Catálogo de publicaciones - revistas

<jats:title>Facile Fluorination</jats:title> <jats:p> Fluorine atoms have become a useful substituent in pharmaceuticals. However, they remain challenging to introduce synthetically because present methods for carbon-fluorine bond formation require either corrosive conditions or somewhat exotic, and thus expensive, reagents. A sticking point has been the failure of traditional palladium catalysts to couple aryl groups with coordinated fluoride. <jats:bold> Watson <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="1661" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1178239">1661</jats:related-article> , published online 13 August; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5948" page="1630" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179671">Gouverneur</jats:related-article> </jats:bold> ) show that pairing palladium with a well-designed phosphine ligand produces a versatile catalyst for aryl fluorination using simple fluoride salts. The method tolerates a range of functional groups and should facilitate efficient syntheses of multiple fluoroaromatic targets. </jats:p>

<jats:title>Polymer Photodetectors</jats:title> <jats:p> Optical sensing is used in a wide range of applications, such as low-light detection systems in cars and cameras. Most photodetectors have a limited spectral range and can only detect a narrow range of wavelengths. <jats:bold> Gong <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="1665" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176706">1665</jats:related-article> , published online 13 August) developed polymer photodetectors with extremely broad spectral response and exceptionally high sensitivity that can exceed the response of an inorganic semiconductor detector at liquid helium temperature. A key aspect in the device design is the inclusion of blocking layers to reduce significantly the dark current or noise in the devices. </jats:p>

<jats:title>Tin Two-Step</jats:title> <jats:p> Doubly and triply bonded carbon compounds have a well-studied tendency to link up with one another and form rings. The rates of these reactions and their relative susceptibilities to acceleration by heat versus light are encapsulated in the decades-old Woodward-Hoffmann rules. More recently, alkene and alkyne analogs have been prepared with heavier elements such as silicon and tin substituted for carbon. <jats:bold> Peng <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="1668" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176443">1668</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="5948" page="1631" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179881">Sita</jats:related-article> </jats:bold> ) have now discovered that two distannynes (compounds with triply bonded tins) react readily with ethylene to form cycloadducts, with tin-carbon σ bonds taking the place of C-C and Sn-Sn π bonds. These products, characterized spectroscopically and crystallographically, are only loosely bound at room temperature, easily reverting to their multiply bonded precursors on gentle heating. </jats:p>

<jats:title>Bonding Oxides and Metals</jats:title> <jats:p> The binding of noble metals that can act as catalysts to metal oxides that are reducible is assumed to occur at the exposed cation of the oxide. For nonreducable oxides such as aluminum oxide, it is not so obvious how the metal can bind strongly. <jats:bold> Kwak <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="1670" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176745">1670</jats:related-article> ) used a combination of high-resolution transmission electron microscopy and solid-state magic-angle spinning nuclear magnetic resonance to study the anchoring of platinum at high and low loadings on alumina. At the surface, the Al <jats:sup>3+</jats:sup> ions were penta-coordinated. Density functional calculations support a model in which the cation binds three oxygen atoms in the alumina and two from platinum oxide. </jats:p>

<jats:title>Martian Impact</jats:title> <jats:p> Impact craters form frequently on Mars, exposing material that would otherwise remain hidden below the surface. <jats:bold> Byrne <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="1674" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175307">1674</jats:related-article> ) identified mid-latitude craters that formed over the last few years, imaged them in great detail with a camera on board the Mars Reconnaissance Orbiter, and monitored subsequent changes. The craters excavated buried water ice, which was later seen sublimating away. In addition, some craters might have excavated completely through the ice. The observations are consistent with models and other observations that suggest water ice should be stable decimeters to about 1 meter below the martian surface at latitudes poleward of about 40°; and suggest that, in the recent past, Mars had a wetter atmosphere than at present. </jats:p>

<jats:title>Togetherness</jats:title> <jats:p> Two of the most important questions in paleoclimatology are, how are the climates of the Northern and Southern Hemispheres linked, and what are the roles of the high latitudes and the tropics in driving and transmitting climate changes? Past investigations have concentrated on the study of large, rapid climate changes like deglaciations or the Younger Dryas because they are the easiest ones to see and to date. <jats:bold> Licciardi <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="1677" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175010">1677</jats:related-article> ) expand the scope of these investigations by determining precise cosmogenic isotope ages for glacial moraines formed in the Peruvian Andes during the Holocene (the last 11,000 years). The precision of these data reveals a broad correlation between Peruvian glacial advances and climate in the North Atlantic region, revealing important climate linkages between the tropics and higher latitudes. </jats:p>

