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Articles 691 - 720 of 962

Full-Text Articles in Chemistry

Stability Of Warfarin Solutions For Drug–Protein Binding Measurements: Spectroscopic And Chromatographic Studies, Annette C. Moser, Charles A. Kingsbury, David S. Hage Jan 2006

Stability Of Warfarin Solutions For Drug–Protein Binding Measurements: Spectroscopic And Chromatographic Studies, Annette C. Moser, Charles A. Kingsbury, David S. Hage

Department of Chemistry: Faculty Publications

Warfarin is commonly used in drug–protein binding studies as a displacement marker for Sudlow site I on the protein human serum albumin (HSA). This study examined the stability of aqueous warfarin solutions prepared for such experiments. This was investigated using NMR spectroscopy and affinity chromatography. It was found by 1H NMR that warfarin underwent a slow first-order conversion in aqueous solution. The rate of this reaction increased with temperature, giving rate constants at pH 7.4 of 0.0086 h−1 at 25 °C and 0.041 h−1 at 37 °C. It was concluded from further 1H and 13C NMR studies, along …

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A Minimum-Impact Method For Measuring Corrosion Rate Of Steel-Hulled Shipwrecks In Seawater, Matthew A. Russell, David L. Conlin, Larry E. Murphy, Donald L. Johnson, Brent M. Wilson, James D. Carr Jan 2006

A Minimum-Impact Method For Measuring Corrosion Rate Of Steel-Hulled Shipwrecks In Seawater, Matthew A. Russell, David L. Conlin, Larry E. Murphy, Donald L. Johnson, Brent M. Wilson, James D. Carr

Department of Chemistry: Faculty Publications

Current research on USS Arizona is focused on a minimum-impact technique for calculating corrosion rate of the battleship’s steel hull by analysing physical and chemical properties of marine encrustation covering the exposed hull. An equation is derived that allows concretion thickness, density, and total iron content to be used to calculate corrosion rate of steel hull plate.

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Cu2O(1 1 0) Formation On Co3O4(1 1 0) Induced By Copper Impurity Segregation, S. C. Petitto, Marjorie Langell Dec 2005

Cu2O(1 1 0) Formation On Co3O4(1 1 0) Induced By Copper Impurity Segregation, S. C. Petitto, Marjorie Langell

Marjorie A. Langell Publications

The surface crystal structure of the Co3O4(1 1 0) spinel was characterized by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Well-defined LEED diffraction patterns showed an unreconstructed Co3O4(1 1 0) surface in Type A termination, and XPS and Auger indicated the surface to be stoichiometric with octahedral and tetrahedral cation sites occupied by 3+ and 2+ cations, respectively. The experimental lattice parameters of 8.22 Å ± 0.2 Å and 5.50 Å ± 0.2 Å in the (0 0 1) and (1¯ 1 0) directions, respectively, …

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M4@Si28 (M=Al,Ga) Metal-Encapsulated Tetrahedral Silicon Fullerene, Yi Gao, Xiao Cheng Zeng Dec 2005

M4@Si28 (M=Al,Ga) Metal-Encapsulated Tetrahedral Silicon Fullerene, Yi Gao, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

It is known that silicon fullerenes cannot maintain perfect cage structures like carbon fullerenes. Previous density-functional theory calculations have shown that even with encapsulated species, nearly all endohedral silicon fullerenes exhibit highly puckered cage structures in comparison with their carbon counterparts. In this work, we present theoretical evidences that the tetrahedral fullerene cage Si28 can be fully stabilized by encapsulating a tetrahedral metallic cluster (Al4 or Ga4). To our knowledge, this is the first predicted endohedral silicon fullerene that can retain perfectly the same cage structure (without puckering) as the carbon fullerene counterpart (Td …

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Large-Scale Molecular-Dynamics Simulation Of Nanoscale Hydrophobic Interaction And Nanobubble Formation, Takahiro Koishi, Kenji Yasuoka, Toshikazu Ebisuzaki, S. Yoo, Xiao Cheng Zeng Nov 2005

Large-Scale Molecular-Dynamics Simulation Of Nanoscale Hydrophobic Interaction And Nanobubble Formation, Takahiro Koishi, Kenji Yasuoka, Toshikazu Ebisuzaki, S. Yoo, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

