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  • richardmitnick 10:17 am on August 17, 2016 Permalink | Reply
    Tags: A miniaturized sensor that can measure chemistry on a chip, , Chemistry,   

    From Cornell: “A miniaturized sensor that can measure chemistry on a chip” 

    Cornell Bloc

    Cornell University

    August 17, 2016
    Bill Steele

    1
    Light traveling through a nanoscale waveguide on a chip spreads beyond the waveguide and can interact with molecules above the surface of the chip. Credit: Cornell University

    By combining expertise in photonics – manipulating light beams in nanoscale waveguides on a chip – and materials science, Cornell researchers have laid the groundwork for a chemical sensor on a chip that could be used in small portable devices to analyze samples in a lab, monitor air and water quality in the field and perhaps even detect explosives.

    The researchers use a phenomenon called “Raman scattering:” when a laser strikes a molecule it kicks back the laser energy as photons of light at a variety of wavelengths that depend on the structure and composition of the molecule.

    To allow this phenomenon to occur on a chip, researchers fire a laser into a waveguide – a strip of transparent material made of titanium dioxide, where the light bounces off the inside surfaces and becomes confined to the waveguide. Because a waveguide is only a few nanometers (billionths a meter) high, the light waves spread out beyond the waveguide, creating a so-called “evanescent field” above the surface of the chip. The pumping laser can induce Raman scattering in the space above the chip, or in a drop of liquid placed on its surface for analysis, while still confining the light wave to the chip. Light kicked back by the excited molecules also follows the waveguide; a prism at the end of the waveguide can spread that light into a spectrum that is a “fingerprint” identifying the molecule that produced it.

    “If you need a chemical sensor in the lab, that is not a problem,” said Jin Suntivich, assistant professor of materials science and engineering. “But when you are outside, finding a chemical sensor that you can take with you is a challenge. We want to develop a technology that is small enough for a phone, such that your personal electronics can constantly monitor the world around you, and the moment you see something out of the ordinary, the sensor can tell you what it is.”

    Sensors based on Raman scattering have been made before, using silicon nitride waveguides. The Cornell researchers have come up with a design that could make a sensor more sensitive and small enough to be used in the field by using a new material, titanium dioxide.

    “We’re not the first but we’re the best,” said Christopher Evans, a Kavli Postdoctoral Fellow in the Laboratory of Atomic and Solid State Physics and the Kavli Institute at Cornell for Nanoscale Science. Evans is first author of paper describing the new approach published in the July 14 online edition of the American Chemical Society journal ACS Photonics. Co-authors are Suntivich and Chengyu Liu, a doctoral student in the School of Applied and Engineering Physics

    2
    A circular waveguide tangent to a straight guide causes light to circulate around and around, giving it more time to interact with material above the chip. The ring is about the diameter of a human hair.

    Titanium dioxide has a much higher refractive index, making a greater contrast with the space above the chip, which creates a stronger evanescent field. The material is also transparent to light at visible wavelengths, a condition that allows researchers to use a laser at shorter, visible wavelengths, which induce better scattering. The researchers tested with a green laser pointer as a light source.

    For a future device, a tiny laser unit can be built into a chip, as can a component that can spread out the wavelengths of the kicked off light onto a photosensitive device to read the spectrum. One possibility is to read the spectrum with the camera in a phone.

    Interaction of the pumping laser with the material above the chip increases with the length of the waveguide. But the researchers also offer a way to increase the interaction without having to make the chip larger. The solution is a “ring resonator.” When a circular waveguide is set tangent to a straight guide, some of the light will enter the ring and continue to circle around it, letting the light interact continually with the material above the chip many times. The circumference of the ring can be adjusted to resonate with the wavelength of the light, intensifying the effect. “We have shown that we can increase the amount of peak signal from our sensors by an order of magnitude (or more), while simultaneously reducing the device footprint down to the cross-section of a human hair,” Evans said.

    Potential applications include portable sensors to monitor air and water quality or conduct laboratory tests in the field. Chemists could and observe chemical reactions while they occur.

    The work was supported in part by the Cornell Center for Materials Reseach and used the Cornell Nanoscale Facility, both funded by the National Science Foundation. Additional support was provided by the Samsung Advanced Institute of Technology and the Kavli Institute at Cornell for Nanoscale Science.

    See the full article here .

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    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 11:50 am on August 12, 2016 Permalink | Reply
    Tags: , , Chemistry, , Todd Hyster   

    From Princeton: “Professor explores new territory by bridging chemistry, biology” 

    Princeton University
    Princeton University

    August 11, 2016
    Tien Nguyen, Department of Chemistry

    In any given year, a synthetic chemist may set up several hundred chemical reactions. Many of these reactions will fail, so chemists temper their expectations.

    But not Todd Hyster, a Princeton University assistant professor who joined the Department of Chemistry last summer.

    1
    Todd Hyster (right), a Princeton University assistant professor of chemistry, focuses his research on novel reactions in an area just emerging among American chemists — the merger of classic organic synthesis and biocatalysis. As one of the few synthetic chemists who understands biological systems, he is uniquely equipped to identify the reactions that would be most impactful for organic synthesis and make them happen. He encourages researchers in his lab, such as chemistry graduate student Braddock Sandoval (left), to harness chemistry and biology to bring about seemingly unlikely reactions. (Photos by C. Todd Reichart, Department of Chemistry)

    “Todd gets really excited about these crazy ideas and he’s always confident that it’s going to work, even if we think it’s a long shot,” said Braddock Sandoval, a graduate researcher in Hyster’s lab.

    Hyster focuses his research on novel reactions at the merger of two areas in which he has extensive experience: classic organic synthesis, which uses small molecules that perform an expansive range of reactions, and biocatalysis, which uses large biological systems such as enzymes to execute only specific reactions, but does so very efficiently. Researchers at the intersection of these fields propose to modify powerful enzymes so that they can be used in more organic reactions.

    The majority of the work in this area has come from biology labs that are well acquainted with wrangling complex biological systems, but the field hasn’t seen the same level of engagement from chemists, especially in the United States. Essentially, chemists can have difficulty dealing with biological systems because they must learn how to grow cells and work with complicated enzymes. Yet, biologists may not know which of the thousands of possible reactions organic chemists would find most valuable and useful.

