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Articles 721 - 750 of 939
Full-Text Articles in Chemistry
A High Level Theoretical Investigation Of The Cyclic Hydrogen Fluoride Trimer, Gregory S. Tschumper, Yukio Yamaguchi, Henry F. Schaefer
A High Level Theoretical Investigation Of The Cyclic Hydrogen Fluoride Trimer, Gregory S. Tschumper, Yukio Yamaguchi, Henry F. Schaefer
Chemistry Faculty Research & Creative Works
A high-level ab initio theoretical investigation of the cyclic hydrogen fluoride trimer was carried out. The structures of the hydrogen fluoride monomer, dimer, and trimer were fully optimized at the coupled-cluster level of theory including single, double, and perturbatively applied connected triple excitations [CCSD(T)] using three large basis sets. Geometrical parameters, dipole moments, harmonic vibrational frequencies, infrared intensities, and total energies are reported for each equilibrium structure. Changes in bond lengths and shifts in HF stretching frequencies relative to the monomer, as well as the dissociation energies corresponding to various fragmentation pathways, are given for the dimer, trimer, and their …
Stereoselective Adsorptive Bubble Process, Daniel W. Armstrong, Yubing Tang
Stereoselective Adsorptive Bubble Process, Daniel W. Armstrong, Yubing Tang
Chemistry Faculty Research & Creative Works
Process for enriching the concentration of an enantiomer (or a diastereomer) in a mixture of optically active isomers. The process includes preparing a solution containing the mixture of the optically active isomers and a chiral collector in which the chiral collector and the enantiomer (or diastereomer) are associated with each other. A gas is bubbled through a pool of the solution to form a foam, the surfaces of the bubbles in the foam having the chiral collector and the enantiomer (or diastereomer) preferentially adsorbed thereto so that the concentration ratio of the optically active isomers at said bubble surfaces differs …
Xenon Isotope Record Of Nucleosynthesis And The Early Solar System, Jauh-Tzuoh Lee, Bin Li, Oliver Manuel
Xenon Isotope Record Of Nucleosynthesis And The Early Solar System, Jauh-Tzuoh Lee, Bin Li, Oliver Manuel
Chemistry Faculty Research & Creative Works
No abstract provided.
Magnetic And Structural Properties Of Nd₂Fe₁₇₋ₓmnₓ Solid Solutions, Peter C. Ezekwenna, G. K. Marasinghe, William Joseph James, Oran Allan Pringle, Gary J. Long, H. Luo, Z. Hu, William B. Yelon, Ph. I'Héritier
Magnetic And Structural Properties Of Nd₂Fe₁₇₋ₓmnₓ Solid Solutions, Peter C. Ezekwenna, G. K. Marasinghe, William Joseph James, Oran Allan Pringle, Gary J. Long, H. Luo, Z. Hu, William B. Yelon, Ph. I'Héritier
Chemistry Faculty Research & Creative Works
A series of Nd2Fe17-xMnx solid solutions with x values between 0 and and 6 were prepared and analyzed using magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. All of the Nd2Fe17-xMnx samples crystallized in the Th2Zn17-x-type rhombohedral structure. The lattice parameters and unit cell volumes decrease with increasing manganese content up to ∼ x equal to 2, and then increase for higher manganese content. The magnetizations of Nd2Fe17-xMnx decrease with increasing manganese content and Nd2Fe17-xMnx is paramagnetic …
An Analysis Of Iron-Iron Interatomic Distances In Several Rare Earth Transition Metal Intermetallics, G. K. Marasinghe, Peter C. Ezekwenna, William Joseph James, Z. Hu, William B. Yelon
An Analysis Of Iron-Iron Interatomic Distances In Several Rare Earth Transition Metal Intermetallics, G. K. Marasinghe, Peter C. Ezekwenna, William Joseph James, Z. Hu, William B. Yelon
Chemistry Faculty Research & Creative Works
