Catálogo de publicaciones - revistas

<jats:title>Unrestricted Travel in Solar Cells</jats:title> <jats:p> In the past 2 years, organolead halide perovskites have emerged as a promising class of light-harvesting media in experimental solar cells, but the physical basis for their efficiency has been unclear (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="317" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1245473">Hodes</jats:related-article> </jats:bold> ). Two studies now show, using a variety of time-resolved absorption and emission spectroscopic techniques, that these materials manifest relatively long diffusion paths for charge carriers energized by light absorption. <jats:bold> Xing <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="344" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243167">344</jats:related-article> ) independently assessed (negative) electron and (positive) hole diffusion lengths and found them well-matched to one another to the ~100-nanometer optical absorption depth. <jats:bold> Stranks <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="341" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243982">341</jats:related-article> ) uncovered a 10-fold greater diffusion length in a chloride-doped material, which correlates with the material's particularly efficient overall performance. Both studies highlight effective carrier diffusion as a fruitful parameter for further optimization. </jats:p>

<jats:title>Unrestricted Travel in Solar Cells</jats:title> <jats:p> In the past 2 years, organolead halide perovskites have emerged as a promising class of light-harvesting media in experimental solar cells, but the physical basis for their efficiency has been unclear (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="317" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1245473">Hodes</jats:related-article> </jats:bold> ). Two studies now show, using a variety of time-resolved absorption and emission spectroscopic techniques, that these materials manifest relatively long diffusion paths for charge carriers energized by light absorption. <jats:bold> Xing <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="344" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243167">344</jats:related-article> ) independently assessed (negative) electron and (positive) hole diffusion lengths and found them well-matched to one another to the ~100-nanometer optical absorption depth. <jats:bold> Stranks <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="341" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243982">341</jats:related-article> ) uncovered a 10-fold greater diffusion length in a chloride-doped material, which correlates with the material's particularly efficient overall performance. Both studies highlight effective carrier diffusion as a fruitful parameter for further optimization. </jats:p>

<jats:title>Return of the Steroid</jats:title> <jats:p> Trace levels of organic contaminants enter aquatic ecosystems from a variety of sources, including runoff of from agricultural lands. When these compounds and their metabolites break down, it is generally assumed that they become inert and pose less ecological risk. <jats:bold> Qu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="347" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243192">347</jats:related-article> , published online 26 September) tracked the sunlight-mediated transformation of metabolites of trenbolone acetate (TBA)—a common growth-promoting steroid given to beef cattle—across a number of conditions in the laboratory and in the field. When the degradation products were exposed to dark conditions following photodegradation, they surprisingly reverted back to TBA metabolites, including analog steroidal compounds similar to TBA with unknown biological effects. </jats:p>

<jats:title>Catching a Carbene &gt;&gt;</jats:title> <jats:p> Divalent carbon fragments, or carbenes, vary widely in their stability, depending on their substituents. Some, such as <jats:italic>N</jats:italic> -heterocyclic carbenes, are independently isolatable. Others can be isolated in coordination complexes with metals. <jats:bold> Kornecki <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="351" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243200">351</jats:related-article> , published online 12 September) synthesized a carbene coordinated to a rhodium dimer representative of an elusive class of short-lived intermediates long postulated to underlie a series of cyclopropanation and C-H insertion reactions. </jats:p>

<jats:title>No Methane to Be Found</jats:title> <jats:p> On Earth, atmospheric methane is mostly produced biologically. Atmospheric methane has also been detected on Mars, but these reports have been controversial. Based on data from the Sample Analysis at Mars instrument suite on the Curiosity rover, which arrived at the surface of Mars in August 2012, <jats:bold> Webster <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="355" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1242902">355</jats:related-article> , published online 19 September) report no methane, with an upper limit of only 1.3 parts per billion by volume, about 6 times lower than previous measurements. </jats:p>

