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Iowa State University

2011

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Articles 1 - 25 of 25

Full-Text Articles in Physical Sciences and Mathematics

Label-Free Electrochemical Monitoring Of Concentration Enrichment During Bipolar Electrode Focusing, Eoin Sheridan, Dzmitry Hlushkou, Robbyn K. Anand, Derek R. Laws, Ulrich Tallrek, Richard M. Crooks Aug 2011

Label-Free Electrochemical Monitoring Of Concentration Enrichment During Bipolar Electrode Focusing, Eoin Sheridan, Dzmitry Hlushkou, Robbyn K. Anand, Derek R. Laws, Ulrich Tallrek, Richard M. Crooks

Robbyn Anand

We show that a label-free electrochemical method can be used to monitor the position of an enriched analyte band during bipolar electrode focusing in a microfluidic device. The method relies on formation of a depleted buffer cation region, which is responsible for concentration enrichment of the charged analyte. However, this depletion region also leads to an increase in the local electric field in the solution near a bipolar electrode (BPE), and this in turn results in enhanced faradaic reactions (oxidation and reduction of water) at the BPE. Therefore, it is possible to detect the presence of the concentrated analyte band …

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Overview Of Corn-Based Fuel Ethanol Coproducts: Production And Use, Kurt A. Rosentrater Aug 2011

Overview Of Corn-Based Fuel Ethanol Coproducts: Production And Use, Kurt A. Rosentrater

Kurt A. Rosentrater

Modern societies face many challenges, including growing populations, increased demands for food, clothing, housing, consumer goods, and the raw materials required to produce all of these. Additionally, there is a growing need for energy, which is most easily met by use of fossil fuels (e.g., coal, natural gas, petroleum). For example, in 2008, the overall U.S. demand for energy was 99.3 x 1015 Btu (1.05 x 1014 MJ); 84% of this was supplied by fossil sources. Transportation fuels accounted for 28% of all energy consumed during this time, and nearly 97% of this came from fossil sources. Domestic production of …

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Net Exchanges Of Co2, Ch4, And N2o Between China's Terrestrial Ecosystems And The Atmosphere And Their Contributions To Global Climate Warming, Hanqin Tian, Xiaofeng Xu, Chaoqun (Crystal) Lu, Mingliang Liu, Wei Ren, Guangsheng Chen, Jerry Melillo, Jiyuan Liu Jun 2011

Net Exchanges Of Co2, Ch4, And N2o Between China's Terrestrial Ecosystems And The Atmosphere And Their Contributions To Global Climate Warming, Hanqin Tian, Xiaofeng Xu, Chaoqun (Crystal) Lu, Mingliang Liu, Wei Ren, Guangsheng Chen, Jerry Melillo, Jiyuan Liu

Chaoqun (Crystal) Lu

China's terrestrial ecosystems have been recognized as an atmospheric CO2 sink; however, it is uncertain whether this sink can alleviate global warming given the fluxes of CH4 and N2O. In this study, we used a process-based ecosystem model driven by multiple environmental factors to examine the net warming potential resulting from net exchanges of CO2, CH4, and N2O between China's terrestrial ecosystems and the atmosphere during 1961–2005. In the past 45 years, China's terrestrial ecosystems were found to sequestrate CO2 at a rate of 179.3 Tg C yr−1 with a 95% confidence range of (62.0 Tg C yr−1, 264.9 Tg …

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Impacts Of Tropospheric Ozone And Climate Change On Net Primary Productivity And Net Carbon Exchange Of China's Forest Ecosystems, Wei Ren, Hanqin Tian, Bo Tao, Arthur Chappelka, Ge Sun, Chaoqun (Crystal) Lu, Mingliang Liu, Guangsheng Chen, Xiaofeng Xu May 2011

Impacts Of Tropospheric Ozone And Climate Change On Net Primary Productivity And Net Carbon Exchange Of China's Forest Ecosystems, Wei Ren, Hanqin Tian, Bo Tao, Arthur Chappelka, Ge Sun, Chaoqun (Crystal) Lu, Mingliang Liu, Guangsheng Chen, Xiaofeng Xu

