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Articles 961 - 990 of 1553

Full-Text Articles in Chemistry

A Magnetic And Crystallographic Study Of (Sm/Gd)₂(Fe/Si)₁₇CZ Solid Solutions, Peter C. Ezekwenna, G. K. Marasinghe, J. H. Nam, William Joseph James, William B. Yelon, M. Ellouze, Ph. I'Héritier May 2000

A Magnetic And Crystallographic Study Of (Sm/Gd)₂(Fe/Si)₁₇CZ Solid Solutions, Peter C. Ezekwenna, G. K. Marasinghe, J. H. Nam, William Joseph James, William B. Yelon, M. Ellouze, Ph. I'Héritier

Chemistry Faculty Research & Creative Works

The crystallographic and magnetic properties of SmyGd2-yFe17-xSix (0 ≤ x ≤ 3 and y = 1 and 1.5) solid solutions and their interstitial carbides have been investigated using x-ray diffraction and magnetic measurements. The SmyGd2-yFe17-xSix samples crystallized in the rhombohedral Th2Zn17 structure with less than 5 mol % of impurities. The unit cells of the mixed rare-earth (R) samples are smaller than those of Sm2Fe17 and Gd2Fe17. The carbided samples contain up to a total of …

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The Atomic And Magnetic Structure Of Ndmn(₆₋ₓ)Feₓge₆ Solid Solutions, J. Han, G. K. Marasinghe, William Joseph James, Muguo Chen, William B. Yelon, I. Dubenko, Naushad Ali May 2000

The Atomic And Magnetic Structure Of Ndmn(₆₋ₓ)Feₓge₆ Solid Solutions, J. Han, G. K. Marasinghe, William Joseph James, Muguo Chen, William B. Yelon, I. Dubenko, Naushad Ali

Chemistry Faculty Research & Creative Works

The magnetic and crystallographic properties of induction-melted NdMn(6-x)FexGe6 intermetallics (x = 0, 1.0, and 1.5) in the temperature range of 30-475 K have been studied by x-ray and neutron diffraction techniques and SQUID measurements. All of the samples crystallized in the YCo6Ge6-type structure (P6/mmm). A small amount ( < 5 mol%) of Nd(MnFe)2Ge2 is present as an impurity. As expected, iron replaces manganese at the 3g site. The unit cell volume decreases slightly with increasing iron content at an average rate of 1.3% per substituted atom. Lattice parameters a and c contract at …

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Role Of The Carbohydrate Moieties In Chiral Recognition On Teicoplanin- Based Lc Stationary Phases, Alain Berthod, Xianghong Chen, John P. Kullman, Daniel W. Armstrong, Francesco Gasparrini, Ilaria D'Acquarica, Claudio Villani, Angelo Carotti Apr 2000

Role Of The Carbohydrate Moieties In Chiral Recognition On Teicoplanin- Based Lc Stationary Phases, Alain Berthod, Xianghong Chen, John P. Kullman, Daniel W. Armstrong, Francesco Gasparrini, Ilaria D'Acquarica, Claudio Villani, Angelo Carotti

Chemistry Faculty Research & Creative Works

For this study, we used the macrocyclic antibiotic teicoplanin, a molecule consisting of an aglycone peptide 'basket' with three attached carbohydrate (sugar) moieties. The sugar units were removed and the aglycone was purified. Two chiral stationary phases (CSPs) were prepared in a similar way, one with the native teicoplanin molecule and the other with the aglycone. Twenty-six compounds were evaluated on the two CSPs with seven RPLC mobile phases and two polar organic mobile phases. The compounds were 13 amino acids or structurally related compounds (including DOPA, folinic acid, etc.) and 13 other compounds (such as carnitine, bromacil, etc.). The …

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Solid-State Deuterium Nuclear Magnetic Resonance Of The Methyl Dynamics Of Poly(Alpha-Methylstyrene) And Polymethylphenylsilane, Robert D. O'Connor, Eric J. Ginsburg, Frank D. Blum Apr 2000

