Sunday, April 10, 2011

Mussel adhesive inspires tough coating for living cells

Inspired by Mother Nature, scientists are reporting development of a protective coating with the potential to enable living cells to survive in a dormant condition for long periods despite intense heat, dryness and other hostile conditions. In a report in Journal of the American Chemical Society, they liken the coating to the armor that encloses the spores that protect anthrax and certain other bacterial cells, making those microbes difficult to kill.

Insung S. Choi and colleagues say their simple method for coating the yeast cells could "serve as a new strategy for controlling cell division and protection of artificial spore like structures in a designed way." The technique could be used to encapsulate individual cells for a variety of purposes, including the creation of tiny chemical probes, single-cell chemical factories, and perhaps armor for transplanted cells used in anti-cancer therapies.

The new coating is an called polydopamine, chemically similar to mussel adhesive. In laboratory experiments, the coating slowed down cell division in the yeast, while protecting them from cell-digesting chemicals. "We believe that polydopamine encapsulation would be a good starting point for both fundamental research and applications based on artificial ," Choi and colleagues note in their study, "as it endows living cells with durability against harsh environments, controllability in cell cycles, and reactivity for cell-surface modification."

Provided by American Chemical Society (news : web)

Exploring the possibilities for zeolites

Some people collect stamps and coins, but when it comes to sheer utility, few collections rival the usefulness of Rice University researcher Michael Deem's collection of 2.6 million zeolite structures.

Zeolites are materials -- including some natural minerals -- that act as molecular sieves, thanks to a Swiss-cheese-like arrangement of pores that can sort, filter, trap and chemically process everything from drugs and petroleum to nuclear waste. are particularly useful as catalysts -- materials that spur . There are about 50 naturally occurring zeolites and almost three times as many man-made varieties.

Deem's database, which is described in a new paper that will be featured on the cover of an upcoming issue of the Royal Society of Chemistry's journal , hints at the untapped possibilities for making even more synthetic zeolites.

"For many catalytic applications only a single material has been found," said Deem, the John W. Cox Professor in Biochemical and Genetic Engineering and professor of physics and astronomy. "Expanding the diversity of the zeolite structures would be helpful to improve performance in existing applications, to explore novel functions and to answer basic scientific questions."

Zeolites are useful because of the particular way are mixed and arranged in their porous interiors. Based on these arrangements, zeolites can cause chemicals to react in particular ways, and even subtle changes in the arrangements can alter the reactions that are spurred. Deem's database was created to explore the many zeolite structures that are physically possible, and he said several researchers are already using the information to identify zeolites that could be used for and other applications.

" can play a stimulatory role in the synthesis of new zeolite materials," Deem said. "That is the motivation; that is the challenge that brings us back to zeolites time and again."

In 2007, Deem and his students used both supercomputers and unused computing cycles from more than 4,300 idling desktop PCs to painstakingly calculate every conceivable atomic formulation for zeolites. They created a database of more than 3.4 million atomic formulations of the porous silicate minerals.

In the current study, Deem, Rice graduate student Ramdas Pophale and Purdue University computational analyst Phillip Cheeseman designed tools to examine and compare the physical properties of each entry. Using these tools, they pared down the larger set by removing potential redundancies as well as "low-energy" structures that would either be unstable or impossible to synthesize.

For each of the 2.6 million remaining structures in the database, the team carried out calculations to find specific physical and chemical properties -- including X-ray diffraction patterns, ring-size distributions and dielectric constants -- that could help guide researchers interested in synthesizing them or in finding a new type of zeolite for a specific application.

Deem said the new database has been deposited in the publicly available Predicted Crystallography Open Database.

Provided by Rice University (news : web)

Pond alga could help scientists design effective method for cleaning up nuclear waste

Researchers from Northwestern University and Argonne National Laboratory have an enhanced understanding of a common freshwater alga and its remarkable ability to remove strontium from water. Insight into this mechanism ultimately could help scientists design methods to remove radioactive strontium from existing nuclear waste.

