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Articles 691 - 720 of 939
Full-Text Articles in Chemistry
Separation Of Enantiomers By Capillary Electrophoresis Using Pentosan Polysulfate, Xiande Wang, Jauh Tzuoh Lee, Daniel W. Armstrong
Separation Of Enantiomers By Capillary Electrophoresis Using Pentosan Polysulfate, Xiande Wang, Jauh Tzuoh Lee, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Pentosan polysulfate, a semisynthetic polysaccharide, was employed as a chiral un buffer additive in capillary electrophoresis. Twenty-eight racemic analytes were resolved. The separations were successful only at low pH when the analytes were significantly protonated. This suggests that ionic interactions were the dominant associative interactions between the anionic pentosan polysulfate and the positively charged analytes. Compared to other linear, carbohydrate-based chiral selectors (i.e., chondroitin sulfates, heparin and dextran sulfate) pentosan polysulfate has some characteristics common of anionic polysaccharides; yet it has several differences in its structure and properties which account for its unusual enantioselectivity. The effects of pH, concentration of …
Avoparcin, A New Macrocyclic Antibiotic Chiral Run Buffer Additive For Capillary Electrophoresis, K. Helen Ekborg-Ott, Gina A. Zientara, Jeffrey M. Schneiderheinze, Kyung Gahm, Daniel W. Armstrong
Avoparcin, A New Macrocyclic Antibiotic Chiral Run Buffer Additive For Capillary Electrophoresis, K. Helen Ekborg-Ott, Gina A. Zientara, Jeffrey M. Schneiderheinze, Kyung Gahm, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Avoparcin, like vancomycin, teicoplanin, and ristocetin A, belongs to the family of macrocyclic glycopeptide antibiotics. These antibiotics have all been used as effective chiral selectors for capillary electrophoresis (CE), thin-layer chromatography (TLC), and high-performance liquid chromatography (HPLC). The present work focuses on avoparcin, which has been shown to be an excellent chiral selector for the CE enantioseparation of many N-blocked amino acids, as well as several anti-inflammatory drugs of pharmaceutical importance. The use of avoparcin as a chiral run buffer additive in CE is discussed, as well as the effects of changing experimental parameters, like avoparcin concentration, pH, organic modifiers, …
Effect Of Temperature On Retention Of Enantiomers Of Β-Methyl Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong, Géza Tóth, Dirk Tourwé
Effect Of Temperature On Retention Of Enantiomers Of Β-Methyl Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong, Géza Tóth, Dirk Tourwé
Chemistry Faculty Research & Creative Works
The isocratic retention of enantiomers of β-methyl amino acids (β-methyltyrosine, β-methylphenylalanine, β-methyltryptophan and β-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) was studied on a teicoplanin-containing chiral stationary phase at different temperatures and at different mobile phase compositions, using the reversed-phase mode. With variation of both mobile phase composition and temperature, almost baseline separations could be achieved for all four enantiomers of sterically hindered amino acids. The retention factors and selectivity factors for the enantiomers of all investigated compounds decreased with increasing temperature. The natural logarithms of the retention factors (ln k) of the investigated compounds depended linearly on the inverse of temperature (1/T). van 't …
Evaluation Of The Macrocyclic Antibiotic Avoparcin As A New Chiral Selector For Hplc, K. Helen Ekborg-Ott, John P. Kullman, Xiande Wang, Kyung Gahm, Lingfeng He, Daniel W. Armstrong
