Catálogo de publicaciones - revistas

<jats:p>Molecular mechanisms that generate biological diversity are rewriting ideas about how evolution proceeds, with implications for treating disease.</jats:p>

<jats:p>Over the past century, x-ray crystallography has transformed scientists' understanding of the structure and behavior of materials.</jats:p>

<jats:p>A technique for crystallizing fragile biomolecules without disrupting them is helping researchers probe the structures of some of the body's most important but elusive proteins: those that usher other chemicals through the cell membrane.</jats:p>

<jats:p>X-ray crystallography has become the leading technique for studying the structure of matter at the atomic and molecular level. Today it underpins all sciences and is widely applied in industry. It is essential in the development of new materials. The technique is very powerful, and the range of materials that can be studied expands as new technologies evolve and are applied in innovative ways to structure solution. It is now possible to record vast amounts of diffraction data in seconds electronically, whereas it took days and months by photographic methods 30 to 40 years ago. Single crystals can be created in various ways; they can be produced from compounds that are liquids or gases at room temperature, and complete molecular structures can be presented within minutes. This short review presents recent developments that are appropriate to the single-crystal x-ray studies of chemical and materials sciences.</jats:p>

<jats:p>The three-dimensional structures of large biomolecules important in the function and mechanistic pathways of all living systems and viruses can be determined by x-ray diffraction from crystals of these molecules and their complexes. This area of crystallography is continually expanding and evolving, and the introduction of new methods that use the latest technology is allowing the elucidation of ever larger and more complex biological systems, which are now becoming tractable to structure solution. This review looks back at what has been achieved and forward at how current and future developments may allow technical challenges to be overcome.</jats:p>

<jats:p>With the recent advances in ultrabright electron and x-ray sources, it is now possible to extend crystallography to the femtosecond time domain to literally light up atomic motions involved in the primary processes governing structural transitions. This review chronicles the development of brighter and brighter electron and x-ray sources that have enabled atomic resolution to structural dynamics for increasingly complex systems. The primary focus is on achieving sufficient brightness using pump-probe protocols to resolve the far-from-equilibrium motions directing chemical processes that in general lead to irreversible changes in samples. Given the central importance of structural transitions to conceptualizing chemistry, this emerging field has the potential to significantly improve our understanding of chemistry and its connection to driving biological processes.</jats:p>

<jats:title>A Soft Molecular Spring</jats:title> <jats:p> In noncontact atomic force microscopy, extremely high resolution has been achieved by attaching a terminal CO molecule to the metal scanning probe tip. This CO molecule can undergo torsional vibrations, and a full understanding of the imaging mechanism requires a measure of this spring constant. <jats:bold> Weymouth <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="6175" page="1120" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1249502">1120</jats:related-article> , published online 6 February; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6175" page="1083" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1251251">Salmeron</jats:related-article> </jats:bold> ) used lateral force microscopy, in which the tip vibrates laterally across the surface, to determine this torsional constant. The stiffness of the isolated CO molecules on the tip was much less than that for CO molecules adsorbed on planar surfaces. </jats:p>

<jats:title>Persistent Plume</jats:title> <jats:p> Energy from the solar wind is carried into Earth's magnetosphere and ionosphere through the reconnection of magnetic lines. When this coupling is strong, changes in the solar wind cause geomagnetic storms that perturb the magnetosphere and allow a plume of cool plasma to be released outward. As the plume rises from the ionosphere, it extends the boundary of its plasmasphere origin toward the magnetopause. Using simultaneous ground-based and satellite observations, <jats:bold> Walsh <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="6175" page="1122" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1247212">1122</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="6175" page="1086" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1250590">Borovsky</jats:related-article> </jats:bold> ) show that this plume can persist for hours, extending all the way from the ionosphere to the magnetopause. </jats:p>

<jats:title>Nanoimaged Polaritons</jats:title> <jats:p> Engineered heterostructures consisting of thin, weakly bound layers can exhibit many attractive electronic properties. <jats:bold> Dai <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="6175" page="1125" related-article-type="in-this-issue" vol="343" xlink:href="10.1126/science.1246833">1125</jats:related-article> ) used infrared nanoimaging on the surface of hexagonal boron nitride crystals to detect phonon polaritons, collective modes that originate in the coupling of photons to optical phonons. The findings reveal the dependence of the polariton wavelength and dispersion on the thickness of the material down to just a few atomic layers. </jats:p>