Chemistry Commons^™

Experimental And Theoretical Study Of Benzene (Acetonitrile)(N) Clusters, N=1-4, M. Samy El-Shall, George M. Daly, Douglas Wright

Chemistry Publications

Well-resolved spectra of benzene–acetonitrile binary clustersBAn, with n=1–4 have been obtained by the (one-color) resonant two-photonionization technique using the benzene’s B2u←A1g 000 and 610 resonances. The spectra reveal a rapid increase in complexity with the number of acetonitrile molecules in the cluster, associated with van der Waal modes and isomeric forms. While only single cluster origins are found for the benzene–acetonitrile (BA) and the BA2clusters, two and four distinct isomers are identified for the BA3 and BA4clusters, respectively. The origins of the BA and BA2clusters are blueshifted with respect to the free benzene molecule by 38 cm⁻¹ and 26 …

Sythesis And Characterization Of [(C5r5) M (Co)2 (L2)]+: R=H, Me And Ph; M=Cr And Mo; L2=Dmpe And Dppe, Brian Dearman

Theses, Dissertations and Capstones

For two decades much research has been concentrated on open-shell transition metal complexes as chemical intermediates. To date, most efforts have concentrated on electron deficient, 17-electron (17e) compounds; however past research has shown that electronically supersaturated, 19-electron (19e) complexes can also participate as intermediates in many reactions. Yet, excluding (C₅ H₅)Fe(C₆ H₆) type complexes, very few of these compounds have been prepared.^2,3 To better understand the nature of 19e, the preparation of another series of compounds is desirable.

The addition of the bidentate Lewis bases 1,2- bis(dimethylphosphino)ethane (dmpe) or 1,2-bis(diphenylphosphino)ethane (dppe) to a …

Studies Of Ppi Dendrimers: Structures, Properties, And Potential Applications, Dian He

Theses, Dissertations and Capstones

The research reported in this thesis focused on poly (propylene imine) (PPI) dendrimers, in terms of their structures, properties and potential applications. Different analytical techniques, including our main research tool, NMR spectroscopy, as well as AFM imaging and UV-vis spectroscopy, were used for the elucidation of structural information. The study showed (1) PPI dendrimers tend to have the extended chain conformation in polar solvents because of the strong interaction between solvent and dendrimer molecules, while in nonpolar solvents the dendrimers are inclined to have the back-folded chain conformation as a result of the weaker interaction between …

Article Are Hydrogen Bonds Unique Among Weak Interactions In Their Ability To Mediate Electronic Coupling?, Emily Cukier '03, Sarah Daniels '02, Eric Vinson '01, Robert J. Cave

All HMC Faculty Publications and Research

Superexchange effects on the electronic coupling element for electron transfer are investigated using water dimers and atomic donors and acceptors. We compare the electronic coupling elements obtained with H-bonded dimers to those obtained for other water dimer geometries at given donor−acceptor and oxygen−oxygen distances. The H-bonded orientation does not yield significantly different coupling elements from non-H-bonded orientations at a given oxygen−oxygen distance. In addition, the distance dependence of the coupling mediated by H-bonds is not significantly different from that for other dimer geometries. It is found that protonation of the intervening waters has a significant effect on coupling elements for …

Atomization Energies And Enthalpies Of Formation Of The Snbin (N=1-3) Gaseous Molecules By Knudsen Cell Mass Spectrometry, Giovanni Meloni, Karl A. Gingerich

Chemistry Faculty Publications

The equilibria involving the gaseous species SnBi, SnBi2, and SnBi3 above the condensed system Bi–Sn contained in a graphite cell have been investigated by the Knudsen effusion technique combined with mass spectrometry. Third law enthalpies for the reactionsSnBin(g)=Sn(cond)+nBi(g), n=1–3, were evaluated. By combining the experimental reactionenthalpies with the appropriate thermodynamic data taken from literature, the following atomization energies, ΔaHo0, and enthalpies of formation,ΔfHo298.15, in kJ mol⁻¹, have been derived: SnBi, 191.1±12.0 and 317.5±12.0; SnBi2, 415.2±15.0 and 303.0±15.0; SnBi3, 603.4±18.0 and 323.0±18.0.

