Chemists design new polymer structures for use as 'plastic electronics'

Iowa State University's Malika Jeffries-EL says she's studying doing structure-property studies so she can teach old polymers new tricks.

Those tricks improve the properties of certain organic polymers that mimic the properties of traditional inorganic semiconductors and could make the polymers very useful in organic solar cells, light-emitting diodes and thin-film transistors.

Conductive polymers date back to the late 1970s when researchers Alan Heeger, Alan MacDiarmid and Hideki Shirakawa discovered that plastics, with certain arrangements of atoms, can conduct electricity. The three were awarded the 2000 Nobel Prize in Chemistry for the discovery.

Jeffries-EL, an Iowa State assistant professor of chemistry, is working with a post-doctoral researcher and nine doctoral students to move the field forward by studying the relationship between polymer structures and the electronic, physical and optical properties of the materials. They're also looking for ways to synthesize the polymers without the use of harsh acids and temperatures by making them soluble in organic solvents.

The building blocks of their work are a variety of benzobisazoles, molecules well suited for electrical applications because they efficiently transport electrons, are stable at high temperatures and can absorb photons.

And if the polymers are lacking in any of those properties, Jeffries-EL and her research group can do some chemical restructuring.

"With these polymers, if you don't have the properties you need, you can go back and change the wheel," Jeffries-EL said. "You can change the chemical synthesis and produce what's missing."

That, she said, doesn't work with silicon and other inorganic materials for semiconductors: "Silicon is silicon. Elements are constant."

The National Science Foundation is supporting Jeffries-EL's polymer research with a five-year, $486,250 Faculty Early Career Development grant. She also has support from the Iowa Power Fund (a state program that supports energy innovation and independence) to apply organic semiconductor technology to solar cells.

The research group is seeing some results, including peer-reviewed papers over the past two years in Physical Chemistry Chemical Physics, Macromolecules, the Journal of Polymer Science Part A: Polymer Chemistry, and the Journal of Organic Chemistry.

"This research is really about fundamental science," Jeffries-EL said. "We're studying the relationships between structure and material properties. Once we have a polymer with a certain set of properties, what can we do?"

She and her research group are turning to the molecules for answers.

"In order to realize the full potential of these materials, they must be engineered at the molecular level, allowing for optimization of materials properties, leading to enhanced performance in a variety of applications," Jeffries-EL wrote in a research summary. "As an organic chemist, my approach to materials begins with small molecules."

Provided by Iowa State University (news : web)

Self-powered, blood-activated sensor detects pancreatitis quickly and cheaply

 

A new low cost test for acute pancreatitis that gets results much faster than existing tests has been developed by scientists at The University of Texas at Austin.

The sensor, which could be produced for as little as a dollar, is built with a 12-cent LED light, aluminum foil, gelatin, milk protein and a few other cheap, easily obtainable materials.

The sensor could help prevent damage from acute pancreatitis, which is a sudden inflammation of the pancreas that can lead to severe stomach pain, nausea, fever, shock and in some cases, death.

"We've turned Reynold's Wrap, JELL-O and milk into a way to look for organ failure," says Brian Zaccheo, a graduate student in the lab of Richard Crooks, professor of chemistry and biochemistry.

The sensor, which is about the size of a matchbox, relies on a simple two-step process to diagnose the disease.

In step one, a bit of blood extract is dropped onto a layer of gelatin and milk protein. If there are high levels of trypsin, an enzyme that is overabundant in the blood of patients with acute pancreatitis, the trypsin will break down the gelatin in much the same way it breaks down proteins in the stomach.

In step two, a drop of sodium hydroxide (lye) is added. If the trypsin levels were high enough to break down that first barrier, the sodium hydroxide can trickle down to the second barrier, a strip of Reynold's wrap, and go to work dissolving it.

The foil corrodes, and with both barriers now permeable, a circuit is able to form between a magnesium anode and an iron salt at the cathode. Enough current is generated to light up a red LED. If the LED lights up within an hour, acute pancreatitis is diagnosed.

"In essence, the device is a battery having a trypsin-selective switch that closes the circuit between the anode and cathode," write Zaccheo and Crooks in a paper recently published in Analytical Chemistry.

Zaccheo and Crooks, who have a provisional patent, can envision a number of potential uses for the sensor. It might help providers in the developing world who don't have the resources to do the more complex tests for pancreatitis. It could be of use in situations where batteries are in short supply, such as after a natural disaster or in remote locations. And because of the speed of the sensor, it could be an excellent first-line measure even in well-stocked hospitals.

