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

Chemistry Commons™

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

Chemistry Faculty Publications

Discipline
Institution
Keyword
Publication Year
File Type

Articles 991 - 1020 of 1129

Full-Text Articles in Chemistry

Atomization Energies And Enthalpies Of Formation Of The Snbin (N=1-3) Gaseous Molecules By Knudsen Cell Mass Spectrometry, Giovanni Meloni, Karl A. Gingerich Jan 2002

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.

Go to article

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 Jan 2002

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 …

Go to article

Site-Specific Modification Of De Novo Designed Coiled-Coil Polypeptides With Inorganic Redox Complexes, Anna Fedorova, Michael Y. Ogawa Jan 2002

Site-Specific Modification Of De Novo Designed Coiled-Coil Polypeptides With Inorganic Redox Complexes, Anna Fedorova, Michael Y. Ogawa

Chemistry Faculty Publications

A stepwise procedure for preparing of site-specific binuclear metallopeptides is described. The modification procedure involves the alkylation of a cysteine side chain by reaction with [Ru(bpy)(2)(phen-ClA)](2+), where bpy = 2,2'-bipyridine and phen-ClA = 5-chloroacetaniido-1,10-phenanthroline, followed by the coordination of a ruthenium pentammine complex to a histidine residue located elsewhere along the sequence. The apo and metalated versions of the peptides C10H21(30-mer) and H10C21(30-mer) display circular dichroism spectra having minima at 208 and 222 nm, with theta(222)/theta(208) = 1.04 to indicate that these peptides exist as a-helical coiled-coils in aqueous solution. When the ruthenium polypyridyl complex is attached to C10H21(30-mer), the …

Go to article

Adsorptive Immobilization Of Cytochrome C On Indium/Tin Oxide (Ito): Electrochemical Evidence For Electron Transfer-Induced Conformational Changes, Asma El Kasmi, Michael C. Leopold, Ryan Galligan, Rebecca T. Robertson, S. Scott Saavedra, Kacem El Kacemi, Edmond F. Bowden Jan 2002

Adsorptive Immobilization Of Cytochrome C On Indium/Tin Oxide (Ito): Electrochemical Evidence For Electron Transfer-Induced Conformational Changes, Asma El Kasmi, Michael C. Leopold, Ryan Galligan, Rebecca T. Robertson, S. Scott Saavedra, Kacem El Kacemi, Edmond F. Bowden

Chemistry Faculty Publications

The adsorptive immobilization and electrochemistry of horse and yeast cytochrome c on indium/tin oxide (ITO) electrodes is reported. Near-monolayer coverage was achieved in pH 7 phosphate buffers of ionic strength equal to 10 and 50 mM, respectively, for the horse and yeast species. The layers exhibit very well-behaved voltammetry and are stable on the timescale of hours to days. Cyclic voltammetry revealed quasireversible behavior that is a product of both electron transfer (ET) kinetics and ET-induced conformational changes. A square scheme mechanism linking the redox states and the conformational states is proposed. Using a simple ET kinetic model that adequately …

Go to article

Synthesis Of A New Hollandite-Type Manganese Oxide With Framework And Interstitial Cr(Iii), Stanton Ching, Peter F. Driscoll, Katarzyna S. Krukowska, Michael R. Marvel, Steven L. Suib Nov 2001

Synthesis Of A New Hollandite-Type Manganese Oxide With Framework And Interstitial Cr(Iii), Stanton Ching, Peter F. Driscoll, Katarzyna S. Krukowska, Michael R. Marvel, Steven L. Suib

Chemistry Faculty Publications

Hollandite with Cr(III) in both tunnel and framework sites has been prepared hydrothermally from layered manganese oxide precursors.