As a part of a systematic study of the dependence of iron-iron exchange interactions on near neighbor iron-iron distances in rare earth transition metal magnetic materials, we have conducted a statistical analysis of interatomic distances in Nd2Fe17, Nd2Fe17N3, and Nd2Fe14B. Results, in general, support the notion that larger near neighbor iron-iron distances promote higher Curie temperatures. In this work, special attention has been paid to the expansion of the Nd2Fe17 lattice due to interstitial nitrogenation and the accompanying increase in the Curie temperature. …
An Electrical Resistivity Study Of Ce₂Fe₁₆.₈ And The Ce₂Fe₁₇₋ₓalₓ And Ce₂Fe₁₇₋ₓsiₓ Solid Solutions, Denis Vandormael, Fernande Grandjean, Hassan Bougrine, Marcel R. Ausloos, D. P. Middleton, K. H. J. Buschow, Gary J. Long
An Electrical Resistivity Study Of Ce₂Fe₁₆.₈ And The Ce₂Fe₁₇₋ₓalₓ And Ce₂Fe₁₇₋ₓsiₓ Solid Solutions, Denis Vandormael, Fernande Grandjean, Hassan Bougrine, Marcel R. Ausloos, D. P. Middleton, K. H. J. Buschow, Gary J. Long
Chemistry Faculty Research & Creative Works
Electrical resistivity measurements have been carried out between 20 and 300 K on Ce2Fe16.8, on the Ce2Fe17-xAlx. solid solutions, with x = 0.4, 1, 2, 5, 6, 8, and 9, and on the Ce2Fe17-xSix solid solutions, with x = 0.2, 0.4, 1, and 2, with the four probe method. The temperature dependence of the resistivity of Ce2Fe16.8 shows an inflection at 110 K, a feature which is also observed in the temperature dependence of the magnetization and is related to a magnetic …
The Hydroperoxyl Radical Dimer: Triplet Ring Or Singlet String?, Justin T. Fermann, Brian C. Huffman, Gregory S. Tschumper, Henry F. Schaefer
The Hydroperoxyl Radical Dimer: Triplet Ring Or Singlet String?, Justin T. Fermann, Brian C. Huffman, Gregory S. Tschumper, Henry F. Schaefer
Chemistry Faculty Research & Creative Works
In order to determine the lowest energy isomer of the hydroperoxyl radical dimer, H2O4, ab initio quantum mechanical methods were employed to predict the geometrical structures, relative energies, harmonic vibrational frequencies, and associated IR intensities of both open chain and cyclic isomers. Two minima were located on the open chain potential energy surface, one of C2 symmetry and one of C1 symmetry. The relative energies of the different H2O4 structures vary strongly with level of theory. The most reliable treatment used in the present study predicted that the global minimum is the closed-shell C1 chain isomer which …
Chiral Separation Of Monoterpenes Using Mixtures Of Sulfated Β-Cyclodextrins And Α-Cyclodextrin As Chiral Additives In The Reversed-Polarity Capillary Electrophoresis Mode, Kyung Hyun Gahm, Lisa W. Chang, Daniel W. Armstrong
Chiral Separation Of Monoterpenes Using Mixtures Of Sulfated Β-Cyclodextrins And Α-Cyclodextrin As Chiral Additives In The Reversed-Polarity Capillary Electrophoresis Mode, Kyung Hyun Gahm, Lisa W. Chang, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The use of mixtures of sulfated β-cyclodextrins and native α-cyclodextrin as chiral additives in capillary electrophoresis was evaluated for the chiral resolution of neutral, cyclic and bicyclic monoterpenes, including α-pinene, (β-pinene, camphene and limonene. Binding properties of sulfated β-cyclodextrins towards these monoterpenes were studied. It was found that there was no enantioresolution of these terpenoids over the concentration range studied. However, the addition of α-cyclodextrin to the running electrolyte in addition to 6.5 mM sulfated β-cyclodextrins, imparted differences in the mobilities of the terpenoid enantiomers and resulted in remarkable enantiomeric separations of α-pinene (R(s)=25), β-pinene (R(s)=12), camphene (R(s)=12) and limonene …
Crystal Structure Of (Μ-Tranis-4,4'-Dinitro-2,2'-Biimidazolato-N,N: N'',N''') Bis[Bis(Triphenylphosphine Copper(I))] N,N-Dimethylformamide, [C42h37cun4o3p2]2, R. G. Baughman, C. A. Hester, Harvest L. Collier
Crystal Structure Of (Μ-Tranis-4,4'-Dinitro-2,2'-Biimidazolato-N,N: N'',N''') Bis[Bis(Triphenylphosphine Copper(I))] N,N-Dimethylformamide, [C42h37cun4o3p2]2, R. G. Baughman, C. A. Hester, Harvest L. Collier
Chemistry Faculty Research & Creative Works
No abstract provided.