Strontium 90, a major waste component, is one of the more dangerous radioactive fission materials created within a . It is present in the approximately 80 million gallons of radioactive waste sludge stored in the United States alone.

The researchers are the first to show quantitatively how Closterium moniliferum, one of the bright often seen in ponds, sequesters (in the form of barium-strontium-sulfate crystals). They are using this understanding to think about a practical sequestration system for that maximizes strontium removal. The possibilities include using the algae for direct bioremediation of waste or accidental spills in the environment or designing a new process for waste treatment inspired by how the algae work.

The results are published by the journal ChemSusChem, a sister journal of Angewandte Chemie.

"Nuclear waste cleanup is a problem we have to solve," said senior author Derk Joester, who experienced Chernobyl's radioactive fallout when he was a teenager living in southern Germany. "Even if all the nuclear reactors were to shut down tomorrow, the existing volume of waste is great, and it is costly to store. We need to isolate highly radioactive 'high-level' waste from 'low-level' waste. The algae offer a mechanism for doing this, which we would like to understand and optimize."

Even though strontium 90 doesn't appear to be a significant environmental threat following the nuclear accident in Japan, the radioactive isotope will need to be dealt with during the power plant and nuclear waste cleanup, Joester said.

Joester is the Morris E. Fine Junior Professor in Materials and Manufacturing at Northwestern's McCormick School of Engineering and Applied Science.

Strontium 90 has a half-life of about 30 years, is chemically very similar to calcium and thus is drawn to bone. The cumulative cancer risk from strontium 90 exposure when strontium is bound in bones for many years is very high.

The crescent-shaped, single-celled organism studied by Joester and his colleagues naturally makes biominerals that include non-radioactive strontium, and it can differentiate strontium from calcium -- a rare feat. The researchers want to learn more about this selectivity because calcium is present in far greater abundance than strontium in nuclear waste, but calcium is harmless. By concentrating the radioactive strontium (Sr-90) in the form of solid crystals with very low solubility, the dangerous high-level waste could be isolated from the rest and dealt with separately.

"Using the algae for direct bioremediation of waste is one approach," said Joester, who began the research years ago with his graduate student Minna Krejci, "but we also are looking at the basic mechanisms of how the algae sequester strontium so we can engineer a more selective process for waste treatment. We want to isolate and concentrate in the crystals the most strontium possible."

The algae's ability to separate strontium from calcium occurs when the crystals are formed inside the cells. The algae first soak up barium, strontium and calcium from their watery environment. Strontium then is sequestered along with barium in the crystals, which remain in the cells, while the calcium is excreted from the cells. (Barium must be present for the organisms to take up strontium.)

Joester and Krejci teamed up with Lydia Finney and Stefan Vogt at the Advanced Photon Source at Argonne National Laboratory to produce maps showing the distribution of barium, strontium, calcium and several other elements in the cells. At the same time, the composition of the crystals made by the cells was determined. (The crystals are located in the organism's vacuoles, at the tips of the cells.)

The researchers varied the amount of barium and strontium in the algae's environment and then measured the amount of strontium taken up into the cell. They found the ratio of barium to strontium in the water affected the amount of strontium incorporated into each crystal. Depending on the medium's composition, the strontium measured in a crystal ranged from less than 1 percent up to 45 percent. This gives the researchers an avenue for making the process more strontium-selective.

"The synchrotron X-ray microscopy available at the Advanced Photon Source was absolutely critical to this study," Joester said. "It allowed us to visualize where calcium, strontium and barium go inside the cells." These sorts of experiments, he noted, are only possible at three synchrotron radiation facilities in the world: the Advanced Photon Source, the European Synchrotron Radiation Facility in France and the SPring-8 in Japan.

Nonradioactive strontium, which is chemically identical to the radioactive version, was used in the experiments. The researchers do not know how well the algae would survive in a radioactive environment, although the organisms have proven resistant in other harsh environments.