    Hyster, however, can do both. As one of the few synthetic chemists who also understands biological systems, he is uniquely equipped to identify the reactions that would be most impactful for organic synthesis and make them happen.

    “Todd has the ability to connect these enzymes to reaction mechanisms people aren’t even thinking about,” said David MacMillan, the James S. McDonnell Distinguished University Professor of Chemistry at Princeton. “He’s at the vanguard of something new in biocatalysis and I think it’s going to be incredibly exciting.”

    Building up to biocatalysis

    As a graduate student under the direction of Tomislav Rovis at Colorado State University, Hyster began research in transition-metal catalysis and, at the time, wanted nothing to do with biology. “I remember saying that I was ‘repulsed’ by biology,” Hyster said with a laugh, “probably one of the most naïve things I’ve ever said.”

    It wasn’t until his third year of graduate school that his attitude began to shift. He became intrigued by a conference presentation on using mutated proteins to catalyze a specific reaction and even chose the general topic — directed evolution — for his departmental seminar. Then Rovis went on sabbatical in France and presented Hyster with the opportunity to collaborate with a research group working at the interface of biology and organometallic chemistry at the University of Basel in Switzerland, opening a new area of research for the Rovis lab in biocatalysis.

    Rovis recalled emailing Hyster late at night from Europe to pitch him the collaboration idea. The usual strategy to improve the reaction is to change the small molecule known as the ligand. Instead, Rovis suggested keeping the ligand constant and changing the reaction environment using a biological system developed by the group in Basel. Hyster replied the next morning that he loved the idea and was game to try it.

    “He’s someone who had the vision to see the real impact and potential of the idea, and who certainly doesn’t pay attention at all to how hard it might be. That’s the kind of researcher he is,” Rovis said.

    In order to make the collaboration work, Hyster spent four months in Basel in Professor of Chemistry Thomas Ward’s laboratory learning how to work with proteins, ultimately bringing those skills back to the lab in Colorado.

    “His fearlessness is his best quality,” Rovis said. “It’s what allowed him to embrace this new field that he had no prior experience with and successfully tackle the problem.”

    The resulting work — published in the journal Science in 2012 — was the first example of a biological environment that could be engineered to promote the formation of new bonds. The reaction took advantage of the extremely strong binding affinity between the large protein streptavidin and the compound biotin, which is referred to as “molecular Velcro.” By attaching the ligand-metal complex to biotin, the researchers could lock the metal catalyst into the highly controlled binding pocket of streptavidin.

    For his postdoctoral study, Hyster began to shift his focus onto biocatalysis. He joined the laboratory of one of the pioneers of biocatalysis, Frances Arnold, professor of chemical engineering, bioengineering and biochemistry at the California Institute of Technology.

    In a 2014 paper published in the Journal of the American Chemical Society during his time in the Arnold lab, Hyster developed variants of the enzyme P450 — one of the most well-known enzymes that break down organic molecules in the liver — to catalyze a particularly unfavorable bond connection. In this type of reaction, known as an amination reaction, the catalyst typically breaks the weakest existing carbon-hydrogen bond to form the new bond. The specially designed P450 mutant, however, adopts a specific shape that favors the bond disconnection at the neighboring carbon, giving the researchers access to a reaction that would be difficult to accomplish by organic catalysis.

    Focusing on the puzzles

    At Princeton, Hyster is applying what he learned from his time in Rovis’ and Arnold’s labs in terms of both the science and mentorship. Their relaxed styles and flexibility in letting students follow their own interests were really effective, he said, and he hopes to emulate them.

    Hyster is hands-off, but always available to answer questions, Sandoval said. The whole group works long hours in the lab and is eager to establish themselves in the research community. Hyster is very driven, Sandoval said, and his confidence and excitement for the work has inspired them to set up reactions that they may not have tried otherwise.

    “If you pursue what you’re most passionate about, I think that’s when you can do your greatest possible amount of good,” Hyster said. Pursuing his own passion is already starting to pay off. Since starting up less than a year ago, the Hyster lab is already preparing to publish research about an enzyme-mediated light-based reaction that hasn’t been seen before.

    Though pleased about these initial successes, for Hyster, the real satisfaction comes from the research process.

    “I just like thinking about these problems. When I wake up, at home, all the time, it’s what I enjoy thinking about and that’s rewarding enough for me,” Hyster said. “It’s just an added bonus that these reactions might be valuable.”

    See the full article here .

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    Princeton University Campus

    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.

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  • richardmitnick 2:55 pm on July 28, 2016 Permalink | Reply
    Tags: Chemistry, , , U illinois Chicago   

    From U Illinois Chicago: “Breakthrough solar cell captures CO2 and sunlight, produces burnable fuel” 

    U Illinois bloc

    University of Illinois

    1

    July 28, 2016
    Bill Burton

    1
    Simulated sunlight powers a solar cell that converts atmospheric carbon dioxide directly into syngas.

    Researchers at the University of Illinois at Chicago have engineered a potentially game-changing solar cell that cheaply and efficiently converts atmospheric carbon dioxide directly into usable hydrocarbon fuel, using only sunlight for energy.

    The finding is reported in the July 29 issue of Science and was funded by the National Science Foundation and the U.S. Department of Energy. A provisional patent application has been filed.

    Unlike conventional solar cells, which convert sunlight into electricity that must be stored in heavy batteries, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel, solving two crucial problems at once. A solar farm of such “artificial leaves” could remove significant amounts of carbon from the atmosphere and produce energy-dense fuel efficiently.

    “The new solar cell is not photovoltaic — it’s photosynthetic,” says Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author on the study.

    “Instead of producing energy in an unsustainable one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight,” he said.

    While plants produce fuel in the form of sugar, the artificial leaf delivers syngas, or synthesis gas, a mixture of hydrogen gas and carbon monoxide. Syngas can be burned directly, or converted into diesel or other hydrocarbon fuels.

    The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete.

    Chemical reactions that convert CO2 into burnable forms of carbon are called reduction reactions, the opposite of oxidation or combustion. Engineers have been exploring different catalysts to drive CO2 reduction, but so far such reactions have been inefficient and rely on expensive precious metals such as silver, Salehi-Khojin said.

    “What we needed was a new family of chemicals with extraordinary properties,” he said.

    2
    Amin Salehi-Khojin (left), UIC assistant professor of mechanical and industrial engineering, and postdoctoral researcher Mohammad Asadi with their breakthrough solar cell that converts atmospheric carbon dioxide directly into syngas.

