Iron and Superconductors

About 100 years ago, scientists discovered materials that could conduct electrons without losing energy to resistance, but, these "superconductors" had to be very cold. The electron-electron repulsion in these low-temperature superconductors was so weak that electrons could overcome it, pair up and move freely.

In 1986, scientists discovered new materials that became superconductors at temperatures above 100K. These high-temperature superconductors were made of layers of copper alloys sandwiched between layers of nonconducting material that were doped with trace amounts of material that could contribute a few extra electrons to the mix. If these materials were not doped with insulating material they did not conduct electricity as the electrons locked themselves at a distance from their neighbours. This locked pattern was named the "Mott localization".

In 2008 a second class of high-temperature superconductors was discovered. These pnictides are iron-based superconductors which are also layered and need to be doped. However, undoped pnictides are not Mott insulators.

Early in 2010, scientists replaced arsenic atoms in one of the intervening layers of a pnictide with slightly smaller phosphorous atoms. This brought the iron atoms a little closer together and further away from the Mott tipping point.

Rice University researchers are now using iron oxychalcogenides which are layered materials like pnictides, but with greater distance between the iron atoms, and this greater distance is enough to push the system into a Mott insulating state.

A better understanding of the behaviour of high-temperature superconductors is essential to future improvements in electric generators, MRI scanners, high-speed trains and other devices.

Reference:
Jian-Xin Zhu, Rong Yu, Hangdong Wang, Liang L. Zhao, M. D. Jones, Jianhui Dai, Elihu Abrahams, E. Morosan, Minghu Fang, and Qimiao Si. Band Narrowing and Mott Localization in Iron Oxychalcogenides La₂O₂Fe₂O(Se,S)₂. Physical Review Letters, 2010; 104 (21): 216405 DOI: 10.1103/PhysRevLett.104.216405

Graphane and Quantum Dots

Graphene is a honeycomb-like form of carbon that is just one atom thick. Graphane is produced when hydrogen atoms are added to both sides of the graphene matrix, making graphane an insulator.

Rice University scientists have discovered that the strategic extraction of hydrogen atoms from a two-dimensional sheet of graphane opens up hexagonal spaces of pure graphene that look and act like quantum dots. Quantum dots interact with light and magnetic fields in unique ways and can be used for chemical sensors, solar cells, medical imaging and nanoscale circuitry.

Reference:
Abhishek K. Singh, Evgeni S. Penev, Boris I. Yakobson. Vacancy Clusters in Graphane as Quantum Dots. ACS Nano, 2010; : 100513111745088 DOI: 10.1021/nn1006072

MALDI-MSI and Fingerprints

A fingerprint is made up of material from the surface of the skin and from gland secretions, which can be detected and analysed. Fingerprints found at a crime scene are often lifted using a powder, and compared with prints on a database to identify a suspect.

Matrix-Assisted Laser Desorption/Ionisation Mass Spectrometry Imaging (MALDI-MSI) is usually used to map different molecules within tissue sections, but, scientists at Sheffield Hallam University have just used the technique to analyse and produce images of fingerprints. Fingerprints analysed this way provided a wider range of information, eg, the technique can detect the presence of drugs and medication, and can provide information about a person's diet.

Reference:
Rosalind Wolstenholme, Robert Bradshaw, Malcolm R. Clench, Simona Francese. Study of latent fingermarks by matrix-assisted laser desorption/ionisation mass spectrometry imaging of endogenous lipids. Rapid Communications in Mass Spectrometry, 2009; 23 (19): 3031 DOI: 10.1002/rcm.4218

Organic Chemicals in Smoker's Breath

The Chemistry Department of the University of Girona (UdG) has been investigating the chemicals present in the breath of smokers. They analysed some volatile organic compounds such as benzene, 2,5-dimethylfurane, toluene, o-xylene and p-xylene, which could be used as bio-indicators of the condition of a smoker, and have shown that only 2,5-dimethylfuran provides effective results for breath samples. 2,5-dimethylfuran can also be present in the breath of passive smokers if they have had direct contact with tobacco smoke over a prolonged period.

Benzene is only useful as a bio-indicator when tobacco consumption is relatively high and when testing takes place 1-2 hours after a smoking a cigarette.

Toluene and xylene levels are only significant for those who smoke a lot and when little time has passed since smoking the last cigarette.

Reference:
Monica Alonso, Mar Castellanos, Juan M. Sanchez. Evaluation of potential breath biomarkers for active smoking: assessment of smoking habits. Analytical and Bioanalytical Chemistry, 2010; 396 (8): 2987 DOI: 10.1007/s00216-010-3524-z

Uniqueness of Helium

Helium. He, is used to fill balloons, in lasers for eye surgery, as a cooling agent in nuclear reactors, and as a pressurizing agent for liquid fuel rockets in space exploration.