Go to article

Micromagnetics Simulation Of Deep-Submicron Supermalloy Disks, Scott Whittenburg Nov 2001

Micromagnetics Simulation Of Deep-Submicron Supermalloy Disks, Scott Whittenburg

Chemistry Faculty Publications

The results of recent micromagnetic simulations of deep submicron supermalloy disks are presented. A recent experimental measurement of the hysteresis and magnetic domain structure in supermalloy disks with diameters ranging from 55 to 500 nm and thickness ranging from 6 to 15 nm has been reported. Our micromagnetic simulations show remarkable agreement with the experimental hysteresis loops. The simulation results show that for thin or small diameter disks a single magnetic domain exists with all spins aligned. The hysteresis loop represents free rotation of these spins. For larger diameter disks or as the thickness increases the hysteresis loops change shape …

Go to article

Simultaneous Determination Of Enantiomers Of Structurally Related Anticholinergic Analogs In Human Serum By Liquid Chromatography–Electrospray Ionization Mass Spectrometry With On-Line Sample Cleanup, Vladimı́R Čápka, Yan Xu Oct 2001

Simultaneous Determination Of Enantiomers Of Structurally Related Anticholinergic Analogs In Human Serum By Liquid Chromatography–Electrospray Ionization Mass Spectrometry With On-Line Sample Cleanup, Vladimı́R Čápka, Yan Xu

Chemistry Faculty Publications

Trihexyphenidyl, biperiden and procyclidine are anticholinergic drugs produced as racemates for the treatment of Parkinson’s disease. This paper describes a simple and sensitive LC–MS method for the simultaneous determination of these compounds in human serum. An on-line sample clean-up procedure was used, where serum samples were directly injected into a “restricted-access media” pre-column. After the exclusion of the serum proteins, the drug molecules were eluted to a β-cyclodextrin analytical column for chiral separation. The quantitation was done by electrospray ionization MS using diphenidol as an internal standard. The method developed has limits of detection of 1 ng/ml, at least two-orders-of-magnitude …

Go to article

Effect Of Surface Charges On The Rates Of Intermolecular Electron-Transfer Between De Novo Designed Metalloproteins, Anna Y. Kornilova, James F. Wishart, Michael Y. Ogawa Oct 2001

Effect Of Surface Charges On The Rates Of Intermolecular Electron-Transfer Between De Novo Designed Metalloproteins, Anna Y. Kornilova, James F. Wishart, Michael Y. Ogawa

Chemistry Faculty Publications

A de novo designed coiled-coil metalloprotein was prepared that uses electrostatic interactions to control both its conformational and bimolecular electron-transfer properties. The title protein exists as a coiled-coil heterodimer of the [Ru(trpy)(bpy)-KK(37-mer)] and [Ru(NH3)(5)-EE(37-mer)] polypeptides which is formed by interhelix electrostatic attractions. Circular dichroism studies show that the electrostatic heterodimer has Kd 0.19 +/- 0.03 muM and is 96% helical at high concentrations. Intercomplex electron-transfer reactions were studied that involve the [Ru(NH3)(5)-H21](2+) electron-donor and the [Ru(trpy)(bpy)H21](3+) electron-acceptor belonging to different electrostatic dimers. An important feature of the designed metalloprotein is its two cationic redox centers embedded within protein surfaces having …

Go to article

Infrared Spectroscopy Of H-Bonded Bridges Stretched Across The Cis-Amide Group: Ii. Ammonia And Mixed Ammonia/Water Bridges, A. V. Fedorov, John R. Cable, Joel R. Carney, Timothy S. Zwier Sep 2001

Infrared Spectroscopy Of H-Bonded Bridges Stretched Across The Cis-Amide Group: Ii. Ammonia And Mixed Ammonia/Water Bridges, A. V. Fedorov, John R. Cable, Joel R. Carney, Timothy S. Zwier