Varietal Differences In The Total And Enantiomeric Composition Of Theanine In Tea, K. Helen Ekborg-Ott, Andre Taylor, Daniel W. Armstrong
Varietal Differences In The Total And Enantiomeric Composition Of Theanine In Tea, K. Helen Ekborg-Ott, Andre Taylor, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Theanine is the main amino acid component in tea. It usually constitutes between 1 and 2% of the dry weight of the tea leaves. It is as prevalent in tea as all other free amino acids combined. Both enantiomers of theanine were found to have a similar sweet taste, with little or no aftertaste. It was found that black and half-green teas (except for Formosa Oolong) contained as much, or more, theanine as green teas. No correlation was found between the absolute concentration of theanine in tea and its enantiomeric composition. An inverse correlation was found between certain grades of …
Immunologic And Hematopoietic Effects Of Cd40 Stimulation After Syngeneic Bone Marrow Transplantation In Mice, Satoshi Funakoshi, Dennis D. Taub, Miriam R. Anver, Arati Raziuddin, Osamu Asai, Prakash Reddy, Helen C. Rager, William C. Fanslow, Dan L. Longo, William J. Murphy
Immunologic And Hematopoietic Effects Of Cd40 Stimulation After Syngeneic Bone Marrow Transplantation In Mice, Satoshi Funakoshi, Dennis D. Taub, Miriam R. Anver, Arati Raziuddin, Osamu Asai, Prakash Reddy, Helen C. Rager, William C. Fanslow, Dan L. Longo, William J. Murphy
Chemistry Faculty Research & Creative Works
CD40 is a molecule present on multiple cell types including B lymphocyte lineage cells. CD40 has been shown to play an important role in B cell differentiation and activation in vitro, although little is known concerning the effects of CD40 stimulation in vivo. We therefore examined the effects of CD40 stimulation in mice using a syngeneic bone marrow transplantation (BMT) model in an effort to augment B cell recovery after high dose therapy with hematopoietic reconstitution. After the BMT, mice were treated with or without 2-6 μg of a soluble recombinant murine CD40 ligand (srmCD40L) given intraperitoneally twice a week. …
Elucidation Of Vancomycin's Enantioselective Binding Site Using Its Copper Complex, Usha B. Nair, Samuel S.C. Chang, Daniel W. Armstrong, Yasir Y. Rawjee, Drake S. Eggleston, James V. Mcardle
Elucidation Of Vancomycin's Enantioselective Binding Site Using Its Copper Complex, Usha B. Nair, Samuel S.C. Chang, Daniel W. Armstrong, Yasir Y. Rawjee, Drake S. Eggleston, James V. Mcardle
Chemistry Faculty Research & Creative Works
Vancomycin forms a stable complex with Cu2+ in neutral aqueous solutions. The enantioselectivity of native vancomycin was compared to that of the copper-vancomycin complex using capillary electrophoresis (CE). There were significant differences in their enantioselectivities. This can be attributed to the fact that copper ion coordinates with some of the same functional groups in vancomycin that are essential for chiral recognition and enantioresolution. An amine moiety that provides one of the more important enantioselective interactions was identified. This chiral interaction site was illustrated using a color-coded, space-filling model of the X-ray crystal structure of the copper-vancomycin complex. Successful enantioselective interactions …
Mechanism Of Signal Suppression By Anionic Surfactants In Capillary Electrophoresis-Electrospray Ionization Mass Spectrometry, Kimber L. Rundlett, Daniel W. Armstrong
Mechanism Of Signal Suppression By Anionic Surfactants In Capillary Electrophoresis-Electrospray Ionization Mass Spectrometry, Kimber L. Rundlett, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Micellar-mediated capillary electrophoresis (CE) is used for a wide variety of applications, including the separation of pharmaceuticals, environmental contaminants, illicit drugs, DNA fragments, and many other biological samples. The electrospray ionization interface is one of the most common CE-MS interfaces. Coupling micellar-mediated CE separations with MS detection combines two very powerful, widely applicable analytical techniques. Some types of surfactants strongly interfere with electrospray ionization mass spectrometric (ESI-MS) detection of analytes, and in many cases the ESI-MS analyte signals are completely quenched. Only a few reports have appeared that describe the ESI-MS detection of analytes in the presence of surfactants; however, …
