Catálogo de publicaciones - revistas

<jats:title>An x-ray view of C–F and S–F bond breaks</jats:title> <jats:p> X-ray absorption spectroscopy is a useful probe of element-specific dynamics in molecular reactions. However, the required x-ray fluxes have rarely been available outside expensive dedicated facilities such as synchrotrons. Pertot <jats:italic>et al.</jats:italic> developed a tabletop laser-based high-harmonic source that extends far enough into the x-ray region to probe carbon K-edge and sulfur L-edge absorptions with femtosecond temporal resolution. They used this source to track the previously elusive dissociative dynamics of gaseous carbon tetrafluoride and sulfur hexafluoride after laser-induced ionization. </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="6322" page="264" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aah6114">264</jats:related-article> </jats:p>

<jats:title>Alcohols remove lithium to make nanowires</jats:title> <jats:p> Many existing routes for making metal and metal oxide nanowires are complex, require harsh solvents, or are not easily scaled up. Lei <jats:italic>et al.</jats:italic> developed an extraction process to remove lithium from aluminum or magnesium alloys by using alcohol solvents. The resulting highly reactive Al or Mg atoms formed alkoxide nanowires, which could be converted into oxides by high-temperature treatment. The authors used this approach to produce Al <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> separators that enhanced the safety of lithium batteries. </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="6322" page="267" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aal2239">267</jats:related-article> </jats:p>

<jats:title>Moving transistors downscale</jats:title> <jats:p> One option for extending the performance of complementary metal-oxide semiconductor (CMOS) devices based on silicon technology is to use semiconducting carbon nanotubes as the gates. Qiu <jats:italic>et al.</jats:italic> fabricated top-gated carbon nanotube field-effect transistors with a gate length of 5 nm. Thin graphene contacts helped maintain electrostatic control. A scaling trend study revealed that, compared with silicon CMOS devices, the nanotube-based devices operated much faster and at much lower supply voltage, and they approached the limit of one electron per switching operation. </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="6322" page="271" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aaj1628">271</jats:related-article> </jats:p>

<jats:title>Sea surface temperatures of the past</jats:title> <jats:p> Understanding how warm intervals affected sea level in the past is vital for projecting how human activities will affect it in the future. Hoffman <jats:italic>et al.</jats:italic> compiled estimates of sea surface temperatures during the last interglacial period, which lasted from about 129,000 to 116,000 years ago. The global mean annual values were ∼0.5°C warmer than they were 150 years ago and indistinguishable from the 1995–2014 mean. This is a sobering point, because sea levels during the last interglacial period were 6 to 9 m higher than they are now. </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="6322" page="276" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aai8464">276</jats:related-article> </jats:p>

<jats:title>Keeping roots water-tight</jats:title> <jats:p> The Casparian strip provides a waterproofing function to plant roots, protecting them against unregulated influxes of water and minerals. The integrity of the Casparian strip depends on a receptor-like kinase. Doblas <jats:italic>et al.</jats:italic> and Nakayama <jats:italic>et al.</jats:italic> now identify the peptide ligands in the core of the root (the stele) that help regulate Casparian strip formation. The receptor is expressed on the outward-facing surface of the root endodermal cells that surround the stele. When the endodermal layer is sealed by the Casparian strip, the peptide ligands cannot reach their receptors. When the endodermal layer is breached, whether by damage or during development, the peptides reach their receptors and activate signaling that encourages lignin deposition, shoring up the strips. </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="6322" page="280" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aaj1562">280</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6322" page="284" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aai9057">284</jats:related-article> </jats:p>

<jats:title>Keeping roots water-tight</jats:title> <jats:p> The Casparian strip provides a waterproofing function to plant roots, protecting them against unregulated influxes of water and minerals. The integrity of the Casparian strip depends on a receptor-like kinase. Doblas <jats:italic>et al.</jats:italic> and Nakayama <jats:italic>et al.</jats:italic> now identify the peptide ligands in the core of the root (the stele) that help regulate Casparian strip formation. The receptor is expressed on the outward-facing surface of the root endodermal cells that surround the stele. When the endodermal layer is sealed by the Casparian strip, the peptide ligands cannot reach their receptors. When the endodermal layer is breached, whether by damage or during development, the peptides reach their receptors and activate signaling that encourages lignin deposition, shoring up the strips. </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="6322" page="280" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aaj1562">280</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6322" page="284" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aai9057">284</jats:related-article> </jats:p>

<jats:title>Small peptides allow rapid responses</jats:title> <jats:p> RALFs (rapid alkalinization factors), a family of small peptides in plants, are produced in response to rapidly changing conditions. Stegmann <jats:italic>et al.</jats:italic> studied the agility and diversity built into this signaling network. Some RALFs, such as RALF23 and its relative RALF33, are activated by proteolytic cleavage. Others, such as RALF32, are not. RALF23 and RALF33 are called into play after a pathogen triggers immune responses. RALF32, on the other hand, regulates seedling growth. All three of these RALFs use the same receptor kinase, which can interact with other signaling components. Thus, plant responses can be fine-tuned by rapid release of peptides. </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="6322" page="287" related-article-type="in-this-issue" vol="355" xlink:href="10.1126/science.aal2541">287</jats:related-article> </jats:p>

<jats:p>With early life likely to have existed in a hot environment, enzymes had to cope with an inherent drop in catalytic speed caused by lowered temperature. Here we characterize the molecular mechanisms underlying thermoadaptation of enzyme catalysis in adenylate kinase using ancestral sequence reconstruction spanning 3 billion years of evolution. We show that evolution solved the enzyme’s key kinetic obstacle—how to maintain catalytic speed on a cooler Earth—by exploiting transition-state heat capacity. Tracing the evolution of enzyme activity and stability from the hot-start toward modern hyperthermophilic, mesophilic, and psychrophilic organisms illustrates active pressure versus passive drift in evolution on a molecular level, refutes the debated activity/stability trade-off, and suggests that the catalytic speed of adenylate kinase is an evolutionary driver for organismal fitness.</jats:p>