Chemistry Commons^™

Anchoring The Potential Energy Surface Of The Cyclic Water Trimer, Julie A. Andersen, Kelly Crager, Lisa Fedoroff, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

Six cyclic stationary points on the water trimer potential energy surface have been fully optimized at the MP2 level with the aug-cc-pVQZ basis set. In agreement with previous work, harmonic vibrational frequencies indicate that two structures are minima, three are transition states connecting minima on the surface while the remaining stationary point is a higher-order saddle point. The 1-and n-particle limits of the electronic energies of each of these six structures were estimated by systematically varying both the basis sets and theoretical methods. The former limit was approached with the cc-pVXZ and aug-cc-pVXZ families of basis sets (X=2-7) while MP2, …

Mössbauer Spectral Study Of The Magnetocaloric Femnp₁₋ₓasₓ Compounds, Raphäel P. Hermann, Ojied Tegus, Ekkehard H. Brück, K. H. J. Buschow, Frank R. De Boer, Gary J. Long, Fernande Grandjean

Chemistry Faculty Research & Creative Works

The magnetic phase transitions in the FeMnP_1-xAs_x compounds with x= 0.25, 0.35, 0.45, 0.50, and 0.55, have been studied by iron-57 Mössbauer spectroscopy. The ferromagnetic and antiferromagnetic spectra have been analyzed with a model that takes into account the random distribution of the P and As near-neighbor anions of a given iron site. This distribution is a binomial distribution of the contributions to the spectra of each iron with n As near neighbors. A magnetostriction model has been used to characterize the temperature induced paramagnetic to ferromagnetic first-order phase transition and order parameters, η_F=2.6, 2.3, …

Additive-Assisted Cerium-Based Electrolytic Coating Process For Corrosion Protection Of Aluminum Alloys, James O. Stoffer, Thomas J. O'Keefe, Eric L. Morris, Scott Hayes, Paul Yu, Alex Williams, Xuan Lin

Chemistry Faculty Research & Creative Works

The corrosion resistance of an aluminum or aluminum alloy component is enhanced by immersing an aluminum alloy to act as a cathode and an oxygen-evolving anode in an electrolyte comprising water, cerium ions, and an additive selected from among animal gelatin, derivatives of animal gelatin, and amino acids, then passing an electrical current through the electrolyte to deposit a cerium-based coating onto the aluminum-based component.

Solvent And Method For Extraction Of Triglyceride Rich Oil, Shubhender Kapila, Paul Ki-Souk Nam, V. J. Flanigan

Chemistry Faculty Research & Creative Works

The present invention relates to a solvent for use in extracting oil from an oil bearing material, such as soybeans, with the solvent resulting in the selective extraction of a triglyceride rich oil, which contains 95% or greater triglycerides and non-polar constituents, with the solvent comprised of a hydrocarbon, preferably hexane, and a fluorocarbon, so that the solvent has a viscosity less than 2.6 centipoise and a polarity of less than 0.1. The present invention also relates to a method of using the solvent to extract the triglyceride rich oil, with the method including preferably extracting the oil at a …

Solvent And Method For Extraction Of Triglyceride Rich Oil, Shubhender Kapila, Paul Ki-Souk Nam, V. J. Flanigan

Chemistry Faculty Research & Creative Works

The present invention relates to a solvent for use in extracting oil from an oil bearing material, such as soybeans, with the solvent resulting in the selective extraction of a triglyceride rich oil, which contains 95% or greater triglycerides and non-polar constituents, with the solvent comprised of a hydrocarbon, preferably hexane, and a fluorocarbon, so that the solvent has a viscosity less than 2.6 centipoise and a polarity of less than 0.1. The present invention also relates to a method of using the solvent to extract the triglyceride rich oil, with the method including preferably extracting the oil at a …

A Magnetic And Mössbauer Spectral Study Of The Spin Reorientation In Ndfe₁₁Ti And Ndfe₁₁Th, Cristina Piquer, Fernande Grandjean, Olivier Isnard, Viorel Pop, Gary J. Long

