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Science Concentrates

June 13, 2005 | A version of this story appeared in Volume 83, Issue 24

5-Deoxystrigol lures fungi to plants

Most plants enjoy a symbiotic relationship with soil fungi: The fungi provide the plants with nutrients from the soil, and the plants provide fungi with carbohydrates derived from photosynthesis. In the absence of a plant, the fungal life cycle essentially shuts down. But if a plant is present, the fungi grow and branch, reaching out to make contact with the plant's roots. Scientists figured that some kind of chemical signal must pass from plant root to fungi to initiate this growth. Yet researchers have been unable to identify the signal because of the compound's low concentration and instability. Now Kohki Akiyama of Japan's Osaka Prefecture University and colleagues have isolated and concentrated the signaling agent (Nature 2005, 435, 824). Using several spectroscopic methods and backing their results with a confirmatory chemical synthesis, they identified the compound as the strigolactone 5-deoxystrigol (shown). Strigolactones can also be detected by parasitic weeds that sap plants of water and nutrients. The authors suggest that chemical communication may provide a strategy to control beneficial fungi and harmful weeds in agriculture and natural ecosystems.

Self-heating fuel cell

A propane-burning solid-oxide single-chamber fuel cell that does not need an external heater could potentially be used to operate small portable electrical and electromechanical devices. The fuel cell--a thin disk, similar in size and shape to a watch battery--was designed by Sossina M. Haile at Caltech and coworkers (Nature 2005, 435, 795). The samaria-doped ceria (SDC) electrolyte is supported on a nickel/SDC anode coated with a porous ruthenium/ceria layer that enhances the catalysis of propane partial oxidation at lower temperatures. The heat released in the process is used to sustain the fuel-cell temperature in the absence of external heating. The partial oxidation of the fuel yields carbon monoxide and hydrogen, which are then electrochemically oxidized at the anode to produce electricity. The authors point out that several hurdles remain but that "these results demonstrate the viability of high-energy-density hydrocarbon fuels for portable power applications."


Low-threshold microfluidic laser

A dye laser based on a microfluidic waveguide that can be incorporated into miniature devices to provide a light source for spectroscopy or detection has been described by George M. Whitesides of Harvard University, Daniel G. Nocera and Moungi G. Bawendi of MIT, and coworkers (J. Am. Chem. Soc., published online June 3, To make the waveguide, two streams of fluid with a low refractive index form the "cladding" around a high-refractive-index core fluid as all three streams flow through a single channel about 10 mm long and 400 mm wide. In this example, pure methanol forms the cladding around a 2-mM solution of the dye rhodamine 640 perchlorate in methanol. The dye molecules are excited with rapid pulses of 532-nm laser light, and lasing starts at a low pump energy threshold of 22 mJ. The properties of the waveguide can be modified by adjusting the difference in refractive index between the cladding and the core, and the emission wavelength can be tuned simply by changing the core solvent.


Light shifts polymer's shape

Once a cross-linked polymer has gelled, it can be difficult to change the shape of the material without degrading its mechanical properties or introducing substantial stress. Now, a team led by Christopher N. Bowman and Timothy F. Scott of the University of Colorado, Boulder, reports that they have prepared a cross-linked polymer that, when exposed to light, can be reshaped without sacrificing material properties (Science 2005, 308, 1615). The group attributes the polymer's stress-free malleability to the allyl sulfide functional groups in its backbone. Upon exposure to light, a photoinitiator introduces a radical into the polymer matrix. The radical reversibly cleaves the backbone via the radical addition-fragmentation chain-transfer mechanism shown, where R represents various monomers in the polymer network. Each reaction with a radical generates a new radical, so that the process changes the topology of the polymer network, introducing plasticity. The polymer's chemistry and network connectivity are unchanged, which is how the material maintains its properties.

Marine mammal die-offs linked to brevetoxins

Algal blooms of the dinoflagellate Karenia brevis produce poisonous brevetoxins, killing large numbers of fish and rendering shellfish populations unfit for human consumption. Biologists now link the deadly blooms, so-called red tides, to several "unusual mortality events" in the past few years in which manatees and dolphins along the Florida coast died in droves (Nature 2005, 435, 755). The mysterious deaths occurred during lulls in algal blooming. Autopsies, however, revealed high concentrations of brevetoxins in the stomach contents of the manatees and dolphins. The researchers from the Fish & Wildlife Research Institute in St. Petersburg, Fla., and the University of North Carolina, Wilmington, found high levels of brevetoxins in sea grass eaten by manatees. They also demonstrated that brevetoxins could accumulate to harmful levels in small fish, commonly eaten by dolphins, without killing the fish. The small fish accumulated brevetoxins by feeding on red-tide algae and contaminated shellfish. The findings suggest that brevetoxins can climb the food chain and pose a threat to marine mammals, even when algal blooms are not present.


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