We performed large-scale molecular-dynamics simulation of nanoscale hydrophobic interaction manifested by the formation of nanobubble between nanometer-sized hydrophobic clusters at constrained equilibrium. Particular attention is placed on the tendency of formation and stability of nanobubbles in between model nanoassemblies which are composed of hydrophobic clusters (or patches) embedded in a hydrophilic substrate. On the basis of physical behavior of nanobubble formation, we observed a change from short-range molecular hydrophobic interaction to midrange nanoscopic interaction when the length scale of hydrophobe approaches to about 1 nm. We investigated the behavior of nanobubble formation with several different patterns of nonpolar-site distribution on …

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Roadmap For High Efficiency Solid-State Neutron Detectors, R. J. Nikolic, Chin Li Cheung, C. E. Reinhardt, T. F. Wang Oct 2005

Roadmap For High Efficiency Solid-State Neutron Detectors, R. J. Nikolic, Chin Li Cheung, C. E. Reinhardt, T. F. Wang

Barry Chin Li Cheung Publications

Solid-state thermal neutron detectors are generally fabricated in a planar configuration by coating a layer of neutron-to-alpha converter material onto a semiconductor. The as-created alpha particles in the material are expected to impinge the semiconductor and create electron-hole pairs which provide the electrical signal. These devices are limited in efficiency to a range near (2-5%)/cm2 due to the conflicting thickness requirements of the converter layer. In this case, the layer is required to be thick enough to capture the incoming neutron flux while at the same time adequately thin to allow the alpha particles to reach the semiconductor. A …

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Structures And Stability Of Medium-Sized Silicon Clusters. Iii. Reexamination Of Motif Transition In Growth Pattern From Si15 To Si20, Soohaeng Yoo, Xiao Cheng Zeng Oct 2005

Structures And Stability Of Medium-Sized Silicon Clusters. Iii. Reexamination Of Motif Transition In Growth Pattern From Si15 To Si20, Soohaeng Yoo, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

It has been established from experiments that stable medium-sized ionic clusters Si15–Si20 are prolate in shape. Density-functional theories (DFTs) also predict that nearly all low-lying neutral clusters in this size range are prolate in shape. Moreover, most of them are built onto two generic structural motifs, either the tricapped-trigonal-prism (TTP) Si9 motif or the six/six Si6/Si6 (sixfold-puckered hexagonal ring Si6 plus six-atom tetragonal bipyramid Si6) motif. However, it appears that the exact location of the TTP-to-six/six motif transition is dependent on the functional (e.g., PBE or BLYP) used in the …

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Coarse-Grained Free-Energy-Functional Treatment Of Quasistatic Multiscale Processes In Heterogeneous Materials, H. Zhou, Ruqiang Feng, Dennis J. Diestler, Xiao Cheng Zeng Oct 2005

Coarse-Grained Free-Energy-Functional Treatment Of Quasistatic Multiscale Processes In Heterogeneous Materials, H. Zhou, Ruqiang Feng, Dennis J. Diestler, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

A new treatment of quasistatic (reversible) multiscale processes in heterogeneous materials at nonzero temperature is presented. The system is coarse grained by means of a finite-element mesh. The coarse-grained free-energy functional (of the positions of the nodes of the mesh) appropriate to the thermodynamic-state variables controlled in the relevant process is minimized. Tests of the new procedure on a Lennard-Jonesium crystal yield thermomechanical properties in good agreement with the “exact” atomistic results.

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The Cytolethal Distending Toxin B Sub-Unit Of Helicobacter Hepaticus Is A Ca2+- And Mg2+-Dependent Neutral Nuclease, Rohana P. Dassanayake, Mark A. Griep, Gerald Duhamel Oct 2005

The Cytolethal Distending Toxin B Sub-Unit Of Helicobacter Hepaticus Is A Ca2+- And Mg2+-Dependent Neutral Nuclease, Rohana P. Dassanayake, Mark A. Griep, Gerald Duhamel

