Chemistry Commons^™

Magnetic Properties Of The Mnbi Intermetallic Compound, Jinbo Yang, Kishore Kamaraju, William B. Yelon, William Joseph James, Qingsheng Cai, A. Bollero

Physics Faculty Research & Creative Works

A MnBi alloy containing over 90 wt% low-temperature phase (LTP) has been obtained by high-temperature sintering and magnetic purification. The coercivity of the bonded MnBi magnet increases with increasing temperatures. A coercivity of 2.0 T has been achieved at 400 K. The maximum energy product (BH)_max; of the magnet is 7.7 MGOe (61 kJ/m³) and 4.6 MGOe (37 kJ/m³) at room temperature and 400 K, respectively. Neutron diffraction and magnetic data reveal a spin reorientation, which gives rise to low anisotropy fields and coercivity at lower temperatures for the LTP MnBi alloy.

Magnetic And Conversion Electron Mössbauer Spectral Study Of Amorphous Thin Films Of Dyₓfe₁₀₀₋ₓ And Dy₂₀Fe80-YCoY, Karl Fleury-Frenette, Jacques P. Delwiche, Fernande Grandjean, Denis Vandormael, Gary J. Long

Chemistry Faculty Research & Creative Works

Amorphous thin films of Dy_xFe_100-x and Dy₂₀Fe_80-yCo_y, with various x and y values and of ~40 nm thickness, have been prepared by sputtering on polyimide films. Their magnetization curves and the Mössbauer spectra indicate that at 295 K the iron moments are preferentially oriented parallel to the film in Dy₂Fe₉₈ and that Dy₆Fe₉₄ is paramagnetic. The Dy_xFe_100-x thin films, where x is 17, 20, 24, 29, 32, 35, and 37, show perpendicular magnetic anisotropies and moderate coercive fields of at most 150 …

Surfactant-Assisted Synthesis Of Semiconductor Nanotubes And Nanowires, Chintamani Nagesa Ramachandra Rao, A. Govindaraj, F. L. Deepak, N. A. Gunari, Manashi Nath

Chemistry Faculty Research & Creative Works

Nanotubes and nanowires of CdSe and CdS have been obtained from solutions containing a surfactant such as Triton 100-X. They have been characterized by x-ray diffraction, electron microscopy, and optical spectroscopy.

Synthons And Design In Metal Phosphates And Oxalates With Open Architectures, Chintamani Nagesa Ramachandra Rao, Srinivasan R. Natarajan, Amitava Choudhury, Sharma Neeraj, Ramamurthy Vaidhyanathana

Chemistry Faculty Research & Creative Works

We briefly describe the structures of open-framework metal phosphates with different dimensionalities, such as the one-dimensional linear-chain and ladder structures, two-dimensional layer structures and three-dimensional structures with channels. We demonstrate the role of the zero-dimensional four-membered ring monomer and of the one-dimensional ladder structure as the starting building units or synthons involved in the formation of the complex architectures. Thus, we show how the one-dimensional ladder structure transforms to two- and three-dimensional structures under mild conditions. The two-dimensional layer structures also transform to three-dimensional structures, while the zero-dimensional monomer transforms to layered and three-dimensional structures under ordinary reaction conditions. These …

Probing The Relative Timing Of Hydrogen Abstraction Steps In The Flavocytochrome B2 Reaction With Primary And Solvent Deuterium Isotope Effects And Mutant Enzymes, P. Sobrado, S. C. Daubner, P. F. Fitzpatrick

Chemistry Faculty Research & Creative Works

Flavocytochrome b2 catalyzes the oxidation of lactate to pyruvate. Primary deuterium and solvent kinetic isotope effects have been used to determine the relative timing of cleavage of the lactate O - H and C - H bonds by the wild-type enzyme, a mutant protein lacking the heme domain, and the D282N enzyme. The DVmax and D(V/Klactate) values are both 3.0 with the wild-type enzyme at pH 7.5 and 25 °C, increasing to about 3.6 with the flavin domain and increasing further to about 4.5 with the D282N enzyme. Under these conditions, the D20Vmax values are 1.38, 1.18, and 0.98 for …

