Parai R.,Harvard University |
Mukhopadhyay S.,Harvard University |
Standish J.J.,American Chemical Society
Earth and Planetary Science Letters | Year: 2012
Variations in heavy noble gas (Ne, Ar, Xe) isotopic compositions provide unique insights into the nature of heterogeneities in the mantle. However, few precise constraints on mantle source heavy noble gas isotopic compositions are available due to ubiquitous shallow-level atmospheric contamination. As a result, the extent of heterogeneity in mid-ocean ridge basalt (MORB) mantle source Ne, Ar and Xe isotopic compositions is unknown. Basalts from the ultra-slow spreading Southwest Indian Ridge (SWIR) between 7°E and 25°E exhibit remarkable variability in He isotopic composition: SWIR 4He/3He spans half the total range observed in all mantle-derived basalts. Therefore, basalts from the SWIR provide a unique window into upper mantle heterogeneity and present an ideal opportunity to characterize variations in upper mantle heavy noble gas isotopic composition. Here we present new high-precision Ne, Ar and Xe isotopic compositions as well as He, CO2, Ne, Ar and Xe abundances measured in basalt glasses from the SWIR. After correcting the measured values for shallow-level atmospheric contamination, significant and systematic variations in mantle source Ne, Ar and Xe compositions are observed. We note that large variations in source 40Ar/36Ar and 129Xe/130Xe are observed in basalts removed from the influence of known hotspots, indicating a heterogeneous mid-ocean ridge basalt source. Thus, SWIR heavy noble gas data reveal a greater degree of source heterogeneity than is evident in the 4He/3He systematics alone. The observed heavy noble gas isotopic heterogeneities imply that the average MORB source 40Ar/36Ar and 129Xe/130Xe ratios are not yet well-determined.Variation in MORB source 40Ar/36Ar and 129Xe/130Xe at a given 4He/3He and 21Ne/22Ne may reflect heterogeneous recycling of atmospheric Ar and Xe. In particular, we find low mantle source 40Ar/36Ar and 129Xe/130Xe ratios in the eastern region of the study area, which may reflect the noble gas signature of the Dupal mantle domain. Our observations require that the sampled mantle domain either is very ancient (>4.45Ga) or has been metasomatized by subduction zone fluids carrying recycled atmospheric Ar and Xe. However, our Xe isotopic measurements indicate that differences between MORB and ocean island basalt (OIB) source noble gas compositions cannot be explained by recycling of atmospheric noble gases alone. Instead, a relatively undegassed mantle reservoir is required to account for OIB noble gases. The SWIR data demonstrate that the reservoir supplying primordial noble gases to mantle plumes differentiated from the MORB source early in Earth history, and the two reservoirs have not been homogenized over 4.45Ga of mantle convection. © 2012 Elsevier B.V. Source
Weinberg D.R.,University of North Carolina at Chapel Hill |
Weinberg D.R.,Colorado Mesa University |
Gagliardi C.J.,University of North Carolina at Chapel Hill |
Hull J.F.,University of North Carolina at Chapel Hill |
And 7 more authors.
Chemical Reviews | Year: 2012
Proton-coupled electron transfer (PCET) has a major role in chemistry and biology and its implications for catalysis and energy conversion. Photosynthesis is a spectacular example of PCET in action with the transfer of 24 e- and 24 H+ driven by at least 48 photons. In PCET half reactions, variations in pH influence driving force. Both HAT (H-atom transfer) and EPT (electron-proton transfer) are elementary steps by which PCET reactions can occur. In H-atom transfer (HAT), both the transferring electron and proton come from the same bond in one of the reactants. Multiple Site Electron-Proton Transfer (MS-EPT) is microscopically more complex than electron or proton transfer. It shares with electron transfer requirements for medium and intramolecular reorganization but with the additional complexity of a coupled proton transfer. PCET plays a critical role in many enzymatic pathways that control life such as photosynthesis, respiration, and DNA repair. Source
American Chemical Society | Date: 2013-09-06
Systems and methods are provided for evaluating composition of a first file representing a document to be evaluated. An evaluation method transforms the first file to a second file. The second file includes a plurality of objects corresponding to the composition of the first file. The evaluation method also determines parameters based on the plurality of objects; evaluates the parameters based on a plurality of composition rules provided by a rule engine; generates evaluation findings and stores the evaluation findings; and generates an evaluation conclusion based on the evaluation findings. The evaluation conclusion indicates compliance of the document according to the composition rules.