Solid-State Deuterium Nuclear Magnetic Resonance Of The Methyl Dynamics Of Poly(Alpha-Methylstyrene) And Polymethylphenylsilane, Robert D. O'Connor, Eric J. Ginsburg, Frank D. Blum

Chemistry Faculty Research & Creative Works

The methyl-d3 dynamics of two relatively similar polymers, poly(alpha-methylstyrene) (PAMS-d3) and polymethylphenylsilane (PMPS-d3), are investigated via deuterium NMR relaxation experiments. Our analysis of the relaxation data uses the entire solid-echo spectra to maximize the precision of the experiments with regard to the information available on the methyl dynamics. The analysis is novel in that it does not use M[infinity] or M0 to fit the relaxation data. Additionally, the three-site symmetric jump model is shown to not have an observable azimuthal angular dependence for T1 relaxation. The methyl dynamics are quantified with taum, sigma, and f which are the log-average correlation …

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4-Chloroacetophenone [1-(4-Methoxyphenyl)Ethylidene]Hydrazone, Michael A. Lewis, Charles Leslie Barnes, Rainer Glaser Mar 2000

4-Chloroacetophenone [1-(4-Methoxyphenyl)Ethylidene]Hydrazone, Michael A. Lewis, Charles Leslie Barnes, Rainer Glaser

Chemistry Faculty Research & Creative Works

The crystal structure of the title mixed azine, C17H17CIN2O, contains four independent molecules, A-D, and molecule B is disordered. All four molecules have an N-N gauche conformation, with C-N-N-C torsion angles of 136.5 (4), 137.0 (4), -134.7 (4) and -134.7 (4)°, respectively. The phenyl rings are also somewhat twisted with respect to the plane defined by Cipso and the imine bond. On average, the combined effect of these twists results in an angle of 64.7° between the best planes of the two phenyl rings. Arene-arene double T-contacts are the dominant intermolecular interaction. The …

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Conceptual Problems With Remote Element Synthesis, Oliver Manuel Mar 2000

Conceptual Problems With Remote Element Synthesis, Oliver Manuel

Chemistry Faculty Research & Creative Works

The notion of remote element synthesis has recently been modified to explain the presence of nucleogenetic isotopic anomalies and decay products of short-lived nuclides by injection of a small amount of exotic nucleogenetic material. Even with this modification, remote element synthesis seems inconsistent with the following observations: Evidence of coupled variations in the chemical and isotopic compositions of the source material for meteorites. Residual coupling of chemical and isotopic heterogeneities across planetary distances in the solar system today. The mass-fractionation relationship seen across isotopes of elements in the planetary system, in the solar wind, and in solar flares. Linkage of …

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High-Performance Liquid Chromatographic Separation Of The Enantiomers Of Unusual Α-Amino Acid Analogues, Antal Péter, Edit Olajos, Richard Casimir, Dirk Tourwé, Quirinus B. Broxterman, Bernard Kaptein, Daniel W. Armstrong Feb 2000

High-Performance Liquid Chromatographic Separation Of The Enantiomers Of Unusual Α-Amino Acid Analogues, Antal Péter, Edit Olajos, Richard Casimir, Dirk Tourwé, Quirinus B. Broxterman, Bernard Kaptein, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

The direct and indirect stereochemical resolution of the enantiomers of ring- and α-methyl-substituted phenylalanines and phenylalanine amides was attempted by high-performance liquid chromatographic methods. The direct separation was carried out on two chiral stationary phases, the crown-ether- based Crownpak CR (+), and the teicoplanin-based Chirobiotic T, while the indirect resolution was performed by applying pre-column derivatization with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl isothiocyanate (GITC) and Nα- (2,4-dinitro-5-fluorophenyl)-L-alanine amide (Marfey's reagent, FDAA). The Chirobiotic T column was efficient in the separation of ring- and α-methyl- substituted phenylalanine analogues but was ineffective for the amides of these analogues. The Crownpak CR (+) column separated the ring-substituted …

