Colloidal quantum dots: Performance boost next-generation solar cell technology

Researchers from the University of Toronto (U of T), the King Abdullah University of Science & Technology (KAUST) and Pennsylvania State University (Penn State) have created the most efficient solar cell ever made based on colloidal quantum dots (CQD).

The discovery is reported in the latest issue of Nature Materials.

Quantum dots are nanoscale semiconductors that capture light and convert it into an energy source. Because of their small scale, the dots can be sprayed on to flexible surfaces, including plastics. This enables the production of solar cells that are less expensive to produce and more durable than the more widely-known silicon-based version. In the work highlighted by the Nature Materials paper, the researchers demonstrate how the wrappers that encapsulate the quantum dots can be shrunk to a mere layer of atoms.

"We figured out how to shrink the passivating materials to the smallest imaginable size," states Professor Ted Sargent, corresponding author on the work and holder of the Canada Research Chair in Nanotechnology at U of T.

A crucial challenge for the field has been striking a balance between convenience and performance. The ideal design is one that tightly packs the quantum dots together. The greater the distance between quantum dots, the lower the efficiency.

However the quantum dots are usually capped with organic molecules that add a nanometer or two. When working on a nanoscale, that is bulky. Yet the organic molecules have been an important ingredient in creating a colloid, which is a substance that is dispersed in another substance. This allows the quantum dots to be painted on to other surfaces.

To solve the problem, the researchers have turned to inorganic ligands, which bind the quantum dots together while using less space. The result is the same colloid characteristics but without the bulky organic molecules.

"We wrapped a single layer of atoms around each particle. As a result, they packed the quantum dots into a very dense solid," explains Dr. Jiang Tang, the first author of the paper who conducted the research while a post-doctoral fellow in The Edward S. Rogers Department of Electrical & Computer Engineering at U of T.

The team showed the highest electrical currents, and the highest overall power conversion efficiency, ever seen in CQD solar cells. The performance results were certified by an external laboratory, Newport, that is accredited by the US National Renewable Energy Laboratory.

"The team proved that we were able to remove charge traps -- locations where electrons get stuck -- while still packing the quantum dots closely together," says Professor John Asbury of Penn State, a co-author of the work.

The combination of close packing and charge trap elimination enabled electrons to move rapidly and smoothly through the solar cells, thus providing record efficiency.

"This finding proves the power of inorganic ligands in building practical devices," states Professor Dmitri Talapin of The University of Chicago, who is a research leader in the field. "This new surface chemistry provides the path toward both efficient and stable quantum dot solar cells. It should also impact other electronic and optoelectronic devices that utilize colloidal nanocrystals. Advantages of the all-inorganic approach include vastly improved electronic transport and a path to long-term stability."

"At KAUST we were able to visualize, with incredible resolution on the sub-nanometer length scale, the structure and composition of this remarkable new class of materials," states Professor Aram Amassian of KAUST, a co-author on the work.

"We proved that the inorganic passivants were tightly correlated with the location of the quantum dots; and that it was this new approach to chemical passivation, rather than nanocrystal ordering, that led to this record-breaking colloidal quantum dot solar cell performance," he adds.

As a result of the potential of this research discovery, a technology licensing agreement has been signed by U of T and KAUST, brokered by MaRS Innovations (MI), which will will enable the global commercialization of this new technology.

"The world -- and the marketplace -- need solar innovations that break the existing compromise between performance and cost. Through U of T's, MI's, and KAUST's partnership, we are poised to translate exciting research into tangible innovations that can be commercialized," said Sargent.

Story Source:

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

Journal Reference:

Jiang Tang, Kyle W. Kemp, Sjoerd Hoogland, Kwang S. Jeong, Huan Liu, Larissa Levina, Melissa Furukawa, Xihua Wang, Ratan Debnath, Dongkyu Cha, Kang Wei Chou, Armin Fischer, Aram Amassian, John B. Asbury, Edward H. Sargent. Colloidal-quantum-dot photovoltaics using atomic-ligand passivation. Nature Materials, 2011; DOI: 10.1038/nmat3118

Lasers could be used to detect roadside bombs

 A research team at Michigan State University has developed a laser that could detect roadside bombs -- the deadliest enemy weapon encountered in Iraq and Afghanistan.

The laser, which has comparable output to a simple presentation pointer, potentially has the sensitivity and selectivity to canvas large areas and detect improvised explosive devices -- weapons that account for around 60 percent of coalition soldiers' deaths. Marcos Dantus, chemistry professor and founder of BioPhotonic Solutions, led the team and has published the results in the current issue of Applied Physics Letters.

The detection of IEDs in the field is extremely important and challenging because the environment introduces a large number of chemical compounds that mask the select few molecules that one is trying to detect, Dantus said.

"Having molecular structure sensitivity is critical for identifying explosives and avoiding unnecessary evacuation of buildings and closing roads due to false alarms," he said.

Since IEDs can be found in populated areas, the methods to detect these weapons must be nondestructive. They also must be able to distinguish explosives from vast arrays of similar compounds that can be found in urban environments. Dantus' latest laser can make these distinctions even for quantities as small as a fraction of a billionth of a gram.

The laser beam combines short pulses that kick the molecules and make them vibrate, as well as long pulses that are used to "listen" and identify the different "chords." The chords include different vibrational frequencies that uniquely identify every molecule, much like a fingerprint. The high-sensitivity laser can work in tandem with cameras and allows users to scan questionable areas from a safe distance.

"The laser and the method we've developed were originally intended for microscopes, but we were able to adapt and broaden its use to demonstrate its effectiveness for standoff detection of explosives," said Dantus, who hopes to net additional funding to take this laser from the lab and into the field.

This research is funded in part by the Department of Homeland Security. BioPhotonic Solutions is a high-tech company Dantus launched in 2003 to commercialize technology invented in a spinoff from his research group at MSU.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Michigan State University.

Journal Reference:

Marshall T. Bremer, Paul J. Wrzesinski, Nathan Butcher, Vadim V. Lozovoy, Marcos Dantus. Highly selective standoff detection and imaging of trace chemicals in a complex background using single-beam coherent anti-Stokes Raman scattering. Applied Physics Letters, 2011; 99 (10): 101109 DOI: 10.1063/1.3636436

A guiding light for new directions in energy production: Optofluidics could help solve the energy challenge

The science of light and liquids has been intimately entwined since Léon Foucault discovered the speed of light in 1862, when he observed that light travels more slowly in water than in air. This physical harmony between the two materials is now being harnessed to collect and drive light to where it can be the most useful. October's issue of Nature Photonics focuses on optofluidics, the study of microfluidics -- the microscopic delivery of fluids through extremely small channels or tubes -- combined with optics. In a review written by Demetri Psaltis, Dean of EPFL's School of Engineering, he and his co-authors argue that optofluidics is poised to take on one of this century's most important challenges: energy.

"By directing the light and concentrating where it can be most efficiently used, we could greatly increase the efficiency of already existing energy producing systems, such as biofuel reactors and solar cells, as well as innovate entirely new forms of energy production" explains Psaltis. "EPFL is the world leader in optofluidics, our institution is in a position to develop truly efficient and disruptive energy sources."

