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Articles 1 - 11 of 11
Full-Text Articles in Condensed Matter Physics
Phonons Of Single Quintuple Bi2te3 And Bi2se3 Films And Bulk Materials, Wei Cheng, Shang-Fen Ren
Phonons Of Single Quintuple Bi2te3 And Bi2se3 Films And Bulk Materials, Wei Cheng, Shang-Fen Ren
Faculty publications – Physics
Phonons of single quintuple films of Bi2Te3 and Bi2Se3 and corresponding bulk materials are calculated in detail by MedeA (a trademark of Materials Design) and Vienna ab initio simulation package (VASP). The calculated results with and without spin-orbit couplings are compared, and the important roles that the spin-orbit coupling plays in these materials are discussed. A symmetry breaking caused by the anharmonic potentials around Bi atoms in the single quintuple films is identified and discussed. The observed Raman intensity features in Bi2Te3 and Bi2Se3 quintuple films are explained.
Use Of Di- And Tripropionate Substrate Analogs To Probe The Active Site Of Human Recombinant Coproporphyrinogen Oxidase, Justin B. Morgenthaler, Reyna L. Barto, Timothy D. Lash, Marjorie A. Jones
Use Of Di- And Tripropionate Substrate Analogs To Probe The Active Site Of Human Recombinant Coproporphyrinogen Oxidase, Justin B. Morgenthaler, Reyna L. Barto, Timothy D. Lash, Marjorie A. Jones
Faculty Publications – Chemistry
Background: Defects in the enzyme coproporphyrinogen oxidase result in accumulation of porphyrins which may affect the severity of a subset of porphyrias. Thus evaluation of this enzyme for substrate selectivity is of value. Kinetic evaluations of recombinant human coproporphyrinogen oxidase have been undertaken using six di- and tripropionate analogs of the natural substrate coproporphyrinogen-III. These Substrate analogs were modified by having alkyl groups in place of one or both of the ring 13- or 17-propionate moieties. Material/Methods: Cloned human enzyme was incubated with analogs under apparent first order conditions and with various substrate concentrations. The kinetic values, K-m and V-max, …
Investigation Of The Catalytic And Structural Roles Of Conserved Histidines Of Human Coproporphyrinogen Oxidase Using Site-Directed Mutagenesis, Shani J. Gitter, Christopher L. Cooper, Jon A. Frieson, Timothy D. Lash, Marjorie A. Jones
Investigation Of The Catalytic And Structural Roles Of Conserved Histidines Of Human Coproporphyrinogen Oxidase Using Site-Directed Mutagenesis, Shani J. Gitter, Christopher L. Cooper, Jon A. Frieson, Timothy D. Lash, Marjorie A. Jones
Faculty Publications – Chemistry
Background: The catalytic contribution of four conserved histidines of human coproporphyrinogen oxidase (CPO) has been investigated using site-directed mutagenesis to change histidine (H) into alanine (A). Material/Methods: The wild-type and mutant enzyme forms were analyzed for their ability to utilize coproporphyrinogen-III, mesoporphvrinogen-VI, and harderoporphyrinogen as substrates. Results: Wild-type CPO had specific activities of 4.9 +/- 0.9 nmole product/min/mg for coproporphyrinogen-III, 1.7 +/- 0.7 nmole ptoduct/min/mg for mesoporphyrinogen-VI, and 5.1 +/- 1.8 nmole product/min/mg for harderoporphyrinogen. The four mutant enzymes were catalytically competent With all three substrates, but to varying degrees. The most affected Mutant was the H158A enzyme which exhibited …
Kinetic Evaluation Of Human Cloned Coproporphyrinogen Oxidase Using A Ring Isomer Of The Natural Substrate, Marjorie A. Jones, Christopher L. Cooper, Timothy D. Lash
Kinetic Evaluation Of Human Cloned Coproporphyrinogen Oxidase Using A Ring Isomer Of The Natural Substrate, Marjorie A. Jones, Christopher L. Cooper, Timothy D. Lash
Faculty Publications – Chemistry
Background: The enzyme coproporphyrinogen oxidase (copro'gen oxidase) converts coproporphyrinogen-Ill (GIII) to protoporphyrinogen-IX via an intermediary monovinyl porphyrinogen. The A ring isomer coproporphyrinogen-IV (C-IV) has previously been shown to be a substrate for copro'gen oxidase derived from avian erythrocytes. In contrast to the authentic substrate (GIII) where only a small amount of the monovinyl intermediate is detected, C-IV gives rise to a monovinyl intermediate that accumulates before being converted to an isomer of protoporphyrinogen-IX. No kinetic studies have been carried out using the purified human copro'gen oxidase to evaluate its ability to process both the authentic substrate as well as analogs. …
Microscopic Theory Of The Low Frequency Raman Modes In Germanium Nanocrystals, Shang-Fen Ren, Peter Y. Yu
Microscopic Theory Of The Low Frequency Raman Modes In Germanium Nanocrystals, Shang-Fen Ren, Peter Y. Yu
Faculty publications – Physics
We have studied the Raman intensities of low-frequency phonon modes in germanium (Ge) nanocrystals (NC) with varying sizes by using a microscopic valence force field model. The results are compared with the predictions of the continuum model of Lamb using a projection method. We found that the l=0 spheroidal Lamb modes are Raman active in the parallel polarization scattering geometry, while the l=2 spheroidal Lamb modes are active in the crossed polarization geometry. This result agrees with the group theory prediction that the torsional Lamb modes are not Raman active, but is in disagreement with the identification of torsional Lamb …