« easyJet to trial electric taxi system in aircraft; H2 fuel cells, batteries and wheel motors | Main | OSU-led team demonstrates effective vibration energy harvesting platform inspired by trees » Researchers at Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, have developed a highly efficient homogeneous Ru-based catalyst system for the production of methanol (CH OH) from CO and H in an ethereal solvent (initial turnover frequency = 70 h−1 at 145 °C). In a paper published in the Journal of the American Chemical Society, they reported demonstrating for the first time that CO captured from air can be directly converted to CH OH in 79% yield using the new homogeneous catalytic system. They demonstrated ease of separation of CH OH by simple distillation from the reaction mixture. They recycled the catalyst over five runs without significant loss of activity (turnover number > 2000). Various sources of CO can be used for this reaction including air, despite its low CO concentration (400 ppm). Implementing the method in a flow system could deliver continuous production of CH OH, the researchers said. The work, led by G.K. Surya Prakash and George Olah of the USC Dornsife College of Letters, Arts and Sciences, is part of a broader effort to stabilize the amount of carbon dioxide in the atmosphere by using renewable energy to transform the greenhouse gas into its combustible cousin. Methanol is a clean-burning fuel for internal combustion engines, a fuel for fuel cells and a raw material used to produce many petrochemical products. The researchers bubbled air through an aqueous solution of pentaethylenehexamine (or PEHA), adding a catalyst to encourage hydrogen to latch onto the CO under pressure. They then heated the solution, converting 79% of the CO into methanol. Though mixed with water, the resulting methanol can be easily distilled, Prakash said. Prakash and Olah hope to refine the process to the point that it could be scaled up for industrial use, though that may be 5 to 10 years away. Of course it won’t compete with oil today, at around $30 per barrel. But right now we burn fossilized sunshine. We will run out of oil and gas, but the sun will be there for another five billion years. So we need to be better at taking advantage of it as a resource. Despite its outsized impact on the environment, the actual concentration of CO in the atmosphere is relatively small—400 parts per million is 0.04% of the total volume. (For a comparison, there’s more than 23 times as much the noble gas Argon in the atmosphere—which still makes up less than 1% of the total volume.) Previous efforts have required a slower multistage process with the use of high temperatures and high concentrations of CO , meaning that renewable energy sources would not be able to efficiently power the process, as Olah and Prakash hope. The new system operates at around 125 to 165 degrees Celsius (257 to 359 degrees Fahrenheit), minimizing the decomposition of the catalyst—which occurs at 155 degrees Celsius (311 degrees Fahrenheit). It also uses a homogeneous catalyst, making it a quicker “one-pot” process. Olah and Prakash collaborated with graduate student Jotheeswari Kothandaraman and senior research associates Alain Goeppert and Miklos Czaun of USC Dornsife. The research was supported by the USC Loker Hydrocarbon Research Institute.
News Article | August 25, 2016
Every day, millions of Americans with diabetes have to inject themselves with insulin to manage their blood-sugar levels. But less painful alternatives are emerging. Scientists are developing a new way of administering the medicine orally with tiny vesicles that can deliver insulin where it needs to go without a shot. They shared their in vivo testing results at the 252nd National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting through Thursday. It features more than 9,000 presentations on a wide range of science topics. “We have developed a new technology called a CholestosomeTM,” says Mary McCourt, Ph.D., a leader of the research team. “A CholestosomeTM is a neutral, lipid-based particle that is capable of doing some very interesting things.” The biggest obstacle to delivering insulin orally is ushering it through the stomach intact. Proteins such as insulin are no match for the harsh, highly acidic environment of the stomach. They degrade before they get a chance to move into the intestines and then the bloodstream where they’re needed. Some efforts have been made to overcome or sidestep this barrier. One approach packages insulin inside a protective polymer coating to shield the protein from stomach acids and is being tested in clinical trials. Another company developed and marketed inhalable insulin, but despite rave reviews from some patients, sales were a flop. Now its future is uncertain. McCourt, Lawrence Mielnicki, Ph.D., and undergraduate student Jamie Catalano — all from Niagara University — have a new tactic. Using the patented CholestosomesTM developed in the McCourt/Mielnicki lab, the researchers have successfully encapsulated insulin. The novel vesicles are made of naturally occurring lipid molecules, which are normal building blocks of fats. But the researchers say that they are unlike other lipid-based drug carriers, called liposomes. “Most liposomes need to be packaged in a polymer coating for protection,” says Mielnicki. “Here, we’re just using simple lipid esters to make vesicles with the drug molecules inside.” Computer modeling showed that once the lipids are assembled into spheres, they form neutral particles resistant to attack from stomach acids. Drugs can be loaded inside, and the tiny packages can pass through the stomach without degrading. When CholestosomesTM reach the intestines, the body recognizes them as something to be absorbed. The vesicles pass through the intestines, into the bloodstream, and then cells take them in and break them apart, releasing insulin. The team has delivered multiple molecules with these vesicles into cells in the lab. To pack the most insulin into the CholestosomesTM, the researchers determined the optimal pH and ionic strength of the drug-containing solution. They then moved the most promising candidates on to animal testing. Studies with rats showed that certain formulations of CholestosomesTM loaded with insulin have high bioavailability, which means the vesicles travel into the bloodstream where the insulin needs to be. Next, the team plans to further optimize the formulations, conduct more animal testing and develop new partnerships to move forward into human trials.