Mark A. Griep Publications

The cytolethal distending toxin B (CdtB) of the mouse pathogen Helicobacter hepaticus has cation binding and DNA catalysis residues in common with members of the mammalian deoxyribonuclease I (DNase I) family. The purpose of the present study was to characterize CdtB nuclease. To establish optimal digestion conditions and to evaluate co-factor requirements, a novel and sensitive fl uorometric assay that quantitatively determines double stranded DNA digestion was developed. Although the Ca2+- and Mg2+-dependence and neutral properties of CdtB were similar to DNase I, hydrolysis of DNA by CdtB was approximately 100-fold less active than DNase I …

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Digital Commons Presentation For Chemistry Department Faculty, Paul Royster Sep 2005

Digital Commons Presentation For Chemistry Department Faculty, Paul Royster

Department of Chemistry: Department Information

Why you should put your publications and other work online; how the Digital Commons can help you do that; copyright status of your publications; policies of publishers; policy of American Chemical Society.

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Chemistry Weekly, Volume 1 Issue 23, September 5 - 9, 2005 Sep 2005

Chemistry Weekly, Volume 1 Issue 23, September 5 - 9, 2005

Department of Chemistry: Department Information

COLLOQUIUM, Professor Bruce S. Hudson: “Vibrations of Molecules in Solids: Periodic DFT and Inelastic Neutron Scattering”
NEW CHEMISTRY DEPARTMENT STAFF; UNL EMPLOYEE SERVICE AWARDS; Hamilton Hall - Renovation News;
EHS COLLOQUIUM SERIES FOR RESEARCH PIs presents “Personal Protective Equipment (Laboratory),” Dr. Jim Zeigler, DuPont Personal Protection;
SEMINAR Sponsored By: Center for Materials Research & Analysis / NSF-MRSEC Title: Q & A on Synthesis of Nanoparticles and Nanotubes Speaker: Professor Stephen O'Brien, Dept. of Materials Science & Engineering, Columbia University;
Nebraska MRSEC 3rd Annual Review & Symposium—SEPT. 20-21

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Monomethyl Histone H3 Lysine 4 As An Epigenetic Mark For Silenced Euchromatin In Chlamydomonas, Karin V. Van Dijk, Katherine E. Marley, Byeong-Ryool Jeong, Jianping Xu, Jennifer Hesson, Ronald Cerny, Jakob H. Waterborg, Heriberto D. Cerutti Sep 2005

Monomethyl Histone H3 Lysine 4 As An Epigenetic Mark For Silenced Euchromatin In Chlamydomonas, Karin V. Van Dijk, Katherine E. Marley, Byeong-Ryool Jeong, Jianping Xu, Jennifer Hesson, Ronald Cerny, Jakob H. Waterborg, Heriberto D. Cerutti

Ronald Cerny Publications

Histone Lys methylation plays an important role in determining chromatin states and is mostly catalyzed by SET domain– containing proteins. The outcome, transcriptional repression or activation, depends on the methylated histone residue, the degree of methylation, and the chromatin context. Dimethylation or trimethylation of histone H3 Lys 4 (H3K4me2 or H3K4me3) has been correlated with transcriptionally competent/active genes. However, H3K4 methylation has also been implicated in gene silencing. This dualistic nature of the H3K4 methyl mark has thus far remained unresolved. In the green alga Chlamydomonas reinhardtii, Mut11p, related to a subunit of trithorax-like methyltransferase complexes, is required for transcriptional …

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Chlorella Virus-Encoded Deoxyuridine Triphosphatases Exhibit Different Temperature Optima, Yuanzheng Zhang, Hideaki Moriyama, Kohei Homma, James L. Van Etten Aug 2005

Chlorella Virus-Encoded Deoxyuridine Triphosphatases Exhibit Different Temperature Optima, Yuanzheng Zhang, Hideaki Moriyama, Kohei Homma, James L. Van Etten

Hideaki Moriyama Publications

A putative deoxyuridine triphosphatase (dUTPase) gene from chlorella virus PBCV-1 was cloned, and the recombinant protein was expressed in Escherichia coli. The recombinant protein has dUTPase activity and requires Mg2+ for optimal activity, while it retains some activity in the presence of other divalent cations. Kinetic studies of the enzyme revealed a Km of 11.7 μ M, a turnover kcat of 6.8 s-1, and a catalytic efficiency of kcat/Km = 5.8 x 105 M-1 s-1. dUTPase genes were cloned and expressed from two other chlorella viruses …

