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Articles 601 - 630 of 939
Full-Text Articles in Chemistry
Ft-Ir Studies Of Stereo Regular Pmma On Silica: Drying Effects, Bing Zhang, Suntree Kulkeratiyut, Suriyaphongse Kulkeratiyut, Frank D. Blum
Ft-Ir Studies Of Stereo Regular Pmma On Silica: Drying Effects, Bing Zhang, Suntree Kulkeratiyut, Suriyaphongse Kulkeratiyut, Frank D. Blum
Chemistry Faculty Research & Creative Works
A great amount of work has been done on the configuration of surface adsorbed poly(methyl methacrylate) (PMMA), especially on surfaces to which they have a strong attraction. Some studies have been make on the relationships between configuration and tacticity, molecular weight, adsorbed amount, and density of surface hydroxyl groups. The effect of tacticity on the conformation of alumina-adsorbed PMMA in solution and dry spin-coated films were studied by Grohen et al. Their results showed that surface-adsorbed PMMA chains adopted a relatively flat configuration, but iso-PMMA (isotactic) adsorbed on aluminum, with a much larger fraction of the bound carbonyl groups, had …
Deuterium Nmr Studies Of Bulk And Silica-Absorbed Polystyrene, Macduff O. Okuom, Jinhua Yang, Frank D. Blum
Deuterium Nmr Studies Of Bulk And Silica-Absorbed Polystyrene, Macduff O. Okuom, Jinhua Yang, Frank D. Blum
Chemistry Faculty Research & Creative Works
Thin polymer films are used in applications such as electronics, biomedical devices and coatings. As the trend to make the devices smaller continues, a film's influence on a material's overall properties becomes more prominent. Previous studies have shown that thin polymer films have characteristics slightly different from those of bulk polymers. Film behavior has been characterized by examining thermal expansion, diffusion, conformation, density and glass transitions. The dynamics of glassy polystyrene has been investigated using a wide variety of theoretical and experimental methods. Schaefer et al., using 13C NMR, reported that ~7% of phenyl rings in polystyrene undergo -flips. Using …
A Hmm Based Semantic Analysis Framework For Sports Game Event Detection, Gu Xu, Yu-Fei Ma, Hong-Jiang Zhang, Shiqiang Yang
A Hmm Based Semantic Analysis Framework For Sports Game Event Detection, Gu Xu, Yu-Fei Ma, Hong-Jiang Zhang, Shiqiang Yang
Chemistry Faculty Research & Creative Works
Video events detection or recognition is one of important tasks in semantic understanding of video content. Sports game video should be considered as a rule-based sequential signal. Therefore, it is reasonable to model sports events using hidden Markov models. In this paper, we present a generic, scalable and multilayer framework based on HMMs, called SG-HMMs (sports game HMMs), for sports game event detection. At the bottom layer of this framework, event HMMs output basic hypotheses based on low-level features. The upper layers are composed of composition HMMs, which add constraints on those hypotheses of the lower layer. Instead of isolated …
Molecular Mass And Dynamics In Pma-D₃ In The Glass Transition Region, Burak Metin, Frank D. Blum
Molecular Mass And Dynamics In Pma-D₃ In The Glass Transition Region, Burak Metin, Frank D. Blum
Chemistry Faculty Research & Creative Works
The segmental dynamics through the glass transition region, by which the glassy polymer becomes rubbery, are not well understood. Free volume, thermodynamic and kinetic theories have been used to describe the phenomenon behind the glass transition and some of those theories were tested with computer simulations. Different experimental techniques, such as NMR, thermo-mechanical analysis (TMA), differential scanning calorimetry (DSC), dilatometry and dynamic mechanical analysis (DMA) have all been also used to probe this important phenomena. Deuterium (2H) NMR has been a valuable tool for the investigation of the dynamics of macromolecules. Deuteration of macromolecules at specific locations on the chains …