High-Performance Liquid Chromatographic And Capillary Electrophoretic Enantioseparation Of Plant Growth Regulators And Related Indole Compounds Using Macrocyclic Antibiotics As Chiral Selectors, F. Hui, K. H. Ekborg-Ott, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Enantioseparation of plant growth regulators, such as 3-(3-indolyl)-butyric acid, abscisic acid and structurally related molecules including a variety of substituted tryptophan compounds, has been achieved by HPLC and/or CE. The covalently bonded macrocyclic antibiotics, teicoplanin, ristocetin A and vancomycin, were used as chiral stationary phases (CSPs) in HPLC. Most of the racemates were baseline resolved in the reversed-phase mode (EtOH-H2O) using the teicoplanin CSP. The chiral recognition mechanism is discussed in regard to the structure of the analytes. In CE, the three aforementioned macrocyclic antibiotics were used as chiral additives in a phosphate run buffer. The effect of pH and …

Electronic Structures And Magnetism Of Lani₅₋ₓfeₓ Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James

Physics Faculty Research & Creative Works

A systematic study of the magnetic moments and hyperfine interactions of the LaNi_5-xFe_x compounds was performed using the spin-polarized tight-binding-linear-muffin-tin-orbital methods (TBLMTO). The calculated results were compared with neutron diffraction and Mössbauer experimental data and found to be in good agreement. Fe atoms exhibit more localized magnetic moments in LaNi_5-xFe_x when the Fe content x is lower than 1.0. The calculated magnetic moments of the Fe atoms approach values as large as 2.5μ_B due to the dilution effect. The strong s-d hybridization between the Ni and La atoms and the neighboring Fe in …

Structural, Electronic, And Magnetic Properties Of Lani₅₋ₓtₓ (T = Fe, Mn) Compounds, Jinbo Yang, Chiu-Ying Tai, G. K. Marasinghe, George Daniel Waddill, Oran Allan Pringle, William Joseph James, Y. Kong

Physics Faculty Research & Creative Works

Structures and magnetic properties of the LaNi_5-xFe_x and LaNi_5-xMn_x compounds have been investigated using neutron diffraction and first-principles tight-binding-linear-muffin-tin-orbital methods. Both neutron diffraction refinement data and total energy calculations show that the Fe and Mn atoms preferentially occupy the 3g sites in the hexagonal CaCu₅-type structure. The calculated magnetic moments of Fe and Ni atoms are of 2.4-2.5μ_B and 0.2-0.5μ_B in LaNi_5-xFe_x, respectively. The magnetic structure exhibits more localized moments at Fe atoms in LaNi_5-xFe_x when x ≤ 1.0. Electronic structure calculations indicate …

Dynamics Of Polyacrylates In Concentrated Chloroform Solutions, Frank D. Blum, Raj B. Durairaj

Chemistry Faculty Research & Creative Works

The dynamics of polymers in polymer solutions have not been probed in great enough detail to provide a coherent picture of the behavior of these polymers, especially in more concentrated solutions. To help understand this behavior further, we have prepared a series of backbone-labeled polymers including poly(n-butyl acrylate)-d1 (PNBA). These provide a basis for comparison of the behavior among a group of related polymers. The dynamics have been probed by using deuterium relaxation times. Since the relaxation times are relatively fast and the quadrupolar relaxation mechanism is well understood, data from this technique provide a convenient means for comparison of …

Glass Transition Behavior Of Pmma Thin Films, Moses T. Kabomo, Frank D. Blum

Chemistry Faculty Research & Creative Works

In the last decade there has been an increased interest in the study of the properties of supported thin polymer films. This has been prompted by the incorporation of thin films into device applications and many other technologies. Although not without controversy, a large body of experimental work indicates departures from bulk behavior by thin films. Strong evidence from both theoretical and experimental work shows that the interaction of polymer with a substrate alters the polymer conformation and mobility. A variety of techniques has been employed to probe the mobility of thin supported polymer films. Some of these techniques indirectly …