Familial Als-Associated Mutations Decrease The Thermal Stability Of Distinctly Metallated Species Of Human Copper/Zinc Superoxide Dismutase, Daryl K. Eggers, J. A. Rodriguez, J. S. Valentine, J. A. Roe, A. Tiwari, R. H. Brown, L. J. Hayward

Faculty Publications, Chemistry

We report the thermal stability of wild type (WT) and 14 different variants of human copper/zinc superoxide dismutase (SOD1) associated with familial amyotrophic lateral sclerosis (FALS). Multiple endothermic unfolding transitions were observed by differential scanning calorimetry for partially metallated SOD1 enzymes isolated from a baculovirus system. We correlated the metal ion contents of SOD1 variants with the occurrence of distinct melting transitions. Altered thermal stability upon reduction of copper with dithionite identified transitions resulting from the unfolding of copper-containing SOD1 species. We demonstrated that copper or zinc binding to a subset of “WT-like” FALS mutants (A4V, L38V, G41S, G72S, D76Y, …

Chemical Analysis By X-Ray Spectroscopy Near Phase Transitions In The Solid State, Juana Vivó Acrivos, L. Nguyen, T. Norman, C. T. Lin, W. Y. Liang, J. M. Honig, P Somasundaran

Faculty Publications, Chemistry

The methods discussed in this work show that the types of changes which may be observed, by precise XAS measurements of Absorbance A versus temperature, across a phase transition are: the changes in the relaxation time of the final states  due to fluctuations near a phase transition; the detection of the anomalous Bragg condition coupled to phonon modes XAS enhancement that identifies the temperature interval where the phonon modes are active, the symmetry changes which introduce new allowed transitions to finite states below an element edge, near Tc indicate what symmetry changes occur, and the method of XTDAFST0 = …

Calorimetric Study Of Block-Copolymers Of Poly(N-Butyl Acrylate) And Gradient Poly(N-Butyl Acrylate-Co-Methyl Methacrylate), A I. Buzin, M Pyda, P Costanzo, K Matyjaszewski, B Wunderlich

Chemistry and Biochemistry

The nanophase separation in diblock and triblock copolymers consisting of immiscible poly(n-butyl acrylate) (block A) and gradient copolymers of methyl methacrylate (MMA) and n-butyl acrylate (n BA) (block M/A) were investigated by means of their heat capacity, C_p, as a function of the composition of the blocks M/A and temperature. In all copolymers studied, both blocks are represented by their C_p and glass transition temperature, T_g, as well as the broadening of the transition-temperature range. The low-temperature transition of the blocks A is always close to that of the …

The Crystal Packing Of 4,7-Dichloro- And 4,7-Dibromobenzo[C]Furazan 1-Oxide, D. Britton, Frank B. Mallory, C. W. Mallory

Chemistry Faculty Research and Scholarship

The molecular structures of 4,7-dichlorobenzo[c]furazan 1-oxide, C6H2Cl2N2O2, (I), and 4,7-dibromobenzo[c]furazan 1-oxide, C6H2Br2N2O2, (II), are normal. Compound (I) occurs in two polymorphic forms. One polymorph contains one molecule in the asymmetric unit, organized into two-dimensional sheets involving intermolecular N...Cl and O...Cl interactions. The second polymorph has three molecules in the asymmetric unit, organized into two crystallographically different two-dimensional sheets with similar interactions. Compound (II) is isomorphous with the second polymorph of (I). The three two-dimensional sheets in the two polymorphs comprise a set of three two-dimensional polymorphic arrangements.

Chemical Composition Of Particles Of D < 0.20 Mu In The Lower Stratospheric Aerosol, Spring 1993, Joseph D. Scott, David M. Chittenden Ii

Journal of the Arkansas Academy of Science

The majority of the mass of stratospheric aerosol collected during the spring of 1993 consisted principally of particles of d >0.20 mu containing a mixture of H2SO4 and (NaK)2SO4. However, the composition of the more numerous particles with d< 0.2 mu was very different. X-ray emission spectra (EDS) of individual particles indicated that there were three different chemical populations of small particles. The most numerous population was almost all C with only traces of S and Na. The second population contained metal sulfates and chlorides, possibly accreted to a C-containing matrix. The third population consisted of S- and Cl- containing species and trace amounts of Na and K ions. The number of equivalents of metal ion was much less than that of S and Cl species, indicating that most of the S and Cl was not ionic, but was covalently bonded, perhaps to a C matrix.

