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Full-Text Articles in Physical Sciences and Mathematics

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 Dec 1996

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 Oct 1996

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 Sep 1996

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 Sep 1996

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 …


Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow Aug 1996

Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow

Physics Faculty Research & Creative Works

Six samples of Ce2Fe17-xGax with nominal Ga content x equal to 0, 0.3, 0.5, 0.7, 1.0, 2.0 have been studied by powder neutron diffraction at room temperature. Both crystalline and magnetic refinements have been carried out. All six samples adopt the Th2Zn17-type rhombohedral structure. The only additional phase found is α-iron. Gallium atoms are found to have high affinity for the iron 18h site, and are absent from the 9d and 18f sites. The Ga substitution for Fe leads to an expansion of both the a and c axes. The Curie …


Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong Aug 1996

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 Apr 1996

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 Magnetic Studies Of Rfe₁₂₋ₓtₓcY (R=Y,Er; T=V,Ti,Mo) Alloys, Z. Hu, William B. Yelon, X. D. Zhang, William Joseph James Apr 1996

Neutron Diffraction And Magnetic Studies Of Rfe₁₂₋ₓtₓcY (R=Y,Er; T=V,Ti,Mo) Alloys, Z. Hu, William B. Yelon, X. D. Zhang, William Joseph James

Physics Faculty Research & Creative Works

RFe12-xTxCy, (R=Y,Er; T=V,Ti,Mo) alloys were prepared by rf induction melting and analyzed using neutron powder diffraction and superconducting quantum interference device (SQUID) measurements. Rietveld analysis of the neutron diffraction data indicates that V, Ti, and Mo atoms all prefer the 8i sites. The refined amount of carbon atoms found in the interstitial sites from neutron diffraction data is significantly less than the nominal carbon content. All samples have the easy direction along the c axis. The Er sublattice couples to the Fe sublattice antiferromagnetically. The average Fe site moments range from 1.3 to 2.8 …


Neutron Diffraction Studies Of Ndₙfeₘ₋ₓ₋YVₓalY [(N,M)=(1,12), (2,17), (3,29)], Z. Hu, William B. Yelon, William Joseph James Apr 1996

Neutron Diffraction Studies Of Ndₙfeₘ₋ₓ₋YVₓalY [(N,M)=(1,12), (2,17), (3,29)], Z. Hu, William B. Yelon, William Joseph James

Physics Faculty Research & Creative Works

Several NdnFem-x-yVxAly [(n,m)=(1,12), (2,17), (3,29)] samples were prepared and analyzed using neutron powder diffraction. Rietveld analysis of the neutron diffraction data indicates that the V and Al substituents take those sites with similar environments in all three phases, as observed in our previous study of Ti-substituted compounds. It was confirmed that the diffraction data of the 3:29 compound can be better refined using the A2/m space group than using the P21/c space group. The SQUID measurements show that all samples have Curie temperatures well above room temperature. The neutron diffraction results …


Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe Apr 1996

Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe

Physics Faculty Research & Creative Works

In order to understand the magnetic properties of the substituted rare-earth-iron alloys, it is especially important to know the location of the substitutional atoms within the iron lattice. The site distributions of some nontransition-metal substituents in the substituted Nd2Fe17-xTx alloys have previously been reported. Here we report the site distributions of some transition-metal substituents (Cu,Zr,Nb,Ti,V) in the Nd2Fe17-xTx alloys and compare them with those of the nontransition-metal substituted compounds. Rietveld analysis of neutron powder diffraction data indicates that the nontransition-metal substituents show very similar site affinity at low substituent content. …


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 Apr 1996

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 Apr 1996

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 Mar 1996

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 Mar 1996

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 Jan 1996

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 Jan 1996

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.


1,1′-Diacetyl-2,2′-Biimidazole, Paula M. Secondo, Colin A. Hester, Harvest L. Collier, Russell G. Baughman, A. W. Cordes Jan 1996

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.


