Tagged: Chemistry Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 5:48 pm on December 3, 2014 Permalink | Reply
    Tags: , , , , Chemistry, , ,   

    From ESA: “The quest for organic molecules on the surface of 67P/C-G” 

    European Space Agency

    From The Rosetta Blog

    ESA Rosetta spacecraft

    This blog post is contributed by Ian Wright and his colleagues from the Ptolemy team.

    Ptolemy on Philae Lander

    For scientists engaged with large complex projects like Rosetta, there is always a delightful period early on when, unbound by practical realities, it is possible to dream. And so it was that at one time the scientists were thinking about having a lander with the capability to hop around a comet’s surface. In this way it would be possible to make measurements from different parts of the comet.

    Interestingly, this unplanned opportunity presented itself on 12 November 2014, when Philae landed not once but three times on Comet 67P/Churyumov-Gerasimenko.

    Comet 67P/Churyumov-Gerasimenko

    The Ptolemy instrument on Philae is a compact mass spectrometer designed to measure the composition of the materials making up 67P/C-G, with a particular focus on organic molecules and mineral components. Earlier in 2014, Ptolemy had collected data at distances of 15,000, 13,000, 30, 20, and 10 km from the comet, while Philae was still attached to Rosetta.

    But from 12 to 14 November, along with some other instruments on the lander, Ptolemy had the chance to operate at more than one location on the comet’s surface.
    Rosetta’s OSIRIS narrow-angle camera images of Philae’s first touchdown on the comet. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA


    Ptolemy performed its first ‘sniffing’ measurements on the comet just after the initial touchdown of Philae. At almost exactly the same moment, the OSIRIS camera on Rosetta was imaging Philae flying back above the surface after the first bounce.

    Later, once Philae had stopped at its final landing site, Ptolemy then made six subsequent sets of measurements, sniffing the comet’s atmosphere at the surface between 13 and 14 November. Finally, a slightly different experiment was also conducted on 14 November, which was completed only 45 minutes before Philae went into hibernation as its primary battery was exhausted.

    For this “last gasp” experiment, the team used a specialised oven, the so-called “CASE” oven, to determine the composition of volatiles (and perhaps any particulates) that had accumulated in it. The Ptolemy team also used the same opportunity to reconfigure their analytical procedures, to see if they could make some isotopic measurements. Unfortunately, there was no chance to use Ptolemy in conjunction with SD2, as this was confined to the sister instrument, COSAC, given the limited power and time available.

    The experiments conducted by Ptolemy on the surface of Comet 67P/C-G. Table courtesy of the Ptolemy team.

    Because of the relatively high power consumption of Ptolemy, it was a race against the clock. The battery had to hold out, both to perform the measurements and to relay the data back to Rosetta and then home. For those involved, it’s hard to describe the shared emotions on that day, helplessly watching a voltage heading towards the end-stop.

    Scientists from the Ptolemy team at the Lander Control Centre at DLR in Cologne, Germany, during the night between 14 and 15 November 2014, just before Philae went into hibernation. Photo courtesy of Ian Wright.

    Nevertheless, the very good news is that Ptolemy definitely returned data from its various stops on the comet. However, the data are complex and will require careful analysis: this will take time. Also, because the instrument was operated in ways that hadn’t initially been planned for, it will be necessary to go back into the laboratory to run some simulated tests, to ensure that the on-comet data obtained in similar configurations can be understood.

    In the first instance, however, the team will be concentrating on the data acquired immediately after the first touchdown. It will be fascinating to compare the rich spectrum of organic compounds detected by Ptolemy with the measurements made by COSAC about 14 minutes later.

    The Ptolemy team has lots of questions. Exactly what organic compounds are present and in what ratios? How did things change between the various sets of measurements? What does these data tell us about the composition of the 10–20 cm depth of surface dust that got kicked up during the first bounce? And what can these materials tell us about the fundamental make-up of comets?

    The team is looking forward to making these analyses over the coming months and sharing the results with you.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

    ESA50 Logo large

  • richardmitnick 2:29 pm on December 2, 2014 Permalink | Reply
    Tags: , , Chemistry,   

    From LBL: “A Better Look at the Chemistry of Interfaces” 

    Berkeley Logo

    Berkeley Lab

    December 2, 2014
    Lynn Yarris (510) 486-5375

    Researchers working at the Advanced Light Source (ALS) of the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have combined key features of two highly acclaimed X-ray spectroscopy techniques into a new technique that offers sub-nanometer resolution of every chemical element to be found at heterogeneous interfaces, such as those in batteries and fuel cells. This new technique is called SWAPPS for Standing Wave Ambient Pressure Photoelectron Spectroscopy, and it combines standing-wave photoelectron spectroscopy (SWPS) with high ambient pressure photoelectron spectroscopy (APPS).

    By utilizing X-ray standing waves to excite photoelectrons, SWAPPS delivers vital information about all the chemical elements at the heterogeneous interfaces found in batteries, fuel cells and other devices.

    “SWAPPS enables us to study a host of surface chemical processes under realistic pressure conditions and for systems related to energy production, such as electrochemical cells, batteries, fuel cells and photovoltaic cells, as well as in catalysis and environmental science,” says Charles Fadley, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the University of California Davis, where he is a Distinguished Professor of Physics. “SWAPPS provides all the advantages of the widely used technique of X-ray photoelectron spectroscopy, including element and chemical-state sensitivity, and quantitative analysis of relative concentrations of all species present. However with SWAPPS we don’t require the usual ultrahigh vacuum, which means we can measure the interfaces between volatile liquids and solids.”

    Fadley is one of three corresponding authors of a paper describing SWAPPS in Nature Communications. The paper is titled Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission. The other two corresponding authors are Hendrik Bluhm, with Berkeley Lab’s Chemical Sciences Division, a pioneer in the development of APPS, and Slavomír Nemšák, now with Germany’s Jülich Peter Grünberg Institute. (See below for the complete list of authors).

