Chemist develops technique to use light to predict molecular crystal structures

A Syracuse University chemist has developed a way to use very low frequency light waves to study the weak forces (London dispersion forces) that hold molecules together in a crystal. This fundamental research could be applied to solve critical problems in drug research, manufacturing and quality control.

The research by Timothy Korter, associate professor of chemistry in SU's College of Arts and Sciences, was the cover article of the March 14 issue of Physical Chemistry Chemical Physics. 

"When developing a drug, it is important that we uncover all of the possible ways the molecules can pack together to form a crystal," Korter says. "Changes in the crystal structure can change the way the drug is absorbed and accessed by the body."

One industry example is that of a drug distributed in the form of a gel capsule that crystallized into a solid when left on the shelf for an extended period of time, Korter explains. The medication inside the capsule changed to a form that could not dissolve in the human body, rendering it useless. The drug was removed from shelves. This example shows that it is not always possible for drug companies to identify all the variations of a drug's crystal structure through traditional experimentation, which is time consuming and expensive.

"The question is," Korter says, "can we leverage a better understanding of London and other weak intermolecular forces to predict these changes in crystal structure?"

Korter's lab is one of only a handful of university-based research labs in the world exploring the potential of THz radiation for chemical and pharmaceutical applications. THz light waves exist in the region between infrared radiation and microwaves and offer the unique advantages of being non-harmful to people and able to safely pass through many kinds of materials. THz can also be used to identify the chemical signatures of a wide range of substances. Korter has used THz to identify the chemical of signatures of molecules ranging from improvised explosives and drug components to the building blocks of DNA.

Korter's new research combines THz experiments with new computational models that accurately account for the effects of the London dispersion forces to predict crystal structures of various substances. London forces are one of several types of intermolecular forces that cause molecules to stick together and form solids. Environmental changes (temperature, humidity, light) impact the forces in ways that can cause the crystal structure to change. Korter's research team compares the computer models with the THz experiments and uses the results to refine and improve the theoretical models.

"We have demonstrated how to use THz to directly visualize these chemical interactions," Korter says. "The ultimate goal is to use these THz signatures to develop theoretical models that take into account the role of these weak forces to predict the crystal structures of pharmaceuticals before they are identified through experimentation."

A National Science Foundation Early Career Development (CAREER) Award funds Korter's research.

Story Source:

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

Journal Reference:

Matthew D. King, William D. Buchanan, Timothy M. Korter. Application of London-type dispersion corrections to the solid-state density functional theory simulation of the terahertz spectra of crystalline pharmaceuticals. Physical Chemistry Chemical Physics, 2011; 13 (10): 4250 DOI: 10.1039/C0CP01595D

Rapid etching X-rayed: Physicists unveil processes during fast chemical dissolution

A breakthrough in the study of chemical reactions during etching and coating of materials was achieved by a research group headed by Kiel physicist, Professor Olaf Magnussen. The team from the Christian-Albrechts-Universität zu Kiel (CAU), Germany, in collaboration with staff from the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, have uncovered for the first time just what happens in manufacturing processes, used for the formation of metal contacts thinner than a human hair in modern consumer electronics, such as flat-screen television.

The results appear in the Journal of the American Chemical Society.

For their research the scientists used the intense X-ray radiation of the experimental station ID32, one of the ESRF's instruments. The X-ray beam was directed onto a gold surface while it dissolved in diluted hydrochloric acid. Because the reflected X-rays are sensitive to tiny changes in the atomic arrangement at the material's surface, the metal removal during the reaction can be precisely measured.

"Such studies were only possible during very slow changes of the material so far," Olaf Magnussen explains. To gain insight into the fast reactions going on in industrially employed processes the speed of the measurements had to be increased more than a hundredfold. Even during very fast etching the removal of the metal proceeded very uniformly. "The material dissolves quasi atomic layer by atomic layer, without formation of deeper holes," Magnussen remarks. In a similar way, the team could follow the attachment of atoms during the chemical coating of materials.

Among the diverse industrial applications of chemical etching and coating are high-tech manufacturing processes, for example in the production of electronic devices. These require precisely controlled reactions. In order to optimize such etching and coating processes they are intensely studied worldwide. Until now it was only possible to analyse the finished product. With the method developed by the scientists, changes within a few thousandth seconds may be detected so that the reactions at the material's surface can be tracked on the atomic scale under realistic conditions.

Christian-Albrechts-Universität zu Kiel is a North German research university with proven international expertise in the field of nanoscience, including research using synchrotron radiation. In a number of research networks, funded by the German Federal Ministry of Education and Research, Kiel scientists develop new methods and instruments. In addition, the CAU competes for a Cluster of Excellence in the area of nanoscience and surface science within the ongoing round of the German Excellence Initiative.

