Open Access. Powered by Scholars. Published by Universities.®

Chemistry Commons™

Open Access. Powered by Scholars. Published by Universities.®

PDF

Portland State University

Chemistry Faculty Publications and Presentations

Discipline
Keyword
Publication Year

Articles 241 - 267 of 267

Full-Text Articles in Chemistry

Europium(Iii) Macrocyclic Complexes With Alcohol Pendant Groups As Chemical Exchange Saturation Transfer Agents, Mark Woods, Donald E. Woessner, Piyu Zhao, Azhar Pasha, Meng-Yin Yang, Ching-Hui Huang, Olga Vasalatiy, Janet R. Morrow, A. Dean Sherry Aug 2006

Europium(Iii) Macrocyclic Complexes With Alcohol Pendant Groups As Chemical Exchange Saturation Transfer Agents, Mark Woods, Donald E. Woessner, Piyu Zhao, Azhar Pasha, Meng-Yin Yang, Ching-Hui Huang, Olga Vasalatiy, Janet R. Morrow, A. Dean Sherry

Chemistry Faculty Publications and Presentations

Paramagnetic lanthanide(III) complexes that contain hyperfine-shifted exchangeable protons offer considerable advantages over diamagnetic molecules as chemical exchange saturation transfer (CEST) agents for MRI. As part of a program to investigate avenues to improve the sensitivity of such agents, the CEST characteristics of europium(III) macrocyclic complexes having appended hydroxyethyl groups were investigated. The CEST spectrum of the asymmetrical complex, EuCNPHC3+, shows five distinct peaks for each magnetically nonequivalent exchangeable proton in the molecule. The CEST spectra of this complex were fitted to NMR Bloch theory to yield exchange rates between each of six exchanging proton pools (five on the …

Go to article

Comments On The Mechanism Of Aging Of Antimony Doped Tin Oxide Based Electrochromic Devices, Joo C. Chan, Nicole A. Hannah, Shankar B. Rananavare, Laura Yeager, Liviu Dinescu, Ashok Saraswat, Pradeep Iyer, James P. Coleman Jan 2006

Comments On The Mechanism Of Aging Of Antimony Doped Tin Oxide Based Electrochromic Devices, Joo C. Chan, Nicole A. Hannah, Shankar B. Rananavare, Laura Yeager, Liviu Dinescu, Ashok Saraswat, Pradeep Iyer, James P. Coleman

Chemistry Faculty Publications and Presentations

Electrochromic effects of antimony doped tin oxide (ATO) nanoparticles are investigated to probe device yellowing (degradation). Voltage vs contrast ratio curves exhibit hysteresis, i.e., image-sticking phenomena due to irreversible charge insertion. X-ray, impedance and optical b* studies suggest that the yellowing/charge trapping is nanoparticle size-dependent with 4 nm size particles exhibiting the least yellowing. Yellowing results in increased impedances of electrode–electrolyte interface and electrode corrosion. Plausible sources of discoloration are formation of insulating complex alkali oxide film, carrier inversion (n-to-p type) through electrochemical Li doping, redeposition of the corroded electrode material and perhaps residual concentration of charge-transfer species.

Go to article

Structural And Chiroptical Properties Of The Two Coordination Isomers Of Ybdota-Type Complexes, Lorenzo Di Bari, Gennaro Pescitelli, A. Dean Sherry, Mark Woods Nov 2005

Structural And Chiroptical Properties Of The Two Coordination Isomers Of Ybdota-Type Complexes, Lorenzo Di Bari, Gennaro Pescitelli, A. Dean Sherry, Mark Woods

Chemistry Faculty Publications and Presentations

Studies of the structural, physical, and chemical properties of the lanthanide(III) complexes of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and related ligands are often complicated by the presence of two coordination isomers in solution. Since these coordination isomers are in exchange and cannot be separated, many techniques offer information only on the weighted average of the two isomers. Lanthanide ion complexes formed with the ligands S(RRRR)NO2BnDOTMA and S(SSSS)NO2BnDOTMA preferentially adopt only one of the two common coordination isomers in solution, so the ytterbium complexes of these ligands offer a unique opportunity to study …

Go to article

Effects Of Gramicidin-A On The Adsorption Of Phospholipids To The Air–Water Interface, Samares C. Biswas, Shankar B. Rananavare, Stephen B. Hall Nov 2005