Chaoqun (Crystal) Lu

We investigated how ozone pollution and climate change/variability have interactively affected net primary productivity (NPP) and net carbon exchange (NCE) across China's forest ecosystem in the past half century. Using the dynamic land ecosystem model (DLEM) in conjunction with 10-km-resolution gridded historical data sets (tropospheric O3 concentrations, climate variability/change, and other environmental factors such as land-cover/land-use change (LCLUC), increasing CO2 and nitrogen deposition), we conducted nine simulation experiments to: (1) investigate the temporo-spatial patterns of NPP and NCE in China's forest ecosystems from 1961–2005; and (2) quantify the effects of tropospheric O3 pollution alone or in combination with climate variability …

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Multizone Paper Platform For 3d Cell Cultures, Ratmir Derda, Sindy K.Y. Tang, Anna Laromaine, Bobak Mosadegh, Estrella Hong, Martin Mwangi, Akiko Mammoto, Donald E. Ingber, George M. Whitesides May 2011

Multizone Paper Platform For 3d Cell Cultures, Ratmir Derda, Sindy K.Y. Tang, Anna Laromaine, Bobak Mosadegh, Estrella Hong, Martin Mwangi, Akiko Mammoto, Donald E. Ingber, George M. Whitesides

Martin M. Thuo

In vitro 3D culture is an important model for tissues in vivo. Cells in different locations of 3D tissues are physiologically different, because they are exposed to different concentrations of oxygen, nutrients, and signaling molecules, and to other environmental factors (temperature, mechanical stress, etc). The majority of high-throughput assays based on 3D cultures, however, can only detect the average behavior of cells in the whole 3D construct. Isolation of cells from specific regions of 3D cultures is possible, but relies on low-throughput techniques such as tissue sectioning and micromanipulation. Based on a procedure reported previously ("cells-in-gels-in-paper" or CiGiP), this paper …

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Developing Criteria For Evaluating The Sustainability Of Emerging Energy, Kurt A. Rosentrater, Elif Kongar Apr 2011

Developing Criteria For Evaluating The Sustainability Of Emerging Energy, Kurt A. Rosentrater, Elif Kongar

Kurt A. Rosentrater

Over the last decade, the interest in and production of biofuels has grown rapidly. Renewable transportation fuels can be produced from a variety of substrates, using various processing strategies. Feedstock preference and factory scale are geographic dependent. However, it is important to understand the implications of deploying these types of systems on a large scale, both throughout the U.S. as well as globally. To assess the sustainability of various biofuel options, it is crucial to evaluate their performance according to a number of attributes. This has been done using Life Cycle Assessment (LCA). Even so, comparisons among biofuel options are …

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Climate And Land Use Controls Over Terrestrial Water Use Efficiency In Monsoon Asia, Hanqin Tian, Chaoqun (Crystal) Lu, Guangsheng Chen, Xiaofeng Xu, Mingliang Liu, Wei Ren, Bo Tao, Ge Sun, Shufen Pan, Jiyuan Liu Mar 2011

Climate And Land Use Controls Over Terrestrial Water Use Efficiency In Monsoon Asia, Hanqin Tian, Chaoqun (Crystal) Lu, Guangsheng Chen, Xiaofeng Xu, Mingliang Liu, Wei Ren, Bo Tao, Ge Sun, Shufen Pan, Jiyuan Liu

Chaoqun (Crystal) Lu

Much concern has been raised regarding how and to what extent climate change and intensive human activities have altered water use efficiency (WUE, amount of carbon uptake per unit of water use) in monsoon Asia. By using a process-based ecosystem model [dynamic land ecosystem model (DLEM)], we examined effects of climate change, land use/cover change, and land management practices (i.e. irrigation and nitrogen fertilization) on WUE in terrestrial ecosystems of monsoon Asia during 1948–2000. Our simulations indicated that due to climate variability/change, WUE in the entire area decreased by 3·6% during the study period, with the largest decrease of 6·8% …

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Pressure-Driven Bipolar Electrochemistry, Ioana Dumitrescu, Robbyn K. Anand, Stephen E. Fosdick, Richard M. Crooks Mar 2011

Pressure-Driven Bipolar Electrochemistry, Ioana Dumitrescu, Robbyn K. Anand, Stephen E. Fosdick, Richard M. Crooks

Robbyn Anand

Here we report that pressure-driven flow alone (no external electrical energy) can be used to drive faradaic electrochemical reactions in microchannels with charged walls. Specifically, we show that solution flow can generate streaming potentials on the order of volts and that this is sufficient to carry out reactions on the anodic and cathodic poles of a bipolar electrode (BPE). The existence of faradaic reactions is proven by electrodissolution of Ag from the anodic end of the BPE.