Evaluation Of The Macrocyclic Antibiotic Avoparcin As A New Chiral Selector For Hplc, K. Helen Ekborg-Ott, John P. Kullman, Xiande Wang, Kyung Gahm, Lingfeng He, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Avoparcin is a macrocyclic glycopeptide antibiotic structurally related to vancomycin, teicoplanin, and ristocetin A. When attached to 5-μm spherical silica gel, the avoparcin proved to be an effective chiral stationary phase (CSP) that could be used in the reversed-phase, normal- phase, and polar-organic modes. The avoparcin CSP was complimentary to the other macrocyclic glycopeptide CSPs in that it could resolve some racemates that the others could not, and vice versa. Some important compounds resolved on the avoparcin CSP include verapamil, thyroxine, mephenytoin, and 2- imidazolidone-4-carboxylic acid. The use of this CSP and the optimization of separations on it are discussed. …
Bubble Fractionation Of Enantiomers From Solution Using Molecularly Imprinted Polymers As Collectors, Daniel W. Armstrong, J. M. Schneiderheinze, Y. S. Hwang, B. Sellergren
Bubble Fractionation Of Enantiomers From Solution Using Molecularly Imprinted Polymers As Collectors, Daniel W. Armstrong, J. M. Schneiderheinze, Y. S. Hwang, B. Sellergren
Chemistry Faculty Research & Creative Works
Adsorptive bubble separation methods have been used to enrich components from both heterogeneous and homogeneous solutions. These methods are particularly effective for processing large solution volumes at low cost Previous work demonstrated that chiral, surface-active collectors could be used to enrich enantiomers from homogeneous solution in a foam fractionation process. In a significant extension of this work, the use of highly selective molecularly imprinted polymers (MIPs) and heterogeneous solutions for the bubble flotation of enantiomers was evaluated. The high selectivity and ease of recycling of the MIP make this a potentially powerful approach for process-scale separations from large-volume bulk solutions. …
Effects Of N-Acetylcysteine And 2,3-Dimercaptosuccinic Acid On Lead Induced Oxidative Stress In Rat Lenses, Rachel Neal, Katherine Cooper, Nuran Ercal, Hande Gürer-Orhan
Effects Of N-Acetylcysteine And 2,3-Dimercaptosuccinic Acid On Lead Induced Oxidative Stress In Rat Lenses, Rachel Neal, Katherine Cooper, Nuran Ercal, Hande Gürer-Orhan
Chemistry Faculty Research & Creative Works
Lead (Pb) is known to disrupt the pro-oxidant/anti-oxidant balance of tissues which leads to biochemical and physiological dysfunction. The present study investigated the previous termeffectsnext term of exposure on the redox status of the lenses of Fisher 344 rats and examined whether antioxidant or chelator administration reversed these changes. Animals were given 5 weeks of 2000 ppm Pb exposure followed by 1 week of either antioxidant, chelator or distilled water administration. Glutathione (GSH) and cysteine (CYS) levels decreased in the Pb-exposed group. N-previous termacetylcysteinenext term or 2,3-dimercaptopsuccinic previous termacidnext term (Succimer) supplementation following Pb intoxication resulted in increases in the …
Highly Enantioselective Hplc Separations Using The Covalently Bonded Macrocyclic Antibiotic, Ristocetin A, Chiral Stationary Phase, K. Helen Ekborg-Ott, Youbang Liu, Daniel W. Armstrong
Highly Enantioselective Hplc Separations Using The Covalently Bonded Macrocyclic Antibiotic, Ristocetin A, Chiral Stationary Phase, K. Helen Ekborg-Ott, Youbang Liu, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The macrocyclic glycopeptide, ristocetin A, was covalently bonded to a silica gel support and evaluated as a liquid chromatographic (LC) chiral stationary phase (CSP). Over 230 racemates were resolved in either the reversed-phase mode, the normal-phase mode, or the polar-organic mode. The retention behavior and selectivity of this CSP were examined in each mode. Optimization of separations on this column is discussed. The ristocetin A CSP appeared to be complimentary to other glycopeptide CSPs (i.e., vancomycin and teicoplanin). Column stability was excellent. The CSP was not irreversibly altered when going from one mobile phase mode to another.
