Friday, September 2, 2011

Climate change and ozone destruction hastened with nitrous oxide used in agriculture

Researchers have discovered a new binding site for nitrous oxide (N2O). Nitrous oxide reductase, an enzyme containing copper, plays a key role in the biochemical process by reducing N2O to N2. This enzyme is highly sensitive to oxygen and is often precipitated in the reaction chain, meaning large amounts of N2O are released by fertilised fields in the farming industry.

Nitrous oxide (N2O) harms Earth's climate in two ways. First, N2O is a colourless and odourless greenhouse gas that is 300 times stronger than carbon dioxide (CO2). Second, under the effect of cosmic radiation, it contributes to the destruction of the ozone layer, like halocarbons, or chlorofluorocarbons (CFCs).

N2O is therefore probably the most critical greenhouse gas of the 21st century and is an unwanted by-product of industrial farming. Nitrous oxide reductase, an enzyme containing copper, plays a key role in the biochemical process by reducing N2O to N2. This enzyme is highly sensitive to oxygen and is often precipitated in the reaction chain, meaning large amounts of N2O are released by fertilised fields in the farming industry.

The functionality and mechanisms of this important enzyme had not been thoroughly researched until Dr Anja Pomowski successfully clarified the structure of a N2O reductase, primed under the strict exclusion of dioxygen (O2). Dr Pomowski belongs to the research group headed by Prof Dr Oliver Einsle, a professor at the Institute of Organic Chemistry and Biochemistry of the University of Freiburg and a member of the BIOSS Cluster of Excellence. Together with Prof Dr Walter Zumft from the Karlsruhe Institute of Technology and Prof Dr Peter Kroneck from the University of Konstanz, the team of researchers is presenting their results in the current issue of the journal Nature.

The newly discovered structure shows first that the ratio and amount of substances in the metal centre of the enzyme have only been described incompletely thus far, and that they contain an additional sulphur atom. Second, the team also identified the binding of the N2O substrate to the metal centre. This binding site was a surprise to the scientists, and it has encouraged them to re-evaluate the mechanisms of the enzyme, whose molecular properties Prof Dr Oliver Einsle's group will continue to research in the future.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Albert-Ludwigs-Universität Freiburg.

Journal Reference:

Anja Pomowski, Walter G. Zumft, Peter M. H. Kroneck, Oliver Einsle. N2O binding at a [4Cu:2S] copper–sulphur cluster in nitrous oxide reductase. Nature, 2011; DOI: 10.1038/nature10332

New method can speed development of organic semiconductors for flexible displays

Organic semiconductors hold immense promise for use in thin film and flexible displays -- picture an iPad you can roll up -- but they haven't yet reached the speeds needed to drive high definition displays. Inorganic materials such as silicon are fast and durable, but don't bend, so the search for a fast, durable organic semiconductor continues.

Now a team led by researchers at Stanford and Harvard universities has developed a new organic semiconductor material that is among the speediest yet. The scientists also accelerated the development process by using a predictive approach that lopped many months -- and could lop years -- off the typical timeline.

For the most part, developing a new organic electronic material has been a time-intensive, somewhat hit-or-miss process, requiring researchers to synthesize large numbers of candidate materials and then test them.

The Stanford and Harvard-led group decided to try a computational predictive approach to substantially narrow the field of candidates before expending the time and energy to make any of them.

"Synthesizing some of these compounds can take years," said Anatoliy Sokolov, a postdoctoral researcher in chemical engineering at Stanford, who worked on synthesizing the material the team eventually settled on. "It is not a simple thing to do."

Sokolov works in the laboratory of Zhenan Bao, an associate professor of chemical engineering at Stanford. They are among the authors of a paper describing the work, published in the Aug. 16 issue of Nature Communications. Alán Aspuru-Guzik, an associate professor of chemistry and chemical biology at Harvard, led the research group there and directed the theory and computation efforts.

The researchers used a material known as DNTT, which had already been shown to be a good organic semiconductor, as their starting point, then considered various compounds possessing chemical and electrical properties that seemed likely to enhance the parent material's performance if they were attached.

They came up with seven promising candidates.

Semiconductors are all about moving an electrical charge from one place to another as fast as possible. How well a material performs that task is determined by how easy is it for a charge to hop onto the material and how easily that charge can move from one molecule to another within the material.