Chemistry Faculty Research & Creative Works

The influence of hydrogenation on the spin reorientation in the presence of neodymium was investigated in NdFe₁₁Ti and NdFe₁₁TH. The magnetic properties of these compounds were determined by utilizing ac magnetic susceptibility, thermomagnetic, and iron-57 Mössbauer spectral analysis. It was found that the these compounds had two advantages as hard magnetic materials such as: a high iron content yielding high magnetization and a high Curie temperature. The investigation results show that these compounds undergo a spin-reorientation transition at ~185 K and at 100± K, from an axial magnetic phase at high temperature to a basal magnetic …

Characterization And Magnetic Properties Of Core/Shell Structured Fe/Au Nanoparticles, Sung-Jin Cho, Susan M. Kauzlarich, Justin Olamit, Kai Liu, Fernande Grandjean, Leïla Rebbouh, Gary J. Long

Chemistry Faculty Research & Creative Works

Au-coated Fe nanoparticles have been prepared by using a reverse micelle method through reduction of an aqueous solution. Characterizations have been carried out over time to probe the oxidation of Fe. Immediately after synthesis, the samples exhibit metallic conduction and a negative magnetoresistance, consistent with the presence of α-Fe. The temperature dependence of magnetization displays a maximum at a blocking temperature of around 150 K. After a period of 1 month, the samples exhibit insulating behavior, indicating the oxidation of the Fe core. Mössbauer spectroscopy indicates the presence of an α-Fe component and a broad distribution of local environments.

Dynamic Correction Of A Distorted Image Using A Photorefractive Polymeric Composite, Jeffrey G. Winiarz, Fassil Ghebremichael, Jayan Sanders Thomas, Gerald R. Meredith, Nasser N. Peyghambarian

Chemistry Faculty Research & Creative Works

We demonstrate, for the first time, the dynamic correction of aberrated images in real-time using a polymeric composite with fast response times. The current novel experimental design is capable of restoring a phase aberrated, image carrying laser beam, to nearly its original quality. The ability to reconstruct images in real-time is demonstrated through the changing of the aberrating medium at various speeds. In addition, this technique allows for the correction of images in motion, demonstrated through the oscillatory movement of the resolution target. We also have demonstrated that important parameters of the materials in the study such as response times, …

Real Versus Artifactual Symmetry-Breaking Effects In Hartree-Fock, Density-Functional, And Coupled-Cluster Methods, Nicholas J. Russ, T. Daniel Crawford, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

The relative abilities of Hartree-Fock, density-functional theory (DFT) and coupled-cluster theory were used to investigate symmetry breaking in polyatomic molecules. It was observed that for degenerate electronic states, symmetry breaking in the nuclear framework may result from first-order Jahn-Teller (SOJT) effects. Displacements along Non totally symmetric nuclear coordinates, however, may lead to mixing of the states if their respective irreducible representations correlate in the reduced symmetry point group. Coupled-cluster theory correctly describes the strength of SOJT coupling, assuming that the full CCSDT method provides a reasonable approximation of the exact wave function.

Ab Initio Studies Of Π⋯Π Interactions: The Effects Of Quadruple Excitations, Brian W. Hopkins, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

To examine the effects of including quadruple excitations in the electron correlation treatment when computing the binding energy of van der Waals dimers, we have calculated MP2, CCSD, CCSD(T), and CCSD(TQ) interaction energies for several van der Waals complexes ranging from helium dimer to furan dimer. Through comparison of CCSD(TQ) and CCSD(T) binding energies the first direct assessment of the effects of quadruple excitations on π⋯π interactions is presented. The influence of triple excitations is assessed not only in the conventional manner that permeates the literature (comparison of CCSD(T) and MP2 interaction energies) but also via comparison of CCSD(T) and …

Extending The Oniom Integrated Mo/Mo Approach To Hydrogen Bonding In Biologic Systems: Serine-Water And Threonine-Water Dimers, Brian W. Hopkins, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