Neutron Diffraction And Mössbauer Spectral Study Of Nd₂Fe₁₆Ti And Its Nitride, Fernande Grandjean, Peter C. Ezekwenna, Gary J. Long, Oran Allan Pringle, P. H. L'Héritier, Mohamed Ellouze, H. P. Luo, William B. Yelon
Neutron Diffraction And Mössbauer Spectral Study Of Nd₂Fe₁₆Ti And Its Nitride, Fernande Grandjean, Peter C. Ezekwenna, Gary J. Long, Oran Allan Pringle, P. H. L'Héritier, Mohamed Ellouze, H. P. Luo, William B. Yelon
Chemistry Faculty Research & Creative Works
The 295 K powder neutron diffraction patterns and the temperature dependence of the Mössbauer spectra of Nd2Fe17-xTix and Nd2Fe17-xTixNx have been measured. A Rietveld refinement of the neutron diffraction patterns yields the Nd2Fe16.32Ti0.68 and Nd2Fe16.32Ti0.68N2.7 stoichiometries for the two compounds and indicates that titanium occupies only the 6c crystallographic site and nitrogen only the 9e site in the rhombohedral Th2Zn17 structure. The insertion of interstitial nitrogen into Nd2Fe16.32Ti0.68 …
Enantiomeric Separation Of Unusual Secondary Aromatic Amino Acids, A. Péter, G. Török, G. Tóth, W. Van Den Nest, G. Laus, D. Tourwé, Daniel W. Armstrong
Enantiomeric Separation Of Unusual Secondary Aromatic Amino Acids, A. Péter, G. Török, G. Tóth, W. Van Den Nest, G. Laus, D. Tourwé, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
High-performance liquid chromatographic and gas chromatographic methods were developed for the separation of unusual secondary aromatic amino acids. Amino acids containing 1,2,3,4-tetrahydroisoquinoline, 1,2,3,4-tetrahydronorharmane-1-carboxylic acid and 1,2,3,4-tetrahydro-3-carboxy-2-carboline moieties were synthetized in racemic or chiral forms. The high-performance liquid chromatography was carried out either on a teicoplanin-containing chiral stationary phase or on an achiral C18 column. In the latter case the diastereomers of the amino acids formed by precolumn derivatization with the chiral reagents 2,3,3,6-tetra-O-acetyl-β-D-glucopyranosyl isothiocyanate or 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide were separated. The gas chromatographic analyses were based on separation on a Chirasil-L-Val column.
A Mössbauer Spectral Study Of Tb₂Fe₁₇ And The Tb₂Fe₁₇₋ₓsiₓ Solid Solutions, Dimitri Hautot, Gary J. Long, Peter C. Ezekwenna, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow
A Mössbauer Spectral Study Of Tb₂Fe₁₇ And The Tb₂Fe₁₇₋ₓsiₓ Solid Solutions, Dimitri Hautot, Gary J. Long, Peter C. Ezekwenna, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow
Chemistry Faculty Research & Creative Works
The Mössbauer spectra of a series of rhombohedral Tb2Fe17-xSix solid solutions, with x equal to 0, 1, 2, and 3, have been measured as a function of temperature. Although the spectra of Tb2Fe17 change substantially upon cooling from 295 to 85 K, it has been possible to fit them with a consistent seven sextet model corresponding to a basal magnetization. The spectral analysis yields reasonable hyperfine parameters and the expected changes with temperature. The resulting weighted average effective iron recoil mass of 66 g/mol and the Mössbauer temperature of 395 K are …
A Comparison Between The Cisd[Tq] Wave Function And Other Highly Correlated Methods: Molecular Geometry And Harmonic Vibrational Frequencies Of Mgh2, Gregory S. Tschumper, Henry F. Schaefer
A Comparison Between The Cisd[Tq] Wave Function And Other Highly Correlated Methods: Molecular Geometry And Harmonic Vibrational Frequencies Of Mgh2, Gregory S. Tschumper, Henry F. Schaefer
Chemistry Faculty Research & Creative Works
The linear MgH2 molecule was selected as a model system to compare the total electronic energy (ETOT). equilibrium bond length (re), and vibrational frequency (ωn) predictions from six different configuration interaction (CI) and coupled cluster (CC) methods using three large correlation consistent basis sets. The three CI procedures employed incorporated all single and double substitutions (CISD) as well as all triple and quadruple substitutions (CISDTQ) or limited triple and quadruple substitutions (CISD[TQ]). The remaining three CC schemes included all single and double excitations (CCSD) as well as all triple excitations (CCSDT) or a perturbative approximation of the triple excitations [CCSD(T)]. …
