Physical Sciences and Mathematics Commons^™

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 …

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 …

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 …

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 …

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.

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, …

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 …

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 …

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

Chemistry Faculty Research & Creative Works

The crystallographic and magnetic properties of Sm_yGd_2-yFe_17-xSi_x (0 ≤ x ≤ 3 and y = 1 and 1.5) solid solutions and their interstitial carbides have been investigated using x-ray diffraction and magnetic measurements. The Sm_yGd_2-yFe_17-xSi_x samples crystallized in the rhombohedral Th₂Zn₁₇ structure with less than 5 mol % of impurities. The unit cells of the mixed rare-earth (R) samples are smaller than those of Sm₂Fe₁₇ and Gd₂Fe₁₇. The carbided samples contain up to a total of …

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

Chemistry Faculty Research & Creative Works

The magnetic and crystallographic properties of induction-melted NdMn_(6-x)Fe_xGe₆ intermetallics (x = 0, 1.0, and 1.5) in the temperature range of 30-475 K have been studied by x-ray and neutron diffraction techniques and SQUID measurements. All of the samples crystallized in the YCo₆Ge₆-type structure (P6/mmm). A small amount ( < 5 mol%) of Nd(MnFe)₂Ge₂ is present as an impurity. As expected, iron replaces manganese at the 3g site. The unit cell volume decreases slightly with increasing iron content at an average rate of 1.3% per substituted atom. Lattice parameters a and c contract at …

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

Conceptual Problems With Remote Element Synthesis, Oliver Manuel

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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

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

Chemistry Faculty Research & Creative Works

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