Microscopic Investigation Of Phonon Modes In Sige Alloy Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Microscopic Investigation Of Phonon Modes In Sige Alloy Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Faculty publications – Physics
Phonon modes in spherical silicon germanium alloy (SiGe) nanocrystals containing up to 1147 atoms (3.6 nm) have been investigated as a function of the Si concentration. Microscopic details of phonon modes, including phonon frequencies and vibrational amplitudes, phonon density-of-states are calculated directly from the dynamic matrices. In particular, the dependence of phonon frequency on the configuration (such as a different ratio of Si to Ge atoms), and location (surface or interior) of clusters of atoms in SiGe alloy nanocrystals have been investigated. Low frequency surface phonons that are related to the spheroidal and torsional modes of a continuum sphere are …
Theoretical Investigation Of The Surface Vibrational Modes In Germanium Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Theoretical Investigation Of The Surface Vibrational Modes In Germanium Nanocrystals, Shang-Fen Ren, Wei Cheng, Peter Y. Yu
Faculty publications – Physics
We have used a microscopic lattice dynamical model to study phonon modes in germanium (Ge) NC with size varying between 47 to 7289 atoms (diametersimilar to6.8 nm). By separating these atoms into bulk and surface atoms we have found that surface modes can exist in Ge NC both at low frequencies (<50>cm(-1)) and at high frequency (similar to260 cm(-1)). The latter mode is a resonant mode which occurs in the "pseudogap" between the acoustic and optical phonon branches in bulk Ge. From the low frequency surface modes we have been able to reconstruct the spheroidal and torsional Lamb modes …
Calculations Of Surface Effects On Phonon Modes And Raman Intensities Of Ge Quantum Dots, Shang-Fen Ren, Wei Cheng
Calculations Of Surface Effects On Phonon Modes And Raman Intensities Of Ge Quantum Dots, Shang-Fen Ren, Wei Cheng
Faculty publications – Physics
Phonon modes and Raman intensities of Ge quantum dots (QDs) with two different types of surfaces, a free standing surface or a fixed surface, in a size range from five atoms to 7 nm in diameter, are calculated by using a microscopic valence force field model. The results are compared, and the effects of surfaces on phonon properties of QDs are investigated. It is found that phonon modes and Raman intensities of QDs with these two different types of surfaces have obvious differences which clearly reveal the effects of the surfaces of QDs. The calculated results agree with existing experimental …
Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren
Calculations On The Size Effects Of Raman Intensities Of Silicon Quantum Dots, Wei Cheng, Shang-Fen Ren
Faculty publications – Physics
Raman intensities of Si quantum dots (QD's) with up to 11489 atoms (about 7.6 nm in diameter) for different scattering configurations are calculated. First, phonon modes in these QD's, including all vibration frequencies and vibration amplitudes, are calculated directly from the lattice-dynamic matrix by using a microscopic valence force field model combined with the group theory. Then the Raman intensities of these quantum dots are calculated by using a bond-polarizability approximation. The size effects of the Raman intensity in these QD's are discussed in detail based on these calculations. The calculations are compared with the available experimental observations. We are …
Phonon Modes In Inas Quantum Dots, Shang-Fen Ren, G Qin, Deyu Lu
Phonon Modes In Inas Quantum Dots, Shang-Fen Ren, G Qin, Deyu Lu
Faculty publications – Physics
Phonon modes in spherical InAs quantum dots (QDs) with up to 11 855 atoms (about 8.5 nm in diameter) are calculated by using a valence force field model, and all the vibration frequencies and vibration amplitudes of the QDs are calculated directly from the lattice-dynamic matrix. The projection operators of the irreducible representations of the group theory are employed to reduce the computational intensity, which further allows us to investigate the quantum confinement effect of phonon modes with different symmetries. It is found that the size effects of phonon modes depend on the symmetry of the modes. For zinc-blende structure, …
Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard
Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard
Faculty Publications – Chemistry
Electrons near roughened Ag and Au surfaces with chemisorbed dielectric overlayers of alkanethiol or alkaneselenol self-assembled monolayers are shown to move within the sulfur or selenium head-group layer on the metal terraces. The electrons exist in image states with respect to Ag or Au step edges. There is no substantial image force between the electrons and the terraces.