Sunlight is already used for energy production besides conventional solar panels. For example, it is used to convert water and carbon dioxide into methane in large industrial biofuel plants. Prisms and mirrors are commonly employed to direct and concentrate sunlight to heat water on the roofs of homes and apartment buildings. These techniques already employ the same principles found in optofluidics -- control and manipulation of light and liquid transfer -- but often without the precision offered by nano and micro technology.

A futuristic example: Optofluidic solar lighting system

How can we better exploit the light that hits the outside of a building? Imagine sunlight channelled into the building An optofluidic solar lighting system could capture sunlight from a roof using a light concentrating system that follows the sun's path by changing the angle of the water's refraction, and then distribute the sunlight throughout the building through light pipes or fibre optic cables to the ceilings of office spaces, indoor solar panels, or even microfluidic air filters. Using sunlight to drive a microfluidic air filter or aliment an indoor solar panel -- which would be protected from the elements and last longer -- is a novel way to use solar energy to supplement non-renewable resources.

In such a system, it would be essential to deviate from the secondary devices such as air filtrage and solar panels to maintain a comfortable constant light source for ceiling lighting -- the flickering of the light source due to a cloud passing over would be intolerable. In order to modulate these different channels to maintain a constant light source, a system using electrowetting could deviate light from one channel into another both easily and inexpensively. A droplet of water sits on the outer surface of light tube. A small current excites the ions in the water, pushing them to the edge of the droplet and expanding it just enough for it to touch the surface of another tube. This expanded droplet then creates a light bridge between the two parallel light tubes, effectively moderating the amount of light streaming through either one.

Up-scaling for industrial use

"The main challenge optofluidics faces in the energy field is to maintain the precision of nano and micro light and fluid manipulation while creating industrial sized installations large enough to satisfy the population's energy demand," explains David Erickson, professor at Cornell University and visiting professor at EPFL. "Much like a super computer is built out of small elements, up-scaling optofluidic technology would follow a similar model -- the integration of many liquid chips to create a super-reactor."

Since most reactions in liquid channels happen at the point of contact between the liquid and the catalyst-lined tubes, the efficiency of a system depends on how much surface area is available for reactions to take place. Scaling down the size of the channels to the micro and nano level allows for thousands more channels in the same available space, greatly increasing the overall surface area and leading to a radical reduction of the size needed (and ultimately the cost) for catalytic and other chemical reactions. Adding a light source as a catalyst to the directed flow of individual molecules in nanotubes allows for extreme control and high efficiency.

Their review in Nature Phontonics lays out several possibilities for up-scaling optofluidics, such as using optical fibers to transport sunlight into large indoor biofuel reactors with mass-produced nanotubes. They point out that the use of smaller spaces could increase power density and reduce operating costs; optofluidics offers flexibility when concentrating and directing sunlight for solar collection and photovoltaic panels; and by increasing surface area, the domain promises to reduce the use of surface catalysts -- the most expensive element in many reactors.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Ecole Polytechnique Fédérale de Lausanne, via EurekAlert!, a service of AAAS.

Journal Reference:

David Erickson, David Sinton, Demetri Psaltis. Optofluidics for energy applications. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.209

New method to grow synthetic collagen unveiled: New material may find use in reconstructive surgery, cosmetics, tissue engineering

In a significant advance for cosmetic and reconstructive medicine, scientists at Rice University have unveiled a new method for making synthetic collagen. The new material, which forms from a liquid in as little as an hour, has many of the properties of natural collagen and may prove useful as a scaffold for regenerating new tissues and organs from stem cells.

"Our work is significant in two ways," said Rice's Jeffrey Hartgerink, the lead author of a new paper about the research in Nature Chemistry. "Our final product more closely resembles native collagen than anything that's previously been made, and we make that material using a self-assembly process that is remarkably similar to processes found in nature."

Collagen, the most abundant protein in the body, is a key component of many tissues, including skin, tendons, ligaments, cartilage and blood vessels. Biomedical researchers in the burgeoning field of regenerative medicine, or tissue engineering, often use a combination of stem cells and collagen-like materials in their attempts to create laboratory-grown tissues that can be transplanted into patients without risk of immunological rejection.

Animal-derived collagen, which has some inherent immunological risks, is the form of collagen most commonly used in reconstructive and cosmetic surgery today. Animal-derived collagen is also used in many cosmetics.

Despite the abundance of collagen in the body, deciphering or recreating it has not been easy for scientists. One reason for this is the complexity collagen exhibits at different scales. For example, just as a rope is made of many interwoven threads, collagen fibers are made of millions of proteins called peptides. Like a rope net that can trap and hold items, collagen fibers can form three-dimensional structures called hydrogels that trap and hold water.

"Our supramolecules, fibers and hydrogels form in a similar way to native collagen, but we start with shorter peptides," said Hartgerink, associate professor of chemistry and of bioengineering.

With an eye toward mimicking collagen's self-assembly process as closely as possible, Hartgerink's team spent several years perfecting its design for the peptides.

Hartgerink said it's too early to say whether the synthetic collagen can be substituted medically for human or animal-derived collagen, but it did clear the first hurdle on that path; the enzyme that the body uses to break down native collagen also breaks down the new material at a similar speed.

A faculty investigator at Rice's BioScience Research Collaborative, Hartgerink said scientists must next determine whether cells can live and grow in the new material and whether it performs the same way in the body that native collagen does. He estimated that clinical trials, if they prove warranted, are at least five years away.

The paper's co-authors include Rice graduate students Lesley O'Leary, Jorge Fallas, Erica Bakota and Marci Kang. The research was funded by the National Science Foundation, the Robert A. Welch Foundation and the Norman Hackerman Advanced Research Program of Texas.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Rice University.

Journal Reference:

Lesley E. R. O'Leary, Jorge A. Fallas, Erica L. Bakota, Marci K. Kang, Jeffrey D. Hartgerink. Multi-hierarchical self-assembly of a collagen mimetic peptide from triple helix to nanofibre and hydrogel. Nature Chemistry, 2011; DOI: 10.1038/nchem.1123

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

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

New material synthesized: Graphene nanoribbons inside of carbon nanotubes

Physicists from Umea University (Sweden) and Finland have found an efficient way to synthesize graphene nanoribbons directly inside of single-walled carbon nanotubes.

The result was recently published in the journal Nano Letters.

Graphene, a one atom thin flake of plain carbon, has a wide range of unusual and highly interesting properties. As a conductor of electricity it performs as well as copper. As a conductor of heat it outperforms all other known materials. There are possibilities to achieve strong variations of the graphene properties by making graphene in the form of belts with various widths, so called nanoribbons. These nanoribbons are now the real focus of attention in physics and an extremely promising material for electronics, solar cells and many other things. However, it is has not been easy to make such ribbons.

Associate professor Alexandr Talyzin and his research group at the Department of Physics, Umea University, have together with colleagues from Professor Esko Kauppinen´s group, Aalto University in Finland, discovered a way to use the hollow space inside carbon nanotubes as a one-dimensional chemical reactor to make encapsulated graphene. An intriguing property of this space is that chemical reactions occur differently here compared to under bulk three-dimensional conditions.