<jats:title>Malaria Chloroquine Resistance Transporter</jats:title> <jats:p> Malaria is one of the most deadly infectious diseases in the world today, and the emergence and spread of chloroquine-resistant parasites has been a disaster for world health. The Chloroquine Resistance Transporter (PfCRT) was originally identified because mutations in this protein confer chloroquine resistance in the human malaria parasite, <jats:italic>Plasmodium falciparum</jats:italic> . However, the mechanism by which they do so has been the subject of ongoing debate. <jats:bold> Martin <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="1680" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175667">1680</jats:related-article> ) have now succeeded in expressing PfCRT at the surface of <jats:italic>Xenopus laevis</jats:italic> oocytes, establishing a robust and reproducible heterologous system for the study of this protein. The resistance-conferring form of the protein mediates the transport of chloroquine, whereas wild-type PfCRT does not. Thus, as suspected, chloroquine resistance in the malaria parasite indeed arises as a result of the transport of the drug via mutant PfCRT. </jats:p>

<jats:title>Cataloging Kinase Targets</jats:title> <jats:p> Protein phosphorylation is a central mechanism in the control of many biological processes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5948" page="1635" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1180331">Collins</jats:related-article> </jats:bold> ). It remains a challenge to determine the complete range of substrates and phosphorylation sites altered by a kinase like cyclin-dependent kinase 1 (Cdk1), which controls cell division in yeast. <jats:bold> Holt <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="1682" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172867">1682</jats:related-article> ) engineered a strain of yeast to express a modified Cdk1 molecule that could be inhibited by a specific small-molecule inhibitor. The range of Cdk1-dependent phosphorylation was assessed by quantitative mass spectrometry, which revealed many previously uncharacterized substrates for Cdk1. In addition to phosphorylation on serine and threonine residues, which appears to be evolutionarily ancient, tyrosine phosphorylation occurs primarily in multicellular organisms. <jats:bold> Tan <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="1686" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174301">1686</jats:related-article> , published online 9 July) compared the overall presence of tyrosine residues in human proteins (which are frequently phosphorylated) and in yeast proteins (which are not). Loss of tyrosine residues has occurred during evolution, presumably to reduce adventitious tyrosine phosphorylation. </jats:p>

<jats:title>Cataloging Kinase Targets</jats:title> <jats:p> Protein phosphorylation is a central mechanism in the control of many biological processes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5948" page="1635" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1180331">Collins</jats:related-article> </jats:bold> ). It remains a challenge to determine the complete range of substrates and phosphorylation sites altered by a kinase like cyclin-dependent kinase 1 (Cdk1), which controls cell division in yeast. <jats:bold> Holt <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="1682" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172867">1682</jats:related-article> ) engineered a strain of yeast to express a modified Cdk1 molecule that could be inhibited by a specific small-molecule inhibitor. The range of Cdk1-dependent phosphorylation was assessed by quantitative mass spectrometry, which revealed many previously uncharacterized substrates for Cdk1. In addition to phosphorylation on serine and threonine residues, which appears to be evolutionarily ancient, tyrosine phosphorylation occurs primarily in multicellular organisms. <jats:bold> Tan <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="1686" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174301">1686</jats:related-article> , published online 9 July) compared the overall presence of tyrosine residues in human proteins (which are frequently phosphorylated) and in yeast proteins (which are not). Loss of tyrosine residues has occurred during evolution, presumably to reduce adventitious tyrosine phosphorylation. </jats:p>

<jats:title>From Retrogene to Phenolic Metabolism</jats:title> <jats:p> Metabolic plasticity, which involves the creation of new genes, is an essential feature of plant adaptation and speciation. Studying plants from the mustard family, <jats:bold> Matsuno <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="1688" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174095">1688</jats:related-article> ) show that variants of the cytochrome P450 enzyme family were derived through retroposition, duplication, and subsequent mutaton. Evolutionary changes increased the volume of the substrate pocket altering with what sorts of substrates the enzymes could interact. The enzymes formed the basis for a new metabolic pathway, the products of which include constituents of pollen and of phenylpropanoid metabolism. </jats:p>