    Salehi-Khojin and his coworkers focused on a family of nano-structured compounds called transition metal dichalcogenides — or TMDCs — as catalysts, pairing them with an unconventional ionic liquid as the electrolyte inside a two-compartment, three-electrode electrochemical cell.

    The best of several catalysts they studied turned out to be nanoflake tungsten diselenide.

    “The new catalyst is more active; more able to break carbon dioxide’s chemical bonds,” said UIC postdoctoral researcher Mohammad Asadi, first author on the Science paper.

    In fact, he said, the new catalyst is 1,000 times faster than noble-metal catalysts — and about 20 times cheaper.

    Other researchers have used TMDC catalysts to produce hydrogen by other means, but not by reduction of CO2. The catalyst couldn’t survive the reaction.

    “The active sites of the catalyst get poisoned and oxidized,” Salehi-Khojin said. The breakthrough, he said, was to use an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water.

    “The combination of water and the ionic liquid makes a co-catalyst that preserves the catalyst’s active sites under the harsh reduction reaction conditions,” Salehi-Khojin said.

    The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 square centimeters to harvest light; the tungsten diselenide and ionic liquid co-catalyst system on the cathode side; and cobalt oxide in potassium phosphate electrolyte on the anode side.

    When light of 100 watts per square meter – about the average intensity reaching the Earth’s surface – energizes the cell, hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode.

    “The hydrogen ions diffuse through a membrane to the cathode side, to participate in the carbon dioxide reduction reaction,” said Asadi.

    The technology should be adaptable not only to large-scale use, like solar farms, but also to small-scale applications, Salehi-Khojin said. In the future, he said, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide, if the planet is also found to have water.

    “This work has benefitted from the significant history of NSF support for basic research that feeds directly into valuable technologies and engineering achievements,” said NSF program director Robert McCabe.

    “The results nicely meld experimental and computational studies to obtain new insight into the unique electronic properties of transition metal dichalcogenides,” McCabe said. “The research team has combined this mechanistic insight with some clever electrochemical engineering to make significant progress in one of the grand-challenge areas of catalysis as related to energy conversion and the environment.”

    Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid is online at http://www.eurekalert.org/jrnls/sci/ or by contacting scipak@aaas.org.

    Co-authors with Asadi and Salehi-Khojin are Kibum Kim, Aditya Venkata Addepalli, Pedram Abbasi, Poya Yasaei, Amirhossein Behranginia, Bijandra Kumar and Jeremiah Abiade of UIC’s mechanical and industrial engineering department, who performed the electrochemical experiments and prepared the catalyst under NSF contract CBET-1512647; Robert F. Klie and Patrick Phillips of UIC’s physics department, who performed electron microscopy and spectroscopy experiments; Larry A. Curtiss, Cong Liu and Peter Zapol of Argonne National Laboratory, who did Density Functional Theory calculations under DOE contract DE-ACO206CH11357; Richard Haasch of the University of Illinois at Urbana-Champaign, who did ultraviolet photoelectron spectroscopy; and José M. Cerrato of the University of New Mexico, who did elemental analysis.

    See the full article here .

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    U Illinois campus

    The University of Illinois at Urbana-Champaign community of students, scholars, and alumni is changing the world.

    With our land-grant heritage as a foundation, we pioneer innovative research that tackles global problems and expands the human experience. Our transformative learning experiences, in and out of the classroom, are designed to produce alumni who desire to make a significant, societal impact.

     
  • richardmitnick 7:40 am on May 17, 2016 Permalink | Reply
    Tags: , , Chemistry, , Pontifical Catholic University of Chile (PUC)   

    From Notre Dame: “Notre Dame chemistry and biochemistry hosts faculty from Pontifical Catholic University of Chile” 

    Notre Dame bloc

    Notre Dame University

    May 16, 2016
    Brian Wallheimer

    1
    No image caption. No image credit.
    _________________________________________________________

    Seven members of the Pontifical Catholic University of Chile (PUC) visited Notre Dame last week to strengthen developing research partnerships and plan upcoming workshops in biochemistry and chemistry, the latest in a partnership between the universities started in 2013.

    Notre Dame and PUC signed a memorandum of understanding in 2013 that formalized research partnerships, as well as faculty and student exchange programs. Much of the work and collaborations have been possible through the Luksic Grants Program through Notre Dame International.

    “The department has fully embraced the opportunity to work with PUC Chile,” says Ken Henderson, chair of the Department of Chemistry and Biochemistry at Notre Dame. “The latest visit by PUC Chile faculty to Notre Dame demonstrates the enthusiasm for building this relationship.”

    Since the universities formally partnered, they have held joint graduate summer schools in Santiago, Chile, along with the University of Heidelberg, which Notre Dame entered into a similar agreement with in 2014. Last year, the three schools organized the Santander International Summer School on molecular catalysts in Chile, focused on fundamentals and developments in molecular catalysts. Students from Germany, France, Chile, Brazil, Spain, Switzerland and the United States attended.

    Notre Dame has hosted PUC graduate student research visits, and nine Notre Dame faculty have visited Chile over the past two years.

    The universities are working to develop a dual doctoral program over the next few months, and there will be a graduate workshop on X-ray crystallography and a joint symposium on drug discovery in Chile in the next academic year.

    See the full article here .

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    Notre Dame Campus

    The University of Notre Dame du Lac (or simply Notre Dame /ˌnoʊtərˈdeɪm/ NOH-tər-DAYM) is a Catholic research university located near South Bend, Indiana, in the United States. In French, Notre Dame du Lac means “Our Lady of the Lake” and refers to the university’s patron saint, the Virgin Mary.

    The school was founded by Father Edward Sorin, CSC, who was also its first president. Today, many Holy Cross priests continue to work for the university, including as its president. It was established as an all-male institution on November 26, 1842, on land donated by the Bishop of Vincennes. The university first enrolled women undergraduates in 1972. As of 2013 about 48 percent of the student body was female.[6] Notre Dame’s Catholic character is reflected in its explicit commitment to the Catholic faith, numerous ministries funded by the school, and the architecture around campus. The university is consistently ranked one of the top universities in the United States and as a major global university.

