CAUGHT BY A CRYSTAL MATERIALS SCIENCE: Fleeting
intermediate observed in a porous coordination network
A
N ELUSIVE hemiaminal intermediate—in
which a hydroxyl and an amine are attached to the same carbon—has been observed by X-ray crystallography, thanks to a porous crystalline material that stabilizes the transient species (Nature 2009, 461, 633). The researchers who developed the crystalline trapping strategy say it could help chemists take snapshots of other fleeting intermediates. Although scientists had previously glimpsed shortlived hemiaminals via X-ray analysis, they had to do so by using exceptional experimental methods, such as creating a mutant enzyme that traps the intermediate via kinetic stabilization. To build a simpler trap for the hemiaminal, Makoto Fujita, Masaki Kawano, and colleagues at Japan’s University of Tokyo employed porous crystalline coordination networks. They reasoned these “crystalline molecular flasks,” as Fujita describes them, could sequester a substrate and allow it to undergo a reaction without decomposing the surrounding crystal. Seth M. Cohen, a chemistry professor at the University of California, San Diego, likens the porous networks to climbing frames—organic ligands form the bars, and metal ions play the role of the rivets that hold the structure together. “The result is a grand structure that consists largely of empty space,” Cohen writes in a commentary that accompanies the paper. “Just as children play within the lattice of a climbing frame, so molecules can diffuse and interact within
the lattice of a coordination network.” The Tokyo researchers observed TRAPPED the hemiaminal by carrying out the Crystalline coordination reaction of an aldehyde and an amine network catches a hemiaminal at low temperature in an X-ray diffracfor X-ray observation. (C tometer. This way, X-ray “snapshots” is gray in the crystal and could be taken at each stage. They green in the hemiaminal, first embedded 1-aminotriphenylene N is blue, O is red, and H is within the crystalline network of zinc light gray; some Hs have ions and triazine derivatives. Next, been omitted for clarity.) acetaldehyde was diffused through the network to form the hemiaminal, which was kinetically trapped. Finally, raising the temperature allowed the reaction to proceed to its Schiff base product. “We believe that porous coordination networks and the approach illustrated here offer a general method for acquiring sequential X-ray snapshots of chemical reactions, which will provide valuable direct mechanistic insights not obtainable by other means,” Fujita says. The group plans to use the technique to explore organometallic transformations with unclear reaction mechanisms, as well as highly explosive and toxic substances that have not been well studied. “This is a breakthrough, especially if it can be extended to other reactions that are currently under debate,” comments J. N. H. (Joost) Reek, a supramolecular chemistry and catalysis expert at the University of Amsterdam. “I can imagine that especially the area of transitionmetal catalysis would benefit from this if the strategy is amenable for transition-metal complexes,” he tells C&EN.—BETHANY HALFORD
CLEANTECH Government support lured in venture investors in the third quarter Third-quarter venture capital investments in clean technology increased 10% from the second quarter, according to a preliminary report from research firm Cleantech Group. Funding totaled about $1.6 billion, still 42% below the same period a year ago. In the midst of a slow economic recovery, “government spending is emboldening private capital to get back in the game,” says Dallas Kachan, managing director of Cleantech Group. For example, the largest funding round of the quarter, $198 million for thin-film solar firm Solyndra, was raised in conjunction with
a $535 million loan guarantee from the Department of Energy. In addition to renewed interest in solar energy, Kachan says, biofuels investment has been healthy, and the sector is attracting significant funding from large energy firms. Renewable fuels and chemicals firm LS9 said last week that it raised $25 million in private funding, led by Chevron Technology Ventures. The recent initial public offering of stock by lithium-ion battery maker A123Systems may signal that the public markets are also thawing. The longawaited IPO raised $350 million for A123.
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IPO activity was all but nonexistent in the first half of 2009, blocking the traditional avenue by which venture capitalists recoup their investments. Meanwhile, venture capital firms continue to raise money to invest in cleantech. CMEA Capital, an investor in Solyndra and A123, has raised an additional $100 million to spend on the alternative energy sector in a commitment to the Clinton Global Initiative, part of the William J. Clinton Foundation. CGI members meet annually to commit to solving challenges such as cutting CO2 emissions.— MELODY VOITH
M AKOTO F UJITA
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