Effects Of Gramicidin-A On The Adsorption Of Phospholipids To The Air–Water Interface, Samares C. Biswas, Shankar B. Rananavare, Stephen B. Hall

Chemistry Faculty Publications and Presentations

Prior studies suggest that the hydrophobic surfactant proteins, SP-B and SP-C, promote adsorption of the lipids in pulmonary surfactant to an air–water interface by stabilizing a negatively curved rate-limiting structure that is intermediate between bilayer vesicles and the surface film. This model predicts that other peptides capable of stabilizing negative curvature should also promote lipid adsorption. Previous reports have shown that under appropriate conditions, gramicidin-A (GrA) induces dioleoyl phosphatidylcholine (DOPC), but not dimyristoyl phosphatidylcholine (DMPC), to form the negatively curved hexagonal-II (HII) phase. The studies reported here determined if GrA would produce the same effects on adsorption of DMPC and …

Go to article

Towards The Rational Design Of Mri Contrast Agents: A Practical Approach To The Synthesis Of Gadolinium Complexes That Exhibit Optimal Water Exchange, Mark Woods, Mauro Botta, Stefano Avedano, Jing Wang, A. Dean Sherry Sep 2005

Towards The Rational Design Of Mri Contrast Agents: A Practical Approach To The Synthesis Of Gadolinium Complexes That Exhibit Optimal Water Exchange, Mark Woods, Mauro Botta, Stefano Avedano, Jing Wang, A. Dean Sherry

Chemistry Faculty Publications and Presentations

The gadolinium(III) complex of S-SSSS-NO2BnDOTMA exhibits water exchange kinetics that are optimal for use in high relaxivity or targeted contrast agents. However, the synthesis of this ligand is hampered by the steric encumbrance imparted upon the cyclen ring by the nitrobenzyl substituent. A relatively simple modification has been used to enable the synthesis of larger quantities of a bifunctional ligand that retains similar fast water exchange properties. The gadolinium complex of S-SSS-NO2BnDO3MA-1A is shown to retain the rapid water exchange kinetics characteristic of a twisted square antiprismatic (TSAP) …

Go to article

The Subsystems Approach To Genome Annotation And Its Use In The Project To Annotate 1000 Genomes, Ross Overbeek, Tadhg Begley, Ralph M. Butler, Jomuna V. Choudhuri, Han-Yu Chuang, Matthew Cohoon, Valérie De Crécy-Lagard, Naryttza Diaz, Terry Disz, Robert Edwards, Michael Fonstein, Ed D. Frank, Svetlana Gerdes, Elizabeth M. Glass, Alexander Goesmann, Andrew Hanson, Dirk Iwata-Reuyl, Roy Jensen, Neema Jamshidi, Lutz Krause, Michael Kubal, Niels Larsen, Burkhard Linke, Alice C. Mchardy, Folker Meyer, Heiko Neuweger, Gary Olsen, Robert Olson, Andrei Osterman, Vasiliy Portnoy, Gordon D. Pusch, Dmitry A. Rodionov, Christian Rückert, Jason Steiner, Rick Stevens, Ines Thiele, Olga Vassieva, Yuzhen Ye, Olga Zagnitko, Veronika Vonstein Jan 2005

The Subsystems Approach To Genome Annotation And Its Use In The Project To Annotate 1000 Genomes, Ross Overbeek, Tadhg Begley, Ralph M. Butler, Jomuna V. Choudhuri, Han-Yu Chuang, Matthew Cohoon, Valérie De Crécy-Lagard, Naryttza Diaz, Terry Disz, Robert Edwards, Michael Fonstein, Ed D. Frank, Svetlana Gerdes, Elizabeth M. Glass, Alexander Goesmann, Andrew Hanson, Dirk Iwata-Reuyl, Roy Jensen, Neema Jamshidi, Lutz Krause, Michael Kubal, Niels Larsen, Burkhard Linke, Alice C. Mchardy, Folker Meyer, Heiko Neuweger, Gary Olsen, Robert Olson, Andrei Osterman, Vasiliy Portnoy, Gordon D. Pusch, Dmitry A. Rodionov, Christian Rückert, Jason Steiner, Rick Stevens, Ines Thiele, Olga Vassieva, Yuzhen Ye, Olga Zagnitko, Veronika Vonstein

