Giant super-Earths made of diamond are possible, study suggests

A planet made of diamonds may sound lovely, but you wouldn't want to live there.

A new study suggests that some stars in the Milky Way could harbor "carbon super-Earths" -- giant terrestrial planets that contain up to 50 percent diamond.

But if they exist, those planets are likely devoid of life as we know it.

The finding comes from a laboratory experiment at Ohio State University, where researchers recreated the temperatures and pressures of Earth's lower mantle to study how diamonds form there.

The larger goal was to understand what happens to carbon inside planets in other solar systems, and whether solar systems that are rich in carbon could produce planets that are mostly made of diamond.

Wendy Panero, associate professor in the School of Earth Sciences at Ohio State, and doctoral student Cayman Unterborn used what they learned from the experiments to construct computer models of the minerals that form in planets composed with more carbon than Earth.

The result: "It's possible for planets that are as big as fifteen times the mass of the Earth to be half made of diamond," Unterborn said. He presented the study Tuesday at the American Geophysical Union meeting in San Francisco.

"Our results are striking, in that they suggest carbon-rich planets can form with a core and a mantle, just as Earth did," Panero added. "However, the cores would likely be very carbon-rich -- much like steel -- and the mantle would also be dominated by carbon, much in the form of diamond."

Earth's core is mostly iron, she explained, and the mantle mostly silica-based minerals, a result of the elements that were present in the dust cloud that formed into our solar system. Planets that form in carbon-rich solar systems would have to follow a different chemical recipe -- with direct consequences for the potential for life.

Earth's hot interior results in geothermal energy, making our planet hospitable.

Diamonds transfer heat so readily, however, that a carbon super-Earth's interior would quickly freeze. That means no geothermal energy, no plate tectonics, and -- ultimately -- no magnetic field or atmosphere.

"We think a diamond planet must be a very cold, dark place," Panero said.

She and former graduate student Jason Kabbes subjected a tiny sample of iron, carbon, and oxygen to pressures of 65 gigapascals and temperatures of 2,400 Kelvin (close to 9.5 million pounds per square inch and 3,800 degrees Fahrenheit -- conditions similar to the Earth's deep interior).

As they watched under the microscope, the oxygen bonded with the iron, creating iron oxide -- a type of rust -- and left behind pockets of pure carbon, which became diamond.

Based on the data from that test, the researchers made computer models of Earth's interior, and verified what geologists have long suspected -- that a diamond-rich layer likely exists in Earth's lower mantle, just above the core.

That result wasn't surprising. But when they modeled what would happen when these results were applied to the composition of a carbon super-Earth, they found that the planet could become very large, with iron and carbon merged to form a kind of carbon steel in the core, and vast quantities of pure carbon in the mantle in the form of diamond.

The researchers discussed the implications for planetary science.

"To date, more than five hundred planets have been discovered outside of our solar system, yet we know very little about their internal compositions," said Unterborn, who is an astronomer by training.

"We're looking at how volatile elements like hydrogen and carbon interact inside the Earth, because when they bond with oxygen, you get atmospheres, you get oceans -- you get life," Panero said. "The ultimate goal is to compile a suite of conditions that are necessary for an ocean to form on a planet."

This work contrasts with the recent discovery by an unrelated team of researchers who found a so-called "diamond planet" which is actually the remnant of a dead star in a binary system.

The Ohio State research suggests that true terrestrial diamond planets can form in our galaxy. Exactly how many such planets might be out there and their possible internal composition is an open question -- one that Unterborn is pursuing with Ohio State astronomer Jennifer Johnson.

This research was funded by Panero's CAREER award from the National Science Foundation.

 

Story Source:

The above story is reprinted from materials provided by Ohio State University. The original article was written by Pam Frost Gorder.

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

Making a light-harvesting antenna from scratch: Biomimetic antenna for gathering sunlight may one day transform solar-powered devices

Sometimes when people talk about solar energy, they tacitly assume that we're stuck with some version of the silicon solar cell and its technical and cost limitations. Not so.

The invention of the solar cell, in 1941, was inspired by a newfound understanding of semiconductors, materials that can use light energy to create mobile electrons -- and ultimately an electrical current.

Silicon solar cells have almost nothing to do with the biological photosystems in tree leaves and pond scum that use light energy to push electrons across a membrane -- and ultimately create sugars and other organic molecules.

At the time, nobody understood these complex assemblages of proteins and pigments well enough to exploit their secrets for the design of solar cells.

But things have changed.

At Washington University in St. Louis's Photosynthetic Antenna Research Center (PARC) scientists are exploring native biological photosystems, building hybrids that combine natural and synthetic parts, and building fully synthetic analogs of natural systems.

