Catálogo de publicaciones - revistas

<jats:title>Layering on solar cell power and stability</jats:title> <jats:p> Solar cells made from carbon-based polymers are helpfully flexible. However, there's been a frustrating tradeoff between cell stability and efficiency when converting solar power to electrical power. Page <jats:italic>et al.</jats:italic> offer a strategy to partially resolve this dilemma by inserting a layer of polar organic compound (a fullerene derivative) between the cathode (the positive pole in the circuit) and the rest of the cell. Aluminum is an efficient cathode material but is prone to oxidative degradation. The easily applied polar layer enables the use of more stable metals, such as silver and copper, for the cathode, while counteracting their tendencies to diminish power conversion efficiency. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="441" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1255826">441</jats:related-article> </jats:p>

<jats:title>How to make vanadium dioxide metallic</jats:title> <jats:p> At about 70°C, the material vanadium dioxide (VO <jats:sub>2</jats:sub> ) switches from being a semiconductor to a metal. The switch happens so fast that it may be useful in electronic devices, but it is not clear whether the switch is primarily caused by enhanced interactions between electrons or by a change in the crystal structure. Morrison <jats:italic>et al.</jats:italic> shone laser light on a sample of VO <jats:sub>2</jats:sub> , initially in a semiconducting state. They used electron diffraction to monitor the changes in the material's crystal structure and simultaneously measured its optical properties to monitor the electronic state. For certain laser powers, VO <jats:sub>2</jats:sub> switched to a long-lived metallic state even though it preserved its initial crystal structure. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="445" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1253779">445</jats:related-article> </jats:p>

<jats:title>Making use of graphene's valleys</jats:title> <jats:p> Graphene has two distinct valleys in its electronic structure, in which the electrons have the same energy. Theorists have predicted that creating an asymmetry between the two valleys will coax graphene into exhibiting the so-called valley Hall effect (VHE). In this effect, electrons from the two valleys move across the sample in opposite directions when the experimenters run current along the sample. Gorbachev <jats:italic>et al.</jats:italic> achieved this asymmetry by aligning graphene with an underlying layer of hexagonalboron nitride (hBN) (see the Perspective by Lundeberg and Folk). The authors measured the transport characteristics of the sample, which were consistent with the theoretical predictions for the VHE. The method may in the future lead to information processing using graphene's valleys. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="448" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1254966">448</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="422" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1260989">422</jats:related-article> </jats:p>

<jats:title>Ensuring handedness when breaking C-H bonds</jats:title> <jats:p> Many organic compounds are chiral: They manifest two distinct mirror-image variants, or enantiomers. Kinetic resolution can transform one enantiomer to a desired product while leaving its mirror image unmodified. Chu <jats:italic>et al.</jats:italic> applied this strategy to a reaction that replaces aryl carbon–hydrogen bonds with carbon-iodine bonds. They used a chiral palladium catalyst that reacts selectively with just one of two enantiomers of various benzylamine derivatives. In medicinal chemistry, such selective synthesis of individual enantiomers is essential for screening interactions with chiral biomolecules such as proteins. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="451" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1258538">451</jats:related-article> </jats:p>

<jats:title>How bacteria break down organohalides</jats:title> <jats:p> Anaerobic bacteria can break down a range of organohalide pollutants. To do so, they use unusual reductive dehalogenase enzymes that remove the halogen ion from the molecule, making the pollutants less toxic. Bommer <jats:italic>et al.</jats:italic> describe x-ray crystal structures of one such enzyme from <jats:italic>Sulfurospirillum multivorans</jats:italic> (see the Perspective by Edwards). Vitamin B <jats:sub>12</jats:sub> , present near the substrate binding site, catalyzes the reduction of trichloroethylene in concert with two iron-sulfur clusters. The structures provide mechanistic clues for how to engineer enzymes to recognize other pollutants. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="455" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1258118">455</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6208" page="424" related-article-type="in-this-issue" vol="346" xlink:href="10.1126/science.1261194">424</jats:related-article> </jats:p>