A series of two-layer ONIOM (MO:MO) methods have been systematically applied to two biologically important hydrogen-bonded dimers. Single conformations of the serine-water dimer and of the threonine-water dimer were optimized with the MP2 technique and a DZP++ basis set. The counterpoise corrected and uncorrected dissociation energies of the dimers were then computed with RHF, B3LYP, MP2, and CCSD(T) electronic structure techniques with 3-21G, 6-31+G(d), and DZP++ basis sets as well as every possible two-layer ONIOM permutation using either CCSD(T)/DZP++ or MP2/DZP++ as the high-level method. To judge the performance of each technique, the data are compared to results obtained with …

Biologically Important Thiols In Various Vegetables And Fruits, Omca Demirkol, Craig D. Adams, Nuran Ercal

Chemistry Faculty Research & Creative Works

Biological thiols are important antioxidants, and recent studies showed that their contents vary depending on the groups of foodstuffs. Therefore, we investigated the levels of some biological thiols in various vegetables and fruits by using a sensitive high-performance liquid chromatography (HPLC) technique. Biological thiols measured in some vegetables and fruits include glutathione (L-glutamyl-L-cysteinly glycine, GSH), N-acetylcysteine (NAC), captopril [CAP (C9H15NO3S)], homocysteine (HCYS), cysteine (CYS), and -glutamyl cysteine (GGC). Our results show that biological thiol contents are between 3-349 nM/g wet weight in vegetables and 4-136 nM/g wet weight in fruits. CAP is only found in asparagus (28 nM/g wet weight). …

2,4-Dinitrophenylhydrazones Of 2,4-Dihydroxybenzaldehyde, 2,4-Dihydroxyacetophenone And 2,4-Dihydroxybenzophenone, Russell G. Baughman, Kenneth L. Martin, Rajendra K. Singh, James O. Stoffer

Chemistry Faculty Research & Creative Works

In 2,4-dihydroxybenzaldehyde 2,4-dinitrophenylhydrazone N,N-dimethylformamide solvate (or 4-[(2,4-dinitrophenyl)-hydrazonomethyl]benzene-1,3-diol N,N-dimethylformamide solvate

Solvent And Primary Deuterium Isotope Effects Show That Lactate Ch And Oh Bond Cleavages Are Concerted In Y254f Flavocytochrome B2, Consistent With A Hydride Transfer Mechanism, Pablo Sobrado, Paul F. Fitzpatrick

Chemistry Faculty Research & Creative Works

Yeast flavocytochrome b2 catalyzes the oxidation of lactate to pyruvate; because of the wealth of structural and mechanistic information available, this enzyme has served as the model for the family of flavoproteins catalyzing oxidation of α-hydroxy acids. Primary deuterium and solvent isotope effects have now been used to analyze the effects of mutating the active site residue Tyr254 to phenylalanine. Both the Vmax and the V/Klactate values decrease about 40-fold in the mutant enzyme. The primary deuterium isotope effects on the Vmax and the V/K lactate values increase to 5.0, equivalent to the intrinsic isotope effect for the wild-type enzyme. …

Macrocyclic Antibiotics As Separation Agents, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Macrocyclic antibiotics having ring structures with at least 10 members act as separation agents in crystallization, precipitation, filtration, electrophoresis, and chromatography. The macrocyclic antibiotics include ansamacrolides, macrolides, macrocyclic peptides, polyenes and derivatives thereof. The process has been found to be especially advantageous for separation of optical isomers by electrophoresis and chromatography.