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Hydrogen Bonding In Alcohol Clusters: A Comparative Study By Infrared Cavity Ringdown Laser Absorption Spectroscopy, Robert A. Provencal, Raphael N. Casaes, Katja Roth, Joshua B. Paul, Chris N. Chapo, Richard J. Saykally, Gregory S. Tschumper, Henry F. Schaefer Feb 2000

Hydrogen Bonding In Alcohol Clusters: A Comparative Study By Infrared Cavity Ringdown Laser Absorption Spectroscopy, Robert A. Provencal, Raphael N. Casaes, Katja Roth, Joshua B. Paul, Chris N. Chapo, Richard J. Saykally, Gregory S. Tschumper, Henry F. Schaefer

Chemistry Faculty Research & Creative Works

Infrared cavity ringdown laser absorption spectroscopy has been used to study the O-H stretching vibrations of jet-cooled ethanol and butanol clusters. Three bonded O-H stretches were attributed to the ethanol dimer, indicating the presence of more than one conformer in the molecular beam. One unresolved feature was measured for both the trimer and tetramer. To facilitate spectral assignment, the vibrational frequencies and intensities have been calculated for the ethanol dimer using second-order Moller-Plesset perturbation theory. Three bonded O-H stretches have also been measured for the butanol dimer, suggesting that more than one conformer is present in the molecular beam. Vibrational …

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Observations Of Particulates Within The North Atlantic Flight Corridor: Polinat 2, September-October 1997, J. D. Paladino, Donald E. Hagen, Philip D. Whitefield, Alfred Raymond Hopkins, Otmar Schmid, M. R. Wilson, Hans Schlager, Peter Schulte Feb 2000

Observations Of Particulates Within The North Atlantic Flight Corridor: Polinat 2, September-October 1997, J. D. Paladino, Donald E. Hagen, Philip D. Whitefield, Alfred Raymond Hopkins, Otmar Schmid, M. R. Wilson, Hans Schlager, Peter Schulte

Physics Faculty Research & Creative Works

This paper discusses particulate concentration and size distribution data gathered using the University of Missouri-Rolla Mobile Aerosol Sampling System (UMR-MASS), and used to investigate the southern extent of the eastern end of the North Atlantic Flight Corridor (NAFC) during project Pollution From Aircraft Emissions in the North Atlantic Flight Corridor/Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (POLINAT 2/SONEX) from September 19 to October 23, 1997. The analysis presented in this paper focuses on "the corridor effect," or enhancement of pollutants by jet aircraft combustion events. To investigate the phenomena, both vertical and horizontal profiles of the corridor, and regions …

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Applicability Of Ozone In Small Drinking Water Systems, Craig D. Adams, Justin Sutherland Jan 2000

Applicability Of Ozone In Small Drinking Water Systems, Craig D. Adams, Justin Sutherland

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

The use of ozone in water treatment plants is expanding rapidly in the United States. Ozone offers excellent disinfection properties (including chlorine-resistant pathogens) and does not form trihalomethanes. Additionally, ozone can be used to achieve or control many other water quality parameters such as color, taste and odor, and inorganic and organic contaminant concentrations. Control of ozone's disinfection byproducts such as bromate (formed in high bromide waters) is required. This presentation will review the synergistic effects of ozone applicable to use in small water treatment plants.

