Catálogo de publicaciones - revistas

<jats:title>Nanoparticle synthesis gets a shock</jats:title> <jats:p> Nanoparticles are useful in a wide range of applications such as catalysis, imaging, and energy storage. Yao <jats:italic>et al.</jats:italic> developed a method for making nanoparticles with up to eight different elements (see the Perspective by Skrabalak). The method relies on shocking metal salt-covered carbon nanofibers, followed by rapid quenching. The “carbothermal shock synthesis” can be tuned to select for nanoparticle size as well. The authors successfully created PtPdRhRuCe nanoparticles to catalyze ammonia oxidation. </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="6383" page="1489" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aan5412">1489</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6383" page="1467" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aat1471">1467</jats:related-article> </jats:p>

<jats:title>Now you see it, now you don't</jats:title> <jats:p> Thermal vision cameras detect differences in temperature by sensing infrared wavelengths. If a coating could be developed that showed dynamic tuning of the effective temperature, it might be possible to hide objects from infrared sensing. Xu <jats:italic>et al.</jats:italic> started with a basic Bragg reflector made up of multiple layers of alternating materials with varying refractive index. The authors designed structures that were wavy to begin with so that they could be flattened out by electrical activation. This changed the infrared reflectivity and, thus, the effective temperature of the object observed in its infrared profile. </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="6383" page="1495" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar5191">1495</jats:related-article> </jats:p>

<jats:title>Attacking olefins with chiral acids</jats:title> <jats:p> A little acid can accelerate a wide range of chemical reactions. The advent of chiral phosphoric acid derivatives has been useful for biasing these reactions toward just one of two mirror-image products. For the most part, though, these chiral catalysts have interacted with basic sites such as carbonyl groups. Tsuji <jats:italic>et al.</jats:italic> now extend asymmetric acid catalysis to simple carbon-carbon double bonds. Their custom imidodiphosphate forms a pocket that orients olefins to achieve mainly intramolecular alkoxylation on just one face after protonation. </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="6383" page="1501" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aaq0445">1501</jats:related-article> </jats:p>

<jats:title>Shaking the small from the even smaller</jats:title> <jats:p> Gently oscillate a can of mixed nuts, and eventually the larger Brazil nuts will rise to the top. Skaug <jats:italic>et al.</jats:italic> created three-dimensional patterned surfaces to which they applied electric fields. Combined with gentle shaking to induce a rocking Brownian motion, they were able to guide particles smaller than 100 nm along complicated paths. They could also quickly separate particles with different sizes and shapes. </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="6383" page="1505" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aal3271">1505</jats:related-article> </jats:p>

<jats:title>Active camouflage from a polymer</jats:title> <jats:p> Human skin is soft and compliant, but it can quickly become stiff when deformed to prevent injury. Chameleon skin can change color when the animal goes from a relaxed to an excited state. Although these properties can be captured individually in synthetic materials, the combination of different dynamic responses can be hard to control. Vatankhah-Varnosfaderani <jats:italic>et al.</jats:italic> created triblock copolymers of the ABA variety, where the A blocks have a linear structure and the B blocks are like bottlebrushes. When strained, these polymers stiffened like human skin and changed color, thus giving the materials a range of adaptive properties. </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="6383" page="1509" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar5308">1509</jats:related-article> </jats:p>

<jats:title>Healing away the dendrites</jats:title> <jats:p> The formation of lithium dendrites during charge-discharge cycles limits the development of lithium metal batteries, because the dendrites can cause electrical shorting of the cells. A number of tricks have been used to try to prevent dendrite formation. Li <jats:italic>et al.</jats:italic> took the opposite approach (see the Perspective by Mukhopadhyay and Jangid). They operated their cells at higher current densities, under which one would expect dendrites to form owing to the higher nucleation rates. However, under these conditions, the dendrites that started to form heated up and annealed, leading to their disappearance. </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="6383" page="1513" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aap8787">1513</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6383" page="1463" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aat2452">1463</jats:related-article> </jats:p>

<jats:title>Resistance is not futile</jats:title> <jats:p> The fungal disease chytridiomycosis has wreaked havoc on amphibians worldwide. The disease is caused by the organism <jats:italic>Batrachochytrium dendrobatidis</jats:italic> and was first identified in the late 1990s. Voyles <jats:italic>et al.</jats:italic> revisited protected areas in Panama where catastrophic amphibian losses were recorded a decade ago (see the Perspective by Collins). Although disease theory predicts that epidemics should result in reduced pathogenicity, they found no evidence for such a reduction. Despite this, the amphibian community is displaying signs of recovery—including some species presumed extinct after the outbreak. Increased host resistance may be responsible for this recovery. </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="6383" page="1517" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao4806">1517</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6383" page="1458" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aat1996">1458</jats:related-article> </jats:p>

<jats:title>Iron's grip on malaria</jats:title> <jats:p> Malaria parasites have coevolved with their human and mammalian hosts. These <jats:italic>Plasmodium</jats:italic> species invade the iron-rich environment of red blood cells. Zhang <jats:italic>et al.</jats:italic> found that the iron transporter ferroportin persists on the surface of mature mammalian red blood cells. Red blood cells are at risk of oxidative damage if their hemoglobin releases its iron; ferroportin is thus important to expel this iron. The authors also found that the transporter can deprive malaria parasites of the iron they need for proliferation. The Q248H mutation in the human ferroportin gene enhances ferroportin expression during development and seems to provide protection against malaria. This effect may explain the enrichment of the Q248H mutation among African populations. </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="6383" page="1520" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aal2022">1520</jats:related-article> </jats:p>

<jats:title>Rebalancing mechanisms during sleep</jats:title> <jats:p> Synapses are often strengthened during wake periods and thus need to be homeostatically readjusted during sleep. During slow-wave sleep, synaptic depression is dominant. Sharp wave and ripple events are transient high-frequency field oscillations that occur spontaneously during slow-wave sleep in the brain. Norimoto <jats:italic>et al.</jats:italic> found that these events induced long-term depression of hippocampal synapses and may thus help to refine recently acquired memories (see the Perspective by Draguhn). </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="6383" page="1524" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao0702">1524</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6383" page="1461" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aat1493">1461</jats:related-article> </jats:p>

<jats:title>How a pathogen holds on to its host</jats:title> <jats:p> <jats:italic>Staphylococcus epidermidis</jats:italic> and <jats:italic>Staphylococcus aureus</jats:italic> are pathogens that can form biofilms on implants and medical devices. Central to biofilm formation is a very tight interaction between microbial surface proteins called adhesins and components of the extracellular matrix of the host. Milles <jats:italic>et al.</jats:italic> used atomic force microscopy-based single-molecule force spectroscopy combined with steered molecular dynamics to explore how the bond between staphylococcal adhesin SdrG and its target fibrinogen peptide can withstand forces greater than 2 nanonewtons (see the Perspective by Herman-Bausier and Dufrêne). The peptide is confined in a coiled geometry in a deep and rigid pocket through hydrogen bonds between SdrG and the peptide backbone. If pulled, the load is distributed over all hydrogen bonds so that all bonds must be broken at once to break the interaction. </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="6383" page="1527" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar2094">1527</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6383" page="1464" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aat3764">1464</jats:related-article> </jats:p>