The ESRF is a European research institution, funded by 19 nations, providing and utilizing brilliant synchrotron X-rays for advanced scientific research.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Christian-Albrechts-Universitaet zu Kiel.

Journal Reference:

Frederik Golks, Klaus Krug, Yvonne Gru¨nder, Jo¨rg Zegenhagen, Jochim Stettner, Olaf M. Magnussen. High-Speed in situ Surface X-ray Diffraction Studies of the Electrochemical Dissolution of Au(001). Journal of the American Chemical Society, 2011; 133 (11): 3772 DOI: 10.1021/ja1115748

The drive toward hydrogen vehicles just got shorter

Researchers have revealed a new single-stage method for recharging the hydrogen storage compound ammonia borane. The breakthrough makes hydrogen a more attractive fuel for vehicles and other transportation modes.

In an article appearing recently in the journal Science, Los Alamos National Laboratory (LANL) and University of Alabama researchers working within the U.S. Department of Energy's Chemical Hydrogen Storage Center of Excellence describe a significant advance in hydrogen storage science.

Hydrogen is in many ways an ideal fuel. It possesses a high energy content per unit mass when compared to petroleum, and it can be used to run a fuel cell, which in turn can be used to power a very clean engine. On the down side, H2 has a low energy content per unit volume versus petroleum (it is very light and bulky). The crux of the hydrogen issue has been how to get enough of the element on board a vehicle to power it a reasonable distance.

Work at LANL and elsewhere has focused on chemical hydrides for storing hydrogen, with one material in particular, ammonia borane, taking center stage. Ammonia borane is attractive because its hydrogen storage capacity approaches a whopping 20 percent by weight -- enough that it should, with appropriate engineering, permit hydrogen-fueled vehicles to go farther than 300 miles on a single "tank," a benchmark set by the U.S. Department of Energy.

Hydrogen release from ammonia borane has been well demonstrated, and its chief drawback to use has been the lack of energy-efficient methods to reintroduce hydrogen into the spent fuel once burned. In other words, until now, after hydrogen release, the ammonia borane couldn't be recycled efficiently enough.

The Science paper describes a simple scheme that regenerates ammonia borane from a hydrogen depleted "spent fuel" form (called polyborazylene) back into usable fuel via reactions taking place in a single container. This "one pot" method represents a significant step toward the practical use of hydrogen in vehicles by potentially reducing the expense and complexity of the recycle stage. Regeneration takes place in a sealed pressure vessel using hydrazine and liquid ammonia at 40 degrees Celsius and necessarily takes place off-board a vehicle. The researchers envision vehicles with interchangeable hydrogen storage "tanks " containing ammonia borane that are used, and sent back to a factory for recharge.

The Chemical Hydrogen Storage Center of Excellence was one of three Center efforts funded by DOE. The other two focused on hydrogen sorption technologies and storage in metal hydrides. The Center of Excellence was a collaboration between Los Alamos, Pacific Northwest National Laboratory, and academic and industrial partners.

LANL researcher Dr. John Gordon, a corresponding author for the paper, credits collaboration encouraged by the Center model with the breakthrough.

"Crucial predictive calculations carried out by University of Alabama Professor Dave Dixon's group guided the experimental work of the Los Alamos team, which included researchers from both the Chemistry Division and the Materials Physics and Applications Division at LANL," Gordon said.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Los Alamos National Laboratory.

Journal Reference:

A. D. Sutton, A. K. Burrell, D. A. Dixon, E. B. Garner, J. C. Gordon, T. Nakagawa, K. C. Ott, J. P. Robinson, M. Vasiliu. Regeneration of Ammonia Borane Spent Fuel by Direct Reaction with Hydrazine and Liquid Ammonia. Science, 2011; 331 (6023): 1426 DOI: 10.1126/science.1199003

Self-strengthening nanocomposite created

Researchers at Rice University have created a synthetic material that gets stronger from repeated stress much like the body strengthens bones and muscles after repeated workouts.

Work by the Rice lab of Pulickel Ajayan, professor in mechanical engineering and materials science and of chemistry, shows the potential of stiffening polymer-based nanocomposites with carbon nanotube fillers. The team reported its discovery this month in the journal ACS Nano.

The trick, it seems, lies in the complex, dynamic interface between nanostructures and polymers in carefully engineered nanocomposite materials.

Brent Carey, a graduate student in Ajayan's lab, found the interesting property while testing the high-cycle fatigue properties of a composite he made by infiltrating a forest of vertically aligned, multiwalled nanotubes with polydimethylsiloxane (PDMS), an inert, rubbery polymer. To his great surprise, repeatedly loading the material didn't seem to damage it at all. In fact, the stress made it stiffer.

Carey, whose research is sponsored by a NASA fellowship, used dynamic mechanical analysis (DMA) to test their material. He found that after an astounding 3.5 million compressions (five per second) over about a week's time, the stiffness of the composite had increased by 12 percent and showed the potential for even further improvement.