Particle Concentration Characterization For Jet Engine Emissions Under Cruise Conditions, Jonathan D. Paladino, Philip D. Whitefield, Donald E. Hagen, Alfred R. Hopkins, Max B. Trueblood
Particle Concentration Characterization For Jet Engine Emissions Under Cruise Conditions, Jonathan D. Paladino, Philip D. Whitefield, Donald E. Hagen, Alfred R. Hopkins, Max B. Trueblood
Chemistry Faculty Research & Creative Works
Airborne particle measurements during NASA project SUCCESS have shown that particle concentration profiles serve as good indicators of aircraft exhaust plume encounters. During exhaust plume penetrations there is a strong anticorrelation between the ratio of nonvolatile/total particulates and Nitrogen Oxide (NO) concentrations. an increase in fuel sulfur content was found to increase the total particle emission index, while the nonvolatile emission index remained unchanged. the EI's increased by a factor of 2.6 as the fuel sulfur increased from 70 - 700 ppm. the large particle size distribution (200-400 nm) was seen as a good long term indicator of an aircraft …
Mössbauer-Effect And X-Ray-Absorption Spectral Study Of Sonochemically Prepared Amorphous Iron, Gary J. Long, Dimitri Hautot, Quentin A. Pankhurst, Denis Vandormael, Fernande Grandjean, Jean Pierre Gaspard, Valérie Briois, Taeghwan Hyeon, Kenneth S. Suslick
Mössbauer-Effect And X-Ray-Absorption Spectral Study Of Sonochemically Prepared Amorphous Iron, Gary J. Long, Dimitri Hautot, Quentin A. Pankhurst, Denis Vandormael, Fernande Grandjean, Jean Pierre Gaspard, Valérie Briois, Taeghwan Hyeon, Kenneth S. Suslick
Chemistry Faculty Research & Creative Works
The Mössbauer spectra of amorphous iron, prepared by using sonochemical methods, exhibit a broad magnetic hyperfine sextet at both 78 and 295 K. The spectra do not change with time if the amorphous iron is not exposed to oxygen or moisture. An analysis of the spectra with the method of Lines and Eibschütz yields average magnetic hyperfine fields of 29.1 and 25.9 T at 78 and 295 K, respectively. The corresponding moments of 1.9B and 1.7B agree well with values obtained from earlier magnetization studies and, further, provide strong experimental support for earlier calculations of the magnetic moments …
Quantitative And Stereoisomeric Determination Of Light Biomarkers In Crude Oil And Coal Samples, Alain Berthod, Xiande Wang, Kyung H. Gahm, Daniel W. Armstrong
Quantitative And Stereoisomeric Determination Of Light Biomarkers In Crude Oil And Coal Samples, Alain Berthod, Xiande Wang, Kyung H. Gahm, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Indans and tetralins are considered biological markers (biomarkers). These C9-C11 hydrocarbons are present in small amounts in organic geological samples. Methyl substituted indans or tetralins may possess a stereogenic center (carbon). Thus they can exist as enantiomers and, in the case of disubstituted enties, also as diastereoisomers. The concentrations of 1-methylindan, 1,3-dimethylindan, 1-methyltetralin, and 2-methyltetralin were determined in 16 crude oil samples of different sources and in 14 coal samples of different sources and ranks. Deuterated homologues were synthesized as standards to spike the samples and to assure accurate quantitative analysis. A procedure using HPLC fractionation followed by GC/MS analysis …
Characterization And Evaluation Of D-(+)-Tubocurarine Chloride As A Chiral Selector For Capillary Electrophoretic Enantioseparations, Usha B. Nair, Daniel W. Armstrong, Willie L. Hinze
Characterization And Evaluation Of D-(+)-Tubocurarine Chloride As A Chiral Selector For Capillary Electrophoretic Enantioseparations, Usha B. Nair, Daniel W. Armstrong, Willie L. Hinze
Chemistry Faculty Research & Creative Works
A new macrocyclic of the bis(benzylisoquinoline) alkaloid family, d- (+)-tubocurarine chloride (DTC), has been evaluated as a chiral selector for the separation of optical isomers of organic carboxylates using capillary electrophoresis (CE). The pertinent physicochemical properties, such as absorption spectrum, isoionic point, and solution conformation, of DTC were determined. The effects of varying such experimental parameters as DTC concentration, pH, and methanol content in the running buffer were assessed. CE separation of the enantiomers of 18 different compounds was achieved using DTC as the chiral selector under optimized background electrolytic conditions.