Helium has a number of characteristics that make it special. It is the most stable of all the elements and has the lowest boiling point. It becomes a fluid at temperatures close to absolute zero (0K) while most other materials are solid. In fact, helium is a liquid even at 0K and becomes a solid only under high pressure, and, helium is the only substance to exhibit superfluidity.

Of all the elements, helium is closest to the ideal gas. Two helium atoms form the weakest bound diatomic molecule, or dimer. All the properties of temperature, a measure of the kinetic energy of particles in matter, can be modeled if the force acting between a pair of helium atoms is known.
University of Delaware scientists have now predicted that the average separation between the helium atoms is 47 angstroms, compared to a typical bond length of 1 angstrom (one ten billionth of a meter or 0.0001 micron), and that the binding energy is 6,790 times smaller than the potential depth.

Reference:
M. Przybytek, W. Cencek, J. Komasa, G. %u0141ach, B. Jeziorski, K. Szalewicz. Relativistic and Quantum Electrodynamics Effects in the Helium Pair Potential. Physical Review Letters, 2010; 104 (18): 183003 DOI: 10.1103/PhysRevLett.104.183003

Silver Isotopes to Date the Earth

The Earth is depleted in some elements, such as hydrogen, carbon, nitrogen and silver, compared to the Solar System as a whole. What scientists can not tell us is when this depletion occurred. Carnegie Institute scientists have used the isotopic ratios of silver in primitive meteorites and rocks from the Earth's mantle to determine the history of Earth's volatiles relative to the formation of Earth's iron core.

Silver has two stable isotopes of which silver-107 was produced in the early Solar System by the rapid nuclear decay of palladium-107, which is so unstable that virtually all of it decayed within the first 30 million years. Silver is more volatile than palladium, while palladium is more likely to bond with iron. The silver isotope evidence suggests that the core formed between 5 and 10 million years after the origin of the Solar System.

Studies using hafnium and tungsten isotopes indicate that the core formed between 30 and 100 million years after the origin of the Solar System.

These apparently contradictory results support the "Heterogeneous Accretion" model of planetary growth in which the Earth's building block's changed composition as the planet accreted. So, at first the Earth accreted volatile-depleted material until it reached about 85% of its final mass and then accreted volatile-rich material in the last stages of its formation, about 26 million years after the Solar System's origin.

Reference:
Carnegie Institution (2010, May 14). Water was present during birth of Earth, study of silver suggests. ScienceDaily. Retrieved May 17, 2010, from http://www.sciencedaily.com­ /releases/2010/05/100513143457.htm

Killer Seaweed in Coral Reefs

Studies have shown that several species of seaweed common in both the Pacific and Caribbean Oceans can kill corals upon contact using chemical means.

The study used racks of transplanted coral placed next to different types of common seaweed as well as plastic plants to simulate the effects of shading and mechanical damage. For comparison, other coral racks had neither seaweed not plastic plants near them. In as little as two days the corals in direct contact with the some seaweeds bleached and died.

Chemicals were extracted from the seaweeds causing death. These chemicals were applied to the corals in a gel matrix. As a control, the gel without the chemicals was added to a different group of corals. The results confirmed that these chemicals were responsible for the death of corals in contact with the killer seaweeds.

Overfishing of herbivorous fishes has resulted in more seaweeds being present amongst corals, and some of these seaweeds are responsible for the death of coral. The less coral there is, the fewer fish will be recruited into the area to feed, so the number of seaweeds increase, more coral dies.

Reference:
Douglas B. Rasher, Mark E. Hay. Chemically rich seaweeds poison corals when not controlled by herbivores. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.0912095107

Chemistry of Archaeopteryx

A fossil specimen of the half-dinosaur/half-bird, archaeopteryx, has been placed under the X-ray beam at the Stanford Synchrotron Radiation Lightsource(SSRL). By recording how the X-rays interacted with the fossil, the scientists have been able to identify the precise locations of chemical elements hidden within. The concentration of elements in the fossil differs significantly from those in the surrounding rock, ruling out the possibility that the elements have leached from the surrounding rock into the fossil.

The results show that portions of the feathers are not just impressions of long-decomposed organic material as previously believed, but are actually fossilized feathers containing phosphorous and sulfur, the elements found in modern bird feathers. Trace amounts of copper and zinc have been found in the fossil's bones, just as in the bones of modern birds.

Reference:
U. Bergmann, R. W. Morton, P. L. Manning, W. I. Sellers, S. Farrar, K. G. Huntley, R. A. Wogelius, P. Larson. Archaeopteryx feathers and bone chemistry fully revealed via synchrotron imaging. Proceedings of National Academy of Sciences, 2010; DOI: 10.1073/pnas.1001569107

Photosynthesis Caught on Camera

Researchers at the University of Gothenburg and the Chalmers University of Technology have used a special X-ray camera at the European Synchrotron Radiation Facility in Grenoble to photograph the dynamics of photosynthesis. The X-ray image shows how a protein, central to the conversion of chemical energy during photosynthesis, temporarily stores the light energy immediately before a chemical bond forms.
In time, it is hoped to imitate the sophisticated energy conversion of photosynthesis in the production of solar panels of the future.