"It took a bit of tweaking to get the instrument to do this," Carey said. "DMA generally assumes that your material isn't changing in any permanent way. In the early tests, the software kept telling me, 'I've damaged the sample!' as the stiffness increased. I also had to trick it with an unsolvable program loop to achieve the high number of cycles."

Materials scientists know that metals can strain-harden during repeated deformation, a result of the creation and jamming of defects -- known as dislocations -- in their crystalline lattice. Polymers, which are made of long, repeating chains of atoms, don't behave the same way.

The team is not sure precisely why their synthetic material behaves as it does. "We were able to rule out further cross-linking in the polymer as an explanation," Carey said. "The data shows that there's very little chemical interaction, if any, between the polymer and the nanotubes, and it seems that this fluid interface is evolving during stressing."

"The use of nanomaterials as a filler increases this interfacial area tremendously for the same amount of filler material added," Ajayan said. "Hence, the resulting interfacial effects are amplified as compared with conventional composites.

"For engineered materials, people would love to have a composite like this," he said. "This work shows how nanomaterials in composites can be creatively used."

They also found one other truth about this unique phenomenon: Simply compressing the material didn't change its properties; only dynamic stress -- deforming it again and again -- made it stiffer.

Carey drew an analogy between their material and bones. "As long as you're regularly stressing a bone in the body, it will remain strong," he said. "For example, the bones in the racket arm of a tennis player are denser. Essentially, this is an adaptive effect our body uses to withstand the loads applied to it.

"Our material is similar in the sense that a static load on our composite doesn't cause a change. You have to dynamically stress it in order to improve it."

Cartilage may be a better comparison -- and possibly even a future candidate for nanocomposite replacement. "We can envision this response being attractive for developing artificial cartilage that can respond to the forces being applied to it but remains pliable in areas that are not being stressed," Carey said.

Both researchers noted this is the kind of basic research that asks more questions than it answers. While they can easily measure the material's bulk properties, it's an entirely different story to understand how the polymer and nanotubes interact at the nanoscale.

"People have been trying to address the question of how the polymer layer around a nanoparticle behaves," Ajayan said. "It's a very complicated problem. But fundamentally, it's important if you're an engineer of nanocomposites.

"From that perspective, I think this is a beautiful result. It tells us that it's feasible to engineer interfaces that make the material do unconventional things."

Story Source:

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

Journal Reference:

Brent J. Carey, Prabir K. Patra, Lijie Ci, Glaura G. Silva, Pulickel M. Ajayan. Observation of Dynamic Strain Hardening in Polymer Nanocomposites. ACS Nano, 2011; 110321121458018 DOI: 10.1021/nn103104g

Neutron analysis yields insight into bacteria for solar energy

Structural studies of some of nature's most efficient light-harvesting systems are lighting the way for new generations of biologically inspired solar cell devices.

Researchers from Washington University in St. Louis and the Department of Energy's Oak Ridge National Laboratory used small-angle neutron scattering to analyze the structure of chlorosomes in green photosynthetic bacteria. Chlorosomes are efficient at collecting sunlight for conversion to energy, even in low-light and extreme environments.

"It's one of the most efficient light harvesting antenna complexes found in nature," said co-author and research scientist Volker Urban of ORNL's Center for Structural Molecular Biology, or CSMB.

Neutron analysis performed at the CSMB's Bio-SANS instrument at the High Flux Isotope Reactor allowed the team to examine chlorosome structure under a range of thermal and ionic conditions.

"We found that their structure changed very little under all these conditions, which shows them to be very stable," Urban said. "This is important for potential biohybrid applications -- if you wanted to use them to harvest light in synthetic materials like a hybrid solar cell, for example."

The size, shape and organization of light-harvesting complexes such as chlorosomes are critical factors in electron transfer to semiconductor electrodes in solar devices. Understanding how chlorosomes function in nature could help scientists mimic the chlorosome's efficiency to create robust biohybrid or bio-inspired solar cells.

"What's so amazing about the chlorosome is that this large and complicated assembly is able to capture light effectively across a large area and then funnel the light to the reaction center without losing it along the way," Urban said. "Why this works so well in chlorosomes is not well understood at all."

"We're trying to find out general principles that are important for capturing, harvesting and transporting light efficiently and see how nature has solved that," Urban said.

Small-angle neutron scattering enabled the team to clearly observe the complicated biological systems at a nanoscale level without damaging the samples.

"With neutrons, you have an advantage that you get a very sharp contrast between these two phases, the chlorosome and the deuterated buffer. This gives you something like a clear black and white image," Urban said.

The team, led by Robert Blankenship of Washington University, published its findings in the journal Langmuir. The research was supported through the Photosynthetic Antenna Research Center, an Energy Frontier Research Center funded by DOE's Office of Science. Both HFIR and the Bio-SANS facility at ORNL's Center for Structural Molecular Biology are also supported by DOE's Office of Science.