Experimental And Computational Study Of The New Gaseous Molecules Omnf And Omnf[Sub 2], G Balducci, M Campodonico, G Gigli, Giovanni Meloni, S N. Cesaro

Chemistry Faculty Publications

The new gaseous species OMnF and OMnF2 were identified and studied by high-temperature Knudsen Cell Mass Spectrometry. Their thermochemical atomization energies were derived through the study of several all-gas equilibria in the temperature range 1735–1913 K. FTIR matrix isolation experiments together with ab initio and density functional calculations were performed to determine the molecular parameters, bond distances, and vibrational frequencies of OMnF(g) and OMnF2(g) . The results allowed us to evaluate a set of thermal functions for the new species that were used in the evaluation of the equilibrium data. The proposed atomization energies and enthalpies of formation are DaH0 …

Time-Dependent Density Functional Theory Investigation Of The Ground And Excited States Of Coumarins 102, 152, 153, And 343, Robert J. Cave, Edward W. Castner Jr.

All HMC Faculty Publications and Research

We present calculations of various properties of the ground and excited electronic states of coumarins 102, 152, 153, and 343. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT), we examine the excitation energies to the S₁ and S₂ states, the ground and excited-state dipole moments, and the lowest ionization potentials of these coumarins. In the case of C153, we locate two distinct S₀ minima due to differing conformations of the julolidyl ring structure and compare properties for the syn and anti conformers. For C343, we examine the possibility of proton transfers in the ground …

An On-Line Acid-Base Titration Applet In The Generic Tutorial System For The Sciences Project, Thomas Lee Gummo

Theses Digitization Project

The purpose of this Master's Project was to develop an Acid-Base Titration Simulator. It was also to be a part of the California State University - San Bernardino's GTSS, Generic Tutorial System for the Sciences, project. The main benefit is that students will be able to conduct titration experiments over the Internet without being in the laboratory and without costly equipment or dangerous chemicals. Instructors at the high school and college level can demonstrate the key principles of titration.

Synthesis And Chemistry Of Naphthalene Annulated Trienyl Iron Complexes: Potential Anticancer Dna Alkylation Reagents, Traci Means

Inquiry: The University of Arkansas Undergraduate Research Journal

Iron complex chemistry that opens a new door to the medicinal and pharmaceutical worlds is the aim of this research. Specifically, ortho-quinone methide moieties are intermediates in several antitumor drugs and have been identified as bioreductive alkylators of DNA. In our research, a class of iron compounds has been targeted to resemble these quinone methides. It is hoped that these new compounds could be modified to provide a window of opportunity toward the discovery of a selective mode of drug delivery. We have focused our efforts on generating a reactive transition metal complexed 5-membered ring analog of o-quinone methide based …

Electronic Structure And Bonding In Unligated And Ligated Feii Porphyrins, M.-S. Liao, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The electronic structure and bonding in a series of unligated and ligated Fe^II porphyrins (FeP) are investigated by density functional theory (DFT). All the unligated four-coordinate iron porphyrins have a ³A_2g ground state that arises from the (d_xy)²(d_z²)²(d_π)² configuration. The calculations confirm experimental results on Fe tetraphenylporphine but do not support the resonance Raman assignment of Fe octaethylporphine as ³E_g, nor the early assignment of Fe octamethyltetrabenzporphine as ⁵B_2g. For the six-coordinate Fe–P( …

Electronic Structure And Bonding In Metal Porphyrins, Metal=Fe, Co, Ni, Cu, Zn, M.-S. Liao, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

A systematic theoretical study of the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, M=Fe, Co, Ni, Cu, Zn has been carried out using a density functional theory method. The calculations provide a clear elucidation of the ground states for the MTPPs and for a series of [MTPP]^x ions (x = 2+, 1+, 1−, 2−, 3−, 4−), which aids in understanding a number of observed electronic properties. The calculation supports the experimental assignment of unligated FeTPP as ³A_2g, which arises from the configuration (d_xy)²(d_{z …}

An Adaptive, Kink-Based Approach To Path Integral Calculations, Randal W. Hall

Collected Faculty Scholarship

A kink-based expression for the canonical partition function is developed using Feynman’s path integral formulation of quantum mechanics and a discrete basis set. The approach is exact for a complete set of states. The method is tested on the 3×3 Hubbard model and overcomes the sign problem seen in traditional path integral studies of fermion systems. Kinks correspond to transitions between different N-electron states, much in the same manner as occurs in configuration interaction calculations in standard ab initio methods. The different N-electron states are updated, based on which states occur frequently during a Monte Carlo simulation, giving better estimates …

