Nano Focus: Slowly cooled DNA transforms disordered nanoparticles into orderly crystal
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acteria construct tiny flagella “nanomachines” outside the cell
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esearchers at the University of Cambridge have uncovered the mechanism by which bacteria build their surface propellers (flagella). The results, published in the November 10, 2013 online edition of Nature (DOI:10.1038/ nature12682), demonstrate how the mechanism is powered by the subunits of the flagella themselves as they link in a chain that is pulled to the flagellum tip. Previously, scientists thought that the building blocks for flagella were either pushed or diffused from the flagellum base through a central channel in the structure to assemble at the flagellum tip, which is located far outside the cell. However, these theories are incompatible with recent
Nano Focus Slowly cooled DNA transforms disordered nanoparticles into orderly crystal
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ingle crystals are the backbone of many things we rely on—diamonds for beauty as well as industrial applications, sapphires for lasers, and silicon for electronics,” said nanoscientist Chad A. MRS BULLETIN
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VOLUME 39 • JANUARY 2014
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energy threshold for electrical currents, dubbed the energetic “pseudogap,” which grows as the crystal cools, revealing progressive localization of charges around the nickel atoms. The scientists then examined the dynamics of LSNO in pump-probe experiments, where they melted stripes with an initial ultrafast pulse of laser light and measured the optical changes with a second, delayed pulse. This allowed them to map out the early steps of charge ordering, exposing surprisingly fast localization dynamics preceding the development of organized stripe patterns. A final twist came when they probed the vibrations between nickel and oxygen atoms, uncovering a strong
coupling to the localized electrons with synchronous dynamics. Beyond the ultrafast measurements, the team also studied x-ray scattering and the infrared reflectance of the material to develop a thorough, cohesive understanding of the stripe phase and why it forms. Having illuminated the origins of the stripe phase in LSNO, the researchers expect their results to provide new impetus to understand the pseudogap in other correlated oxides—especially in hightemperature superconductors where fluctuating stripes occur while their role in the superconductivity mechanism remains unclear. Alison Hatt
research that shows that flagella grow at a constant rate. The unexpected chain mechanism, in which subunits linked in a chain pull themselves through the flagellum, transforms current understanding of how flagellum assembly is energized. The research team, led by Gillian Fraser and Colin Hughes, found that as each flagellum “nanomachine” is assembled, thousands of subunit building blocks are made in the cell and are then unfolded and exported across the cell membrane. Like other processes inside cells, this initial export phase consumes chemical energy. However, when subunits pass out of the cell into the narrow channel at the center of the growing flagellum, there is no conventional energy source and they must someho
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