Chemistry Faculty Publications

Clusters of two model cis amides, oxindole and 3,4-dihydro-2(IH)-quinolinone, containing one and two ammonia molecules have been studied in the IR hydride stretch region using resonant ion-dip IR spectroscopy. The spectra confirm that ammonia is able to form hydrogen-bonded bridges across the adjacent amide N-H and C=O sites in a manner very similar to that of water. Such bridged structures require that ammonia assume the role of a hydrogen bond donor. Further similarities of the hydrogen bonding capabilities of ammonia and water have been revealed by investigations of ternary clusters containing an amide, one ammonia, and one water molecule. Experimentally, …

Go to article

Jno2 At High Solar Zenith Angles In The Lower Stratosphere, R. S. Gao, L. A. Del Negro, W. H. Swartz, R. J. Salawitch, S. A. Lloyd, M. H. Proffitt, D. W. Fahey, Stephen G. Donnelly Ph.D., J. A. Neuman, R. M. Stimpfle, T. P. Bui Jun 2001

Jno2 At High Solar Zenith Angles In The Lower Stratosphere, R. S. Gao, L. A. Del Negro, W. H. Swartz, R. J. Salawitch, S. A. Lloyd, M. H. Proffitt, D. W. Fahey, Stephen G. Donnelly Ph.D., J. A. Neuman, R. M. Stimpfle, T. P. Bui

Chemistry Faculty Publications

In situ measurements of NO, NO2, O3, HO2, C1O, pressure, and temperature have been made at high solar zenith angles (SZA, 70° - 93°) in the lower stratosphere. These measurements are used to derive the photolysis rate of NO2, JNO2, using a time-dependent method. The resultant JNO2 values and the results of a multiple-scattering actinic flux model show a linear relationship throughout the SZA range. The difference of the two sets of JNO2 values of about 11% suggests that the model scattering calculation is very accurate at high SZA conditions near sunrise and sunset.

Go to article

Determination Of Lysophosphatidic Acids By Capillary Electrophoresis With Indirect Ultraviolet Detection, Yi Lung Chen, Yan Xu Apr 2001

Determination Of Lysophosphatidic Acids By Capillary Electrophoresis With Indirect Ultraviolet Detection, Yi Lung Chen, Yan Xu

Chemistry Faculty Publications

Lysophosphatidic acid (LPA) is the simplest form of lysophospholipid. Molecular species of LPA have been identified as the potent components in the ovarian cancer activation factor. The elevated plasma LPAs may be used as potential biomarkers for the early detection of ovarian cancer. This paper is the first report on the quantitative analysis of molecular species of LPA using capillary electrophoresis. In this work, the separation of LPAs was achieved within 14 min in an adenosine monophosphate-borate–methanol–water solution, and the measurement was accomplished by indirect UV detection. With LPA (D) as internal standard, the method had linear calibration ranges for …

Go to article

Infrared Spectroscopy Of H-Bonded Bridges Stretched Across The Cis-Amide Group: I. Water Bridges, Joel R. Carney, A. V. Fedorov, John R. Cable, Timothy S. Zwier Apr 2001

Infrared Spectroscopy Of H-Bonded Bridges Stretched Across The Cis-Amide Group: I. Water Bridges, Joel R. Carney, A. V. Fedorov, John R. Cable, Timothy S. Zwier

Chemistry Faculty Publications

The water-containing clusters of oxindole (OI) and 3,4-dihydro-2(1H)-quinolinone (DQ) have been studied in the hydride stretch region of the infrared by the technique of resonant ion-dip infrared spectroscopy (RIDIRS). Both OI and DQ are constrained cis-amides with adjacent N-H and C=O groups between which water can form H-bonded bridges. The hydride stretch fundamentals of OI-W-n with n = 1-3 and DQ-W-n with n = 1, 2 without exception divide up into free OH stretch fundamentals near 3700 cm(-1) and a set of H-bonded bridge fundamentals in the 3200-3450 cm(-1) region. The bridge fundamentals show a distribution of intensities that reflects …

Go to article

Adenosine Triphosphate-Dependent Degradation Of A Fluorescent Λ N Substrate Mimic By Lon Protease, Irene Lee, Anthony J. Berdis Apr 2001