Graduated Segmental Mobility In Polymer Layers On Silica, Frank D. Blum, Crystal E. Porter, Wuu-Yung Lin

Chemistry Faculty Research & Creative Works

The behavior of thin polymer layers on oxide substrates has gotten a great deal of attention as the size of materials, and hence polymer films, has gotten smaller. Indeed, the properties of adsorbed polymers are such that they can be different from those of bulk polymers, especially when the films are very thin. A wide variety of studies have been made on adsorbed polymers and sometimes the results seem contradictory. One of the properties often measured in thin films is the apparent glasstransition temperature, Tg. In principle, many techniques are sensitive to phenomenological changes occurring around Tg and, therefore, can …

Thermal Analysis Of Ultrathin Ps-R-Pmma Copolymer Films On Silica, Bing Zhang, Frank D. Blum

Chemistry Faculty Research & Creative Works

Composite materials represent a major part of man-made materials that are used in many applications. The interaction of polymers with surfaces plays a crucial role in the final properties of these materials and, by understanding the surface processes and adsorption mechanisms, better systems can be designed. Therefore, the behavior of polymer molecules at interfaces has been the topic of many studies in recent years and a rough picture has been obtained. Keddie et al. Obtained experimental results showing the dependence of the glass transition temperature (Tg) on the thickness of supported polystyrene films using ellipsometry. Later, they also investigated supported …

Dynamics Of Poly(Vinyl Acetate)-D₃ On Silica, Robert D. O'Connor, Frank D. Blum, Gu Xu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Poly(vinyl acetate) (PVAc) is an important polymer in applications because of both its bulk and surface characteristics. Its chain architecture gives it a low Tg and, generally, good qualities for processing and applications, which include paints, adhesives, thin films and surface coatings. In this study, we investigate the surface dynamics of PVAc absorbed onto silica with deuterium nuclear magnetic resonance (2H NMR). For dynamics studies, 2H NMR is an excellent technique because it uses an innocuous probe that can report on correlation times (τc) from approximately 10-8 s to 10 s. We report the use of two-dimensional exchange NMR (2D-X) …

Structural, Magnetic, And Mössbauer Spectral Study Of Er₂Fe₁₇ And Its Hydrides, Fernande Grandjean, Olivier Isnard, Dimitri Hautot, Gary J. Long

Chemistry Faculty Research & Creative Works

The structural and magnetic properties of the Er₂Fe₁₇H_x compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermal and ac magnetic susceptibility measurements, and iron-57 Mössbauer spectroscopy. The Er₂Fe₁₇H_x compounds crystallize in the hexagonal P6₃/mmc space group with the Th₂Ni₁₇-like structure, a structure which has both an iron-rich stoichiometry and disorder of the erbium and iron-iron 4f-4f dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the …

Chemically Accurate Conformational Energies For Aziridine-2-Carbonitrile, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

The energy of trans-aziridine-2-carbonitrile relative to cis-aziridine-2-carbonitrile was determined by carrying out extensive ab initio computations. The coupled cluster technique was used to determine the higher order computations, that includes perturbative estimate of the triple excitations. The electronic energy of the transition structure connecting the two conformers was determined to be 77.15 kJ/mol higher than the cis-isomer.

High-Performance Liquid Chromatographic Separation Of Enantiomers Of Synthetic Amino Acids On A Ristocetin A Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong, Géza Tóth, Dirk Tourwé

Chemistry Faculty Research & Creative Works

A macrocyclic glycopeptide, ristocetin A, was used as chiral stationary phase for the high-performance liquid chromatographic separation of enantiomers of 28 unnatural amino acids, such as analogues of phenylalanine, tyrosine and tryptophan, and analogues containing 1,2,3,4-tetrahydroisoquinoline, tetraline or 1,2,3,4-tetrahydro-2-carboline skeletons. Excellent resolutions were achieved for most of the investigated compounds by using reversed-phase or a new polar-organic mobile phase system. The conditions of separation were optimized by variation of the mobile phase composition, temperature and flowrate. Copyright (C) 2000 Elsevier Science B.V.

