Light converts monomers into large single-crystal linear polymers
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le organic compounds. However, the sensor also demonstrated selectivity and specificity for molecules with lower vapor pressures, like many explosives and environmental toxins. They engineered a phage surface sensitive to TNT, a common explosive, by modifying the phage to display a TNT-binding peptide motif. As TNT vapor concentration increased, the binding of TNT to the substrate induced structural changes in the phage bundles and a color change of the material. A key advantage of Lee’s design over other colorimetric sensors is the viewing-angle independent coloration of the phage bundles. This color fidelity, combined with the simplicity of
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fabrication and portability, makes these sensors powerful and practical tools for detecting toxins. Marya Lieberman studies self-assembly of biomolecules at the University of Notre Dame. “Though the stability, reproducibility, and interferences still need to be characterized, this is a really clever way to translate a chemical interaction on the nanometer scale into a visual output on the centimeter scale. When a sensor can be read visually, it cuts the cost of making the sensor and makes it more practical for field use,” Lieberman said. Laurel Hamers
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Light converts monomers into large single-crystal linear polymers
d = ~3 nm
10.7 nm
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beaker left in the sunlight has brought the world an unusual class of polymer crystals. A research team based at the University of California at Los Angeles and at Santa Barbara reports in the January 14 issue of Science (DOI: 10.1126/science.1245875, p. 272) the quantitative conversion of a class of monomers into large singlecrystal linear polymers after exposure to visible light. “This is fascinating because they have a monomer that can undergo a topochemical polymerization to generate enormous [1.5 cm long] single crystals with exceedingly long polymers that are highly oriented,” said Paula Hammond of the Massachusetts Institute of Technology. In a topochemical polymerization, monomers are pre-assembled into their approximate end positions, with reaction initiated by heat or light. “Growth of a polymer crystal is really a pain. What [first author] Letian [Dou] found is a way to trigger the reaction, make everything very simple, and it takes just an hour,” said Yang Yang of UCLA, one of the corresponding authors. Fred Wudl (UCSB), the other corresponding author, said, “In general, when anyone does an organic photochemical reaction in the solid state, the
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(a) Conventional polymer by mechanical exfoliation versus (b) single-crystal polymer by mechanical exfoliation. Note the entanglement of the conventional polymer. (c) Reversibility: under heating the polymer (yellow) reverts to monomer (orange).
product absorbs more than the starting material, and in the same region [of the spectrum, blocking further reaction].... This is probably the first case where a quantitative solid–solid reaction has been observed.” The researchers found th
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