    (From left) Chuck Fadley, Ioannis Zegkinoglou, Slavomir Nemsak, Osman Karslioglu, Andrey Shavorskiy and Hendrik Bluhm at Beamline 11.0.2 of the Advanced Light Source (photo by Roy Kaltschmidt)

    In terms of energies and wavelengths, X-rays serve as excellent probes of chemical processes. In the alphabet soup of X-ray analytical techniques, two in particular stand out for the study of chemistry at the interface where layers of two different materials or phases of matter meet. The first is SWPS, developed at the ALS by Fadley and his research group, which made it possible for the first time to selectively study buried interfaces in a sample with either soft or hard X-rays. The second is APPS, also developed at the ALS by a team that included Bluhm, which made it possible for the first time to use X-ray photoelectron spectroscopy under pressures and humidities similar to those encountered in natural or practical environments.

    “Heterogeneous processes at solid/gas, liquid/gas and solid/liquid interfaces are ubiquitous in modern devices and technologies but often difficult to study quantitatively,” Bluhm says. “Full characterization requires measuring the depth profiles of chemical composition and state with enhanced sensitivity in narrow interfacial regions at the nanometer scale. By combining features of SWPS and APPS techniques, we can use SWAPPS to measure the elemental and chemical composition of heterogeneous interfaces with sub-nanometer resolution in the direction perpendicular to the interface.”

    Says Fadley, “We believe SWAPPS will deliver vital information about the structure and chemistry of liquid/vapor and liquid/solid interfaces, in particular the electrical double layer whose structure is critical to the operation of batteries, fuel cells and all of electrochemistry, but which is still not understood at a microscopic level.”

    Fadley, Bluhm, Nemšák and their collaborators used their SWAPPS technique to study a model system in which a nanometer layer of an aqueous electrolyte of sodium hydroxide and cesium hydroxide was grown on an iron oxide (hematite) solid. The spatial distributions of the electrolyte ions and the carbon contaminants across the solid/liquid and liquid/gas interfaces were directly probed and absolute concentrations of the chemical species were determined. The observation of binding-energy shifts with depth provided additional information on the bonding and/or depth-dependent potentials in the system.

    “We determined that the sodium ions are located close to the iron oxide/solution interface, while cesium ions are on average not in direct contact with the solid/liquid interface,” Bluhm says. “We also discovered that there are two different kinds of carbon species, one hydrophobic, which is located exclusively in a thin film at the liquid/vapor interface, and a hydrophilic carbonate or carboxyl that is evenly distributed throughout the liquid film.”

    SWAPPS measures the depth profiles of chemical elements with sub-nanometer resolution in the direction perpendicular to the interface, utilizing an X-ray standing wave field that can be tailored to focus on specific depths, i.e., near the surface or near the iron oxide interface.

    SWAPPS measures the depth profiles of chemical elements with sub-nanometer resolution in the direction perpendicular to the interface utilizing an X-ray standing wave field that can be tailored to focus on specific depths, i.e., near the surface or near the iron oxide interface.

    A key to the success of this study was the use of X-ray standing waves to excite the photoelectrons. A standing wave is a vibrational pattern created when two waves of identical wavelength interfere with one another: one is the incident X-ray and the other is the X-ray reflected by a mirror. Interactions between standing waves and core-level electrons reveal much about the depth distributions of each chemical species in a sample.

    “Tailoring the X-ray wave field into a standing wave can be used to achieve greater depth sensitivity in photoelectron spectroscopy,” Fadley says. “Our combination of an oscillatory standing-wave field and the exponential decay of the photoelectron signal at each interface gives us unprecedented depth resolution.”

    In their Nature Communications paper, the authors say that future time-resolved SWAPPS studies using free-electron laser or high-harmonic generation light sources would also permit, via pump-probe methods, looking at the timescales of processes at interfaces on the femtosecond time scale.

    “The range of future applications and measurement scenarios for SWAPPS is enormous,” Fadley says.

    This work was carried out at ALS Beamline 11.0.2, which is operated by Berkeley Lab’s Chemical Sciences Division and hosts two ambient-pressure photoemission spectroscopy endstations.

    In addition to Fadley, Bluhm and Nemšák, other authors of the Nature Communications paper describing SWAPPS were Andrey Shavorskiy, Osman Karslioglu, Ioannis Zegkinoglou, Peter Greene, Edward Burks, Arunothai Rattanachata, Catherine Conlon, Armela Keqi, Farhad Salmassi, Eric Gullikson, See-Hun Yang and Kai Liu.

    This research was primarily funded by the DOE Office of Science. The Advanced Light Source is a DOE Office of Science User Facility.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal

  • richardmitnick 4:56 pm on November 28, 2014 Permalink | Reply
    Tags: , Chemistry, ,   

    From physicsworld.com: “Medical-isotope breakthrough made at Canadian lab” 


    Nov 28, 2014
    Andrew Williams

    The first commercial shipment of medical isotopes produced using a new particle-accelerator-based technique has been made by scientists at the Canadian Light Source (CLS). Molybdenum-99 (Mo-99) decays to create technetium-99m (Tc-99m), which is used to tag radiopharmaceuticals and plays a unique and vital role in medical imaging. Unlike nuclear reactors, which currently make most of the world’s Mo-99, the system is small enough to be deployed within a large hospital and could thereby improve the supply of the short-lived isotopes.

    Canadian Light Source
    Canadian Light Source

    The material is made at the Medical Isotope Project (MIP) facility at the CLS, which is located at the University of Saskatchewan in Saskatoon. According to Mark de Jong, director of accelerators at the CLS, the facility is the first of its kind anywhere in the world, and uses a small high-power industrial electron linear accelerator to produce a flux of high-energy X-rays through bremsstrahlung radiation. The X-rays strike a target made of enriched Mo-100, in the process “knocking out” a neutron from the nuclei of some of the target atoms to produce Mo-99.

    Isotope maker: Mark de Jong at MIP

    No fission required

    “The main advantage of this method is the complete avoidance of any use of uranium or fission, with all the problems that arise from both volatile short-lived isotopes, as well as disposing of the long-lived radioactive waste,” says De Jong.

    After several days of irradiation at the CLS facility, the target is shipped 800 km to the Winnipeg Health Sciences Centre’s Radio-Pharmacy Department, where it is dissolved and the Tc-99m is extracted. Transport across long distances is possible because Mo-100 has a half-life of 66 hours, but significant losses do occur. The half-life of Tc-99m is just 6 hours, so it must be produced as near as possible to where it will be used.