Investigation On Enantiomeric Separations Of Fluorenylmethoxycarbonyl Amino Acids And Peptides By High-Performance Liquid Chromatography Using Native Cyclodextrins As Chiral Stationary Phases, Y. Tang, J. Zukowski, Daniel W. Armstrong
Investigation On Enantiomeric Separations Of Fluorenylmethoxycarbonyl Amino Acids And Peptides By High-Performance Liquid Chromatography Using Native Cyclodextrins As Chiral Stationary Phases, Y. Tang, J. Zukowski, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
A systematic study was carried out to investigate enantiomeric separations of fluorenylmethoxycarbonyl (FMOC) amino acids and their peptides. Twenty amino acids were derivatized by 9-fluorenylmethyl chloroformate (FMOC-Cl) and its analogues, FMOC-glycyl-Cl and FMOC-β-alanyl-Cl. All derivatives were chromatographed on native β- and γ-cyclodextrin columns using acetonitrile as the main mobile phase component. The results indicated that glycyl and β-alanyl groups between FMOC and amino acid moieties enhanced chiral selectivities of amino acid derivatives. The addition of modifiers, triethylamine, acetic acid and methanol, into the mobile phase caused alterations in retention, enantiorecognition and elution order. The structures of amino acids and the …
Proton Spin-Lattice Relaxation Of Water Molecules In Ferrous-Ferric/Agarose Gel System, Tadashi Tokuhiro, Alan Appleby, Armin A. Leghrouz, Rodney Metcalf, Robert Tokarz
Proton Spin-Lattice Relaxation Of Water Molecules In Ferrous-Ferric/Agarose Gel System, Tadashi Tokuhiro, Alan Appleby, Armin A. Leghrouz, Rodney Metcalf, Robert Tokarz
Chemistry Faculty Research & Creative Works
Proton spin-lattice relaxation time (T1) of water in aqueous solutions of ferrous and ferric ions and in the corresponding agarose gel systems have been studied in the light of NMR relaxation theory. The theoretical analysis of 1/T1's has revealed that, at the microscopic level, changes in the solvation states of paramagnetic ions in aqueous or gel environment are greater than difference in the paramagnetism between ferric and ferrous ions. The former change is the primary factor for the exhibition of radiation effect. At the phenomenological level, we have confirmed and demonstrated that: (1) Radiation effect is …
Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong
Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The structurally related glycopeptide antibiotics vancomycin, ristocetin A, and teicoplanin can all be used as chiral selectors in capillary electrophoresis (CE). Both experimental and modeling studies were done to elucidate their similarities and differences. There are identifiable morphological differences in the aglycon macrocyclic portions of these three compounds. In addition, there are other structural distinctions that can affect their CE enantioselectivity, migration times, and efficiency. Teicoplanin is the most distinct of the three and is the only one that is surface active. Its aggregational properties appear to affect its enantioselectivity among other things. The similar but not identical structures of …
Facile Liquid Chromatographic Enantioresolution Of Native Amino Acids And Peptides Using A Teicoplanin Chiral Stationary Phase, Alain Berthod, Youbang Liu, Christina Bagwill, Daniel W. Armstrong
