds, and aryl stacking interactions. The initial structure, phenylether bis-urea, proves that this approach is valid, as it assembles as designed into crystals containing into tubular channels filled with acetic acid guests. The guests can be removed from these crystals forming a porous host that display a type 1 gas adsorption isotherm consistent with an open framework microporous material. Recently it has been shown that crystalline phenylether bis-urea binds guest molecules and that these guests can be removed and rebound reversibly, much like zeolites. In fact, crystalline phenylether bis-urea can be used as a container for reactions, promoting highly stereoselective head-to-tail [2+2] photodimerizations of 2-cyclohexenone in high conversion. Focus will be on the synthesis of bis-urea macrocycles from rigid spacers and ureas that upon self-assembly will display a greater range of cavity sizes and interior properties by modulating the size and shape of the spacers. Functional groups can then be added on the interior to tune the reaction environment and will lead to 'tunable' cavities, designed to bind specific guests and catalyze reactions. Also, these porous materials will be investigated as environments for selective photochemical reactions and as catalysts for alcohol dehydration.The funding of this work by the Organic and Macromolecular Chemistry Program will result in new molecular building blocks that predictably self-assemble into tubular supramolecular assemblies and porous solids that have been sought for applications as sensors, templates for directed reactions, as separation and catalyst supports, and for metal sequestering agents. Graduate students trained in this program will receive a broad multidisciplinary background that will empower them to pursue a wide range of scientific careers. This award will support the first research experiences of undergraduates and high school students. This award will also support the enhancement and continuation of a chemistry outreach program that fosters interactions between K-12 students and teachers and skilled scientific researchers. New experiments to meet teacher requests and to relate to science standards will be incorporated.