For Zaccheo, the most appealing aspect of the project isn't so much the specific sensor. It is the idea we might be able to save time, money and even lives by adopting this kind of low-tech approach.

"I want to develop biosensors that are easy to use but give a high level of sensitivity," he says. "All you need for this, for instance, is to know how to use a dropper and a timer."

Provided by University of Texas at Austin (news : web)

Understanding how glasses 'relax' provides some relief for manufacturers

 Researchers at the National Institute of Standards and Technology and Wesleyan University have used computer simulations to gain basic insights into a fundamental problem in material science related to glass-forming materials, offering a precise mathematical and physical description of the way temperature affects the rate of flow in this broad class of materials -- a long-standing goal.

Manufacturers who design new materials often struggle to understand viscous liquids at a molecular scale. Many substances including polymers and biological materials change upon cooling from a watery state at elevated temperatures to a tar-like consistency at intermediate temperatures, then become a solid "glass" similar to hard candy at lower temperatures. Scientists have long sought a molecular-level description of this theoretically mysterious, yet common, "glass transition" process as an alternative to expensive and time-consuming trial-and-error material discovery methods. Such a description might permit the better design of plastics and containers that could lengthen the shelf life of food and drugs.

A fundamental question is why many materials behave differently when temperature changes. In some "fragile" glass-forming materials, a modest variation in temperature can make the material change from highly fluid to extremely viscous, while in "strong" fluids this change in viscosity is much more gradual. This effect influences how long a manufacturer has to work with a material as it cools. "For decades, material scientists have heavily relied on empirical rules of thumb to characterize these materials," says NIST theoretician Jack Douglas. "But if you want to design a material that does precisely what you want, you need a molecular understanding of the underlying physical processes involved."

According to Douglas, the increasingly viscous nature of glass-forming liquids is related to molecules that move together in long strings around other atoms that are almost frozen in their motion. The growth of these snake-like structures leads to an increase in the viscosity of the liquid: the lower the temperature, the longer the chains, and the more viscous the fluid. The team found that the rate at which these spontaneously organizing snake-like strings grow in size as the material cools is quantitatively related mathematically to the fluid fragility -- confirming intuitive arguments made nearly half a century ago by physicists G. Adams and J.H. Gibbs, but now bolstering them with a firm computational underpinning.

Douglas and his collaborator Francis Starr of Wesleyan University achieved a large variation of fluid fragility through use of a computer model, which mimics a polymer fluid that includes tiny nanometer-sized particles. Portraying the addition of various amounts of nanoparticles and varying their interaction with the polymers, Starr says, gave the team a sort of "knob to tweak" to reveal how the fluidity changed with temperature and how the motion of the clusters was quantitatively related to changes in the fluid's properties. This tuning of cooperative motion in glass-forming liquids and fragility should be crucial in material design. Douglas says.

Story Source:

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

Journal Reference:

Francis Starr, Jack Douglas. Modifying Fragility and Collective Motion in Polymer Melts with Nanoparticles. Physical Review Letters, 2011; 106 (11) DOI: 10.1103/PhysRevLett.106.115702

Scientists engineer nanoscale vaults to encapsulate 'nanodisks' for drug delivery

There's no question, drugs work in treating disease. But can they work better, and safer? In recent years, researchers have grappled with the challenge of administering therapeutics in a way that boosts their effectiveness by targeting specific cells in the body while minimizing their potential damage to healthy tissue.

The development of new methods that use engineered nanomaterials to transport drugs and release them directly into cells holds great potential in this area. And while several such drug-delivery systems -- including some that use dendrimers, liposomes or polyethylene glycol -- have won approval for clinical use, they have been hampered by size limitations and ineffectiveness in accurately targeting tissues.

Now, researchers at UCLA have developed a new and potentially far more effective means of targeted drug delivery using nanotechnology.

In a study to be published in the May 23 print issue of the journal Small, they demonstrate the ability to package drug-loaded "nanodisks" into vault nanoparticles, naturally occurring nanoscale capsules that have been engineered for therapeutic drug delivery. The study represents the first example of using vaults toward this goal.

The UCLA research team was led by Leonard H. Rome and included his colleagues Daniel C. Buehler and Valerie Kickhoefer from the UCLA Department of Biological Chemistry; Daniel B. Toso and Z. Hong Zhou from the UCLA Department of Microbiology, Immunology and Molecular Genetics; and the California NanoSystems Institute (CNSI) at UCLA.