Identification Of Tyr413 As An Active Site Residue In The Flavoprotein Tryptophan 2-Monooxygenase And Analysis Of Its Contribution To Catalysis, Pablo Sobrado, Paul F. Fitzpatrick

Chemistry Faculty Research & Creative Works

The flavoenzyme tryptophan 2-monooxygenase catalyzes the oxidation of tryptophan to indole acetamide, carbon dioxide, and water. The enzyme is a homologue of L-amino acid oxidase. In the structure of L-amino acid oxidase complexed with aminobenzoate, Tyr372 hydrogen bonds with the carboxylate of the inhibitor in the active site. All 10 conserved tyrosine residues in tryptophan 2-monooxygenase were mutated to phenylalanine; steady state kinetic characterization of the purified proteins identified Tyr413 as the residue homologous to Tyr372 of L-amino acid oxidase. Y413F and Y413A tryptophan 2-monooxygenase were characterized more completely with tryptophan as the substrate to probe the contribution of this …

Analysis Of The Role Of The Active Site Residue Arg98 In The Flavoprotein Tryptophan 2-Monooxygenase, A Member Of The L-Amino Oxidase Family, Pablo Sobrado, Paul F. Fitzpatrick

Chemistry Faculty Research & Creative Works

The flavoprotein tryptophan 2-monooxygenase catalyzes the oxidative decarboxylation of tryptophan to indole acetamide. We have previously identified tryptophan 2-monooxygenase as a homologue of L-amino acid oxidase [Sobrado, P., and Fitzpatrick, P. F. (2002) Arch. Biochem. Biophys. 402, 24-30]. On the basis of the sequence comparisons of the different LAAO family members, Arg98 of tryptophan 2-monooxygenase can be identified as an active site residue which interacts with the carboxylate of the amino acid substrate. The catalytic properties of R98K and R98A tryptophan 2-monooxygenase have been characterized to evaluate the role of this residue. Mutation of Arg98 to lysine decreases the first-order …

An Alternative Mechanism For The Dimerization Of Formic Acid, Nicole R. Brinkmann, Gregory S. Tschumper, Ge Yan, Henry F. Schaefer

Chemistry Faculty Research & Creative Works

Gas-phase formic acid exists primarily as a cyclic dimer. The mechanism of dimerization has been traditionally considered to be a synchronous process; however, recent experimental findings suggest a possible alternative mechanism by which two formic acid monomers proceed through an acyclic dimer to the cyclic dimer in a stepwise process. To investigate this newly proposed process of dimerization in formic acid, density functional theory and second-order Møller - Plesset perturbation theory (MP2) have been used to optimize cis and trans monomers of formic acid, the acyclic and cyclic dimers, and the acyclic and cyclic transition states between minima. Single-point energies …

Study Of The Electronic Properties Of Some Ytterbium Filled Skutterudites By Magnetic Susceptibility And X-Ray Absorption And Tin-119 Mössbauer Spectroscopy, Fernande Grandjean, Gary J. Long, Bernard M. Mahieu, Ji Hui Yang, Gregory P. Meisner, Donald T. Morelli

Chemistry Faculty Research & Creative Works

Magnetic susceptibility, ytterbium L_III-edge x-ray absorption and tin-119 Mössbauer spectral measurements have been carried out to probe the electronic structure of ytterbium and tin in the filled or partially filled skutterudite compounds, Yb_yCo₄Sb_12-xSn_x, over a range of x and y values. The ytterbium valence obtained from the magnetic susceptibility and ytterbium L_III-edge x-ray absorption measurements is in excellent agreement and clearly reveals an evolution from intermediate valence ytterbium for x=0 to nearly divalent ytterbium for x=0.8. This evolution parallels an increase in the unit cell volume and hence …

Melanoma And Seborrheic Keratosis Differentiation Using Texture Features, Srinivas V. Deshabhoina, Scott E. Umbaugh, William V. Stoecker, Randy Hays Moss, Subhashini K. Srinivasan

Chemistry Faculty Research & Creative Works

Purpose: To explore texture features in two-dimensional images to differentiate seborrheic keratosis from melanoma.