Adenosine Triphosphate-Dependent Degradation Of A Fluorescent Λ N Substrate Mimic By Lon Protease, Irene Lee, Anthony J. Berdis

Chemistry Faculty Publications

Escherichia coli Lon exhibits a varying degree of energy requirement toward hydrolysis of different substrates. Efficient degradation of protein substrates requires the binding and hydrolysis of ATP such that the intrinsic ATPase of Lon is enhanced during protein degradation. Degradation of synthetic tetrapeptides, by contrast, is achieved solely by ATP binding with concomitant inhibition of the ATPase activity. In this study, a synthetic peptide (FRETN 89-98), containing residues 89–98 of λ N protein and a fluorescence donor (anthranilamide) and quencher (3-nitrotyrosine), has been examined for ATP-dependent degradation by E. coli and human Lon proteases. The cleavage profile of FRETN 89-98 …

Go to article

Dansylation Of Hydroxyl And Carboxylic Acid Functional Groups, Ronald Bartzatt Feb 2001

Dansylation Of Hydroxyl And Carboxylic Acid Functional Groups, Ronald Bartzatt

Chemistry Faculty Publications

Fluorescent labeling of primary and secondary amines using dansyl chloride has been widely used in the past. Its application provides an extremely sensitive means to detect amine functional groups to amounts of less than 1 mg of material. This work describes a method for the dansylation of hydroxyl (–OH) and carboxylic acid (–COOH) functional groups. This technique is demonstrated with ethanol, gamma hydroxy butyric acid (GHB), benzoic acid, and p-chloroaniline. Sensitivity of detection for all compounds are microgram or microliter. For the compounds ethanol and GHB which are liquids at room temperature, as little as 1 ml quantity can be …

Go to article

Rayleigh And Raman Scattering, David W. Ball Feb 2001

Rayleigh And Raman Scattering, David W. Ball

Chemistry Faculty Publications

Details the molecular aspect of Raman spectroscopy. Overview on the molecular absorption process; Information on Rayleigh scattering; Effects of the Raman scattering.

Go to article

Simulations Of Ice And Liquid Water Over A Range Of Temperatures Using The Fluctuating Charge Model, Steven W. Rick Feb 2001

Simulations Of Ice And Liquid Water Over A Range Of Temperatures Using The Fluctuating Charge Model, Steven W. Rick

Chemistry Faculty Publications

The temperature dependence of the thermodynamic and dynamical properties of liquid water using the polarizable fluctuating charge (FQ) model is presented. The properties of ice Ih, both for a perfect lattice with no thermal disorder and at a temperature of 273 K, are also presented. In contrast to nonpolarizable models, the FQ model has a density maximum of water near 277 K. For ice, the model has a dipole moment of the perfect lattice of 3.05 Debye, in good agreement with a recent induction model calculation. The simulations at 273 K and the correct density find that thermal motion decreases …

Go to article

Tectorna: Modular Assembly Units For The Construction Of Rna Nano-Objects, Neocles B. Leontis, Luc Jaeger, Eric Westhof Jan 2001

Tectorna: Modular Assembly Units For The Construction Of Rna Nano-Objects, Neocles B. Leontis, Luc Jaeger, Eric Westhof

Chemistry Faculty Publications

Structural information on complex biological RNA molecules can be exploited to design tectoRNAs or artificial modular RNA units that can self-assemble through tertiary interactions thereby forming nanoscale RNA objects. The selective interactions of hairpin tetraloops with their receptors can be used to mediate tectoRNA assembly. Here we report on the modulation of the specificity and the strength of tectoRNA assembly tin the nanomolar to micromolar range) by variation of the length of the RNA subunits, the nature of their interacting motifs and the degree of flexibility of linker regions incorporated into the molecules. The association is also dependent on the …

Go to article

Thermodynamic Investigation Of The Si7 And Si8 Clusters By Knudsen Cell Mass Spectrometry, Giovanni Meloni, Karl A. Gingerich Jan 2001

