Largest ever gas mix caught in ultra-freeze trap

A team of scientists have made it easier to study atomic or subatomic-scale properties of the building blocks of matter (which also include protons, neutrons and electrons) known as fermions by slowing down the movement of a large quantity of gaseous atoms at ultra-low temperature.

This is according to a study recently published in The European Physical Journal D as part of a cold quantum matter special issue, by researchers from the Paris-based École Normale Supérieure and the Non-Linear Institute at Nice Sophia-Antipolis University in France.

Thanks to the laser cooling method for which Claude Cohen-Tannoudji, Steven Chu and William D. Phillips received the Nobel Prize in 1997, Armin Ridinger and his colleagues succeeded in creating the largest Lithium 6 (6Li) and Potassium 40 (40K) gas mixture to date. The method used involved confining gaseous atoms under an ultra-high vacuum using electromagnetic forces, in an ultra-freeze trap of sorts.

This trap enabled them to load twice as many atoms than previous attempts at studying such gas mixtures, reaching a total on the order of a few billion atoms under study at a temperature of only a few hundred microKelvins (corresponding to a temperature near the absolute zero of roughly -273 °C).

Given that the results of this study significantly increased the number of gaseous atoms under study, it will facilitate future simulation of subatomic-scale phenomena in gases. In particular, it will enable future experiments in which the gas mixture is brought to a so-called degenerate state characterised by particles of different species with very strong interactions. Following international efforts to produce the conditions to study subatomic-scale properties of matter under the quantum simulation program, this could ultimately help scientists to understand quantum mechanical phenomena occurring in neutron stars and so-called many-body problems such as high-temperature superconductivity.

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Journal Reference:

A. Ridinger, S. Chaudhuri, T. Salez, U. Eismann, D. R. Fernandes, K. Magalhaes, D. Wilkowski, C. Salomon, F. Chevy. Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms. The European Physical Journal D, 2011; 65 (1-2): 223 DOI: 10.1140/epjd/e2011-20069-4

Bacterial protein caught in the act of secreting sticky appendages

New atomic-level "snapshots" published in the June 2, 2011, issue of Nature reveal details of how bacteria such as E. coli produce and secrete sticky appendages called pili, which help the microbes attach to and infect human cells. "These crystal structures unravel a complex choreography of protein-protein interactions that will aid in the design of new antibacterial drugs," said Huilin Li, a biophysicist at the U.S. Department of Energy's Brookhaven National Laboratory and a professor at Stony Brook University, who participated in the research with a number of collaborators in the U.S. and in Europe.

Many E. coli strains live harmlessly in our guts, but when they find their way into the urinary tract, they produce pili with sticky ends that allow them to attach to bladder cells and cause infection. Finding ways to interfere with pili formation could help thwart urinary tract infections, which affect millions of women around the world each year.

Previously, Li's group at Brookhaven/Stony Brook and colleagues at Washington University School of Medicine and University College London solved individual pieces of the puzzle. In 2008, they combined their efforts to publish the first complete structure of the pore-like protein complex that traverses the bacterial membrane and transports pili components from the microbe cell's interior to its outer surface.

But the scientists were still not sure how the transporter protein's various parts worked to "recruit" and bring together the many subunits that make up the pili - or how it assembled and moved these structures through the membrane to the bacterial cell's surface. The new work, again combining efforts from the two teams, uses a range of imaging techniques and computer modeling to arrive at a more complete picture of the assembly process and transport mechanism.

"This is the first view of a protein transporter in the act of secreting its substrate," said Li.

At the European Synchrotron Radiation Facility in Grenoble, France, the Washington University/UK group determined the atomic-level crystal structure of the entire transporter protein, known as an "usher," bound to the sticky adhesin subunit that forms the end of a pilus and another helper protein, called a chaperone, that shuttles the pilus subunits to the usher one at a time. Meanwhile, Li's group worked at the National Synchrotron Light Source at Brookhaven to produce new images of the unbound usher protein in its closed, inactive state.