"We used coronene and perylene, which are large organic molecules, as building blocks to produce long and narrow graphene nanoribbons inside the tubes. The idea of using these molecules as building blocks for graphene synthesis was based on our previous study," says Talyzin.

This study revealed that coronene molecules can react with each other at certain conditions to form dimers, trimers and longer molecules in a bulk powder form. The result suggested that coronene molecules can possibly be used for synthesis of graphene but need to be somehow aligned in one plane for the required reaction. The inner space of single-walled carbon nanotubes seemed to be an ideal place to force molecules into the edge-to-edge geometry required for the polymerization reaction.

In the new study, the researchers show that this is possible. When the first samples were observed by electron microscopy by Ilya Anoshkin at Aalto University, exciting results were revealed: all nanotubes were filled inside with graphene nanoribbons.

"The success of the experiments also depended a lot on the choice of nanotubes. Nanotubes of suitable diameter and in high quality were provided by our co-authors from Aalto University," says Talyzin.

Later the researchers found that the shape of encapsulated graphene nanoribbons can be modified by using different kinds of aromatic hydrocarbons. The properties of nanoribbons are very different depending on their shape and width. For example, nanoribbons can be either metallic or semiconducting depending on their width and type. Interestingly, carbon nanotubes can also be metallic, semiconducting (depending on their diameter) or insulating when chemically modified.

"This creates an enormous potential for a wide range of applications. We can prepare hybrids that combine graphene and nanotubes in all possible combinations in the future," says Talyzin.

For example, metallic nanoribbons inside insulating nanotubes are very thin insulated wires. They might be used directly inside carbon nanotubes to produce light thus making nano-lamps. Semiconducting nanoribbons can possibly be used for transistors or solar cell applications and metallic-metallic combination is in fact a new kind of coaxial nano-cable, macroscopic cables of this kind are used e.g. for transmitting radio signals.

The new method of hybrid synthesis is very simple, easily scalable and allows obtaining almost 100 percent filling of tubes with nanoribbons. The theoretical simulations, performed by Arkady Krasheninnikov in Finland, also show that the graphene nanoribbons keep their unique properties inside the nanotubes while protected from the environment by encapsulation and aligned within bundles of single-walled nanotubes.

"The new material seems very promising, but we have a lot of inter-disciplinary work ahead of us in the field of physics and chemistry. To synthesize the material is just a beginning. Now we want to learn its electric, magnetic and chemical properties and how to use the hybrids for practical applications," says Talyzin.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Umea University.

Journal Reference:

Alexandr V. Talyzin, Ilya V. Anoshkin, Arkady V. Krasheninnikov, Risto M. Nieminen, Albert G. Nasibulin, Hua Jiang, Esko I. Kauppinen. Synthesis of Graphene Nanoribbons Encapsulated in Single-Walled Carbon Nanotubes. Nano Letters, 2011; 110902093500003 DOI: 10.1021/nl2024678

New light on detection of bacterial infection: Polymers fluoresce in the presence of bacteria

 Researchers at the University of Sheffield have developed polymers that fluoresce in the presence of bacteria, paving the way for the rapid detection and assessment of wound infection using ultra-violet light.

When contained in a gel and applied to a wound, the level of fluorescence detected will alert clinicians to the severity of infection. The polymers are irreversibly attached to fragments of antibiotics, which bind to either gram negative or gram positive bacteria -- both of which cause very serious infections -- informing clinicians as to whether to use antibiotics or not, and the most appropriate type of antibiotic treatment to prescribe. The team also found that they could use the same gels to remove the bacteria from infected wounds in tissue engineered human skin.

Professor Sheila MacNeil, an expert in tissue engineering and wound healing, explained: "The polymers incorporate a fluorescent dye and are engineered to recognise and attach to bacteria, collapsing around them as they do so. This change in polymer shape generates a fluorescent signal that we´ve been able to detect using a hand-held UV lamp."

"The availability of these gels would help clinicians and wound care nurses to make rapid, informed decisions about wound management, and help reduce the overuse of antibiotics," added project lead Dr Steve Rimmer.

Currently, determining significant levels of bacterial infection involves swabbing the wound and culturing the swabs in a specialist bacteriology laboratory with results taking several days to be available. The team is confident that its technology can ultimately reduce the detection of bacterial infection to within a few hours, or even less.

The research has already demonstrated that the polymer (PNIPAM), modified with an antibiotic (vancomycin) and containing a fluorescent dye (ethidium bromide), shows a clear fluorescent signal when it encounters gram negative bacteria. Other polymers have been shown to respond to S. aureus, a gram positive bacteria. These advances mean that a hand-held sensor device can now be developed to be used in a clinical setting.

The research is the result of a three-year project which started in 2006, part-funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Defence Science and Technology Laboratory (Dstl) -- an agency of the Ministry of Defence, interested in the medical application of the research in battlefield conditions, and a subsequent EPSRC funded PhD studentship.

The team is also investigating whether using a sophisticated technique called fluorescence Non Radiative Energy Transfer (NRET) to generate the light signal could enable a highly refined sensor technology that could have applications in other areas.

"For example, we think that NRET could be very useful in an anti-terrorist and public health capacity, detecting pathogen release or bacterial contamination, whether accidental or deliberate," says Dr Rimmer. "NRET also allows us to learn more about how the polymers collapse around the bacteria, which is important in developing our understanding of how bacteria interact with these novel responsive polymers."

The team is interested in talking to potential partners to take this technology forward.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Sheffield.

'Inexhaustible' source of hydrogen may be unlocked by salt water, engineers say

 A grain of salt or two may be all that microbial electrolysis cells need to produce hydrogen from wastewater or organic byproducts, without adding carbon dioxide to the atmosphere or using grid electricity, according to Penn State engineers.

"This system could produce hydrogen anyplace that there is wastewater near sea water," said Bruce E. Logan, Kappe Professor of Environmental Engineering. "It uses no grid electricity and is completely carbon neutral. It is an inexhaustible source of energy."

Microbial electrolysis cells that produce hydrogen are the basis of this recent work, but previously, to produce hydrogen, the fuel cells required some electrical input. Now, Logan, working with postdoctoral fellow Younggy Kim is using the difference between river water and seawater to add the extra energy needed to produce hydrogen.

Their results, published Sept. 19 in the Proceedings of the National Academy of Sciences, "show that pure hydrogen gas can efficiently be produced from virtually limitless supplies of seawater and river water and biodegradable organic matter."

Logan's cells were between 58 and 64 percent efficient and produced between 0.8 to 1.6 cubic meters of hydrogen for every cubic meter of liquid through the cell each day. The researchers estimated that only about 1 percent of the energy produced in the cell was needed to pump water through the system.

The key to these microbial electrolysis cells is reverse-electrodialysis or RED that extracts energy from the ionic differences between salt water and fresh water. A RED stack consists of alternating ion exchange membranes -- positive and negative -- with each RED contributing additively to the electrical output.

"People have proposed making electricity out of RED stacks," said Logan. "But you need so many membrane pairs and are trying to drive an unfavorable reaction."

