Sunday, September 11, 2011

Novel alloy could produce hydrogen fuel from sunlight

Scientists from the University of Kentucky and the University of Louisville have determined that an inexpensive semiconductor material can be "tweaked" to generate hydrogen from water using sunlight.

The research, funded by the U.S. Department of Energy, was led by Professors Madhu Menon and R. Michael Sheetz at the University of Kentucky Center for Computational Sciences, and Professor Mahendra Sunkara and graduate student Chandrashekhar Pendyala at the University of Louisville Conn Center for Renewable Energy Research. Their findings were published Aug. 1 in the Physical Review B.

The researchers say their findings are a triumph for computational sciences, one that could potentially have profound implications for the future of solar energy.

Using state-of-the-art theoretical computations, the University of Kentucky-University of Louisville team demonstrated that an alloy formed by a 2 percent substitution of antimony (Sb) in gallium nitride (GaN) has the right electrical properties to enable solar light energy to split water molecules into hydrogen and oxygen, a process known as photoelectrochemical (PEC) water splitting. When the alloy is immersed in water and exposed to sunlight, the chemical bond between the hydrogen and oxygen molecules in water is broken. The hydrogen can then be collected.

"Previous research on PEC has focused on complex materials," Menon said. "We decided to go against the conventional wisdom and start with some easy-to-produce materials, even if they lacked the right arrangement of electrons to meet PEC criteria. Our goal was to see if a minimal 'tweaking' of the electronic arrangement in these materials would accomplish the desired results."

Gallium nitride is a semiconductor that has been in widespread use to make bright-light LEDs since the 1990s. Antimony is a metalloid element that has been in increased demand in recent years for applications in microelectronics. The GaN-Sb alloy is the first simple, easy-to-produce material to be considered a candidate for PEC water splitting. The alloy functions as a catalyst in the PEC reaction, meaning that it is not consumed and may be reused indefinitely. University of Louisville and University of Kentucky researchers are currently working toward producing the alloy and testing its ability to convert solar energy to hydrogen.

Hydrogen has long been touted as a likely key component in the transition to cleaner energy sources. It can be used in fuel cells to generate electricity, burned to produce heat, and utilized in internal-combustion engines to power vehicles. When combusted, hydrogen combines with oxygen to form water vapor as its only waste product. Hydrogen also has wide-ranging applications in science and industry.

Because pure hydrogen gas is not found in free abundance on Earth, it must be manufactured by unlocking it from other compounds. Thus, hydrogen is not considered an energy source, but rather an "energy carrier." Currently, it takes a large amount of electricity to generate hydrogen by water splitting. As a consequence, most of the hydrogen manufactured today is derived from non-renewable sources such as coal and natural gas.

Sunkara says the GaN-Sb alloy has the potential to convert solar energy into an economical, carbon-free source for hydrogen.

"Hydrogen production now involves a large amount of CO2 emissions," Sunkara said. "Once this alloy material is widely available, it could conceivably be used to make zero-emissions fuel for powering homes and cars and to heat homes."

Menon says the research should attract the interest of other scientists across a variety of disciplines.

"Photocatalysis is currently one of the hottest topics in science," Menon said. "We expect the present work to have a wide appeal in the community spanning chemistry, physics and engineering."

Story Source:

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

Journal Reference:

R. Sheetz, Ernst Richter, Antonis N. Andriotis, Sergey Lisenkov, Chandrashekhar Pendyala, Mahendra K. Sunkara, Madhu Menon. Visible-light absorption and large band-gap bowing of GaN_{1-x}Sb_{x} from first principles. Physical Review B, 2011; 84 (7) DOI: 10.1103/PhysRevB.84.075304

Nano-thermometers show first temperature response differences within living cells

 Using a modern version of open-wide-and-keep-this-under-your-tongue, scientists have reported taking the temperature of individual cells in the human body, and finding for the first time that temperatures inside do not adhere to the familiar 98.6 degree Fahrenheit norm. They presented the research at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held in Denver.