One team has just succeeded in making a crucial photosystem component -- a light-harvesting antenna -- from scratch. The new antenna is modeled on the chlorosome found in green bacteria.

Chlorosomes are giant assemblies of pigment molecules. Perhaps Nature's most spectacular light-harvesting antennae, they allow green bacteria to photosynthesize even in the dim light in ocean deeps.

Dewey Holten, PhD, professor of chemistry in Arts & Sciences, ard collaborator Christine Kirmaier, PhD, research professor of chemistry are part of a team that is trying to make synthetic chlorosomes. Holten and Kirmaier use ultra-fast laser spectroscopy and other analytic techniques to follow the rapid-fire energy transfers in photosynthesis.

His team's latest results were described in a recent issue of New Journal of Chemistry.

Chlorosomes

Biological systems that capture the energy in sunlight and convert it to the energy of chemical bonds come in many varieties, but they all have two basic parts: the light harvesting complexes, or antennae, and the reaction center complexes. The antennae consist of many pigment molecules that absorb photons and pass the excitation energy to the reaction centers.

In the reaction centers, the excitation energy sets off a chain of reactions that create ATP, a molecule often called the energy currency of the cell because the energy stored ATP powers most cellular work. Cellular organelles selectively break those bonds in ATP molecules when they need an energy hit for cellular work.

Green bacteria, which live in the lower layers of ponds, lakes and marine environments, and in the surface layers of sediments, have evolved large and efficient light-harvesting antennae very different from those found in plants bathing in sunlight on Earth's surface.

The antennae consist of highly organized three-dimensional systems of as many as 250,000 pigment molecules that absorb light and funnel the light energy through a pigment/protein complex called a baseplate to a reaction center, where it triggers chemical reactions that ultimately produce ATP.

In plants and algae (and in the baseplate in the green bacteria) photo pigments are bound to protein scaffolds, which space and orient the pigment molecules in such a way that energy is efficiently transferred between them.

But chlorosomes don't have a protein scaffold. Instead the pigment molecules self -assemble into a structure that supports the rapid migration of excitation energy.

This is intriguing because it suggests chlorosome mimics might be easier to incorporate in the design of solar devices than biomimetics that are made of proteins as well as pigments.

Synthetic pigments

The goal of the work described in the latest journal article was to see whether synthesized pigment molecules could be induced to self-assemble. The process by which the pigments align and bond is not well understood.

"The structure of the pigment assemblies in chlorosomes is the subject of intense debate," Holten says, "and there are several competing models for it."

Given this uncertainty, the scientists wanted to study many variations of a pigment molecule to see what favored and what blocked assembly.

A chemist wishing to design pigments that mimic those found in photosynthetic organisms first builds one of three molecular frameworks. All three are macrocycles, or giant rings: porphyrin, chlorin and bacteriochlorin.

"One of the members of our team, Jon Lindsey can synthesize analogs of all three pigment types from scratch," says Holten. (Lindsey, PhD, is Glaxo Professor of Chemistry at North Carolina State University.)

In the past, chemists making photo pigments have usually started with porphyrins, which are the easiest of the three types of macrocycles to synthesize. But Lindsey also has developed the means to synthesize chlorins, the basis for the pigments found in the chlorosomes of green bacteria. The chlorins push the absorption to the red end of the visible spectrum, an area of the spectrum scientists would like to be able to harvest for energy.

Key to pigment self-assembly are the metal atoms and hydroxyl (OH) and carbonyl (C=O) groups in the pigment molecules (the groups shown in color in the above illustration).

Doctoral student Olga Mass and coworkers in Lindsey's lab synthesized 30 different chlorins, systematically adding or removing chemical groups thought to be important for self-assembly but also attaching peripheral chemical groups that take up space and might make it harder for the molecules to stack or that shift around the distributions of electrons so that the molecules might stack more easily.

Testing for aggregation

The powdered pigments were carefully packaged and shipped by Fed Ex (because the Post Office won't ship chemicals) to Holten's lab at WUSTL and to David Bocian's lab at the University of California at Riverside.

Scientists in both labs made up green-tinctured solutions of each of the 30 molecules in small test tubes and then poked and prodded the solutions by means of analytical techniques to see whether the pigment had aggregated and, if so, how much had formed the assemblies. Holten's lab studied their absorption of light and their fluorescence (which indicated the presence of monomers, since assemblies don't normally fluoresce) and Bocian's lab studied their vibrational properties, which are determined by the network of bonds in the molecule or pigment aggregate as a whole.