Enantioselective Reversed-Phase And Non-Aqueous Capillary Electrochromatography Using A Teicoplanin Chiral Stationary Phase, Charlotte Karlsson, Håkan Wikström, Daniel W. Armstrong, Paul K. Owens

Chemistry Faculty Research & Creative Works

Enantiomeric separation of chiral pharmaceuticals is carried out in aqueous and non-aqueous packed capillary electrochromatography (CEC) using a teicoplanin chiral stationary phase (CSP). Capillaries were slurry packed with 5 μm 100-A porous silica particles modified with teicoplanin and initially evaluated using a non-aqueous polar organic mode system suitability test for the separation of metoprolol enantiomers (R(s)=2.3 and 53 000 plates m-1). A number of pharmaceutical drugs were subsequently screened with enantioselectivity obtained for 25 racemic solutes including examples of neutral, acidic and basic molecules such as coumachlor (R(s)=3.0 and 86 000 plates m-1) and alprenolol (R(s)=3.3 and 135 000 plates …

Evaluation Of The Macrocyclic Glycopeptide A-40,926 As A High-Performance Liquid Chromatographic Chiral Selector And Comparison With Teicoplanin Chiral Stationary Phase, Alain Berthod, Timothy Yu, John P. Kullman, Daniel W. Armstrong, Francesco Gasparrini, Ilaria D'Acquarica, Domenico Misiti, Angelo Carotti

Chemistry Faculty Research & Creative Works

A new macrocyclic antibiotic of the vancomycin family, referred to by its industrial designation as A-40,926, was bonded to 5 μm silica particles and utilized as a chiral stationary phase (CSP). Since A-40,926 is structurally related to teicoplanin, the A-40,926 CSP was compared to a commercially available teicoplanin CSP. A set of 28 chiral compounds, including amino-acids and related compounds, compounds with a ring containing the stereogenic centre, compounds bearing aromatic structures near their stereogenic centres and alcohols, was tested for enantioseparation on the two CSPs. The results are compared and discussed in terms of enantioselective Gibbs energy difference. The …

Second-Harmonic And Sum-Frequency Imaging Of Organic Nanocrystals With Photon Scanning Tunneling Microscope, Yuzhen Shen, Jacek Swiatkiewicz, Jeffrey G. Winiarz, Przemyslaw P. Markowicz, Paras N. Prasad

Chemistry Faculty Research & Creative Works

Second-harmonic generation and sum-frequency generation with photon scanning tunneling microscopy and shear-force detection are used to map the nonlinear optical response and the surface topograph of N-(4-nitrophenyl)-(L)-prolinol crystals with a subdiffraction-limited resolution. The domain-size dependence of the spatial feature is obtained, which shows the local orientational distribution of the optical near field radiated by nonlinear nanocrystals and reveals the difference between nanoscopic and macroscopic second-order optical nonlinearities of molecular crystals.

Cerium Liii-Edge X-Ray Absorption Study Of The Ceₓfe4-YCoYSb₁₂ Skutterudites, Fernande Grandjean, Gary J. Long, Robert Cortès, Donald T. Morelli, Gregory P. Meisner

Chemistry Faculty Research & Creative Works

The cerium L_III-edge x-ray absorption near-edge spectra of the Ce_xFe_4-yCo_ySb₁₂ compounds have been obtained at 295 K and unambiguously indicate that cerium is in the 4f¹ electronic ground state for all values of 0.22≤x≤0.98 and 0.0≤y≤3.5. This stable trivalent state of cerium is in agreement with the proposed (CeFe₄Sb₁₂) _1-α(Co₄Sb₁₂)α, solid solution structure, in which the cerium atoms are always surrounded by twelve antimony first neighbors and six iron second neighbors, the observed magnetic properties of CeFe₄Sb₁₂ and …

Detection Of Solid Pigment In Dermatoscopy Images Using Texture Analysis, Murali Anantha, William V. Stoecker, Randy Hays Moss

Chemistry Faculty Research & Creative Works

Background/aims: Epiluminescence microscopy (ELM), also known as dermoscopy or dermatoscopy, is a non-invasive, in vivo technique, that permits visualization of features of pigmented melanocytic neoplasms that are not discernable by examination with the naked eye. ELM offers a completely new range of visual features. One such feature is the solid pigment, also called the blotchy pigment or dark structureless area. Our goal was to automatically detect this feature and determine whether its presence is useful in distinguishing benign from malignant pigmented lesions.