For RED technology to hydrolyze water -- split it into hydrogen and oxygen -- requires 1.8 volts, which would in practice require about 25 pairs of membrane sand increase pumping resistance. However, combining RED technology with exoelectrogenic bacteria -- bacteria that consume organic material and produce an electric current -- reduced the number of RED stacks to five membrane pairs.

Previous work with microbial electrolysis cells showed that they could, by themselves, produce about 0.3 volts of electricity, but not the 0.414 volts needed to generate hydrogen in these fuel cells. Adding less than 0.2 volts of outside electricity released the hydrogen. Now, by incorporating 11 membranes -- five membrane pairs that produce about 0.5 volts -- the cells produce hydrogen.

"The added voltage that we need is a lot less than the 1.8 volts necessary to hydrolyze water," said Logan. "Biodegradable liquids and cellulose waste are abundant and with no energy in and hydrogen out we can get rid of wastewater and by-products. This could be an inexhaustible source of energy."

Logan and Kim's research used platinum as a catalyst on the cathode, but subsequent experimentation showed that a non-precious metal catalyst, molybdenum sulfide, had a 51 percent energy efficiency. The King Abdullah University of Science and Technology supported this work.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Penn State.

Journal Reference:

Younggy Kim, Bruce E. Logan. Hydrogen production from inexhaustible supplies of fresh and salt water using microbial reverse-electrodialysis electrolysis cells. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1106335108

Scientists solve long-standing plant biochemistry mystery

 Scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and collaborators at the Karolinska Institute in Sweden have discovered how an enzyme "knows" where to insert a double bond when desaturating plant fatty acids. Understanding the mechanism -- which relies on a single amino acid far from the enzyme's active site -- solves a 40-year mystery of how these enzymes exert such location-specific control.

The work, published in the Proceedings of the National Academy of Sciences the week of September 19, 2011, may lead to new ways to engineer plant oils as a renewable replacement for petrochemicals.

"Plant fatty acids are an approximately $150-billion-dollar-a-year market," said Brookhaven biochemist John Shanklin, lead author on the paper. "Their properties, and therefore their potential uses and values, are determined by the position of double bonds in the hydrocarbon chains that make up their backbones. Thus the ability to control double bond positions would enable us to make new designer fatty acids that would be useful as industrial raw materials."

The enzymes responsible for double-bond placement, called desaturases, remove hydrogen atoms and insert double bonds between adjacent carbon atoms at specific locations on the hydrocarbon chains. But how one enzyme knows to insert the double bond at one location while a different but closely related enzyme inserts a double bond at a different site has been a mystery.

"Most enzymes recognize features in the molecules they act on that are very close to the site where the enzyme's action takes place. But all the carbon-hydrogen groups that make up fatty-acid backbones are very similar with no distinguishing features -- it's like a greasy rope with nothing to hold onto," said Shanklin.

In describing his group's long-standing quest to solve the desaturation puzzle, Shanklin quotes Nobel laureate Konrad Bloch, who observed more than 40 years ago that such site-specific removal of hydrogen "would seem to approach the limits of the discriminatory power of enzymes."

Shanklin and his collaborators approached the problem by studying two genetically similar desaturases that act at different locations: a castor desaturase that inserts a double bond between carbon atoms 9 and 10 in the chain (a 'delta-9' desaturase); and an ivy desaturase that inserts a double bond between carbon atoms 4 and 5 (delta-4). They reasoned that any differences would be easy to spot in such extreme examples.

But early attempts to find a telltale explanation -- which included detailed analyses of the two enzymes' atomic-level crystal structures -- turned up few clues. "The crystal structures are almost identical," Shanklin said.

The next step was to look at how the two enzymes bind to their substrates -- fatty acid chains attached to a small carrier protein. First the scientists analyzed the crystal structure of the castor desaturase bound to the substrate. Then they used computer modeling to further explore how the carrier protein "docked" with the enzyme.

"Results of the computational docking model exactly matched that of the real crystal structure, which allows carbon atoms 9 and 10 to be positioned right at the enzyme's active site," Shanklin said.

Next the scientists modeled how the carrier protein docked with the ivy desaturase. This time it docked in a different orientation that positioned carbon atoms 4 and 5 at the desaturation active site. "So the docking model predicted a different orientation that exactly accounted for the specificity," Shanklin said.

To identify exactly what was responsible for the difference in binding, the scientists then looked at the amino acid sequence -- the series of 360 building blocks that makes up each enzyme. They identified amino acid locations that differ between delta-9 and delta-4 desaturases, and focused on those locations that would be able to interact with the substrate, based on their positions in the structural models.

The scientists identified one position, far from the active site, where the computer model indicated that switching a single amino acid would change the orientation of the bound fatty acid with respect to the active site. Could this distant amino-acid location remotely control the site of double bond placement?

To test this hypothesis, the scientists engineered a new desaturase, swapping out the aspartic acid normally found at that location in the delta-9 castor desaturase for the lysine found in the delta-4 ivy desaturase. The result: an enzyme that was castor-like in every way, except that it now seemed able to desaturate the fatty acid at the delta-4 carbon location. "It's quite remarkable to see that changing just one amino acid could have such a striking effect," Shanklin said.

The computational modeling helped explain why: It showed that the negatively charged aspartic acid in the castor desaturase ordinarily repels a negatively charged region on the carrier protein, which leads to a binding orientation that favors delta-9 desaturation; substitution with positively charged lysine results in attraction between the desaturase and carrier protein, leading to an orientation that favors delta-4 desaturation.

Understanding this mechanism led Ed Whittle, a research associate in Shanklin's lab, to add a second positive charge to the castor desaturase in an attempt to further strengthen the attraction. The result was a nearly complete switch in the castor enzyme from delta-9 to delta-4 desaturation, adding compelling support for the remote control hypothesis.

"I really admire Ed's persistence and insight in taking what was already a striking result and pushing it even further to completely change the way this enzyme functions," Shanklin said.

"It's very rewarding to have finally solved this mystery, which would not have been possible without a team effort drawing on our diverse expertise in biochemistry, genetics, computational modeling, and x-ray crystallography.

"Using what we've now learned, I am optimistic we can redesign enzymes to achieve new desirable specificities to produce novel fatty acids in plants. These novel fatty acids would be a renewable resource to replace raw materials now derived from petroleum for making industrial products like plastics," Shanklin said.

This work was funded by the DOE Office of Science. Additional collaborators include: Jodie Guy, Martin Moche, and Ylva Lindqvist of the Karolinska Institute, and Johan Lengqvist, now at AstraZeneca R&D in Sweden. The scientists analyzed crystal structures at several synchrotrons including: the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory, the European Synchrotron Radiation Facility (ESRF) in France, the Dutch Electron Synchrotron (DESY), and the MAX-lab National Laboratory for Synchrotron Radiation in Sweden.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Brookhaven National Laboratory.

Journal Reference:

Jodie E. Guy, Edward Whittle, Martin Moche, Johan Lengqvist, Ylva Lindqvist, John Shanklin. Remote control of regioselectivity in acyl-acyl carrier protein-desaturases. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1110221108

Researchers power line-voltage light bulb with nanotube wire

 Cables made of carbon nanotubes are inching toward electrical conductivities seen in metal wires, and that may light up interest among a range of industries, according to Rice University researchers.