Recent Applications Of Flame Atomic Absorption Spectrometry To Environmental Measurements, Michael A. Janusa

Faculty Publications

Atomic absorption spectroscopy is very useful for the determination of a large number of elements, especially at trace levels. It is a widely used technique for analysis of a wide variety of sample matrices including biota, soils, and water. Atomic absorption spectroscopy is a very reputable technique that is inexpensive and delivers accurate results even in a complex matrix. This review focuses on the applications of flame atomic absorption spectroscopy to environmental measurements, and is mainly based on papers published from 1999–2002.

3-Methoxy-1'-Phenyl-4'[Beta],5-Di­Hydro-1h-Pyrazolo­[4',3':16,17]­Estra-1,3,5(10)-Triene, Veronica Konig, Thomas R. Schneider, E. Frank, Beatrix Aukszi, Gyula Schneider, Janos Wolfling

Chemistry and Physics Faculty Articles

The regio- and stereochemistry of the title compound, C26H30N2O, has been established by X-ray analysis. The configuration of the stereogenic centre at C-16 proved to be S and the H atom at C-16 adopts the position.

Pyridoimidazolium Cationic Dyes: Theory, Synthesis, And Sub-Cellular Localization, Robert William Rambacher

Theses, Dissertations and Capstones

(PICs, Figure 1) are a new class of fluorescent dyes which are prepared by an exceedingly flexible methodology. Using computational chemical methods, the excitation and emission maxima of these dyes were simulated. This was best accomplished through geometry optimization (MM+) followed by calculating the electronic spectrum with ZINDO/S. This protocol has been found to be effective and has the potential to greatly streamline the design of new longer wavelength dyes. Several new longer wavelength dyes have now been identified as synthetic targets.

The presence of amino groups on a known fluorescent ring system is well established to markedly affect the …

Stimulation And Modeling Of Pond Formations On The Asteroid 433 Eros, Justin Thompson

Inquiry: The University of Arkansas Undergraduate Research Journal

"Ponds" are surface features that appear to be the result of the deposition of finer material on the asteroid's regolith, the layer of loose sediment that blankets the entire asteroid. Ponds were discovered by the NEAR Shoemaker spacecraft in January, 2001, on the asteroid 433 Eros. The objective of experimentation is to simulate the development of these ponds in the Andromeda planetary sciences environmental chamber. The Andromeda Chamber offers a unique ability to simulate surface environments that occur on Eros. The chamber was used to simulate the processes that occur as Eros emits gas through its outer surface, including the …

Base Hydrolysis Kinetics Of Cobalt(Iii) Spiro-Octaamine Dimer, Yakup Baran, Geoffrey Lawrence

Turkish Journal of Chemistry

The preparation and characterisation of a cobalt (III) complex of octaaza ligand, 5, 5'-bis(4-amino-2-azabutyl)-1,9-diamino-3,7-diazanonane (octaam) is described. The base hydrolysis kinetics of bis cobalt(III) of octaam has been studied spectrophotometrically by the stopped-flow technique. A consequent reaction is observed in the base hydrolysis of the spiro-octaamine with the fast reaction having k_{OH} = 3.55 M^{-1}s^{-1} and the slower reaction k_{OH} = 0.72 M^{-1}s^-1} at 298 K with \Delta H^{\#} = 89 kJ/mol for the fast stage and \Delta H^{\#} = 102 kJ/mol for the slow stage (I = 0.4 M NaClO_4). The fast reaction is assigned to the hydrolysis of …

Theoretical Investigation Of The Ground And Excited States Of Coumarin 151 And Coumarin 120, Robert J. Cave, Kieron Burke, Edward W. Castner Jr.

