Pentagonal tiles pave the way towards organic electronics

 New research paves way for the nanoscale self-assembly of organic building blocks, a promising new route towards the next generation of ultra-small electronic devices.

Ring-like molecules with unusual five-fold symmetry bind strongly to a copper surface, due to a substantial transfer of charge, but experience remarkably little difficulty in sideways diffusion, and exhibit surprisingly little interaction between neighbouring molecules. This unprecedented combination of features is ideal for the spontaneous creation of high-density stable thin films, comprising a pavement of these organic pentagonal tiles, with potential applications in computing, solar power and novel display technologies.

Currently, commercial electronics use a top-down approach, with the milling or etching away of inorganic material, such as silicon, to make a device smaller. For many years the computing power of a given size of computer chip has been doubling every eighteen months (a phenomenon known as Moore's law) but a limit in this growth is soon expected. At the same time, the efficiency of coupling electronic components to incoming or outgoing light (either in the generation of electricity from sunlight, or in the generation of light from electricity in flat-screen displays and lighting) is also fundamentally limited by the development of fabrication techniques at the nanometre scale (a nanometre being one billionth of a metre).

Researchers are therefore looking for ingenious solutions in the creation of ever smaller electronics. The field of nanotechnology is taking a bottom-up approach of creating electronics using naturally self-assembling organic components, such as polymers, which will be capable of spontaneously forming devices with the desired electronic or optical characteristics.

The latest findings are from scientists at the University of Cambridge and Rutgers University who are working on the development of new classes of organic thin films on surfaces. By studying the fundamental forces at play in self-assembling thin films, they are developing the knowledge that will allow them to tailor these films into molecular-scale organic-electronic devices, creating smaller components than would ever be possible with conventional fabrication techniques.

Dr Holly Hedgeland, of the Department of Physics at the University of Cambridge, one of the co-authors of the paper reporting the research, said: "With the semiconductor industry currently worth an estimated $249 billion per year there is a clear motivation towards a molecular scale understanding of innovative technologies that could come to replace those we use today."

It is not simply the electronic properties of a molecule on a surface that will control its potential to form part of a device, but also whether it will move by itself into the required structural configuration and remain stable in that position even if the device becomes heated in use.

Molecules that are strongly bound to the substrate with a high degree of transfer of charge offer a range of new possibilities, though little is currently known of their behaviour. A number of organic molecules, usually featuring carbon rings across which electronic charge can conduct, potentially demonstrate the right electronic properties, but the long-range forces which will govern their self-assembly during the first phases of growth often remain a mystery.

Now the interdisciplinary team based in the Departments of Physics and Chemistry at the University of Cambridge, and the Department of Chemistry and Chemical Biology at Rutgers University, have reported the first dynamical measurements for a new class of organic thin film where cyclopentadienyl molecules (C5H5) receive significant electronic charge from the surface, yet diffuse easily across the surface and show interactions with each other that are much weaker than would typically be expected for the amount of charge transferred.

Hedgeland explained: "By coupling the experimental helium spin echo technique with advanced first-principles calculations, we were able to study the dynamic behaviour of a cyclopentendienyl layer on a copper surface, and to deduce that the charge transfer between the metal and the organic molecule was occurring in a counter-intuitive sense."

Dr Marco Sacchi, of the Department of Chemistry at the University of Cambridge, who carried out the calculations that helped explain the startling new experimental results, said that "the key to the unique behavior of cyclopentadienyl lies in its pentagonal (five-fold) symmetry, which prevents it latching onto any one site within the triangular (three-fold) symmetry of the copper surface through directional covalent bonds, leaving it free to move easily from site to site; at the same time, its internal electronic structure is just one electron short of an extremely stable `aromatic' configuration, encouraging a high degree of charge transfer from the surface and creating a strong non-directional ionic bond."

The researchers' findings, reported in Physical Review Letters on May 6, highlight the potential of a new category of molecular adsorbate, which could fulfill all the criteria required for useful application.

Hedgeland concluded: "The unusual character of the charge transfer in this case prevents the large repulsive interactions between adjacent molecules that would otherwise have been expected, and hence should enable the formation of unusually high-density films. At the same time, the molecules remain highly mobile and yet strongly bound to the surface, with a large degree of thermal stability. In all, this is a combination of physical properties that offers huge potential benefit to the development of new classes of self-assembled organic films relevant for technological applications."

Story Source:

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

Journal Reference:

H. Hedgeland, B. Lechner, F. Tuddenham, A. Jardine, W. Allison, J. Ellis, M. Sacchi, S. Jenkins, B. Hinch. Weak Intermolecular Interactions in an Ionically Bound Molecular Adsorbate: Cyclopentadienyl/Cu(111). Physical Review Letters, 2011; 106 (18) DOI: 10.1103/PhysRevLett.106.186101

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

A renewable twist on fossil fuels

 Pulling valuable fuels out of thin air? It sounds like magic, but Joel Rosenthal, a chemist at the University of Delaware, is working to transform carbon dioxide (CO2), a greenhouse gas in the atmosphere, into gas for your car and clean-energy future fuels.