Facile Liquid Chromatographic Enantioresolution Of Native Amino Acids And Peptides Using A Teicoplanin Chiral Stationary Phase, Alain Berthod, Youbang Liu, Christina Bagwill, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The glycopeptide antibiotic teicoplanin is shown to be a highly effective stationary phase chiral selector for the resolution of underivatized amino-acid and imino-acid enantiomers. Fifty four of these compounds (including all chiral protein amino acids) as well as a number of dipeptides were resolved. Hydro-organic mobile phases are used and no buffers or added salts are needed in most cases. Hence the purified analytes are easily isolated in pure form, if needed, by evaporating of the solvent. The effect of pH, organic modifier type and amount are discussed. The enantioselective separation mechanism is examined using both molecular modeling and retention …
Neutron Diffraction And Mössbauer Spectral Study Of The Nd₂Fe₁₆Ticₓ Solid Solutions, Gaya Kanishka Marasinghe, Peter C. Ezekwenna, William Joseph James, Gary J. Long, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, Fernande Grandjean
Neutron Diffraction And Mössbauer Spectral Study Of The Nd₂Fe₁₆Ticₓ Solid Solutions, Gaya Kanishka Marasinghe, Peter C. Ezekwenna, William Joseph James, Gary J. Long, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, Fernande Grandjean
Chemistry Faculty Research & Creative Works
Three samples of , with x equal to 0.0, 0.3, and 2.8, with the Th2Zn17-type rhombohedral structure, have been studied by powder x-ray and neutron diffraction, magnetic measurements, and Mössbauer spectroscopy. Nd2Fe16Ti and Nd2Fe16TiC0.3 were synthesized by induction melting stoichiometric amounts of the constituent elements, whereas Nd2Fe16TiC2.8 was synthesized by methane-derived gas phase insertion of carbon into finely ground Nd2Fe16Ti at 600 K. The neutron diffraction determined titanium site occupancies are similar in both Nd2Fe16 …
A Spin Reorientation In Pr₂Fe₁₇D₃ As Revealed By Mössbauer Spectroscopy, Fernande Grandjean, Dimitri Hautot, Gary J. Long, Olivier Isnard, Salvatore Miraglia, Daniel Fruchart
A Spin Reorientation In Pr₂Fe₁₇D₃ As Revealed By Mössbauer Spectroscopy, Fernande Grandjean, Dimitri Hautot, Gary J. Long, Olivier Isnard, Salvatore Miraglia, Daniel Fruchart
Chemistry Faculty Research & Creative Works
The Mössbauer effect spectra of Pr2Fe17D3, which have been measured between 85 and 295 K, indicate the presence of a spin reorientation of the iron magnetic moments at 105±5 K. At this magnetic transition a large increase of ~50 kOe in the 6c iron magnetic hyperfine field and abrupt changes in all of the remaining hyperfine fields are observed. A study of the changes in the quadrupole shifts at the transition indicates that this spin reorientation takes place within the basal plane of this rhombohedral compound. As expected, the temperature dependence of the isomer …
Evaluation Of The Concentration And Enantiomeric Purity Of Selected Free Amino Acids In Fermented Malt Beverages (Beers), K. Helen Ekborg-Ott, Daniel W. Armstrong
Evaluation Of The Concentration And Enantiomeric Purity Of Selected Free Amino Acids In Fermented Malt Beverages (Beers), K. Helen Ekborg-Ott, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Even though amino acids are important trace components in the brewing of beers, they have not been extensively evaluated in these beverages. Studies involving the enantiomeric composition of these amino acids are even less prevalent. A brief summary of the brewing process for malt beverages is given. The total concentration and enantiomeric composition of three amino acids (leucine, phenylalanine, and proline) were determined in 25 different beers. Proline tended to have the highest average absolute concentration and the lowest percentage of the D-enantiomer in most samples. In some cases the relative amounts of D-phenylalanine and D-leucine exceeded 10% of the …
A Magnetic Neutron Diffraction, And Mössbauer Spectral Study Of The Ce₂Fe₁₇₋ₓalₓ Solid Solutions, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, Zhongbo Hu, William B. Yelon, Fernande Grandjean, K. H. J. Buschow
A Magnetic Neutron Diffraction, And Mössbauer Spectral Study Of The Ce₂Fe₁₇₋ₓalₓ Solid Solutions, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, Zhongbo Hu, William B. Yelon, Fernande Grandjean, K. H. J. Buschow
Chemistry Faculty Research & Creative Works