    The university today is organized into five colleges and one professional school, and its graduate program has 15 master’s and 26 doctoral degree programs.[7][8] Over 80% of the university’s 8,000 undergraduates live on campus in one of 29 single-sex residence halls, each of which fields teams for more than a dozen intramural sports, and the university counts approximately 120,000 alumni.[9]

    The university is globally recognized for its Notre Dame School of Architecture, a faculty that teaches (pre-modernist) traditional and classical architecture and urban planning (e.g. following the principles of New Urbanism and New Classical Architecture).[10] It also awards the renowned annual Driehaus Architecture Prize.

     
  • richardmitnick 1:18 pm on May 16, 2016 Permalink | Reply
    Tags: , Chemistry, Modeling quantum friction,   

    From Princeton: “Theorists smooth the way to solving one of quantum mechanics oldest problems: Modeling quantum friction (J. Phys. Chem. Letters)” 

    Princeton University
    Princeton University

    May 16, 2016
    Tien Nguyen, Department of Chemistry

    1
    From left to right: Herschel Rabitz, Renan Cabrera, Andre Campos and Denys Bondar. Photo credit: C. Todd Reichart

    Theoretical chemists at Princeton University have pioneered a strategy for modeling quantum friction, or how a particle’s environment drags on it, a vexing problem in quantum mechanics since the birth of the field. The study was published* in the Journal of Physical Chemistry Letters.

    “It was truly a most challenging research project in terms of technical details and the need to draw upon new ideas,” said Denys Bondar, a research scholar in the Rabitz lab and corresponding author on the work.

    Quantum friction may operate at the smallest scale, but its consequences can be observed in everyday life. For example, when fluorescent molecules are excited by light, it’s because of quantum friction that the atoms are returned to rest, releasing photons that we see as fluorescence. Realistically modeling this phenomenon has stumped scientists for almost a century and recently has gained even more attention due to its relevance to quantum computing.

    “The reason why this problem couldn’t be solved is that everyone was looking at it through a certain lens,” Bondar said. Previous models attempted to describe quantum friction by considering the quantum system as interacting with a surrounding, larger system. This larger system presents an impossible amount of calculations, so in order to simplify the equations to the pertinent interactions, scientists introduced numerous approximations.

    These approximations led to numerous different models that could each only satisfy one or the other of two critical requirements. In particular, they could either produce useful observations about the system, or they could obey the Heisenberg Uncertainty Principle, which states that there is a fundamental limit to the precision with which a particle’s position and momentum can be simultaneous measured. Even famed physicist Werner Heisenberg’s attempt to derive an equation for quantum friction was incompatible with his own uncertainty principle.

    The researchers’ approach, called operational dynamic modeling (ODM) and introduced in 2012 by the Rabitz group, led to the first model for quantum friction to satisfy both demands. “To succeed with the problem, we had to literally rethink the physics involved, not merely mathematically but conceptually,” Bondar said.

    Bondar and his colleagues focused on the two ultimate requirements for their model – that it should obey the Heisenberg principle and produce real observations – and worked backwards to create the proper model.

    “Rather than starting with approximations, Denys and the team built in the proper physics in the beginning,” said Herschel Rabitz, the Charles Phelps Smyth ’16 *17 Professor of Chemistry and co-author on the paper. “The model is built on physical and mathematical truisms that must hold. This distinct approach creates a new rigorous and practical formulation for quantum friction,” he said.

    The research team included research scholar Renan Cabrera and Ph.D. student Andre Campos as well as Shaul Mukamel, professor of chemistry at the University of California, Irvine.

    Their model opens a way forward to understand not only quantum friction but other dissipative phenomena as well. The researchers are interested in exploring the means to manipulate these forces to their advantage. Other theorists are rapidly taking up the new paradigm of operational dynamic modeling, Rabitz said.

    Reflecting on how they arrived at such a novel approach, Bondar recalled the unique circumstances under which he first started working on this problem. After he received the offer to work at Princeton, Bondar spent four months awaiting a US work visa (he is a citizen of the Ukraine) and pondering fundamental physics questions. It was during this time that he first thought of this strategy. “The idea was born out of bureaucracy, but it seems to be holding up,” Bondar said.

    Read the full article here:

    Bondar, D. I.; Cabrera, R.; Campos, A.; Mukamel, S.; Rabitz, H. A. Wigner-Lindblad Equations for Quantum Friction.” J. Phys. Chem. Lett. 2016, 7, 1632.

    This work was supported by the US National Science Foundation CHE 1058644, the US Department of Energy DE-FG02-02ER-15344, and ARO-MURI W911NF-11-1-0268.

    *Science paper:
    Wigner–Lindblad Equations for Quantum Friction

    See the full article here .

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    Princeton University Campus

    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.

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  • richardmitnick 8:21 pm on May 11, 2016 Permalink | Reply
    Tags: , , , Chemistry, , Which Elements Will Never Be Made By Our Sun?   

    From Ethan Siegel: “Which Elements Will Never Be Made By Our Sun?” 

    Starts with a Bang

    May 11, 2016
    Ethan Siegel

    1
    A high-resolution spectrum showing the elements in the Sun, by their visible-light absorption properties. Image credit: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.

    Our Sun is the greatest source of heat and light in the entire Solar System, fusing hydrogen into helium in a nuclear chain reaction in its core. Because an atomic nucleus of helium is 0.7% lighter than the four hydrogen nuclei that it’s created from, that act of nuclear fusion releases a tremendously efficient amount of energy. Over the course of its 4.5 billion year lifetime (so far), the Sun had lost about the mass of Saturn due to the amount of hydrogen that’s fused into helium, through Einstein’s E = mc^2, which is the root source of all the sunlight we receive here on Earth. The Sun has a lot more going on inside of it than just fusing hydrogen (the lightest element) into helium (the second lightest), though, and is capable of making so many more elements than that. But the periodic table has a whole slew of elements the Sun can never make.

    Periodic Table 2016
    Periodic Table 2016

    We’re pretty fortunate that our Sun wasn’t among the very first stars in the Universe. Shortly after the Big Bang, the Universe was made exclusively of hydrogen and helium: 99.999999% of the Universe was composed of these two elements alone. Yet the first massive stars didn’t just fuse hydrogen into helium, but eventually fused helium into carbon, carbon into oxygen, oxygen into silicon and sulfur, and then silicon and sulfur into iron, nickel and cobalt. When the inner core reached a large enough concentration of those heavy elements, a catastrophic supernova occurred, creating a rapid burst of neutrons that were scattered into the other nuclei. Very quickly, the types of elements present in the Universe climbed up and up the periodic table, creating everything we’ve ever found in nature and many elements even heavier than that. Even the very first core-collapse supernovae created elements that are beyond the limit of what we find on Earth: elements heavier than even uranium and plutonium.