Chemistry Faculty Publications and Presentations

The release of the 1000th complete microbial genome will occur in the next two to three years. In anticipation of this milestone, the Fellowship for Interpretation of Genomes (FIG) launched the Project to Annotate 1000 Genomes. The project is built around the principle that the key to improved accuracy in high through put annotation technology is to have experts annotate single subsystems over the complete collection of genomes, rather than having an annotation expert attempt to annotate all of the genes in a single genome. Using the subsystems approach, all of the genes implementing the subsystem are analyzed by …

Go to article

The Reno Aerosol Optics Study: An Evaluation Of Aerosol Absorption Measurement Methods, Patrick J. Sheridan, W. Patrick Arnott, John A. Ogren, Elisabeth Andrews, Dean B. Atkinson, David S. Covert, Hans Moosmüller, Andreas Petzold, Beat Schmid, Anthony W. Strawa, Ravi Varma, Aki Virkkula Jan 2005

The Reno Aerosol Optics Study: An Evaluation Of Aerosol Absorption Measurement Methods, Patrick J. Sheridan, W. Patrick Arnott, John A. Ogren, Elisabeth Andrews, Dean B. Atkinson, David S. Covert, Hans Moosmüller, Andreas Petzold, Beat Schmid, Anthony W. Strawa, Ravi Varma, Aki Virkkula

Chemistry Faculty Publications and Presentations

The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative humidity conditions and delivered to each measurement system. The aerosol mixing and delivery system was constantly monitored using particle counters and nephelometers to ensure that the same aerosol number concentration and amount reached the different instruments. The aerosol light-scattering measurements …

Go to article

Toward The Design Of Mr Agents For Imaging Β-Cell Function, Mark Woods, Shanrong Zhang, A. Dean Sherry Dec 2004

Toward The Design Of Mr Agents For Imaging Β-Cell Function, Mark Woods, Shanrong Zhang, A. Dean Sherry

Chemistry Faculty Publications and Presentations

The chemistry of Gd3+-based MRI agents has advanced considerably during the past decade toward agents with higher relaxivity and agents that respond to physiology and / or metabolism. This review describes various approaches that have been taken toward the development of responsive contrast agents and discusses the importance of fast water exchange for advancement of targeted Gd3+-based agents with higher sensitivity. The recent discovery of Eu3+ complexes having extraordinarily slow water exchange has opened a new avenue in contrast agent design based upon the chemical exchange saturation transfer (CEST) mechanism. These new paramagnetic complexes called PARACEST agents offer new possibilities …

Go to article

Synthesis, Relaxometric And Photophysical Properties Of A New Ph-Responsive Mri Contrast Agent: The Effect Of Other Ligating Groups On Dissociation Of A P-Nitrophenolic Pendant Arm, Mark Woods, Garry Kiefer, Simon G. Bott, Aminta Castillo-Muzquiz, Carrie Eshelbrenner, Lydie Michaudet, Kenneth Mcmillan, Siva D.K. Mudigunda, Doug Ogrin, Gyula Tircso, Shanrong Zhang, Piyu Zhao, A. Dean Sherry Aug 2004

Synthesis, Relaxometric And Photophysical Properties Of A New Ph-Responsive Mri Contrast Agent: The Effect Of Other Ligating Groups On Dissociation Of A P-Nitrophenolic Pendant Arm, Mark Woods, Garry Kiefer, Simon G. Bott, Aminta Castillo-Muzquiz, Carrie Eshelbrenner, Lydie Michaudet, Kenneth Mcmillan, Siva D.K. Mudigunda, Doug Ogrin, Gyula Tircso, Shanrong Zhang, Piyu Zhao, A. Dean Sherry

Chemistry Faculty Publications and Presentations

Two gadolinium(III) chelates, GdNP-DO3A (1-methlyene-(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triAcetate) and GdNP-DO3AM (1-methlyene(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide), containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The properties of the gadolinium, terbium, and dysprosium complexes of these ligands were examined as a function of pH. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes. The water relaxivity of Gd(NP-DO3A) increases from 4.1 …