In one crucial test Joseph Springer, a PhD student in Holten's lab, compared the absorption spectrum of a pigment in a polar solvent that would prevent it from self-assembling to the spectrum of the pigment in a nonpolar solvent that would allow the molecules to interact with one another and form assemblies.

"You can see them aggregate," Springer says. "A pigment that is totally in solution is clear, but colored a brilliant green. When it aggregates, the solution becomes a duller green and you can see tiny flecks in the liquid."

The absorption spectra indicated that some pigments formed extensive assemblies and that the steric and electronic properties of the molecules predicted the degree to which they would assemble.

Up next

Although this project focused on self-assembly, the PARC scientists have already taken the next step toward a practical solar device. "With Pratim Biswas, PhD, the Lucy and Stanley Lopata Professor and chair of the Department of Energy, Environmental & Chemical Engineering, we've since demonstrated that we can get the pigments to self-assemble on surfaces, which is the next step in using them to design solar devices," says Holten.

"We're not trying to make a more efficient solar cell in the next six months," Holten cautions. "Our goal instead is to develop fundamental understanding so that we can enable the next generation of more efficient solar powered devices."

Biomimicry hasn't always worked. Engineers often point out early flying machines that attempted to mimic birds didn't work and that flying machines stayed aloft only when nventors abandoned biological models and came up with their own designs.

But there is nothing predestined or inevitable about this. As biological knowledge has exploded in the past 50 years, mimicking nature has become a smarter strategy. Biomimetic or biohybrid designs already have solved significant engineering problems in other areas and promise to greatly improve the design of solar powered devices as well.

After all, Nature has had billions of years to experiment with ways to harness the energy in sunlight for useful work.

Story Source:

The above story is reprinted from materials provided by Washington University in St. Louis. The original article was written by Diana Lutz.

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

Journal Reference:

Olga Mass, Dinesh R. Pandithavidana, Marcin Ptaszek, Koraliz Santiago, Joseph W. Springer, Jieying Jiao, Qun Tang, Christine Kirmaier, David F. Bocian, Dewey Holten, Jonathan S. Lindsey. De novo synthesis and properties of analogues of the self-assembling chlorosomal bacteriochlorophylls. New Journal of Chemistry, 2011; 35 (11): 2671 DOI: 10.1039/C1NJ20611G

Crystalizing the foundations of better antihistamines

Histamine, which is released by mast cells of the immune system, is an important mediator of allergic and inflammatory reactions. It exerts its effects by activating cell-surface receptors, thereby triggering cell signaling events. Of the four known human histamine receptor types, H1R is expressed by various tissues, including airways, the vasculature, and the brain.

Pharmacologists have developed various antihistamine drugs that interfere with histamine–receptor interactions. “Many of us will have taken antihistamines to alleviate the symptoms of hay fever, for example, or to stop the swelling and itchiness caused by insect bites,” Iwata says.

Iwata and his collaborators solved the structure of H1R with bound doxepin using x-ray crystallography. Like all proteins, H1R is composed of amino-acid building blocks. The amino acid tryptophan is found at a particular position in H1R and is known to be important for receptor activation. The researchers revealed that doxepin sits deep within a binding pocket in the receptor, where it interacts directly with this key amino acid (Fig. 1), helping to explain its pharmacological activity.

Doxepin was one of the first antihistamines that effectively blocks histamine receptor activation. Unfortunately, however, these drugs also bind other related receptors. “This low selectivity along with their ability to enter the brain means that these first-generation drugs have considerable side effects such as sedation, mouth dryness, and heart arrhythmias,” explains Iwata.

The researchers’ structural findings suggested that the low selectivity of doxepin is due to the hydrophobic (‘water hating’) nature of the binding pocket, a characteristic found in other receptors to which the drug binds. However, they found that the binding pocket of H1R has a distinctive region occupied by the negatively charged ion phosphate. Through molecular modeling, they demonstrated that the second-generation drugs such as olopatadine would interact with this region, which is not conserved in other related receptors. This explains why these drugs are more selective and have fewer side effects compared with doxepin.

“Our findings demonstrate how minor differences in receptors affect drug selectivity and will be useful in the development of the next generation of antihistamines,” says Iwata.

More information: Shimamura, T., et al. Structure of the human histamine H1 receptor complex with doxepin. Nature 475, 65–70 (2011).

Provided by RIKEN (news : web)

Four new leads identified for anti-cancer drugs

Lead author Jason Smith undertook a comprehensive study that combined existing knowledge of an enzyme with a specifically tailored computational chemistry approach to identify novel inhibitors. The enzyme (indoleamine 2,3-dioxygenase) has generated excitement amongst researchers over the last decade due to its increasingly recognised role as a drug target, particularly in cancer.

