NEWS OF THE WEEK
MOLECULAR PUMP DEVELOPED
THREAD, THEN REPEAT A molecular pump threads a ring on a dumbbell-shaped molecule (shown) and then repeats the process (not shown). Pluses and dots are oxidized and reduced forms of charged groups, respectively.
MOLECULAR MACHINES: Carrierprotein mimic threads two rings onto a dumbbell-shaped rod
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YNTHETIC MOLECULAR machines that can
shuttle molecules around could one day be used to create artificial muscles or transport molecules across membranes. Researchers have now brought such applications one step closer to reality by creating a molecular system that threads and traps large rings on a dumbbell-shaped molecular rod (Nat. Nanotechnol. 2015, DOI: 10.1038/nnano.2015.96). J. Fraser Stoddart and coworkers at Northwestern University modeled this system on carrier proteins, which pump electrons, protons, ions, or molecules across membranes to produce concentration gradients in cells. The work is “a fascinating example” of a nanoscale molecular system with a machinelike function, comments functional materials expert Ben L. Feringa of the University of Groningen, in the Netherlands. Although it is primitive compared with biological transporter proteins, it illustrates how an entirely artificial system can mimic key functions that have evolved in biological systems, Feringa says. Stoddart’s team employed a clever design, says molecular machine specialist Jean-Pierre Sauvage of the University of Strasbourg, in France. It enables the pump to use redox reactions and heat to fish two cyclobis(paraquat-p-phenylene) rings out of solution and thread them, one at a time, onto a dumbbell-shaped molecule, where the rings become trapped in a high energy state. To start the pumping process, the ring in solution and viologen on the dumbbell are reduced, making them mutually attractive. The attraction pulls
SOURCE: Adapted from Nat. Nanotechnol.
the ring over a dimethylpyridinium end cap on the dumbbell, and the ring forms a complex with viologen. Oxidation then returns the ring and viologen to their original states, making them repel one another and driving the ring toward an isopropylphenylene barrier. Mild heating enables the ring to slip over the barrier. This traps the ring, far from equilibrium, on an oligomethylene chain terminated with a diisopropylphenyl end cap. The second ring slips onto the dumbbell the same way. It takes about two hours to capture each ring. Relative to previous work in the field, “the most remarkable improvement” of the new study is that it got two rings together onto a chain instead of just one, Sauvage says. Stoddart notes that the design is so versatile that threading more than two rings, and even an unlimited number, may eventually be possible.—STU BORMAN
SOLAR INDUSTRY China’s Yingli warns investors about struggles with costs and debt China’s Yingli Green Energy, a large producer of solar power wafers, cells, and panels, warned investors last week that it risks going out of business as a result of its cost structure and debt load. Yingli posted a net loss in 2014 of $209 million, adding to three straight years of significant losses, according to a report filed with the U.S. Securities & Exchange Commission. Although based in China, Yingli trades on the New York Stock Exchange. In addition, the company owes payments on $1.6 billion in debt.
Since the recession began in 2008, the solar industry has experienced periods of both boom and bust, but the main trend has been a sharp decrease in the prices of solar panels. Falling prices forced many firms, particularly in the West, to go bankrupt, leaving only low-cost producers, most of which are based in China. “Yingli was willing to make panels at very low prices and aimed to be a highvolume producer,” explains Jenny Chase, head of solar at analysis firm Bloomberg New Energy Finance. That strategy meant
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low margins, and Yingli was not alone for a time in running its factories at a loss. But other Chinese firms, including Jinko Solar and Trina Solar, have regained profitability. Yingli may have survived thus far because it has patient lenders, according to Chase. In the filing, Yingli says it will look to raise cash from its current shareholders, lower its costs, and work with banks to refinance its debt. The firm may also benefit from domestic demand: China is now leading the world in solar panel installations.—MELODY BOMGARDNER