Superfluidity In The Solar Interior: Implications For Solar Eruptions And Climate, Oliver Manuel, Barry W. Ninham, Stig Friberg
Superfluidity In The Solar Interior: Implications For Solar Eruptions And Climate, Oliver Manuel, Barry W. Ninham, Stig Friberg
Chemistry Faculty Research & Creative Works
Efforts to understand unusual weather or abrupt changes in climate have been plagued by deficiencies of the standard solar model (SSM) [1]. Although it assumes that our primary source of energy began as a homogeneous ball of hydrogen (H) with a steady, well-behaved H-fusion reactor at its core, observations instead reveal a very heterogeneous, dynamic Sun. As examples, the upward acceleration and departure of H+ ions from the surface of the quiet Sun and abrupt climatic changes, including geomagnetic reversals and periodic magnetic storms that eject material from the solar surface are not explained by the SSM. The present …
Superconvergent Perturbation Theory For An Anharmonic Oscillator, Gregory S. Tschumper, Mark R. Hoffmann
Superconvergent Perturbation Theory For An Anharmonic Oscillator, Gregory S. Tschumper, Mark R. Hoffmann
Chemistry Faculty Research & Creative Works
A computationally facile super convergent perturbation theory for the energies and wavefunctions of the bound states of one-dimensional anharmonic oscillators is suggested. The proposed approach uses a Kolmogorov repartitioning of the Hamiltonian with perturbative order. The unperturbed and perturbed parts of the Hamiltonian are defined in terms of projections in Hilbert space, which allows for zero-order wavefunctions that are linear combinations of basic functions. The method is demonstrated on quartic anharmonic oscillators using a basis of generalized coherent states and, in contrast to usual perturbation theories, converges absolutely. Moreover, the method is shown to converge for excited states, and it …
Electronic Structure Of Thallium Filled Skutterudites Studied By X-Ray Absorption And Mössbauer Spectroscopy, Gary J. Long, Bernard M. Mahieu, Brian C. Sales, Raphäel P. Hermann, Fernande Grandjean
Electronic Structure Of Thallium Filled Skutterudites Studied By X-Ray Absorption And Mössbauer Spectroscopy, Gary J. Long, Bernard M. Mahieu, Brian C. Sales, Raphäel P. Hermann, Fernande Grandjean
Chemistry Faculty Research & Creative Works
The electronic structure of the three sites in the thallium filled skutterudites was studied. Two series of thallium filled skutterudites were formed because thallium has a formal valence of +1 and iron or tin must replace some of the cobalt or antimony respectively, to maintain charge neutrality. Large atomic mean-square displacements were observed for the thallium filling atoms and it helps to produce the large thermal resistivity observed for these skutterudites.
An Ab Initio Excursion On The Lowest 18 Electronic Surfaces Of The Ncl + Ncl System: Some Insight Into The Long-Range Self-Quenching Pathways Of The First Excited State Of Ncl, Gregory S. Tschumper, Michael C. Heaven, Keiji Morokuma
An Ab Initio Excursion On The Lowest 18 Electronic Surfaces Of The Ncl + Ncl System: Some Insight Into The Long-Range Self-Quenching Pathways Of The First Excited State Of Ncl, Gregory S. Tschumper, Michael C. Heaven, Keiji Morokuma
Chemistry Faculty Research & Creative Works