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Dynamics Of Interfacial Polymers In Composites, Frank D. Blum, Wuu-Yung Lin Jan 2000

Dynamics Of Interfacial Polymers In Composites, Frank D. Blum, Wuu-Yung Lin

Chemistry Faculty Research & Creative Works

Much experimental and theoretical work has been done on the behavior of adsorbed polymers. However, not much work has focused on the dynamics, especially segmental dynamics, of the adsorbed polymers. This is especially true of filled polymer or composite systems as the interfacial layers in these systems are difficult to study with most techniques. NMR is not restricted to use in optically clear samples and its use in the characterization in the surface polymers has been reviewed. In our laboratory, we have found that deuterium NMR could be used to probe the segmental dynamics of adsorbed polymers. The position of …

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Chemical Oxidation Of Mtbe Under O2-Rich And O2-Limited Environments Coupled With Biological Degradation Of Oxidation Byproducts, J. Sutherland, B. Panka, Craig D. Adams, Joel Gerard Burken Jan 2000

Chemical Oxidation Of Mtbe Under O2-Rich And O2-Limited Environments Coupled With Biological Degradation Of Oxidation Byproducts, J. Sutherland, B. Panka, Craig D. Adams, Joel Gerard Burken

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

The H2O2/UV Advanced Oxidation Process (AOP) Was Investigated to Determine Byproduct Formation under Different Experimental Conditions (PH, Alkalinity, and H2O2/UV Dose). a Key Factor in the Efficiency of the AOP Was the Dissolved Oxygen Concentration. Gas Chromatography/mass Spectrometry (GC/MS) Analysis Was Used to Identify Byproducts Resulting from Oxidation under Oxygen-Rich and Oxygen-Limited Conditions. Resultant Oxidation Byproducts Were Analyzed for their Susceptibility to Biological Degradation. Biodegradation Rate Constants Were Determined and Modeled for the Primary Byproducts of the Advanced Oxidation Process. Inhibition Resulting from the Presence of Multiple Byproducts in a Biological System Was Investigated as Well. Effects of Process Parameters …

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Application Of Electron-Attachment Reactions To Enhance Selectivity Of Electron-Capture Detector For Nitroaromatic Explosives, Mark Gehrke, Shubhender Kapila, V. J. Flanigan Jan 2000

Application Of Electron-Attachment Reactions To Enhance Selectivity Of Electron-Capture Detector For Nitroaromatic Explosives, Mark Gehrke, Shubhender Kapila, V. J. Flanigan

Chemistry Faculty Research & Creative Works

The differences in the extent of electron-attachment reactions between thermal electrons and selected classes of organic molecules with high electron affinities were investigated. the investigations showed that interactions of thermal electrons with nitroaromatic compounds lead to the formation of neutral products with very low electron affinities. by contrast, a number of other analytes with high electron affinities such as polyhalogenated organic compounds, lead to products with high electron affinities. This difference was exploited to differentiate between nitroaromatic and polychlorinated organic compounds with a tandem arrangement consisting of two electron-capture detectors connected in series with an electron-attachment reactor.

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Computerised Evaluation Of Cognitive And Motor Function, B. Kisačanin, G. C. Agarwal, J. Taber, D. (Daniel) Hier Jan 2000

Computerised Evaluation Of Cognitive And Motor Function, B. Kisačanin, G. C. Agarwal, J. Taber, D. (Daniel) Hier

Chemistry Faculty Research & Creative Works

In This Paper, We Present a Clinical Study of Computerized Tracking in the Evaluation of Cognitive and Motor Function. We Investigate its Use in the Assessment of Effectiveness of Antiepileptic Drugs (AEDs) as Well as in the Process of Following the Progress of Alzheimer's Disease (AD). to Simplify the Experiments, We Introduce Real-Time Adaptation of the Target Speed. in the Study with Epileptic Patients, Three Result Groups Are Compared: Blood Levels of AEDs, Scores on Standard Neuropsychological Tests, and Scores on Computerized Tracking and Reaction Time Tests. It is Found that the Computerized Tests Are Repeatable, Reliable and Sensitive and …

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Crystal And Magnetic Structures Of Lani₅₋ₓmnₓ, Chiu-Ying Tai, G. K. Marasinghe, Oran Allan Pringle, William Joseph James, Muguo Chen, William B. Yelon, I. Dubenko, Naushad Ali, Ph. I'Héritier Jan 2000