A Rice lab made such a cable from double-walled carbon nanotubes and powered a fluorescent light bulb at standard line voltage -- a true test of the novel material's ability to stake a claim in energy systems of the future.

The work appears this week in the Nature journal Scientific Reports.

Highly conductive nanotube-based cables could be just as efficient as traditional metals at a sixth of the weight, said Enrique Barrera, a Rice professor of mechanical engineering and materials science. They may find wide use first in applications where weight is a critical factor, such as airplanes and automobiles, and in the future could even replace traditional wiring in homes.

The cables developed in the study are spun from pristine nanotubes and can be tied together without losing their conductivity. To increase conductivity of the cables, the team doped them with iodine and the cables remained stable. The conductivity-to-weight ratio (called specific conductivity) beats metals, including copper and silver, and is second only to the metal with highest specific conductivity, sodium.

Yao Zhao, who recently defended his dissertation toward his doctorate at Rice, is the new paper's lead author. He built the demo rig that let him toggle power through the nanocable and replace conventional copper wire in the light-bulb circuit.

Zhao left the bulb burning for days on end, with no sign of degradation in the nanotube cable. He's also reasonably sure the cable is mechanically robust; tests showed the nanocable to be just as strong and tough as metals it would replace, and it worked in a wide range of temperatures. Zhao also found that tying two pieces of the cable together did not hinder their ability to conduct electricity.

The few centimeters of cable demonstrated in the present study seems short, but spinning billions of nanotubes (supplied by research partner Tsinghua University) into a cable at all is quite a feat, Barrera said. The chemical processes used to grow and then align nanotubes will ultimately be part of a larger process that begins with raw materials and ends with a steady stream of nanocable, he said. The next stage would be to make longer, thicker cables that carry higher current while keeping the wire lightweight. "We really want to go better than what copper or other metals can offer overall," he said.

The paper's co-authors are Tsinghua researcher Jinquan Wei, who spent a year at Rice partly supported by the Armchair Quantum Wire Project of Rice University's Smalley Institute for Nanoscale Science and Technology; Robert Vajtai, a Rice faculty fellow in mechanical engineering and materials science; and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and professor of chemistry and chemical and biomolecular engineering.

The Research Partnership to Secure Energy for America, the Department of Energy and Air Force Research Laboratory supported the project.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Rice University.

Journal Reference:

Yao Zhao, Jinquan Wei, Robert Vajtai, Pulickel M. Ajayan, Enrique V. Barrera. Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals. Scientific Reports, 2011; 1 DOI: 10.1038/srep00083

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 silicon dioxide 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 micromotor 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 monomer 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, http://dx.doi.org/ … 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 caterpillars. The Department of Bioorganic Chemistry at the Max Planck Institute for Chemical Ecology studies interactions between insects and microorganisms 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 hydrolysis of conjugates of the amino acid glutamine with fatty acids. 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 DNA molecules 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 Max Planck 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 host plants 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 Büchler, 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 dairy farms, 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 ammonia emissions. 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)

Chemical research could help solve radioactive waste concerns

The controversial problem of storing some of the most radioactive elements of nuclear waste could be close to being solved thanks to experts from the University of Reading.

Researchers in the Department of Chemistry have discovered a class of molecules that can selectively extract extremely radioactive components - ‘minor actinides' - that remain after spent fuel has been reprocessed, making the eventual waste far less radiotoxic. The minor actinides can potentially be fed back into nuclear reactors, providing extra energy and, in turn, be converted to non-radioactive products.

The UK nuclear power industry produces about 10,000 megawatts of power each year. Although the vast bulk of the spent fuel from a reactor can be reprocessed and fed back into the fuel cycle, a residue, consisting of corrosion products, lanthanides and minor actinides, must be sent to storage.

For every 500kg of spent fuel, there is 15kg of waste, of which the minor actinides, such as americium, curium and neptunium, constitute less than 1kg. However, these present an extreme hazard as they are intensely radioactive and long-lived nuclides that cause serious concern when it comes to storing them for more than 100,000 years.

Professor Laurence Harwood, who led the research at Reading, said: "The minor actinides are highly radioactive and have half lives up to millions of years. If these can be removed they could be used as fuel in the new generation of nuclear reactors that will come on-stream around 2025 and converted to non-radioactive material.  Being able to separate out the minor actinides even now already makes storage simpler and reduces the security risk as well.

"Our research has produced molecules capable of removing 99.9%of the minor actinides left after reprocessing spent fuel, ensuring much smaller levels of radioactive waste would accrue and remain hazardous for a much shorter period of time; a few hundred years, rather than effectively forever."

More information: The research, ‘Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand', can be viewed at http://centaur.rea … 0000170.html

Provided by University of Reading

First chemical complex consisting of rare earth metals and boron atoms produces unexpected results

Boron is an intriguing member of the periodic table because it readily forms stable compounds using only six electrons—two fewer than most other main-group elements. This means that chemists can easily add boron to unsaturated hydrocarbons, and then use electron-rich atoms, such as oxygen, to change organoborons into versatile units such as alcohols and esters. Recently, researchers found that combining transition metals with boron ligands produces catalysts powerful enough to transform even fully saturated hydrocarbons into new organic functionalities with high selectivity.

Now, Zhaomin Hou and colleagues from the RIKEN Advanced Science Institute in Wako have made another breakthrough in this field: they have created the first-ever complexes between boron ligands and rare earth metals1. Because these novel chemical combinations display a surprising ability to incorporate molecules such as carbon monoxide into their frameworks, they have potential applications that range from synthesizing organic substrates to controlling noxious emissions.

Rare earth metals are hot commodities because they are vital for products in high demand such as smartphones and electric cars (Fig. 1). However, full chemical studies of these elements are only in their infancy since they are difficult to handle under normal conditions. 

According to Hou, typical methods to prepare transition metal–boron complexes—halogen or metal exchange reactions, for example—seemed unsuitable for rare earth metals. Instead, the team used a vigorous lithium–boron compound to handle the reactive rare earth precursors, producing previously unseen scandium–(Sc–B) and gadolinium–boron (Gd–B) complexes in good yields, but not without difficulty. “Rare earth–boron compounds are air- and moisture-sensitive and sometimes thermally unstable,” says Hou. “They therefore require great care in isolation and handling.”

To determine whether or not the Sc–B complex could act as a nucleophile—an important electron-donating reagent in organic chemistry—the team reacted it with N,N,-diisopropylcarbodiimide, a molecule that easily accepts electrons to change into an amidinate salt. X-ray analysis revealed that initially, the carbodiimide became incorporated between Sc and carbon ligands on the rare earth metal, but extra quantities of the reagent became incorporated between the Sc–B bond. Furthermore, adding carbon monoxide to this mixture also caused a rare earth–boron insertion, accompanied by an unexpected rearrangement into a cyclic structure. 

Because chemists rely on insertion reactions to efficiently transform ligands into a diverse range of products, these findings should enable development of brand new synthetic techniques—opportunities that Hou and his team are actively pursuing.

More information: Li, S., et al.  Rare earth metal boryl complexes: Synthesis, structure, and insertion chemistry. Angewandte Chemie International Edition 50, 6360–6363 (2011). 