Methods: Here, a texture-based algorithm is developed for the detection of solid pigment. The factors d and a …

Mössbauer Spectral Study Of The Magnetic Properties Of Ce₂Fe₁₇Hₓ (X=0, 1, 2, 3, 4, And 5), Dimitri Hautot, Gary J. Long, Fernande Grandjean, Olivier Isnard

Chemistry Faculty Research & Creative Works

The Mössbauer spectra of Ce₂Fe₁₇H_x, where x=0, 1, 2, 3, 4, and 5, have been measured and analyzed between 4.2 and 295 K. Because Ce₂Fe₁₇ exhibits a helical magnetic order between 225 and 90 K and a fan magnetic order below 90 K, its Mössbauer spectra were fit with a distribution of hyperfine fields and θ angles for four of the eight magnetically inequivalent sites. Because the hydrides exhibit a magnetization within the basal plane of the hexagonal cell, their Mössbauer spectra were fit with seven sextets. The four isomer shifts …

Rapid Identification Of The Bacterial Pathogens Responsible For Urinary Tract Infections Using Direct Injection Ce, Daniel W. Armstrong, Jeffrey M. Schneiderheinze

Chemistry Faculty Research & Creative Works

The use of high-performance capillary electrokinetic techniques for the separation, identification, and quantitation of intact microbes represents a new frontier for separation science. In this work, it is demonstrated that pathogens most responsible for urinary tract infections can be distinguished from one another after direct injection of untreated urine. High efficiencies (often exceeding 1 000 000 plates/m) and short analysis times (< 10 min) are characteristics of this approach. The concentration of the urine matrix appears to be able to cause a small, but definite, change in the electroosmotic flow velocity. This high-efficiency separation-based approach could prove to be invaluable for the diagnosis and tracking of certain diseases. It also could form the basis for a variety of rapid microbial assays.

Evaluation Of A Vancomycin Chiral Stationary Phase In Capillary Electrochromatography Using Polar Organic And Reversed-Phase Modes, Charlotte Karlsson, Lars Karlsson, Daniel W. Armstrong, Paul K. Owens

Chemistry Faculty Research & Creative Works

A vancomycin chiral stationary phase (CSP) was fully evaluated in capillary electrochromatography (CEC) in reversed phase and polar organic modes for a number of racemic pharmaceutical compounds. High efficiency and resolution values were obtained for a number of compound classes including thalidomide in both the polar organic mode (190 000 plates meter-1 and Rs = 13.8) and reversed-phase mode (125 000 plates meter-1 and Rs = 13.0). Experimental parameters, including organic modifier, organic solvent ratio, ionic strength, pH, temperature, and voltage, were examined in both the aqueous and nonaqueous modes to deduce their effect on the resultant EOF, retention times, …

Electroweak Quantum Chemistry For Possible Precursor Molecules In The Evolution Of Biomolecular Homochirality, Robert Berger, Martin Quack, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

The unified 'electroweak' theory of the electromagnetic and weak nuclear interactions in physics predicts a small energy difference (ΔE(pv)) between the left- and right-handed enantiomers of chiral molecules. Thus, electroweak theory provides one of several possible explanations for the origin of biomolecular homochirality (nature's preference for L-amino acids and D-monosaccharides). Recent systematic electroweak quantum-chemical studies find ΔE(pv) to be an order of magnitude larger than previously anticipated, which has sparked renewed interest in the subject. The present paper addresses, for the first time, the question of the relative stability of certain possible prebiotic precursor molecules suggested in the work of …

Reply To "Comment On 'Mössbauer Effect Study Of Filled Antimonide Skutterudites'", Gary J. Long, Gary J. Long, Dimitri Hautot, Fernande Grandjean, Donald T. Morelli, Gregory P. Meisner

