SCIENCE & TECHNOLOGY
CONCENTRATES Polyene dyes improve solar cells Highly efficient solar cells that employ novel organic-dye photosensitizers to harvest light have been developed by scien tists in Japan. The team, led by Hironori Arakawa, a director at the National Institute of Advanced Industrial Science & Tech nology, Ibaraki, designed and synthesized a group of poly enes that contain an electrondonating Ν,Ν-dimethylaniline moiety and an electronaccepting carboxyl group ΓY [Chem. Comm., 2 0 0 3 , 252]. \ Electron excitation and trans fer occur when the dyes are exposed to light. Solar cells based on one of the polyenes (shown) produced a 6.8% solar en ergy-to-electricity conversion efficiency—the highest value to date for organic-dye-sensitized solar cells. The cells, prepared using nanocrystalline T i 0 2 photoelectrodes coated with the dye, offer the prospect of low-cost production owing to the dye's simple molecular structure and synthesis, the authors sug gest. The dye is relatively stable under irradiation over several days, the team notes, adding that long-term stability of the dye and cell performance will be investigated in detail.
New detergent keeps membrane proteins stable Specially designed lipopeptide detergents effectively mim ic lipid bilayers in stabilizing purified membrane proteins. The lipopeptides are based on peptides that fold into an ahelix and to which long-chain fatty acids are appended at ei ther terminus. The lipopep tides form cylindrical micelles, with the peptide forming a hydrophilic shell and the fatty acids making up a lipid core. Membrane proteins enveloped in such micelles nicely meet the requirement of being beside a lipid, precluding the aggrega tion that often happens with purified membrane proteins that are not adequately stabi lized. The lipopeptides were designed, prepared, and tested by Gilbert G. Privé, an associate professor of medical biophysics and biochemistry at the University of Toronto, and HTTP://WWW.CEN-ONLINE.ORG
coworkers [Nature Biotechnol., published onlineJan. 13,http:// dx.doi.org/10.1038/nbt776]. They have shown that lipopeptide complexes with α-helical proteins such as bacteriorhodopsin and lactose permease, as well as with β-barrels such as the Escherichia colt PagP pro tein, are stable and suitable for N M R structural studies. The researchers are working on preparing complexes for X-ray crystallographic studies.
Nanowire-based injection lasers shine brightly In electrically driven laser systems, laser light is produced
when positive and negative charges that have been injected on opposite sides of a hetero-
junction are driven to recombine. Now, Harvard University chemistry professor Charles M. Lieber and research associates Xiangfeng Duan, Yu Huang, and Ritesh Agarwal have used a single-step procedure to con struct injection lasers based on cadmium sulfide nanowires and a novel charge-injection scheme [Nature, 421,241 (2003)]. The CdS-based devices emit intense light in the visible region. But according to the researchers, radiation in the UV to near-IR spectral region and multicol ored laser arrays (shown sche matically) can be produced by using nanowires of GaN, InP, and other materials.
Tuning metal nanoshells' properties By varying the size of the core and outer shell of metal nanoshells, researchers at Rice University are able to fine-tune t h e e l e c t r o m a g n e t i c field surrounding the tiny particles [Appl. Phys. Lett, 8 2 , 257 (2003)]. The field, in turn, con trols the magnitude of the sur face-enhanced Raman scat tering (SERS) of molecules bound to the nanoparticle sur face, according to Naomi J. Halas, professor of electrical and computer engineering and of chemistry, and her cowork ers at Rice. The scientists con structed a series of nanoshells with silica cores of 65 or 79 nm and coated them with layers of silver ranging in thickness from 5 to 20 nm. They then measured the Raman spectra of/>-mercaptoaniline adsorbed onto the nanoshell surfaces, observing a maximum effective SERS enhancement of 10 6 . "There are widespread appli cations for this technology in environmental science, chem istry, and biosensing," Halas says.
Engineered relief for cows' indigestion Plants genetically engineer ed by scientists at the Samuel Roberts Noble Foundation in Ardmore, Okla., express ex tended flavonoid polymers called condensed tannins [5aence, 2 9 9 , 396 (2003)]. Sup plementing cows' diets with these molecules reduces the amount of methane they pro duce during normal diges tion—protecting them from potentially lethal indigestion as well as reducing a significant source ofgreenhouse gas emissions. Condensed tannins (shown; R1 and R 2 can be ei-
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ther O H or H) normally con sist of a string of 2,3-cis flavonol units capped with a single 2,3-trans one. Both subunits are thought to be made from a common 2,3-trans in termediate. Just how the cis subunit arises, however, has re mained a mystery Plant biolo gist Richard A. Dixon, postdoc De-Yu Xie, and coworkers show that the 2,3-cis subunit is made by converting the trans intermediate to an achiral anthocyanidin, which is then con verted to the 2,3-cis subunit by an enzyme called anthocyanidin reductase. Tobacco plants engineered to express this en zyme produce high levels of condensed tannins in their flowers. The team is now work ing to engineer the enzyme in to the leaves of alfalfa and oth er plants that cows like to eat. C&EN / JANUARY 20, 2003
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