Vault nanoparticles are found in the cytoplasm of all mammalian cells and are one of the largest known ribonucleoprotein complexes in the sub-100-nanometer range. A vault is essentially barrel-shaped nanocapsule with a large, hollow interior -- properties that make them ripe for engineering into a drug-delivery vehicles. The ability to encapsulate small-molecule therapeutic compounds into vaults is critical to their development for drug delivery.

Recombinant vaults are nonimmunogenic and have undergone significant engineering, including cell-surface receptor targeting and the encapsulation of a wide variety of proteins.

"A vault is a naturally occurring protein particle and so it causes no harm to the body," said Rome, CNSI associate director and a professor of biological chemistry. "These vaults release therapeutics slowly, like a strainer, through tiny, tiny holes, which provides great flexibility for drug delivery."

The internal cavity of the recombinant vault nanoparticle is large enough to hold hundreds of drugs, and because vaults are the size of small microbes, a vault particle containing drugs can easily be taken up into targeted cells.

With the goal of creating a vault capable of encapsulating therapeutic compounds for drug delivery, UCLA doctoral student Daniel Buhler designed a strategy to package another nanoparticle, known as a nanodisk (ND), into the vault's inner cavity, or lumen.

"By packaging drug-loaded NDs into the vault lumen, the ND and its contents would be shielded from the external medium," Buehler said. "Moreover, given the large vault interior, it is conceivable that multiple NDs could be packaged, which would considerably increase the localized drug concentration."

According to researcher Zhou, a professor of microbiology, immunology and molecular genetics and director of the CNSI's Electron Imaging Center for NanoMachines, electron microscopy and X-ray crystallography studies have revealed that both endogenous and recombinant vaults have a thin protein shell enclosing a large internal volume of about 100,000 cubic nanometers, which could potentially hold hundreds to thousands of small-molecular-weight compounds.

"These features make recombinant vaults an attractive target for engineering as a platform for drug delivery," Zhou said. "Our study represents the first example of using vaults toward this goal."

"Vaults can have a broad nanosystems application as malleable nanocapsules," Rome added.

The recombinant vaults are engineered to encapsulate the highly insoluble and toxic hydrophobic compound all-trans retinoic acid (ATRA) using a vault-binding lipoprotein complex that forms a lipid bilayer nanodisk.

The research was supported by the UC Discovery Grant Program, in collaboration with the research team's corporate sponsor, Abraxis Biosciences Inc., and by the Mather's Charitable Foundation and an NIH/NIBIB Award.

Story Source:

The above story is reprinted (with editorial adaptation) from materials provided by University of California - Los Angeles.

Journal Reference:

Daniel C. Buehler, Daniel B. Toso, Valerie A. Kickhoefer, Z. Hong Zhou, Leonard H. Rome. Vaults Engineered for Hydrophobic Drug Delivery. Small, 2011; DOI: 10.1002/smll.201002274

 

 

Molecular architecture of key NMDA receptor subunit revealed

Structural biologists at Cold Spring Harbor Laboratory (CSHL) in collaboration with colleagues at Emory University have determined the molecular structure of a key portion, or subunit, of a receptor type commonly expressed in brain cells. The receptor is one of several NMDA (N-methyl-D-aspartate) receptor variants, and the subunit in question is that which specifically binds with excitatory neurotransmitters, most notably glutamate, the brain's most prevalent excitatory neurotransmitter.

The discovery is important because knowledge of the receptor subunit's precise physical shape and biochemical characteristics can now form a basis upon which to design new drugs that will interact with the receptor, whose dysfunction is known to be implicated in depression, schizophrenia, Parkinson's and Alzheimer's diseases as well as stroke-related brain injuries.

The release and reception of neurotransmitters at synaptic junctions that form between nerve cells mediates a majority of communication between these cells. NMDA receptors are comparatively large multi-unit proteins found at the membrane of a particular class of nerve cells. "The way in which neurotransmitter molecules bind to a receptor determines the strength of neuronal activities," explains CSHL Associate Professor Hiro Furukawa, who led the effort to obtain and "solve" the structure of an NMDA receptor subunit called GluN2D.

Somewhat like a child's building-block puzzle, NMDA receptors are assembled out of combinations of two types of subunits, called GluN1s and GluN2s. While two "blocks" of each are present in every complete NMDA receptor, Furukawa and colleagues focused on solving the structure of one of four possible variants of the GluN2 subunit, which are designated with the letters "A" through "D."