A Mössbauer Spectral Study Of Nd₆Fe₁₃X, Where X Is Cu, Ag, And Au And Of The Spin Reorientation In Nd₆Fe₁₃Si, Dimitri Hautot, Gary J. Long, Fernande Grandjean, C. H. De Groot, K. H. Buschow
A Mössbauer Spectral Study Of Nd₆Fe₁₃X, Where X Is Cu, Ag, And Au And Of The Spin Reorientation In Nd₆Fe₁₃Si, Dimitri Hautot, Gary J. Long, Fernande Grandjean, C. H. De Groot, K. H. Buschow
Chemistry Faculty Research & Creative Works
The Mössbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 80 and 500 K. A model corresponding to a basal alignment of the magnetic moments leads to excellent, internally consistent, fits for the Cu, Ag, and Au compounds. The resulting temperature dependences of the spectral hyperfine parameters are uniform and reveal for each Fe site the expected correlations between the isomer shift and the Wigner-Seitz cell volume and the hyperfine field and the number of Fe near neighbors. For Nd6Fe13Si, a different model must be …
High-Performance Liquid Chromatographic Separation Of Enantiomers Of Unusual Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong
High-Performance Liquid Chromatographic Separation Of Enantiomers Of Unusual Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
A glycopeptide antibiotic, teicoplanin, was used as chiral stationary phase for the high-performance liquid chromatographic (HPLC) separation of enantiomers of more than 30 unnatural amino acids, such as phenylalanine and tyrosine analogues and analogues containing 1,2,3,4-tetrahydroisoquinoline, tetraline, 1,2,3,4-tetrahydro-2-carboline, cyclopentane, cyclohexane, cyclohexene, bicyclo[2.2.1]heptane or heptene skeletons. Excellent resolutions were achieved for most of the investigated compounds by using a hydro-organic mobile-phase system. The effects of organic modifier content, temperature and flow-rate on the resolution were investigated and the conditions of separation were optimized.
Chiral Separations Of Indan, Tetralin And Benzosuberan Derivatives By Capillary Electrophoresis, Kyung Hyun Gahm, Jauh Tzuoh Lee, Lisa W. Chang, Daniel W. Armstrong
Chiral Separations Of Indan, Tetralin And Benzosuberan Derivatives By Capillary Electrophoresis, Kyung Hyun Gahm, Jauh Tzuoh Lee, Lisa W. Chang, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Several indan, tetralin and benzosuberan derivatives of diverse polarities were enantio-resolved by the use of sulfated β-cyclodextrins (CDs) or mixtures of sulfated β-CDs and γ-CD as chiral additives in capillary electrophoresis. Mixtures of sulfated 13-CDs and hydroxypropy1 β- CDs were also successfully utilized for enantiomeric and diastereomeric separations of some of the tetralin derivatives with two stereogenic centers. Both neutral and anionic analytes were resolved in the reversed electrophoretic polarity mode. Cationic amino derivatives of indan and tetralin were enantio-resolved in the conventional electrophoretic polarity mode.
Mechanism Of Capillary Electrophoresis Enantioseparations Using A Combination Of An Achiral Crown Ether Plus Cyclodextrins, Daniel W. Armstrong, L. W. Chang, S. S.C. Chang
Mechanism Of Capillary Electrophoresis Enantioseparations Using A Combination Of An Achiral Crown Ether Plus Cyclodextrins, Daniel W. Armstrong, L. W. Chang, S. S.C. Chang
Chemistry Faculty Research & Creative Works
The addition of an achiral crown ether (18-crown-6) to a cyclodextrin- based separation can significantly affect the capillary electrophoresis (CE) enantioresolution of organic racemates that contain a primary amine functional group. In most cases an enhancement of the enantioseparation was observed. However, there are also cases where the addition of 18-crown-6 was detrimental to a cyclodextrin-based CE enantioseparation. The effect of concentration of the two complexing additives as well as the effect of pH and added potassium ion were examined. A specific three-body complex involving simultaneous, dual inclusion complex formation can be used to explain both the enhanced and diminished …
Visual Form Of Alzheimer's Disease And Its Response To Anticholinesterase Therapy, Stacey Warren, Daniel B. Hier, Dan Pavel
Visual Form Of Alzheimer's Disease And Its Response To Anticholinesterase Therapy, Stacey Warren, Daniel B. Hier, Dan Pavel
Chemistry Faculty Research & Creative Works
In a 60-Year-Old Woman with the Visual Variant of Alzheimer's Disease, Single Photon Emission Computed Tomography Abnormalities Were Most Marked in the Parieto-Occipital Regions of the Brain. after Treatment with Donepezil, Improvement is Noted on Neuropsychological Testing and on Brain SPECT, Including Increased Perfusion (Metabolism) in the Occipital Lobes.
