Sunday, April 3, 2011

Researchers electrify polymerization

Scientists led by Carnegie Mellon University chemist Krzysztof Matyjaszewski are using electricity from a battery to drive atom transfer radical polymerization (ATRP), a widely used method of creating industrial plastics. The environmentally friendly approach, reported in the April 1 issue of Science, represents a breakthrough in the level of control scientists can achieve over the ATRP process, which will allow for the creation of even more complex and specialized materials.

ATRP, first developed by Matyjaszewski in 1995, allows scientists to easily form polymers by putting together component parts, called monomers, in a controlled piece-by-piece fashion. Assembling polymers in such a manner has allowed scientists to create a wide range of polymers with highly specific, tailored functionalities. ATRP has been used to develop cosmetics, coatings, adhesives and drug delivery systems, and is used to develop "smart" materials -- those that respond to environmental changes, such as changes in temperature, light, pressure or pH.

The current study represents the latest in a series of advances Matyjaszewski's research group has made since ATRP's inception that make the technique more precise and more environmentally friendly. In a process they are calling electrochemically mediated ATRP, or eATRP, the researchers used a computer-controlled battery to apply an electrochemical potential across the ATRP reaction.

"This marks the first time that we've paired electrochemistry with ATRP, and the results were startlingly successful," said Matyjaszewski, the J.C. Warner Professor of Natural Sciences at CMU. "We found that by adjusting the current and voltage we could slow and speed up, or even start and stop the reaction on-demand. This gives us a great deal more flexibility in conducting our reactions that should lead to the development of precisely engineered materials."

In traditional ATRP reactions scientists use a copper catalyst to grow a complex polymer structure by adding a few monomeric units at a time to the polymer chain. The process relies on paired reduction-oxidation (redox) reactions between two species of copper -- the activator CuI and deactivator CuII -- where the two catalysts exchange electrons back and forth. Occasionally, one of the exchanges will spontaneously stop, called a radical termination, resulting in the accumulation of CuII. To keep the polymerization going, researchers must rebalance the system by compensating for the excess CuII.

In the early ATRP experiments, scientists addressed this problem by adding more CuI to the system. This generated materials with high, sometimes toxic, levels of copper, reaching around 5,000 parts-per-million (ppm). Such levels of copper are hard to remove using current industrial equipment. As an alternative, Matyjaszewski and colleagues developed novel methods for using activators and reducing agents to reactivate the CuII. Most notably, they found that environmentally friendly reducing agents like sugars or vitamin C were highly effective in reducing the amount of copper catalyst used in ATRP reactions.

In the current study, Matyjaszewski and Visiting Assistant Professor of Chemistry Andrew Magenau looked to electrochemistry as a means for maintaining balance in ATRP reactions. They found that adding electricity capitalized on the redox reaction by moderating the transfer of electrons. This allowed them to compensate for the radical terminations and reduce the amount of copper needed to run ATRP. As a result the amount of copper in the system was reduced to 50 ppm, a 100-fold decrease. In terms of creating a greener, less toxic form of ATRP, this amount rivaled Matyjaszewski's previous studies that used vitamin C and sugars as reducing agents, but has the added benefit of not requiring the addition of any additional organic or inorganic reducing agents.

The researchers found that applying electricity to the system also gave them more precise control over the reaction. The computer-controlled battery allowed them to manipulate the ATRP process in real-time by changing the current or voltage.

The researchers have used this process to create the standard types of polymers made with ATRP: star, brush and block copolymers. They believe that the meticulous control eATRP gives them over the rate of polymerization will allow for the creation of polymers with even more complex architectures.

Co-authors of the study include Nicholas Strandwitz from the Kavli Nanoscience Institute and Beckman Institute at the California Institute of Technology and Armando Gennaro of the University of Padova, Italy.

The study was funded by the National Science Foundation and the CRP Consortium at Carnegie Mellon.