Haw Yang and Liwei Lin, who collaborated on the research, did not use a familiar fever thermometer to check the temperature of cells, the 100 trillion or so microscopic packages of skin, nerve, heart, liver and other material that make up the human body. Cells are so small that almost 60,000 would fit on the head of a common pin. Yang is with Princeton University and Lin is with the University California-Berkeley.

"We used 'nano-thermometers'," Yang explained. "They are quantum dots, semiconductor crystals small enough to go right into an individual cell, where they change color as the temperature changes. We used quantum dots of cadmium and selenium that emit different colors (wavelengths) of light that correspond to temperature, and we can see that as a color change with our instruments."

Yang said that information about the temperatures inside cells is important, but surprisingly lacking among the uncountable terabytes of scientific data available today.

"The inside of a cell is so complicated, and we know very little about it," he pointed out. "When one thinks about chemistry, temperature is one of the most important physical factors that can change in a chemical reaction. So, we really wanted to know more about the chemistry inside a cell, which can tell us more about how the chemistry of life occurs."

Scientists long have suspected that temperatures vary inside individual cells. Yang explained that thousands of biochemical reactions at the basis of life are constantly underway inside cells. Some of those reactions produce energy and heat. But some cells are more active than others, and the unused energy is discharged as heat. Parts of individual cells also may be warmer because they harbor biochemical power plants termed mitochondria for producing energy.

The researchers got that information by inserting the nano-thermometers into mouse cells growing in laboratory dishes. They found temperature differences of a few degrees Fahrenheit between one part of some cells and another, with parts of cells both warmer and cooler than others. Their temperature measurements are not yet accurate enough to give an exact numerical figure. Yang's team also intentionally stimulated cells in ways that boosted the biochemical activity inside cells and observed temperature changes.

Yang says that those temperature changes may have body-wide impacts in determining health and disease. Increases in temperature inside a cell, for instance, may change the way that the genetic material called DNA works, and thus the way that the genes, which are made from DNA, work. Changing the temperature will also change how protein molecular machines operate. At higher temperatures, some proteins may become denatured, shutting down production.

"With these nano thermometer experiments, I believe we are the first to show that the temperature responses inside individual living cells are heterogeneous -- or different," said Yang. "This leads us to our next hypothesis, which is that cells may use differences in temperature as a way to communicate."

Yang's team is now conducting experiments to determine what regulates the temperature inside individual cells. One goal is to apply the information in improving prevention, diagnosis and treatment of diseases.

Story Source:

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

Researchers discover superdense aluminum

An international research team has discovered a new material, superdense aluminum, which has never before been found on Earth.

In a paper published in Nature Communications, the researchers from Australia, the USA and Japan, describe how the material can only exist under extreme pressure, similar to that found in our planet's core.

According to team member Professor Saulius Juodkazis from Swinburne University of Technology, the researchers were able to create the superdense aluminum, which is around 40 per cent stronger and denser than its conventional counterpart, by simulating the conditions found at the center of Earth.

"At extreme pressures and temperatures, such as those found in our Earth's core, common materials form new dense phases with compacted atomic arrangements and unusual physical properties.

"Because we can't physically see or sample materials from the extreme depths of Earth, we need to come up with other ways to prove the existence of superdense materials. In this case, we replicated the high pressure conditions on a nano scale," he said.

"By focusing single short laser pulses of light onto a sapphire we were able to induce a micro explosion within it. This process mimics the kind of seismic forces that have shaped the Earth and other planets, melting and reforming materials under intense pressure, allowing us to synthesize the superdense aluminum material."

According to Professor Juodkazis, the discovery could significantly advance applications which rely on nanostructured materials.

"Using this focused laser technique, we may now be able create a range of superdense metals that have extraordinary properties," he said. "The creation of superdense silver or gold, for example, could lead to many new possibilities for bio-sensing and plasmonics."

He said the discovery was also likely to catch the attention of earth and climate scientists. "By examining the mechanical and electrical properties of this type of material, we may be able to gain a greater understanding of the electrical conductivity of the interior regions of the planet. This is particularly important in the context of global climate change observed over long geological time spans."

Professor Juodkazis said the experiment was conducted using a standard bench-top laser common in many research laboratories and manufacturing operations.