    De Jong says that future implementations will not necessarily require such long-distance shipping. “The electron linear accelerator is small enough to be located close to where the Mo-99 is required, possibly even within major hospitals, reducing the losses caused by decay in shipping Mo-99. In the present fission-based production, more than 80% of the Mo-99 produced has decayed before it reaches the hospitals,” he adds.

    Reactor shutdowns

    The MIP was created in the wake of serious Mo-99 shortages in 2007 and 2009, which were both related to two unscheduled shutdowns of the ageing NRU nuclear reactor at Atomic Energy of Canada’s Chalk River Laboratories. NRU provides most of Mo-99 for North America, and isotope production is an important industry in Canada. In 2010, fearful of damage to the industry, the Canadian government launched a call under its Non-nuclear-reactor-based Isotope Supply Program (NISP) to encourage alternative isotope production using either photo-neutron production of Mo-99, or direct production of Tc-99m using proton cyclotrons. The CLS proposal was one of two photo-neutron production projects funded, the other being run by Winnipeg-based Prairie Isotope Production Enterprise (PIPE).

    “Once the work to approve the processes involved – Mo-99 production, target dissolution and Tc-99m extraction – is completed by Health Canada, the facility should produce enough for the hospitals serving a population of more than two million people. The health approvals are the next phase that we are working on with our colleagues at PIPE. We hope to have the New Drug Application (NDA) submitted to the authorities by the end of 2015, with routine clinical use possible by the end of 2016,” says De Jong.
    Other options

    In 2012 scientists at the Vancouver-based TRIUMF national laboratory for particle and nuclear physics pioneered two methods for producing Tc-99m using Mo-100 targets and medical cyclotron-based accelerator technology. Cyclotrons are particle accelerators that rely on electricity and magnets to create isotopes by accelerating ions and bombarding non-radioactive materials.

    “Our process is suitable for large population bases, using medical cyclotrons already installed and operational in our major hospitals throughout the country. We have demonstrated that cyclotrons in Vancouver, London and Hamilton have sufficient capacity to supply their respective hospital catchments with Tc-99m,” says TRIUMF’s Melissa Baluk.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics

  • richardmitnick 2:23 pm on November 7, 2014 Permalink | Reply
    Tags: , , Chemistry, ,   

    From Caltech: “Unexpected Findings Change the Picture of Sulfur on the Early Earth” 

    Caltech Logo

    Kimm Fesenmaier

    Scientists believe that until about 2.4 billion years ago there was little oxygen in the atmosphere—an idea that has important implications for the evolution of life on Earth. Evidence in support of this hypothesis comes from studies of sulfur isotopes preserved in the rock record. But the sulfur isotope story has been uncertain because of the lack of key information that has now been provided by a new analytical technique developed by a team of Caltech geologists and geochemists. The story that new information reveals, however, is not what most scientists had expected.

    2.5 billion-year-old sedimentary strata exposed in the Northern Cape Province of South Africa. Credit: Jess Adkins/Caltech

    Reef mounds formed of radiating calcium carbonate crystal fans on the Archean seafloor. Credit: Jess Adkins/Caltech

    Cross-section view of calcium carbonate crystal fans that grew on the seafloor circa 2.6 billion years ago. Credit: Jess Adkins/Caltech

    “Our new technique is 1,000 times more sensitive for making sulfur isotope measurements,” says Jess Adkins, professor of geochemistry and global environmental science at Caltech. “We used it to make measurements of sulfate groups dissolved in carbonate minerals deposited in the ocean more than 2.4 billion years ago, and those measurements show that we have been thinking about this part of the sulfur cycle and sulfur isotopes incorrectly.”

    The team describes their results in the November 7 issue of the journal Science. The lead author on the paper is Guillaume Paris, an assistant research scientist at Caltech.

    Nearly 15 years ago, a team of geochemists led by researchers at UC San Diego discovered there was something peculiar about the sulfur isotope content of rocks from the Archean era, an interval that lasted from 3.8 billion to about 2.4 billion years ago. In those ancient rocks, the geologists were analyzing the abundances of stable isotopes of sulfur.

    When sulfur is involved in a reaction—such as microbial sulfate reduction, a way for microbes to eat organic compounds in the absence of oxygen—its isotopes are usually fractionated, or separated, from one another in proportion to their differences in mass. That is, 34S gets fractionated from 32S about twice as much as 33S gets fractionated from 32S. This process is called mass-dependent fractionation, and, scientists have found that it dominates in virtually all sulfur processes operating on Earth’s surface for the last 2.4 billion years.

    However, in older rocks from the Archean era (i.e., older than 2.4 billion years), the relative abundances of sulfur isotopes do not follow the same mass-related pattern, but instead show relative enrichments or deficiencies of 33S relative to 34S. They are said to be the product of mass-independent fractionation (MIF).

    The widely accepted explanation for the occurrence of MIF is as follows. Billions of years ago, volcanism was extremely active on Earth, and all those volcanoes spewed sulfur dioxide high into the atmosphere. At that time, oxygen existed at very low levels in the atmosphere, and therefore ozone, which is produced when ultraviolet radiation strikes oxygen, was also lacking. Today, ozone prevents ultraviolet light from reaching sulfur dioxide with the energy needed to fractionate sulfur, but on the early Earth, that was not the case, and MIF is the result. Researchers have been able to reproduce this effect in the lab by shining lasers onto sulfur dioxide and producing MIF.

    Geologists have also measured the sulfur isotopic composition of sedimentary rocks dating to the Archean era, and found that sulfides—sulfur-bearing compounds such as pyrite (FeS2)—include more 33S than would be expected based on normal mass-dependent processes. But if those minerals are enriched in 33S, other minerals must be correspondingly lacking in the isotope. According to the leading hypothesis, those 33S-deficient minerals should be sulfates—oxidized sulfur-bearing compounds—that were deposited in the Archean ocean.

    “That idea was put forward on the basis of experiment. To test the hypothesis, you’d need to check the isotope ratios in sulfate salts (minerals such as gypsum), but those don’t really exist in the Archean rock record since there was very little oxygen around,” explains Woody Fischer, professor of geobiology at Caltech and a coauthor on the new paper. “But there are trace amounts of sulfate that got trapped in carbonate minerals in seawater.”