Neutron Diffraction And Magnetic Studies Of Nd₂Fe₁₇₋ₓtₓ (T=Si, Mn) Alloys, William B. Yelon, Z. Hu, Mingxing Chen, H. Luo, F. Pourarian, Peter C. Ezekwenna, G. K. Marasinghe, K. H. J. Buschow, D. P. Middleton, William Joseph James Jan 1996

Neutron Diffraction And Magnetic Studies Of Nd₂Fe₁₇₋ₓtₓ (T=Si, Mn) Alloys, William B. Yelon, Z. Hu, Mingxing Chen, H. Luo, F. Pourarian, Peter C. Ezekwenna, G. K. Marasinghe, K. H. J. Buschow, D. P. Middleton, William Joseph James

Physics Faculty Research & Creative Works

We have carried out neutron and magnetic studies on Nd2Fe17-xTx (T=Si, Mn) alloys. the unit cell of the compounds contracts with both Si and Mn substitution. Si atoms avoid the 6c site, prefer the 18h site strongly, fill the 9d site steadily and fill the 18f site only at relatively high Si concentration. Mn atoms avoid the 9d sites but prefer the 6c site strongly, while the 18f site and 18h site fill slowly. the Si site occupancies appear to be dominated by the crystal environment while the Mn site occupancies are dominated by steric …


Enantiomeric Composition And Prevalence Of Some Bicyclic Monoterpenoids In Amber, Daniel W. Armstrong, Eve Y. Zhou, Janusz Zukowski, Barbara Kosmowska-Ceranowicz Jan 1996

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) …


Capillary Electrophoretic Enantiomeric Separations Using The Glycopeptide Antibiotic, Teicoplanin, Kimber L. Rundlett, Mary P. Gasper, Eve Y. Zhou, Daniel W. Armstrong Jan 1996

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 …


Dynamics Of Poly(Vinyl Acetate) In Bulk And On Silica, Frank D. Blum, Gu Xu, Minghua Liang, Charles G. Wade Jan 1996

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. …


Sixth International Symposium On Chiral Discrimination, Daniel W. Armstrong Jan 1996

Sixth International Symposium On Chiral Discrimination, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

No abstract provided.


Biodegradation Of Nonionic Surfactants And Effects Of Oxidative Pretreatment, Craig D. Adams, S. Spitzer, R. M. Cowan Jan 1996

Biodegradation Of Nonionic Surfactants And Effects Of Oxidative Pretreatment, Craig D. Adams, S. Spitzer, R. M. Cowan

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

The aerobic biodegradability of nonionic, ethoxylated surfactants and model compounds, and the effect of advanced oxidation pretreatment on the biodegradability of the biorefractory surfactants were examined. Bioassays conducted using a mixed microbial seed showed that the linear primary alcohol ethoxylates, the fatty acid ethoxylates, and also polyethylene glycol were all degradable. The biomineralization of the linear secondary alcohol ethoxylate, ethylene oxide/propylene oxide block copolymer, and alkylphenol ethoxylate was observed to be inhibited to varying degrees. Additional bioassays were conducted on model compounds to examine the effect of specific structural components on biodegradability. Advanced oxidation pretreatment using hydrogen peroxide in combination …


Treatability Of S-Triazine Herbicide Metabolites Using Powdered Activated Carbon, Craig D. Adams, Tammy L. Watson Jan 1996

Treatability Of S-Triazine Herbicide Metabolites Using Powdered Activated Carbon, Craig D. Adams, Tammy L. Watson

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

Widespread use of s-triazine herbicides such as atrazine, simazine, and cyanazine has led to the contamination of many ground-water and surface-water supplies with the parent compounds as well as by primary metabolites (e.g., deethylatrazine, deisopropylatrazine, and deethylcyanazine). Ozonation has been shown to produce many of the same byproducts. Activated carbon adsorption has been designated by the U.S. Environmental Protection Agency as the best available technology (BAT) for the treatment of herbicides in drinking water. Little data is available, however, on the applicability of activated carbon treatment for the control of the primary degradation products of herbicides. In this study, the …