Methods: A systematic approach to consistent classification of skin tumors is described. Texture features, based on the second-order histogram, were used to identify the features or a combination of features that could consistently differentiate a malignant skin tumor (melanoma) from a benign one (seborrheic keratosis). Two hundred and seventy-one skin tumor images were separated into training and test sets for accuracy and consistency. Automatic induction was applied to generate classification rules. Data analysis and modeling tools were used to gain further insight into the feature space. …

Single-Walled Carbon Nanotube Bundles Intercalated With Semiconductor Nanoparticles, Manashi Nath, Pallavi V. Teredesai, D. V. S. Muthu, A. K. Sood, Chintamani Nagesa Ramachandra Rao

Chemistry Faculty Research & Creative Works

Nanoparticles of CdSe, CdS and ZnSe have been incorporated in the inter-tubular gaps of single-walled carbon nanotube (SWNT) bundles. Electron microscope, X-ray diffraction (XRD), electronic spectroscopy and Raman studies have been employed to characterize these systems. The lengths of the intercalate inside the bundles could be varied by changing the reaction conditions. Electronic absorption and photoluminescence studies from the semiconductor intercalates show the expected blue-shift with respect to the corresponding bulk samples in CdS and ZnS samples. The SWNT lattice is expanded on incorporating CdSe as confirmed by XRD in the low-angle range. The expansion in the lattice is also …

Ab Initio Theoretical Studies Of Potential Energy Surfaces In The Photodissociation Of The Vinyl Radical. I. Ã State Dissociation, Peng Zhang, Stephan Irle, Keiji Morokuma, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

The mechanism of photodissociation of the vinyl radical, C₂H₃ was studied with high-level ab initio methods. Geometry optimizations of stationary points and surface crossing seams were performed with complete active space self-consistent field method. Both internal conversion and intersystem crossing channels which bring the excited vinyl radical down to ground state potential energy surface were identified.

A Multicentered Approach To Integrated Qm/Qm Calculations. Applications To Multiply Hydrogen Bonded Systems, Brian W. Hopkins, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

A multicentered integrated QM/QM technique has been developed. By separating high-level calculations in distinct regions of molecules, the multicentered approach supplants a single large high-level calculation with several smaller calculations. Due to the step polynomial scaling of traditional ab initio quantum chemical methods, this separation significantly enhances the computational efficiency of QM/QM methods. The straightforward implementation of this multicentered approach is illustrated with several large poly-alcohols that form hydrogen bonds with water. The largest alcohol-water complex contains 81 atoms. For properly selected model systems, this multicentered approach introduces essentially no error in the dissociation energies of these complexes relative to …

One-Step Processing Of Spinel Ferrites Via The High-Energy Ball Milling Of Binary Oxides, V. G. Harris, D. J. Fatemi, J. O. Cross, E. E. Carpenter, V. M. Browning, J. P. Kirkland, Amitabh Mohan, Gary J. Long

Chemistry Faculty Research & Creative Works

MnZn ferrites have been produced via the high-energy ball milling of binary oxide precursors. The milled ferrites have a nonequilibrium cation site distribution, with an unusually high population of Zn cations on the octahedral sites. The particle size distribution drops precipitously with milling time from 60±1 to ∼14±1 nm at 10 h, but increases to 18.5±1 nm after long durations (20–40 h) concurrent with the formation of nearly pure ferrite. A 1 h anneal at 673 K facilitates a redistribution of cations to their near equilibrium sites. This processing approach circumvents the need for deleterious high-temperature heat treatments that often …

Solvent And Method For Extraction Of Triglyceride Rich Oil, Shubhender Kapila, Paul Ki-Souk Nam, V. J. Flanigan

Chemistry Faculty Research & Creative Works

The present invention relates to a solvent for use in extracting oil from an oil bearing material, such as soybeans, with the solvent resulting in the selective extraction of a triglyceride rich oil, which contains 95% or greater triglycerides and non-polar constituents, with the solvent comprised of a hydrocarbon, preferably hexane, and a fluorocarbon, so that the solvent has a viscosity less than 2.6 centipoise and a polarity of less than 0.1. The present invention also relates to a method of using the solvent to extract the triglyceride rich oil, with the method including preferably extracting the oil at a …

Properties Of A Mixed-Valent Iron Compound With The Kagomé Lattice, Chintamani Nagesa Ramachandra Rao, Geo L. Paul, Amitava Choudhury, Echur Varadadesikan Sampathkumaran, Arup Kumar R. Raychaudhuri, Suryanarayanasastry Ramasesha, Indranil Rudra