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Odd-Even Effects In Charge Transport Across Self-Assembled Monolayers, Martin M. Thuo, William F. Reus, Christian A. Nijhuis, Jabulani R. Barber, Choongik Kim, Michael D. Schulz, George M. Whitesides Mar 2011

Odd-Even Effects In Charge Transport Across Self-Assembled Monolayers, Martin M. Thuo, William F. Reus, Christian A. Nijhuis, Jabulani R. Barber, Choongik Kim, Michael D. Schulz, George M. Whitesides

Martin M. Thuo

This paper compares charge transport across self-assembled monolayers (SAMs) of n-alkanethiols containing odd and even numbers of methylenes. Ultraflat template-stripped silver (Ag(TS)) surfaces support the SAMs, while top electrodes of eutectic gallium-indium (EGaIn) contact the SAMs to form metal/SAM//oxide/EGaIn junctions. The EGaIn spontaneously reacts with ambient oxygen to form a thin (∼1 nm) oxide layer. This oxide layer enables EGaIn to maintain a stable, conical shape (convenient for forming microcontacts to SAMs) while retaining the ability to deform and flow upon contacting a hard surface. Conical electrodes of EGaIn conform (at least partially) to SAMs and generate high yields of …

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Bipolar Electrode Focusing: Faradaic Ion Concentration Polarization, Robbyn K. Anand, Eoin Sheridan, Kyle N. Knust, Richard M. Crooks Feb 2011

Bipolar Electrode Focusing: Faradaic Ion Concentration Polarization, Robbyn K. Anand, Eoin Sheridan, Kyle N. Knust, Richard M. Crooks

Robbyn Anand

Bipolar electrode (BPE) focusing locally enriches charged analytes in a microchannel along an electric field gradient that opposes a counter-flow. This electric field gradient forms at the boundary of an ion depletion zone generated by the BPE. Here, we demonstrate concentration enrichment of a fluorescent tracer by up to 500 000-fold. The use of a dual-channel microfluidic configuration, composed of two microchannels electrochemically connected by a BPE, enhances the rate of enrichment (up to 71-fold/s). Faradaic reactions at the ends of the BPE generate ion depletion and enrichment zones in the two, separated channels. This type of device is equivalent …

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Experimental And Molecular Dynamics Investigation Into The Amphiphilic Nature Of Sulforhodamine B, Baris E. Polat, Shangchao Lin, Jonathan D. Mendenhall, Brett Vanveller, Robert Langer, Daniel Blankschtein Jan 2011

Experimental And Molecular Dynamics Investigation Into The Amphiphilic Nature Of Sulforhodamine B, Baris E. Polat, Shangchao Lin, Jonathan D. Mendenhall, Brett Vanveller, Robert Langer, Daniel Blankschtein

Brett VanVeller

Sulforhodamine B (SRB), a common fluorescent dye, is often considered to be a purely hydrophilic molecule, having no impact on bulk or interfacial properties of aqueous solutions. This assumption is due to the high water solubility of SRB relative to most fluorescent probes. However, in the present study, we demonstrate that SRB is in fact an amphiphile, with the ability to adsorb at an air/water interface and to incorporate into sodium dodecyl sulfate (SDS) micelles. In fact, SRB reduces the surface tension of water by up to 23 mN/m, and the addition of SRB to an aqueous SDS solution induces …

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Kernel Regression In The Presence Of Correlated Errors, Kris De Brabanter, Jos De Brabanter, Johan A.K. Suykens, Bart De Moor Jan 2011

Kernel Regression In The Presence Of Correlated Errors, Kris De Brabanter, Jos De Brabanter, Johan A.K. Suykens, Bart De Moor