Crystal And Magnetic Structures Of Lani₅₋ₓmnₓ, Chiu-Ying Tai, G. K. Marasinghe, Oran Allan Pringle, William Joseph James, Muguo Chen, William B. Yelon, I. Dubenko, Naushad Ali, Ph. I'Héritier

Physics Faculty Research & Creative Works

The crystallographic and magnetic properties of LaN5-xMnx with x = 1, 1.5, and 2, have been investigated using x-ray and neutron diffraction, vibrating sample magnetometer and superconducting quantum interference device measurements. All the samples crystallize in the hexagonal CaCu5-type (P6/mmm) structure. Manganese atoms preferentially occupy the 3 g site in the LaNi5 structure. The bulk magnetization of the LaNi5-xMnx powder samples decreases rapidly as nickel is replaced by manganese. A ferrimagnetic model is applied to describe the magnetic structure of the LaNi5-xMnx samples for x = 1.5 and …

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The Effects Of Substituting Iron For Manganese In Smmn₆Ge₆: Magnetic And Crystallographic Properties, J. Han, William B. Yelon, Naushad Ali, I. Dubenko, G. K. Marasinghe, Ph. I'Héritier, William Joseph James Jan 2000

The Effects Of Substituting Iron For Manganese In Smmn₆Ge₆: Magnetic And Crystallographic Properties, J. Han, William B. Yelon, Naushad Ali, I. Dubenko, G. K. Marasinghe, Ph. I'Héritier, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.

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Pyrolysis-Mass Spectrometry For Rapid Classification Of Oysters According To Rearing Area, J. Krupcík, P. Oswald, I. Spánik, P. Májek, M. Bajdichová, P. Sandra, Daniel W. Armstrong Jan 2000

Pyrolysis-Mass Spectrometry For Rapid Classification Of Oysters According To Rearing Area, J. Krupcík, P. Oswald, I. Spánik, P. Májek, M. Bajdichová, P. Sandra, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Current concern for the safety and traceability of food, as well as the desire of oyster farmers, for marketing reason, to emphasize the geographical origin of their production, requires new methods to make possible a real product identification. In this study, 181 oyster samples were analyzed to determine their origin area. These samples were collected in nine French rearing areas at four different times of the year (spring, summer, and the beginning and end of autumn) and from four to eight sites in each area to provide a variability parameter. Analysis of fingerprints after Curie point pyrolysis-mass spectrometry, by an …

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Enantiomeric High-Performance Liquid Chromatographic Separation Of Β- Substituted Tryptophan Analogues, G. Török, A. Péter, E. Vékes, J. Sápi, M. Laronze, J. Y. Laronze, Daniel W. Armstrong Jan 2000

Enantiomeric High-Performance Liquid Chromatographic Separation Of Β- Substituted Tryptophan Analogues, G. Török, A. Péter, E. Vékes, J. Sápi, M. Laronze, J. Y. Laronze, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

The high-performance liquid chromatographic enantioresolution of β- substituted tryptophan analogues by direct and indirect methods is reported. The direct separation was carried out on chiral crown ether-bonded, on the macrocyclic antibiotic teicoplanin-bonded or on different derivatized β- cyclodextrin-bonded phases. The indirect resolution was achieved by applying pre-column derivatization with the chiral reagents 1-fluoro-2,4- dinitrophenyl-5-L-alanine amide (FDAA) and 2,3,4,6-tetra-O-acetyl-β-D- glucopyranosyl isothiocyanate (GITC). In the separation of all four isomers of the analytes, the indirect methods seemed to be more efficient than the direct methods. In most cases, the FDAA derivatives of the stereoisomers could be separated with better selectivity in methanol-containing …

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Macrocyclic Antibiotics As Separation Agents, Daniel W. Armstrong Oct 1999

Macrocyclic Antibiotics As Separation Agents, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Macrocyclic antibiotics having ring structures with at least 10 members act as separation agents in crystallization, precipitation, filtration, electrophoresis and chromatography. The macrocyclic antibiotics include ansamacrolides, macrolides, macrocyclic peptides, polyenes and derivatives thereof. The process has been found to be especially advantageous for separation of optical isomers by electrophoresis and chromatography.