A series of state-averaged complete active space self-consistent field (SA-CASSCF) computations were carried out in search of low-energy self-annihilation pathways for two NCl molecules in their first excited state (a1Δ). Numerous scans of the lowest 18 electronic surfaces that correlate with the interaction of two NCl molecules in the X3Σ-, a1Δ, and b1Σ+ states are reported. Eight long-range, low-energy pathways were located (four in C2v and eight in C2h symmetry) that connect NCl(a1Δ) + NCl(a1Δ) to NCl(X3Σ-) + NCl(b1Σ+) and NCl(X3Σ-) + NCl(a1Δ). It was possible to rigorously characterize the minima on four of these seams of crossings (MSXs). The …
Polarized Neutron Diffraction And Mössbauer Spectral Study Of Short-Range Magnetic Correlations In The Ferrimagnetic Layered Compounds (Pph₄) [FeIiFeIii(Ox)₃] And (Nbu₄) [FeIiFeIii(Ox)₃], Simon G. Carling, Dirk W. Visser, Dimitri Hautot, Ian D. Watts, Peter Day, Jürgen Ensling, Phillip Gütlich, Gary J. Long, Fernande Grandjean
Polarized Neutron Diffraction And Mössbauer Spectral Study Of Short-Range Magnetic Correlations In The Ferrimagnetic Layered Compounds (Pph₄) [FeIiFeIii(Ox)₃] And (Nbu₄) [FeIiFeIii(Ox)₃], Simon G. Carling, Dirk W. Visser, Dimitri Hautot, Ian D. Watts, Peter Day, Jürgen Ensling, Phillip Gütlich, Gary J. Long, Fernande Grandjean
Chemistry Faculty Research & Creative Works
Short-range antiferromagnetic correlations have been studied in the layered compounds (PPh4) [FeIIFeIII(ox)3] and (NBu4) [FeIIFeIII(ox)3] by neutron polarization analysis and Mössbauer spectroscopy. Polarized neutron diffraction profiles obtained between 2 and 50 K on (d20-Pph4) [FeIIFeIII(ox)3] show no magnetic Bragg scattering; the lack of such scattering indicates the absence of long-range magnetic order. However, a broad asymmetric feature observed at a Q of ca. 0.8 Å-1 is attributed to two-dimensional short-range magnetic correlations, which …
Morphologic And Magnetic Properties Of Pd₁₀₀₋ₓfeₓ Nanoparticles Prepared By Ultrasound Assisted Electrochemistry, Maribel Guzman, Jean Luc Delplancke, Gary J. Long, Jacques P. Delwiche, Marie Jeanne Hubin-Franskin, Fernande Grandjean
Morphologic And Magnetic Properties Of Pd₁₀₀₋ₓfeₓ Nanoparticles Prepared By Ultrasound Assisted Electrochemistry, Maribel Guzman, Jean Luc Delplancke, Gary J. Long, Jacques P. Delwiche, Marie Jeanne Hubin-Franskin, Fernande Grandjean
Chemistry Faculty Research & Creative Works
Nanopowdered alloys of Pd100-xFex, with x=4, 6, 8, and 12, have been prepared by ultrasound assisted electrochemistry. The composition of the individual particles, as determined by x-ray fluorescence, and the bulk composition, as determined by atomic absorption, are in agreement within experimental error. Transmission electron microscopy indicates that the nanopowders consist of agglomerates of small grains with a radius of approximately 5 nm, a radius which is confirmed by the broadening of the reflections in the x-ray powder diffraction patterns. X-ray fluorescence analysis of individual grains indicates a homogeneous distribution of palladium and iron throughout the …
Synthesis Of The Abc Ring System Of Azaspiracid. 2. A Systematic Study Into The Effect Of C16 And C17 Substitution On Bis-Spirocyclization, Rich G. Carter, David E. Graves, Melissa A. Gronemeyer, Gregory S. Tschumper
Synthesis Of The Abc Ring System Of Azaspiracid. 2. A Systematic Study Into The Effect Of C16 And C17 Substitution On Bis-Spirocyclization, Rich G. Carter, David E. Graves, Melissa A. Gronemeyer, Gregory S. Tschumper
Chemistry Faculty Research & Creative Works
(matrix presented) A systematic study into the effect of C16 and C17 substitution on the stereochemical outcome of bis-Spiro cyclization to form the ABC ring system of azaspiracid is disclosed. Successful construction of the natural 10R,13R bis-spirocyclic stereochemistry has been accomplished on the C16 benzyloxy-containing precursor.