Story Source:

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

Journal Reference:

Andrew J. D. Magenau, . Nicholas C. Strandwitz, . Armando Gennaro and Krzysztof Matyjaszewski. Electrochemically Mediated Atom Transfer Radical Polymerization. Science, 1 April 2011: Vol. 332 no. 6025 pp. 81-84 DOI: 10.1126/science.1202357

Advance toward making biodegradable plastics from waste chicken feathers

In a scientific advance literally plucked from the waste heap, scientists have described a key step toward using the billions of pounds of waste chicken feathers produced each year to make one of the more important kinds of plastic. They described the new method at the 241st National Meeting & Exposition of the American Chemical Society, being held in Anaheim, California the week of March 28.

"Others have tried to develop thermoplastics from feathers," said Yiqi Yang, Ph.D., who reported on the research. "But none of them perform well when wet. Using this technique, we believe we're the first to demonstrate that we can make chicken-feather-based thermoplastics stable in water while still maintaining strong mechanical properties."

Thermoplastics are one of two major groups of plastics, and include nylon, polyethylene, polystyrene, polyvinyl chloride, and dozens of other kinds. They are used to make thousands of consumer and industrial products ranging from toothbrush bristles to soda pop bottles to car bumpers. Thermoplastics got that name because they need heat (or chemicals) to harden from a liquid into a final shape, and can be melted and remolded time and again. The other group, thermosetting plastics, harden once and can't be remelted again.

Yang pointed out that both kinds of plastics are made mainly from ingredients obtained from oil or natural gas. Because of concerns about petroleum supplies, prices, and sustainability, dozens of scientific teams are working to find alternative ingredients. One major goal is to use agricultural waste and other renewable resources to make bioplastics that have an additional advantage of being biodegradable once discarded into the environment.

"We are trying to develop plastics from renewable resources to replace those derived from petroleum products," said Yang, who is an authority on biomaterials and biofibers in the Institute of Agriculture & Natural Resources at the University of Nebraska-Lincoln. "Utilizing current wastes as alternative sources for materials is one of the best approaches toward a more sustainable and more environmentally responsible society."

Chicken feathers are an excellent prospect, Yang explained, because they are inexpensive and abundant. Few shoppers think about it, but every shrink-wrapped broiler in the supermarket cooler leaves behind a few ounces of feathers. Annually there are more than 3 billion pounds of waste chicken feathers in the United States alone. These feathers can be processed into a low-grade animal feed, but that adds little value to the feathers and may also cause diseases in the animals. All too often, they become a waste disposal/environmental pollution headache, incinerated or stored in landfills.

Yang explained that chicken feathers are made mainly of keratin, a tough protein also found in hair, hoofs, horns, and wool that can lend strength and durability to plastics. Yang added that the mechanical properties of feather films outperform other biobased products, such as modified starch or plant proteins.

To develop the new water-resistant thermoplastic, Yang and colleagues processed chicken feathers with chemicals, including methyl acrylate, a colorless liquid found in nail polish that undergoes polymerization -- that's the process used in producing plastics in which molecules link together one by one into huge chains. This process resulted in films of what Yang's group terms "feather-g-poly(methyl acrylate)" plastic. It had excellent properties as a thermoplastic, was substantially stronger and more resistant to tearing than plastics made from soy protein or starch, and as a first among chicken-feather plastics had good resistance to water.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by American Chemical Society.

Neutral atoms made to act like electrically charged particles

Completing the story they started by creating synthetic magnetic fields, scientists from the Joint Quantum Institute (JQI), a collaboration of the National Institute of Standards and Technology (NIST) and the University of Maryland, have now made atoms act as if they were charged particles accelerated by electric fields.

Reported in the journal Nature Physics, these synthetic electric fields make each atom in a gas act, individually, as if it were a charged particle, but collectively they remain neutral, uncharged particles. This dual personality will help researchers simulate and study fundamental electrical phenomena and may lead to a deeper understanding of exotic phenomena involving charged particles such as superconductivity, the flow of electricity without resistance, or the quantum Hall effect, used by NIST to create a standard of electrical resistance.