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Effect Of Interfacial Mobility On Flexural Strength And Fracture Toughness Of Glass/Epoxy Laminates, T. W. H. Wang, Frank D. Blum, Lokeswarappa R. Dharani Oct 1999

Effect Of Interfacial Mobility On Flexural Strength And Fracture Toughness Of Glass/Epoxy Laminates, T. W. H. Wang, Frank D. Blum, Lokeswarappa R. Dharani

Chemistry Faculty Research & Creative Works

Mechanical testing and surface fractography were used to characterize the fracture of E-glass fiber reinforced epoxy composites as a function of the silane coupling agent used. gamma-Aminopropyltriethoxysilane (APS) and delta-aminobutyltriethoxysilane (ABS) were used because these have been shown to have different interfacial mobilities at multilayer coverage. The values of the properties studied generally increased from untreated c, as determined from a Mode I translaminar fracture toughness tests, for the untreated composites (10.5 ± 0.4 kJ/m2) was lower than that for the ABS-treated composites (14.3 ± 2.1 kJ/m2) which was lower than that for the APS-treated composites (17.1 ± 2.4 kJ/m2). …

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Evaluation Of The Enantiomeric Composition Of Amino Acids In Tobacco, John P. Kullman, Xianghong Chen, Daniel W. Armstrong Oct 1999

Evaluation Of The Enantiomeric Composition Of Amino Acids In Tobacco, John P. Kullman, Xianghong Chen, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Despite the fact that several studies have reported the concentrations of various free amino acids in tobacco, their enantiomeric composition is unknown. Both the absolute and enantiomeric compositions of proline, alanine, asparagine, aspartic acid, valine, methionine, leucine, and phenylalanine were determined for three strains of tobacco leaf, three types of smokeless tobacco, and six different blended filtered and nonfiltered reference cigarettes. Some of the highest levels of D-amino acids ever found in agricultural products were observed. Possible mechanisms for the production of these D-amino acids are considered. The relevance of D-amino acids in tobacco is discussed.

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Contour Temperature Programmed Desorption For Monitoring Multiple Chemical Reaction Products, Charles C. Chusuei, J. V. De La Peña, John A. Schreifels Sep 1999

Contour Temperature Programmed Desorption For Monitoring Multiple Chemical Reaction Products, Charles C. Chusuei, J. V. De La Peña, John A. Schreifels

Chemistry Faculty Research & Creative Works

A simple method for obtaining a comprehensive overview of major compounds desorbing from the surface during temperature programmed desorption (TPD) experiments is outlined. Standard commercially available equipment is used to perform the experiment. The method is particularly valuable when high molecular mass compounds are being studied. The acquisition of contour temperature programmed desorption (CTPD) spectra, sampling 50-dalton mass ranges at a time in the thermal desorption experiments, is described and demonstrated for the interaction of benzotriazole adsorbed on a Ni(111) surface. Conventional two-dimensional TPD spectra can be extracted from the CTPD by taking vertical slices of the contour.

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Mössbauer Effect Study Of Filled Antimonide Skutterudites, Gary J. Long, Dimitri Hautot, Fernande Grandjean, Donald T. Morelli, Gregory P. Meisner Sep 1999

Mössbauer Effect Study Of Filled Antimonide Skutterudites, Gary J. Long, Dimitri Hautot, Fernande Grandjean, Donald T. Morelli, Gregory P. Meisner

Chemistry Faculty Research & Creative Works

The iron-57 Mössbauer spectra of a series of Ce-filled antimonide skutterudites, CexFe4-yCoySb12, where x varies from 0.22 to 0.98 and y varies from 0 to 3.5, have been measured at 295 K. In addition, the spectra of Ce0.60Fe2Co2Sb12 and Ce0.82Fe3CoSb12 have been measured from 85 to 295 K and the spectra of Ce0.35FeCo3Sb12 and Ce0.98Fe4Sb12 have been measured from 4.2 to 295 K. The spectra, all of which consist of …