The Relationship Between Magnetic Interactions And Near Neighbor Interatomic Distances In The Transition Metal Sublattice Of R(Mn/Fe)₆A₆(R=Nd Or Sm, A=Ge Or Sn), G. K. Marasinghe, J. Han, William Joseph James, William B. Yelon, Naushad Ali
The Relationship Between Magnetic Interactions And Near Neighbor Interatomic Distances In The Transition Metal Sublattice Of R(Mn/Fe)₆A₆(R=Nd Or Sm, A=Ge Or Sn), G. K. Marasinghe, J. Han, William Joseph James, William B. Yelon, Naushad Ali
Chemistry Faculty Research & Creative Works
The magnetic and crystallographic structures of R(Fe/Mn)6A6 (R=Nd or Sm and A = Ge or Sn) intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides (A = Sn) and germanides (A = Ge), the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (x ≤2 ) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties …
A New Layered Iron Fluorophosphates, Amitava Choudhury
A New Layered Iron Fluorophosphates, Amitava Choudhury
Chemistry Faculty Research & Creative Works
A new iron fluorophosphate of the composition, [C6N4H21] [Fe2F2(HPO4)3][H2PO4]·2H2O, I. has been prepared by the hydrothermal route. This compound contains iron fluorophosphate layers and the H2PO4- anions are present in the interlayer space along with the protonated amine and water molecules. The compound crystallizes in the monoclinic space group P21/c. (a = 13.4422(10) Å, b = 9.7320(10) Å, c = 18.3123(3) Å, ? = 92.1480°, V = 2393.92(5) Å3, Z = 4, …
A Mössbauer Spectral Study Of The Magnetic Properties Of Ho₂Fe₁₇ And Ho₂Fe₁₇D₃.₈, Gary J. Long, Olivier Isnard, Fernande Grandjean
A Mössbauer Spectral Study Of The Magnetic Properties Of Ho₂Fe₁₇ And Ho₂Fe₁₇D₃.₈, Gary J. Long, Olivier Isnard, Fernande Grandjean
Chemistry Faculty Research & Creative Works
The Mössbauer spectra of Ho2Fe17 and Ho2Fe17D3.8 have been measured between 4.2 and 295 K and analyzed with a model which takes into account both the disordered nonstoichiometric hexagonal Th2Ni17-like structure and the basal orientation of the iron magnetic moments. The isomer shifts of the five crystallographically inequivalent iron sites in both Ho2Fe17 and Ho2Fe17D3.8 follow the sequence of Wigner-Seitz cell volumes and their temperature dependence follows the typical second-order Doppler shift. An increase in the weighted average isomer shift …
Magnetic And Mössbauer Spectral Evidence For The Suppression Of The Magnetic Spin Reorientation In Tm₂Fe₁₇ By Deuterium, Fernande Grandjean, Olivier Isnard, Gary J. Long
Magnetic And Mössbauer Spectral Evidence For The Suppression Of The Magnetic Spin Reorientation In Tm₂Fe₁₇ By Deuterium, Fernande Grandjean, Olivier Isnard, Gary J. Long
Chemistry Faculty Research & Creative Works
The structural and magnetic properties of Tm2Fe17 and Tm2Fe17D3.2 are investigated by means of x-ray-diffraction, thermal, and ac magnetic susceptibility measurements, and iron-57 Mössbauer spectroscopy. Both compounds crystallize in a hexagonal P63/mmc space group with a Th2Ni17-like structure. Deuterium insertion into Tm2Fe17 induces large increases in the unit-cell volume, the saturation magnetization, and the ordering temperature. The unit-cell expansion is anisotropic, with a larger increase in the a lattice parameter than the c lattice parameter. A spin reorientation is observed at 90 K …
Potent Enantioselective Auxin: Indole-3-Succinic Acid, Daniel W. Armstrong, Yan Song Liu, Lingfeng He, K. Helen Ekborg-Ott, Charles L. Barnes, Charles F. Hammer
Potent Enantioselective Auxin: Indole-3-Succinic Acid, Daniel W. Armstrong, Yan Song Liu, Lingfeng He, K. Helen Ekborg-Ott, Charles L. Barnes, Charles F. Hammer
Chemistry Faculty Research & Creative Works
Low levels of synthetic auxins are used as root growth promoters for a wide variety of botanicals. When properly used, they can produce earlier and more prolific root growth. Indole-3-succinic acid (ISA) is a chiral compound that can be synthesized as a racemate. Its enantiomers were resolved by both chromatography and diastereomeric crystallization. The absolute configuration of each enantiomer was determined by X-ray crystallography and then tested for auxin activity. The relative effectiveness of the ISA enantiomers was determined and compared to the achiral synthetic auxin indole-3-butyric acid and to the natural auxin indole-3-acetic acid.