More information: Joester, Krejci, Finney and Vogt all are authors of the paper, titled "Selective Sequestration of Strontium in Desmid Green Algae by Biogenic Co-precipitation with Barite." It can be viewed at http://onlinelibra … 448/abstract

Provided by Northwestern University (news : web)

Simple chemical cocktail shows first promise for limb re-growth in mammals

Move over, newts and salamanders. The mouse may join you as the only animal that can re-grow their own severed limbs. Researchers are reporting that a simple chemical cocktail can coax mouse muscle fibers to become the kinds of cells found in the first stages of a regenerating limb. Their study, the first demonstration that mammal muscle can be turned into the biological raw material for a new limb, appears in the journal ACS Chemical Biology.

Darren R. Williams and Da-Woon Jung say their "relatively simple, gentle, and reversible" methods for creating the early stages of limb regeneration in mouse cells "have implications for both and stem cell biology." In the future, they suggest, the chemicals they use could speed wound healing by providing new cells at the injured site before the wound closes or becomes infected. Their methods might also shed light on new ways to switch adult cells into the all-purpose, so-called "pluripotent," stem cells with the potential for growing into any type of tissue in the body.

The scientists describe the chemical cocktail that they developed and used to turn mouse into muscle cells. Williams and Jung then converted the turned into fat and bone cells. Those transformations were remarkably similar to the initial processes that occur in the tissue of newts and that is starting to regrow severed limbs.

Provided by American Chemical Society (news : web)

Golden window electrodes developed for organic solar cells

Researchers at the University of Warwick have developed a gold plated window as the transparent electrode for organic solar cells. Contrary to what one might expect, these electrodes have the potential to be relatively cheap since the thickness of gold used is only 8 billionths of a metre.

This ultra-low thickness means that even at the current high gold price the cost of the gold needed to fabricate one square metre of this electrode is only around L4.5. It can also be readily recouped from the organic solar cell at the end of its life and since gold is already widely used to form reliable interconnects it is no stranger to the electronics industry.

Organic solar cells have long relied on Indium Tin Oxide (ITO) coated glass as the transparent electrode, although this is largely due to the absence of a suitable alternative. ITO is a complex, unstable material with a high surface roughness and tendency to crack upon bending if supported on a plastic substrate. If that wasn't bad enough one of its key components, indium, is in short supply making it relatively expensive to use.

An ultra-thin film of air-stable metal like gold would offer a viable alternative to ITO, but until now it has not proved possible to deposit a film thin enough to be transparent without being too fragile and electrically resistive to be useful.

Now research led by Dr Ross Hatton and Professor Tim Jones in the University of Warwick 's department of Chemistry has developed a rapid method for the preparation of robust, ultra-thin gold films on glass. Importantly this method can be scaled up for large area applications like solar cells and the resulting electrodes are chemically very well-defined.

Dr Hatton says "This new method of creating gold based transparent electrodes is potentially widely applicable for a variety of large area applications, particularly where stable, chemically well-defined, ultra-smooth platform electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronics and nanophotonics."

The paper documents the team's success in creating this simple, practical and effective method of depositing the films onto glass, and also reports how the optical properties can be fine tuned by perforating the film with tiny circular holes using something as simple as polystyrene balls. The University of Warwick research team has also had some early success in depositing ultra-thin gold films directly on plastic substrates, an important step towards realising the holy grail of truly flexible solar cells. This innovation is set to be exploited by Molecular Solar Ltd, a Warwick spinout company dedicated to commercialising the discoveries of its academic founders in the area of organic solar cells.

This work was supported by the European Regional Development Fund (ERDF) / Advantage West Midlands Science City SCRA AM2 project, the Engineering and Physical Sciences Research Council (EPSRC) and the Royal Academy of Engineering.

Story Source:

The above story is reprinted  from materials provided by University of Warwick.