The magnetic properties of a series of Ce2Fe17-xAlx solid solutions with x equal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9.08, 9.84, and 10.62 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. The compounds crystallize in the rhombohedral Th2Zn17-type structure. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 384 K for Ce2Fe14Al3 and then decreases at higher aluminum content. Powder neutron diffraction results, obtained at 295 K, indicate that aluminum …
Examination Of The Origin, Variation, And Proper Use Of Expressions For The Estimation Of Association Constants By Capillary Electrophoresis, Kimber L. Rundlett, Daniel W. Armstrong
Examination Of The Origin, Variation, And Proper Use Of Expressions For The Estimation Of Association Constants By Capillary Electrophoresis, Kimber L. Rundlett, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Over the last several decades a variety of techniques have been developed to determine apparent equilibrium constants for molecular association in solution (e.g., to micelles, proteins, cyclodextrins, antibiotics, etc.). The relationships describing binding isotherms appear in several forms and have been given several different names. It is well known that most of these expressions are closely related and that some may be more advantageous than others for experimental or statistical reasons. In the case of electrophoresis, association constants are calculated from the relationship between ligand concentration and the measured electrophoretic mobility of the solute. This relationship has appeared in many …
1,1′-Diketone And 1,1′-Dinitrile Derivatives Of 2,2′-Biimidazole, Paula M. Secondo, William M. Barnett, Harvest L. Collier, Russell G. Baughman
1,1′-Diketone And 1,1′-Dinitrile Derivatives Of 2,2′-Biimidazole, Paula M. Secondo, William M. Barnett, Harvest L. Collier, Russell G. Baughman
Chemistry Faculty Research & Creative Works
The crystal structures of 2,2′-biimidazole-1,1′-diacetone, C12H14N4O2, and 2,2′-biimidazole-1,1′-diacetonitrile, C10H8N6, have been determined. Both molecules crystallize with coplanar rings having substituents in a trans disposition with a center of inversion located midway between the bridging C atoms.
Structures, Thermochemistry, And Electron Affinities Of The Pfn And Pfn- Series, N=1-6, Gregory S. Tschumper, Justin T. Fermann, Henry F. Schaefer
Structures, Thermochemistry, And Electron Affinities Of The Pfn And Pfn- Series, N=1-6, Gregory S. Tschumper, Justin T. Fermann, Henry F. Schaefer
Chemistry Faculty Research & Creative Works
A quantum mechanical study of the phosphorus fluorides and their singly charged anions was carried out. A range of density functional methods was used. Optimized geometries, adiabatic electron affinities, vertical electron affinities, vertical detachment energies, and stabilities toward the loss of a single fluorine atom or fluorine ion are reported. These properties were evaluated exhaustively using four exchange-correlation functionals: Becke's 1988 exchange functional with the correlation functional of Lee, Yang, and Parr, Becke's 1988 exchange functional with the 1986 correlation functional of Perdew, Becke's three parameter Hartree-Fock/density functional hybrid exchange functional with the correlation functional of Lee, Yang, and Parr …
1,1′-Diacetyl-2,2′-Biimidazole, Paula M. Secondo, Colin A. Hester, Harvest L. Collier, Russell G. Baughman, A. W. Cordes
1,1′-Diacetyl-2,2′-Biimidazole, Paula M. Secondo, Colin A. Hester, Harvest L. Collier, Russell G. Baughman, A. W. Cordes
Chemistry Faculty Research & Creative Works
A crystallographic twofold rotation axis passes through the C-C bond joining the imidazole rings of the title compound, C10H10N4O2. the molecule crystallizes in a cis disposition. the planar acetyl group is twisted by 5.0 (3)° with respect to the imidazole ring and the two imidazole rings are tilted by 60.53 (5)° in relation to one another.
Sixth International Symposium On Chiral Discrimination, Daniel W. Armstrong
Sixth International Symposium On Chiral Discrimination, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
No abstract provided.