Anchoring The Water Dimer Potential Energy Surface With Explicitly Correlated Computations And Focal Point Analyses, Gregory S. Tschumper, Matthew L. Leininger, Brian C. Hoffman, Edward F. Valeev, Henry F. Schaefer, Martin Quack
Anchoring The Water Dimer Potential Energy Surface With Explicitly Correlated Computations And Focal Point Analyses, Gregory S. Tschumper, Matthew L. Leininger, Brian C. Hoffman, Edward F. Valeev, Henry F. Schaefer, Martin Quack
Chemistry Faculty Research & Creative Works
The extensive ab initio quantum chemical study of ten stationary point on the water dimer potential energy surface (PES) was discussed. The geometry optimizations were carried out using the CCSD(T) method in conjunction with the [TZ2P(f,d) + dif] basis set. The study showed that the optimized structures of (H2O)2 PES were quite similar to those obtained at the MP2 level with much smaller basis sets and the number of imaginary vibrational frequencies or hessian index of each stationary point was unchanged despite fairly significant geometrical differences for some of the optimized structures.
Synthetic, Structural, Magnetic, And Mössbauer Spectral Study Of {Fe[Hc(3,5-Me2pz)3]2}I2 And Its Spin-State Crossover Behavior, Daniel L. Reger, Christine A. Little, Mark D. Smith, Arnold L. Rheingold, Kin Chung Lam, Thomas L. Concolino, Gary J. Long, Raphaël P. Hermann, Fernande Grandjean
Synthetic, Structural, Magnetic, And Mössbauer Spectral Study Of {Fe[Hc(3,5-Me2pz)3]2}I2 And Its Spin-State Crossover Behavior, Daniel L. Reger, Christine A. Little, Mark D. Smith, Arnold L. Rheingold, Kin Chung Lam, Thomas L. Concolino, Gary J. Long, Raphaël P. Hermann, Fernande Grandjean
Chemistry Faculty Research & Creative Works
The complex {Fe [HC(3,5-Me2pz)3]2} I2 (1) has been prepared from the reaction of FeI2 and HC(3,5-Me2pz)3 (pz = pyrazolyl ring) in a 1:2 ratio. The complex is high spin in both the solid state and in solution at ambient temperature. In the solid state, magnetic susceptibility and Mössbauer spectral studies indicate that samples of the complex that have been crystallized and dried change completely from high-spin to low-spin upon cooling below 195 K, with a substantial two-step thermal hysteresis in the transition. The spin-crossover properties of 1 are sample …
Atomic And Molecular Electron Affinities: Photoelectron Experiments And Theoretical Computations, Jonathan C. Rienstra-Kiracofe, Gregory S. Tschumper, Henry F. Schaefer, Sreela Nandi, G. Barney Ellison
Atomic And Molecular Electron Affinities: Photoelectron Experiments And Theoretical Computations, Jonathan C. Rienstra-Kiracofe, Gregory S. Tschumper, Henry F. Schaefer, Sreela Nandi, G. Barney Ellison
Chemistry Faculty Research & Creative Works
A review is given of the experimental determination of electron affinities (EAs). Also considered is the ability of computational chemistry methods to predict electron affinities. The development and present status of computational chemistry techniques for the prediction of atomic molecular EAs is also reviewed in a historical context. Through comparisons to experimental EAs and results from other theoretical methods, analysis of DFT EAs is given. In the context of other theoretical methods, the successes and failures of DFT EA predictions are detailed.