    However, because those sulfates are present in such small amounts, no one has been able to measure well their isotopic composition. But using a device known as a multicollector inductively-coupled mass spectrometer to precisely measure multiple sulfur isotopes, Adkins and his colleague Alex Sessions, a professor of geobiology, developed a method that is sensitive enough to measure the isotopic composition of about 10 nanomoles of sulfate in just a few tens of milligrams of carbonate material.

    The authors used the method to measure the sulfate content of carbonates from an ancient carbonate platform preserved in present-day South Africa, an ancient version of the depositional environments found in the Bahamas today. Analyzing the samples, which spanned 70 million years and a variety of marine environments, the researchers found exactly the opposite of what had been predicted: the sulfates were actually enriched by 33S rather than lacking in it.

    “Now, finally, we’re looking at this sulfur cycle and the sulfur isotopes correctly,” Adkins says.

    What does this mean for the atmospheric conditions of the early Earth? “Our findings underscore that the oxygen concentrations in the early atmosphere could have been incredibly low,” Fischer says.

    Knowledge of sulfate isotopes changes how we understand the role of biology in the sulfur cycle, he adds. Indeed, the fact that the sulfates from this time period have the same isotopic composition as sulfide minerals suggests that the sulfides may be the product of microbial processes that reduced seawater sulfate to sulfide (which later precipitated in sediments in the form of pyrite). Previously, scientists thought that all of the isotope fractionation could be explained by inorganic processes alone.

    In a second paper also in the November 7 issue of Science, Paris, Adkins, Sessions, and colleagues from a number of institutions around the world report on related work in which they measured the sulfates in Indonesia’s Lake Matano, a low-sulfate analog of the Archean ocean.

    At about 100 meters depth, the bacterial communities in Lake Matano begin consuming sulfate rather than oxygen, as do most microbial communities, yielding sulfide. The researchers measured the sulfur isotopes within the sulfates and sulfides in the lake water and sediments and found that despite the low concentrations of sulfate, a lot of mass-dependent fractionation was taking place. The researchers used the data to build a model of the lake’s sulfur cycle that could produce the measured fractionation, and when they applied their model to constrain the range of concentrations of sulfate in the Archean ocean, they found that the concentration was likely less than 2.5 micromolar, 10,000 times lower than the modern ocean.

    “At such low concentration, all the isotopic variability starts to fit,” says Adkins. “With these two papers, we were able to come at the same problem in two ways—by measuring the rocks dating from the Archean and by looking at a model system today that doesn’t have much sulfate—and they point toward the same answer: the sulfate concentration was very low in the Archean ocean.”

    Samuel M. Webb of the Stanford Synchrotron Radiation Lightsource is also an author on the paper, “Neoarchean carbonate-associated sulfate records positive Δ33S anomalies.” The work was supported by funding from the National Science Foundation’s Division of Earth Sciences, the Henry and Camille Dreyfus Foundation’s Postdoctoral Program in Environmental Chemistry, and the David and Lucile Packard Foundation.

    Paris is also a co-lead author on the second paper, Sulfate was a trace constituent of Archean seawater. Additional authors on that paper are Sean Crowe and CarriAyne Jones of the University of British Columbia and the University of Southern Denmark; Sergei Katsev of the University of Minnesota Duluth; Sang-Tae Kim of McMaster University; Aubrey Zerkle of the University of St. Andrews; Sulung Nomosatryo of the Indonesian Institute of Sciences; David Fowle of the University of Kansas; James Farquhar of the University of Maryland, College Park; and Donald Canfield of the University of Southern Denmark. Funding was provided by an Agouron Institute Geobiology Fellowship and a Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellowship, as well as by the Danish National Research Foundation and the European Research Council.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
    Caltech buildings
    ScienceSprings relies on technology from

    MAINGEAR computers



  • richardmitnick 8:36 pm on November 4, 2014 Permalink | Reply
    Tags: , , Chemistry, DESI Petra III   

    From DESY: “Photosynthesis in X-ray Vision” 


    No Writer Credit

    New technology facilitates analysis of biomolecules in a near-natural state

    Photosynthesis is one of the most important processes in nature. The complex method with which all green plants harvest sunlight and thereby produce the oxygen in our air is, however, still not fully understood. Researchers using DESY’s X-ray light source PETRA III have examined a photosynthesis subsystem in a near-natural state. According to the scientists led by Privatdozentin Dr. Athina Zouni from the Humboldt University (HU) Berlin, the X-ray experiments on what is known as photosystem II reveal, for example, yet unknown structures. Their results are published in the scientific journal Structure. The technology utilised could also be of interest for analysing other biomolecules.

    Molecular structure of photosystem II, which arranges itself in rows. Credit: Martin Bommer/HU Berlin

    DESI Petra III
    DESI Petra III interior
    DESI Petra III

    Photosystem II forms part of the photosynthetic machinery where water, with the help of sunlight, is split into hydrogen and oxygen. As one of the membrane proteins, it sits in the cell membrane. Membrane proteins are a large and vital group of biomolecules that are, for example, important in addressing a variety of medical issues. In order to decode the protein structure and reveal details on how biomolecules function, researchers use the very bright and short-wave X-rays of PETRA III and other similar facilities. Small crystals, however, must initially be grown from these biomolecules. “The structure of single molecules cannot be directly seen even with the brightest X-rays,” explains co-author and DESY researcher Dr. Anja Burkhardt of Measuring Station P11, where the experiments were carried out. “In a crystal, however, a multitude of these molecules are arranged in a highly symmetrical fashion. Thus the signal, resulting from X-ray diffraction of these molecules, is amplified. The molecular structure can then be calculated from the diffraction images.”

    Biomolecules – and especially membrane proteins – cannot easily be compelled into crystal form as it is contrary to their natural state. Preparing suitable samples is therefore a crucial step in the whole analysis process. For instance, photosystem II must be first separated from the membrane, where it is bound to numerous small fat molecules (lipids). Researchers use special detergents for this purpose, such as those also principally found in soap. The catch: instead of lipids, the biomolecules are now surrounded by detergents, which may make the crystals spongy under certain conditions, thus exacerbating the analysis. “What we want is to come as close as possible to nature,” stresses Zouni. The closer the proteins in the crystal are to their natural state, the better the results.

