Self-assembled porous materials from cyclic ureas

University South Carolina Research Foundation, Columbia SC

Investigators

Abstract

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.