Provided by RIKEN (news : web)

New material shows promise for trapping pollutants

Water softening techniques are very effective for removing minerals such as calcium and magnesium, which occur as positively-charged ions in "hard" water. But many heavy metals and other inorganic pollutants form negatively-charged ions in water, and existing water treatment processes to remove them are inefficient and expensive.

Chemists at the University of California, Santa Cruz, have now developed a new type of material that can soak up negatively-charged pollutants from water. The new material, which they call SLUG-26, could be used to treat polluted water through an ion exchange process similar to water softening. In a water softener, sodium ions weakly attached to a negatively-charged resin are exchanged for the hard-water minerals, which are held more tightly by the resin. SLUG-26 provides a positively-charged substrate that can exchange a nontoxic negative ion for the negatively-charged pollutants.

"Our goal for the past 12 years has been to make materials that can trap pollutants, and we finally got what we wanted. The data show that the exchange process works," said Scott Oliver, associate professor of chemistry at UC Santa Cruz.

The chemical name for SLUG-26 is copper hydroxide ethanedisulfonate. It has a layered structure of positively-charged two-dimensional sheets with a high capacity for holding onto negative ions. Oliver and UCSC graduate student Honghan Fei described the compound in a paper that will be published in the journal Angewandte Chemie and is currently available online.

The researchers are currently focusing on the use of SLUG-26 to trap the radioactive metal technetium, which is a major concern for long-term disposal of radioactive waste. Technetium is produced in nuclear reactors and has a long half-life of 212,000 years. It forms the negative ion pertechnetate in water and can leach out of solid waste, making groundwater contamination a serious concern.

"It's a problem because of its environmental mobility, so they need new ways to trap it," Oliver said.

In their initial studies, the researchers used manganese, which forms the negative ion permanganate, as a non-radioactive analog for technetium and pertechnetate. The next step will be to work with technetium and see if SLUG-26 performs as effectively as it did in the initial studies.

"Whether or not it can be used in the real world is still to be seen, but so far it looks very promising," Oliver said.

Provided by University of California - Santa Cruz (news : web)

Early detection of plant disease

Each year, plant viruses and fungal attacks lead to crop losses of up to 30 percent. That is why it is important to detect plant disease early on. Yet laboratory tests are expensive and often time-consuming. Researchers are now developing a low-cost quick test for use on site.

The farmer casts a worried gaze at his potato field: where only recently a lush green field of plants was growing, much of the foliage has now turned brown – presumably the result of a fungal disease. Usually, by the time the disease becomes visible, it is already too late. The course of the disease is then so advanced that there is little the farmer can do to counteract the damage done. To determine early on whether and how severely his plants are diseased, he would have to submit samples to a laboratory on a regular basis. There, researchers usually employ the ELISA method, a conventional detection method based on an antibody-antigen reaction. “These tests are expensive, though. It also takes up to two weeks before the farmer has the results of the tests. And by then, the disease has usually spread out across the entire field,” explains Dr. Florian Schröper of the Fraunhofer Institute for Molecular Biology and Applied Ecology IME in Aachen, Germany.

Researchers at the IME are now working on a new quick test that is to provide the farmer a low-cost analysis right there in the field. At the heart of the test is a magnetic reader devised by scientists at the Peter Grünberg Institute of the Forschungszentrum Jülich. The device has several excitation and detection coils arrayed in pairs. The excitation coils generate a high- and low-frequency magnetic field, while the detection coils measure the resulting mixed field. If magnetic particles penetrate the field, the measuring signal is modified. The result is shown on a display, expressed in millivolts. This permits conclusions about the concentration of magnetic particles in the field.

Researchers are making use of this mechanism to track down pathogens. “What we detect is not the virus itself but the magnetic particles that bond with the virus particles,” Schröper notes. These are first equipped with antibodies so that these can specifically target and dock onto the pathogens. This way, essentially there is a virus particle “stuck” to each magnetic particle. To ensure that these are in proportion to one another, researchers use a method that functions similarly to the ELISA principle. They introduce plant extract into a tiny filtration tube filled with a polymer matrix to which specific antibodies were bound. When the plant solution passes through the tube, the virus particles are trapped in the matrix. Following a purification step, the experts add the magnetic particles modified with antibodies. These, in turn, dock onto the antigens in the matrix. A subsequent purification step removes all of the unbound particles. The tube is then placed in an appliance in the magnet reader to measure the concentration of magnetic particles. The researchers have already achieved promising results in initial tests involving the grapevine virus: the measured values reached a level of sensitivity ten times that of the ELISA method. Currently, Schröper and his team are working to expand their tests to other pathogens such as the mold spore Aspergillus flavus.

The mobile mini-lab needs to be made more user-friendly, however, before it is ready for widespread use in the field. Rather than grapple with measurements in millivolts, farmers should be able to consult the display and determine directly how severe the level of crop disease is. If possible, the scientists also want to reduce the number of analytical steps, and hence the detection time involved.

Provided by Fraunhofer-Gesellschaft (news : web)

Scientists pinpoint shape-shifting mechanism critical to protein signaling

In a joint study, scientists from the California and Florida campuses of The Scripps Research Institute have shown that changes in a protein's structure can change its signaling function and they have pinpointed the precise regions where those changes take place.

The new findings could help provide a much clearer picture of potential drugs that would be both effective and highly specific in their biological actions.

The study, led by Patrick Griffin of Scripps Florida and Raymond Stevens of Scripps California, was published in a recent edition of the journal Structure.

The new study focuses on the ß2-adrenergic receptor, a member of the G protein-coupled receptor family. G protein-coupled receptors convert extracellular stimuli into intracellular signals through various pathways. Approximately one third of currently marketed drugs (including for diabetes and heart disease) target these receptors.

Scientists have known that when specific regions of the receptor are activated by neurotransmitters or hormones, the structural arrangement (conformation) of the receptor is changed along with its function.

"While it's accepted that these receptors adopt multiple conformations and that each conformation triggers a specific type of signaling, the molecular mechanism behind that flexibility has been something of a black box," said Griffin, who is chair of the Scripps Research Department of Molecular Therapeutics and director of the Scripps Florida Translational Research Institute. "Our findings shed significant light to it."

The study describes in structural detail the various regions of the receptor that are involved in the changes brought about by selective ligands (ligands are molecules that bind to proteins to form an active complex), which, like a rheostat, run the gamut among activating the receptor, shutting it down, and reversing its function, as well as producing various states in between.

To achieve the results described in the study, the team used hydrogen-deuterium (HDX) mass spectrometry to measure the impact of interaction of various functionally selective ligands with the ß2-adrenergic receptor. A mass spectrometer determines the mass of fragments from the receptor by measuring the mass-to-charge ratio of their ions. HDX has been used to examine changes in the shape of proteins and how these shape changes relate to protein function. The approach is often used to characterize protein-protein interactions that are critical for signal transduction in cells and to study protein-folding pathways that are critical to cell survival.