"Over the past ten years, scientists have learnt that compounds inhibiting this enzyme allow the immune system to attack cancer cells. They have found that if you use these inhibitors alone, they slow tumour growth. Even more exciting is that in combination with chemotherapy, these inhibitors have the potential to destroy a tumour entirely," Smith explains.

After conducting virtual screening of a database of almost 60,000 compounds, Smith found 18 compounds that could hold potential as inhibitors of this enzyme. He then tested them in the lab and found four compounds with particularly exciting prospects.

Smith sees many strengths in the approach taken. "Computational chemistry means we don't have to spend years testing thousands of compounds in the lab. We can analyse all the potential compounds and narrow them down in a matter of 6 month's preparation and virtual screening, instead of years. In fact, after all the preparation and groundwork, the screening itself takes around 100 hours."

This research was conducted as part of a collaboration between the Department of Chemistry and Biomolecular Sciences at Macquarie University and the School of Medical Sciences/Pharmacology, University of New South Wales.

Although the leads are a way off from clinical trials, Smith and the team are excited about the future development of this research. Smith, a completing Master of Philosophy student, plans to continue study on these enzyme inhibitors as part of a Doctoral degree in 2012.

Provided by Macquarie University

Graphene foam detects explosives, emissions better than today's gas sensors

 A new study from Rensselaer Polytechnic Institute demonstrates how graphene foam can outperform leading commercial gas sensors in detecting potentially dangerous and explosive chemicals. The discovery opens the door for a new generation of gas sensors to be used by bomb squads, law enforcement officials, defense organizations, and in various industrial settings.

The new sensor successfully and repeatedly measured ammonia (NH3) and nitrogen dioxide (NO2) at concentrations as small as 20 parts-per-million. Made from continuous graphene nanosheets that grow into a foam-like structure about the size of a postage stamp and thickness of felt, the sensor is flexible, rugged, and finally overcomes the shortcomings that have prevented nanostructure-based gas detectors from reaching the marketplace.

Results of the study were published November 28 in the journal Scientific Reports, published by Nature Publishing Group.

"We are very excited about this new discovery, which we think could lead to new commercial gas sensors," said Rensselaer Engineering Professor Nikhil Koratkar, who co-led the study along with Professor Hui-Ming Cheng at the Shenyang National Laboratory for Materials Science at the Chinese Academy of Sciences. "So far, the sensors have shown to be significantly more sensitive at detecting ammonia and nitrogen dioxide at room temperature than the commercial gas detectors on the market today."

Over the past decade researchers have shown that individual nanostructures are extremely sensitive to chemicals and different gases. To build and operate a device using an individual nanostructure for gas detection, however, has proven to be far too complex, expensive, and unreliable to be commercially viable, Koratkar said. Such an endeavor would involve creating and manipulating the position of the individual nanostructure, locating it using microscopy, using lithography to apply gold contacts, followed by other slow, costly steps. Embedded within a handheld device, such a single nanostructure can be easily damaged and rendered inoperable. Additionally, it can be challenging to "clean" the detected gas from the single nanostructure.

The new postage stamp-sized structure developed by Koratkar has all of the same attractive properties as an individual nanostructure, but is much easier to work with because of its large, macroscale size. Koratkar's collaborators at the Chinese Academy of Sciences grew graphene on a structure of nickel foam. After removing the nickel foam, what's left is a large, free-standing network of foam-like graphene. Essentially a single layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques, graphene is an atom-thick sheet of carbon atoms arranged like a nanoscale chicken-wire fence. The walls of the foam-like graphene sensor are composed of continuous graphene sheets without any physical breaks or interfaces between the sheets.

Koartkar and his students developed the idea to use this graphene foam structure as a gas detector. As a result of exposing the graphene foam to air contaminated with trace amounts of ammonia or nitrogen dioxide, the researchers found that the gas particles stuck, or adsorbed, to the foam's surface. This change in surface chemistry has a distinct impact upon the electrical resistance of the graphene. Measuring this change in resistance is the mechanism by which the sensor can detect different gases.

Additionally, the graphene foam gas detector is very convenient to clean. By applying a ~100 milliampere current through the graphene structure, Koratkar's team was able to heat the graphene foam enough to unattach, or desorb, all of the adsorbed gas particles. This cleaning mechanism has no impact on the graphene foam's ability to detect gases, which means the detection process is fully reversible and a device based on this new technology would be low power -- no need for external heaters to clean the foam -- and reusable.