Journal Reference:

Helena M. Stec, Rebecca J. Williams, Tim S. Jones, Ross A. Hatton. Ultrathin Transparent Au Electrodes for Organic Photovoltaics Fabricated Using a Mixed Mono-Molecular Nucleation Layer. Advanced Functional Materials, 2011; DOI: 10.1002/adfm.201002021

The atom and its quantum mirror image: Physicists experimentally produces quantum-superpositions, simply using a mirror

Standing in front of a mirror, we can easily tell apart ourselves from our mirror image. The mirror does not affect our motion in any way. For quantum particles, this is much more complicated. In a spectacular experiment in the labs of the University of Heidelberg, a group of physicists at the University Heidelberg, together with colleagues at TU Munich and TU Vienna extended a 'thought experiment' by Einstein and managed to blur the distinction between a particle and its mirror image.

The results of this experiment have now been published in the journal Nature Physics.

Emitted Light, Recoiling Atom

When an atom emits light (i.e. a photon) into a particular direction, it recoils in the opposite direction. If the photon is measured, the motion of the atom is known too. The scientists placed atoms very closely to a mirror. In this case, there are two possible paths for any photon travelling to the observer: it could have been emitted directly into the direction of the observer, or it could have travelled into the opposite direction and then been reflected in the mirror. If there is no way of distinguishing between these two scenarios, the motion of the atom is not determined, the atom moves in a superposition of both paths.

"If the distance between the atom and the mirror is very small, it is physically impossible to distinguish between these two paths," Jiri Tomkovic, PhD student at Heidelberg explains. The particle and its mirror image cannot be clearly separated any more. The atom moves towards the mirror and away from the mirror at the same time. This may sound paradoxical and it is certainly impossible in classical phyiscs for macroscopic objects, but in quantum physics, such superpositions are a well-known phenomenon.

"This uncertainty about the state of the atom does not mean that the measurement lacks precision," Jörg Schmiedmayer (TU Vienna) emphasizes. "It is a fundamental property of quantum physics: The particle is in both of the two possible states simultaneousely, it is in a superposition." In the experiment the two motional states of the atom -- one moving towards the mirror and the other moving away from the mirror -- are then combined using Bragg diffraction from a grating made of laser light. Observing interference it can be directly shown that the atom has indeed been traveling both paths at once.

On Different Paths at the Same Time

This is reminiscent of the famous double-slit experiment, in which a particle hits a plate with two slits and passes through both slits simultaneously, due to its wave-like quantum mechanical properties. Einstein already discussed that this can only be possible if there is no way to determine which path the particle actually chose, not even precise measurements of any tiny recoil of the double slit plate itself. As soon as there even a theoretically possible way of determining the path of the particle, the quantum superposition breaks down.

"In our case, the photons play a role similar to the double slit," Markus Oberthaler (University of Heidelberg) explains. "If the light can, in principle, tell us about the motion of the atom, then the motion is unambiguously determined. Only when it is fundamentally undecidable, the atom can be in a superposition state, combining both possibilities." And this fundamental undecidability is guaranteed by the mirror which takes up the photon momentum.

Quantum Effect -- Using Only a Mirror

Probing under which conditions such quantum-superpositions can be created has become very important in quantum physics. Jörg Schmiedmayer and Markus Obertaler came up with the idea for this experiment already a few years ago. "The fascinating thing about this experiment," the scientists say, "is the possibility of creating a quantum superposition state, using only a mirror, without any external fields." In a very simple and natural way the distinction between the particle and its mirror image becomes blurred, without complicated operations carried out by the experimenter.

Story Source:

The above story is reprinted  from materials provided by Vienna University of Technology.

Journal Reference:

Jiří Tomkovič, Michael Schreiber, Joachim Welte, Martin Kiffner, Jörg Schmiedmayer, Markus K. Oberthaler. Single spontaneous photon as a coherent beamsplitter for an atomic matter-wave. Nature Physics, 2011; DOI: 10.1038/nphys1961

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