    The group led by Zouni has now managed to produce photosystem II crystals, which no longer contain detergents so that the biomolecules are frozen in a near-natural state. “The trick was to use a detergent that strongly differs from the lipids in composition and structure,” explains the researcher. Before examining the biomolecular crystals using X-rays, a portion of the water is extracted and replaced by an anti-freeze. The crystals are usually frozen for the experiments because the high-energy X-ray doesn’t damage them so quickly in the frozen state. During this process, the researchers would like to avoid ice formation. “The dehydration process removed not only the water in our samples, but also completely removed the detergent, something we didn’t expect,” says Zouni.“Our samples are closer to the natural state than what has been reported before.”

    Consequently, the investigation’s spatial resolution increased from about 0.6 nanometres (a millionth of a millimetre) to 0.244 nanometres. This is not, in fact, the highest resolution ever achieved in a photosystem II study, but the analysis shows that the photosystem II proteins are arranged within the crystals as pairs of rows, something that also occurs in the natural environment.

    Electron microscope investigations by Professor Egbert Boekema’s group at the University of Groningen in the Netherlands had already shown the photosystems’ crystal like arrangement in the natural membrane — a kind of tiny solar cell. Electron microscopy could better recognize connections using direct observation of the native membrane while X-ray crystallography could reveal the smallest details. “We placed the structural data over the electron microscope images – they matched precisely,” says Zouni. The investigation also revealed structures that were invisible before. “We can see exactly where the bonds to the lipids are located,” the scientist explains. The more the researchers discover about photosystem II, the better they understand exactly how it functions.

    The procedure of using a new detergent, however, is not only interesting in terms of photosystem II. “The method can potentially be applied to many membrane proteins,” stresses Zouni. In the future, many biomolecules could maybe examined in a more natural state than ever before.

    See the full article here.


    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

    ScienceSprings relies on technology from

    MAINGEAR computers



  • richardmitnick 5:33 pm on October 27, 2014 Permalink | Reply
    Tags: , Chemistry   

    From Princeton: “What makes a tumor switch from dormant to malignant?” 

    Princeton University
    Princeton University

    October 27, 2014
    Tien Nguyen, Department of Chemistry

    Cancer constantly wages war on the human body. Battles are won, lost or sometimes end in a stalemate. This stalemate, known as tumor dormancy, is extremely difficult to study in both cellular and animal models.

    A new computational model developed in the laboratory of Salvatore Torquato, a professor of chemistry at Princeton University, offers a way to probe the conditions surrounding tumor dormancy and the switch to a malignant state. Published Oct. 16 in the journal “PLOS ONE,” the so-called cellular automaton model simulated various scenarios of tumor growth leading to tumor dormancy or proliferation.
    Researchers from Princeton University have developed a computer model that simulates the competition between tumor dormancy and proliferation under various conditions. Through a series of simulations, they generated a phase diagram, pictured here, that could be used by experimentalists to predict when the tumor will be in a proliferative or dormant state. (Image courtesy of Salvatore Torquato Lab)

    “The power of the model is that it lets people test medically realistic scenarios,” said Torquato, who is also affiliated with the Princeton Institute for the Science and Technology of Materials. In future collaborations, these scenarios could be engineered in laboratory experiments and the observed outcomes could be used to calibrate the model.

    For each scenario, a set of rules is imposed on the virtual cell population. Rules are possible interactions, such as neighboring cell death or immune system suppression, that dictate cell division through probabilities derived from past experimental data. Once the researchers programmed the rules, they watched as the simulated competition unfolded between the tumor and the environmental factors that may suppress its growth.

    “We were very surprised to observe this phenomena where the tumor all of a sudden began to rapidly divide,” said Duyu Chen, graduate student in the Torquato lab and lead author on the article. This was the first time that the emergent switch behavior, which has been observed clinically, occurred spontaneously in a model, Chen said.

    The researchers evaluated a number of factors that could affect tumor cell growth including spontaneous cell mutations, mechanical properties, and the rate and strength of suppression factors such as the immune system. One of the model’s findings was the likely suppression of tumors in harsh environments, characterized by high density and pressure.

    “The way [the researchers] built their model system is that the dormancy state is not one of cells simply sleeping, in fact it’s an active state, it’s just that the whole system is held in equilibrium or stalemate,” said Micheal Espey, program manager at the National Cancer Institute who was not involved in the research. “That’s a very interesting viewpoint.”

    The research team also predicted that if the number of actively dividing cells within the proliferative rim reached a certain critical level, the tumor was very likely to begin growing rapidly. This result could provide insight into early cancer treatment, Chen said.

    Through repeated simulations the research team constructed a phase diagram that revealed the boundary between a dormant and proliferative state. If experimental data was incorporated into the model, Espey said, researchers could predict when the tumor was in a dormant state and when it was heading toward a proliferative state. “That’s the value,” he said.

    The research was supported by the National Cancer Institute under Award No. U54CA143803.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield
    ScienceSprings relies on technology from

    MAINGEAR computers



  • richardmitnick 1:45 pm on October 17, 2014 Permalink | Reply
    Tags: , , Chemistry   

    From AAAS: “Would-be drug mimics ‘good’ cholesterol” 



    16 October 2014
    Robert F. Service

    A new drug candidate designed to mimic the body’s “good” cholesterol shows a striking ability in mice to lower cholesterol levels in the blood and dissolve artery-clogging plaques. What’s more, the compound works when given orally, rather than as an injection. If the results hold true in humans—a big if, given past failures at transferring promising treatments from mice—it could provide a new way to combat atherosclerosis, the biggest killer in developed countries.

    Although doctors already have effective cholesterol-lowering agents, such as statins, at their disposal, there’s room for improvement. Statins have significant side effects in some people and don’t always reduce cholesterol enough in others. “There is still plenty of heart disease out there even among people who take statins,” says Godfrey Getz, an experimental pathologist at the University of Chicago in Illinois.