"An NMDA receptor displays different characteristics, depending on which of the four GluN2 subunits it contains," explains Furukawa. "What's especially interesting about the GluN2D subunit is that its presence means the receptor will take about 40 times longer to deactivate after being stimulated, as compared with a receptor containing the GluN2A subunit. We and others in the field think this unique property is important for early brain development as well as in the normal function of neurons expressing receptors with this subunit in the mature brain."

Using x-ray crystallography -- a method that features exposing a crystal of the molecule under study to very high-energy x-ray beams, which reveals its features -- the team was able to visualize a unique conformation of the GluN2D subunit that is suited to mediate "slow" neuronal deactivation. The team's data, published online April 26 in Nature Communications, revealed that a glutamate variant called L-glutamate, when docked with the GluN2D receptor subunit, elicits a much slower deactivation of the receptor as compared with other excitatory neurotransmitter molecules.

"We were able to show a unique structural conformation in that pairing that is coincident with the slower deactivation time," Furukawa says. This gives the team a basis for understanding why deactivation time is so dramatically different depending on which of the GluN2 subunits is involved in linking up with the excitatory neurotransmitter molecule.

Surprisingly, this conformation was observed only when GluN2D was bound to glutamate, but not other known excitatory neurotransmitters, such as aspartate. "It is as if glutamate were acting as a special neurotransmitter expressly designed to mediate a slow response when acting on GluN2D subunits," says Furukawa. "This stunning aspect of GluN2D function is extremely important for the field of neuropharmacology because it now predicts that GluN2D may not be as slowly de-activating as previously expected in neurons where aspartate is used as a primary neurotransmitter."

More information: "Ligand-specific deactivation time course of GluN1/GluN2D NMDA receptors" appears online April 26 in Nature Communications. The authors are: Katie M. Vance, Noriko Simorowski, Stephen F. Traynelis and Hiro Furukawa. The paper can be accessed online by using the DOI: 10.1038/ncomms1295

Provided by Cold Spring Harbor Laboratory (news : web)

Scorpion venom -- bad for bugs, good for pesticides

Fables have long cast scorpions as bad-natured killers of hapless turtles that naively agree to ferry them across rivers. Michigan State University scientists, however, see them in a different light.

Ke Dong, MSU insect toxicologist and neurobiologist, studied the effects of scorpion venom with the hopes of finding new ways to protect plants from bugs. The results, which are published in the current issue of the Journal of Biological Chemistry, have revealed new ways in which the venom works.

Past research identified scorpion toxin's usefulness in the development of insecticides. Its venom attacks various channels and receptors that control their prey's nervous and muscular systems. One major target of scorpion toxins is the voltage-gated sodium channel, a protein found in nerve and muscle cells used for rapid electrical signaling.

"Interestingly, some scorpion toxins selectively affect one type of sodium channels, but not others," Dong said. "The goal of our scorpion toxin project is to understand why certain scorpion toxins act on insect sodium channels, but not their mammalian counterparts."

Dong and a team of researchers were able to identify amino acid residues in insect sodium channels that make the channels more vulnerable to the venom from the Israeli desert scorpion. The team also discovered that an important sodium channel voltage sensor can influence the potency of the scorpion toxin.

"Investigating the venom's effect on the voltage-gated sodium channel could provide valuable information for designing new insecticides that work by selectively targeting insect sodium channels," Dong said.

Several classes of insecticides act on sodium channels, but insects become resistant to them over time. The researchers are studying how insects develop resistance and what alternatives can be created to control resistant pests, Dong added.

Provided by Michigan State University (news : web)

Laser printing speeds parts on demand to manufacturers

Pull into the auto repair shop with a smashed bumper, and there's no wait while they order a replacement. Instead, the technician downloads specifications from the manufacturer's database. You both watch as a laser beam probing a container of liquid plastic material almost magically builds a new bumper inch by inch.

The scenario may sound like science fiction, but advances in polymer materials are moving the technology for 3-D printing" of prosthetic limbs, hearing aids, designer furniture, surgical tools and other products out of the designer's studio and into the marketplace. That's the topic of an article in the current edition of Chemical & Engineering News, ACS' weekly news magazine.

In the article, Alexander H. Tullo, C&EN senior editor, explains that the technology –– termed stereolithography, laser sintering, rapid prototyping, and additive manufacturing –– has been in limited use for decades to produce models of new products and for other design-shop applications. With polymer manufacturers developing new raw materials for the process, this so-called "additive manufacturing" technology is now moving into a new phase –– making actual products. The market has been expanding at an average annual rate of 26 percent, and exceeded $1 billion in 2009.

More information: "Parts on Demand" This story is available at http://pubs.acs.or … 917bus1.html

Provided by American Chemical Society (news : web)