All HMC Faculty Publications and Research

We present calculations of various properties of the ground and excited states of Coumarins 151 and 120. These and related coumarins are important in investigating ultrafast solvation processes in liquids and complex solutions as well as being important acceptors in model electron-transfer systems. We calculate the following:  (1) the electronic excitation energies to several low-lying singlet states, (2) ground and excited-state dipole moments, (3) solvation effects on excitation energies, and (4) the properties of single Coumarin 151-water complexes. We test our Time-Dependent Density Functional Theory (TDDFT) calculations against CASSCF, CASPT2 (both single and multistate versions), CIS, and ZINDO. Using TDDFT, …

Multistate Effects In Calculations Of The Electronic Coupling Element For Electron Transfer Using The Generalized Mulliken−Hush Method, Michael Rust '01, Jason Lappe '00, Robert J. Cave

All HMC Faculty Publications and Research

A simple diagnostic is developed for the purpose of determining when a third state must be considered to calculate the electronic coupling element for a given pair of diabatic states within the context of the generalized Mulliken−Hush approach (Chem. Phys. Lett. 1996, 275, 15−19). The diagnostic is formulated on the basis of Löwdin partitioning theory. In addition, an effective 2-state GMH expression is derived for the coupling as it is modified by the presence of the third state. Results are presented for (i) a model system involving charge transfer from ethylene to methaniminium cation, (ii) a …

Reduction Of Dendrite Formations To Improve The Appearance Of The Powder Cured Films For Automotive Industry, Alexandru S. Biris, C. U. Yurteri, Malay K. Mazumder, Robert A. Sims, P. H. Williams

Journal of the Arkansas Academy of Science

The appearance of powder-coated films is dependent upon powder chemistry and spraying parameters. One of the most important physical factors controlling the powder film appearance is the microdeposition of the powder particles on the grounded substrate. During the electrostatic deposition of powder, the formation of dendrites and agglomerates was observed; these formations have an adverse effect on the final film appearance and their elimination may result in smoother and glossier films. Dendrites are generated due to bipolar charging and inter-particulate electrostatic attractive forces. The corona charging technique is mostly used in industrial powder coating applications. At low corona voltages (- …

Quality Of Tap Water In 20 Selected Areas In Selangor, Christine Boon Hwee Ong

Student Works (2000-2009)

The quality of tap water is becoming of great concern to the public all over the wor1d. However, this study only covers the issue of tap water in Selangor and public's reactions towards it. Many of us question whether our tap water is clear, clean and safe enough for consumption. To many of us, the water problem that we face is acid water, contains iron and minerals, bacteria and it is hard water. Acid water Is a real problem nowadays as the environment gets more and more polluted due to gas emitted from industries, for example S02 and CO2. Acid …

Formation Of Copper Dots In Copper Decoration Technique, Swee Yong Pung

Student Works (2000-2009)

Copper ions are dissolved from highly pure copper plate into the methanol during copper decoration process. As a result, copper concentration in methanol is increased with time. The copper concentration in methanol measured by ICP-OES is correlated well with the calculated value based on the magnitude of current and time during the process. Consequently, higher magnitude of current can be applied to build up copper concentration in methanol in shorter period. When copper ions are ejected in methanol, they are positively charged. They experience force from electric field and migrate towards oxide surface. Eventually, these copper ions will be discharged …

Motion Based Event Recognition Using Hmm, Gu Xu, Yu-Fei Ma, Hong-Jiang Zhang, Shiqiang Yang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Motion is an important cue for video understanding and is widely used in many semantic video analyses. We present a new motion representation scheme in which motion in a video is represented by the responses of frames to a set of motion filters. Each of these filters is designed to be most responsive to a type of dominant motion. Then we employ hidden Markov models (HMMs) to characterize the motion patterns based on these features and thus classify basketball video into 16 events. The evaluation by human satisfaction rate to classification result is 75%, demonstrating effectiveness of the proposed approach …

Electrical And Magnetotransport Properties Of Canted Antiferromagnet Dy₅Si₂Ge₂, R. Nirmala, V. Sankaranarayanan, K. Sethupathi, Zili Chu, William B. Yelon, V. Prasad, A. V. Morozkin, Satish K. Malik, S. V. Subramanyam

Physics Faculty Research & Creative Works

Summary form only given. Since the giant magnetocaloric effect is encountered in a ferromagnetic Gd5Si2Ge2 alloy near room temperature it is considered as a suitable material for magnetic refrigerator applications. Also a commensurate structural transition occurs at the magnetic transition temperature and there is a good correlation between the crystal structure and magnetic properties. Such observations have triggered numerous experimental studies on similar rare earth alloys and compounds. We have synthesized its Dy- analogue, namely, Dy5Si2Ge2 and have characterized it by means of room temperature X-ray diffraction, ac magnetic susceptibility (15 K - 300 K), electrical resistivity (at zero field …

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 …