Using the expected chemical and structural properties of the modified materials, the Harvard team predicted that two of the seven candidates would most readily accept a charge. They calculated that one of those two was markedly faster in passing that charge from molecule to molecule, so that became their choice. From their analysis, they expected the new material to be about twice as fast as its parent.

Sokolov, the Stanford researcher, said it took about a year and a half to perfect the synthesis of the new compound and make enough of it to test. "Our final yield from what we produced was something like 3 percent usable material and then we still had to purify it."

When the team members tested the final product, their predictions were borne out. The modified material doubled the speed of the parent material. For comparison, the new material is more than 30 times faster than the amorphous silicon currently used for liquid crystal displays in products such as flat panel televisions and computer monitors.

"It would have taken several years to both synthesize and characterize all the seven candidate compounds. With this approach, we were able to focus on the most promising candidate with the best performance, as predicted by theory," Bao said. "This is a rare example of truly 'rational' design of new high performance materials."

The researchers hope their predictive approach can serve as a blueprint for other research groups working to find a better material for organic semiconductors.

And they're eager to apply their method to the development of new, high-efficiency material for organic solar cells.

"In the case of renewable energy, we have no time for synthesizing all the possible candidates, we need theory to complement synthetic approaches to accelerate materials discovery," said Aspuru-Guzik.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Stanford University. The original article was written by Louis Bergeron.

Journal Reference:

Anatoliy N. Sokolov, Sule Atahan-Evrenk, Rajib Mondal, Hylke B. Akkerman, Roel S. Sánchez-Carrera, Sergio Granados-Focil, Joshua Schrier, Stefan C.B. Mannsfeld, Arjan P. Zoombelt, Zhenan Bao, Alán Aspuru-Guzik. From computational discovery to experimental characterization of a high hole mobility organic crystal. Nature Communications, 2011; 2: 437 DOI: 10.1038/ncomms1451

How to efficiently merge microdroplets using an electric field

ScienceDaily (Aug. 24, 2011) — In microfluidic devices, small separated droplets flow in a stream of carrier liquid. Occasionally, selected droplets have to be merged to carry out a chemical reaction. This can be greatly facilitated with the use of electric field, through a process of electrocoalescence that has been used industrially in large scale applications. Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences have discovered the laws governing the process and how to maximise the efficiency of the merging.

Small droplets in emulsions can merge much faster in the presence of an alternating electric field. The phenomenon is called electrocoalescence and is of essential importance for the operation of advanced microfluidic devices, allowing one to carry out chemical reactions in microliter volume or less. A recent study carried out at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) allows for improved control of electrocoalescence and for optimisation of the course of the process.

Electrocoalescence has been known for over 100 years. Originally, it has been used in the oil industry. Crude oil extracted from the sea floor contains significant amount of water in a form of droplets. Engineers have noticed that in the presence of an alternating electric field these droplets merge quickly and fall on the tank bottom from where the water can be easily removed. "Electrocoalescence has started its career untypically, from large scale applications in the oil industry. In microfluidics the phenomenon has been applied to merging of droplets only within the last few years," says Dr Piotr Garstecki from the IPC PAS.

Microfluidic devices are miniaturised chemical reactors resembling a credit card in size. Chemical reactions take place inside the droplets that are suspended in a neutral liquid flowing through appropriately designed microchannels. The droplets can be very small: from a fraction of a microliter even down to nano- or picoliters.

"The primary challenge in microfluidic techniques is to combine the stability of droplets with the ability to merge them. Stabilization requires covering the interface with a surfactant, i.e., a surface active agent," explains Tomasz Szymborski, a PhD student at the Institute of Physical Chemistry of the PAS. Surfactant molecules are composed of a hydrophilic (water-loving) and a hydrophobic (water-hating) part. If a water droplet is placed in oil, the surfactant covers it so that the hydrophilic parts are immersed in the droplet, whereas the hydrophobic ones remain in oil. "From outside, the droplets covered with surfactant resemble rolled up hedgehogs and have no chance to touch each other. Their stability is increased due to the fact that surfactant molecules repel each other via electrostatic and entropic forces," explains Szymborski.

Problems appear when precisely selected droplets of different reagents are to be merged in a microfluidic device to carry out a chemical reaction. Since recently electric field has been used to induce merging. Electrocoalescence is known for its macro scale industrial applications, yet how the mechanism and efficiency of the process depends on the parameters of the electric field was largely an open question.