Kris De Brabanter

It is a well-known problem that obtaining a correct bandwidth and/or smoothing parameter in nonparametric regression is difficult in the presence of correlated errors. There exist a wide variety of methods coping with this problem, but they all critically depend on a tuning procedure which requires accurate information about the correlation structure. We propose a bandwidth selection procedure based on bimodal kernels which successfully removes the correlation without requiring any prior knowledge about its structure and its parameters. Further, we show that the form of the kernel is very important when errors are correlated which is in contrast to the …

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Understanding Student Pathways In Context-Rich Problems, Pavlo Antonenko, John Jackman, Piyamart Kumsaikaew, Rahul Marathe, Dale Niederhauser, Craig Ogilvie, Sarah Ryan Jan 2011

Understanding Student Pathways In Context-Rich Problems, Pavlo Antonenko, John Jackman, Piyamart Kumsaikaew, Rahul Marathe, Dale Niederhauser, Craig Ogilvie, Sarah Ryan

Sarah M. Ryan

In this paper we investigate the ways that students' problem-solving behaviors evolve when solving multi-faceted, context-rich problems within a structured, computer-based learning environment. During the semester, groups of two or three students worked on several problems that required drawing on more than one concept and, hence, could not be readily solved with simple "plug-and-chug" strategies. The problems were presented to students in a data-rich, online problem-solving environment that tracked which information items were selected by students as they attempted to solve the problem. The students also completed a variety of tasks, like entering an initial qualitative analysis into an online …

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Enantioselective Total Syntheses Of (−)-Taiwaniaquinone H And (−)-Taiwaniaquinol B By Iridium-Catalyzed Borylation And Palladium-Catalyzed Asymmetric Α-Arylation, Xuebin Liao, Levi M. Stanley, John F. Hartwig Jan 2011

Enantioselective Total Syntheses Of (−)-Taiwaniaquinone H And (−)-Taiwaniaquinol B By Iridium-Catalyzed Borylation And Palladium-Catalyzed Asymmetric Α-Arylation, Xuebin Liao, Levi M. Stanley, John F. Hartwig

Levi M. Stanley

We report a concise, enantioselective total synthesis of (−)-taiwaniaquinone H and the first enantioselective total synthesis of (−)-taiwaniaquinol B by a route that includes asymmetric palladium-catalyzed α-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C−H borylation. This asymmetric α-arylation creates the benzylic quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic …

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Time-Resolved Resonance Raman And Computational Investigation Of The Influence Of 4-Acetamido And 4-N-Methylacetamido Substituents On The Chemistry Of Phenylnitrene, Jiaden Xue, Shubham Vyas, Yong Du, Hoi-Ling Luk, Yung-Ping Chuang, Tracy Yuen Sze But, Patrick H. Toy, Jin Wang, Arthur Winter, David Lee Phillips, Christopher M. Hadad, Matthew S. Platz Jan 2011

Time-Resolved Resonance Raman And Computational Investigation Of The Influence Of 4-Acetamido And 4-N-Methylacetamido Substituents On The Chemistry Of Phenylnitrene, Jiaden Xue, Shubham Vyas, Yong Du, Hoi-Ling Luk, Yung-Ping Chuang, Tracy Yuen Sze But, Patrick H. Toy, Jin Wang, Arthur Winter, David Lee Phillips, Christopher M. Hadad, Matthew S. Platz

Arthur Winter

A time-resolved resonance Raman (TR3) and computational investigation of the photochemistry of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide in acetonitrile is presented. Photolysis of 4-acetamidophenyl azide appears to initially produce singlet 4-acetamidophenylnitrene which undergoes fast intersystem crossing (ISC) to form triplet 4-acetamidophenylnitrene. The latter species formally produces 4,4′-bisacetamidoazobenzene. RI-CC2/TZVP and TD-B3LYP/TZVP calculations predict the formation of the singlet nitrene from the photogenerated S1 surface of the azide excited state. The triplet 4-acetamidophenylnitrene and 4,4′-bisacetamidoazobenzene species are both clearly observed on the nanosecond to microsecond time-scale in TR3 experiments. In contrast, only one species can be observed in analogous TR3 experiments after …

