Catálogo de publicaciones - revistas

<jats:p>A molecule with a trefoil knot topology can form spontaneously through noncovalent interactions, avoiding deliberate anchoring and assembly steps.</jats:p>

<jats:p>A single hydrogen molecule can be used to drive the tip motion of a scanning tunneling microscope.</jats:p>

<jats:p>A simple diagnostic circumvents the need for measuring cloud properties, helping to improve climate sensitivity estimates.</jats:p>

<jats:p>Mammalian methylomes reveal how DNA methylation is influenced by the underlying nucleotide sequence.</jats:p>

<jats:title>Double-Edged Iron</jats:title> <jats:p> Hepcidin is a small peptide hormone discovered by three groups investigating iron-regulated liver genes and antimicrobial peptides. This new hormone turned out not only to regulate iron but also to have homology with peptides required for innate immune responses. <jats:bold>Drakesmith and Prentice</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="768" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1224577">768</jats:related-article> ) review the importance of hepcidin during infection, explaining how it is involved in withholding iron from microbial pathogens to curtail replication and how intracellular bacteria are able to thwart this host response. Recent work highlights the potential hazards of iron-supplementation in infection, particularly in malaria, whereby an overload of iron, meant to treat malaria-induced anemia, may negate the protective effects of hepcidin. </jats:p>

<jats:title>Not Single After All</jats:title> <jats:p> Planetary nebulae form toward the end of the lives of sunlike stars. They appear after the star has shed its outer layers, and radiation from what is left of it ionizes the surrounding medium. Using the Very Large Telescope in Chile, <jats:bold> Boffin <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="773" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1225386">773</jats:related-article> ) obtained spectra of the star at the center of Fleming 1, a point-symmetric planetary nebula with rotating bipolar jets. It has long been assumed that jets like these arose from an interacting binary system. Indeed, the data reveal that the central star in Fleming 1 has a companion in a very close orbit. </jats:p>

<jats:title>Thermally Transforming Thin Films</jats:title> <jats:p> Nanoscale features can be created by the phase separation that occurs in block copolymers that join together polymer segments with different wetting properties. For applications such as lithography, it is useful to generate small features and to orient them through simple processing steps. Top-layer coatings should be able to help drive alignment, but it is difficult to coat a layer that also has strong enough interactions to influence assembly. <jats:bold> Bates <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="775" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1226046">775</jats:related-article> ) developed a water-soluble polymer that can top-coat lamellaforming block copolymers and that transforms during thermal annealing into a neutral wetting layer that helps drive the formation of vertically oriented lamellae. </jats:p>

<jats:title>Putting Noise to Work</jats:title> <jats:p> Extracting energy from a noisy system (one that moves randomly) is possible if a mechanical system can induce periodicity on its motion, a phenomenon called stochastic resonance. <jats:bold> Lotze <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="779" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227621">779</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6108" page="754" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230530">Bockrath</jats:related-article> </jats:bold> ) created stochastic resonances between the cantilever attached to a scanning tunneling microscope tip and a hydrogen molecule adsorbed on a copper surface at cryogenic temperatures. The tunneling electrons at a particular bias voltage could excite the hydrogen molecules and couple their random motion to that of the cantilever, driving periodic oscillations. </jats:p>

<jats:title>An Organic Knot</jats:title> <jats:p> When people tie knots, they grasp both ends of a strand and loop them around each other. The task is rather more difficult at the molecular level, when there is no top-down organizing framework, and the strand needs to be coaxed into looping around itself. Recently, chemists have taken advantage of the tight geometrical restrictions of metal-ligand coordination to produce knot morphologies. <jats:bold> Ponnuswamy <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="783" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1227032">783</jats:related-article> ; see the Perspective by <jats:italic> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6108" page="752" related-article-type="in-this-issue" vol="338" xlink:href="10.1126/science.1230319">Siegel</jats:related-article> </jats:italic> ) now demonstrate the spontaneous assembly of a trefoil knot from organic fragments without assistance from metal centers. The topology appears to be driven by hydrophobic interactions among aromatic segments that minimize exposure to surrounding water through their overlap. </jats:p>