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Examination Of Ionic Liquids And Their Interaction With Molecules, When Used As Stationary Phases In Gas Chromatography, Daniel W. Armstrong, Lingfeng He, Yan Song Liu Sep 1999

Examination Of Ionic Liquids And Their Interaction With Molecules, When Used As Stationary Phases In Gas Chromatography, Daniel W. Armstrong, Lingfeng He, Yan Song Liu

Chemistry Faculty Research & Creative Works

Stable room-temperature ionic liquids (RTILs) have been used as novel reaction solvents. They can solubilize complex polar molecules such as cyclodextrins and glycopeptides. Their wetting ability and viscosity allow them to be coated onto fused silica capillaries. Thus, 1-butyl-3- methylimidazolium hexafluorophosphate and the analogous chloride salt can be used as stationary phases for gas chromatography (GC). Using inverse GC, one can examine the nature of these ionic liquids via their interactions with a variety of compounds. The Rohrschneider-McReynolds constants were determined for both ionic liquids and a popular commercial polysiloxane stationary phase. Ionic liquid stationary phases seem to have a …

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Assignment Of The Infrared Spectra Of The Methanol Trimer, Gregory S. Tschumper, Jason M. Gonzales, Henry F. Schaefer Aug 1999

Assignment Of The Infrared Spectra Of The Methanol Trimer, Gregory S. Tschumper, Jason M. Gonzales, Henry F. Schaefer

Chemistry Faculty Research & Creative Works

Second-order Möller-Plesset perturbation theory (MP2) and density functional theory (DFT) were employed to optimize two cyclic conformations of the methanol trimer, denoted "bowl" and "chair," as well as a third noncyclic, "open-chain" conformation. This is the first time all three methanol trimer conformations have been studied at the same level of theory. Harmonic vibrational frequencies confirm that all stationary points are minima on the intermolecular potential energy hypersurface. The chair is consistently predicted to be the most stable conformer. The bowl and open-chain conformers are only slightly less stable and lie within 3 kcal/mol. Results indicate that the bowl structure …

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Electrodeposition Of Cerium-Based Coatings For Corrosion Protection Of Aluminum Alloys, James O. Stoffer, Thomas J. O'Keefe, Xuan Lin, Eric L. Morris, Pu Yu, Srinivas Pravin Sitaram Aug 1999

Electrodeposition Of Cerium-Based Coatings For Corrosion Protection Of Aluminum Alloys, James O. Stoffer, Thomas J. O'Keefe, Xuan Lin, Eric L. Morris, Pu Yu, Srinivas Pravin Sitaram

Chemistry Faculty Research & Creative Works

A process for enhancing the corrosion resistance of an aluminum-containing component with a cerium based coating. An aluminum-containing cathode and an oxygen- evolving anode are immersed in an electrolyte comprising water, solvent, oxidizing agent and cerium ions. An electrical current is passed through the electrolyte by applying electrical current to deposit a cerium based coating onto the cathode. An electrolyte for use in depositing a cerium based coating. An electrodeposited cerium-based coating. An aluminum aircraft structural component having a cerium-based coating thereon.

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Hydrogen Dynamics In The Hydrides Of Pr₂Fe₁₇ As Revealed By Mössbauer Spectroscopy, Dimitri Hautot, Gary J. Long, Fernande Grandjean, Olivier Isnard, Salvatore Miraglia Aug 1999

Hydrogen Dynamics In The Hydrides Of Pr₂Fe₁₇ As Revealed By Mössbauer Spectroscopy, Dimitri Hautot, Gary J. Long, Fernande Grandjean, Olivier Isnard, Salvatore Miraglia

