Catálogo de publicaciones - revistas

<jats:title>Lensing approach to the Hubble constant</jats:title> <jats:p> The current expansion rate of the Universe is parametrized by the Hubble constant, <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> . Different methods of measuring <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> produce results that disagree with each other, which could be a sign of new physics or of systematic errors in the methods. Jee <jats:italic>et al.</jats:italic> have analyzed two gravitational lensing systems to determine their distances (see the Perspective by Davis). They use these as benchmarks for a measurement of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> . The precision is not sufficient to resolve the debate but does bypass some of the systematic uncertainties. Observations of more lensing systems will be required to narrow down the value of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> . </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="6458" page="1134" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aat7371">1134</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6458" page="1076" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aay1331">1076</jats:related-article> </jats:p>

<jats:title>Catching a copper nitrene</jats:title> <jats:p> Nitrogen typically forms three bonds in its stable compounds. If only one bond is available, the resultant electron-deficient nitrene can react rapidly with hydrocarbons to fill out its valence shell. Metal-stabilized nitrenes have been widely implicated in carbon-nitrogen bond-forming reactions, but the putative intermediates have rarely been synthesized directly. Carsch <jats:italic>et al.</jats:italic> now report preparation of a copper nitrene complex from an azide precursor. X-ray absorption and diffraction studies support a triplet electronic state that does not engage in multiple bonding with the copper center. </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="6458" page="1138" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax4423">1138</jats:related-article> </jats:p>

<jats:title>Assembly pathway for mitoribosome</jats:title> <jats:p> The biogenesis of ribosomes is a multistep process facilitated by assembly factors. Saurer <jats:italic>et al.</jats:italic> provided structural information on the maturation process of the mitochondrial ribosome, or mitoribosome, in the parasitic protozoan <jats:italic>Trypanosoma brucei</jats:italic> (see the Perspective by Karbstein). Cells evolved a dedicated machinery for maturation of the small subunit of the mitoribosome, including the formation of three distinct and well-structured assembly intermediates. Comparison of intermediates and the mature mitoribosome reveals how assembly factors and ribosomal proteins work together to fold and stabilize ribosomal RNA. </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="6458" page="1144" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aaw5570">1144</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6458" page="1077" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aay7771">1077</jats:related-article> </jats:p>

<jats:title>Flipping a lipid</jats:title> <jats:p> The membranes of eukaryotic cells have different lipid compositions in their inner and outer leaflets. Enzymes known as flippases and floppases use the energy from adenosine triphosphate (ATP) hydrolysis to translocate lipids against a concentration gradient from the outer to inner or inner to outer leaflets, respectively. Flippases are P4-type ATPases that are important in processes such as membrane trafficking, signaling, and apoptosis. Hiraizumi <jats:italic>et al.</jats:italic> report the cryo–electron microscopy structure of six intermediates of the human flippase ATP8A1 bound to the partner protein it requires for function, CDC50. ATP binding and autophosphorylation of ATP8A1 drive a cycle of conformations in which lipids bind differently, powering translocation. </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="6458" page="1149" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aay3353">1149</jats:related-article> </jats:p>

<jats:title>Tweezing cold molecules</jats:title> <jats:p> Arrays of optical tweezers have been used to trap atoms, but trapping and laser-cooling molecules in this setting is tricky. Such an approach would, however, be generalizable to many molecular species. Anderegg <jats:italic>et al.</jats:italic> created an optical tweezer array of calcium monofluoride molecules, which were laser cooled to their ground state (see the Perspective by Kotochigova). By distinguishing between single and multiple molecules in the tweezers, the researchers were able to observe molecular collisions. Boasting exquisite control over individual molecules, the optical tweezer array platform holds much promise for extending the applications of ultracold molecules. </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="6458" page="1156" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax1265">1156</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6458" page="1079" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aay3989">1079</jats:related-article> </jats:p>

<jats:title>Stabilizing rougher nanoparticles</jats:title> <jats:p> For many reactions catalyzed by metal nanoparticles, the more exposed metal atoms on high-index faces can be more active than metal atoms on smooth, low-index faces. Surface ligands can be used to stabilize high-index surfaces, but they can also be hard to remove. Huang <jats:italic>et al.</jats:italic> report the solid-state synthesis of metal nanoparticles such as platinum and chromium that can form tetrahexahedral nanoparticles with high-index faces. Metals such as bismuth and lead were alloyed with the transition metals at high temperatures and then evaporatively dealloyed during a quench to room temperature. </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="6458" page="1159" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aax5843">1159</jats:related-article> </jats:p>

<jats:title>How to define a light path topologically</jats:title> <jats:p> Controlling the flow of light in a robust and flexible manner will be critical for the development of the next generation of photonic integrated devices. Exploiting the inherent protection afforded by topology, topological photonics provides a solution for the robust propagation of light. Devices so far, however, have been fixed in their functionality. Zhao <jats:italic>et al.</jats:italic> created light paths that can be arbitrarily switched on and off by optical illumination. Propagation can be topologically steered along desired pathways by manipulating regions of gain and loss within the photonic structure through optical excitation. This approach provides a route to controlling topologically protected light paths in an integrated optical platform. </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="6458" page="1163" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aay1064">1163</jats:related-article> </jats:p>

<jats:title>Active sites that move together</jats:title> <jats:p> Enzymes often form dimers or higher-order oligomers, even when each active site is isolated and the reactions are simple. But the effect of a neighbor can be profound. Mehrabi <jats:italic>et al.</jats:italic> used a photolabile compound to initiate a reaction in the enzyme fluoroacetate dehalogenase, which they could follow by time-resolved serial synchrotron crystallography. Snapshots of the reaction revealed coupled allosteric motions between the two active sites of the dimeric enzyme. Each active site traded the ability to bind substrate and catalyze the reaction, such that only one was engaged at a time. This behavior is common in enzymes but is rarely visualized and still poorly understood. </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="6458" page="1167" related-article-type="in-this-issue" vol="365" xlink:href="10.1126/science.aaw9904">1167</jats:related-article> </jats:p>