Catálogo de publicaciones - revistas

<jats:title>Planetary Midwifery</jats:title> <jats:p> Planets form from the materials left behind after a star is formed. Unlike the Sun, most stars are members of binary systems. <jats:bold> Mayama <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="306" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179679">306</jats:related-article> , published online 19 November) present an infrared image of the protoplanetary disks around a young binary star system taken with the coronagraph mounted on the Subaru Telescope in Hawaii. Each individual disk is clearly visible around its star, and comparison with numerical simulations suggests that there could be gas flow from one disk to the other. The nature of this potential gas flow is important in determining where planets could form in binary systems. </jats:p>

<jats:title>It's the Network</jats:title> <jats:p> Numerous reactions of small molecules and ions in the atmosphere take place in the confines of watery aerosols. <jats:bold> Relph <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="308" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177118">308</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5963" page="280" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184555"> <jats:bold>Siefermann and Abel</jats:bold> ) </jats:related-article> </jats:bold> explored the specific influence of a water cluster's geometry on the transformation of solvated nitrosonium (NO <jats:sup>+</jats:sup> ) to nitrous acid (HONO). The reaction involves (O)N–O(H) bond formation with one water molecule, concomitant with proton transfer to additional, surrounding water molecules. Vibrational spectroscopy and theoretical simulations suggest that certain arrangements of the surrounding water network are much more effective than others in accommodating this charge transfer, and thus facilitating the reaction. </jats:p>

<jats:title>Oxalate from Air</jats:title> <jats:p> In light of increasing concerns about the consequences of excessive atmospheric carbon dioxide, there is demand for methods to use carbon dioxide in the preparation of more elaborate compounds. Though reactions with hydroxide salts to form carbonates tend to proceed fairly cleanly, reductive processes to form carboxylic acids, esters, and alcohols are often rather unselective. <jats:bold> Angamuthu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="313" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177981">313</jats:related-article> ; see the news story by <jats:bold> <jats:related-article issue="5963" page="257-a" related-article-type="in-this-issue" vol="327">Service</jats:related-article> </jats:bold> ) discovered that a copper complex exhibited remarkable selectivity in reductively coupling carbon dioxide to form oxalate through coordinative electron transfer, even in the presence of excess oxygen, normally a much more potent electron acceptor. Precipitation of the oxalate as a lithium salt and electrochemical re-reduction of the copper produced a preliminary catalytic cycle, demonstrated through six turnovers. </jats:p>

<jats:title>Heck of an Alternative</jats:title> <jats:p> The Mizoroki-Heck reaction is widely used in organic synthesis to link together unsaturated carbon fragments such as olefins and arenes. However, one of its drawbacks is the need to append a reactive group such as a halogen to one of the reagents beforehand. <jats:bold> Wang <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="315" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1182512">315</jats:related-article> , published online 26 November) present an alternative palladium-catalyzed reaction that links olefins directly to aryl acids. Oxygen added to the reaction medium concurrently oxidizes the aryl C-H bond at the linkage site, eliminating the need for prior halogenation. Introducing amino acid–derived ligands tunes the aryl site at which the reaction takes place, and efficient reactivity can be achieved across a diverse range of substrates. </jats:p>

<jats:title>Methanol Coupling Catalyzed with Gold</jats:title> <jats:p> Gold surfaces can be effective catalysts for partial oxidation reactions, in part because lower interaction strengths of molecules absorbed on gold allow products to desorb before further unwanted oxidations occur. One challenge in these reactions is the low rate of formation of reactive atomic surface oxygen. <jats:bold> Wittstock <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="319" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183591">319</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5963" page="278" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184203">Christensen and Nørskov</jats:related-article> </jats:bold> ) created high–surface area gold catalysts by leaching silver from gold-silver alloys. This material proved to be an effective catalyst for partial oxidative coupling of methanol, yielding methyl formate. Residual silver appears to play a key role in activating the dissociation of molecular oxygen. </jats:p>

<jats:title>Measuring Methanogenesis</jats:title> <jats:p> After carbon dioxide, methane is the second most important greenhouse gas, and an important species in terms of its role in atmospheric chemistry. The sources and sinks of methane, particularly the natural ones, are too poorly quantified, however, even to explain why the decades-long, steady increase of its concentration in the atmosphere was interrupted between 1999 and 2006. <jats:bold> Bloom <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="322" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1175176">322</jats:related-article> ) use a combination of satellite data, which indicate water table depth and surface temperature, and atmospheric methane concentrations to determine the location and strength of methane emissions from wetlands, the largest natural global source. The constraints placed on these sources should help to improve predictions of how climate change will affect wet-land emissions of methane. </jats:p>

<jats:title>Predator Avoidance Strategy</jats:title> <jats:p> Selective pressures influencing bird migration can include availability of food, pressure from parasites and pathogens, and predation risk. The importance of the last of these is revealed by <jats:bold> McKinnon <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="326" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183010">326</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5963" page="276" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184964">Gilg and Yoccoz</jats:related-article> </jats:bold> ), who present an experimental analysis of the benefits of long-distance migration for reproduction in arctic-nesting birds. Measurements of a controlled effect of predation risk along a 3350-kilometer north-south gradient across arctic Canada provides evidence that the risk of nest predation decreases with latitude. Thus, birds migrating further north may acquire reproductive benefits in the form of reduced predation risk. </jats:p>

<jats:title> The Art of <jats:italic>Artemisia</jats:italic> </jats:title> <jats:p> As the malaria parasite, which is transmitted through mosquito vectors, develops resistance, previously useful control mechanisms are beginning to fail. Combination therapies based on the plant product artemisinin are a promising alternative. <jats:bold> Graham <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="328" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1182612">328</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5963" page="279" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184780">Milhous and Weina</jats:related-article> </jats:bold> ) have now developed a genetic map of the plant <jats:italic>Artemisia annua</jats:italic> from which artemisinin is derived. The results lay the foundation for improving agricultural productivity of this natural product, which is becoming increasingly important in the fight against malaria. </jats:p>

<jats:title>Targeting Copper Clusters</jats:title> <jats:p> Tetrathiomolybdate (TM) is a copper-depleting agent that has potential in treating copper-dependent diseases. <jats:bold> Alvarez <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="331" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179907">331</jats:related-article> , published online 26 November) used spectroscopic and structural studies to show that TM inhibits the yeast copper chaperone Atx1 by forming a TM-Cu-ATx1 complex that is stabilized by a sulfur-bridged copper-molybdenum cluster. Cluster formation prevents transfer of copper from the chaperone to target enzymes. The results provide a basis for developing drugs that target metallation pathways. </jats:p>

<jats:title>To Stall or Not to Stall</jats:title> <jats:p> Recent studies in mammals and <jats:italic>Drosophila</jats:italic> have shown that RNA polymerase II frequently stalls shortly after initiating messenger RNA synthesis and that this stalling is important for proper expression of genes. Although several protein factors that affect polymerase stalling are known, the role of DNA sequence in this process has remained unclear. Now <jats:bold> Nechaev <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="335" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181421">335</jats:related-article> , published online 10 December) report that the initially transcribed sequences of many genes contain a signal that works like a stop sign for the elongating polymerase. Expression of genes may thus be regulated by a combination of a DNA signal that induces promoter-proximal stalling and protein factors that alter its duration. </jats:p>