    For that reason, researchers around the globe are searching for novel drugs that affect cholesterol levels in one of two ways. The first has been to reduce levels of low-density lipoprotein (LDL), commonly known as bad cholesterol, which has been associated with higher heart disease risk. This is the goal of statins, which block an enzyme involved in cholesterol production. The second strategy is to increase levels of good cholesterol, or high-density lipoprotein (HDL), which seems to boost heart health in people who have a lot of it. But producing HDL-raising drugs that prevent heart disease has proven difficult. In the body, a large protein called apolipoprotein A-I (apoA-I) wraps around fatty lipid molecules to create HDL particles that sop up LDL and ferry it to the liver where it is eliminated. So for several decades researchers have been designing and testing small protein fragments called peptides to see if they could mimic the behavior of apoA-I. One such peptide, known as 4F, did not reduce serum cholesterol levels, but it did shrink arterial plaques in mice, rabbits, and monkeys. And in an early clinical trial by researchers at Bruin Pharma Inc. in Beverly Hills, California, that was designed only to measure its safety in people, 4F didn’t appear to show any beneficial effect.

    Multiple copies of a four-armed peptide wrap around lipids to create particles that mimic the behavior of HDL, the “good” cholesterol.
    Y.Zhao et al., J. Am. Chem. Soc

    M. Reza Ghadiri, a chemist at the Scripps Research Institute in San Diego, California, and his colleagues took a slightly different tack, creating a peptide that mimics another part of the apoA-I protein than 4F does. Initial in vitro studies suggested the peptide formed HDL-like particles and sopped up LDL, an encouraging result that prompted them to push it further. Ghadiri and his Scripps colleagues have now tested their compound in mice that develop artery clogging plaques when fed a Western-style high-fat diet. One group of animals received the peptide intravenously. For another group, the researchers simply added the compound to the animals’ water, a strategy they considered unlikely to work, because the gut contains high amounts of proteases designed to chop proteins apart. To their surprise, in both groups, serum cholesterol levels dropped 40% from their previous levels within 2 weeks of starting to take the drug. And by 10 weeks, the number of artery-clogging lesions had been reduced by half, the team reports in the October issue of the Journal of Lipid Research. What remains puzzling, however, is that Ghadiri and his colleagues did not detect their peptides in the blood of their test animal. Ghadiri says this suggests that the new peptide may work by removing cholesterol precursors in the gut before they enter the bloodstream.

    “It’s a very interesting result,” Getz says. But he cautions that the work has been tested only in animals, and many therapies—including the closely related 4F peptide—fail to transfer to humans. That said, Getz notes that some of the initial promising results with this peptide and other apoA-I mimics offer hope that researchers may soon come up with novel drugs capable of dissolving artery-clogging plaques before they can wreak their havoc.

    See the full article here.

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

    ScienceSprings relies on technology from

    MAINGEAR computers



  • richardmitnick 9:02 am on October 17, 2014 Permalink | Reply
    Tags: , Chemistry, ,   

    From MIT: “Nanoparticles get a magnetic handle” 

    MIT News

    October 9, 2014
    David L. Chandler | MIT News Office

    A long-sought goal of creating particles that can emit a colorful fluorescent glow in a biological environment, and that could be precisely manipulated into position within living cells, has been achieved by a team of researchers at MIT and several other institutions. The finding is reported this week in the journal Nature Communications.

    Elemental mapping of the location of iron atoms (blue) in the magnetic nanoparticles and cadmium (red) in the fluorescent quantum dots provide a clear visualization of the way the two kinds of particles naturally separate themselves into a core-and-shell structure. Image courtesy of the researchers

    The new technology could make it possible to track the position of the nanoparticles as they move within the body or inside a cell. At the same time, the nanoparticles could be manipulated precisely by applying a magnetic field to pull them along. And finally, the particles could have a coating of a bioreactive substance that could seek out and bind with particular molecules within the body, such as markers for tumor cells or other disease agents.

    “It’s been a dream of mine for many years to have a nanomaterial that incorporates both fluorescence and magnetism in a single compact object,” says Moungi Bawendi, the Lester Wolfe Professor of Chemistry at MIT and senior author of the new paper. While other groups have achieved some combination of these two properties, Bawendi says that he “was never very satisfied” with results previously achieved by his own team or others.

    For one thing, he says, such particles have been too large to make practical probes of living tissue: “They’ve tended to have a lot of wasted volume,” Bawendi says. “Compactness is critical for biological and a lot of other applications.”

    In addition, previous efforts were unable to produce particles of uniform and predictable size, which could also be an essential property for diagnostic or therapeutic applications.

    Moreover, Bawendi says, “We wanted to be able to manipulate these structures inside the cells with magnetic fields, but also know exactly what it is we’re moving.” All of these goals are achieved by the new nanoparticles, which can be identified with great precision by the wavelength of their fluorescent emissions.

    The new method produces the combination of desired properties “in as small a package as possible,” Bawendi says — which could help pave the way for particles with other useful properties, such as the ability to bind with a specific type of bioreceptor, or another molecule of interest.

    In the technique developed by Bawendi’s team, led by lead author and postdoc Ou Chen, the nanoparticles crystallize such that they self-assemble in exactly the way that leads to the most useful outcome: The magnetic particles cluster at the center, while fluorescent particles form a uniform coating around them. That puts the fluorescent molecules in the most visible location for allowing the nanoparticles to be tracked optically through a microscope.

    “These are beautiful structures, they’re so clean,” Bawendi says. That uniformity arises, in part, because the starting material, fluorescent nanoparticles that Bawendi and his group have been perfecting for years, are themselves perfectly uniform in size. “You have to use very uniform material to produce such a uniform construction,” Chen says.

    Initially, at least, the particles might be used to probe basic biological functions within cells, Bawendi suggests. As the work continues, later experiments may add additional materials to the particles’ coating so that they interact in specific ways with molecules or structures within the cell, either for diagnosis or treatment.

    The ability to manipulate the particles with electromagnets is key to using them in biological research, Bawendi explains: The tiny particles could otherwise get lost in the jumble of molecules circulating within a cell. “Without a magnetic ‘handle,’ it’s like a needle in a haystack,” he says. “But with the magnetism, you can find it easily.”

    A silica coating on the particles allows additional molecules to attach, causing the particles to bind with specific structures within the cell. “Silica makes it completely flexible; it’s a well developed material that can bind to almost anything,” Bawendi says.

    For example, the coating could have a molecule that binds to a specific type of tumor cells; then, “You could use them to enhance the contrast of an MRI, so you could see the spatial macroscopic outlines of a tumor,” he says.

