Professor Linda Shimizu of the University of South Carolina is supported by the Macromolecular, Supramolecular and Nanochemistry Program of the Division of Chemistry to develop bis-urea macrocycles that predictably assemble into columnar structures with homogeneous channels with diameters of ~ 1 nm or less. This proposal develops new self-assembling macrocycles, explores the use of these materials to absorb reactive molecules, and investigates the effects of carrying out reactions within this confined space.
Fundamental understanding of the factors that govern the reaction of molecules in small spaces could lead to new methods for organic synthesis that utilize less reactive and safer reagents. Such synthetic improvements would be environmentally friendly and economical. This research provides training for undergraduates and graduate students in organic and materials chemistry. In addition, this award supports the continuation of a chemical demonstration program that brings chemists into South Carolina K-12 classrooms to showcase the scientific method and foster interest in chemistry and the natural sciences.
. This work examined the utility of porous crystals to absorb, transport and organize guests within straw-like channel with diameters of less than one nanometer. These porous crystals were made by the stacking and self-assembly of the small molecule building blocks, the bis-urea macrocycles (Figure 1). We found that these materials have very regular, homogeneous structures and are excellent substrates for studying the absorption and transport of small molecules. The mobility of the guests through the nanochannels is a function of the size and shape and interior properties of the macrocycle. New properties arise due to the assembly of these macrocycles into the supramolecular straw structures. We observed the formation of stable organic radicals under ambient conditions and the facile generation of single oxygen when the material was UV-irradiated under an oxygen atmosphere. Specifically, we looked at reactions that occur when the substrates are irradiated with UV-light (photochemical reactions) and oxidation reactions (Scheme 1). These substrates provide controlled model systems of known structures to test the effects of confinement on reaction pathway and on the product distribution. A number of these reactions proceeded in high yield and with high selectivity to give products that are either not observed in solution or are formed as minor products in solution. Fundamental understanding of the processes of absorption, diffusion, and storage in tiny straw-like channels with diameters of 1 nm or less has practical application in separations and catalysis. We studied the effects of carrying out organic reactions in these small spaces. Ultimately, a better understanding of a reaction mechanism should aid in the development of safer, more environmentally friendly and more economical reagents for organic synthesis. For example, the control use of oxygen, the simplest oxidant, for small molecule oxidation reactions could lead to greener industrial processes. This research provided training for high school students, undergraduates, and graduate students in organic and materials chemistry. In addition, this award supported our chemical demonstration program that connects chemical scientists with South Carolina K-12 classrooms to showcase the scientific method and to foster interest in chemistry and in the natural sciences.