Capillary Electrophoretic Enantiomeric Separations Using The Glycopeptide Antibiotic, Teicoplanin, Kimber L. Rundlett, Mary P. Gasper, Eve Y. Zhou, Daniel W. Armstrong
Capillary Electrophoretic Enantiomeric Separations Using The Glycopeptide Antibiotic, Teicoplanin, Kimber L. Rundlett, Mary P. Gasper, Eve Y. Zhou, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Teicoplanin is the third in a series of macrocyclic glycopeptide antibiotics that has been evaluated as a chiral selector in capillary electrophoresis (CE). It was used to resolve over 100 anionic racemates at low selector concentrations. Like the other related glycopeptide antibiotics, its enantioselectivity tends to be opposite to that of the ansa-type antibiotics which prefers cationic compounds-particularly amines. Factors that affect teicoplanin-based enantioseparations include the selector concentration, pH, and the concentration of the organic modifier. The temperature and the nature and strength of the buffer are also known to affect the stability of the chiral selector as well as …
Enantiomeric Composition And Prevalence Of Some Bicyclic Monoterpenoids In Amber, Daniel W. Armstrong, Eve Y. Zhou, Janusz Zukowski, Barbara Kosmowska-Ceranowicz
Enantiomeric Composition And Prevalence Of Some Bicyclic Monoterpenoids In Amber, Daniel W. Armstrong, Eve Y. Zhou, Janusz Zukowski, Barbara Kosmowska-Ceranowicz
Chemistry Faculty Research & Creative Works
Among the more prevalent chiral monoterpenoid compounds in conifers are α-pinene, β-pinene, and smaller amounts of camphene and limonene. The most prevalent chiral monoterpenoid compounds in fossilized resin (referred to as amber in this paper) appear to be borneol, isoborneol, and camphene. Most of these compounds have easily measured enantiomeric excesses. The borneol and isoborneol in some amber samples have pronounced enantiomeric excesses despite the fact that they are tens of millions of years old. The enantiomeric ratios of the monoterpenoids in different ambers vary tremendously and often are distinct. However, in any single amber sample, the stereochemistry (absolute configuration) …
Dynamics Of Poly(Vinyl Acetate) In Bulk And On Silica, Frank D. Blum, Gu Xu, Minghua Liang, Charles G. Wade
Dynamics Of Poly(Vinyl Acetate) In Bulk And On Silica, Frank D. Blum, Gu Xu, Minghua Liang, Charles G. Wade
Chemistry Faculty Research & Creative Works
Quadrupole echo deuterium NMR has been used to probe the dynamics of poly(vinyl acetate-d3) in bulk and at saturation coverage (from toluene) on silica at the solid-air interface. In bulk and at lower temperatures, the deuterium powder pattern of the labeled methyl group was found to be consistent with fast threefold jumps with a small asymmetry due to the interaction of the methyl deuteron with the carbonyl oxygen. This apparent asymmetry was a result either of a distortion in the C-C-D bond angle or a reduction of the axial symmetry of the electric field gradient along the C-D bond vector. …
A Magnetic, Neutron-Diffraction, And Mössbauer Spectral Study Of The Ce₂Fe₁₇₋ₓsiₓ Solid Solutions, D. P. Middleton, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, Fernande Grandjean, K. H. J. Buschow
A Magnetic, Neutron-Diffraction, And Mössbauer Spectral Study Of The Ce₂Fe₁₇₋ₓsiₓ Solid Solutions, D. P. Middleton, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, Fernande Grandjean, K. H. J. Buschow
Chemistry Faculty Research & Creative Works
The magnetic properties of a series of Ce2Fe17-xSix solid solutions with x equal to 0.0, 0.23, 0.4, 0.6, 0.8, 1.02, 1.98, and 3.20 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. An x-ray-diffraction study indicates that the compounds adopt the rhombohedral Th2Zn 17-type structure. The substitution of silicon for iron in Ce 2Fe17 leads to a contraction of the a axis by 0.2%, an expansion of the c axis by 0.2%, and a consequent reduction of the unit-cell volume by about 0.2% per substituted silicon. Magnetization studies …