    The next step for the team is to test the new nanoparticles in a variety of biological settings. “We’ve made the material,” Chen says. “Now we’ve got to use it, and we’re working with a number of groups around the world for a variety of applications.”

    Christopher Murray, a professor of chemistry and materials science and engineering at the University of Pennsylvania who was not connected with this research, says, “This work exemplifies the power of using nanocrystals as building blocks for multiscale and multifunctional structures. We often use the term ‘artificial atoms’ in the community to describe how we are exploiting a new periodic table of fundamental building blocks to design materials, and this is a very elegant example.”

    The study included researchers at MIT; Massachusetts General Hospital; Institut Curie in Paris; the Heinrich-Pette Institute and the Bernhard-Nocht Institute for Tropical Medicine in Hamburg, Germany; Children’s Hospital Boston; and Cornell University. The work was supported by the National Institutes of Health, the Army Research Office through MIT’s Institute for Soldier Nanotechnologies, and the Department of Energy.

    See the full article, with video, here.

    ScienceSprings relies on technology from

    MAINGEAR computers



  • richardmitnick 9:08 am on October 15, 2014 Permalink | Reply
    Tags: , , Chemistry   

    From AAAS: “Storing greenhouse gas underground—for a million years” 



    14 October 2014
    Jia You

    When Canada switched on its Boundary Dam power plant earlier this month, it signaled a new front in the war against climate change. The commercial turbine burns coal, the dirtiest of fossil fuels, but it traps nearly all the resulting carbon dioxide underground before it reaches the atmosphere. Part of this greenhouse gas is pumped into porous, water-bearing underground rock layers. Now, a new study provides the first field evidence that CO2 can be stored safely for a million years in these saline aquifers, assuaging worries that the gas might escape back into the atmosphere.

    Geologist Martin Cassidy, who co-authored the new study, samples a gas well at Bravo Dome, the world’s largest natural CO2 reservoir.

    “It’s a very comprehensive piece of work,” says geochemist Stuart Gilfillan of the University of Edinburgh in the United Kingdom, who was not involved in the study. “The approach is very novel.”

    There have been several attempts to capture the carbon dioxide released by the world’s 7000-plus coal-fired plants. Pilot projects in Algeria, Japan, and Norway indicate that CO2 can be stored in underground geologic formations such as depleted oil and gas reservoirs, deep coal seams, and saline aquifers. In the United States, saline aquifers are believed to have the largest capacity for CO2 storage, with potential sites spread out across the country, and several in western states such as Colorado also host large coal power plants. CO2 pumped into these formations are sealed under impermeable cap rocks, where it gradually dissolves into the salty water and mineralizes. Some researchers suggest the aquifers have enough capacity to store a century’s worth of emissions from America’s coal-fired plants, but others worry the gas can leak back into the air through fractures too small to detect.

    To resolve the dilemma, geoscientists need to know how long it takes for the trapped CO2 to dissolve. The faster the CO2 dissolves and mineralizes, the less risk that it would leak back into the atmosphere. But determining the rate of dissolution is no easy feat. Lab simulations suggest that the sealed gas could completely dissolve over 10,000 years, a process too slow to be tested empirically.

    So computational geoscientist Marc Hesse of the University of Texas, Austin, and colleagues turned to a natural lab: the Bravo Dome gas field in New Mexico, one of the world’s largest natural CO2 reservoirs. Ancient volcanic activities there have pumped the gas into a saline aquifer 700 meters underground. Since the 1980s, oil companies have drilled hundreds of wells there to extract the gas for enhanced oil recovery, leaving a wealth of data on the site’s geology and CO2 storage.

    To find out how fast CO2 dissolves in the aquifers, the researchers needed to know two things: the total amount of gas dissolved at the reservoir and how long it has been there. Because the gas is volcanic in origin, the researchers reasoned that it must have arrived at Bravo Dome steaming hot—enough to warm up the surrounding rocks. So they examined the buildup of radiogenic elements in the mineral apatite. These elements accumulate at low temperatures, but are released if the mineral is heated above 75°C, allowing the researchers to determine when the mineral was last heated above such a high temperature. The team estimated that the CO2 was pumped into the reservoir about 1.2 million years ago.

    Then the scientists calculated the amount of gas dissolved over the millennia, using the helium-3 isotope as a tracer. Like CO2, helium-3 is released during volcanic eruptions, and it is rather insoluble in saline water. By studying how the ratio of helium-3 to CO2 changes across the reservoir, the researchers found that out of the 1.6 gigatons of gas trapped underground at the reservoir, only a fifth has dissolved over 1.2 million years. That’s the equivalent of 75 years of emissions from a single 500-megawatt coal power plant, they report online this week in the Proceedings of the National Academy of Sciences.

    More intriguingly, the analysis also provided the first field evidence of how CO2 dissolves after it is pumped into the aquifers. In theory, the CO2 dissolves through diffusion, which takes place when the gas comes into contact with the water surface. But the process could move faster if convection—in which water saturated with CO2 sinks and fresh water flows into its place to absorb more gas—were also at work. Analysis revealed that at Bravo Dome, 10% of the total gas at the reservoir dissolved after the initial emplacement. Diffusion alone cannot account for that amount, the researchers argue, as the gas accumulating at the top of the reservoir would have quickly saturated still water. Instead, convection most likely occurred.

    Hesse says constraints on convection might explain why CO2 dissolves much more slowly in saline aquifers at Bravo Dome than previously estimated, at a rate of 0.1 gram per square meter per year. The culprit would be the relatively impermeable Brava Dome rocks, which limit water flow and thus the rate of convective CO2 dissolution. At storage sites with more porous rocks, the gas could dissolve much faster and mineralize earlier, he says.

    Even so, the fact that CO2 stayed locked up underground for so long at Bravo Dome despite ongoing industrial drilling should allay concerns about potential leakage, Hesse says. Carbon capture and storage “can work, if you do it in the right place,” he says. “[This is] an enormous amount of CO2 that has sat there, for all we can tell, very peacefully for more than a million years.”

    See the full article here.