The researchers at the IPC PAS observed merging of water microdroplets in a carried liquid, hexadecane. The rate of droplet merging increased in line with applied voltage and the frequency of electric field oscillations. For each voltage there was a limiting frequency, above which the droplets became stable again. "We showed that the merging proceeded at its maximum rate when the electric field oscillated with a frequency close to a threshold one and we found a simple function allowing to estimate the value of the threshold quickly," says Szymborski.

Rapid merging of droplets is related, i.a., to a periodic movement of ions contained in the droplets that are stimulated by an alternating electric field. The ions separate in the oil-droplet interface while charging it electrically. The droplets with opposite charges attract strongly, which results in droplet merging in spite of the presence of stabilizing surfactants. The results of the study suggest that there is a simple relation between the nanoscopic electrostatic screening length and the optimum frequency for merging of droplets.

The data collected at the IPC PAS will be helpful for practical optimisation of processes involving electrocoalescence, both in microfluidic devices and industrial plants. The results will also facilitate formulation of universal laws describing the efficiency of electrocoalescence in non-equilibrium systems such as flowing liquids.

The research has been financed from a TEAM grant from the Foundation for Polish Science and the Iuventus-Plus Programme of the Polish Ministry of Science and Higher Education.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Institute of Physical Chemistry of the Polish Academy of Sciences, via AlphaGalileo.

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.

New set of building blocks for simple synthesis of complex molecules

 Assembling chemicals can be like putting together a puzzle. University of Illinois chemists have developed a way of fitting the pieces together to more efficiently build complex molecules, beginning with a powerful and promising antioxidant.

Led by chemistry professor Martin Burke, the team published its research on the cover of the chemistry journal Angewandte Chemie.

Burke's group is known for developing a synthesis technique called iterative cross-coupling (ICC) that uses simple, stable chemical "building blocks" sequentially joined in a repetitive reaction. With more than 75 of the building blocks available commercially, pharmaceutical companies and other laboratories use ICC to create complex small molecules that could have medicinal properties.

"There's pre-installed functionality and stereochemistry, so everything is set in the building blocks, and all you have to do is couple them together," said graduate student Seiko Fujii, the first author of the paper.

However, ICC has been limited to only molecules with one type of polarity. Now, the group has developed reverse-polarity ICC, which allows a chemist to optimize the ICC process to match the target molecules' electronic structure. The reversal in polarity enables a whole new class of building blocks, so researchers can synthesize molecules more efficiently and even construct molecules that standard ICC cannot.

For example, in the paper, the group used the new method to make synechoxanthin (pronounced sin-ecko-ZAN-thin), a molecule first isolated from bacteria in 2008 that shows great promise as an antioxidant. Studies suggest that synechoxanthin allows the bacteria that produce it to live and thrive in highly oxidative environments.

"We as humans experience a lot of oxidative stress, and it can be really deleterious to human health," said Burke, who also is affiliated with the Howard Hughes Medical Institute. "It can lead to diseases like cancer and atherosclerosis and neurodegenerative disorders. Evidence strongly suggests that synechoxanthin is a major part of the bacteria's solution to this problem. We're excited to ask the question, what can we learn from the bug? Can it also protect a human cell?"

Studies on the activity of synechoxanthin have been limited by the difficulty of extracting the molecule from bacterial cultures. Burke's group successfully synthesized it from a mere three types of readily available, highly stable, non-toxic building blocks. Thanks to the ease of ICC, they can produce relatively large quantities of synechoxanthin for study as well as derivatives to test against the natural product.

"Because this building-block-based design is inherently flexible, once we've made the natural product, we can make any derivative we want simply by swapping in one different building block, and then using the reverse-polarity ICC to snap them together," Burke said. "That's where synthesis is so powerful. Oftentimes, the cleanest experiment will require a molecule that doesn't exist, unless you can piece it together."

Researchers can also use blocks that have been "tagged" with a fluorescent or radioactive dye to make it easier to study the molecule and its activity. For example, Fujii next plans to synthesize both synechoxanthin and its apolar derivative with tags so that NMR imaging can reveal its location and orientation within a cell's membrane, possibly providing clues to its activity.