Reference:
A. B. Wohri, G. Katona, L. C. Johansson, E. Fritz, E. Malmerberg, M. Andersson, J. Vincent, M. Eklund, M. Cammarata, M. Wulff, J. Davidsson, G. Groenhof, R. Neutze. Light-Induced Structural Changes in a Photosynthetic Reaction Center Caught by Laue Diffraction. Science, 2010; 328 (5978): 630 DOI: 10.1126/science.1186159

Gold Nanoparticle Dispersion

Queensland University of Technology (QUT) scientists have developed a new technique for dispersing metals in nanoparticle form throughout polymers or plastic materials.

The properties of metals change when they are in nano form. When nanoparticles are added to plastics, a new range of composite materials are formed.

When gold nanoparticles are added to paint, essentially a plastic, the intensity of colours and durability are increased.

Mixing gold nanoparticles with titanium dioxide, TiO₂, using a plastic mould makes a very efficient catalyst for water purification as the titania absorbs light, converting it into electricity which is then passed into the conductive gold.

Queensland University of Technology (2010, May 6). Gold nanoparticles promise to enrich everyday products. ScienceDaily. Retrieved May 8, 2010, from http://www.sciencedaily.com­ /releases/2010/05/100505092004.htm

Scientists See in the Dark

Conventional night vision goggles use a photocathode, a cathode ray tube-like vacuum tube made of thick glass, to convert infrared light photons into electrons which are then accelerated under high voltage and driven into a phosphorous screen producing greenish images of objects invisible to the naked eye in the darkness.

University of Florida scientists have produced an imaging device that replaces the photocathode with several layers of organic semiconductor thin film materials. The photodetector is connected in series with an LED. Infrared light photons are converted into electrons in the photodetector which are then injected into the LED which generates visible light. This imaging device would be light-weight and inexpensive to produce since it could be made using the same equipment currently used to produce laptop screens and flat-screen TVs. This new night-vision technology could be used on mobile phones, car windshields, even standard glasses.

Do Young Kim, Dong Woo Song, Neetu Chopra, Pieter De Somer, Franky So. Organic Infrared Upconversion Device. Advanced Materials, 2010; DOI: 10.1002/adma.200903312

Fluorinated Compounds Block Radiation

NASA and Purdue University researchers have released a new study that could be used by Industrial Chemists to develop alternatives with less global warming potential than materials now in common use. The study looked at fluorine containing compounds such as hydrofluorocarbons, perfluorocarbons, hydrofluoroethers, hydrofluoroolefins and sulfur and nitrogen fluorides.

Fluorinated compounds are more efficient at blocking radiation in the atmospheric window, the frequency range in the infrared region of the electromagnetic spectrum through which radiation from Earth is released into space which helps cool the planet. When radiation is blocked instead of being released a greenhouse effect results, warming the planet.

The number and placement of fluorine atoms in a molecule's structure is instrumental in determining its ability to block radiation. Fluorine atoms are very electronegative and form highly polar bonds with carbon and sulfur. Fluorine atoms tend to change the bond polarity of molecules, modifying the bonds holding the atoms in the structure, which, in turn, effects how a molecule absorbs infrared radiation.

Fluorinated compounds also persist longer in the atmosphere than carbon dioxide and other major global warming agents. Even if fluorinated compounds are emitted in lower quantities they might have a cumulative effect and some don't break down for thousands of years.

Partha P. Bera, Joseph S. Francisco, Timothy J. Lee. Design strategies to minimize the radiative efficiency of global warming molecules. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.0913590107

Molybdenum-oxo Complex to Split Water

Hydrogen gas, when used as a fuel, emits only water vapor as a product, making it potentially the 'cleanest' fuel around. Unfortunately, hydrogen gas has to produced and most of this comes from natural gas which is a fossil fuel. While the technique to produce hydrogen from natural gas is not expensive, it does add enormous quantities of carbon emissions to the atmosphere.

Hydrogen gas can be produced through the electrolysis of water, a cleaner and more sustainable method of producing hydrogen if the electricity required is generated via renewable technology such as solar or wind, but it requires a water-splitting catalyst.

Plants use enzymes, hydrogenases, during photosynthesis to split water, but these enzymes are highly unstable and de-activate when removed from their native environment.

Metal catalysts such as platinum are commercially available to split water, but these do tend to be expensive.

Scientists in the USA have found a molybdenum-oxo complex that acts as a catalyst for spiltting water without the use of additional acids or organic co-solvents. The new catalyst generates hydrogen from neutral buffered water or even sea water with a turnover frequency of ~2.4moles of hydrogen per mole of catalyst per second.

Hemamala I. Karunadasa, Christopher J. Chang, Jeffrey R. Long. A molecular molybdenum-oxo catalyst for generating hydrogen from water. Nature, 2010; 464 (7293): 1329 DOI: 10.1038/nature08969