"Because of the simple nature of the experiment, other scientists will be able to replicate it without needing any sophisticated, expensive, equipment," he said. "As such, many researchers now have the means to create these high density, high pressure materials, opening the door to many exciting new possibilities."

The paper was authored by Dr Arturas Vailionis from Stanford University, Associate Professor Eugene Gamaly and Professor Andrei Rode from the Australian National University, Associate Professor Vygantas Mizeikis from Shizuoka University, Dr Wenge Yang from the Carnegie Institute of Washington and Professor Juodkazis from Swinburne.

Story Source:

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

Journal Reference:

Arturas Vailionis, Eugene G. Gamaly, Vygantas Mizeikis, Wenge Yang, Andrei V. Rode, Saulius Juodkazis. Evidence of superdense aluminium synthesized by ultrafast microexplosion. Nature Communications, 2011; 2: 445 DOI: 10.1038/ncomms1449

Sex gives clues to new lung cancer treatment

Research into an enzyme that produces a hormone released after sex has inspired Australian National University chemists to create new treatments for small-cell lung cancer.

Led by Professor Chris Easton and PhD student Ms. Lucy Cao from the ARC Centre of Excellence for Free Radical Chemistry and at ANU, the team are working to reduce the number of small-cell deaths by building that target the biology underlying the disease. Their work has been published in the latest edition of The Royal Society Chemistry journal, Medicinal Chemistry Communications.

“Given that one in every 28 Australians are diagnosed with lung cancer and it is the most common cause of cancer death, there is a real need to develop new pharmaceuticals to treat this disease. Although it is still early days our results are very promising,” said Professor Easton.

The team are investigating an enzyme, known as PAM, which activates a number of important peptide hormones. These include calcitonin, which promotes cell proliferation, and oxytocin, dubbed the ‘love hormone’, as it produces feelings of contentment following orgasm. Imbalances in peptide hormones have been shown to cause inflammatory diseases, asthma, and various cancers.

“Increased levels of calcitonin are correlated with poor survival rates in small-cell lung cancer patients. So we are working to reduce the levels of calcitonin, particularly through controlling the activity of the PAM enzyme,” said Ms. Cao.

Using a novel cell culture experiment that they developed for this project, the researchers have been able to model the effect of their new chemicals on small-cell lung cancer cells.

“We were excited to find that a number of our compounds are very effective in reducing the activity of PAM and decreasing calcitonin levels,” said Professor Easton.

“As we look to take these compounds into formal clinical trials we hope to provide a sexy new drug treatment to improve and extend the lives of many lung cancer sufferers,” he added.

Provided by Australian National University

Chemists discover most naturally variable protein in dental plaque bacterium

Two UC San Diego chemists have discovered the most naturally variable protein known to date in a bacterium that is a key player in the formation of dental plaque.

The , who announced their discovery in this week's early online edition of the journal , say they believe the extreme variability of the protein they discovered in the Treponema denticola evolved to adhere to the hundreds of different kinds of other bacteria that inhabit people's mouths. They call the protein they discovered "Treponema variable protein," or TvpA for short, and estimate that it is a million to a billion times more variable than the proteins that play a primary role in vertebrate immune systems—the only other known natural system for massive protein variation.

"In Treponema denticola, we found a protein we call TvpA, that varies considerably more than proteins of the and, to our knowledge, this protein is the most variable natural described to date," said Partho Ghosh, a professor of chemistry and biochemistry at UC San Diego who headed the research effort. "We don't know what it does in this bacterium, but our hypothesis is that it enables it to adhere to the biofilm, commonly known as , that exists in people's mouths."

Ghosh explained that dental plaque varies from person-to-person in the kinds of bacteria that adhere to the teeth to form this biofilm. Because plaque grows in a sequential way and because T. denticola is one of the last key players in the formation of plaque, Ghosh said the bacterium has no idea what kinds of other bacteria will be present to adhere to.

"We suspect that by varying TvpA, T. denticola is able to find a TvpA variant that is able to adhere to whichever bacterium is already present in the biofilm," Ghosh said.

Provided by University of California - San Diego (news : web)