Neutron scattering provides window into surface interactions

To better understand the fundamental behavior of molecules at surfaces, researchers at the U.S. Department of Energy's Oak Ridge National Laboratory are combining the powers of neutron scattering with chemical analysis.

Scientists have a fundamental interest in how molecules behave at solid surfaces because surface interactions influence chemistry, such as in materials for catalysis, drug delivery and carbon sequestration. Understanding these interactions allows researchers to tailor materials for a specific desirable outcome.

Michelle Kidder and A.C. Buchanan, physical organic chemists, and Ken Herwig, neutron scattering scientist, used neutron scattering to study the physical motion of a chemically attached organic molecule inside a silica nanopore, MCM41.

"There is a connection between a molecule's dynamic behavior or motion to its surroundings." Herwig said. "In particular, restricting the ability of a molecule to freely move by confining it to a small volume dramatically affects both the range and character of its movement. We are trying to gain insight into the connection between the changes in molecular motion and the changes in chemistry that occur when molecules are attached to a solid surface."

Herwig used neutron scattering to gain a unique perspective into molecular motion because neutrons are sensitive to the hydrogen atoms, which are present in many molecules that researchers are interested in. Additionally, neutron scattering simultaneously tells researchers how rapid the motion is and what type of motion they are observing on the atomic and nanoscale.

If scientists understand how pore size affects surface interactions, they can modify pore size to change a chemical product outcome.

To study surface interactions, Kidder synthesized both the organic molecules and MCM41 of different pore sizes, then chemically attached the molecules to the silica pore surface, which forms an organic-inorganic hybrid material. This hybrid material is used in studies to understand chemical decomposition pathways, where surface interactions were presumed to play a role.

"We are interested in understanding the thermo decomposition of molecules similar to those found in biomass resources," Kidder said. "What we have seen is that there are many local environmental factors that influence chemical reactivity and products, and one of those large influences occurs when a molecule is confined to a pore wall, where even the pore size has a large impact on reactivity."

This research was funded by DOE's Office of Science.

Story Source:

The above story is reprinted from materials provided by DOE/Oak Ridge National Laboratory.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Edward J. Kintzel, Michelle K. Kidder, A. C. Buchanan, Phillip F. Britt, Eugene Mamontov, Michaela Zamponi, Kenneth W. Herwig. Dynamics of 1,3-Diphenylpropane Tethered to the Interior Pore Surfaces of MCM-41. The Journal of Physical Chemistry C, 2012; 116 (1): 923 DOI: 10.1021/jp209458a

Evolution provides clue to blood clotting

A simple cut to the skin unleashes a complex cascade of chemistry to stem the flow of blood. Now, scientists at Washington University School of Medicine in St. Louis have used evolutionary clues to reveal how a key clotting protein assembles. The finding sheds new light on common bleeding disorders.

The long tube-shaped protein with a vital role in blood clotting is called von Willebrand Factor (VWF). Made in cells that form the inner lining of blood vessels, VWF circulates in the blood seeking out sites of injury. When it finds them, its helical tube unfurls to catch platelets and form blood clots. Defects in VWF cause von Willebrand Disease, the most common inherited bleeding disorder in humans.

"The challenge for the cell is how to build this massive protein without clogging the machinery," says J. Evan Sadler, MD, PhD, professor of medicine and senior author of the study published in July in the Journal of Biological Chemistry. "The cell has solved this problem by making the assembly of von Willebrand Factor dependent on its location in the cell."

And VWF knows its location in a cell because pH, a measure of how acidic or basic a liquid is, varies from one cellular structure to the next. On a scale of 0 to 14, pure water has a neutral pH of about 7; human blood is slightly basic with a pH of 7.4.

In a cell, the building blocks of VWF form in an area with the same pH as blood. Then these building blocks are shipped to an area that is more acidic. Called the Golgi, this cellular compartment is known for its role in packaging proteins and has a pH of about 6.2. In this acidic environment, the building blocks of VWF are able to form long chains and fold into its signature helical tubules. But how this assembly process works has not been well understood.

From basic biophysics, Sadler and his colleagues knew that only one amino acid in the long protein chain is likely to "sense" a pH change from 7.4 to 6.2. Moving to an acidic environment, this amino acid, histidine, gains a positive charge. The group suspected that this charge may trigger the VWF building blocks to link together in a long chain.