Go to article

Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel Sep 2003

Pressure-Induced Insulating State In An Organic Superconductor, Gary L. Gard, Javid Mohtasham, J. A. Schlueter, C. Pfleiderer, J. Wosnitza, J. Hagel

Chemistry Faculty Publications and Presentations

The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov–de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter λ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above …

Go to article

Enhanced Magnetic Quantum Oscillations In The Mixed State Of A Two-Dimensional Organic Superconductor, J. Wosnitza, J. Hagel, P. J. Meeson, D. Bintley, J. A. Schlueter, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard Feb 2003

Enhanced Magnetic Quantum Oscillations In The Mixed State Of A Two-Dimensional Organic Superconductor, J. Wosnitza, J. Hagel, P. J. Meeson, D. Bintley, J. A. Schlueter, Javid Mohtasham, Rolf Walter Winter, Gary L. Gard

Chemistry Faculty Publications and Presentations

We report on de Haas–van Alphen (dHvA) oscillations observed in the mixed state of the organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene) utilizing the field-modulation technique and torque magnetometry. At low temperatures (30 mK), the dHvA signal persists down to 1.4 T well below the upper critical field Bc2≈3.6T. Contrary to most theoretical predictions and previous experimental findings, no additional damping of the dHvA-oscillation amplitude, but a reduced damping of the dHvA signal is found. This highly unusual effect might indicate a reduced quasiparticle scattering rate or an additional oscillatory contribution in the superconducting state.

Go to article

Solving Chemical Problems Of Environmental Importance Using Cavity Ring-Down Spectroscopy, Dean B. Atkinson Jan 2003

Solving Chemical Problems Of Environmental Importance Using Cavity Ring-Down Spectroscopy, Dean B. Atkinson

Chemistry Faculty Publications and Presentations

Cavity ring-down (CRD) is a sensitive variant of traditional absorption spectroscopy that has found increasing use in a number of chemical measurement applications. This review focuses on applications of cavity ring-down spectroscopy that will be of interest to environmental chemists and analytical chemists working on environmental problems. The applications are classified into direct monitoring approaches, indirect analysis methods and ancillary studies and a differentiation is made between field-tested instruments and proof of principle studies.

Go to article

Space-Group Revision For 4-Formylphenylboronic Acid, Frank R. Fronczek, Nadia N. St Luce, Robert M. Strongin Dec 2001

Space-Group Revision For 4-Formylphenylboronic Acid, Frank R. Fronczek, Nadia N. St Luce, Robert M. Strongin

Chemistry Faculty Publications and Presentations

The space group of the title compound, C7H7BO3, previously reported to be P, is properly Cc. There is no disorder of the formyl group or in the H atoms of the B(OH)2 group. Molecules lie on approximate twofold axes and are related by approximate centers, which relate all but the formyl O atom and boronic acid H atoms. The B-O distances are 1.363 (2) and 1.370 (2) Å.

Go to article

Trimethylsulfonium Methanesulfonate, Frank R. Fronczek, Rolanda J. Johnson, Robert M. Strongin May 2001

Trimethylsulfonium Methanesulfonate, Frank R. Fronczek, Rolanda J. Johnson, Robert M. Strongin

Chemistry Faculty Publications and Presentations

In the title compound, C3H9S+.CH3O3S-, a thermal decomposition product of dimethyl sulfoxide, both cation and anion lie on mirror planes. In the cation, the S atom lies 0.792 (2) Å out of the plane defined by the three C atoms, with S-C distances of 1.781 (2) and 1.786 (3) Å. In the anion, the S-O distances are 1.4556 (14) and 1.4646 (19) Å, and the S-C distance is 1.759 (3) Å.

Go to article

Structure And Phase Transitions Of The 6, 6-Cyclopropane Isomer Of C_ {61} H_ {2}, M. R. Stetzer, Paul A. Heiney, Peter W. Stephens, R. E. Dinnebier, Q. Zhu, Andrew R. Mcghie, Robert M. Strongin, B. M. Brandt, Amos B. Smith Iii Oct 2000

Structure And Phase Transitions Of The 6, 6-Cyclopropane Isomer Of C_ {61} H_ {2}, M. R. Stetzer, Paul A. Heiney, Peter W. Stephens, R. E. Dinnebier, Q. Zhu, Andrew R. Mcghie, Robert M. Strongin, B. M. Brandt, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

