Wednesday, September 28, 2011

Nuclear detector: New materials hold promise for better detection of nuclear weapons

 Northwestern University scientists have developed new materials that can detect hard radiation, a very difficult thing to do. The method could lead to a handheld device for detecting nuclear weapons and materials, such as a "nuclear bomb in a suitcase" scenario.

"The terrorist attacks of 9/11 heightened interest in this area of security, but the problem remains a real challenge," said Mercouri G. Kanatzidis, who led the research. "We have designed promising semiconductor materials that, once optimized, could be a fast, effective and inexpensive method for detecting dangerous materials such as plutonium and uranium."

Kanatzidis is a Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences. He also holds a joint appointment at Argonne National Laboratory.

The Northwestern materials perform as well as materials that have emerged from five decades of research and development, Kanatzidis said.

To design an effective detector, Kanatzidis and his team turned to the heavy element part of the periodic table. The researchers developed a design concept to make new semiconductor materials of heavy elements in which most of the compound's electrons are bound up and not mobile. When gamma rays enter the compound, they excite the electrons, making them mobile and thus detectable. And, because every element has a particular spectrum, the signal identifies the detected material.

The method, called dimensional reduction, will be published in the Sept. 22 issue of the journal Advanced Materials.

In most materials, gamma rays emitted by nuclear materials would just pass right through, making them undetectable. But dense and heavy materials, such as mercury, thallium, selenium and cesium, absorb the gamma rays very well.

The problem the researchers faced was that the heavy elements have a lot of mobile electrons. This means when the gamma rays hit the material and excite electrons the change is not detectable.

"It's like having a bucket of water and adding one drop -- the change is negligible," Kanatzidis explained. "We needed a heavy element material without a lot of electrons. This doesn't exist naturally so we had to design a new material."

Kanatzidis and his colleagues designed their semiconductor materials to be crystalline in structure, which immobilized their electrons.

The materials they developed and successfully demonstrated as effective gamma ray detectors are cesium-mercury-sulfide and cesium-mercury-selenide. Both semiconductors operate at room temperature, and the process is scaleable.

"Our materials are very promising and competitive," Kanatzidis said. "With further development, they should outperform existing hard radiation detector materials. They also might be useful in biomedicine, such as diagnostic imaging."

The work was a Northwestern team effort, involving three professors and their research groups. Kanatzidis made the materials; Bruce W. Wessels, the Walter P. Murphy Professor of Materials Science and Engineering in the McCormick School of Engineering and Applied Science, measured and evaluated the materials; and Arthur J. Freeman, a Charles E. and Emma H. Morrison Professor of Physics and Astronomy in Weinberg, provided theoretical predictions of the materials' performance.

In addition to Kanatzidis, Wessels and Freeman, other authors include John Androulakis, Sebastian C. Peter, Hao Li, Christos D. Malliakas, John A. Peters, Zhifu Liu, Jung-Hwan Song and Hosub Jin.

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Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Northwestern University, via EurekAlert!, a service of AAAS.

Journal Reference:

John Androulakis, Sebastian C. Peter, Hao Li, Christos D. Malliakas, John A. Peters, Zhifu Liu, Bruce W. Wessels, Jung-Hwan Song, Hosub Jin, Arthur J. Freeman, Mercouri G. Kanatzidis. Dimensional Reduction: A Design Tool for New Radiation Detection Materials. Advanced Materials, 2011; DOI: 10.1002/adma.201102450

Ground glass solution for cleaner water

 British science has led to a use for waste glass that cannot be recycled that could help clean up polluted waterways by acting as an ion-exchange filter to remove lead, cadmium and other toxic metals.

Details are published in a forthcoming issue of the International Journal of Environment and Waste Management.

Only a fraction of waste glass bottles and jars can be recycled, partly because much of the glass is coloured, brown or green, and partly because the market sustains only a limited weight of recyclable glass. Millions of tonnes of waste container glass are generated across Europe. As such, large amounts of waste glass, purportedly for recycling, are shipped to China and elsewhere to be ground up and used as hardcore filling materials for road building.

Now, Nichola Coleman of the University of Greenwich, London, has developed a simple processing method for converting waste container glass, or cullet, into the mineral tobermorite. Tobermorite is hydrated calcium silicate, silicate being the main material that can be extracted from glass. In the form produced, the phase-pure 11-angstrom form -- the mineral can be used as an ion-exchange material that can extract toxic lead and cadmium ions from industrial effluent, waste water streams or contaminated groundwater.

To make the tobermorite, Coleman simply heats a mixture of ground cullet, lime (as a calcium source) and caustic soda (sodium hydroxide solution) to 100 Celsius in a sealed Teflon container. Initial tests show that uptake of lead and cadmium from solution are rather slow, so Coleman suggests that, at this stage of development, the synthetic mineral might best be used in the in situ remediation of groundwater rather than in industrial ex situ effluent filtration processes. The concept is now being extended to create other classes of ion exchange filter from unrecyclable and low-quality waste glass.