Some aspects of electricity are difficult to study because, although oppositely charged particles are attracted to one another, similarly charged particles are repelled by one another. To get around this, NIST physicist Ian Spielman and his colleagues realized that they could make atoms, which are typically electrically neutral, act as if they are charged particles in an electric field -- extending their earlier method for making neutral atoms act like charged particles in a magnetic field.

The researchers create their synthetic electric field in an ultracold gas of several hundred thousand rubidium atoms. Using lasers, the team alters the atoms' energy-momentum relationship. This had the effect of transferring a bit of the lasers' momentum to the atoms, causing them to move. The force on each atom is physically identical -- and mathematically equivalent -- to what a charged particle would feel in an electric field.

So while the neutral atoms each experience the force of this synthetic electric field individually, they do not repel each other as would true charged particles in an ordinary electric field. This is analogous to an experienced group of dancers all following the moves of their instructor without getting in each other's way.

According to Spielman, this work may enable scientists to study the Hall effect, a phenomenon where an electromagnetic field can cause charged particles traveling through a conductor to experience a sideways force, which has of yet been unobserved in cold-atom systems. The work may also facilitate measurements of the atomic equivalents of electrical quantities such as resistance and inductance. For neutral atoms in synthetic electric fields, inductance is a measure of the energy that is stored as a result of the atoms' motion, and resistance is a measure of the dissipation, or energy loss, in the system. Measuring these quantities could provide insights into the properties of charged particles in analogous systems, including superconductors.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Y-J. Lin, R. L. Compton, K. Jiménez-García, W. D. Phillips, J. V. Porto, I. B. Spielman. A synthetic electric force acting on neutral atoms. Nature Physics, 2011; DOI: 10.1038/nphys1954

Imaging the paintings under the paintings of the Old Masters

 Gaze upon Rembrandt's The Night Watch, or one of the great Dutch master's famous self-portraits. Contemplate Caravaggio's Boy with a Basket of Fruit, Supper at Emmaus, or the famed Italian artist's Seven Works of Mercy. Admire Peter Paul Rubens' Prometheus Bound, Portrait of Władysław IV, or the Flemish baroque painter's The Exchange of Princesses.

Speaking at the 241st National meeting & Exposition of the American Chemical Society, an international team of scientists have now described use of a new technique to see the paintings under the paintings of Rembrandt, Caravaggio, Rubens, and other 17th Century Old Master painters. The report by scientists in Belgium, The Netherlands and the United States was among almost two dozen studies presented as part of a symposium on chemistry and art titled "Partnerships and New Analytical Methodologies at the Interface of Chemistry and Art," presented on March 29 in Anaheim, California.

"The underpainting was the first and most important step in creating a work of art," explained lead scientist Matthias Alfeld, who is with the University of Antwerp in Belgium. "It was the sketch that guided the artist through the creative process. The Old Masters generally used to roughly indicate light, shade and contours. Observation of the underpainting would allow us to see the first execution of the artist's vision of the painting. It's a more detailed look over the shoulder of the artist at work. But the underpainting has virtually escaped all imaging efforts. So far, our methods to visualize the underpainting, except in localized cross sections, have been very limited."

Alfeld and colleagues described use of a powerful new technique called scanning macro X-ray fluorescence analysis that allows more detailed imaging of the composition of underpaintings. It is portable enough for use on-the-scene in museums and does not harm priceless artwork. The technology already has provided new insights into the nature of the paint that some Old Masters used in their underpainting.

An analysis of paintings from the workshops of Rembrandt and Caravaggio, for instance, led them to the conclusion that the Old Masters were more frugal than fussy about the paint used for the underpainting. The analysis suggested that this brown pigment mixture in underpaintings actually consisted of recycled leftovers from the artist scraping his palette clean.

"Using the new technique, we hope to disperse doubts about the authenticity of several paintings or to confirm that these paintings were not by the painter they have been attributed to," Alfeld said. "It is nice to show that the world of art can intersect with chemistry. Chemistry is such an all-encompassing science. Imagine, chemistry isn't just about molecules and reactions, but it also involves also the study of something as beautiful as great works of art."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Chemical Society.

