Reversible Process Forms Supramolecular Polymers For Fibers, Molecular-Transport Mechanisms
Nori Yamaguchi, a chemistry graduate student at Virginia Tech (Blacksburg, VA; nyamaguc@vt.edu), and her professor, Harry Gibson, have used hydrogen bonding self-assembly to create large aggregate structures. These may be used to create fibers or transport target molecules. Using the same components—crown ethers as hosts and secondary ammonium ions as guests—they have created two different, novel, and reversible structures based on hydrogen bonding.
How It Works
Presentations And Publications
How It Works (Back to Top)
In one process, the research team created a linear supramolecular pseudorotaxane polymer that can be drawn into fibers. The structure is created by threading one molecular component through another to form a linear aggregate. This can be undone at the molecular level using heat or pH. Yamaguchi and Gibson were the first to demonstrate this linear array.
The second arrangement of the same components resulted in dendritic pseudorotaxanes. To form a macromolecular aggregate, the researchers assembled benzyl ether dendrons (wedge-shaped molecules) with crown-ether hosts at the "focal points" in layers on a three-armed ammonium salt.
The huge supramolecule takes three days to form, creating a "kind of a glob," Gibson says. Within the glob are pockets of a specific size that can be used to trap target molecules, which can then be transported and released by reversing the construction of the dendrimer. Gibson explains that the structures are sensitive to pH—synthesis can be reversed when the supramolecule is exposed to a base.
Presentations And Publications (Back to Top)
The linear supramolecular pseudorotaxane polymer was first published by Yamaguchi and Gibson in Angewandte Chemie. (Angew. Chem. Int. Ed. 1999, 38, No. 1/2: "Formation of Supramolecular Polymers from Homoditopic Molecules Containing Secondary Ammonium Ions and Crown Ether Moieties.")
The dendritic pseudorotaxanes was first described by Yamaguchi, Lesley Hamilton, and Gibson in Angewandte Chemie. (Angew. Chem. Int. Ed. 1998, 37, No. 23: "Dendritic Pseudorotaxanes.")
Yamaguchi presented the work on "Non-covalent synthesis of dendrimers," co-authored by Hamilton and Gibson, at the American Chemical Society National Meeting (Anaheim, CA; March 22, 1999).
For more information, e-mail Gibson at hwgibson@vt.edu or Yamaguchi at nyamaguc@vt.edu.