Thermogravimetric Studies Of Pmma On Silica, Bing Zhang, Frank D. Blum
Thermogravimetric Studies Of Pmma On Silica, Bing Zhang, Frank D. Blum
Chemistry Faculty Research & Creative Works
The thermal degradation of poly(methyl methacrylate) (PMMA) has been studied extensively. It is well accepted that the degradation process is a radical chain reaction involving initiation, depropagation, transfer, and termination reactions. In the degradation process, the factors having observable effects on the decomposition behavior include molecular mass, polydispersity, tacticity, and sample dimensions. The effects of tacticity on the degradation behavior of PMMA were investigated by Kashiwagi et al., Jellinek et al. And Chiamtore et al. The results indicated that both isotactic and syndiotactic PMMA have similar decomposition pathways and activation energies. Isotactic PMMA will decompose at a slightly lower temperature …
Effect Of Polymer-Surface Mobility On Adhesion In Poly(Methyl Methacrylate)-Tape System, Bhavesh C. Gandhi, Frank D. Blum, Lokeswarappa R. Dharani
Effect Of Polymer-Surface Mobility On Adhesion In Poly(Methyl Methacrylate)-Tape System, Bhavesh C. Gandhi, Frank D. Blum, Lokeswarappa R. Dharani
Chemistry Faculty Research & Creative Works
The interaction between two polymer layers, especially adhesion between them, plays an important role in polymer processing and other applications. Detailed knowledge of the molecular structure and dynamics of polymer interfaces, and how they relate to macroscopic mechanical properties, should help designers construct more functional systems. Unfortunately, there have been few studies where both molecular and macroscopic studies have been performed on similar systems. In previous studies from our group, we have probed the dynamics of poly(methyl acrylate) (PMA) and thermal behavior of poly(methyl methacrylate) (PMMA) on silica. These studies helped us paint a picture for strongly bound molecules on …
Highly Plasma Etch-Resistant Photoresist Composition Containing A Photosensitive Polymeric Titania Precursor, Tony D. Flaim, Douglas J. Guerrero, Michelle R. Fowler, William Joseph James, Vladimir Petrovsky, Harlan U. Anderson
Highly Plasma Etch-Resistant Photoresist Composition Containing A Photosensitive Polymeric Titania Precursor, Tony D. Flaim, Douglas J. Guerrero, Michelle R. Fowler, William Joseph James, Vladimir Petrovsky, Harlan U. Anderson
Chemistry Faculty Research & Creative Works
A composition is derived from an addition polymerizable organotitanium polymer which upon exposure to an oxygen plasma or baking in air, is converted to titanium dioxide (titania) or is converted to a mixed, titanium-containing metal oxide. The metal oxide formed in situ imparts etch- resistant action to a patterned photoresist layer. The composition may also be directly deposited and patterned into permanent metal oxide device features by a photolithographic process.
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
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 DyxFe100-x and Dy20Fe80-yCoy, 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 DyxFe100-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
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
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
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
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 …
Chemically Accurate Conformational Energies For Aziridine-2-Carbonitrile, Gregory S. Tschumper
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.
Dynamics Of Polyacrylates In Concentrated Chloroform Solutions, Frank D. Blum, Raj B. Durairaj
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 …
Thermal Analysis Of Ultrathin Ps-R-Pmma Copolymer Films On Silica, Bing Zhang, Frank D. Blum
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 …