But there are many histidines located throughout the chain. Like 26 letters of the alphabet form thousands of words, 20 essential amino acids form all proteins in the body. To identify which histidines might be guiding the amino acid chain to form the long VWF tubules, Sadler and his team looked to evolution.

"If a particular histidine is important in this process, it should be present in the same location across many species," Sadler says.

So Sadler's group, including the paper's first author, Luke T. Dang, who was an undergraduate student when he did this work, gathered the DNA sequences of VWF for humans, 19 other placental mammals, a marsupial, two birds, a reptile, an amphibian and five fish. Dang is now a graduate student at the University of Washington, Seattle.

"By lining up the sequences, we found a relatively small number of histidines that are in the same place across species," Sadler says. "It then becomes manageable to mutate them individually and see if that prevents von Willebrand Factor from assembling."

Out of the many histidines in the amino acid sequence of VWF, they found two that are important in sensing the pH change and guiding the building blocks to form chains in an acidic environment. When Dang replaced either of these histidines with an amino acid that provides no positive charge, the chain did not form. But when Dang forced a positive charge to always be present at these locations, the chain formed again.

"A positive charge at these positions is important for von Willebrand Factor to assemble properly so it can perform its biological function," says Sadler, also a hematologist who specializes in treating patients with blood clotting disorders. "Without VWF, you bleed."

According to Sadler, defects in VWF disproportionately affect women because the protein is especially important for controlling bleeding during menstruation and childbirth. Sadler says this work helps to better understand the defects in pathways that cause von Willebrand Disease and related conditions.

More information: Dang LT, Purvis AR, Huang RH, Westfield LA, Sadler JE. Phylogenetic and functional analysis of histidine residues essential for pH-dependent multimerization of von Willebrand Factor. Journal of Biological Chemistry. July 2011.

Provided by Washington University School of Medicine (news : web)

Salt-loving microbe provides new enzymes for the production of next-gen biofuels

In order to realize the full potential of advanced biofuels that are derived from non-food sources of lignocellulosic biomass—e.g., agricultural, forestry, and municipal waste, and crops such as poplar, switchgrass and miscanthus—new technologies that can efficiently and cost-effectively break down this biomass into simple sugars are required. Existing biomass pretreatment technologies are typically derived from the pulp and paper industry and rely on dilute acids and bases to break down the biomass. The treated biomass product is then exposed to biological catalysts, or enzymes, to liberate the sugars.

A new class of solvents, referred to as ionic liquids, have been reported to be much more efficient in treating the biomass and enhancing the yield of sugars liberated from it. While ionic liquids are useful for breaking down biomass, they can also hinder the ability of the cellulases (usually derived from fungi) used to produce sugars after pretreatment. Ionic liquids are a liquid form of salt that will inactivate enzymes by interfering with the folding of polypeptides—the building-blocks of proteins. To help identify new enzymes that are tolerant of ionic liquids, researchers from the U.S. Department of Energy (DOE) Joint Genome Institute (JGI) and the Joint BioEnergy Institute (JBEI) at DOE's Lawrence Berkeley National Laboratory are turning to those found in the complete genome sequences of halophilic (salt-tolerant) organisms.

As a test of this bioenergy-related application of DNA sequencing and enzyme discovery, researchers led by the Director of the DOE JGI, Eddy Rubin, and the Vice-President of the JBEI Deconstruction Division, Blake Simmons, employed a cellulose-degrading enzyme from a salt-tolerant microbe that was isolated from the Great Salt Lake. The microbe in question, Halorhabdus utahensis, is from the branch of the tree of life known as Archaea; H. utahensis was isolated from the natural environment at the Great Salt Lake and sequenced at the DOE JGI as part of the Genomic Encyclopedia of Bacteria and Archaea (GEBA) project.

"This is one of the only reports of salt-tolerant cellulases, and the only one that represents a true 'genome-to-function' relevant to ionic liquids from a halophilic environment," said Simmons of the study published June 30, 2011 in Green Chemistry. "This strategy enhances the possibility of identifying true obligatory halophilic enzymes." Such salt-tolerant enzymes, particularly cellulases, offer significant advantages for industrial utility over conventional enzymes.