We have used x-ray powder diffraction and differential scanning calorimetry to study the crystalline structures and thermal behavior of the 6,6-cyclopropane isomer of C61H2. At room temperature, the C61H2 cyclopropane molecules, like those of the 6,5-annulene isomer and C60O epoxide, are orientationally disordered and crystallize on a face-centered-cubic lattice such that their methylene groups are statistically disordered among the octahedral voids. Unlike 6,5−C61H2 and C60O, the low-temperature structure is not Pa3¯, but rather a low-symmetry orthorhombic lattice in which a≈b

Go to article

Structure, Dynamics, And Phase Transitions In The Fullerene Derivatives C_{60}O And C_{61}H_{2}, C. Meingast, G. Roth, L. Pintschovius, R. H. Michel, C. Stoermer, M. M. Kappes, Paul A. Heiney, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii Jul 1996

Structure, Dynamics, And Phase Transitions In The Fullerene Derivatives C_{60}O And C_{61}H_{2}, C. Meingast, G. Roth, L. Pintschovius, R. H. Michel, C. Stoermer, M. M. Kappes, Paul A. Heiney, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

The effect of perturbing the icosohedral symmetry of C60 by the addition of the side groups -O and -CH2 upon orientational order-disorder and glass transitions in solid C60 has been studied by a combination of high-resolution capacitance dilatometry and single-crystal x-ray and powder inelastic neutron scattering. Both fullerene derivatives C60O (epoxide) and C61H2 (6,5-annulene) are shown to undergo a sequence of transitions similar to that found in pure C60, i.e., a first-order orientational ordering transition just below room temperature followed by an orientational glass transition at lower temperatures. Although the …

Go to article

Smectic-A —Smectic-C* —Smectic-C Multicritical Point In Ferroelectric Liquid Crystals, Shankar B. Rananavare, V. G. K. M. Pisipati, E. W. Wong May 1994

Smectic-A —Smectic-C* —Smectic-C Multicritical Point In Ferroelectric Liquid Crystals, Shankar B. Rananavare, V. G. K. M. Pisipati, E. W. Wong

Chemistry Faculty Publications and Presentations

We report a smectic-A–smectic-C–smectic-C* (ACC*) multicritical point in mixtures of chiral DOBAMBC [p-(n-decyloxybenzylidene)-p-amino-(2-methyl-butyl)] cinnamate and achiral 10O.8 (4-decyloxybenzylidene-4-octylaniline). Studies of the phase diagram, tilt angle (θ), polarization (P), and helix pitch (p) indicate an ACC* Lifshitz point that can be described in terms of the extended Landau theory. Specifically, the T*AC and the maximum polarization (Pm) exhibit quadratic composition dependence while the helical pitch length (p=2π/q) varies linearly. Both q and Pm vanish discontinuously at the C-C* …

Go to article

Structure And Phase Transition Of The 6,5-Annulene Isomer Of C_{61}H_{2}, Andrea N. Lommen, Paul A. Heiney, Gavin B. M. Vaughan, Peter W. Stephens, Dengfa Liu, Dayin Li, Allan L. Smith, Andrew R. Mcghie, Robert M. Strongin, Laurent Brard, Amos B. Smith Iii May 1994

Structure And Phase Transition Of The 6,5-Annulene Isomer Of C_{61}H_{2}, Andrea N. Lommen, Paul A. Heiney, Gavin B. M. Vaughan, Peter W. Stephens, Dengfa Liu, Dayin Li, Allan L. Smith, Andrew R. Mcghie, Robert M. Strongin, Laurent Brard, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

We have used differential scanning calorimetry and x-ray diffraction to study the crystalline phases of the 6,5-annulene isomer of C61H2. At 308 K the methylenated fullerenes are orientationally disordered in a face-centered cubic lattice with lattice parameter 14.19±0.02 Å. Below Tc=290 K the symmetry is lowered to Pa3¯, a simple-cubic structure. At 20 K the lattice parameter is 14.06±0.02 Å, with substantial statistical disorder remaining. The transition temperature in C61H2 is slightly higher than in C60O and higher still than in C60, but the three compounds exhibit orientationally …