    3
    The various layers of a supernova-bound star. During the supernova itself, many trans-uranic elements are created, through rapid neutron capture. Image credit: Nicolle Rager Fuller of the NSF.

    But our Sun won’t go supernova, and won’t ever make those elements. That rapid burst of neutrons that happens in supernova allows the creation of elements through the r-process, where elements rapidly absorb neutrons and climb the periodic table in great leaps and jumps. Instead, our Sun will burn through the hydrogen in its core, and then will contract and heat up until it can begin fusing helium in its core. This phase of life — where our Sun will become a red giant star — is something that happens to all stars that are at least 40% as massive as our own.

    4
    Red Giant, SSL UC Berkeley

    Reaching the right temperatures and densities, simultaneously, for helium fusion, is what separates red dwarfs (which can’t get there) from all other stars (which can). Three helium atoms fuse together into carbon, and then through another hydrogen-fusion pathway — the CNO cycle — we can create nitrogen and oxygen, while we can continue to add helium to various nuclei to climb up the periodic table. Carbon and helium make oxygen; carbon and oxygen make neon; carbon and neon make magnesium. But two very particular reactions take place that will create the vast majority of elements we know:

    carbon-13 will fuse with helium-4, creating oxygen-16 and a free neutron, and
    neon-22 will fuse with helium-4, creating magnesium-25 and a free neutron.

    5
    Image credit: screenshot from the wikipedia article on the s-process.

    Free neutrons aren’t created in great abundance, just in relatively scarce numbers, since such a small percentage of these atoms actually are carbon-13 or neon-22 at any given time. But these free neutrons can only stick around for about 15 minutes, on average, until they decay away.

    6
    The two types (radiative and non-radiative) of neutron beta decay. Image credit: Zina Deretsky, National Science Foundation.

    Fortunately, the interior of the Sun is dense enough that 15 minutes is more than enough time for this free neutron to run into another atomic nucleus, and when it does, it inevitably gets absorbed, creating a nucleus that’s one atomic mass unit heavier than before the neutron was absorbed. There are a few nuclei this won’t work for: you can’t create a mass-5 nucleus (out of helium-4, for instance) or a mass-8 nucleus (out of lithium-7, for examples), since they’re all inherently too unstable. But everything else will either be stable on timescales of at least tens of thousands of years, or it will decay by emitting an electron (through β-decay), which causes it to move one element up the periodic table.

    8
    Image credit: E. Siegel, based on the original from the University of Oregon’s physics department, via http://zebu.uoregon.edu/2004/a321/lec10.html.

    During any star’s red giant, helium-burning phase, this enabled you to build all the elements between carbon and iron through this process of slow neutron capture, and heavy elements from iron all the way up through lead through that very same process. This process, known as the s-process (because neutrons are produced-and-captured slowly), runs into a problem when it tries to build elements heavier than lead. The most common isotope of lead is Pb-208, with 82 protons and 126 neutrons. If you add a neutron to it, it beta decays to become bismuth-209, which can then capture a neutron and β-decay again to become polonium-210. But unlike the other isotopes, which live for years, Po-210 only lives for days before emitting an alpha particle — or a helium-4 nucleus — and returning back to lead in the form of Pb-206.

    9
    The chain reaction that’s at the end of the line for the s-process. Image credit: E. Siegel and the English Language Wikipedia.

    This leads to a cycle: lead captures 3 neutrons, becomes bismuth, which captures one more and becomes polonium, which then decays back to lead. In our Sun and in all stars that won’t go supernova, that’s the end of the line. Combine that with the fact that there’s no good pathway to get the elements between helium and carbon (lithium, beryllium and boron are produced from cosmic rays, not inside of stars), and you’ll find that the Sun can make a total of 80 different elements: helium and then everything from carbon through polonium, but nothing heavier. For that, you need a supernova or a neutron star collision.

    9
    Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. Image credit: Dana Berry, SkyWorks Digital, Inc.

    But think about that: of all the naturally occurring elements here on Earth, the Sun makes about 90% of them, all from a tiny, non-descript star of no particular cosmic significance. The ingredients for life are literally that easy to come by.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 6:45 am on April 29, 2016 Permalink | Reply
    Tags: , Chemistry, , Earth Has Mystery Gas Delivered from Space,   

    From SA: “Earth Has Mystery Gas Delivered from Space” 

    Scientific American

    Scientific American

    April 28, 2016
    Anthony King, ChemistryWorld

    1
    Credit: Wikimedia Commons/NASA/JPL-Caltech

    Xenon from deep within the Earth’s mantle has shone a light on the planet’s formation and early evolution. The isotopic signature of this earthly xenon has been shown to resemble that of primitive meteorites and differs markedly from the profile of the gas found in the atmosphere, which is mysteriously missing most of its xenon.

    The origin of Earth’s volatile elements such as water, carbon and nitrogen remains a puzzle. It is difficult to determine if these elements originated from solar gas after the solar system formed or were delivered by asteroids or comets.

    A new study, which sampled xenon from carbon dioxide-rich mineral spring gas from the volcanic Eifel province in Germany, points to an asteroidal origin for part of the volatile elements trapped in Earth’s mantle—planetary bodies whose remnants now lie between Mars and Jupiter. The mysterious xenon in the atmosphere came from elsewhere, possibly comets.

    ‘We conclude that this [mantle] component was contributed by asteroids when the proto-Earth was still building up,’ notes senior author Bernard Marty at the University of Lorraine, France. ‘The ancestor atmosphere xenon was contributed later on at the Earth’s surface, by late bombardments, and never mixed up with mantle xenon.’ This late bombardment occurred around 800 million years after Earth’s formation and might have involved cometary bodies. The isotopic signature of xenon on comets is unknown, however.

    The extraterrestrial chondritic xenon found in the mantle has been isolated for 4.45 billion years. It also proves that volcanism in Eifel relates to upwelling from the deep mantle, likely to be over 700 km deep.

