In an article in the Proceedings of the National Academy of Science (doi: 10.1073/pnas.1611467114), David Waldeck and colleagues in Israel propose a mechanism for the enantioselectivity (chiral specificity) of non-covalent interactions between chiral molecules. Their study examines how the non-covalent interactions between molecules give rise to enantioselective interaction energies. Non-covalent interactions do not involve the formation of a bond; rather they include electrostatic interactions between permanent or induced dipoles as the electron clouds of the molecules rearrange and the purely quantum exchange interaction as the wavefunctions of the molecules overlap. Their two part study shows experimentally that charge redistribution in chiral molecules is accompanied by spin polarization and it shows theoretically that the exchange interactions for homochiral (both molecules have the same handedness) interactions differ from heterochiral ones.
In a letter published in the February 2017 issue of Nature Nanotechnology, Ben Hunt and his collaborators at the Massachusetts Institute of Technology, the University of California Santa Barbara, and the National Institute for Materials Science in Tsukuba, Japan describe how they engineered a graphene electron–hole bilayer device into a helical 1-dimensional (1D) conductor and characterized its transport properties. In a helical 1D conductor, electrons moving in opposite directions also have opposite spin polarizations, and such helical states can be obtained by combining two quantum Hall (QH) edge states with opposite spins and opposite momenta relative to the magnetic field (i.e. opposite chiralities).
“My colleagues at MIT came up with this ingenious way of producing helical edge states from two decoupled graphene layers, and then they proved their idea worked with a series of powerful transport experiments,” says Hunt. “I was thrilled to be able to make a contribution to the experiment by using capacitance measurements to help prove that the unique helical states they observe really are edge states.”
Matter-Light Condensates Reach Thermal Equilibrium
Making use of improved microcavities, hybrid condensates of matter and light can be tuned to reach a thermal equilibrium state, despite their finite lifetime.
In a laser, coherent light is created by stimulated emission of photons from an “inverted” state of matter that is significantly out of thermal equilibrium. “Inverted” means that excited states of the matter are more occupied than lower energy states, so that emission is more likely than absorption. The coherence of laser light is closely related to a quite different, and less commonly encountered, state of matter—a Bose-Einstein condensate (BEC). In the textbook description of a BEC, at low enough temperatures or high enough densities, a large number of particles occupy the same state, producing a coherent state of matter. In contrast to laser light, the textbook BEC is in thermal equilibrium. Condensates of polaritons—half-light, half-matter quasiparticles—have so far been found in conditions halfway between those of an equilibrium BEC and those of a laser. Work by David Snoke and colleagues now shows that such polariton condensates can be tuned to reach a thermal equilibrium state. With this tunability between an equilibrium and nonequilibrium state, researchers can explore how the character of phase transitions evolves between the two limits.
Research focused on developing a new catalyst that would lead to large-scale implementation of capture and conversion of carbon dioxide (CO2) was recently published in the Royal Society of Chemistry journal Catalysis Science & Technology. Principal investigator is Karl Johnson, and postdoctoral associate Jingyun Ye is lead author. The article “Catalytic Hydrogenation of CO2 to Methanol in a Lewis Pair Functionalized MOF” is featured on the cover of Catalysis Science & Technology vol. 6, no. 24 and builds upon Johnson’s previous research that identified the two main factors for determining the optimal catalyst for turning atmospheric CO2 into liquid fuel. The research was conducted using computational resources at the University’s Center for Simulation and Modeling.
Scientists Capture Snapshots of the Proton Conduction Process in Water
The motion of protons (positively charged H atoms) in water is associated with water’s conduction of electricity and is involved in many important processes including vision, signaling in biological systems, photosynthesis and, the operation of fuel cells. Both artificial photosynthetic systems and fuel cells are of growing interest for clean energy technologies. However, the details of how protons move in water have remained elusive, and an enhanced understanding of the nature of this process is needed to improve the technologies that depend on proton transfer.
An international team of scientists, including a University of Pittsburgh professor and graduate student, has used spectroscopic methods to obtain snapshots of the process by which a proton is relayed from one water molecule to the next. The research is published in a paper in the December 2, 2016 issue of the journal Science.
Although synthetic chemists typically regard carbon-carbon single bonds as inert, they have used metal catalysts to spring open C–C bonds in strained rings, such as cyclopropanes and cyclobutanes. Performing a similar transformation with less strained but more common five- and six-membered rings, however, has proven more difficult.
Now, synthetic and theoretical chemists report a way of opening up C–C bonds in aryl substituted cyclopentanones to produce α-tetralones. The reaction was developed by University of Chicago’s Guangbin Dong and Ying Xia, and at Pitt, Peng Liu and his post doc Gang Lu studied the mechanism from a quantum chemical point of view with DFT (Density Functional Theory) calculations.
The results are published in the online issue of Nature.
A natural citrus fruit extract has been found to dissolve calcium oxalate crystals, the most common component of human kidney stones, in a finding that could lead to significantly improving kidney stone treatment, according to researchers at the University of Pittsburgh, the University of Houston, and Litholink Corporation, among which is Giannis Mpourmpakis.
In a study published Aug. 8 in the journal Nature, the researchers offer the first evidence that the compound hydroxycitrate (HCA) effectively inhibits calcium oxalate crystal growth and, under certain conditions, is able to dissolve the crystals. HCA shows “promise as a potential therapy to prevent kidney stones,” the researchers wrote.
When it comes to computers, people never look for “bigger and better,” but rather “smaller and faster.” How do we continue to keep up with that demand, making technology smaller, faster, and more energy-efficient? According to Vincent Sokalski, the answer may be in the fundamental origins of magnets—the spin of electrons.
Sokalski and his group studied the interaction of electron spins in magnetic materials poised for use in next-generation cellphones and computers and discovered how to better measure and predict the changing magnetic state of those materials. This new understanding, recently published in Physical Review B under the title "Energetic Molding of Chiral Magnetic Bubbles", is exciting for the future of computing technology because it will allow scientists to explore and develop materials that are more energy-efficient and faster than traditional semiconductor-based materials.
Recently a team of researchers from MIT, the NIST Center for Neutron Research (NCNR), Carnegie Mellon University, and the Beijing Institute of Technology have experimentally demonstrated a "hybrid material" solution to this problem. They studied a compound of three elements, gadolinium, platinum and bismuth, known together as a ternary compound. In their compound, gadolinium supplies the magnetic order while the platinum-bismuth components support a topological electronic structure. These two components acting in concert make a correlated material that is more than the sum of its parts, showing quantum mechanical corrections to electrical properties at an unprecedented scale. Their results were reported July 18 in Nature Physics.
The theoretical aspect of the collaborative effort was with professors Di Xiao of Carnegie Mellon University and Wanxiang Feng of Beijing Institute of Technology, who provided first principles electronic structure calculations based on the experimental data taken at MIT, NCNR, and the NHMFL to determine the underlying electronic character of this new materials system.
PQI faculty Karl Johnson and his team recently identified the two main factors for determining the optimal catalyst for turning atmospheric CO2 into liquid fuel. The results of the study, which appeared in the journal ACS Catalysis, will streamline the search for an inexpensive yet highly effective new catalyst.
Imagine a power plant that takes the excess carbon dioxide (CO2) put in the atmosphere by burning fossil fuels and converts it back into fuel. Now imagine that power plant uses only a little water and the energy in sunlight to operate. The power plant wouldn't burn fossil fuels and would actually reduce the amount of CO2 in the atmosphere during the manufacturing process. For millions of years, actual plants have been using water, sunlight, and CO2 to create sugars that allow them to grow. Scientists around the globe are now adopting their energy-producing behavior.