Thermodynamic Investigation Of The Si7 And Si8 Clusters By Knudsen Cell Mass Spectrometry, Giovanni Meloni, Karl A. Gingerich

Chemistry Faculty Publications

The Knudsen cell mass spectrometric method has been employed to measure the partial pressures of the Si[sub 7] and Si[sub 8] clusters under equilibrium conditions above liquid silicon, contained in a boron nitride liner inside a graphite Knudsen cell. Gaussian 2 (G2) theory and B3LYP density functional method were employed to determine the geometry, the vibrational frequencies, and the binding energy of the Si[sub 8] cluster. From the all-gas analyzed equilibria the following atomization enthalpies, Δ[sub a]H[sub 0][sup o](Si[sub n]), and enthalpies of formation, Δ[sub f]H[sub 298.15][sup o](Si[sub n]), in kJ mol-1, have been obtained: Si[sub 7], 2381±36 and …

Go to article

Structure And Thermodynamic Stability Of The Osc And Osc2 Molecules By Theoretical Calculations And By Knudsen Cell Mass Spectrometry, Giovanni Meloni, L M. Thomson, Karl A. Gingerich Jan 2001

Structure And Thermodynamic Stability Of The Osc And Osc2 Molecules By Theoretical Calculations And By Knudsen Cell Mass Spectrometry, Giovanni Meloni, L M. Thomson, Karl A. Gingerich

Chemistry Faculty Publications

Knudsen cell mass spectrometric equilibrium measurements together with theoretical computations have been employed to gain structural and thermodynamic information of the OsC and OsC[sub 2] molecules. Several levels of theory have been applied to determine the structures, molecular parameters, and physico-chemical properties of OsC(g) and OsC[sub 2](g), and their singly charged ions. Complete active space self-consistent field (CASSCF) calculations were performed on the apparent [sup 3]Σ[sup -] ground state and first [sup 3]Δ excited state of OsC. From the analyzed gaseous equilibria and the thermal functions calculated from the computed molecular parameters, the following atomization enthalpies, Δ[sub a]H[sub 0][sup o](OsC,g) …

Go to article

Increased Severity Of Hsv-1 Keratitis And Mortality In Mice Lacking The 2–5a-Dependent Rnase L Gene, Xiaodong Zheng, Robert H. Silverman, Aimin Zhou, Tomoko Goto, Byoung Se Kwon, Herbert E. Kaufman, James M. Hill Jan 2001

Increased Severity Of Hsv-1 Keratitis And Mortality In Mice Lacking The 2–5a-Dependent Rnase L Gene, Xiaodong Zheng, Robert H. Silverman, Aimin Zhou, Tomoko Goto, Byoung Se Kwon, Herbert E. Kaufman, James M. Hill

Chemistry Faculty Publications

Purpose: The2′,5′-oligoadenylate-dependent RNase L gene functions in the interferon-inducible RNA decay pathway known as the 2–5A system. The purpose of this study was to determine whether the absence of this gene affects the pathogenesis of herpes simplex virus type 1 (HSV-1) ocular infection in the mouse. Methods: HSV-1 (strain McKrae) was applied bilaterally to unscarified corneas of RNase L–null mice and congenic controls. To evaluate the severity of herpetic keratitis, slit lamp examinations (SLE) were performed every other day for 14 days. To study corneal histology and apoptosis, HSV-1–inoculated RNase-L-null and congenic control mice, as well as mock-inoculated mice (apoptosis …

Go to article

Observations Of Apan During Texaqs 2000, James M. Roberts, Frank Flocke, Andrew Weinheimer, Hiroshi Tanimoto, Bertram T. Jobson, Daniel Riemer, Eric Apel, Elliot Atlas, Stephen G. Donnelly Ph.D., Verity Stroud, Kristen Johnson, Rachel Weaver, Fredrick C. Fehsenfeld Jan 2001