    ‘It’s a small step forward to show that mantle xenon came from meteorites, but the big step forward is showing that this component is not related to the atmosphere,’ says Christopher Ballentine, a geochemist at the University of Oxford, UK, who was not involved with this work.

    Atmospheric xenon’s origin was not just from outgassing of the mantle and is more complex, Ballentine explains. ‘Nobody has measured xenon composition in comets yet, so maybe that is the source,’ he adds. Around 90% of the xenon expected to be in Earth’s atmosphere is missing, with various theories posited. The enigma of the ‘missing xenon’ and where it went is one of the big unsolved puzzles in geochemistry.

    ‘Understanding xenon really is a lynchpin for understanding the early formation of volatiles. And resolving how volatiles arrived at the planet tells us something fundamental about the way in which the planets formed,’ Ballentine says.

    See the full article here .

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    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.

     
  • richardmitnick 3:59 pm on April 13, 2016 Permalink | Reply
    Tags: , Chemistry, ,   

    From Princeton: “Electrons slide through the hourglass on surface of bizarre material (Nature)” 

    Princeton University
    Princeton University

    April 13, 2016
    By Staff

    1
    An illustration of the hourglass fermion predicted to lie on the surface of crystals of potassium mercury antimony. (Image credit: Laura R. Park and Aris Alexandradinata)

    A team of researchers at Princeton University has predicted the existence of a new state of matter in which current flows only through a set of surface channels that resemble an hourglass. These channels are created through the action of a newly theorized particle, dubbed the “hourglass fermion,” which arises due to a special property of the material. The tuning of this property can sequentially create and destroy the hourglass fermions, suggesting a range of potential applications such as efficient transistor switching.

    In an article published in the journal Nature* this week, the researchers theorize the existence of these hourglass fermions in crystals made of potassium and mercury combined with either antimony, arsenic or bismuth. The crystals are insulators in their interiors and on their top and bottom surfaces, but perfect conductors on two of their sides where the fermions create hourglass-shaped channels that enable electrons to flow.

    The research was performed by Princeton University postdoctoral researcher Zhi Jun Wang and former graduate student Aris Alexandradinata, now a postdoctoral researcher at Yale University, working with Robert Cava, Princeton’s Russell Wellman Moore Professor of Chemistry, and Associate Professor of Physics B. Andrei Bernevig.

    The new hourglass fermion exists – theoretically for now, until detected experimentally – in a family of materials broadly called topological insulators, which were first observed experimentally in the mid-2000s and have since become one of the most active and interesting branches of quantum physics research. The bulk, or interior, acts as an insulator, which means it prohibits the travel of electrons, but the surface of the material is conducting, allowing electrons to travel through a set of channels created by particles known as Dirac fermions.

    Fermions are a family of subatomic particles that include electrons, protons and neutrons, but they also appear in nature in many lesser known forms such as the massless Dirac, Majorana and Weyl fermions. After years of searching for these particles in high-energy accelerators and other large-scale experiments, researchers found that they can detect these elusive fermions in table-top laboratory experiments on crystals. Over the past few years, researchers have used these “condensed matter” systems to first predict and then confirm the existence of Majorana and Weyl fermions in a wide array of materials.

    The next frontier in condensed matter physics is the discovery of particles that can exist in the so-called “material universe” inside crystals but not in the universe at large. Such particles come about due to the properties of the materials but cannot exist outside the crystal the way other subatomic particles do. Classifying and discovering all the possible particles that can exist in the material universe is just beginning. The work reported by the Princeton team lays the foundations of one of the most interesting of these systems, according to the researchers.

    In the current study, the researchers theorize that the laws of physics prohibit current from flowing in the crystal’s bulk and top and bottom surfaces, but permit electron flow in completely different ways on the side surfaces through the hourglass-shaped channels. This type of channel, known more precisely as a dispersion, was completely unknown before.

    The researchers then asked whether this dispersion is a generic feature found in certain materials or just a fluke arising from a specific crystal model.

    It turned out to be no fluke.

    A long-standing collaboration with Cava, a material science expert, enabled Bernevig, Wang, and Alexandradinata to uncover more materials exhibiting this remarkable behavior.

    “Our hourglass fermion is curiously movable but unremovable,” said Bernevig. “It is impossible to remove the hourglass channel from the surface of the crystal.”

    Bernevig explained that this robust property arises from the intertwining of spatial symmetries, which are characteristics of the crystal structure, with the modern band theory of crystals. Spatial symmetries in crystals are distinguished by whether a crystal can be rotated or otherwise moved without altering its basic character.

    In a paper published in Physical Review X** this week to coincide with the Nature paper, the team detailed the theory behind how the crystal structure leads to the existence of the hourglass fermion.

    2
    An illustration of the complicated dispersion of the surface fermion arising from a background of mercury and bismuth atoms (blue and red). (Image credit: Mingyee Tsang and Aris Alexandradinata)

    “Our work demonstrates how this basic geometric property gives rise to a new topology in band insulators,” Alexandradinata said. The hourglass is a robust consequence of spatial symmetries that translate the origin by a fraction of the lattice period, he explained. “Surface bands connect one hourglass to the next in an unbreakable zigzag pattern,” he said.

    The team found esoteric connections between their system and high-level mathematics. Origin-translating symmetries, also called non-symmorphic symmetries, are described by a field of mathematics called cohomology, which classifies all the possible crystal symmetries in nature. For example, cohomology gives the answer to how many crystal types exist in three spatial dimensions: 230.

    In the cohomological perspective, there are 230 ways to combine origin-preserving symmetries with real-space translations, known as the “space groups.” The theoretical framework to understand the crystals in the current study requires a cohomological description with momentum-space translations.

    “The hourglass theory is the first of its kind that describes time-reversal-symmetric crystals, and moreover, the crystals in our study are the first topological material class which relies on origin-translating symmetries,” added Wang.

    Out of the 230 space groups in which materials can exist in nature, 157 are non-symmorphic, meaning they can potentially host interesting electronic behavior such as the hourglass fermion.

    “The exploration of the behavior of these interesting fermions, their mathematical description, and the materials where they can be observed, is poised to create an onslaught of activity in quantum, solid state and material physics,” Cava said. “We are just at the beginning.”

    The study was funded by the National Science Foundation, the Office of Naval Research, the David and Lucile Packard Foundation, the W. M. Keck Foundation, and the Eric and Wendy Schmidt Transformative Technology Fund at Princeton University.

