Catálogo de publicaciones - revistas

<jats:title>Tumor angiogenesis gets nervous</jats:title> <jats:p> The microenvironment of solid tumors hosts many intercellular conversations that can either enhance or inhibit tumor growth. Interestingly, the tumor cells need not be direct participants in these conversations. Zahalka <jats:italic>et al.</jats:italic> studied genetically manipulated mouse models and found that adrenergic signals from autonomic nerves in the prostate cancer microenvironment fueled tumor growth by altering the metabolism of blood vessel endothelial cells (see the Perspective by Hayakawa and Wang). These nerve-derived signals suppressed oxidative phosphorylation in the endothelial cells, activating an angiogenic switch that facilitated rapid tumor growth. This cross-talk between nerves and endothelial cells could potentially offer a target for cancer therapies. </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="6361" page="321" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aah5072">321</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6361" page="305" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aaq0365">305</jats:related-article> </jats:p>

<jats:title>A MOF sets the stage to make amines</jats:title> <jats:p> Reductive amination is a common method that chemists use to make carbon-nitrogen bonds. The reaction, which often requires precious metal catalysts, couples ammonia or other amines with carbonyl compounds and then with hydrogen. Jagadeesh <jats:italic>et al.</jats:italic> report a class of nonprecious cobalt nanoparticles that catalyze this reaction across a very broad range of substrates, including complex molecules of pharmaceutical interest (see the Perspective by Chen and Xu). The cobalt was first embedded in a metal-organic framework (MOF), which, upon heating, transformed into a graphitic shell. The catalyst could be conveniently separated from products and recycled up to six times. </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="6361" page="326" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aan6245">326</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6361" page="304" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aap8004">304</jats:related-article> </jats:p>

<jats:title>Expanding the world of 2D materials</jats:title> <jats:p> Two-dimensional (2D) materials have a wide variety of potential applications in the electronics industry. However, certain compositions of 2D materials are difficult to obtain owing to the challenges in exfoliating thin sheets from bulk crystals. Zavabeti <jats:italic>et al.</jats:italic> exploited liquid metals to synthesize 2D Ga <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> , HfO <jats:sub>2</jats:sub> , Gd <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> , and Al <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> . The 2D sheets appear as a surface layer in gallium-based liquid metals after the Hf, Gd, or Al is dissolved into the bulk alloy. The 2D oxide that appears on the surface is the oxide with the lowest energy, suggesting that it should be possible to make other 2D oxides by using the same process. </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="6361" page="332" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aao4249">332</jats:related-article> </jats:p>

<jats:title>The quantum mechanics of a hydrogen hop</jats:title> <jats:p> Hydrogen migration between adjacent carbons is widespread in the reaction mechanisms of organic chemistry. DeVine <jats:italic>et al.</jats:italic> used photoelectron spectroscopy to discern the quantum mechanical underpinnings of this 1,2 shift in a prototypical case: conversion of vinylidene (H <jats:sub>2</jats:sub> CC) to acetylene (HCCH). The technique probed specific states of vinylidene by ejecting electrons with varying energies from a negative ion precursor. Experimental data and accompanying theoretical simulations pinpointed a vibrational rocking mode that facilitated the migration. Replacement of hydrogen with its heavier deuterium isotope disrupted this pathway. </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="6361" page="336" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aao1905">336</jats:related-article> </jats:p>

<jats:title>Acid fuels the motion of a threaded ring</jats:title> <jats:p> A central goal in the construction of molecular-scale machines is the efficient achievement of one-way motion. Erbas-Cakmak <jats:italic>et al.</jats:italic> developed a class of machines that transmit pH changes into the two-stage guided motion of molecular rings threaded on a linear or cyclic axle. The design relies on temporary blocking groups and landing sites along the axle that toggle between active and passive states in response to acid or base. Trichloroacetic acid initiates the first stage of motion until it is decomposed by base in the solution, spurring the second phase. </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="6361" page="340" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aao1377">340</jats:related-article> </jats:p>

<jats:title>Harnessing chaos for enhanced coupling</jats:title> <jats:p> Functional optical devices typically require the coupling of light between different components. However, conservation of momentum usually limits the bandwidth of the coupling, often to a near-resonant effect. Jiang <jats:italic>et al.</jats:italic> show that slightly deformed microring resonators might be able to relax those restrictions. The chaotic scattering of the light within the deformed structure can transform optical modes of different angular momenta within a few picoseconds, providing a promising route to develop advanced nanophotonic circuits and devices. </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="6361" page="344" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aao0763">344</jats:related-article> </jats:p>

<jats:title>Tuning porosity with electric fields</jats:title> <jats:p> Many metal-organic framework (MOF) compounds exhibit soft porosity—i.e., their lattices can undergo considerable deformation. Knebel <jats:italic>et al.</jats:italic> formed membrane layers of the MOF ZIF-8 and found that it was converted into a polar polymorph with a stiffer lattice in response to an applied electric field (see the Perspective by Gascon). This change reduced gas transport but, for certain gas mixtures such as propane and propene, also improved their separation factor. </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="6361" page="347" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aal2456">347</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6361" page="303" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aap8267">303</jats:related-article> </jats:p>

<jats:title>Watching growth, step by step</jats:title> <jats:p> Polymers can grow through the stepwise addition of monomers to an active end site. One might think that this would happen in a continuous linear process. With a focus on ring-opening metathesis polymerization of norbornene catalyzed by a Grubbs' catalyst, Liu <jats:italic>et al.</jats:italic> describe the growth of a single polymer chain. By attaching one end of a growing polymer to a bead exerting a constant force on it, they measured the extension occurring during the growth of the polymer. Oddly, the extension of the growing polymer did not increase continuously. Instead, it exhibited consecutive wait-and-jump steps, owing to conformational entanglements formed by newly incorporated monomers. </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="6361" page="352" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aan6837">352</jats:related-article> </jats:p>

<jats:title>Tracking collisions in just one beam</jats:title> <jats:p> Much of what we know about how quantum mechanics dictates chemical dynamics comes from half a century of studying controlled collisions between crossed pairs of molecular beams. Perreault <jats:italic>et al.</jats:italic> now show that even finer detail emerges in a study of hydrogen-deuterium (HD) collisions with D <jats:sub>2</jats:sub> in a single beam. The experimental setup lowers the collision temperature to ∼1 K, allowing precise control over the rotational energy and relative alignment of the colliding partners. Scattering events in which HD loses rotational energy occurred three times as readily if the HD was aligned perpendicular rather than parallel to the beam-propagation axis. </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="6361" page="356" related-article-type="in-this-issue" vol="358" xlink:href="10.1126/science.aao3116">356</jats:related-article> </jats:p>