Unnatural oligomers and polymers consisting of benzene rings linked by ethynyl groups (phenyleneethynylenes) are designed to fold into porous helical structures, enforced by localized intramolecular hydrogen bonds. An oligomer with a sufficiently long backbone folds back on itself, leading to left- and right-handed helices. Such a backbone-based helical programming affords stable helical structures regardless of structural variation of the side groups that determine the outside surface properties. The interior of the resulting helices is lined by aromatic hydrogen atoms, making these tubular cavities rather hydrophobic. The internal diameters of the helices are adjustable (8 angstrom to 40 angstrom and larger), providing access to novel unnatural folding nanotubes with adjustable interior cavities. Furthermore, these unnatural foldamers have backbones that are both helical and unsaturated, features that may endow unusual and useful physical and chemical properties. The design and synthesis of helices with superhydrophobic (fluorinated) or amphiphilic interior cavities, resolution of enantiomers, and induction of helical twist sense by chiral side chains and chiral solvents are also addressed.
Nanosized cavities and channels have numerous potential applications in catalysis, separations, nanodevices (sensors, fluidics, etc.), nanoscaffolds for building larger structures, and design of other nanoporous materials. With the support of the Organic and Macromolecular Chemistry Program, Professor Bing Gong, of the Department of Chemistry at the State University of New York - Buffalo and Professor Xiao Cheng Zeng, of the Department of Chemistry at the University of Nebraska - Lincoln, are studying the synthesis and properties of carbon-based molecules designed to fold selectively and efficiently into helical structures. These helical structures contain nanosized channels of adjustable size and functionality, allowing tuning of their properties and their interactions with other molecules. These studies also provide fundamental information about the folding of other large molecules, both natural and unnatural, Students carrying out these interdisciplinary studies gain skills in organic synthesis, bioorganic and supramolecular organic chemistry, and theoretical chemistry.