Chemistry Faculty Research & Creative Works

The temperature dependence of the isomer shift of α-iron between 4.2 and 990 K and of Dy₃Fe₅O₁₂ between 4.2 and 550 K has been analyzed in terms of the Debye model for the second-order Doppler shift, a model in which an additional parameter, the effective vibrating mass, is included. This mass is found equal to 57 g/mol in the ionic compound, Dy₃Fe₅O₁₂, and equal to 60 g/mol in metallic α-iron. The deviation of this mass from 57 g/mol is a measure of the covalency of the metallic bonding in …

A Structural, Magnetic, And Mössbauer Spectral Study Of Dy2fe17 And Its Hydrides, O. Isnard, Dimitri Hautot, Gary J. Long, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The structural and magnetic properties of the [formula omitted] compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermomagnetic and ac magnetic susceptibility measurements, and iron-57 Mössbauer spectroscopy. The Dy₂Fe₁₇H_x compounds crystallize in a hexagonal Th₂Ni₁₇ -like structure which has both an iron-rich stoichiometry and disorder of the Dy and Fe–Fe dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the dependence of the Mössbauer hyperfine parameters upon hydrogen content support a two-step filling by …

Observation Of Stratospheric Ozone Depletion Associated With Delta Ii Rocket Emissions, Martin N. Ross, Darin W. Toohey, W. T. Rawlins, E. C. Richard, K. K. Kelly, A. F. Tuck, M. H. Proffitt, Donald E. Hagen, Alfred R. Hopkins, Philip D. Whitefield, J. R. Benbrook, W. R. Sheldon

Physics Faculty Research & Creative Works

Ozone, chlorine monoxide, methane, and submicron particulate concentrations were measured in the stratospheric plume wake of a Delta II rocket powered by a combination of solid (NH₄ClO₄/Al) and liquid (LOX/kerosene) propulsion systems. We apply a simple kinetics model describing the main features of gas-phase chlorine reactions in solid propellant exhaust plumes to derive the abundance of total reactive chlorine in the plume and estimate the associated cumulative ozone loss. Measured ozone loss during two plume encounters (12 and 39 minutes after launch) exceeded the estimate by about a factor of about two. Insofar as only the …

High Efficiency Separation Of Microbial Aggregates Using Capillary Electrophoresis, J. M. Schneiderheinze, Daniel W. Armstrong, G. Schulte, David J. Westenberg

Chemistry Faculty Research & Creative Works

Recent advances in the technique of capillary electrophoresis have demonstrated fast, highly efficient separation of mixtures of intact microbes. This paper describes the application of this technique for the separation of microbial aggregates of Micrococcus luteus, Saccharomyces cerevisiae, or Alcaligenes faecalis. The aggregates of these microbes were resolved into several highly efficient peaks with analysis times under 10 min and efficiencies approaching 1 000 000 plates m-1 in some cases. A reproducible relationship was found between the electrophoretic mobility and the aggregation number or size of the cluster under a given set of experimental conditions. Often, cellular aggregation was reversible …

Effects Of Ozone/Hydrogen Peroxide Pretreatment On Aerobic Biodegradability Of Nonionic Surfactants And Polypropylene Glycol, Mehmet Kitis, Craig D. Adams, John Kuzhikannil, Glen T. Daigger

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

Studies were conducted which used the ozone/hydrogen peroxide (O₃/H₂O₂) advanced oxidation process to pretreat three classes of compounds prior to aerobic biological treatment. The study compounds included ethylene oxide/propylene oxide (EO/PO) block copolymers, polypropylene glycols (PPGs), linear secondary alcoholethoxylates (LSAES), and alkylphenolethoxylates (APEs). After preoxidation with ozone and hydrogen peroxide (added at their stoichiometric ratio), 300 mg/L as COD samples were bioassayed in aerobic batch bioassays with a mixed liquor suspended solids concentration of 1500 mg/L. It was found that unoxidized polypropylated compounds (EO/PO block copolymers and PPGs) and LSAEs tended to be biorecalcitrant, …