'Spincasting' holds promise for creation of nanoparticle thin films

 Researchers from North Carolina State University have investigated the viability of a technique called "spincasting" for creating thin films of nanoparticles on an underlying substrate -- an important step in the creation of materials with a variety of uses, from optics to electronics.

Spincasting, which utilizes centrifugal force to distribute a liquid onto a solid substrate, already has a variety of uses. For example, it is used in the electronics industry to deposit organic thin films on silicon wafers to create transistors.

For this study, the researchers first dispersed magnetic nanoparticles coated with ligands into a solution. The ligands, small organic molecules that bond directly to metals, facilitate the even distribution of the nanoparticles in the solution -- and, later, on the substrate itself.

A drop of the solution was then placed on a silicon chip that had been coated with a layer of silicon nitride. The chip was then rotated at high speed, which spread the nanoparticle solution over the surface of the chip. As the solution dried, a thin layer of nanoparticles was left on the surface of the substrate.

Using this technique, the researchers were able to create an ordered layer of nanoparticles on the substrate, over an area covering a few square microns. "The results are promising, and this approach definitely merits further investigation," says Dr. Joe Tracy, an assistant professor of materials science and engineering at NC State and co-author of a paper describing the study.

Tracy explains that one benefit of spincasting is that it is a relatively quick way to deposit a layer of nanoparticles. "It also has commercial potential as a cost-effective way of creating nanoparticle thin films," Tracy says.

However, the approach still faces several hurdles. Tracy notes that modifications to the technique are needed, so that it can be used to coat a larger surface area with nanoparticles. Additional research is also needed to learn how, or whether, the technique can be modified to achieve a more even distribution of nanoparticles over that surface area.

Analysis of the nanoparticle films created using spincasting led to another development as well. The researchers adapted analytical tools to evaluate transmission electron microscopy images of the films they created. One benefit of using these graphical tools is their ability to identify and highlight defects in the crystalline structure of the layer. "These methods for image analysis allow us to gain a detailed understanding of how the nanoparticle size and shape distributions affect packing into monolayers," Tracy says.

The paper, "Formation and Grain Analysis of Spin Cast Magnetic Nanoparticle Monolayers," was published online March 24 by the journal Langmuir. The paper was co-authored by Tracy; NC State Ph.D. student Aaron Johnston-Peck; and former NC State post-doctoral research associate Dr. Junwei Wang. The research was funded by the National Science Foundation, the U.S. Department of Education, and Protochips, Inc.

NC State's Department of Materials Science and Engineering is part of the university's College of Engineering.

Story Source:

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

Journal Reference:

Aaron C. Johnston-Peck, Junwei Wang, Joseph B. Tracy. Formation and Grain Analysis of Spin-Cast Magnetic Nanoparticle Monolayers. Langmuir, 2011; 110324110441093 DOI: 10.1021/la200005q

Blocking carbon dioxide fixation in bacteria increases biofuel production

 Reducing the ability of certain bacteria to fix carbon dioxide can greatly increase their production of hydrogen gas that can be used as a biofuel. Researchers from the University of Washington, Seattle, report their findings in the current issue of online journal mBio®.

"Hydrogen gas is a promising transportation fuel that can be used in hydrogen fuel cells to generate an electric current with water as the only waste product," says Caroline Harwood, who conducted the study with James McKinlay. "Phototrophic bacteria, like Rhodopseudomonas palustris obtain energy from light and carbon from organic compounds during anaerobic growth. Cells can naturally produce hydrogen gas biofuel as a way of disposing of excess electrons."

Feeding these bacteria more electron rich organic compounds though, does not always produce the logically expected result of increased hydrogen production. Harwood and McKinlay analyzed metabolic functions of R. palustris grown on four different compounds to better understand what other variables might be involved.