In collaboration with Jerry Eichler from Ben Gurion University of the Negev in Israel they cloned and expressed a gene from H. utahensis in another haloarchaeal microbe, and were able to identify a salt-dependent enzyme that can tolerate high temperatures and is resistant to ionic liquids. "This project has established a very important link between genomic science and the realization of enzymes that can handle very demanding chemical environments, such as those present in a biorefinery," said Simmons.

The group plans to expand this research to develop a full complement of enzymes that is tailored for the ionic liquid process technology with the goal of demonstrating a complete biomass-to-sugar process, one they hope can enable the commercial viability of advanced biofuels.

Provided by DOE/Joint Genome Institute (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

A loose grip provides better chemotherapy

Researchers at Case Western Reserve University have developed a little bomb that promises a big bang for cancer patients.

Preliminary tests show an anti-cancer drug loosely attached to gold nanoparticles starts accumulating deep inside tumors within minutes of injection and can be activated for an effective treatment within two hours. The same drug injected alone takes two days to gather and attacks the tumor from the surface -- a far less effective route.

The work, titled "Deep Penetration of a PDT Drug into Tumors by Noncovalent Drug-Gold Nanoparticle Conjugates," is published February 4 in the online edition of the Journal of the American Chemical Society.

Speeding anti-cancer drugs directly into tumors enables patients to receive lower doses of the toxic chemicals, thereby saving healthy tissue from damage and other harsh side effects suffered in traditional chemotherapy.

"We hope to lower the dosage by at least a factor of 10," said Clemens Burda, a professor of chemistry at Case Western Reserve and the senior author of the paper.

The key to success? The scientists tied an anti-cancer drug to golden missiles using a weak chemical interaction called a noncovalent bond. In molecule construction, a covalent bond is a heavy rope lashed and knotted; a noncovalent bond is a shoestring tied in a bow.

"Very often, additions to chemical systems change properties of the components of the system," Burda said. Attempts by his and other research groups to use covalent bonds for drug delivery have resulted in such complications and less than hoped-for results.

The researchers, who come from a breadth of disciplines, found that by using a noncovalent bond to attach the drug to coated gold, they eliminated interference among the desired properties of each component.

Burda's group sought to simplify the process by using materials that have well-known properties.

Gold nanoparticles have large surface areas that permit packing a lot in a tiny space. The element is inert inside the body and at less than 5 nanometers across, or less than 1/10,000 the width of a human hair, the particles quickly flow out of the blood stream and across cancer cell membranes to accumulate inside tumors.

A coat of polyethylene glycol links tightly to the gold while providing cargo space to attach other materials.

The coated gold provides an environment to physically prevent activation of the photodynamic therapy drug silicon phthalocyanine, preventing unintended toxic exposures to healthy tissues.

The loosely-held drug is released from the nanoparticle through the attraction of the drug to the lipid membrane of cancer cells. Laser light switches on the freed silicon phthalocyanine, which breaks down and kills cancer cells, shrinking the tumor.

After delivering the drug, the nanoparticles pass through the kidneys and clear the body within a week.

Burda teamed with Yu Cheng, Joseph D. Meyers, Ann-Marie Broome, Malcolm E. Kenney and James Basilion, all of Case Western Reserve.

Their work received a $1.2 million grant from the National Institutes of Health late this fall, to continue development.

Story Source:

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

Journal Reference:

Yu Cheng, Joseph D. Meyers, Ann-Marie Broome, Malcolm E. Kenney, James P. Basilion, Clemens Burda. Deep Penetration of a PDT Drug into Tumors by Noncovalent Drug-Gold Nanoparticle Conjugates. Journal of the American Chemical Society, 2011; : 110204112210047 DOI: 10.1021/ja108846h

New material provides 25 percent greater thermoelectric conversion efficiency

February 15, 2011

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Thermoelectric materials and technology have powered spacecraft for decades. But, thanks to advances in efficiency discovered at the Ames Laboratory, thermoelectric materials may have new, broader ?green? energy applications. Credit: U.S. Dept. of Energy's Ames Laboratory

Automobiles, military vehicles, even large-scale power generating facilities may someday operate far more efficiently thanks to a new alloy developed at the U.S. Department of Energy's Ames Laboratory. A team of researchers at the Lab that is jointly funded by the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering and the Defense Advanced Research Projects Agency, achieved a 25 percent improvement in the ability of a key material to convert heat into electrical energy.