"Each group's work tells only part of the story, but when combined, the results provide unique insights into how the transporter works," said Li. "By comparing the same transporter in the closed and open state, we've determined how the gate should open, and exactly how the structure of the channel changes in response to the gate opening so the growing pilus can reach the exterior of the membrane," Li said.

When no subunits are bound to the usher, the barrel like pore remains plugged, completely sealed off. But when the first chaperoned subunit, the adhesin, arrives, it causes a dramatic conformational change that unplugs the pore and changes its shape from an oval to nearly circular.

"This large conformational rearrangement in the translocation channel upon activation by adhesin-chaperone is unprecedented for these barrel proteins, which until now were considered rigid structures," Li said.

The research also reveals that the usher protein has two binding sites for chaperone-subunit complexes. From the imaging studies and bioassays, it appears that the two operate in concert: While one chaperone-subunit complex remains bound as it moves through the translocation channel, the other site is available to recruit the next chaperone-subunit complex and add it to the growing pilus. Computer models show that the next incoming subunit is positioned in an ideal orientation for addition to the growing pilus structure via a "zip-in-zip-out" binding mechanism.

Blocking or removing either of the two binding sites may therefore be a way to inhibit pilus formation, and this idea is already being explored in new drug-development investigations. The other details of pilus assembly revealed by this study may suggest additional targets for new drugs.

More information: Crystal structure of the FimDusher bound to its cognate FimC-FimH substrate, Nature, DOI:10.1038/nature10109

Provided by Brookhaven National Laboratory (news : web)

Caught red-handed: Detection of latent fingerprints through release of fluorescein from a nanofiber mat

When a forensic agent dusts a surface with powder or exposes it to the vapors of an iodine chamber, mystery fans know what is going on: This is how latent fingerprints are made visible so that they can be compared to those of a suspect. Su Chen and a team at Nanjing University of Technology have now developed a new process for especially rapid and simple detection of fingerprints. As the Chinese researchers report in the journal Angewandte Chemie, all it takes is a special nanofiber mat that is pressed onto the suspect surface and briefly treated with hot air -- the fingerprints appear as red ridge patterns.

When we touch a surface, tiny traces of perspiration and oils stay behind, mirroring the ridge patterns on our fingertips. There are now a number of different methods to make these latent fingerprints visible. The new method is significantly faster than the classic technique of dusting with powder. Unlike spectroscopic methods, it does not require complex technical instruments, and problematic chemicals like ninydrin are not needed either. In addition, it is suitable for all types of surfaces: by lightly pressing the mat onto the surface, the researchers were able to reliably transfer fingerprints from a wide variety of materials, including steel, quartz, glass, plastic, marble, and wood.

The secret of their success is the special mat, a fleece made from nanofibers of thermoplastic polyurethane and fluorescein, a dye. The mat is made in a process called electrospinning. When the mat comes into contact with a fingerprint, components of the perspiration react with the polyurethane, causing cross-linking of the polymer chains. The hot air accelerates the reaction. In the cross-linked regions, the fluorescein cannot remain within the fibers so it comes out as a powdery solid. However, the dye only fluoresces when it is very finely dispersed in the nanofibers, not when it is in small solid clumps. This causes the color of the mat to change from straw yellow to red, making the fingerprint visible within 30 seconds in daylight. The method only works with nanofibers, because only they have enough surface area to produce a visible reaction.

The mat can identify more than mere fingerprints. The researchers were able to "print" an image of a small dragon onto the mat by using an ink-jet printer. Their ink was simply water, which can also cause the cross-linking reaction. The combination of ink-jet printing and the release of a chemical from a nanofiber mat could also be used to produce miniaturized systems such as sensors, microreactors, and diagnostic chips.

More information: Su Chen, et al., A Release-Induced Response for the Rapid Recognition of Latent Fingerprints and Formation of Inkjet-Printed Patterns, Angewandte Chemie International Edition 2011, 50, No. 16, 3706–3709, Permalink to the article: http://dx.doi.org/ … ie.201006537

Provided by Wiley (news : web)