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Automated Sequence- And Stereo-Specific Assignment Of Methyl-Labeled Proteins By Paramagnetic Relaxation And Methyl–Methyl Nuclear Overhauser Enhancement Spectroscopy, Vincenzo Venditti, Nicolas L. Fawzi, G. Marius Clore Jan 2011

Automated Sequence- And Stereo-Specific Assignment Of Methyl-Labeled Proteins By Paramagnetic Relaxation And Methyl–Methyl Nuclear Overhauser Enhancement Spectroscopy, Vincenzo Venditti, Nicolas L. Fawzi, G. Marius Clore

Vincenzo Venditti

Methyl-transverse relaxation optimized spectroscopy is rapidly becoming the preferred NMR technique for probing structure and dynamics of very large proteins up to ~1 MDa in molecular size. Data interpretation, however, necessitates assignment of methyl groups which still presents a very challenging and time-consuming process. Here we demonstrate that, in combination with a known 3D structure, paramagnetic relaxation enhancement (PRE), induced by nitroxide spin-labels incorporated at only a few surface-exposed engineered cysteines, provides fast, straightforward and robust access to methyl group resonance assignments, including stereoassignments for the methyl groups of leucine and valine. Neither prior assignments, including backbone assignments, for the …

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Rh1−Xpdxnanoparticle Composition Dependence In Co Oxidation By Oxygen: Catalytic Activity Enhancement In Bimetallic Systems, James Russell Renzas, Wenyu Huang, Yawen Zhang, Michael E. Grass, Dat Tien Hoang, Selim Alayoglu, Derek R. Butcher, Franklin Tao, Zhi Liu, Gabor A. Somorjai Jan 2011

Rh1−Xpdxnanoparticle Composition Dependence In Co Oxidation By Oxygen: Catalytic Activity Enhancement In Bimetallic Systems, James Russell Renzas, Wenyu Huang, Yawen Zhang, Michael E. Grass, Dat Tien Hoang, Selim Alayoglu, Derek R. Butcher, Franklin Tao, Zhi Liu, Gabor A. Somorjai

Wenyu Huang

Bimetallic 15 nm Rh1−xPdxnanoparticle catalysts of five different compositions and supported on Si wafers have been synthesized, characterized using TEM, SEM, and XPS, and studied in CO oxidation by O2 in two pressure regimes: atmospheric pressure and 100–200 mTorr. The RhPd bimetallic nanocrystals exhibited similar synergetic effect of increased reaction activity at both atmospheric (760 Torr) and moderate (100–200 mTorr) pressures compared with pure Pd or Rh. The magnitude of the effect depends on the relative pressures of the CO and O2 reactant gases and the reaction temperature. The catalytic activity of the nanocrystals measured at moderate pressure is directly …

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2-(3,5-Dinitrophenyl)-1,3-Dithiane Carbanion: A Benzylic Anion With A Low Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, William H. Coldren, Daniel E. Falvey Jan 2011

2-(3,5-Dinitrophenyl)-1,3-Dithiane Carbanion: A Benzylic Anion With A Low Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, William H. Coldren, Daniel E. Falvey

Arthur Winter

Calculations at the DFT level predict that benzyl anions with strong π-electron-withdrawing groups in the meta position(s) have low energy diradical or triplet electronic states. Specifically, the 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion is predicted to have nearly degenerate singlet and triplet states at the (U)B3LYP level as a free anion. Its lithium ion pair is predicted to be a ground-state triplet with a substantial (26 kcal/mol) singlet–triplet energy gap. Experiments on this anion using chemical trapping, NMR, and the Evans method strongly suggest that this anion is either a triplet or a ground-state singlet with a very low energy triplet state.

