Catálogo de publicaciones - revistas

<jats:title>Evidence for ice ages on Mars</jats:title> <jats:p> Models predict that Mars should have undergone ice ages in the past, but evidence has been scant. Smith <jats:italic>et al.</jats:italic> used radar measurements from NASA's Mars Reconnaissance Orbiter to probe the planet's polar ice caps. Clear layers within the ice allowed them to calculate how much ice was deposited at different times. The results provide evidence for a recent ice age on Mars. Understanding the martian climate will help determine when the planet was habitable in the past, and how that changed, and may inform studies of climate change on Earth. </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="6289" page="1075" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aad6968">1075</jats:related-article> </jats:p>

<jats:title>A radical route to ophiobolin rings</jats:title> <jats:p> Chemical ring-closing cascades resemble molecular yoga. One reactive site on a linear precursor can pull the whole molecule into a remarkably complex polycyclic arrangement. Cyclase enzymes rely on substantial internal scaffolding to guide this process during the biosynthesis of the ophiobolin sesterterpene frameworks, which comprise two pentagons sharing edges with an octagon. Brill <jats:italic>et al.</jats:italic> now show that the same motif is accessible abiotically by tweaking the cascade mechanism to rely on neutral radical intermediates in place of the positively charged activated sites in the biosynthetic pathways. </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="6289" page="1078" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf6742">1078</jats:related-article> </jats:p>

<jats:title>Precise control from a metal-free catalyst</jats:title> <jats:p> Polymerization can be a rather dangerous free for all, with molecules joining randomly in chains at a chaotic pace. One of modern chemistry's great accomplishments has been the development of methods to assemble polymers in steady, orderly steps. However, order comes at a price, and often it's the need for metal catalysts that are hard to remove from the plastic product. Theriot <jats:italic>et al.</jats:italic> used theory to guide the design of a metal-free light-activated catalyst that offers precise control in atom transfer radical polymerization, alleviating concerns about residual metal contamination (see the Perspective by Shanmugam and Boyer). </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="6289" page="1082" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf3935">1082</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6289" page="1053" related-article-type="in-this-issue" vol="352" xlink:href="10.1126/science.aaf7465">1053</jats:related-article> </jats:p>