Observations Of Apan During Texaqs 2000, James M. Roberts, Frank Flocke, Andrew Weinheimer, Hiroshi Tanimoto, Bertram T. Jobson, Daniel Riemer, Eric Apel, Elliot Atlas, Stephen G. Donnelly Ph.D., Verity Stroud, Kristen Johnson, Rachel Weaver, Fredrick C. Fehsenfeld

Chemistry Faculty Publications

Measurements of peroxycarboxylic nitric anhydrides (PANs) made in Houston, Texas during TexAQS (Texas Air Quality Study) 2000 showed a relatively abundant PAN compound that had not been identified in previous studies in North America [cf. Williams et al., 2000]. This compound was hypothesized to be peroxyacrylic nitric anhydride { CH2=CHC(O)OONO2, APAN} based on the work of Tanimoto and Akimoto, [2001]. APAN was synthesized and characterized on one of the two GC systems used to make those measurements, subsequent to the TexAQS 2000 field study, confirming that APAN was observed during TexAQS 2000, both on the ground and in airborne measurements. …

Go to article

Identification Of The Domains Of Urer, An Arac-Like Transcriptional Regulator Of The Urease Gene Cluster In Proteus Mirabilis, Carrie A. Poore, Christopher Coker, Jonathan D. Dattelbaum, Harry L.T. Mobley Jan 2001

Identification Of The Domains Of Urer, An Arac-Like Transcriptional Regulator Of The Urease Gene Cluster In Proteus Mirabilis, Carrie A. Poore, Christopher Coker, Jonathan D. Dattelbaum, Harry L.T. Mobley

Chemistry Faculty Publications

Proteus mirabilis urease catalyzes the hydrolysis of urea to CO2 and NH3, resulting in urinary stone formation in individuals with complicated urinary tract infections. UreR, a member of the AraC family, activates transcription of the genes encoding urease enzyme subunits and accessory proteins, ureDABCEFG, as well as its own transcription in the presence of urea. Based on sequence homology with AraC, we hypothesized that UreR contains both a dimerization domain and a DNA-binding domain. A translational fusion of the leucine zipper dimerization domain (amino acids 302 to 350) of C/EBP and the C-terminal half of UreR …

Go to article

Rnase L-Independent Specific 28s Rrna Cleavage In Murine Coronavirus-Infected Cells, Sangeeta Banerjee, Sungwhan An, Aimin Zhou, Robert H. Silverman, Shinji Makino Oct 2000

Rnase L-Independent Specific 28s Rrna Cleavage In Murine Coronavirus-Infected Cells, Sangeeta Banerjee, Sungwhan An, Aimin Zhou, Robert H. Silverman, Shinji Makino

Chemistry Faculty Publications

We characterized a novel 28S rRNA cleavage in cells infected with the murine coronavirus mouse hepatitis virus (MHV). The 28S rRNA cleavage occurred as early as 4 h postinfection (p.i.) in MHV-infected DBT cells, with the appearance of subsequent cleavage products and a decrease in the amount of intact 28S rRNA with increasing times of infection; almost all of the intact 28S rRNA disappeared by 24 h p.i. In contrast, no specific 18S rRNA cleavage was detected in infected cells. MHV-induced 28S rRNA cleavage was detected in all MHV-susceptible cell lines and all MHV strains tested. MHV replication was required …

Go to article

Design And Characterization Of A Synthetic Electron-Transfer Protein, Anna Y. Kornilova, James F. Wishart, Wenzhong Xiao, Robin C. Lasey, Anna Fedorova, Yeon-Kyun Shin, Michael Y. Ogawa Aug 2000

Design And Characterization Of A Synthetic Electron-Transfer Protein, Anna Y. Kornilova, James F. Wishart, Wenzhong Xiao, Robin C. Lasey, Anna Fedorova, Yeon-Kyun Shin, Michael Y. Ogawa