Pressure Induced Reversal Of The Volume Expansion Caused By Interstitial Nitrogen In Nd2fe17n3, G. K. Marasinghe, William Joseph James, P. C. Ezekwenna, H. Luo, W. B. Yelon, Y. Zhao, R. B. Von Dreele, M. Ellouze, Ph L'Héritier
Pressure Induced Reversal Of The Volume Expansion Caused By Interstitial Nitrogen In Nd2fe17n3, G. K. Marasinghe, William Joseph James, P. C. Ezekwenna, H. Luo, W. B. Yelon, Y. Zhao, R. B. Von Dreele, M. Ellouze, Ph L'Héritier
Chemistry Faculty Research & Creative Works
Crystallographic properties of Nd2Fe17N3 have been investigated using powder neutron diffraction techniques at pressures up to 7.3 GPa. With increasing pressure, the unit cell volume of Nd 2Fe17N3 decreases almost linearly at a rate of 6.1 Å3/GPa without undergoing a phase transformation or expelling the interstitial nitrogen atoms. The observed rate of contraction corresponds to a bulk modulus of 1.4x1011 N/m2 for Nd2Fe17N3. The unit cell volume of Nd 2Fe17N3 at 7.3 GPa is approximately equal to that of Nd2Fe17 at atmospheric pressure. Even though the unit cell of Nd2Fe17 expands anisotropically due to nitrogenation, contraction of the Nd2Fe17N3 unit …
The Evolution Of Chiral Stationary Phases For Liquid Chromatography, Daniel W. Armstrong
The Evolution Of Chiral Stationary Phases For Liquid Chromatography, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The development of effective chiral stationary phases (CSPs) and separation strategies for the liquid chromatographic (LC) resolution of enantiomers has been beneficial to many scientific disciplines. Over the last decade the number and type of CSPs has expanded tremendously. Not only have new classes of chiral selectors been introduced, but also many of the first CSPs have been changed and/or improved. The second or third generation of a CSP often can be different from the original. This can be confusing and intimidating to someone just entering the area of LC enantiomeric separations. Fortunately, all CSPs can be categorized in one …
Deuterium Nmr Of Adsorbed Poly(Methyl Acrylate)-D₃, Frank D. Blum, Wuu-Yung Lin
Deuterium Nmr Of Adsorbed Poly(Methyl Acrylate)-D₃, Frank D. Blum, Wuu-Yung Lin
Chemistry Faculty Research & Creative Works
The dynamics of polymers at interfaces are important in a variety of applications, especially where those applications depend on the mechanical or surface properties. Unfortunately, the surface properties of interfacial species like polymers used in composites are not easily measured macroscopically. Microscopic techniques, especially spectroscopic ones, have been successful. In our laboratory we have been successful in applying NMPR to determine the behavior of absorbed polymers. NMR has several advantages for this kind of study, the principal ones being that it can be used on opaque materials, different nuclei can be used as probes, and interfacial material can sometimes be …
Structural And Magnetic Properties Of Rsr₂Fe₃O₉ (R=La, Y, Pr, And Gd), I. Felner, I. Nowik, A. Mehta, Rajvir Singh, William B. Yelon, V. P. S. Awana, S. X. Dou, Satish K. Malik, A. V. Narlikar
Structural And Magnetic Properties Of Rsr₂Fe₃O₉ (R=La, Y, Pr, And Gd), I. Felner, I. Nowik, A. Mehta, Rajvir Singh, William B. Yelon, V. P. S. Awana, S. X. Dou, Satish K. Malik, A. V. Narlikar
Chemistry Faculty Research & Creative Works
No abstract provided.
Methods Of Preparing Three-Dimensional, Macroscopic Assemblages Of Carbon Fibrils And The Products Obtained Thereby, Hyperion Catalysis International, Inc., Howard Tennent, Robert W. Hausslein, Nicholas Leventis, David Moy
Methods Of Preparing Three-Dimensional, Macroscopic Assemblages Of Carbon Fibrils And The Products Obtained Thereby, Hyperion Catalysis International, Inc., Howard Tennent, Robert W. Hausslein, Nicholas Leventis, David Moy
Chemistry Faculty Research & Creative Works
A method of making randomly oriented carbons fibrils having a cylindrical constant diameter with c-axes perpendicular to their cylindrical axis, which are free of pyrolytically deposited carbon, with a diameter of between 3.5 and 70 nanometers, by dispersing carbon fibrils in a medium and separating them from the medium, by filtration or evaporation to form a porous mat or sheet.