"What happened here has not happened anywhere else," said Evgenii Levin, associate scientist at Ames Laboratory and co-principal investigator on the effort, speaking of the significant boost in efficiency documented by the research. Along with Levin, the Ames Lab-based team included: Bruce Cook, scientist and co-principal investigator; Joel Harringa, assistant scientist II; Sergey Bud'ko, scientist; and Klaus Schmidt-Rohr, faculty scientist. Also taking part in the research was Rama Venkatasubramanian, who is director of the Center for Solid State Energetics at RTI International, located in North Carolina.

So-called thermoelectric materials that convert heat into electricity have been known since the early 1800s. One well-established group of thermoelectric materials is composed of tellurium, antimony, germanium and silver, and thus is known by the acronym "TAGS." Thermoelectricity is based on the movement of charge carriers from their heated side to their cooler side, just as electrons travel along a wire.

The process, known as the Seebeck effect, was discovered in 1821 by Thomas Johann Seebeck, a physicist who lived in what is now Estonia. A related phenomenon observed in all thermoelectric materials is known as the Peltier effect, named after French physicist Jean-Charles Peltier, who discovered it in 1834. The Peltier effect can be utilized for solid-state heating or cooling with no moving parts.

In the nearly two centuries since the discovery of the Seebeck and Peltier effects, practical applications have been limited due to the low efficiency with which the materials performed either conversion. Significant work to improve that efficiency took place during the 1950s, when thermoelectric conversion was viewed as an ideal power source for deep-space probes, explained team member Cook. "Thermoelectric conversion was successfully used to power the Voyager, Pioneer, Galileo, Cassini, and Viking spacecrafts," he said.

Despite its use by NASA, the low efficiency of thermoelectric conversion still kept it from being harnessed for more down-to-earth applications – even as research around the world continued in earnest. "Occasionally, you would hear about a large increase in efficiency," Levin explained. But the claims did not hold up to closer scrutiny.

All that changed in 2010, when the Ames Laboratory researchers found that adding just one percent of the rare-earth elements cerium or ytterbium to a TAGS material was sufficient to boost its performance.

The results of the group's work appeared in the article, "Analysis of Ce- and Yb-Doped TAGS-85 Materials with Enhanced Thermoelectric Figure of Merit," published online in November 2010 in the journal Advanced Functional Materials.

The team has yet to understand exactly why such a small compositional change in the material is able to profoundly affect its properties. However, they theorize that doping the TAGS material with either of the two rare-earth elements could affect several possible mechanisms that influence thermoelectric properties.

Team member Schmidt-Rohr studied the materials using Ames Laboratory's solid-state nuclear magnetic resonance spectroscopy instruments. This enabled the researchers to verify that the one percent doping of cerium or ytterbium affected the structure of the thermoelectric material. In order to understand effect of magnetism of rare earths, team member Bud'ko studied magnetic properties of the materials. "Rare-earth elements modified the lattice," said Levin, referring to the crystal structure of the thermoelectric materials.

The group plans to test the material in order to better understand why the pronounced change took place and, hopefully, to boost its performance further.

The durable and relatively easy-to-produce material has innumerable applications, including recycling waste heat from industrial refineries or using auto exhaust heat to help recharge the battery in an electric car. "It's a very amazing area," Levin said, particularly since many years of prior research into TAGS materials enables researchers to understand their nature. Better understanding of the thermoelectric and their improvement can immediately result in applications at larger scale than now.

Additionally, the Ames Laboratory results – dependent as they were on doping TAGS with small amounts of cerium or ytterbium – provide yet more evidence of rare-earth elements' strategic importance. Cerium or ytterbium are members of a group of 15 lanthanides, deemed essential to just about every new technology from consumer electronics and cell phones to hybrid car batteries and generator motors in wind turbines. The Ames Laboratory has been a leader in rare-earth research going back to the closing days of World War II. Fears of shortages of rare-earth elements have caused these little-known materials to be a much-talked-about subject in the news lately.

More information: E.M. Levin, B.A. Cook, J.L. Harringa, S. L. Bud'ko, R. Venkatasubramanian, K. Schmidt-Rohr, "Analysis of Ce- and Yb-Doped TAGS-85 Materials with Enhanced Thermoelectric Figure of Merit," Advanced Functional Materials, 2010, in press. DOI:10.1002/adfm.201001307

Provided by Ames Laboratory (news : web)

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