"At this early stage in understanding GPCR structure and function, it is important to view the entire receptor in combination with probing very specific regions," said Stevens, who is a professor in the Scripps Research Department of Molecular Biology. "Hydrogen-deuterium exchange mass spectrometry has the right timescale and resolution to asked important questions about complete receptor conformations in regards to different pharmacological ligand binding. The HDX data combined with the structural data emerging will really help everyone more fully understand how these receptors work."

"Using the HDX technology we can study the intact receptor upon interaction with ligands and pinpoint regions of the receptor that have undergone change in position or flexibility," Griffin said. "By studying a set of ligands one can start to develop patterns that are tied to activation of the receptor or shutting it down. Once we get a picture of what a functional ligand looks like, it might be possible to develop a drug to produce a highly selective therapeutic effect."

More information: "Ligand-Dependent Perturbation of the Conformational Ensemble for the GPCR b2 Adrenergic Receptor Revealed by HDX," Structure.

Provided by The Scripps Research Institute (news : web)

Need for new magnet materials drives ORNL research

Increasing demand and a shrinking supply of rare earth elements for magnets creates a perfect opportunity for a research team from Oak Ridge National Laboratory and the University of Minnesota. The goal is to create a recipe for a replacement that doesn't use scarce ingredients.

"Worldwide demand for rare earths is expected to exceed supply by some 40,000 tons annually by the end of this decade," said Larry Allard, a researcher in ORNL's Materials Science and Technology Division. "In the past, 95 percent of that material has been supplied to the world by China, but in recent years China has begun limiting exports and by 2015 is expected to become a net importer."

The prospect of not having enough rare earth elements such as neodymium and dysprosium for magnets looms large for industries that need them for products we count on every day.

Most people never give it a second thought, but magnets are used in everything from the motors that power hybrid vehicles and electric windows to windmills, computers and hundreds of items that touch our lives every day. The traction drive components of a Toyota Prius, for example, use about 2 pounds of magnet materials while a 3-megawatt windmill uses 550 pounds. Today's automobiles and light trucks each use between 70 and 150 magnets to operate the speedometer, odometer, gas gauge, antilock brake systems, air bag sensors, fuel pumps and dozens of other systems.

In the home, magnets are even more common as they are found in door chimes, security systems, personal computers, printers, telephones, furnaces and air conditioning systems, garage door openers, refrigerators, freezers, workshop tools, hair dryers and electric shavers. It's difficult to imagine a world with no magnets. From an economics and national security perspective, it would be catastrophic.

That's why researchers like Allard, Edgar Lara-Curzio and Mike Brady of ORNL and Jian-Ping Wang of the University of Minnesota are focused on developing magnets made from abundant and inexpensive materials. Of specific interest is an iron nitride compound with a specific phase that potentially exhibits the highest saturation magnetization ever reported for a material.

"This is a critical parameter related to the highest degree to which a material can be magnetized," said Allard, who noted that this particular iteration of the iron-nitrogen compound has values up to 18 percent higher than the best commercial alloy, iron cobalt. The problem is that this material is metastable and exhibits relatively low coercivity, which means it can be demagnetized easily. The best permanent magnets - such as those made of neodymium-iron-boride - score high in these areas.

Working with Wang, Allard, Lara-Curzio and Brady will devise a method of producing this pure phase iron nitride compound and use specialized modeling methods to better understand the role of alloying additions that might stabilize the material so it retains its magnetic properties. Through their efforts, the researchers hope to better understand the magnetic behavior of the "alpha double prime" phase by correlating microstructure at the atomic level to processing and magnetic behavior.

Once researchers have answered these questions, their goal is to make bulk quantities of the material and move toward their ultimate goal of replacing neodymium-iron-boride magnets for automotive and other energy technology uses. This work with the University of Minnesota builds on previous work with Wang in which ORNL researchers were able to characterize iron nitride films with demonstrated potential. Allard noted that the Spallation Neutron Source made it possible to perform polarized neutron reflectometry, a test performed by Valeria Lauter to determine magnetic property.

In a separate effort, ORNL's David Parker hopes to computationally screen dozens of materials and then mix elements that emerge as promising candidates in a way to create a compound that will behave like rare earth elements. This material must also be scalable, retain its magnetic properties under varying conditions and meet cost-performance criteria. Parker noted that often the compounds identified as having desirable properties consist of elements with greatly differing melting points, stabilities and other traits and can prove very difficult to controllably manufacture. That's where ORNL's unique capabilities come into play.

"We have a suite of conventional and novel processing approaches to try to make the computationally predicted compounds, including a range of powder consolidation and gas reaction approaches," said Parker, who noted that there's nothing "sacred" about rare earth elements.

"Their main advantage is that due to their large nuclear charge, spin-orbit coupling is very strong and serves to fix the magnetization direction of the unpaired electrons," Parker said. "Other heavy elements may play the same role."

By employing strategic computational screening and ORNL's specialized microscopy and characterization skills, Allard and Parker believe they can make great strides toward solving a problem of national importance.

Provided by Oak Ridge National Laboratory (news : web)

Old fruit peel are the new healthy snacks

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A snapshot of Fruit-Peelo. Credit: UiTM

Japanese food researchers Noriham Abdullah, Marina Zulkifli, Mohd Hilmi Hassan, Wan Nur Zahidah Wan Zainon and Nur Ilmiah Alimin have developed a new healthy snack out of fruit peels to fulfil a growing need for fast, on-the-go health food.

There is a growing body of evidence suggesting health conscious consumers are becoming more experimental in selecting their healthier snacks alternatives. In response to this, a team of researchers from the Faculty of Applied Sciences used cheap and abundant agricultural by-products, such as mango and guava peels, to produce a leathery, bite size snacks called Fruity-Peelo.

Fruit peels contain high levels of polyphenols, carotenoids and other bioactive compounds which offer various health benefits. In addition, utilisation of such by-products is a promising measure from an environmental as well as an economic point of view.

Dr. Noriham Abdullah, the lead researcher, says that Fruity-Peelo is a tasty convenience snack with long shelf life that contains healthy compounds such as antioxidants, dietary fibres and Vitamin C.

The growing concerns over climbing obesity levels, combined with efforts to rejuvenate the image of the on-the-go healthy food options, have further improved Fruity Peelo’s prospect to fulfil a growing demand for convenience snacks that are healthy, quick and unique.

Provided by Universiti Teknologi MARA

Pair claim they can make ammonia to fuel cars for just 20 cents per liter

Fleming of SilverEagles Energy and Tim Maxwell from Texas Tech University, say they have developed a way to make ammonia that is cheap enough so that it could be used as fuel for cars. If their claims turn out to be true, many consumers might consider switching over because ammonia, when burned in an engine, emits nothing but nitrogen and water vapor out the tailpipe. And if that’s not enough incentive, they claim they can make the ammonia for just 20 cents a liter (approximately 75 cents a gallon).

The secret to their low cost estimates actually lie in their newly developed method for making hydrogen, which they use to make their ammonia. They say that by using a new kind of transformer that Fleming built, they can reduce the number of cells necessary for electrolysis to such a degree that they can produce hydrogen at almost half the cost of traditional electrolysis methods.