Go to article

Neutron-Scattering Study Of Librations And Intramolecular Phonons In Rb_{2.6}K_{0.4}C_{60}, D. Reznik, W. A. Kamitakahara, D. A. Neumann, J. R. D. Copley, J. E. Fischer, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii Jan 1994

Neutron-Scattering Study Of Librations And Intramolecular Phonons In Rb_{2.6}K_{0.4}C_{60}, D. Reznik, W. A. Kamitakahara, D. A. Neumann, J. R. D. Copley, J. E. Fischer, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from 300 to 12 K. As in K3C60, no change in the width or position of the librational peak was observed when the sample was cooled through the superconducting transition. Thus any coupling of the librations to electronic states is small. The magnitude of the orientational potential barrier was estimated from the librational peak frequency. A flat background observed in the …

Go to article

Orientational Phase Transition In Na_{X}C_{60} (1, T. Yildirim, J. E. Fischer, A. B. Harris, Peter W. Stephens, Dengfa Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii Aug 1993

Orientational Phase Transition In Na_{X}C_{60} (1, T. Yildirim, J. E. Fischer, A. B. Harris, Peter W. Stephens, Dengfa Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

X-ray diffraction and calorimetry data on cubic NaxC60(1<x60, e.g., Tm(x=1.3)=325 K. The ordered phases are the same as in pure C60: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between C60 molecules and and Na ions which we calculate from the local charge density of C60.

Go to article

Existence Of High-Order Superlattices In Orientationally Ordered C_{60}, J. E. Fischer, D. E. Luzzi, K. Kniaź, A. R. Mcghie, D. A. Ricketts-Foot, W. R. Romanow, Gavin B. M. Vaughan, Dayin Li, Allan L. Smith, Robert M. Strongin, M. A. Cichy, Laurent Bard, Amos B. Smith Iii Jun 1993

Existence Of High-Order Superlattices In Orientationally Ordered C_{60}, J. E. Fischer, D. E. Luzzi, K. Kniaź, A. R. Mcghie, D. A. Ricketts-Foot, W. R. Romanow, Gavin B. M. Vaughan, Dayin Li, Allan L. Smith, Robert M. Strongin, M. A. Cichy, Laurent Bard, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

We correlate the presence or absence of high-order modulated structures in solid C60 with the differential scanning calorimetry signature of the orientational ordering transition and other diagnostic data. We have searched for, but not observed, the 2a face-centered cubic structure recently observed in low-temperature electron and single-crystal x-ray diffraction. We conclude that the intrinsic ground state is the previously reported simple cubic structure [space groupPa3¯, a(14 K)=14.06 Å], and that other structures may be stabilized by defects or impurities.

Go to article

Coherence Peak And Superconducting Energy Gap In Rb_{3}C_{60} Observed By Muon Spin Relaxation, R. F. Kiefl, W. A. Macfarlane, K. H. Chow, S. Dunsiger, T. L. Duty, T. M. S. Johnston, J. W. Schneider, J. Sonier, Laurent Brard, Robert M. Strongin, J. E. Fischer, Amos B. Smith Iii Jun 1993

Coherence Peak And Superconducting Energy Gap In Rb_{3}C_{60} Observed By Muon Spin Relaxation, R. F. Kiefl, W. A. Macfarlane, K. H. Chow, S. Dunsiger, T. L. Duty, T. M. S. Johnston, J. W. Schneider, J. Sonier, Laurent Brard, Robert M. Strongin, J. E. Fischer, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

Muon spin relaxation resulting from spin exchange scattering of endohedral muonium (μ+e-) with thermal electronic excitations has been observed in the fullerene superconductor Rb3C60. The temperature dependence of T1-1 shows a coherence peak just below Tc and can be fit to the conventional Hebel-Slichter theory for spin relaxation in a superconductor with a broadened BCS density of states. The average energy gap for electronic excitations, Δ/kB=53(4) K or 2Δ/ kBTc=3.6(3), is consistent with the BCS weak coupling limit.

