Unlike Rubber Bands, Molecular Bonds May Not Break Faster When Pulled

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ScienceDaily (June 22, 2009) — From balloons to rubber bands, things always break faster when stretched. Or do they? University of Illinois scientists studying chemical bonds now have shown this isn't always the case, and their results may have profound implications for the stability of proteins to mechanical stress and the design of new high-tech polymers.

"Our findings contradict the intuitive notion that molecules are like rubber bands in that when we pull on a chemical bond, it should always break faster," said chemistry professor Roman Boulatov, who led the study. "When we stretch a sulfur-sulfur bond, for example, how fast it breaks depends on how the nearby atoms move."
The findings also contradict the conventional interpretation of experimental results obtained by other researchers studying the fragmentation rate of certain proteins containing sulfur-sulfur bonds when stretched with a microscopic force probe. In those experiments, as the force increased, the proteins fragmented faster, leading the researchers to conclude that as the sulfur-sulfur bond was stretched, it reacted faster and broke faster.
"Our experiments suggest a different conclusion," Boulatov said. "We believe the acceleration of the fragmentation was caused by a change in the protein's structure as it was stretched, and had little or nothing to do with increased reactivity of a stretched sulfur-sulfur bond."
In their experiments, the researchers use stiff stilbene as a molecular force probe to generate well-defined forces on molecules atom by atom.
The probe allows reaction rates to be measured as a function of the restoring force. Similar to the force that develops when a rubber band is stretched, the molecular restoring force contains information about how much the molecule was distorted, and in what direction.
In previous work, when Boulatov's team pulled on carbon-carbon bonds with the same force they would later apply to sulfur-sulfur bonds, they found the carbon-carbon bonds broke a million times faster than when no force was applied.
"Because the sulfur-sulfur bond is much weaker than the carbon-carbon bond, you might think it would be much more sensitive to being pulled on," Boulatov said. "We found, however, that the sulfur-sulfur bond does not break any faster when pulled."
Boulatov and his team report their findings in a paper accepted for publication in Angewandte Chemie, and posted on the journal's Web site.
"When we pulled on the sulfur-sulfur bond, the nearby methylene groups prevented the rest of the molecule from relaxing," Boulatov said, "thus eliminating the driving force for the sulfur-sulfur bond to break any faster."
Chemists must bear in mind that even in simple chemical reactions, such as a single bond dissociation, "we must take into account other structural changes in the molecule," Boulatov said. "The elongation alone, which occurs when a bond is stretched, does not represent the full picture of what happens when the reaction occurs."
The good news, Boulatov said, is that not every polymer that is stretched will break faster. "We might be able to design polymers, for example, that would resist fragmentation under modest mechanical stresses," he said, "or will not break along the stretched direction, but in some other desired direction."
With Boulatov, co-authors of the paper are graduate student and lead author Timothy Kucharski, research associate Qing-Zheng Yang, postdoctoral researcher Yancong Tian, and graduate students Zhen Huang, Nicholas Rubin and Carlos Concepcion.
Funding was provided by the National Science Foundation, the U.S. Air Force Office of Scientific Research, the American Chemical Society Petroleum Research Fund, and the U. of I.
Adapted from materials provided by University of Illinois at Urbana-Champaign.

Ultra-dense Deuterium May Be Nuclear Fuel Of The Future

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ScienceDaily (May 12, 2009) — A material that is a hundred thousand times heavier than water and more dense than the core of the Sun is being produced at the University of Gothenburg. The scientists working with this material are aiming for an energy process that is both more sustainable and less damaging to the environment than the nuclear power used today.

Imagine a material so heavy that a cube with sides of length 10 cm weights 130 tonnes, a material whose density is significantly greater than the material in the core of the Sun. Such a material is being produced and studied by scientists in Atmospheric Science at the Department of Chemistry, the University of Gothenburg.
Towards commercial use
So far, only microscopic amounts of the new material have been produced. New measurements that have been published in two scientific journals, however, have shown that the distance between atoms in the material is much smaller than in normal matter. Leif Holmlid, Professor in the Department of Chemistry, believes that this is an important step on the road to commercial use of the material.
The material is produced from heavy hydrogen, also known as deuterium, and is therefore known as “ultra-dense deuterium”. It is believed that ultra-dense deuterium plays a role in the formation of stars, and that it is probably present in giant planets such as Jupiter.
An efficient fuel
So what can this super-heavy material be used for?
“One important justification for our research is that ultra-dense deuterium may be a very efficient fuel in laser driven nuclear fusion. It is possible to achieve nuclear fusion between deuterium nuclei using high-power lasers, releasing vast amounts of energy”, says Leif Holmlid.
The laser technology has long been tested on frozen deuterium, known as “deuterium ice”, but results have been poor. It has proved to be very difficult to compress the deuterium ice sufficiently for it to attain the high temperature required to ignite the fusion.
Energy source of the future
Ultra-dense deuterium is a million times more dense than frozen deuterium, making it relatively easy to create a nuclear fusion reaction using high-power pulses of laser light.
“If we can produce large quantities of ultra-dense deuterium, the fusion process may become the energy source of the future. And it may become available much earlier than we have thought possible”, says Leif Holmlid.
“Further, we believe that we can design the deuterium fusion such that it produces only helium and hydrogen as its products, both of which are completely non-hazardous. It will not be necessary to deal with the highly radioactive tritium that is planned for use in other types of future fusion reactors, and this means that laser-driven nuclear fusion as we envisage it will be both more sustainable and less damaging to the environment than other methods that are being developed.”
Deuterium – brief facts
Deuterium is an isotope of hydrogen that is found in large quantities in water, more than one atom per ten thousand hydrogen atoms has a deuterium nucleus. The isotope is denoted “2H” or “D”, and is normally known as “heavy hydrogen”. Deuterium is used in a number of conventional nuclear reactors in the form of heavy water (D2O), and it will probably also be used as fuel in fusion reactors in the future.
Adapted from materials provided by University of Gothenburg.

