Catálogo de publicaciones - revistas

<jats:p>A bimetallic catalyst selects different ring-opening sites, depending on the chiral configuration of the substrate.</jats:p>

<jats:title>Degrees of Darkness</jats:title> <jats:p> Fruit flies in Africa have a tendency to be darker, the higher the altitude at which they live, because melanization offers a selective advantage. The dark pigmentation seen in some populations of Ugandan <jats:italic>Drosophila melanogaster</jats:italic> is owing to a lack of expression of the ebony gene, and expression results in yellow cuticle. <jats:bold> Rebeiz <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="1663" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178357">1663</jats:related-article> ; see the News story by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5960" page="1612" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.2009.326.5960.326_1612">Pennisi</jats:related-article> </jats:bold> ) show that mutations in <jats:italic>cis</jats:italic> regulatory elements, rather than in the coding region, are responsible for the dark color. A series of five mutations in a modular enhancer element influences the level of <jats:italic>ebony</jats:italic> expression: Three mutations already existed in fly populations with light cuticle color and a further two, more recently acquired dark-specific substitutions, together have created an allele of large effect, which has been swept to high frequency in this population of flies. </jats:p>

<jats:title>Bio-Diodes</jats:title> <jats:p> Inward rectifier potassium channels conduct K <jats:sup>+</jats:sup> ions into the cell at internal negative membrane voltages, but at internal positive membrane voltages they are blocked by intracellular multivalent ions. These channels control the resting membrane voltage and are required for the healthy function of many electrically excitable cells. Mutations can result in transient paralysis causing, for example, heart problems. <jats:bold> Tao <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="1668" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1180310">1668</jats:related-article> ) now report a 3.1 angstrom resolution structure of the inward rectifier, Kir2.2 from chicken, which has a similar structure to the human equivalent. The combination of observations of conductive and inhibitory ion binding sites with electrophysiological data finally explains the mechanism of action of these long-studied channels and reveals how they maintain their low sensitivity to toxins, as well as provides a basis for the design of therapeutic drugs. </jats:p>

<jats:title>Watery Worlds</jats:title> <jats:p> Water vapor has been detected in the protoplanetary disks of a variety of stars. Explaining its origin is important because it bears on our understanding of planet formation. <jats:bold>Bethell and Bergin</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1675" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176879">1675</jats:related-article> ) propose that this water originates in photochemistry occurring in the upper layers of the disks. In these regions, the rate at which water is produced exceeds the rate at which water is destroyed by ultraviolet radiation. Water forming in the upper layers of the disks then shields water vapor within the disks' interiors, allowing that vapor to interact with planet-forming materials and possibly be incorporated into young planets. </jats:p>

<jats:title>Home Is Where the Hearth Is</jats:title> <jats:p> One aspect of human intelligence is the ability to organize our living and working spaces. It was generally thought that this capability arose with modern humans in the past 100,000 years or so. However, <jats:bold> Alperson-Afil <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="1677" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1180695">1677</jats:related-article> ) found evidence of domestic organization 800,000 years ago at a Pleistocene hominin campsite in the Jordan Valley. Around patches of burnt debris, the remains of a wide range of plant and animal foodstuffs were found, including fruits and seeds, as well as remnants of turtles, elephants, and small rodents. Specific types of stone tools appear to have been made around the hearths, where there was also evidence of nut roasting and consumption of crabs and fish. In a more distant area there were signs of intensive flint knapping and food chopping. </jats:p>

<jats:title>Seed for Food</jats:title> <jats:p> The seeds of grain-producing plants are more difficult to harvest than nuts or fruits as food. It has been unclear when early humans began to rely extensively on grains, but <jats:bold>Mercader</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1680" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1173966">1680</jats:related-article> ) has discovered films of starch residues on stone tools at a cave site in Mozambique dating to about 100,000 years ago. The residues are consistent with starch grains from wild sorghum and indicate that early humans relied on cereals much earlier than previously thought. The Mozambican example of sorghum exploitation thus represents the longest known tradition of cereal use in the world. </jats:p>

<jats:title>More Is Different, Few Is Exotic</jats:title> <jats:p> As powerful as theoretical physics can be, when it comes to describing the dynamics of several interacting particles, it stumbles at three. This few-body physics is interesting in many contexts, particularly interactions within the nucleus and between atoms and molecules. Although predicted 40 years ago for the special case of resonant interaction, which occurs at the edge of where two-particle bound states start to form, Efimov trimers were only recently observed in ultracold Bose gases. More work followed, revealing evidence of multiple trimer, and even tetramer, states. Now, <jats:bold> Pollack <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="1683" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1182840">1683</jats:related-article> , published online 19 November; see the Perspective by <jats:bold>Modugno</jats:bold> ) observe as many as 11 features near a lithium resonance that can be directly related to different few-body processes. The positions of the features with respect to each other are in excellent agreement with the theoretical prediction, although some deviations, attributed to short-range interactions, present a challenge for a future, more detailed theory. </jats:p>

<jats:title>Moving Boundaries</jats:title> <jats:p> Classical models of fine-grained metals view grain boundaries as static objects, but this view has been challenged by recent experimental observations. Drawing on techniques used by the fracture mechanics community, <jats:bold> Rupert <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="1686" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178226">1686</jats:related-article> ) present experiments on freestanding aluminum films that show specific geometries cause either stress or strain concentrations on deformation. Confirming recent simulations, shear stresses were found to be a key driver of grain boundary motion. </jats:p>

<jats:title>A Glimpse of Wet Carbonic Acid</jats:title> <jats:p> Both carbon dioxide and bicarbonate play extraordinarily widespread roles in biochemical and geochemical reactions. It is surprising therefore that carbonic acid, the intermediate in the water-coupled interconversion of these two compounds, has never been directly characterized in aqueous solution. <jats:bold> Adamczyk <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="1690" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1180060">1690</jats:related-article> , published online 12 November) have succeeded in glimpsing the elusive acid by inducing an aqueous photoacid (a compound rendered transiently more acidic upon light absorption) to react with dissolved bicarbonate. Using infrared spectroscopy, they show that the carbonic acid product persists for nanoseconds. Analysis of its formation kinetics affords a direct p <jats:italic> K <jats:sub>a</jats:sub> </jats:italic> value of 3.5, substantially lower than the effective value derived from observations of the net bicarbonate/carbon dioxide equilibrium. </jats:p>

<jats:title>Growing on You</jats:title> <jats:p> The human gut and skin harbor diverse microbial communities that are known to vary strikingly among individuals. Here, <jats:bold> Costello <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="1694" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177486">1694</jats:related-article> , published online 5 November) analyzed microbial diversity among several distinct body habitats (including the gut, mouth, inside the ears and nose, and skin) of the same person at different times. They found that body habitat had more influence on microbial community composition than temporal differences and variation among people. Some skin locations, such as the index finger, back of the knee, and sole of the foot, on occasion harbored higher microbial diversity than the gut or oral cavity. </jats:p>