    Read the abstract or preprint.

    *Science paper
    Hourglass fermions

    Science team:
    Zhijun Wang, A. Alexandradinata, R. J. Cava & B. Andrei Bernevig

    Affiliations

    Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
    Zhijun Wang, A. Alexandradinata & B. Andrei Bernevig
    Department of Physics, Yale University, New Haven, Connecticut 06520, USA
    A. Alexandradinata
    Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
    R. J. Cava

    Contributions

    A.A., Z.W. and B.A.B. performed theoretical analysis; Z.W. discovered the KHgX material class and performed the first-principles calculations; R.J.C. provided several other material suggestions.

    ** Not made available

    See the full article here .

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    Princeton University Campus

    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.

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  • richardmitnick 11:07 am on March 25, 2016 Permalink | Reply
    Tags: , Chemistry, ,   

    From Rice: “New tool probes deep into minerals and more” 

    Rice U bloc

    Rice University

    March 25, 2016
    David Ruth
    713-348-6327
    david@rice.edu

    Mike Williams
    713-348-6728
    mikewilliams@rice.edu

    1
    Rice University geologist Gelu Costin monitors an experiment at the Electron Probe MicroAnalyzer. (Credit: Jeff Fitlow/Rice University)

    Rice University installs sophisticated microprobe for fine analysis of metals, minerals

    Rice Earth scientists have many ways to see deep into the planet, from drilling to seismic models to simulations, and now they have a way to see deep into what comes from the depths.

    The Department of Earth Science brought a powerful new instrument online earlier this year that lets researchers view the fine structures and composition of inorganic samples. The tool has also been of use to local industries and other academic institutions.

    The field emission Electron Probe MicroAnalyzer combines the abilities of an electron microscope and sophisticated spectrometers. Installed at Keith-Wiess Geological Laboratories, it allows for the precise quantitative chemical analysis of samples for almost all of the elements on the periodic table, from beryllium to uranium. New spectroscopic capabilities will allow for the identification of very light elements like lithium in the near future, but analyses are already underway for nitrogen and carbon in crystals and glasses.

    Installation of the new microprobe, a state-of-the-art JEOL JXA 8530F Hyperprobe, drew geologist Gelu Costin to Rice last year.

    2
    EOL JXA 8530F Hyperprobe

    Costin joined the department as a staff scientist to manage the scope, which he said is the only one of its kind at a university in the southwest United States.

    “This is a new invention, field emission on a microprobe,” Costin said.

    The instrument bombards samples of rock or other inorganic materials with electrons focused into a tight beam by a series of electromagnetic lenses. The beam interacts with the sample to reveal nanoscale compositional patterns as small as hundreds of nanometers, while allowing the spectrometers to quantify the object’s constituent elements.

    The probe is fitted with four spectrometers to analyze elements that respond to different wavelengths and an energy-dispersive X-ray spectrometer, all of which work in a high-vacuum environment to image and provide fine analysis of samples. Soon the instrument will be fitted with a fifth spectrometer that will allow quantification of trace elements as well.

    “There are not many analytical techniques that allow major- and minor-element chemistry determination down to micron and submicron scales,” said geologist Rajdeep Dasgupta, a Rice professor of Earth sciences whose experimental petrology lab simulates pressures deep in the planet to produce samples of what might be found there. “This new generation of electron microprobe gives the type of spatial resolution required to characterize some of the high-pressure experiments.

    “We can now determine many minor elements, all the major elements and even some of the trace elements in solid phases and quenched glasses from high-pressure experiments,” he said.

    Dasgupta said the instrument expands the range of research the university’s Earth scientists can take on. “In my group we perform experiments to figure out the behavior of minerals and rocks at extreme pressures and how they exchange elements between different phases,” he said. In the past, researchers would take samples to microprobes at Texas A&M and NASA’s Johnson Space Center to analyze them.

    “We weren’t able to tackle projects that required us to do an experiment and analyze it in detail before designing the next step,” he said. “It wasn’t practically feasible to go to another institution to get one sample analyzed. Now we’re taking on more challenging projects, and we are pushing the analytical capabilities.”

    The microprobe is open to all Rice researchers as well as clients from industry and other academic institutions, Costin said. “We’ve already had a few users from outside geology,” he said. “People are coming over from chemistry to study the quality of nanometer-thin silver films deposited on graphite. With our machine, they can easily check the consistency of its thickness because we know that if the composition changes on the surface, the thickness changes as well.

    “People from metallurgy companies around Houston have used our facility to check the microtextures and composition of micron-scaled phases in metallurgical slugs,” he said. “And people working in the repair and testing of metallic tools in the Houston area have come to check the composition of fillings inside microcracks produced during welding. We are open to all varieties of microprobe applications, from geology to planetary, chemistry, material science and more.”

    3
    The Electron Probe MicroAnalyzer uses spectrometers to quantify elements in rocks or other inorganic samples. These wavelength dispersive spectrometry quantitative maps show the distribution of elements in metallurgical slag. Clockwise from top left: a backscattered electron image that shows differences in average atomic weight of the phases, and atomic weight maps of aluminum, carbon and oxygen. Courtesy of the EPMA Laboratory. (Credit: EMPA Laboratory/Rice University)

    3
    A magnetite sample magnified 5,500 times shows fine details that are invisible to the naked eye but can be clearly captured by the new Electron Probe MicroAnalyzer at Rice University. (Credit: EMPA Laboratory/Rice University)

    See the full article here .

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    Rice U campus

    In his 1912 inaugural address, Rice University president Edgar Odell Lovett set forth an ambitious vision for a great research university in Houston, Texas; one dedicated to excellence across the range of human endeavor. With this bold beginning in mind, and with Rice’s centennial approaching, it is time to ask again what we aspire to in a dynamic and shrinking world in which education and the production of knowledge will play an even greater role. What shall our vision be for Rice as we prepare for its second century, and how ought we to advance over the next decade?

    This was the fundamental question posed in the Call to Conversation, a document released to the Rice community in summer 2005. The Call to Conversation asked us to reexamine many aspects of our enterprise, from our fundamental mission and aspirations to the manner in which we define and achieve excellence. It identified the pressures of a constantly changing and increasingly competitive landscape; it asked us to assess honestly Rice’s comparative strengths and weaknesses; and it called on us to define strategic priorities for the future, an effort that will be a focus of the next phase of this process.