Scientists Discover New Way To Make Water

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http://www.sciencedaily.com/releases/2007/10/071031125457.htm

ScienceDaily (Nov. 1, 2007) — In a familiar high-school chemistry demonstration, an instructor first uses electricity to split liquid water into its constituent gases, hydrogen and oxygen. Then, by combining the two gases and igniting them with a spark, the instructor changes the gases back into water with a loud pop.

Scientists at the University of Illinois have discovered a new way to make water, and without the pop. Not only can they make water from unlikely starting materials, such as alcohols, their work could also lead to better catalysts and less expensive fuel cells.
"We found that unconventional metal hydrides can be used for a chemical process called oxygen reduction, which is an essential part of the process of making water," said Zachariah Heiden, a doctoral student and lead author of a paper accepted for publication in the Journal of the American Chemical Society, and posted on its Web site.
A water molecule (formally known as dihydrogen monoxide) is composed of two hydrogen atoms and one oxygen atom. But you can't simply take two hydrogen atoms and stick them onto an oxygen atom. The actual reaction to make water is a bit more complicated: 2H2 + O2 = 2H2O + Energy.
In English, the equation says: To produce two molecules of water (H2O), two molecules of diatomic hydrogen (H2) must be combined with one molecule of diatomic oxygen (O2). Energy will be released in the process.
"This reaction (2H2 + O2 = 2H2O + Energy) has been known for two centuries, but until now no one has made it work in a homogeneous solution," said Thomas Rauchfuss, a U. of I. professor of chemistry and the paper's corresponding author.
The well-known reaction also describes what happens inside a hydrogen fuel cell.
In a typical fuel cell, the diatomic hydrogen gas enters one side of the cell, diatomic oxygen gas enters the other side. The hydrogen molecules lose their electrons and become positively charged through a process called oxidation, while the oxygen molecules gain four electrons and become negatively charged through a process called reduction. The negatively charged oxygen ions combine with positively charged hydrogen ions to form water and release electrical energy.
The "difficult side" of the fuel cell is the oxygen reduction reaction, not the hydrogen oxidation reaction, Rauchfuss said. "We found, however, that new catalysts for oxygen reduction could also lead to new chemical means for hydrogen oxidation."
Rauchfuss and Heiden recently investigated a relatively new generation of transfer hydrogenation catalysts for use as unconventional metal hydrides for oxygen reduction.
In their JACS paper, the researchers focus exclusively on the oxidative reactivity of iridium-based transfer hydogenation catalysts in a homogenous, non-aqueous solution. They found the iridium complex effects both the oxidation of alcohols, and the reduction of the oxygen.
"Most compounds react with either hydrogen or oxygen, but this catalyst reacts with both," Heiden said. "It reacts with hydrogen to form a hydride, and then reacts with oxygen to make water; and it does this in a homogeneous, non-aqueous solvent."
The new catalysts could lead to eventual development of more efficient hydrogen fuel cells, substantially lowering their cost, Heiden said.
The work was funded by the U.S. Department of Energy.
Adapted from materials provided by University of Illinois at Urbana-Champaign.

Fausto Intilla

www.oloscience.com

Hydrogen Economy? Organic Polymer Stores Hydrogen Safely

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http://www.sciencedaily.com/releases/2007/08/070824111031.htm

Science Daily — Cardiff scientists exploring the safe storage of hydrogen to power vehicles as an environmentally friendly alternative to petrol have made a promising new discovery.

Having already developed an organic polymer capable of storing 1.7 per cent hydrogen by weight, Professors Neil McKeown from the School of Chemistry together with Peter Budd of the University of Manchester and David Book from the University of Birmingham can now report the creation of an organic polymer able to store around three per cent hydrogen by weight.
The figure is almost double the amount of hydrogen the group’s preliminary polymers could store last year, and offers hope of producing an organic polymer in the future capable of storing enough hydrogen to successfully power a vehicle.
Commenting on the development, Professor McKeown said: “We are excited to report this recent discovery by our research team of a polymer which can hold around three per cent hydrogen by weight. Although we still have a long way to go, it is clear that we are moving in the right direction, especially as we also have a number of promising new polymers to test. ”
In order to make hydrogen a viable alternative to petrol, a material which can store hydrogen at a weight of over six per cent is required. This figure is estimated by the American Department of Energy as the minimum required to make a fuel tank for hydrogen to power a vehicle for 300 miles.
“In order to obtain a polymer that can store useful quantities of hydrogen we need to make a much more porous material,” said Professor McKeown, “but one in which the holes are very small so as to fit snugly the small hydrogen molecules.”
Professor McKeown and his team are investigating a number of promising methods to enhance pororosity as they attempt to build on their current success and produce a material that can store and release hydrogen safely and effectively. They are also collaborating with Professor Kenneth Harris within the School of Chemistry to develop other types of hydrogen storage materials.
Cardiff is the lead University in the research project, which is funded by the Engineering and Physical Sciences Research Council.
Note: This story has been adapted from a news release issued by Cardiff University.

Fausto Intilla

www.oloscience.com