Chemistry Faculty Publications

A 30-residue polypeptide [H21(30-mer)] with the sequence Ac-K(IEALEGK)(2)(IEALEHK)-(IEALEGK)G-NH2 was synthesized. The circular dichroism (CD) spectrum of the peptide shows minima at 208 and 222 nm and theta(222)/theta(208) = 1.06, which indicates the formation of a self-assembled coiled-coil when dissolved in aqueous solution. The concentration dependence of the CD data can be fit to an expression that describes a two-state monomer-dimer equilibrium for the apopeptide (K-d = 1.5 +/- 0.4 mu M and theta(max) = -23 800 +/- 130 deg cm(2) dmol(-1)), showing that it has a maximum helicity of 69%. A [MTSL-C21(30-mer)] dimer was also prepared in which MTSL is …

Go to article

Synthesis And Antimalarial Activity Of Sixteen Dispiro-1,2,4,5-Tetraoxanes: Alkyl-Substituted 7,8,15,16-Tetraoxadispiro[5.2.5.2]Hexadecanes, Jonathan L. Vennerstrom, Yuxiang Dong, Walter Reed Army Institute Of Research, Arba L. Ager Jr., Hong-Ning Fu, Sheri M. Walters, James K. Wood, Geoffrey Edwards, Alexandra D. Holme, W. Graham Mclean Jul 2000

Synthesis And Antimalarial Activity Of Sixteen Dispiro-1,2,4,5-Tetraoxanes: Alkyl-Substituted 7,8,15,16-Tetraoxadispiro[5.2.5.2]Hexadecanes, Jonathan L. Vennerstrom, Yuxiang Dong, Walter Reed Army Institute Of Research, Arba L. Ager Jr., Hong-Ning Fu, Sheri M. Walters, James K. Wood, Geoffrey Edwards, Alexandra D. Holme, W. Graham Mclean

Chemistry Faculty Publications

Sixteen alkyl-substituted dispiro-1,2,4,5-tetraoxanes (7,8,15,16-tetraoxadispiro[5.2.5.2]hexadecanes) were synthesized to explore dispiro-1,2,4,5-tetraoxane SAR and to identify tetraoxanes with better oral antimalarial activity than prototype tetraoxane 1 (WR 148999). The tetraoxanes were prepared either by peroxidation of the corresponding cyclohexanone derivatives in H2-SO4/CH3CN or by ozonolysis of the corresponding cyclohexanone methyl oximes. Those tetraoxanes with alkyl substituents at the 1 and 10 positions were formed as single stereoisomers, whereas the five tetraoxanes formed without the stereochemical control provided by alkyl groups at the 1 and 10 positions were isolated as mixtures of diastereomers. Three of the sixteen …

Go to article

Spectroscopy Of Hydrogen-Bonded Formanilide Clusters In A Supersonic Jet: Solvation Of A Model Trans Amide, A. V. Fedorov, John R. Cable Jun 2000

Spectroscopy Of Hydrogen-Bonded Formanilide Clusters In A Supersonic Jet: Solvation Of A Model Trans Amide, A. V. Fedorov, John R. Cable

Chemistry Faculty Publications

The gas-phase structures of trans-formanilide (FA) clusters containing varying numbers of water and ammonia molecules have been investigated by resonant two-photon ionization spectroscopy in a supersonic jet expansion. A single structure is found for the 1:1 cluster of FA with ammonia in which the amide NH group functions as a hydrogen bond donor to the ammonia nitrogen. In contrast, vibronically resolved spectra reveal two distinct structures for the 1:1 cluster with water in which either the amide NH group functions as a hydrogen bond donor or the carbonyl oxygen functions as a hydrogen bond acceptor. The 1:1 clusters with both …

Go to article

Visual Test Using Color Frequency Doubling, Scott Whittenburg May 2000

Visual Test Using Color Frequency Doubling, Scott Whittenburg

Chemistry Faculty Publications

A novel psychophysical visual test is proposed for testing a person for glaucoma, and based on the discovery that a frequency doubling phenomenon is produced by isoluminent color visual stimuli. More specifically, it is proposed to construct a visual stimulus for which alternating colors in a grating pattern is the only basis for producing the frequency doubling phenomenon. That is, the colors are of the same luminance or intensity level, i.e., isoluminent, but each grating or pattern alternates from one color to another. Preferably, the colors are complementary color pairs, such as blue and yellow.