To make the ammonia, the hydrogen produced is pumped into a compression chamber where a piston squeezes it, causing it to heat up; in this case to 400C°. The result is then allowed to escape into another compartment where a reaction is set off by an iron oxide catalyst. This makes the hydrogen grow even hotter to the point where it begins creating ammonia. The ammonia and leftover hydrogen is then allowed to cool down and decompress in yet a third compartment, and in so doing causes another piston to move back and forth creating energy that is fed back into the system to help lower electric consumption. Then, the ammonia is chilled to -75C° and pumped into a tank for use.

Cars already on the road can use ammonia as an additive without modification (up to 10%) and flex cars could be, according to Fleming, easily modified to use ammonia in conjunction with ethanol, allowing for a mixture of 85% ammonia.

This is all still new technology of course, and apparently no one else has yet verified the claims of the duo, so until that happens, everyone will just have to wait and see if everything they say pans out. One thing not mentioned is the smell; the strong odor of gasoline at service stations is bad enough, it’s difficult to imagine the exceedingly noxious odor of ammonia permeating the air of such places instead.

More information: via Newscientist

 

Artificial light-harvesting method achieves 100% energy transfer efficiency

In an attempt to mimic the photosynthetic systems found in plants and some bacteria, scientists have taken a step toward developing an artificial light-harvesting system (LHS) that meets one of the crucial requirements for such systems: an approximately 100% energy transfer efficiency. Although high energy transfer efficiency is just one component of the development of a useful artificial LHS, the achievement could lead to clean solar-fuel technology that turns sunlight into chemical fuel.

The researchers, led by Shinsuke Takagi from the Tokyo Metropolitan University and PRESTO of the Japan Science and Technology Agency, have published their study on their work toward an artificial LHS in a recent issue of the Journal of the American Chemical Society.

“In order to realize an artificial light-harvesting system, almost 100% efficiency is necessary,” Takagi told PhysOrg.com. “Since light-harvesting systems consist of many steps of energy transfer, the total energy transfer efficiency becomes low if the energy transfer efficiency of each step is 90%. For example, if there are five energy transfer steps, the total energy transfer is 0.9 x 0.9 x 0.9 x 0.9 x 0.9 = 0.59. In this way, an efficient energy transfer reaction plays an important role in realizing efficient sunlight collection for an artificial light-harvesting system.”

As the researchers explain in their study, a natural LHS (like those in purple bacteria or plant leaves) is composed of regularly arranged molecules that efficiently collect sunlight and carry the excitation energy to the system’s reaction center. An artificial LHS (or “artificial leaf”) attempts to do the same thing by using functional dye molecules.

Building on the results of previous research, the scientists chose to use two types of porphyrin dye molecules for this purpose, which they arranged on a clay surface. The molecules’ tendency to aggregate or segregate on the clay surface made it challenging for the researchers to arrange the molecules in a regular pattern like their natural counterparts.

“A molecular arrangement with an appropriate intermolecular distance is important to achieve nearly 100% energy transfer efficiency,” Takagi said. “If the intermolecular distance is too near, other reactions such as electron transfer and/or photochemical reactions would occur. If the intermolecular distance is too far, deactivation of excited dye surpasses the energy transfer reaction.”

In order to achieve the appropriate intermolecular distance, the scientists developed a novel preparation technique based on matching the distances between the charged sites in the porphyrin molecules and the distances between negatively charged (anionic) sites on the clay surface. This effect, which the researchers call the “Size-Matching Rule,” helped to suppress the major factors that contributed to the porphyrin molecules’ tendency to aggregate or segregate, and fixed the molecules in an appropriate uniform intermolecular distance. As Takagi explained, this strategy is significantly different than other attempts at achieving molecular patterns.

“The methodology is unique,” he said. “In the case of usual self-assembly systems, the arrangement is realized by guest-guest interactions. In our system, host-guest interactions play a crucial role for realizing the special arrangement of dyes. Thus, by changing the host material, it is possible to control the molecular arrangement of dyes on the clay surface.”

As the researchers demonstrated, the regular arrangement of the molecules leads to an excited energy transfer efficiency of up to 100%. The results indicate that porphyrin dye molecules and clay host materials look like promising candidates for an artificial LHS.

“At the present, our system includes only two dyes,” Takagi said. “As the next step, the combination of several dyes to adsorb all sunlight is necessary. One of the characteristic points of our system is that it is easy to use several dyes at once. Thus, our system is a promising candidate for a real light-harvesting system that can use all sunlight. We believe that even photochemical reaction parts can be combined on the same clay surface. If this system is realized and is combined with a photochemical reaction center, this system can be called an ‘inorganic leaf.’”

More information: Yohei Ishida, et al. “Efficient Excited Energy Transfer Reaction in Clay/Porphyrin Complex toward an Artificial Light-Harvesting System.” Journal of the American Chemical Society. DOI:10/1021/ja204425u

 

Fast, cheap, and accurate: Detecting CO2 with a fluorescent twist

Detecting specific gases in the air is possible using a number of different existing technologies, but typically all of these suffer from one or more drawbacks including high energy cost, large size, slow detection speed, and sensitivity to humidity.

Overcoming these deficiencies with a unique approach, a team based at Kyoto University has designed an inexpensive new material capable of quick and accurate detection of a specific gas under a wide variety of circumstances. Moreover, in addition to being reusable, the compound gives off variable degrees of visible light in correspondence with different gas concentrations, providing for development of easy to use monitoring devices.

The findings, published in a recent issue of Nature Materials, describe the use of a flexible crystalline material (porous coordination polymer, or PCP) that transforms according to changes in the environment. When infused with a fluorescent reporter molecule (distyrylbenzene, or DSB), the composite becomes sensitive specifically to carbon dioxide gas, glowing with varying intensity based on changing concentrations of the gas. Lead author for the paper was Dr. Nobuhiro Yanai of the university's Graduate School of Engineering.

"The real test for us was to see whether the composite could differentiate between carbon dioxide and acetylene, which have similar physiochemical properties," explains Assoc. Prof. Takashi Uemura, also of the Graduate School of Engineering. "Our findings clearly show that this PCP-DSB combination reacts very differently to the two gases, making accurate CO2 detection possible in a wide variety of applications."

In its natural state, DSB is a long, flat molecule, which emits a blue light. When adsorbed by the PCP framework, DSB molecules twist, causing the entire PCP structure to also become skewed. In this condition, the glow of DSB diminishes significantly.

"On this occasion we observed that the presence of CO2 causes the DSB molecules to revert to their flat, brightly fluorescent form, while also returning the PCP grid to its usual state," adds Professor and deputy director Susumu Kitagawa of the university's Institute for Integrated Cell-Material Sciences (iCeMS). "And importantly, these steps can be reversed without causing any significant changes to the composite, making possible the development of a wide variety of specific, inexpensive, reusable gas detectors."

More information: "Gas detection by structural variations of fluorescent guest molecules in a flexible porous coordination polymer" by Nobuhiro Yanai, Koji Kitayama, Yuh Hijikata, Hiroshi Sato, Ryotaro Matsuda, Yoshiki Kubota, Masaki Takata, Motohiro Mizuno, Takashi Uemura, and Susumu Kitagawa, Nature Materials, Published online on September 4, 2011.

Provided by Kyoto University