     
  • richardmitnick 12:53 pm on January 14, 2016 Permalink | Reply
    Tags: , Chemistry,   

    From Princeton: “‘Radiolabeling’ lets scientists track the breakdown of drugs” 

    Princeton University
    Princeton University

    January 14, 2016
    Tien Nguyen, Department of Chemistry

    1
    Renyuan Pony Yu, a graduate student working with Princeton Professor Paul Chirik, has discovered a new way to radiolabel compounds for use in drug development.

    A new method for labeling molecules with radioactive elements could let chemists more easily track how drugs under development are metabolized in the body.

    Chemists consider thousands of compounds in the search for a new drug, and a candidate’s metabolism is a key factor that must be evaluated carefully and quickly. Researchers at Princeton University and pharmaceutical company Merck & Co., Inc. report in the journal Nature that scientists can selectively replace hydrogen atoms in molecules with tritium atoms — a radioactive form of hydrogen that possesses two extra neutrons — to “radiolabel” compounds. This technique can be done in a single step while preserving the biological properties of the parent compound.

    While current state-of-the-art techniques are quite reliable, they only work when dissolved in specific solvents, ones that aren’t always capable of dissolving the drug compound of interest. The researchers’ method, however, used an iron-based catalyst that is tolerant to a wider variety of solvents, and it labels the molecules at the opposite positions as compared to existing methods.

    “The fact that you can access other positions is what makes this reaction really special,” said corresponding author Paul Chirik, the Edwards S. Sanford Professor of Chemistry at Princeton. Previous methods only incorporate radioactive tritium atoms into the molecule directly next to an atom or a group of atoms called a directing group. The new iron-catalyzed method does not require a directing group, and instead places tritium at whatever positions in the molecules are the least crowded.

    “Radiolabeled compounds help medicinal chemists get a better picture of what actually happens to the drug by showing how the drug is metabolized and cleared,” said David Hesk, a collaborator at Merck and co-author on the work. By rapidly assessing the compounds’ metabolism early on, scientists can shorten the time it takes to develop and bring a drug to market. “Having another labeling reaction is very powerful because it gives radiochemists another tool in the toolbox,” he said.

    This unique reactivity was actually discovered unexpectedly. Renyuan Pony Yu, a graduate student in the Chirik lab, had originally set out to use their iron catalyst for a different reaction that they were collaborating on with Merck. To study the iron catalyst’s capabilities, Yu subjected it to a technique called proton nuclear magnetic resonance spectroscopy (NMR), which allows chemists to deduce the positions of hydrogen atoms in molecules.

    “We started seeing this beautiful, very systematic pattern of signals in the NMR, but we didn’t really know what they were,” said Yu, who is first author on the new study. Particularly puzzling was the fact that the pattern of signals would disappear over time.

    The researchers turned to Istvan Pelczer, Director of the NMR Facility at Princeton chemistry and co-author on the work, who developed a special technique that helped them analyze the signals with much greater confidence. Using this method, they realized that the iron catalyst was reacting with the liquid solvent used to dissolve the NMR sample. The solvent’s deuterium atoms, another form of hydrogen that has one extra neutron and is not radioactive, were replacing the hydrogen atoms.

    It wasn’t until Yu presented his findings to Matt Tudge, the Princeton authors’ collaborator at Merck, that the catalyst’s potential to introduce tritium atoms into radiolabeled molecules was recognized. “This is a classic example where you really need both partners,” Chirik said. “We were the catalyst experts, but they were the applications experts.”

    Though tritium-labeled compounds are used mostly in metabolism studies, they can also be helpful at the very outset of a drug-discovery project to identify a biological target that the potential drugs can be tested against. The biological target could be an enzyme or protein associated with a certain disease. For example, statins are a well-known class of cholesterol-lowering drugs that target a specific enzyme in the body called HMG-CoA reductase.

    To explore the scope of the reaction, Yu first optimized the reaction to incorporate deuterium atoms, which is commonly accepted as a model system for tritium. He found that the iron catalyst was surprisingly robust and successfully labeled many different types of compounds, including some from Merck’s library of past drug candidates.

    “It was a very exciting project for me because I got to work with real drugs that are fully functionalized and useful,” Yu said. One of their test substrates was Claritin, which Yu bought from a local store; he extracted its active ingredient back in the lab.

    Finally, Yu traveled to Merck’s campus in Rahway, where he received radioactivity training — Chirik’s laboratory isn’t equipped to handle radioactivity — and performed the reactions using tritium gas. The reactions were run in a special apparatus that looks like a steel-lined box and releases radioactive tritium gas. The apparatus can capture any unspent gas to limit the amount of radioactive waste produced.

    Chemists take care to handle radioactive compounds and waste very carefully, but tritium’s radioactivity is so weak that the particles it emits cannot penetrate simple glassware. For this reason, tritium-labeled compounds can’t be used in any human imaging studies such as PET scans, which require radiolabeled compounds that emit high-energy particles.

    This past summer, Yu presented the preliminary results of the iron-catalyzed reaction at the 2015 International Isotope Society Symposia to researchers in the radiolabeling and pharmaceutical community. They were very excited about the research and eager to use the catalyst in their own studies, Yu said.

    But the major challenge for the researchers is that the iron catalyst is extremely air and moisture sensitive, and it can only be handled inside a glovebox, a special chamber in which oxygen and water vapor have been excluded. The Chirik group is working to develop a more stable catalyst that can be made commercially available, and have recently entered into a partnership with Green Center Canada, a company that helps bring academic research to market.

    In the meantime, the Chirik group has found that the iron catalyst can replace hydrogen atoms with other groups besides deuterium and tritium atoms and is extending this chemistry into many other projects in the lab.

    “This project is always going to be a special one for me because it’s kind of a pivot point for the type of chemistry that our group can do,” Chirik said, “and there’s this really cool application.”

    Read the abstract.

    Yu, R. P.; Hesk, D.; Rivera, N.; Pelczer, I.; Chirik, P. J. Iron-Catalyzed Tritiation of Pharmaceuticals. Nature, 2016, DOI: 10.1038/nature16464.

    This work was supported by Merck & Co. and Princeton University’s Intellectual Property Accelerator Fund.

    See the full article here .

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    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.

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