Go to article

Methyl-Substituted Dispiro-1,2,4,5-Tetraoxanes:  Correlations Of Structural Studies With Antimalarial Activity, Kevin J. Mccollough, James K. Wood, Walter Reed Army Institute Of Research, Yuxiang Dong, Jonathan L. Vennerstrom Mar 2000

Methyl-Substituted Dispiro-1,2,4,5-Tetraoxanes:  Correlations Of Structural Studies With Antimalarial Activity, Kevin J. Mccollough, James K. Wood, Walter Reed Army Institute Of Research, Yuxiang Dong, Jonathan L. Vennerstrom

Chemistry Faculty Publications

Two tetramethyl-substituted dispiro-1,2,4,5-tetraoxanes (7,8,15,16-tetraoxadispiro[5.2.5.2]- hexadecanes) 3 and 4 were designed as metabolically stable analogues of the dimethylsubstituted dispiro-1,2,4,5-tetraoxane prototype WR 148999 (2). For a positive control we selected the sterically unhindered tetraoxane 5 (7,8,15,16-tetraoxadispiro[5.2.5.2]hexadecane), devoid of any substituents. Tetraoxanes 3 and 4 were completely inactive in contrast to tetraoxanes 2 and 5. We hypothesize that the two inactive tetraoxanes possess sufficient steric hindrance about the tetraoxane ring due to the two additional axial methyl groups to prevent their activation to presumed parasiticidal carbon radicals by inhibiting electron transfer from heme or other iron(II) species. For each of the tetraoxanes 2-4, …

Go to article

The Nonplanarity Of The Peptide Group: Molecular Dynamics Simulations, Steven W. Rick Mar 2000

The Nonplanarity Of The Peptide Group: Molecular Dynamics Simulations, Steven W. Rick

Chemistry Faculty Publications

The general properties of the peptide bond can be described from a linear combination of two states: a single bond neutral form and a double bond zwitterionic form. However, environmental effects can shift the balance of the linear combination. This would cause the rigidity of torsional rotations of the peptide bond to be environmentally dependent and, in fact, an analysis of protein structures in the protein data bank reveals a different degree of nonplanarity for different secondary structure elements. A potential is presented in which the peptide bond is treated as a linear combination of two states; the coefficients of …

Go to article

9-Phenyl-3,4,4a,9a-Tetrahydrotriptycene And 9-Phenyl-1,2,3,4,4a,9a-Hexahydrotriptycene, John Masnovi, Shaoming Duan, Ronald J. Baker Jan 2000

9-Phenyl-3,4,4a,9a-Tetrahydrotriptycene And 9-Phenyl-1,2,3,4,4a,9a-Hexahydrotriptycene, John Masnovi, Shaoming Duan, Ronald J. Baker

Chemistry Faculty Publications

The structure of 9-phenyl-3,4,4a,9a-tetrahydrotriptycene, C26H22, (I), exhibits regiochemistry consistent with a stepwise mechanism for its formation from photocycloaddition of 1,3- cyclohexadiene and 9-phenylanthracene. Bond distances involving the bridgehead C atoms are similar in (I) and the hydrogenated derivative, 9-phenyl-1,2,3,4,4a,9a-hexahydrotriptycene, C26H24, (II), with bonds to the quaternary-C atoms exhibiting significant elongation [1.581 (2) A Ê in (I) and 1.585 (2) A Ê in (II)]. The molecular geometry precludes significant overlap between the phenyl groups and the interannular bonds in both compounds, indicating that the origin of the bond lengthening is steric in nature.

Go to article

First Prev Next Last