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A Structurally Driven Analysis Of Thiol Reactivity In Mammalian Albumins, Ottavia Spiga, Domenico Summa, Simone Cirri, Andrea Bernini, Vincenzo Venditti, Matteo De Chiara, Raffaella Priora, Simona Frosail, Antonios Margaritis, Danila Di Giuseppe, Paolo Di Simplicio, Neri Niccolai Jan 2011

A Structurally Driven Analysis Of Thiol Reactivity In Mammalian Albumins, Ottavia Spiga, Domenico Summa, Simone Cirri, Andrea Bernini, Vincenzo Venditti, Matteo De Chiara, Raffaella Priora, Simona Frosail, Antonios Margaritis, Danila Di Giuseppe, Paolo Di Simplicio, Neri Niccolai

Vincenzo Venditti

Understanding the structural basis of protein redox activity is still an open question. Hence, by using a structural genomics approach, different albumins have been chosen to correlate protein structural features with the corresponding reaction rates of thiol exchange between albumin and disulfide DTNB. Predicted structures of rat, porcine, and bovine albumins have been compared with the experimentally derived human albumin. High structural similarity among these four albumins can be observed, in spite of their markedly different reactivity with DTNB. Sequence alignments offered preliminary hints on the contributions of sequence-specific local environments modulating albumin reactivity. Molecular dynamics simulations performed on experimental …

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Dead Zones In Porous Catalysts: Concentration Profiles And Efficiency Factors, Roger L. York, Kaitlin M. Bratlie, Lloyd R. Hile, Larry K. Jang Jan 2011

Dead Zones In Porous Catalysts: Concentration Profiles And Efficiency Factors, Roger L. York, Kaitlin M. Bratlie, Lloyd R. Hile, Larry K. Jang

Kaitlin M. Bratlie

This paper examines the conditions under which a dead zone, or a portion of the catalyst devoid of reactant, can form in a porous catalyst in which simultaneous reaction and diffusion are occurring. The condition that allows for the existence of a dead zone is defined by a critical Thiele modulus. When the Thiele modulus - the ratio of chemical reaction to diffusion - is greater than the critical Thiele modulus, a dead zone exists. This dead zone can be mathematically defined by a change of boundary conditions. We examine nth order reactions in isothermal infinite slabs, infinite cylinders, and …

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A Pt-Cluster-Based Heterogeneous Catalyst For Homogeneous Catalytic Reactions: X-Ray Absorption Spectroscopy And Reaction Kinetic Studies Of Their Activity And Stability Against Leaching, Yimin Li, Jack Hung Chang Liu, Cole A. Witham, Wenyu Huang, Matthew A. Marcus, Sirine C. Fakra, Pinar Alayoglu, Zhongwei Zhu, Christopher M. Thompson, Arpana Arjun, Kihong Lee, Elad Gross, F. Dean Toste, Gabor A. Somorjai Jan 2011

A Pt-Cluster-Based Heterogeneous Catalyst For Homogeneous Catalytic Reactions: X-Ray Absorption Spectroscopy And Reaction Kinetic Studies Of Their Activity And Stability Against Leaching, Yimin Li, Jack Hung Chang Liu, Cole A. Witham, Wenyu Huang, Matthew A. Marcus, Sirine C. Fakra, Pinar Alayoglu, Zhongwei Zhu, Christopher M. Thompson, Arpana Arjun, Kihong Lee, Elad Gross, F. Dean Toste, Gabor A. Somorjai

Wenyu Huang

The design and development of metal-cluster-based heterogeneous catalysts with high activity, selectivity, and stability under solution-phase reaction conditions will enable their applications as recyclable catalysts in large-scale fine chemicals production. To achieve these required catalytic properties, a heterogeneous catalyst must contain specific catalytically active species in high concentration, and the active species must be stabilized on a solid catalyst support under solution-phase reaction conditions. These requirements pose a great challenge for catalysis research to design metal-cluster-based catalysts for solution-phase catalytic processes. Here, we focus on a silica-supported, polymer-encapsulated Pt catalyst for an electrophilic hydroalkoxylation reaction in toluene, which exhibits superior …

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Spectroscopic Study Of Platinum And Rhodium Dendrimer (Pamam G4oh) Compounds: Structure And Stability, Yuri Borodko, Christopher M. Thompson, Wenyu Huang, Huseyin B. Yildiz, Heinz Frei, Gabor A. Somorjai Jan 2011

Spectroscopic Study Of Platinum And Rhodium Dendrimer (Pamam G4oh) Compounds: Structure And Stability, Yuri Borodko, Christopher M. Thompson, Wenyu Huang, Huseyin B. Yildiz, Heinz Frei, Gabor A. Somorjai