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Melting Temperature Of Ice IH Calculated From Coexisting Solid-Liquid Phases, J. Wang, S. Yoo, Jaeil Bai, James R. Morris, Xiao Cheng Zeng Jul 2005

Melting Temperature Of Ice IH Calculated From Coexisting Solid-Liquid Phases, J. Wang, S. Yoo, Jaeil Bai, James R. Morris, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

The purpose of this paper is twofold: (1) to compute the melting temperature (Tm) of ice Ih with both TIP4P and TIP5P models by using the two-phase coexistence method and to compare with previously obtained Tm; (2) to compute the Tm using recently improved TIP4P and TIP5P models, namely, the TIP4P-Ew (Ref. 6) and TIP5P-Ew (Ref. 7) models. Both models are developed specifically for use with Ewald techniques. The TIP4P-Ew model, in particular, has shown substantial improvement over the original TIP4P model as it can reproduce the density maximum at about 274 K, …

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Deconvolution Of The Co3O4(110) Fuchs–Kliewer Phonon Spectrum, E.M. Marsh, S.C. Petitto, G.S. Harbison, K.W. Wulser, Marjorie Langell Jul 2005

Deconvolution Of The Co3O4(110) Fuchs–Kliewer Phonon Spectrum, E.M. Marsh, S.C. Petitto, G.S. Harbison, K.W. Wulser, Marjorie Langell

Marjorie A. Langell Publications

The Fuchs–Kliewer phonon spectrum of single crystal Co3O4(110) has been treated with a Fourier transform log deconvolution method, which removes multiple scattering features from the single loss spectrum. Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) were first used to characterize the Co3O4 crystal establishing the cleanliness, composition, and order of the (110) surface. High resolution electron energy loss spectroscopy (HREELS) was then used to obtain the phonon spectrum for an incident electron energy of 3.77 eV. Due to the strong dipole cross section for the Fuchs–Kliewer phonon …

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Biologically Active Fluorescent Farnesol Analogs, Roman Shchepin, Razvan Dumitru, Kenneth W. Nickerson, Miranda Lund, Patrick Dussault Jun 2005

Biologically Active Fluorescent Farnesol Analogs, Roman Shchepin, Razvan Dumitru, Kenneth W. Nickerson, Miranda Lund, Patrick Dussault

Patrick Dussault Publications

We describe ten polyene analogs of farnesol, typified by 3,7,11-trimethyl-2,4,6,8,10-dodecapentenaldehyde oxime, which preserve the length, cross-section, and approximate hydrophobicity of farnesol. Four of the ten display strong quorum- sensing activity in the human pathogen Candida albicans, with IC50 values for inhibition of germ-tube formation as low as 10 μM. The polyenes display absorption maxima between 320 and 380 nm, with the extinction coefficients for the oximes approaching 100,000. All but two of the analogs are fluorescent, with excitation maxima varying over the range of 320–370 nm. Oxime anti-4, which can undergo fluorescence excitation at wavelengths beyond 400 …

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Ab Initio Calculation Of Bowl, Cage, And Ring Isomers Of C20 And C20-, Wei An, Yi Gao, Satya S. Bulusu, Xiao Cheng Zeng May 2005

Ab Initio Calculation Of Bowl, Cage, And Ring Isomers Of C20 And C20-, Wei An, Yi Gao, Satya S. Bulusu, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

High-level ab initio calculations have been carried out to reexamine relative stability of bowl, cage, and ring isomers of C20 and C20-. The total electronic energies of the three isomers show different energy orderings, strongly depending on the hybrid functionals selected. It is found that among three popular hybrid density-functional (DF) methods B3LYP, B3PW91, PBE1PBE, and a new hybrid-meta-DF method TPSSKCIS, only the PBE1PBE method (with cc-pVTZ basis set) gives qualitatively correct energy ordering as that predicted from ab initio CCSD(T)/cc-pVDZ [CCSD(T)—coupled-cluster method including singles, doubles, and noniterative perturbative triples; cc-pVDZ—correlation consistent polarized valence double zeta] …

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Using Databases And Computational Techniques To Infer The Function Of Novel Proteins, Viswanathan Ramanathan, Kelly A. Mercier, Robert Powers, Peter Revesz May 2005