"The cullet-derived sorbent could be used in reactive barriers to prevent the lateral migration of pollutants in groundwater, rather than as a remediation material for waterways," says Coleman. "Heavy metal-contaminated land and groundwater are global problems, arising from industrial and military activities and also from the natural leaching of heavy metal-bearing minerals," she adds.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Inderscience, via AlphaGalileo.

Journal Reference:

Nicola J Coleman. 11 A tobermorite ion exchanger from recycled container glass. International Journal of Environment and Waste Management, 2011; 8 (3/4): 366-382

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

Microspiders: Polymerization reaction drives micromotors

Though it seems like science fiction, microscopic "factories" in which nanomachines produce tiny structures for miniaturized components or nanorobots that destroy tumor cells within the body and scrape blockages from our arteries may become reality in the foreseeable future. Nanomotors could transport drugs to specific target organs more rapidly or pilot analytes through the tiny channels on microchip diagnostic systems. In the journal Angewandte Chemie, Ayusman Sen and his team from Pennsylvania State University (USA) describe a new type of micromotor that is powered by a polymerization reaction and deposits tiny threads along its trail like a microspider.

The motors consist of spheres that are barely a micrometer in size, made half of gold, half of silicon dioxide. Certain catalyst molecules (a Grubbs catalyst) that catalyze polymerizations can be attached to the surface. Sen and his team use norbornene as a monomer. The catalyst opens the rings and strings these monomers together into long chain molecules.

As soon as the reaction begins, the spheres start driving through the surrounding liquid. How is it that such a reaction can cause movement? The secret lies in the two different halves of the spheres. The monomer is only consumed on the side where the catalyst molecules are present. This causes the monomer concentration to decrease until it is lower than on the catalyst-free gold side. The resulting concentration gradient produces osmotic pressure, which causes a tiny current of solvent molecules toward areas with higher monomer concentration—toward the gold side. This miniature current drives the in the opposite direction.

Somatic cells—in processes such as embryogenesis—and certain single-celled organisms can follow concentration gradients of messenger substances or nutrients, a phenomenon known as chemotaxis. The new micromotors are also capable of such directed movement. The scientists used norbornene-filled gels that slowly leach out the monomer. The micromotors sense this and preferentially move towards the gel, following the nutrient gradient like a single-celled organism. The reason for this is that the polymerization goes faster when there is more near the catalyst. This effect causes the local current driving the spheres to become stronger as well.

It is thus possible to direct the micromotors toward their target. In a solvent where the resulting polymer is insoluble, it could be deposited in the trail left behind; a microspider that moves around weaving a web. The micromotors can also be used to detect defects and fractures, moving towards them and sealing them with polymer.

More information: Ayusman Sen, A Polymerization-Powered Motor, Angewandte Chemie International Edition, … ie.201103565

Provided by Wiley (news : web)

Insect gut microbe with a molecular iron reservoir


Microbes are omnipresent on earth. They are found as free-living microorganisms as well as in communities with other higher organisms. Thanks to modern biological techniques we are now able to address the complex communities and study the role of individual microorganisms and enzymes in more detail.

Microbacterium arborescens is a bacterium, which can be found in the guts of herbivorous . The Department of Bioorganic Chemistry at the Max Planck Institute for studies interactions between insects and which live in their digestive system. What is the advantage for both, insects and microbes? How strongly do they depend on each other? Do microbes play a role in mediating interactions between herbivorous insects and host plants? In the course of the experiments to answer these questions the scientists came across an enzyme they had isolated from M. arborescens, a resident in the gut of the Beet Armyworm Spodoptera exigua. It was called N-acyl amino acid hydrolase (AAH) because of its catalytic function: it catalyzes the synthesis and of conjugates of the amino acid glutamine with . The N-acyl glutamines enter the infested plant via oral secretions and intestinal contents of the larvae and trigger the plant's defense responses.

After cloning and sequencing the AAH encoding gene the scientists discovered an interesting result: AAH is closely related to proteins from other microorganisms: the "DNA protection during starvation (DPS)" proteins, which bind to and protect them by crystallization or by removal of dangerous OH• radicals. Jelena Pesek, PhD student in the Department of Bioorganic Chemistry at the institute, was surprised that the enzyme AAH from M. arborescens differs from DPS enzymes in other microbes to the effect that it additionally regulates the concentration of N-acyl glutamine (conjugates of glutamic acid with fatty acids) in the gut, which are important for molecular plant-insect interactions. Moreover, the enzyme is able to store Fe(III)ions in its center. If free Fe(II) is present, hydrogen peroxide (H2O2), which is synthesized by the insect's intestinal cells to fend off microorganisms, is converted to highly reactive hydroxyl radicals. The process is known as the Fenton's Reaction:

Fe2+ + H2O2 › Fe3+ + OH- + •HO (Fenton's Reaction)

The highly reactive hydroxyl radical •HO damages especially the DNA and thus causes dangerous mutations of the genetic material. In cooperation with Kornelius Zeth from the Institute for Developmental Biology in Tuebingen the researchers succeeded in analyzing the iron transport mechanisms by means of crystallization and X-ray structure determination.