Chemistry Faculty Research & Creative Works

The rhombohedral Pr2Fe17Hx compounds with the Th2Zn17 structure have been prepared for x =0-5. Their lattice parameters and Curie temperatures have been determined from powder x-ray diffraction and thermomagnetic measurements, respectively, and their Mössbauer spectra have been measured between 4.2 and 295 K. The Mössbauer spectra for x=0, 1, and 2, obtained between 4.2 and 295 K, and those of Pr2Fe17H3, obtained above 90 K, have been analyzed with a seven sextet model, indicative of a basal magnetization in these compounds. The Mössbauer spectra of Pr …

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High-Performance Liquid Chromatographic Separation Of Novel Atropic Α,Α-Disubstituted-Β-Amino Acids, Either On Different Β-Cyclodextrin-Bonded Phases Or As Their 1-Fluoro-2,4-Dinitrophenyl-5-L-Alanine Amide Derivatives, Gabriella Török, Antal Péter, Anne Gaucher, Michel Wakselman, Jean Paul Mazaleyrat, Daniel W. Armstrong Jun 1999

High-Performance Liquid Chromatographic Separation Of Novel Atropic Α,Α-Disubstituted-Β-Amino Acids, Either On Different Β-Cyclodextrin-Bonded Phases Or As Their 1-Fluoro-2,4-Dinitrophenyl-5-L-Alanine Amide Derivatives, Gabriella Török, Antal Péter, Anne Gaucher, Michel Wakselman, Jean Paul Mazaleyrat, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

The high-performance liquid chromatographic enantioresolution of free and N- and/or C-protected derivatives of (R, S)-2',1':1,2;1',2':3,4-dinaphthcyclohepta-1,3-diene-6-aminomethyl-6 -carboxylic acid (β2-Bin) by direct and indirect methods is reported. The direct separation was carried out on native and different derivatized β -cyclodextrin-bonded phases. The indirect resolution was achieved by applying pre-column derivatization with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide. The effects of different parameters such as the mobile phase composition and the structures of the compounds on the enantiomeric resolution are discussed.

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4-Methoxybenzaldehyde Pentafluorophenyl-Methylidenehydrazone, Michael A. Lewis, Charles Leslie Barnes, Bruce A. Hathaway, Rainer Glaser Jun 1999

4-Methoxybenzaldehyde Pentafluorophenyl-Methylidenehydrazone, Michael A. Lewis, Charles Leslie Barnes, Bruce A. Hathaway, Rainer Glaser

Chemistry Faculty Research & Creative Works

The crystal structure of the mixed azine C15H9F5N2O is described. The molecule has a high degree of planarity. The two phenyl rings deviate from perfect planarity by less than 2° and the dihedral angles between the ipso-C atoms and the azine bridge also show a minute deviation from planarity of less than 2°. The only dihedral angle that indicates any significant twisting is the dihedral angle about the azine bridge [C1-N1-N2-C8 174.8 (6)°], and even this one is relatively small. Face-to-face arene-arene contacts are the dominant intermolecular interactions. There are double …

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Self-Association Of Rifamycin B: Possible Effects On Molecular Recognition, Daniel W. Armstrong, Jeffrey Schneiderheinze, Usha Nair, Linda J. Magid, Paul D. Butler May 1999

Self-Association Of Rifamycin B: Possible Effects On Molecular Recognition, Daniel W. Armstrong, Jeffrey Schneiderheinze, Usha Nair, Linda J. Magid, Paul D. Butler

Chemistry Faculty Research & Creative Works

The macrocyclic antibiotic rifamycin B was found to be highly surface-active and to aggregate in aqueous solution. The aggregational behavior was studied using small-angle neutron scattering (SANS). Aqueous solutions of rifamycin B showed pronounced scattering at both small-length scales (Q ≥ 0.1 Å-1) and at large-length scales (Q ≤ 0.1 Å-1). The larger association colloids appear to be rather open low-density aggregates. The addition of 10% 2-propanol greatly reduces the number and size of the aggregates. Somewhat higher amounts of alcohol appear to completely suppress or eliminate aggregation. The suppression of aggregation coincides with the appearance and enhancement of enantioselective …

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