Wenyu Huang

Hydroxyl-terminated, poly(amidoamine) (PAMAM) dendrimer-capped platinum and rhodium nanoparticles were studied with UV−vis, Fourier transform IR, and UV-Raman spectroscopy. The adsorption bands in the region of 190−900 nm were shown to be sensitive to the electronic structure of Pt compounds in solution and in the solid state. The electron charge-transfer Pt2+ ← N band at 260 nm was attributed to mononuclear Pt2+ compounds, and resonance Raman (244 nm) established that the electron donors are amide nitrogen atoms. Multidentate coordination bonding with Pt2+ causes a strong stabilizing chelate effect, and this entropic factor hinders reduction of Pt2+ by BH4−. UV diffuse-reflectance spectra …

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Rh1−X Pd X Nanoparticle Composition Dependence In Co Oxidation By No, James Russell Renzas, Wenyu Huang, Yawen Zhang, Michael E. Grass, Gabor A. Somorjai Jan 2011

Rh1−X Pd X Nanoparticle Composition Dependence In Co Oxidation By No, James Russell Renzas, Wenyu Huang, Yawen Zhang, Michael E. Grass, Gabor A. Somorjai

Wenyu Huang

Bimetallic 15 nm Pd-core Rh-shell Rh1−x Pd x nanoparticle catalysts have been synthesized and studied in CO oxidation by NO. The catalysts exhibited composition-dependent activity enhancement (synergy) in CO oxidation in high NO pressures. The observed synergetic effect is attributed to the favorable adsorption of CO on Pd in NO-rich conditions. The Pd-rich bimetallic catalysts deactivated after many hours of oxidation of CO by NO. After catalyst deactivation, product formation was proportional to the Rh molar fraction within the bimetallic nanoparticles. The deactivated catalysts were regenerated by heating the sample in UHV. This regeneration suggests that the deactivation was caused …

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Photochemical Heterolysis Of 3,5-Bis(Dimethylamino)Benzyl Alcohols And Esters: Generation Of A Benzyl Cation With A Low-Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, Daniel E. Falvey Jan 2011

Photochemical Heterolysis Of 3,5-Bis(Dimethylamino)Benzyl Alcohols And Esters: Generation Of A Benzyl Cation With A Low-Energy Triplet State, Raffaele R. Perrotta, Arthur Winter, Daniel E. Falvey

Arthur Winter

An earlier computational study (CASPT2/pVDZ) by Winter et al. predicts the 3,5-bis(dimethylamino)benzyl cation to have nearly degenerate singlet and triplet states. Through product studies it is demonstrated that photolysis of 3,5-bis(dimethylamino)benzyl alcohol and its corresponding acetate and phenylacetate esters in alcoholic solvents produces a solvent incorporated adduct, 3,5-bis(dimethylamino)benzyl ethers, and 3,5-bis(dimethylamino)toluene.

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Measured And Predicted Temporal Changes In Soil Nitrate-N Levels From Late Summer To Early Spring In Montana, Andrew W. Lenssen, Clain Jones, Chengci Chen, Kent Mcvay, Bob Stougaard, Mal Westcott, Joyce Eckhoff, Jennifer Weeding, Mark Greenwood Jan 2011

Measured And Predicted Temporal Changes In Soil Nitrate-N Levels From Late Summer To Early Spring In Montana, Andrew W. Lenssen, Clain Jones, Chengci Chen, Kent Mcvay, Bob Stougaard, Mal Westcott, Joyce Eckhoff, Jennifer Weeding, Mark Greenwood

Andrew W. Lenssen

Most soil sampling is conducted from August to November in Montana because of better soil sampling conditions and because it provides more time for growers to make fertilizer decisions prior to application. Fertilizer guidelines in Montana are based on spring nitrate-N levels in the upper 2 ft because they are more indicative of growing season available N than fall nitrate-N levels. It is not known how much nitrate-N levels change between late summer and spring, nor is it known what factors affect these changes, and large changes could result in either over-application of N fertilizer or sub-optimal yields. A three-year …

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