Longitudinal section through the pore along with a representation of the iron uptake mechanism. Entering Fe(II)ions, surrounded by 6 water molecules (spatial representation in the box on the right below), are oxidized to Fe(III)ions with a simultaneous loss of their hydrate shell. The Fe(III) is stored as Fe2O3 in the center of the macromolecule. Credit: Kornelius Zeth, MPI Tuebingen

The protein consists of 12 identical subunits and has a molecular mass of 204 kDa - a considerable size for a single enzyme. The homo-oligomer is round and hollow inside. It can store up to 500 iron atoms as ferric iron (usually in the form of Fe2O3) in the hollow cavity. The iron transport into the cavity is unique: The spherical protein has four selective pores which provide access only to ferrous iron ions along with their hydration shells (six water molecules). At catalytic ferroxidase centers inside the cavity the Fe(II) is oxidized to Fe(III) with simultaneous reduction of the dangerous H2O2 to water (H2O).

The scientists assume that AAH ensures survival of M. arborescens in the larval gut, where conditions may be harsh and constantly changing depending on food quality. The enzyme is protective against oxidative stress, reducing the concentration of free Fe(II) by storing it and simultaneously neutralizing H2O2 as a source for cell damaging radicals. The evolutionary context of these processes as well as the formation and hydrolysis of N-acyl glutamines which are also catalyzed by AAH are still unknown. Because of their detergent character these compounds may help the larvae to better digest the plant food. In the course of evolution, attacked may have "learned" to exploit the conjugates which enter the leaves during herbivory as a chemical alarm signal in order to activate their defense against the insect pest efficiently.

More information: Jelena Pesek, Rita B├╝chler, Reinhard Albrecht, Wilhelm Boland, Kornelius Zeth: Structure and Mechanism of Iron Translocation by a Dps Protein from Microbacterium arborescens. The Journal of Biological Chemistry 286. DOI: 10.1074/jbc.M111.246108

Provided by Max-Planck-Gesellschaft (news : web)

Feeding cows natural plant extracts can reduce dairy farm odors and feed costs

With citizens' groups seeking government regulation of foul-smelling ammonia emissions from large dairy farms, scientists today reported that adding natural plant extracts to cow feed can reduce levels of the gas by one-third while reducing the need to fortify cow feed with expensive protein supplements. They reported here at the 242nd National Meeting & Exposition of the American Chemical Society (ACS).

J. Mark Powell, Ph.D., described the results of three studies undertaken to determine how adding plant substances called "tannins" to cow feed affects the emission of ammonia from dairy barn floors and farm fields fertilized with mixtures of cow manure and urine.

"For , cow urine is the source of the ammonia emission problem," said Powell, who is with the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS). "Dairy cows excrete large amounts of urine, about 3.5 gallons daily for each cow. That's almost 1,300 gallons per year. And there are about 10 million dairy cows in the United States alone. Cows usually are fed a high-protein diet, and they produce various nitrogen compounds when they digest protein. They release the excess nitrogen mainly in their urine, and enzymes convert it into ammonia."

Ammonia has an acrid, eye-tearing odor and has potential adverse health effects on both cows and humans. Citizens' groups several months ago petitioned the U.S. Environmental Protection Agency (EPA) to begin regulating ammonia under the Clean Air Act, intensifying the search for practical, inexpensive ways to reduce emissions of the noxious gas. Besides its pungent odor, ammonia adds to air pollution, forming particles that travel long distances and contribute to environmental issues such as smog, acid rain and nutrient pollution.

The ammonia problem originates with the nitrogen-rich protein in cow feed. Cows' digestive systems are inefficient, and barely one-third of the nitrogen in their feed ends up in milk. The rest exits in urine and feces. The nitrogen in urine is in the form of urea, and enzymes contained in cow manure on the barn floor quickly convert it into ammonia gas.

Tannins apparently reduce urea production by allowing more protein to escape digestion in the stomach and enter the cow's intestines, where it's used to produce milk protein.

Powell began investigating tannins in animal feed 20 years ago in West African communities where he lived and worked. Tannin-rich shrubs were grown as windbreaks to reduce soil erosion and to feed livestock. Tannins also are a key part of the diets of cattle, sheep and goats in tropical areas where vegetation tends to be naturally higher in the astringent plant chemicals. However, tannins have attracted relatively little attention elsewhere, Powell said.

He hopes the addition of tannins to animal feed will become much more widespread in light of the findings about their potential for curbing . The tannin extracts used in the studies are already approved for animal feed and would cost only a few cents a day, he said. Tannins are perhaps best known for their use in tanning leather, and the quebracho and chestnut trees are sources for both leather tanning and cattle feed. Powell said that it may be possible to produce synthetic tannins at a lower cost.

Next on Powell's agenda is research to determine whether tannins also can reduce emissions of methane gas — a potent greenhouse gas involved in global warming — from cattle production. About 25 percent of methane emissions in the United States are from enteric fermentation (mostly belches) of domestic cattle.

Provided by American Chemical Society (news : web)