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Membranes Adopt Guest-Molecules' Properties
Apr 2007
BLACKSBURG, Va., April 2, 2007 -- A block copolymer has been created which forms nanostructured film that can adopt the properties of its "guest" molecules.

Virginia Tech researchers announced last year that they had created a nanostructured membrane that incorporates DNA base pairs in order to impart molecular recognition and binding ability to the synthetic material. This year, they said they have shown -- for the first time -- that these new films, membranes and elastomers are compatible with diverse organic and inorganic molecules and will adopt properties of the guest molecules.

Chemistry professor Tim Long’s research group at Virginia Tech, students affiliated with its Macromolecule and Interfaces Institute (MII) and the US Army Research Laboratory created a block copolymer, where different monomers are linked in a sequential manner and form a nanostructured film. They used adenine and thymine nucleotides, two of the four DNA base pairs that recognize each other. Then the researchers experimented with different kinds of guest molecules with complementary hydrogen bonding sites (hydrogen has a low-energy attraction to many types of atoms).

The research was presented at the 233rd national meeting of the American Chemical Society, held last week in Chicago.

The low-energy attraction means the guest molecules are widely dispersed throughout the membrane, which then takes on the properties of the guest molecules.

“For example,” said Long, “if the guest molecules have ionic sites (sites with positive and negative charges), you will be able to transfer water through a film, because you would have ion channels at the nanoscale. It’s similar to the way a cell membrane works to control the flow of specific ions into a cell. You can create protective clothing -- against chemicals -- that would still allow water vapor through.”

Salts such as ordinary table salt are hydrophilic (water-loving), and their introduction into a block copolymer template permits the placement of the salts at the nanometer dimension. One can imagine forming of channels of salts that are not visible with the human eye but act as a roadway for the transport of water molecules.

The paper, “Nucleobase-containing triblock copolymers as templates for the dispersion of guest molecules at the nanoscale”) was written by Brian Mather of Albuquerque, a chemical engineering doctoral student at MII; Margaux B. Baker, an undergraduate student from the University of Michigan who studied with Long’s group during summer 2006; Long; and Frederick L. Beyer of the US Army Research Laboratory.

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