Using Databases And Computational Techniques To Infer The Function Of Novel Proteins, Viswanathan Ramanathan, Kelly A. Mercier, Robert Powers, Peter Revesz

Department of Chemistry: Faculty Publications

The Human Genome Project and similar efforts have resulted in the identification of an abundance of novel proteins. There is a need to expedite the process of assigning function to novel proteins. Nuclear magnetic resonance (NMR) spectroscopy can be used to infer a general biological function for a protein of unknown function by identifying compounds that preferentially bind the protein and comparing these results against proteins with defined structure and function. The Functional NMR screen generates hundreds of data sets and a manual analysis of these data sets is laborious and time- consuming. It is hypothesized that several sub-tasks of …

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Cooperative Effects In Two-Dimensional Ring-Like Networks Of Three-Center Hydrogen Bonding Interactions, Ruben D. Parra, Satya S. Bulusu, Xiao Cheng Zeng May 2005

Cooperative Effects In Two-Dimensional Ring-Like Networks Of Three-Center Hydrogen Bonding Interactions, Ruben D. Parra, Satya S. Bulusu, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Cooperative effects in two-dimensional cyclic networks containing intermolecular three-centered hydrogen bonding interactions of the type H1&#;A&#;H2 are investigated by means of ab intio molecular orbital and density functional theory calculations. Ring-like clusters consisting of three and up to nine monomers of the cis–cis isomer of carbonic acid H2CO3 are used as basic models, where each unit acts simultaneously as a double hydrogen-bond donor and double hydrogen-bond acceptor. Cooperative effects based on binding energies are evident for (H2CO3)n, where n goes from 2 to 9. Thus, the ZPVE-corrected dissociation …

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Stereoselective Allylation Of Chiral Monoperoxyacetals, Aqeel Ahmed, Patrick Dussault May 2005

Stereoselective Allylation Of Chiral Monoperoxyacetals, Aqeel Ahmed, Patrick Dussault

Patrick Dussault Publications

Neighboring iodo-, alkoxy-, acetoxy- and silyl groups impart useful levels of diastereoselection in the Lewis acid-mediated allylation of monoperoxyacetals. Although monoperoxyacetals are found to be considerably less reactive than corresponding nonperoxidic acetals, similar stereochemical trends are observed in the two series.

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Orientation Of Single Crystals Using Linear Approximations To Nmr Transits, Young-Sik Kye, Xingang Zhao, Gerard S. Harbison May 2005

Orientation Of Single Crystals Using Linear Approximations To Nmr Transits, Young-Sik Kye, Xingang Zhao, Gerard S. Harbison

Gerard S. Harbison Publications

We have derived analytical expressions for determining the orientation of high-symmetry single crystals from line-crossings in a single rotation plot. We demonstrate the utility of the method using the strontium-87 resonance in strontium nitrate. Employing our new method, which we call orientation of single crystals using linear approximations to NMR transits (OSCULANT), in combination with fourth-order perturbation theory, we obtain a highly accurate value for the quadrupole coupling constant, and an estimate for the chemical shielding anisotropy.

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Search For Global Minimum Geometries For Medium Sized Germanium Clusters: Ge12–Ge20, Satya S. Bulusu, S. Yoo, Xiao Cheng Zeng Apr 2005

Search For Global Minimum Geometries For Medium Sized Germanium Clusters: Ge12–Ge20, Satya S. Bulusu, S. Yoo, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

We have performed an unbiased search for the global minimum geometries of small-to-medium sized germanium clusters Gen (12≤n≤18) as well as a biased search (using seeding method) for Gen (17≤n≤20). We employed the basin-hopping algorithm coupled with the plane-wave pseudopotential density functional calculations. For each size, we started the unbiased search with using several structurally very different initial clusters, or we started the biased search with three different seeds. Irrespective of the initial structures of clusters we found that the obtained lowest-energy clusters of the size n=12–16 and 18 are the same. Among …

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The Elastic Constants And Related Properties Of Β-Hmx Determined By Brillouin Scattering, Lewis L. Stevens, Craig J. Eckhardt Apr 2005

The Elastic Constants And Related Properties Of Β-Hmx Determined By Brillouin Scattering, Lewis L. Stevens, Craig J. Eckhardt