"After we have all these molecules in hand, we're really excited to test the antioxidant activity of them in a model membrane," Fujii said.

The National Institutes of Health and the Howard Hughes Medical Institute supported this work.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Illinois at Urbana-Champaign.

Journal Reference:

Seiko Fujii, Stephanie Y. Chang, Martin D. Burke. Total Synthesis of Synechoxanthin through Iterative Cross-Coupling. Angewandte Chemie International Edition, 2011; 50 (34): 7862 DOI: 10.1002/anie.201102688

Nano bundles pack a powerful punch: Solid-state energy storage takes a leap forward

Rice University researchers have created a solid-state, nanotube-based supercapacitor that promises to combine the best qualities of high-energy batteries and fast-charging capacitors in a device suitable for extreme environments.

A paper from the Rice lab of chemist Robert Hauge, to be published in the journal Carbon, reported the creation of robust, versatile energy storage that can be deeply integrated into the manufacture of devices. Potential uses span on-chip nanocircuitry to entire power plants.

Standard capacitors that regulate flow or supply quick bursts of power can be discharged and recharged hundreds of thousands of times. Electric double-layer capacitors (EDLCs), generally known as supercapacitors, are hybrids that hold hundreds of times more energy than a standard capacitor, like a battery, while retaining their fast charge/discharge capabilities.

But traditional EDLCs rely on liquid or gel-like electrolytes that can break down in very hot or cold conditions. In Rice's supercapacitor, a solid, nanoscale coat of oxide dielectric material replaces electrolytes entirely.

The researchers also took advantage of scale. The key to high capacitance is giving electrons more surface area to inhabit, and nothing on Earth has more potential for packing a lot of surface area into a small space than carbon nanotubes.

When grown, nanotubes self-assemble into dense, aligned structures that resemble microscopic shag carpets. Even after they're turned into self-contained supercapacitors, each bundle of nanotubes is 500 times longer than it is wide. A tiny chip may contain hundreds of thousands of bundles.

For the new device, the Rice team grew an array of 15-20 nanometer bundles of single-walled carbon nanotubes up to 50 microns long. Hauge, a distinguished faculty fellow in chemistry, led the effort with former Rice graduate students Cary Pint, first author of the paper and now a researcher at Intel, and Nolan Nicholas, now a researcher at Matric.

The array was then transferred to a copper electrode with thin layers of gold and titanium to aid adhesion and electrical stability. The nanotube bundles (the primary electrodes) were doped with sulfuric acid to enhance their conductive properties; then they were covered with thin coats of aluminum oxide (the dielectric layer) and aluminum-doped zinc oxide (the counterelectrode) through a process called atomic layer deposition (ALD). A top electrode of silver paint completed the circuit.

"Essentially, you get this metal/insulator/metal structure," said Pint. "No one's ever done this with such a high-aspect-ratio material and utilizing a process like ALD."

Hauge said the new supercapacitor is stable and scaleable. "All solid-state solutions to energy storage will be intimately integrated into many future devices, including flexible displays, bio-implants, many types of sensors and all electronic applications that benefit from fast charge and discharge rates," he said.

Pint said the supercapacitor holds a charge under high-frequency cycling and can be naturally integrated into materials. He envisioned an electric car body that is a battery, or a microrobot with an onboard, nontoxic power supply that can be injected for therapeutic purposes into a patient's bloodstream.

Pint said it would be ideal for use under the kind of extreme conditions experienced by desert-based solar cells or in satellites, where weight is also a critical factor. "The challenge for the future of energy systems is to integrate things more efficiently. This solid-state architecture is at the cutting edge," he said.

Co-authors of the paper include graduate student Zhengzong Sun; James Tour, the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science, and Howard Schmidt, adjunct assistant professor of chemical and biomolecular engineering, all of Rice; Sheng Xu, a former graduate student at Harvard; and Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry at Harvard University, who developed ALD.

Story Source:

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

Journal Reference:

Cary L. Pint, Nolan W. Nicholas, Sheng Xu, Zhengzong Sun, James M. Tour, Howard K. Schmidt, Roy G. Gordon, Robert H. Hauge. Three dimensional solid-state supercapacitors from aligned single-walled carbon nanotube array templates. Carbon, 2011; 49 (14): 4890 DOI: 10.1016/j.carbon.2011.07.011