Such a feat could help reduce the rising CO2 levels implicated in global warming and also offer a new method of renewable energy production.

Oak Ridge Associated Universities (ORAU), a consortium of 98 Ph.D.-granting universities, of which UD is a member, has selected Rosenthal to receive the Ralph E. Powe Junior Faculty Enhancement Award to pursue the novel research. Rosenthal is one of 30 award winners nationwide.

The competitive award, which provides $5,000 in seed funding from ORAU and $5,000 in matching funding from the faculty member's university, is intended to enrich the research and educational growth of young faculty and serve as a springboard to new funding opportunities.

Rosenthal and his team are designing electrocatalysts from metals such as nickel and palladium that will freely give away electrons when they react with carbon dioxide, thus chemically reducing this greenhouse gas into energy-rich carbon monoxide or methanol.

Besides its use in making plastics, solvents, carpet and other products, methanol fuels race cars in the United States and currently is being researched as a hydrogen carrier for fuel cell vehicles.

Carbon monoxide is an important precursor to liquid hydrocarbons in the energy arena, in addition to its applications as an industrial chemical for producing plastics to detergents to the acetic acid used in food preservation, drug manufacturing and other fields.

"The catalytic reduction of carbon dioxide to carbon monoxide is an important transformation that would allow for the mitigation of atmospheric CO2 levels, while producing an energy-rich substrate that forms a basis for fuels production," Rosenthal says.

"The chemistry we're doing is energetically uphill -- it's an energy-storing process rather than a downhill, energy-liberating process," he notes. "And our goal is to make liquid fuel renewably from wind and solar sources, not from typical fossil fuel bases."

As early as junior high, Rosenthal said, he realized that basic life processes are linked to molecular energy conversion. Then his undergraduate and graduate research took off on renewables.

He earned his undergraduate degree in organic chemistry from New York University and his doctorate in inorganic chemistry at MIT while studying how metals catalyze various energy conversion processes. His doctoral adviser at MIT was Dan Nocera, a leading scientist in renewable energy research.

The strong reputation of the chemistry and biochemistry department lured Rosenthal, a New York City native, to UD. He joined the UD faculty this past fall and already has a research group of eight focusing on the project -- one postdoctoral researcher, four graduate students and three undergraduates.

"The CO2 problem is very important, and people have to tackle it," Rosenthal says. "It's my hope to be able to map out the molecular design principles for efficient CO2 conversion into fuels. Then you can think about doing this on a commercially relevant scale."

Conservative estimates predict that by 2050, the rate of global energy consumption will roughly double the rate recorded at the end of the 20th century. Most scientists believe that rising carbon dioxide levels are leading to global climate change.

Story Source:

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

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

Natural protection against radiation

In the midst of ongoing concerns about radiation exposure from the Fukushima nuclear power plant in Japan, scientists are reporting that a substance similar to resveratrol — an antioxidant found in red wine, grapes and nuts — could protect against radiation sickness. The report appears in ACS Medicinal Chemistry Letters.

Michael Epperly, Kazunori Koide and colleagues explain that radiation exposure, either from accidents (like recent events in Japan) or from radiation therapy for cancer, can make people sick. High doses can even cause death. The U.S. Food and Drug Administration is currently evaluating a drug for its ability to protect against radiation sickness, but it is difficult to make in large amounts, and the drug has side-effects that prevent its use for cancer patients. To overcome these disadvantages, the researchers studied whether resveratrol — a natural and healthful antioxidant found in many foods — could protect against radiation injuries.

They found that resveratrol protected cells in flasks but did not protect mice (stand-ins for humans in the laboratory) from radiation damage. However, the similar natural product called acetyl resveratrol did protect the irradiated mice. It also can be produced easily in large quantities and given orally. The authors caution that it has not yet been determined whether acetyl resveratrol is effective when orally administered.

More information: “The Use of 3,5,4’-Tri-O-acetylresveratrol as a Potential Prodrug for Resveratrol Protects Mice from gamma-Irradiation-Induced Death” ACS Medicinal Chemistry Letters.

Provided by American Chemical Society (news : web)

Cola detectives test natural flavoring claims for pricey soft drinks

Scientists are reporting development and successful testing of a new way to determine whether cola drinks -- advertised as being made with natural ingredients and sold at premium prices -- really do contain natural flavoring. The report appears in ACS' Journal of Proteome Research.

In the study, Pier Giorgio Righetti and colleagues explain that cola drinks purportedly made from natural cola nuts are becoming popular and are sold in many natural food stores. Genuine cola "nuts" are seeds from the fruit of the cola tree, which is native to African rainforests, and they are expensive to harvest and ship. In West African cultures, people include the nuts in ceremonies and offer them to guests. The nuts also have possible health benefits — they may help treat whooping cough, asthma, migraines and dysentery. Most soft drink manufacturers don't use cola nuts today, but a select few are starting to advertise cola as a natural ingredient in their products — and charge extra for it. To see whether consumers are getting what they pay for, the scientists set out to find a way to finger the drinks with real natural extracts.