Koratkar chose ammonia as a test gas to demonstrate the proof-of-concept for this new detector. Ammonium nitrate is present in many explosives and is known to gradually decompose and release trace amounts of ammonia. As a result, ammonia detectors are often used to test for the presence of an explosive. A toxic gas, ammonia also is used in a variety of industrial and medical processes, for which detectors are necessary to monitor for leaks.

Results of the study show the new graphene foam structure detected ammonia at 1,000 parts-per-million in 5 to 10 minutes at room temperature and atmospheric pressure. The accompanying change in the graphene's electrical resistance was about 30 percent. This compared favorably to commercially available conducting polymer sensors, which undergo a 30 percent resistance change in 5 to 10 minutes when exposed to 10,000 parts-per-million of ammonia. In the same time frame and with the same change in resistance, the graphene foam detector was 10 times as sensitive. The graphene foam detector's sensitivity is effective down to 20 parts-per-million, much lower than the commercially available devices. Additionally, many of the commercially available devices require high power consumption since they provide adequate sensitivity only at high temperatures, whereas the graphene foam detector operates at room temperature.

Koratkar's team used nitrogen dioxide as the second test gas. Different explosives including nitrocellulose gradually degrade, and are known to produce nitrogen dioxide gas as a byproduct. As a result, nitrogen dioxide also is used as a marker when testing for explosives. Additionally, nitrogen dioxide is a common pollutant found in combustion and auto emissions. Many different environmental monitoring systems feature real-time nitrogen dioxide detection.

The new graphene foam sensor detected nitrogen dioxide at 100 parts-per-million by a 10 percent resistance change in 5 to 10 minutes at room temperature and atmospheric pressure. It showed to be 10 times more sensitive than commercial conducting polymer sensors, which typically detect nitrogen dioxide at 1,000 part-per-million in the same time and with the same resistance chance at room temperature. Other nitrogen dioxide detectors available today require high power consumption and high temperatures to provide adequate sensitivity. The graphene foam sensor can detect nitrogen dioxide down to 20 parts-per-million at room temperature.

"We see this as the first practical nanostructure-based gas detector that's viable for commercialization," said Koratkar, a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer. "Our results show the graphene foam is able to detect ammonia and nitrogen dioxide at a concentration that is an order of magnitude lower than commercial gas detectors on the market today."

The graphene foam can be engineered to detect many different gases beyond ammonia and nitrogen dioxide, he said.

Studies have shown the electrical conductivity of an individual nanotube, nanowire, or graphene sheet is acutely sensitive to gas adsorbtion. But the small size of individual nanostructures made it costly and challenging to develop into a device, plus the structures are delicate and often don't yield consistent results.

The new graphene foam gas sensor overcomes these challenges. It is easy to handle and manipulate because of its large, macroscale size. The sensor also is flexible, rugged, and robust enough to handle wear and tear inside of a device. Plus it is fully reversible, and the results it provides are consistent and repeatable. Most important, the graphene foam is highly sensitive, thanks to its 3-D, porous structure that allows gases to easily adsorb to its huge surface area. Despite its large size, the graphene foam structure essentially functions as a single nanostructure. There are no breaks in the graphene network, which means there are no interfaces to overcome, and electrons flow freely with little resistance. This adds to the foam's sensitivity to gases.

"In a sense we have overcome the Achilles' heel of nanotechnology for chemical sensing," Koratkar said. "A single nanostructure works great, but doesn't mean much when applied in a real device in the real world. When you try to scale it up to macroscale proportions, the interfaces defeats what you're trying to accomplish, as the nanostructure's properties are dominated by interfaces. Now we're able to scale up graphene in a way that the interfaces are not present. This allows us to take advantage of the intrinsic properties of the nanostructure, yet work with a macroscopic structure that gives us repeatability, reliability, and robustness, but shows similar sensitivity to gas adsorbtion as a single nanostructure."

Along with Koratkar, co-authors of the paper are: Rensselaer graduate students Fazel Yavari and Abhay Varghese Thomas; along with professors W.C. Ren, H.M. Cheng and graduate student Z.P. Chen of the Shenyang National Laboratory for Materials Science at the Chinese Academy of Sciences.

This research was supported in part by the Advanced Energy Consortium (AEC), the National Science Foundation of China, and the Chinese Academy of Sciences.

Story Source:

The above story is reprinted from materials provided by Rensselaer Polytechnic Institute.

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

Journal Reference:

Fazel Yavari, Zongping Chen, Abhay V. Thomas, Wencai Ren, Hui-Ming Cheng, Nikhil Koratkar. High Sensitivity Gas Detection Using a Macroscopic Three-Dimensional Graphene Foam Network. Scientific Reports, 2011; 1 DOI: 10.1038/srep00166