Craig J. Eckhardt Publications

By scattering from a variety of acoustic phonons, a complete stiffness tensor has been determined for crystalline β-HMX. The results are compared with recent experimental and theoretical determinations of the elastic constants and bulk modulus. Reasons for disagreement are discussed in terms of experimental limitations and anharmonic effects. The observed ordering of stiffness constants, C11 (18.4 GPa), C22 (14.4 GPa), and C33 (12.4 GPa), is qualitatively associated with physical phenomena including cleavage planes, patterns in crystal growth, and molecular packing. This interpretation is further corroborated by the linear compressibilities plotted in three crystallographic planes. The Voigt–Reuss–Hill bulk …

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Determining The Optimal Size Of Small Molecule Mixtures For High Throughput Nmr Screening, Kelly A. Mercier, Robert Powers Mar 2005

Determining The Optimal Size Of Small Molecule Mixtures For High Throughput Nmr Screening, Kelly A. Mercier, Robert Powers

Robert Powers Publications

High-throughput screening (HTS) using NMR spectroscopy has become a common component of the drug discovery effort and is widely used throughout the pharmaceutical industry. NMR provides additional information about the nature of small molecule-protein interactions compared to traditional HTS methods. In order to achieve comparable efficiency, small molecules are often screened as mixtures in NMR-based assays. Nevertheless, an analysis of the efficiency of mixtures and a corresponding determination of the optimum mixture size (OMS) that minimizes the amount of material and instrumentation time required for an NMR screen has been lacking. A model for calculating OMS based on the application …

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Developing A Genetic System For Functional Manipulations Of Fum1, A Polyketide Synthase Gene For The Biosynthesis Of Fumonisins In Fusarium Verticillioides, Fengan Yu, Xiangcheng Zhu, Liangcheng Du Feb 2005

Developing A Genetic System For Functional Manipulations Of Fum1, A Polyketide Synthase Gene For The Biosynthesis Of Fumonisins In Fusarium Verticillioides, Fengan Yu, Xiangcheng Zhu, Liangcheng Du

Liangcheng Du Publications

Fumonisins are mycotoxins produced by Fusarium verticillioides, a filamentous fungus that is a widespread pathogen of corn. The biosynthesis of fumonisins is catalyzed by an iterative modular polyketide synthase (PKS). The study of the biosynthetic mechanism for these reduced fungal polyketides has been challenging due to the difficulties in detecting the intermediates with a linear carbon chain and manipulating the 7-domain PKS gene from the filamentous fungus. Here, we described the development of a genetic system for functionally manipulating the methyltransferase domain of FUM1 that is responsible for the assembly of a dimethylated 18-carbon chain. Using a two-stage screening strategy, …

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Atomic Force Microscopy Investigation Of Virus Aggregation And Assembly At Chemical Templates Formed By Scanned Probe Nanolithography, Chin Li Cheung, S. -W. Chung, J. J. De Yoreo, A. Chatterji, T. Lin, J. E. Johnson Feb 2005

Atomic Force Microscopy Investigation Of Virus Aggregation And Assembly At Chemical Templates Formed By Scanned Probe Nanolithography, Chin Li Cheung, S. -W. Chung, J. J. De Yoreo, A. Chatterji, T. Lin, J. E. Johnson

Barry Chin Li Cheung Publications

Aggregation and assembly of macromolecules are important processes in a number of scientific fields including structural biology, medicine, and materials science. For example, growth of well-ordered two-dimensional (2-D) arrays and bulk crystals remains the rate-limiting step in macromolecular structure determination. Uncontrolled aggregation of proteins is the source of a number of devastating pathologies such as Creutzfeldt-Jakob syndrome. Moreover, the demonstrated ability of engineered viruses and proteins to act as templates for growth of inorganic nanostructures is driving a need for methods to deterministically pattern their assembly at surfaces in order to fabricate hierarchical materials and devices.

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Planar-To-Tubular Structural Transition In Boron Clusters: B20 As The Embryo Of Single-Walled Boron Nanotubes, Boggavarapu Kiran, Satya S. Bulusu, Hua-Jin Zhai, Soohaeng Yoo, Xiao Cheng Zeng, Lai-Sheng Wang Jan 2005

Planar-To-Tubular Structural Transition In Boron Clusters: B20 As The Embryo Of Single-Walled Boron Nanotubes, Boggavarapu Kiran, Satya S. Bulusu, Hua-Jin Zhai, Soohaeng Yoo, Xiao Cheng Zeng, Lai-Sheng Wang

Xiao Cheng Zeng Publications

Experimental and computational simulations revealed that boron clusters, which favor planar (2D) structures up to 18 atoms, prefer 3D structures beginning at 20 atoms. Using global optimization methods, we found that the B20 neutral cluster has a double-ring tubular structure with a diameter of 5.2 Å. For the B20- anion, the tubular structure is shown to be isoenergetic to 2D structures, which were observed and confirmed by photoelectron spectroscopy. The 2D-to-3D structural transition observed at B20, reminiscent of the ring-to-fullerene transition at C20 in carbon clusters, suggests it may be considered as the embryo …

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Regional Scale Evidence For Improvements In Surface Water Chemistry 1990-2001, B. L. Skjelkvåle, J. L. Stoddard, D. S. Jeffries, K. Tørseth, T. Høgåsen, J. Bowman, J. Mannio, D. T. Monteith, R. Mosello, M. Rogora, D. Rzychon, J. Vesely, J. Wieting, A. Wilander, A. Worsztynowicz Jan 2005

Regional Scale Evidence For Improvements In Surface Water Chemistry 1990-2001, B. L. Skjelkvåle, J. L. Stoddard, D. S. Jeffries, K. Tørseth, T. Høgåsen, J. Bowman, J. Mannio, D. T. Monteith, R. Mosello, M. Rogora, D. Rzychon, J. Vesely, J. Wieting, A. Wilander, A. Worsztynowicz

United States Environmental Protection Agency: Publications

The main aim of the international UNECE monitoring program ICP Waters under the Convention of Long-range Transboundary Air Pollution (CLRTAP) is to assess, on a regional basis, the degree and geographical extent of the impact of atmospheric pollution, in particular acidification, on surface waters. Regional trends are calculated for 12 geographical regions in Europe and North America, comprising 189 surface waters sites. From 1990-2001 sulphate concentrations decreased in all but one of the investigated regions. Nitrate increased in only one region, and decreased in three North American regions. Improvements in alkalinity and pH are widely observed. Results from the ICP …

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The Composition Of Coexisting Jarosite-Group Minerals And Water From The Richmond Mine, Iron Mountain, California, Heather E. Jamieson, Clare Robinson, Charles N. Alpers, D. Kirk Nordstrom, Alexei Poustovetov, Heather A. Lowers Jan 2005

The Composition Of Coexisting Jarosite-Group Minerals And Water From The Richmond Mine, Iron Mountain, California, Heather E. Jamieson, Clare Robinson, Charles N. Alpers, D. Kirk Nordstrom, Alexei Poustovetov, Heather A. Lowers

United States Geological Survey: Staff Publications

Jarosite-group minerals accumulate in the form of stalactites and fine-grained mud on massive pyrite in the D drift of the Richmond mine, Iron Mountain, California. Water samples were collected by placing beakers under the dripping stalactites and by extracting pore water from the mud using a centrifuge. The water is rich in Fe3+ and SO42–, with a pH of approximately 2.1, which is significantly higher than the extremely acidic waters found elsewhere in the mine. Electron-microprobe analysis and X-ray mapping indicate that the small crystals (<10 > μm in diameter) are compositionally zoned with respect to Na …

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In Situ Screening To Optimize Variables In Organic Reactions, David Berkowitz, Mohua Bose, Sungjo Choi Jan 2005

In Situ Screening To Optimize Variables In Organic Reactions, David Berkowitz, Mohua Bose, Sungjo Choi

Department of Chemistry: Faculty Publications

A biphasic process for rapid screening of organic reactions comprising monitoring relative rates of parallel organic reactions. The screening process is suitable to determine the efficacy of different reactants, process conditions, and process enhancers such as catalysts or promoters. The biphasic process also allows multiple samples to be analyzed/monitored simultaneously. In addition because enzymes are used to monitor the reaction product in this invention, when that product is chiral and an enantio-discriminating enzyme is used to monitor the product, in addition to the relative rates, enantioselectivities of a set of parallel organic reactions can also be determined. The monitoring is …

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