One factor involved appears to be the Calvin cycle, a series of biochemical reactions responsible for the process known as carbon dioxide fixation. The Calvin cycle converts carbon dioxide and electrons into organic compounds. Therefore carbon dioxide-fixation and hydrogen production naturally compete for electrons.

When they tested a strain of the bacterium, which had been genetically modified to block carbon dioxide-fixation they observed an increased output of hydrogen from all four substrates.

The Calvin cycle was not the only variable affecting hydrogen production that Harwood and McKinlay identified in the paper. They also determined that the metabolic route a growth substrate took on its way to becoming a building block for making new cells also played a role.

"Our work illustrates how an understanding of bacterial metabolism and physiology can be applied to engineer microbes for the production of sustainable biofuels," says Harwood.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by American Society for Microbiology, via EurekAlert!, a service of AAAS.

Journal Reference:

J. B. McKinlay, C. S. Harwood. Calvin Cycle Flux, Pathway Constraints, and Substrate Oxidation State Together Determine the H2 Biofuel Yield in Photoheterotrophic Bacteria. mBio, 2011; 2 (2): e00323-10 DOI: 10.1128/mBio.00323-10

Biological molecules select their spin

Do the principles of quantum mechanics apply to biological systems? Until now, says Prof. Ron Naaman of the Institute's Chemical Physics Department (Faculty of Chemistry), both biologists and physicists have considered quantum systems and biological molecules to be like apples and oranges. But research he conducted together with scientists in Germany, which appeared recently in Science, definitively shows that a biological molecule -- DNA -- can discern between quantum states known as spin.

Quantum phenomena, it is generally agreed, take place in extremely tiny systems -- single atoms, for instance, or very small molecules. To investigate them, scientists must usually cool their material down to temperatures approaching absolute zero. Once such a system exceeds a certain size or temperature, its quantum properties collapse, and "every day" classical physics takes over. Naaman: "Biological molecules are quite large, and they work at temperatures that are much warmer than the temperatures at which most quantum physics experiments are conducted. One would expect that the quantum phenomenon of spin, which exists in two opposing states, would be scrambled in these molecules -- and thus irrelevant to their function."

But biological molecules have another property: they are chiral. In other words, they exist in either "left-" or "right-handed" forms that can't be superimposed on one another. Double-stranded DNA molecules are doubly chiral -- both in the arrangement of the individual strands and in the direction of the helices' twist. Naaman knew from previous studies that some chiral molecules can interact in different ways with the two different spins. Together with Prof. Zeev Vager of the Particle Physics and Astrophysics Department, research student Tal Markus, and Prof. Helmut Zacharias and his research team at the University of Münster, Germany, he set out to discover whether DNA might show some spin-selective properties.

The researchers fabricated self-assembling, single layers of DNA attached to a gold substrate. They then exposed the DNA to mixed groups of electrons with both directions of spin. Indeed, the team's results surpassed expectations: The biological molecules reacted strongly with the electrons carrying one of those spins, and hardly at all with the others. The longer the molecule, the more efficient it was at choosing electrons with the desired spin, while single strands and damaged bits of DNA did not exhibit this property. These findings imply that the ability to pick and choose electrons with a particular spin stems from the chiral nature of the DNA molecule, which somehow "sets the preference" for the spin of electrons moving through it.

In fact, says Naaman, DNA turns out to be a superb "spin filter," and the team's findings could have relevance for both biomedical research and the field of spintronics. If further studies, for instance, bear out the finding that DNA only sustains damage from spins pointing in one direction, then exposure might be reduced and medical devices designed accordingly. On the other hand, DNA and other biological molecules could become a central feature of new types of spintronic devices, which will work on particle spin rather than electric charge, as they do today.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Weizmann Institute of Science.

Journal Reference:

B. Gohler, V. Hamelbeck, T. Z. Markus, M. Kettner, G. F. Hanne, Z. Vager, R. Naaman, H. Zacharias. Spin Selectivity in Electron Transmission Through Self-Assembled Monolayers of Double-Stranded DNA. Science, 2011; 331 (6019): 894 DOI: 10.1126/science.1199339