Kurt Mislow Honorary Issue Of Chirality, Daniel W. Armstrong
Kurt Mislow Honorary Issue Of Chirality, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
No abstract provided.
Temperature-Dependence Studies Of Photorefractive Effect In A Low Glass-Transition-Temperature Polymer Composite, Bogdan Swedek, Ning Cheng, Yiping Cui, Jaroslaw W. Zieba, Jeffrey G. Winiarz, Paras N. Prasad
Temperature-Dependence Studies Of Photorefractive Effect In A Low Glass-Transition-Temperature Polymer Composite, Bogdan Swedek, Ning Cheng, Yiping Cui, Jaroslaw W. Zieba, Jeffrey G. Winiarz, Paras N. Prasad
Chemistry Faculty Research & Creative Works
The temperature dependence of the photorefractive effect in a polymer composite containing poly(9-vinycarbazole), tricresyl phosphate, buckminsterfullerene, and 4-(N,N-diethylamino)-β-nitrostyrene is presented. The photoconductive, electro-optic and photorefractive properties of the material have been studied in the temperature range of 22-61°C. An apparent increase of electro-optic modulation with temperature and its eventual saturation is observed. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. The polarization anisotropy between the p- and s-polarized readouts is consistent with what would be expected on the basis of directly measured effective electro-optic coefficients. By correlating the electro-optic value with the diffraction …
Scanning Probe Nanolithography Of Conducting Metal Oxides, Chen-Jen Hung, Jianian Gui, Jay A. Switzer
Scanning Probe Nanolithography Of Conducting Metal Oxides, Chen-Jen Hung, Jianian Gui, Jay A. Switzer
Chemistry Faculty Research & Creative Works
The scanning tunneling microscope (STM) was used to form nanometer-size holes in thin conducting films of thallium (III) oxide. Hole formation was only observed when the process was performed in humid ambient conditions. The hole formation was attributed to localized electrochemical etching reactions beneath the STM tip. etching reactions consistent with the observed hole formation are a direct electrochemical reduction of thallium (III) oxide to soluble T1 (I) at negative sample bias, and local reduction of pH at positive sample bias. The fastest etching was observed at negative sample bias. Holes as small as 10 nm or as large as …
X-Ray-Absorption Spectral Study Of The R₂Fe₁₇₋ₓmₓ Solid Solutions (R=Ce, Nd And M=Al, Si), Denis Vandormael, Fernande Grandjean, Valérie Briois, D. P. Middleton, K. H. Buschow, Gary J. Long
X-Ray-Absorption Spectral Study Of The R₂Fe₁₇₋ₓmₓ Solid Solutions (R=Ce, Nd And M=Al, Si), Denis Vandormael, Fernande Grandjean, Valérie Briois, D. P. Middleton, K. H. Buschow, Gary J. Long
Chemistry Faculty Research & Creative Works
The x-ray-absorption near-edge structure (XANES) spectra obtained at the cerium LIII edge of the Ce2Fe17-xAlx solid solutions and Ce2Fe14Si3, show two absorption peaks characteristic of the 4f1 and 4f0 configurations of cerium, peaks which indicate that cerium is in a mixed valent state in these compounds. All the XANES spectra have been consistently and excellently fit with one sigmoidal function and two Gaussianbroadened Lorentzian functions. The cerium spectroscopic valence obtained from the relative areas of the two peaks decreases from 3.64 to 3.43 between x=0 and …
Predicting Electron Affinities With Density Functional Theory: Some Positive Results For Negative Ions, Gregory S. Tschumper, Henry F. Schaefer
Predicting Electron Affinities With Density Functional Theory: Some Positive Results For Negative Ions, Gregory S. Tschumper, Henry F. Schaefer
Chemistry Faculty Research & Creative Works
The atomic electron affinities of the eight first row (H,Li,...,F) atoms as well as the adiabatic electron affinities of 12 first row diatomic and 15 first row triatomic molecules were determined using six different densities functional or hybrid Hartree-Fock/density functional methods. The 35 species were selected for having relatively well-established experimental electron affinities. Harmonic zero-point vibrational energy corrected electron affinities are also reported for the diatomic and triatomic molecules. Equilibrium geometries and harmonic vibrational frequencies are given for the 27 molecules and their anions as determined with each density functional method. Discussion focuses on comparison of theoretical and experimental electron …