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Kuo-Hsiang Tang, Liying Zhu, Volker S. Urban, Aaron M. Collins, Pratim Biswas, Robert E. Blankenship. Temperature and Ionic Strength Effects on the Chlorosome Light-Harvesting Antenna Complex. Langmuir, 2011; 110315121146005 DOI: 10.1021/la104532b

New model predicts the optical properties of nano-structures

UBC chemists have developed a new model to predict the optical properties of non-conducting ultra-fine particles.

The finding could help inform the design of tailored nano-structures, and be of utility in a wide range of fields, including the remote sensing of atmospheric pollutants and the study of cosmic dust formation.

Aerosols and nano-particles play a key role in atmospheric processes as industrial pollutants, in interstellar chemistry and in drug delivery systems, and have become an increasingly important area of research. They are often complex particles made up of simpler building blocks.

Now research published this week by UBC chemists indicates that the optical properties of more complex non-conducting nano-structures can be predicted based on an understanding of the simple nano-objects that make them up. Those optical properties in turn give researchers and engineers an understanding of the particle's structure.

"Engineering complex nano-structures with particular infrared responses typically involves hugely complex calculations and is a bit hit and miss," says Thomas Preston, a researcher with the UBC Department of Chemistry.

"Our solution is a relatively simple model that could help guide us in more efficiently engineering nano-materials with the properties we want, and help us understand the properties of these small particles that play an important role in so many processes."

The findings were published this week in the Proceedings of the National Academy of Sciences.

"For example, the properties of a more complex particle made up of a cavity and a core structure can be understood as a hybrid of the individual pieces that make it up," says UBC Professor Ruth Signorell, an expert on the characterization of molecular nano-particles and aerosols and co-author of the study.

The experiment also tested the model against CO2 aerosols with a cubic shape, which play a role in cloud formation on Mars.

The research was supported by the Natural Sciences and Engineering Research Council of Canada and the Canada Foundation for Innovation.

Story Source:

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

Journal Reference:

T. C. Preston, R. Signorell. Vibron and phonon hybridization in dielectric nanostructures. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1100170108

Sticking power: New adhesive could find place in space

A recently patented adhesive made by Kansas State University researchers could become a staple in every astronaut's toolbox.

The patent, "pH dependent adhesive peptides," was issued to the Kansas State University Research Foundation.*

It was created by John Tomich, professor of biochemistry, and Xiuzhi "Susan" Sun, professor of grain science and industry. Assisting in the research was Takeo Iwamoto, an adjunct professor in biochemistry, and Xinchun Shen, a former postdoctoral researcher.

"The adhesive we ended up developing was one that formed nanoscale fibrils that become entangled, sort of like Velcro. It has all these little hooks that come together," Tomich said. "It's a mechanical type of adhesion, though, not a chemical type like most commercial adhesives."

Because of its unusual properties, applications will most likely be outside the commercial sector, Tomich said.

For example, unlike most adhesives that become brittle as moisture levels decrease, the K-State adhesive's bond only becomes stronger. Because of this, it could be useful in low-moisture environments like outer space, where astronauts could use it to reattach tiles to a space shuttle.

Conversely, its deterioration from water could also serve a purpose.

"It could be used as a timing device or as a moisture detection device," Tomich said. "There could be a circuit or something that when the moisture got to a certain level, the adhesive would fail and break the circuit, sounding an alarm."

The project began nearly a decade ago as Sun and a postdoctal researcher were studying the adhesive properties of soybean proteins. Needing an instrument to synthesize protein peptides, Sun contacted Tomich.

Serendipitously, Tomich's lab had developed a peptide some time ago that had cement-like properties. Tomich said he knew it was unusual but had set it aside to pursue other interests.

"When Dr. Sun and I resurrected this protein, we didn't use the whole thing -- just a segment of it," Tomich said. "We isolated a certain segment where the cells are highly attracted to each other and form these fibrils."

Since their collaboration Tomich has taken the same sequence and changed the way it was designed. The new peptide, he said, will have an eye toward gene therapy.

Sun's lab is trying to optimize the sequence against adhesion, as well as study how peptide sequences influence adhesion properties and surface energy.

"I continue studying protein structures and functional properties in terms of adhesion -- folding, aggregation, surface energy and gelling properties -- so we can rationally design and develop biobased adhesives using plant proteins," she said.

*Kansas State University Research Foundation is a nonprofit corporation responsible for managing technology transfer activities of K-State. The research foundation is working with the National Institute for Strategic Technology Acquisition and Commercialization to license the patent. The patent covers an adhesive made from peptides -- a compound containing two or more amino acids that link together -- that increases in strength as moisture is removed.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Kansas State University.