<jats:title>Changing the Code</jats:title> <jats:p> Easily and efficiently expanding the genetic code could provide tools to genome engineers with broad applications in medicine, energy, agriculture, and environmental safety. <jats:bold> Lajoie <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="357" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1241459">357</jats:related-article> ) replaced all known UAG stop codons with synonymous UAA stop codons in <jats:italic>Escherichia coli</jats:italic> MG1655, as well as release factor 1 (RF1; terminates translation at UAG), thereby eliminating natural UAG translation function without impairing fitness. This made it possible to reassign UAG as a dedicated codon to genetically encode nonstandard amino acids while avoiding deleterious incorporation at native UAG positions. The engineered <jats:italic>E. coli</jats:italic> incorporated nonstandard amino acids into its proteins and showed enhanced resistance to bacteriophage T7. In a second paper, <jats:bold> Lajoie <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="361" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1241460">361</jats:related-article> ) demonstrated the recoding of 13 codons in 42 highly expressed essential genes in <jats:italic>E. coli.</jats:italic> Codon usage was malleable, but synonymous codons occasionally were nonequivalent in unpredictable ways. </jats:p>

<jats:title>Changing the Code</jats:title> <jats:p> Easily and efficiently expanding the genetic code could provide tools to genome engineers with broad applications in medicine, energy, agriculture, and environmental safety. <jats:bold> Lajoie <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="357" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1241459">357</jats:related-article> ) replaced all known UAG stop codons with synonymous UAA stop codons in <jats:italic>Escherichia coli</jats:italic> MG1655, as well as release factor 1 (RF1; terminates translation at UAG), thereby eliminating natural UAG translation function without impairing fitness. This made it possible to reassign UAG as a dedicated codon to genetically encode nonstandard amino acids while avoiding deleterious incorporation at native UAG positions. The engineered <jats:italic>E. coli</jats:italic> incorporated nonstandard amino acids into its proteins and showed enhanced resistance to bacteriophage T7. In a second paper, <jats:bold> Lajoie <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="361" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1241460">361</jats:related-article> ) demonstrated the recoding of 13 codons in 42 highly expressed essential genes in <jats:italic>E. coli.</jats:italic> Codon usage was malleable, but synonymous codons occasionally were nonequivalent in unpredictable ways. </jats:p>

<jats:title>Invade and Adapt</jats:title> <jats:p> The mechanisms by which plant and animal species spread into new habitats have become an increasing focus of ecological research, particularly in the context of climate change and species invasions. <jats:bold>Colautti and Barrett</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="364" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1242121">364</jats:related-article> ) examined the ecological consequence of local adaptation evolving rapidly along a 1000-kilometer climatic gradient in purple loosestrife <jats:italic>(Lythrum salicaria)</jats:italic> , one of the most notorious invasive plant species in North America. These invasive populations have evolved to become locally adapted within 50 to 100 years with important ecological consequences—increasing reproductive output by more than an order of magnitude. </jats:p>

<jats:title>Breaking Frog Defenses</jats:title> <jats:p> The first line of immune defense against most fungal infections consists of innate immune effector cells, including macrophages and neutrophils. However, <jats:bold> Fites <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="366" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1243316">366</jats:related-article> ) have found that the fungus currently decimating the world's amphibia, <jats:italic>Batrachochytrium dendrobatidis</jats:italic> , is readily engulfed by these cells, but that this does not effectively control the infection. The fungus releases cell-wall components that induce lymphocyte apoptosis and inhibit the proliferation of other nonlymphoid cell types, disarming lymphocyte-mediated responses to infection. </jats:p>

<jats:title>Capturing Binding Location and Speed</jats:title> <jats:p> Transcription factor–binding sites in chromatin can be mapped by the chromatin immunoprecipitation (ChIP) assay, which analyzes formaldehyde-fixed chromatin fragments obtained from cells. However, the standard ChIP assay does not provide information about how stable the inter-actions are. Other approaches, including live-cell imaging, can reveal aspects of the dynamic behavior of transcription factors but are limited either in location precision or time resolution. <jats:bold> Poorey <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6156" page="369" related-article-type="in-this-issue" vol="342" xlink:href="10.1126/science.1242369">369</jats:related-article> , published online 3 October) developed a model to explain how the ChIP signal relates to formaldehyde cross-linking time, and they developed a method to measure chromatin site–specific binding dynamics with high temporal resolution. </jats:p>