Go to article

Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii May 1993

Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

X-ray diffraction and differential scanning calorimetry of MxC60, with x∼1 and M=K, Rb, or Cs, reveal an unusual T-dependent phase sequence. A low-symmetry ground state is found, while the high-T limit is an ordered rocksalt structure in which only the octahedral sites are occupied. The unusual high-T stability of this ordered phase is attributed to the entropy of molecular orientational disorder and/or thermal disorder of the alkali-metal ions within the octahedral sites. Unique to KxC60 with x≥1.4, we find at intermediate temperatures an fcc site-disordered lattice gas …

Go to article

Bis(1h+-Pyrazinium N4-Oxide) Dichromate, Gary L. Gard, Roger D. Willett, W. W. Paudler, R. M. Sheets, Mark R. Pressprich Sep 1990

Bis(1h+-Pyrazinium N4-Oxide) Dichromate, Gary L. Gard, Roger D. Willett, W. W. Paudler, R. M. Sheets, Mark R. Pressprich

Chemistry Faculty Publications and Presentations

2C₄H₅N₂O⁺.Cr₂O²₇⁻, Mᵣ=410∙2, monoclinic, P2₁, a=8∙(2), b=6∙132 (2), c=14∙493 (4) Å, β=94∙50 (2)°, V=708∙8 (3) ų, Z=2, Dₓ=1∙92 g cm⁻³, Mο Κα, λ=0∙71069 Å, μ=15∙5 cm⁻¹, F(000)=412, T=293 K, R=0∙0602 for 1980 unique observed reflections with F≥3σ(F). The structure consists of discrete dinegative dichromate anions hydrogen bonded to monopositive pyrazinium N-oxide cations (N―H∙∙∙O=2∙724, 2∙644 Å). A strong hydrogen bond to the bridging O atom in the Cr₂O²₇⁻ anion leads to significant lengthening of the bridging Cr―O bonds. A short C―H∙∙∙O interaction (3∙180 Å) is also observed.

Go to article

Medium Resolution Atmospheric Pressure Ionization Mass Spectrometer, Andrew H. Grange, Robert J. O'Brien, Douglas F. Barofsky Jan 1988

Medium Resolution Atmospheric Pressure Ionization Mass Spectrometer, Andrew H. Grange, Robert J. O'Brien, Douglas F. Barofsky

Chemistry Faculty Publications and Presentations

An atmospheric pressure ionization (API) source for a VG 7070E‐HF mass spectrometer has been built and successfully operated at an accelerating potential of 6 kV. Hydrated protons and hydrated organic ions formed in the API source can be either partially or completely disaggregated by collisionally induced dissociation before entering the mass analyzer. The protonated molecular ions of pinacolone and 2,4‐pentanedione can be fully separated (R=2800, m/z 101,

Go to article

Generalized Response Of Chemiluminescence Analyzers, A. A. Mehrabzadeh, Robert J. O'Brien, Thomas M. Hard Aug 1983

Generalized Response Of Chemiluminescence Analyzers, A. A. Mehrabzadeh, Robert J. O'Brien, Thomas M. Hard

Chemistry Faculty Publications and Presentations

The mass flow and chemical kinetic equations for a gaseous chemiluminescence (CL) analyzer are formulated and solved. The resultant equation can be used to predict the absolute response of the analyzer as a function of the sample flow rate, the sample gas pressure, the chamber pressure, the chamber volume, the mass flow rate and mole fraction of the reagent gas, and the rate constants of the relevant chemical processes. Thus, the equation allows optimization of these parameters. It is shown that for varying sample pressure the analyzer can be used to measure either concentration or mole fraction and that interfering …

Go to article

Pressure Dependence Of Fluorescent And Photolytic Interferences In Ho Detection By Laser-Excited Fluorescence, Thomas M. Hard, Robert J. O'Brien, T. B. Cook Jul 1980

Pressure Dependence Of Fluorescent And Photolytic Interferences In Ho Detection By Laser-Excited Fluorescence, Thomas M. Hard, Robert J. O'Brien, T. B. Cook

Chemistry Faculty Publications and Presentations

In the measurement of HO concentrations by laser-excited fluorescence, expansion of the sampled air offers a way to reduce fluorescent and photolytic interference by other species. The decrease in [HO] upon expansion is balanced by an increase in HO fluorescence yield over a wide range of pressures. Background air fluorescence is reduced if the responsible species have fluorescence yields higher than those of HO. Preliminary experiments indicate that most of the fluorescence observed in laboratory air is due to such species. Upon expansion, the suppression of fluorescent interference can be no greater than the reduction in pressure, whereas the suppression …

Go to article

First Prev