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

    ScienceSprings relies on technology from

    MAINGEAR computers



  • richardmitnick 3:11 pm on September 28, 2014 Permalink | Reply
    Tags: , Chemistry, ,   

    From Scientific American: “Weak Nuclear Force Shown to Give Asymmetry to Biochemistry of Life” 

    Scientific American

    Scientific American

    Sep 26, 2014
    Elizabeth Gibney and Nature magazine

    Physicists have found hints that the asymmetry of life — the fact that most biochemical molecules are ‘left-handed’ or ‘right-handed’ — could have been caused by electrons from nuclear decay in the early days of evolution. In an experiment that took 13 years to perfect, the researchers have found that these electrons tend to destroy certain organic molecules slightly more often than they destroy their mirror images.

    Life is made largely of molecules that are different than their mirror images.
    Credit: Brett Weinstein via Flickr

    Many organic molecules, including glucose and most biological amino acids, are ‘chiral’. This means that they are different than their mirror-image molecules, just like a left and a right glove are. Moreover, in such cases life tends to consistently use one of the possible versions — for example, the DNA double helix in its standard form always twists like a right-handed screw. But the reason for this preference has long remained a mystery.

    Many scientists think that the choice was simply down to chance. Perhaps, in one of the warm little ponds filled with organic chemicals where life arose, a statistical fluke generated a small imbalance in the relative amounts of the two versions of one chemical. This small imbalance could have then amplified over time.

    But an asymmetry in the laws of nature has led others to wonder whether some physical phenomenon could have tipped the balance during the early stages of life. The weak nuclear force, which is involved in nuclear decay, is the only force of nature known to have a handedness preference: electrons created in the subatomic process known as β decay are always ‘left-handed’. This means that their spin — a quantum property analogous to the magnetization of a bar magnet — is always opposite in direction to the electron’s motion.

    In 1967, biochemist Frederic Vester and environmental scientist Tilo Ulbricht proposed that photons generated by these so-called spin-polarized electrons — which are produced in the decay of radioactive materials or of cosmic-ray particles in the atmosphere — could have destroyed more of one kind of molecule than another, creating the imbalance. Some physicists have since suggested that the electrons themselves might be the source of the asymmetry.

    But the hunt to find chemical processes through which electrons or photons could preferentially destroy one version of a molecule over its mirror image has seen little success. Many claims have proven impossible to reproduce. The few experiments in which electron handedness produced a chiral imbalance could not identify the chemical process behind it, says Timothy Gay, a chemical physicist at the University of Nebraska–Lincoln and a co-author of the latest study. But pinpointing a chemical reaction would help scientists to rule out some candidate causes of the process and to better understand the physics that underlie it, he adds.

    Taking it slow

    Gay and Joan Dreiling, a physicist also at the University of Nebraska–Lincoln, fired low-energy, spin-polarized electrons at a gas of bromocamphor, an organic compound used in some parts of the world as a sedative. In the resulting reaction, some electrons were captured by the molecules, which then were kicked into an excited state. The molecules then fell apart, producing bromide ions and other highly reactive compounds. By measuring the flow of ions produced, the researchers could see how often the reaction occurred for each handedness of electron.

    The researchers found that left-handed bromocamphor was just slightly more likely to react with right-handed electrons than with left-handed ones. The converse was true when they used right-handed bromocamphor molecules. At the lowest energies, the direction of the preference flipped, causing an opposite asymmetry.

    In all cases the asymmetry was tiny, but consistent, like flipping a not-quite-fair coin. “The scale of the asymmetry is as though we flip 20,000 coins again and again, and on average, 10,003 of them land on heads while 9,997 land on tails,” says Dreiling.

    The low speed of the electrons was the key to why the experiment finally worked after so many years, Dreiling says. “The interaction takes longer, and it was that insight, I think, that led to our success,” she says.

    The test offers an explanation for how a chiral excess could — at least in principle — arise, Gay says. The research was published in Physical Review Letters on 12 September.

    The idea that spin-polarized electrons could transmit their asymmetry to organic molecules is attractive, says Uwe Meierhenrich, an analytical chemist at the University of Nice Sophia Antipolis in France. The tiny effect that Gay and Dreiling observed would have to be amplified to affect the chemistry of life as a whole — but there are known mechanisms for such amplification, he says. “From my point of view, the main question does not concern the amplification processes, but the first chiral-symmetry breaking,” he says.

    Meierhenrich says that he would like to see the experiment repeated with chiral molecules that are relevant to the origin of life, such as amino acids, to see whether the left-handed electrons produce the same effect.

    Primordial cause

    Even if spin-polarized electrons caused life to become chirally selective, it is still unclear what would have produced those electrons in the first place. Sources of β particles include phosphorus-32 decaying into sulphur-32, or the decay of muons, elementary particles produced at the end of a chain of decays that begin when cosmic ray particles hit the atmosphere. In both cases, the electrons would have been travelling much faster than in Gay’s reaction, but he says that it is possible for electrons to slow down without losing their chirality.

    Slower-moving, left-handed electrons are produced in other ways than via β decay, says Richard Rosenberg, a chemist at the Argonne National Laboratory in Illinois. In 2008 he and his team showed that irradiating a layer of magnetized iron with X-rays could also produce a chirality preference. Chirality could therefore also have been created in molecules stuck to magnetized particles in a dust cloud or comet, he says.

    Gay and his colleagues plan to look at similar reactions with other varieties of camphor molecules to understand how the spin of an electron dictates which of two chiral molecules it prefers.

    The interaction of left-handed electrons with organic molecules is not the only potential explanation for the chiral asymmetry of life.. Meierhenrich favors an alternative — the circularly polarized light that is produced by the scattering of light in the atmosphere and in neutron stars. In 2011, Meierhenrich and colleages showed that such light could transfer its handedness to amino acids.

    But even demonstrating how a common physical phenomenon would have favoured left-handed amino acids over right-handed ones would not tell us that this was how life evolved, adds Laurence Barron, a chemist at the University of Glasgow, UK. “There are no clinchers. We may never know.”

    See the full article here.

    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

    ScienceSprings relies on technology from

    MAINGEAR computers



Compose new post
Next post/Next comment
Previous post/Previous comment
Show/Hide comments
Go to top
Go to login
Show/Hide help
shift + esc

Get every new post delivered to your Inbox.

Join 377 other followers

%d bloggers like this: