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Articles 30541 - 30570 of 34556

Full-Text Articles in Physical Sciences and Mathematics

Highly Enantioselective Capillary Electrophoretic Separations With Dilute Solutions Of The Macrocyclic Antibiotic Ristocetin A, Daniel W. Armstrong, Mary P. Gasper, Kimber L. Rundlett Jan 1995

Highly Enantioselective Capillary Electrophoretic Separations With Dilute Solutions Of The Macrocyclic Antibiotic Ristocetin A, Daniel W. Armstrong, Mary P. Gasper, Kimber L. Rundlett

Chemistry Faculty Research & Creative Works

Ristocetin A is one of a series of structurally related amphoteric, glycopeptide, macrocyclic antibiotics. These compounds have several features that make them attractive as chiral selectors. These include spatially oriented functional groups that are known to provide the types of interactions that are conducive to enantio-recognition, a somewhat rigid "pocket" that can provide a site for hydrophobic interactions and polar, flexible arms (i.e., pendent sugar moieties) that can rotate to hydrogen bond and otherwise interact with a variety of chiral analytes. In addition, these compounds are sufficiently soluble in water, aqueous buffers and aqueous-organic solvents that are commonly used in …

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Fragment Flow And The Multifragmentation Phase Space, G. J. Kunde, W. C. Hsi, W. D. Kunze, A. Schüttauf, A. Wörner, M. Begemann-Blaich, Th. Blaich, D. R. Bowman, R. J. Charity, A. Cosmo, A. Ferrero, C. K. Gelbke, J. Hubele, G. Imme, I. Iori, P. Kreutz, V. Lindenstruth, M. A. Lisa, W. G. Lynch, U. Lynen, M. Mang, T. Möhlenkamp, A. Moroni, W. F.J. Müller, M. Neumann, B. Ocker, C. A. Ogilvie, Graham F. Peaslee, J. Pochodzalla, G. Raciti, T. Rubehn, H. Sann, W. Seidei, V. Serfling, L. G. Sobotka, J. Stroth, L. Stuttge, S. Tomasevic Jan 1995

Fragment Flow And The Multifragmentation Phase Space, G. J. Kunde, W. C. Hsi, W. D. Kunze, A. Schüttauf, A. Wörner, M. Begemann-Blaich, Th. Blaich, D. R. Bowman, R. J. Charity, A. Cosmo, A. Ferrero, C. K. Gelbke, J. Hubele, G. Imme, I. Iori, P. Kreutz, V. Lindenstruth, M. A. Lisa, W. G. Lynch, U. Lynen, M. Mang, T. Möhlenkamp, A. Moroni, W. F.J. Müller, M. Neumann, B. Ocker, C. A. Ogilvie, Graham F. Peaslee, J. Pochodzalla, G. Raciti, T. Rubehn, H. Sann, W. Seidei, V. Serfling, L. G. Sobotka, J. Stroth, L. Stuttge, S. Tomasevic

Faculty Publications

Fragment distributions have been measured for Au + Au collisions at EA=100 and 1000 MeV. A high detection efficiency for fragments was obtained by combining the ALADIN spectrometer and the MSU-Miniball/WU-Miniwall array. At both energies the maximum multiplicity of intermediate mass fragments (IMF) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at EA=100 MeV may be related to a reduction of the density in momentum space which is caused by the collective expansion.

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Electrochemical Studies Of Hemoglobin And Cross-Linked Hemoglobin, Ayoola O. Alabi Jan 1995

Electrochemical Studies Of Hemoglobin And Cross-Linked Hemoglobin, Ayoola O. Alabi

Master's Theses

No abstract provided.

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Effect Of Electrolyte Concentration, Temperature And Clay Type On The Diffusional Properties Of Anions In Clay-Modified Electrodes, Jennifer A. Stein Jan 1995

Effect Of Electrolyte Concentration, Temperature And Clay Type On The Diffusional Properties Of Anions In Clay-Modified Electrodes, Jennifer A. Stein

Dissertations

No abstract provided.

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Preparation Of Doped Polycarbynes, Reuben D. Rieke Jan 1995

Preparation Of Doped Polycarbynes, Reuben D. Rieke

Chemistry Department: Faculty Publications

Polycarbynes, such as doped polycarbynes, prepared from a soluble source of electrons and an organic monomer or co-monomer containing at least one carbyne group and, optionally, containing a doping agent, in an ethereal, poly ethereal, or hydrocarbon solvent are presented. A wide variety of arylcarbyne and/or alkylcarbyne monomers and co-monomers can be combined with a source of electrons soluble in an ethereal, polyethereal, or hydrocarbon solvent to form novel polycarbyne polymers. These polycarbyne polymers can be used to form synthetic diamond materials, fibers, and other materials that can withstand extreme con ditions.

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Aggregation Of Chlorophyll A Probed By Resonance Light Scattering Spectroscopy, J. C. De Paula, J. H. Robblee, Robert F. Pasternack Jan 1995

Aggregation Of Chlorophyll A Probed By Resonance Light Scattering Spectroscopy, J. C. De Paula, J. H. Robblee, Robert F. Pasternack

Chemistry & Biochemistry Faculty Works

We report the resonance light scattering (RLS) spectra of chlorophyll a aggregated in a 9:1 solution of formamide and pH 6.8 phosphate buffer. The aggregate formed after 2 h of mixing, referred to as Chl(469), shows a strong scattering feature at 469 nm (Soret band) and a much weaker feature at 699 nm (Q(y) band). A kinetic investigation confirmed that the aggregation process is cooperative, and also detected one intermediate (Chl(458)) with a strong RLS spectrum but only a weak CD spectrum. We propose that aggregation proceeds via at least three steps: 1) formation of a nucleating species, probably a …

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Ground Breaking Ceremony For The Marine Chemistry & Toxicology Building, Virginia Institute Of Marine Science, School Of Marine Science, College Of William And Mary Jan 1995

Ground Breaking Ceremony For The Marine Chemistry & Toxicology Building, Virginia Institute Of Marine Science, School Of Marine Science, College Of William And Mary

Miscellaneous

Ceremony held April 13, 1995. Program of the event.

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Synthesis Of Fluorinated Proline Analogs For The Potential Inhibition Of Proline Oxidase, Brent Hilbert Jan 1995

Synthesis Of Fluorinated Proline Analogs For The Potential Inhibition Of Proline Oxidase, Brent Hilbert

Honors Theses, 1963-2015

Proline oxidase is an enzyme that has been isolated from the inner membrane of rat liver mitochondria. It is the catalyst in the first step of the metabolic pathway for proline-glutamate interconversion. The enzyme is specific for L-proline which is oxidized to Æ-pyrroline- 5-carboxylic acid. 4,4- difluoro-L-proline has demonstrated irreversible inhibition of proline oxidase. Further kinetic studies of this inhibition need to be performed in order to elucidate a mechanism for the inhibition. Information regarding the site of the oxidation of proline may also be obtained from these studies. New synthetic routes to 4,4-difluoro-L-proline, and the "cis" and "trans" non- …

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X-Ray Crystallographic Studies On Cross-Linked Hemoglobins, Elias J. Fernandez Jan 1995

X-Ray Crystallographic Studies On Cross-Linked Hemoglobins, Elias J. Fernandez

Dissertations

No abstract provided.

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Enantiomerically Enriched Α-Methyl Amino Acids. Use Of An Acyclic, Chiral Alanine-Derived Dianion With A High Diastereofacial Bias., David B. Berkowitz, Marianne K. Smith Jan 1995

Enantiomerically Enriched Α-Methyl Amino Acids. Use Of An Acyclic, Chiral Alanine-Derived Dianion With A High Diastereofacial Bias., David B. Berkowitz, Marianne K. Smith

David Berkowitz Publications

Hindered esters derived from N-benzoylalanine and the following chiral alcohols have been synthesized: (1) (−)-isopinocampheol; (2) (−)-trans-2-phenylcyclohexanol and (3) (−)-8-phenylmenthol. Sequential treatment of these esters with LDA (1.2 equiv.) and n-butyllithium (2.4 equiv.) at −78°C in THF generates the corresponding chiral dianions. Alkylation of each of these with benzyl bromide reveals that only the (−)-8-phenylmenthyl auxiliary confers a high diastereofacial bias upon its derivative dianion. In fact, that dianion (6) consistently displays diastereomeric ratios in the range of 89:11 to 94:6 for alkylations with a spectrum of nine alkyl halides. If one recrystallization step is …

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63. Ivan Panayotov, Otto Vogl, Christo Tsvetanov Jan 1995

63. Ivan Panayotov, Otto Vogl, Christo Tsvetanov

Otto Vogl

No abstract provided.

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Absolute Integrated Cross Sections For Some O2 Herzberg I Transitions Near 248–249 Nm, Zhen-Chuan Bao, Edward Yu, John R. Baker Jan 1995

Absolute Integrated Cross Sections For Some O2 Herzberg I Transitions Near 248–249 Nm, Zhen-Chuan Bao, Edward Yu, John R. Baker

Edward Yu

A frequency doubled tunable dye laser system with ∼0.4 cm−1 resolution was used to measure the integrated absorption cross sections of more than 20 rotational transitions in the O2 Herzberg I (A  3Σ+ u ←X  3Σ− g ) 8‐0 and 9‐0 vibrational bands near 248 nm and 249 nm. Oxygen pressures from 200 to 800 Torr and path lengths from 5 to 25 m were employed. The measured absorbances were fitted using a nonlinear least squares analysis and Beer’s Law to obtain absolute values for the individual transition integrated cross sections in good agreement with a recent spectral simulation and …

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Precise Experimental Test Of Models For The Breakdown Of The Born-Oppenheimer Separation: The Rotational Spectra Of Isotopic Variants Of Lithium Hydride, Thomas D. Varberg, M. Bellini, P. De Natale, M. Inquscio, J. M. Brown Jan 1995

Precise Experimental Test Of Models For The Breakdown Of The Born-Oppenheimer Separation: The Rotational Spectra Of Isotopic Variants Of Lithium Hydride, Thomas D. Varberg, M. Bellini, P. De Natale, M. Inquscio, J. M. Brown

Thomas D. Varberg

No abstract provided.

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Refinement Of The Solution Structure Of A Branched Dna Three-Way Junction, Neocles B. Leontis, Igor V. Ouporov Jan 1995

Refinement Of The Solution Structure Of A Branched Dna Three-Way Junction, Neocles B. Leontis, Igor V. Ouporov

Chemistry Faculty Publications

We have refined the structure of the DNA Three-Way Junction complex, TWJ- TC, described in the companion paper by quantitative analysis of two 2D NOESY spectra (mixing times 60 and 200 ms) obtained in D2O solution. NOESY crosspeak intensities extracted from these spectra were used in two kinds of refinement procedure: 1) distance-restrained energy minimization (EM) and molecular dynamics (MD) and 2) full relaxation matrix back calculation refinement. The global geometry of the refined model is very similar to that of a published, preliminary model (Leontis, 1993). Two of the helical arms of the junction are stacked. These are Helix …

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Synthesis, Characterization, And Molecular Structure Of Bis(Tetraphenylcyclopentdienyl)Rhodium(Ii)⊗, James E. Collins, Michael Castellani, Arnold L. Rheingold, Edward J. Miller, William E. Geiger, Anne L. Rieger, Philip H. Rieger Jan 1995

Synthesis, Characterization, And Molecular Structure Of Bis(Tetraphenylcyclopentdienyl)Rhodium(Ii)⊗, James E. Collins, Michael Castellani, Arnold L. Rheingold, Edward J. Miller, William E. Geiger, Anne L. Rieger, Philip H. Rieger

Chemistry Faculty Research

A 5 day diglyme reflux of Rh(acac)3 and K(C5HPh4), followed by treatment with aqueous HPF6, produces orange-yellow [(C5HPh4)2Rh]PF66 in 40 - 50% yield. Reduction of [(C5HPh4)2Rh]PF6 with sodium amalgam in THF yields olive green (C5HPh4)2Rh in 70% yield. (C5HPh4)2Rh crystallizes in the triclinic [Error : unloaded OLE object or mail attachment]space group with unit-cell parameters of a = 8.622 (3) Å, b = 10.778 (4) Å, c = 12.894 (5) Å, a = 65.58 (3)°, b = 72.66 (3)°, g = 83.52 (3)°, and Z = 1. The least squares data refined to RF = 7.63% and …

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Neutron Investigations Of Novel Magnetic Phases, William B. Yelon Jan 1995

Neutron Investigations Of Novel Magnetic Phases, William B. Yelon

Physics Faculty Research & Creative Works

Recent years have seen a renewed search for Fe based permanent magnets, spurred by the discovery of Nd2Fe14B and interstitially modified rare-earth iron binaries. The insights derived from those compounds have suggested a number of routes to the development of such systems, including selective site substitution and combinations of site substitution and interstitial modification. Neutron diffraction is an essential component of this work, since it provides systematic information about the location of substitutional and interstitial atoms, and about the effects these changes have on the magnetic interactions in the systems of interest

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Hammett Correlations Of Carbonyl 13c Chemical Shifts In A Series Of N-(4-Substituted Phenyl)-6-Chloro-5-Fluoronicotinamides, Frank L. Setliff, John W. Hawley, Alan D. Toland Jan 1995

Hammett Correlations Of Carbonyl 13c Chemical Shifts In A Series Of N-(4-Substituted Phenyl)-6-Chloro-5-Fluoronicotinamides, Frank L. Setliff, John W. Hawley, Alan D. Toland

Journal of the Arkansas Academy of Science

A series of nine N-(4-substituted phenyl)-6-chloro-5- fluoronicotinamides exhibited excellent correlations of their carbonyl 13C shifts (5CO,ppm as measured in DMSO) with the standard Hammett substituent constants (c?R) of the substituent inthe 4-position. The linear relationship was defined by the equation 8CO ¦ 1.22

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Spectroscopic Temperature Measurements For A Direct Current Arcjet Diamond Chemical Vapor Deposition Reactor, Scott W. Reeve, Wayne A. Weimer Jan 1995

Spectroscopic Temperature Measurements For A Direct Current Arcjet Diamond Chemical Vapor Deposition Reactor, Scott W. Reeve, Wayne A. Weimer

Journal of the Arkansas Academy of Science

The diamond thin filmcommercial market isprojected to exceed one billion dollars by the year 2000. Potential applications of diamond thin films range from cutting tools to electronics tomedical devices. The explosion ofinterest in this fieldresults from the extreme properties diamond possesses: itis the hardest material known toman and yet, has a coefficient of friction similar to Teflon;its ability to conduct heat is five times that of copper; and diamond is completely inert. However, despite the tremendous economic incentive, there are still several technological barriers preventing diamond filmscale-up to commercial production. Included among these are a fundamental understanding of the gas …

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Organochlorine Pesticide Residues In The Neotropical Migratory Passerine Birds, Birthe Borup Jan 1995

Organochlorine Pesticide Residues In The Neotropical Migratory Passerine Birds, Birthe Borup

Honors Projects

In 1874 Othmar Ziedlert a German chemist was working on the synthesis and characterization of substituted aromatic hydrocarbons. In the process of his work he synthesized dichloro-diphenyl-trichloro-ethane commonly known as DDT. It was not until 1930 that its use as an insecticide was detected by Paul Muller who found that it was effective against potato beetles (Leptinotarsal declineata) and clothes moths, (Tineola besselliella ) (Dunlap 1981). Pure DDT is a white crystalline solid with a melting point of 109 C, and a vapor pressure of 0.025mPa at 20 C. Technical grade DDT is a white amorphous powder, consisting of a …

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Vehicle Measurements For Co, Hc And No In El Paso, Texas And Juarez, Mexico, Donald H. Stedman, Yi Zhang, Jon M. Lesko Jan 1995

Vehicle Measurements For Co, Hc And No In El Paso, Texas And Juarez, Mexico, Donald H. Stedman, Yi Zhang, Jon M. Lesko

Fuel Efficiency Automobile Test Publications

No abstract provided.

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On-Road Remote Sensing Of Vehicle Emissions In Monterrey, N. L. Mexico, Gary A. Bishop, Donald H. Stedman Jan 1995

On-Road Remote Sensing Of Vehicle Emissions In Monterrey, N. L. Mexico, Gary A. Bishop, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

No abstract provided.

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Playing With Fire, Science And Politics Of Air Pollution From Cars, Donald H. Stedman Jan 1995

Playing With Fire, Science And Politics Of Air Pollution From Cars, Donald H. Stedman

Fuel Efficiency Automobile Test Publications

No abstract provided.

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Theoretical Study Of Solvent Effects On The Electronic Coupling Element In Rigidly Linked Donor-Acceptor Systems, Robert J. Cave, Marshall D. Newton, Krishna Kumar, Matthew B. Zimmt Jan 1995

Theoretical Study Of Solvent Effects On The Electronic Coupling Element In Rigidly Linked Donor-Acceptor Systems, Robert J. Cave, Marshall D. Newton, Krishna Kumar, Matthew B. Zimmt

All HMC Faculty Publications and Research

The recently developed generalized Mulliken-Hush approach for the calculation of the electronic coupling matrix element for electron-transfer processes is applied to two rigidly linked donor-bridge-acceptor systems having dimethoxyanthracene as the donor and a dicarbomethoxycyclobutene unit as the acceptor. The dependence of the electronic coupling matrix element as a function of bridge type is examined with and without solvent molecules present. For clamp-shaped bridge structures solvent can have a dramatic effect on the electronic coupling matrix element. The behavior with variation of solvent is in good agreement with that observed experimentally for these systems.