The group found that testing for proteins was an accurate way to verify natural flavoring claims. They detected plant proteins in a drink claiming to have "organic agave syrup and cola nut extracts". On the other hand, Coca Cola products — which do not claim to include cola extract — have no protein. The scientists say, "The identifications here obtained represent the quality mark of this beverage and, in a way, give a certificate of authenticity."

More information: “Going nuts for nuts? The trace proteome of a Cola drink, as detected via combinatorial peptide ligand libraries” Journal of Proteome Research.

Provided by American Chemical Society (news : web)

Simulating amyloid formation

Many neurodegenerative diseases are characterized by proteins that assume an abnormal configuration, which leads to their aggregation and deposition in and around rve cells, causing cell death. This process, called amyloid formation, is a common pathological feature in diseases such as Alzheimer’s, Parkinson’s and prion diseases, as well as type II diabetes. Charlotte Hauser and co-workers from the A*STAR Institute of Bioengineering and Nanotechnology and Institute of High Performance Computing along with colleagues in Europe have now designed a class of ultrasmall peptides that simulate the self-assembly of abnormally folded proteins in such neurodegenerative conditions.

Hauser and her co-workers designed ultrasmall peptides consisting of three to six amino acid residues, each containing a characteristic motif—a ‘tail’ of uncharged residues with decreasing affinity to water capped by a polar ‘head’ residue. These peptides spontaneously self-assembled in water to form fibril structures (pictured) resembling those that make up the amyloid-ß plaques found in the brains of Alzheimer’s patients.

The researchers hypothesize that fiber assembly is a complex stepwise mechanism involving at least three distinct stages. Individual peptide molecules first bond to each other in an anti-parallel arrangement to form dimers. The pairs then line up to form single ?-helical fibers as intermediate structures, which continue to assemble and then condense into fibrous scaffolds in the form of solid hydrogels.

The team further examined the driving forces for self-assembly and found that gel formation was critically dependent on the length of the tail and the polar nature of the head. Peptides containing six amino acid residues formed gels more readily than the others, and the strongest gels were formed by peptides containing an acidic head residue. A minimum peptide concentration was required for fiber formation, and increasing the temperature was found to accelerate the self-assembly process.

Investigation into the assembly process and experimental results were verified by computer simulations. This helped the research team confirm that the formation of peptide pairs precedes fiber formation, suggesting that the peptides have a strong tendency to aggregate because the sheet-like structures have a lower free energy state than individual fibers, and are therefore more stable.

“Understanding the driving forces that enable these ultrasmall peptides to stably self-assemble into macromolecular structures will shed light on aggregate formation in amyloidogenesis,” says Hauser. “This would facilitate the design of new therapeutics to prevent and control plaque formation in neurodegenerative disorders and a wide range of other debilitating diseases.”

More information: Hauser, C. A. E. et al. Natural tri- to hexapeptides self-assemble in water to amyloid ß-type fiber aggregates by unexpected ?-helical intermediate structures. Proceedings of the National Academy of Sciences 108, 1361–1366 (2011). http://dx.doi.org/ … s.1014796108

Abstract
Many fatal neurodegenerative diseases such as Alzheimer’s, Parkinson, the prion-related diseases, and non-neurodegenerative disorders such as type II diabetes are characterized by abnormal amyloid fiber aggregates, suggesting a common mechanism of pathogenesis. We have discovered that a class of systematically designed natural tri- to hexapeptides with a characteristic sequential motif can simulate the process of fiber assembly and further condensation to amyloid fibrils, probably via unexpected dimeric ?-helical intermediate structures. The characteristic sequence motif of the novel peptide class consists of an aliphatic amino acid tail of decreasing hydrophobicity capped by a polar head. To our knowledge, the investigated aliphatic tripeptides are the shortest ever reported naturally occurring amino acid sequence that can adopt ?-helical structure and promote amyloid formation. We propose the stepwise assembly process to be associated with characteristic conformational changes from random coil to ?-helical intermediates terminating in cross-ß peptide structures. Circular dichroism and X-ray fiber diffraction analyses confirmed the concentration-dependent conformational changes of the peptides in water. Molecular dynamics simulating peptide behavior in water revealed monomer antiparallel pairing to dimer structures by complementary structural alignment that further aggregated and stably condensed into coiled fibers. The ultrasmall size and the dynamic facile assembly process make this novel peptide class an excellent model system for studying the mechanism of amyloidogenesis, its evolution and pathogenicity. The ability to modify the properties of the assembled structures under defined conditions will shed light on strategies to manipulate the pathogenic amyloid aggregates in order to prevent or control aggregate formation.

Provided by Agency for Science, Technology and Research (A*STAR)