Chemistry Faculty Research & Creative Works

An organically templated iron sulfate of the formula [HN(CH₂)₆NH][Fe^III Fe₂ ^IIF₆(SO₄)₂] ·[H₃O] possessing the kagomé lattice has been prepared and characterized by single-crystal crystallography and other techniques. This mixed-valent iron compound shows complex magnetic properties including spin-glass behavior and magnetic hysteresis. The low-temperature specific heat data show deviation from the T² behavior found in two-dimensional frustrated systems. Simple calculations have been carried out to understand the properties of this kagomé compound.

Einstein Oscillators In Thallium Filled Antimony Skutterudites, Raphaël P. Hermann, Rongying Jin, Werner Schweika, Fernande Grandjean, David G. Mandrus, Brian C. Sales, Gary J. Long

Chemistry Faculty Research & Creative Works

Heat capacity measurements were performed on Tl_0.8Co₄Sb₁₁Sn. An Einstein vibrating behavior for the thallium atoms was found. The inelastic neutron scattering measurements on T_0.8Co₄Sb₁₁Sn, Tl_0.5Co_3.5Fe_0.5Sb₁₂, and Tl_0.8Co₃FeSb₁₂ showed a localized vibrational mode, which confirmed this Einstein vibrational behavior. Furthermore, the 56±2 K temperature of the Einstein vibrational mode obtained from the heat capacity measurements showed excellent agreement with the 5 meV energy or 57±2 K values obtained from the neutron scattering measurements.

Concerning The Stability Of Dichlorodiazene, Gregory S. Tschumper, Michael C. Heaven, Keiji Morokuma

Chemistry Faculty Research & Creative Works

The stability of N2Cl2 with respect to dissociation into N2 + 2Cl has been investigated using ab initio electronic structure techniques. Triple-ζ basis sets with d- and f-functions were required to obtain qualitative agreement between multi-reference and highly correlated single reference methods regarding the stability of the cis- and trans-isomers. The CCSD(T) method predicts a barrier to dissociation of 7-8 kcal mol-1 for the two isomers. CASPT2 barrier heights are substantially smaller (≤1.5 kcal mol^-1), indicating that these species are barely bound. © 2003 Elsevier Science B.V. All rights reserved.

Magnetic And Mössbauer Spectral Study Of Erfe₁₁Ti And Erfe₁₁Tih, Cristina Piquer, Raphäel P. Hermann, Fernande Grandjean, Gary J. Long, Olivier Isnard

Chemistry Faculty Research & Creative Works

The influence of the insertion of hydrogen into the crystal lattice of ErFe₁₁Ti upon its spin reorientation was investigated. It was found that the insertion of hydrogen into ErFe₁₁Ti to form ErFe₁₁TiH expanded the lattice by 1% and increased the Curie temperature by 56 K. The presence of one titanium near neighbor in the environment of an iron site decreased the hyperfine field by ~2T and changed the isomer shift by ~0.05 mm/s.

Dynamics Of Adsorbed Poly(Methyl Acrylate) And Poly(Methyl Methacrylate) On Silica, Frank D. Blum, Wuu-Yung Lin, Crystal E. Porter

Chemistry Faculty Research & Creative Works

Deuterium NMR and modulated differential scanning calorimetry (MDSC) were used to probe the behavior of ultrathin adsorbed poly(methyl acrylate) (PMA). The spectra for the bulk methyl-labeled PMA-d3 were consistent with the motions of the polymer segments being spatially homogeneous. For the polymers adsorbed on silica, multicomponent line shapes were observed. The segmental mobility of the surface polymers increased with increased adsorbed amounts. In contrast to the behavior of the polymers in bulk, the adsorbed lower-molecular-mass PMA-d3 was less mobile than the adsorbed high-molecular-mass polymer. The presence of a polymer overlayer was sufficient to suppress the enhanced mobility of the more-mobile …