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Free Α-Oxiranyl Amino Acids, David B. Berkowitz, Michelle L. Pedersen Jan 1995

Free Α-Oxiranyl Amino Acids, David B. Berkowitz, Michelle L. Pedersen

David Berkowitz Publications

Analogues of natural amino acids, in which the α-proton is replaced by an unsubstituted epoxide ring, are potential mechanism-based inhibitors for pyridoxal phosphate dependent enzymes.1 Yet, free α-oxiranyl amino acids have remained elusive until now. The synthesis of an α-(phenyl-substituted)oxiranyl amino ester has been reported. However, the accessibility and stability of the corresponding free, zwitterionic α-oxiranyl amino acid remained an open question.9

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Determination And Use Of Rohrschneider-Mcreynolds Constants For Chiral Stationary Phases Used In Capillary Gas Chromatography, Alain Berthod, Eve Yiwen Zhou, Kang Le, Daniel W. Armstrong Jan 1995

Determination And Use Of Rohrschneider-Mcreynolds Constants For Chiral Stationary Phases Used In Capillary Gas Chromatography, Alain Berthod, Eve Yiwen Zhou, Kang Le, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants. Most of the columns (i.e., 18) were wall-coated, and four were of the wall-immobilized or of the so-called "bonded" type. A wall-coated capillary squalane column was specially prepared as a polarity reference column. All but two of the CSPs were based on derivatized cyclodextrins (CDs) of different sizes. The overall properties of the CSPs are discussed in terms of the five Rohrschneider-McReynolds constants and their average values. It was found that the derivatized cyclodextrin CSP …

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Synthesis Of Model Tripeptides And Approaches To The Preparation Of A Transition State Analogue Of Phosphoramidon, Nadina Monberg Jan 1995

Synthesis Of Model Tripeptides And Approaches To The Preparation Of A Transition State Analogue Of Phosphoramidon, Nadina Monberg

Master's Theses

No abstract provided.

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Scf-Mo Conformational Analysis Of Polycroconaine, T. E. Ezell, Jerry A. Darsey Jan 1995

Scf-Mo Conformational Analysis Of Polycroconaine, T. E. Ezell, Jerry A. Darsey

Journal of the Arkansas Academy of Science

Abinitio calculations at the STO-3G basis set level using GAUSSIAN 92 were conducted on the monomer unit of polycroconaine, a conducting polymer with conductive properties similar to several metals, in order to determine the most probable conformation of the monomer. We also compared the energy difference between the highest occupied and lowest unoccupied molecular orbitals. Successive calculations were performed at dihedral angle intervals of 30° around the central bond of the monomer. Minimum energy was observed at 0° bond rotation, consistent with a theory that the polymer owes many of its conductive properties to a planar configuration in combination with …

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The Synthesis Of Benzophenane 3,5-Dicarboxylic Acid For The Double Capping Of Beta-Cyclodextrin, Jaydee Dones Cabral Jan 1995

The Synthesis Of Benzophenane 3,5-Dicarboxylic Acid For The Double Capping Of Beta-Cyclodextrin, Jaydee Dones Cabral

Dissertations, Theses, and Masters Projects

No abstract provided.

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Azidotetrakis(Trimethylphosphine)Nickel(Ii) Tetrafluoroborate, Caryn C. Carson, Robert D. Pike Jan 1995

Azidotetrakis(Trimethylphosphine)Nickel(Ii) Tetrafluoroborate, Caryn C. Carson, Robert D. Pike

Arts & Sciences Articles

The title complex, [Ni(N3)(C3H9P)4]BF4, is a nearly perfect trigonal bipyramid with the azide group at an apical position. The metal-azide bond angle, Nil-- NlmN2, of 138.6(5) ° is the largest observed for a terminal azide ligand.

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Syntheses Of Cross-Linking Agents, Molecular Modeling Of Oligonucleotides And Polypeptide-Ion Complexes, Michael J. Yunes Jan 1995

Syntheses Of Cross-Linking Agents, Molecular Modeling Of Oligonucleotides And Polypeptide-Ion Complexes, Michael J. Yunes

Honors Theses

Each section of this thesis will be subdivided into three parts encompassing all of the research in which I have been involved during the past three years. These will be referred to under the headings "Syntheses:' "Molecular Modeling," and "Cross-linking Efficiencies." Each of these subdivisions may have divisions within them when necessary in order to fully detail the research.

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