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Articles 751 - 780 of 1105

Full-Text Articles in Chemistry

Electrophilic Aromatic Nitrosation. Isolation And X-Ray Crystallography Of The Metastable No+ Complex With Nitrosoarene, Sergey V. Lindeman, E. Bosch, Jay K. Kochi Jan 2000

Electrophilic Aromatic Nitrosation. Isolation And X-Ray Crystallography Of The Metastable No+ Complex With Nitrosoarene, Sergey V. Lindeman, E. Bosch, Jay K. Kochi

Chemistry Faculty Research and Publications

Isolation of the unstable 1∶1 complex of 4-nitrosoanisole with NO+PF6− allows its precise X-ray structural characterization. The charge-transfer crystal is formed via strong N⋯N coordination [the distance of 1.938(5) Å corresponding to a σ-bond order of ≈0.2] in the mean plane of the planar 4-nitrosoanisole donor. Thorough analysis of its molecular geometry in terms of valence resonance and MO schemes reveals a strong charge polarization with a local negative charge localized on the nitroso group and a local positive charge distributed over the adjacent p-methoxybenzyl moiety. Such a charge distribution accommodates the well-known passivation of …

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Novel (Heteromolecular) Π-Complexes Of Aromatic Cation Radicals. Isolation And Structural Characterization, P. Le Maguères, Sergey V. Lindeman, Jay K. Kochi Jan 2000

Novel (Heteromolecular) Π-Complexes Of Aromatic Cation Radicals. Isolation And Structural Characterization, P. Le Maguères, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Extensive (electron) delocalization in the novel heteromolecular π-complex of the hindered naphthalene cation radical (OMN+•) with naphthalene (NAP) accompanies the pronounced charge-transfer absorption band at ∼1100 nm in the near-IR. X-ray crystallography establishes the viability of the unusual “club sandwich” structure despite the repulsive electrostatic forces inherent to the dicationic unit.

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Cross-Linking Of Polystyrene By Friedel-Crafts Chemistry: Multi-Functional Additives, Hongyang Yao, Jin Zhu, Michael A. Mckinney, Charles A. Wilkie Jan 2000

Cross-Linking Of Polystyrene By Friedel-Crafts Chemistry: Multi-Functional Additives, Hongyang Yao, Jin Zhu, Michael A. Mckinney, Charles A. Wilkie

Chemistry Faculty Research and Publications

Various multifunctional aromatic compounds were synthesized and tested to ascertain if they were able to cross-link polystyrene. Catalysis and inhibition at high temperature were studied to achieve control over the cross-linking temperature, in order to develop suitable formulations which may function as flame retardants.

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On The Stabilizing Action Of Protein Denaturants: Acetonitrile Effect On Stability Of Lysozyme In Aqueous Solutions, Evgenii L. Kovrigin, Sergey A. Potekhin Jan 2000

On The Stabilizing Action Of Protein Denaturants: Acetonitrile Effect On Stability Of Lysozyme In Aqueous Solutions, Evgenii L. Kovrigin, Sergey A. Potekhin

Chemistry Faculty Research and Publications

Stability of hen lysozyme in the presence of acetonitrile (MeCN) at different pH values of the medium was studied by scanning microcalorimetry with a special emphasis on determination of reliable values of the denaturational heat capacity change. It was found that the temperature of denaturation decreases on addition of MeCN. However, the free energy extrapolation showed that below room temperature the thermodynamic stability increases at low concentrations of MeCN in spite of the general destabilizing effect at higher concentrations and temperatures. Charge-induced contribution to this stabilization was shown to be negligible (no pH-dependence was found); therefore, the most probable cause …

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Silver(I) Complexation Of (Poly)Aromatic Ligands. Structural Criteria For Depth Penetration Into Cis-Stilbenoid Cavities, Sergey V. Lindeman, Rajendra Rathore, Jay K. Kochi Jan 2000

Silver(I) Complexation Of (Poly)Aromatic Ligands. Structural Criteria For Depth Penetration Into Cis-Stilbenoid Cavities, Sergey V. Lindeman, Rajendra Rathore, Jay K. Kochi

Chemistry Faculty Research and Publications

Silver(I) complexes with aromatic donors are thoroughly analyzed (with aid of the Cambridge Crystallographic Database) to identify the basic structural factors inherent to the bonding of an arene ligand. Most strikingly, the distance parameter d (which simply measures the normal separation of Ag from the mean aromatic plane) is singularly invariant at d = 2.41 ± 0.05 Å for all silver/arene complexes, independent of the hapticity (η1 or η2), hybridization, or multiple coordination. As such, a systematic series of stilbenoid ligands has been successfully designed to precisely modulate the penetration of silver(I) into the ligand cleft, and …

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Synthesis And Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Model Studies For The Preparation Of The 8E,10Z,16E,18E-Tetraene Segment Of Macrolactin A, Abdel-Aziz S. El-Ahl, Young Yun, William A. Donaldson Dec 1999

Synthesis And Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Model Studies For The Preparation Of The 8E,10Z,16E,18E-Tetraene Segment Of Macrolactin A, Abdel-Aziz S. El-Ahl, Young Yun, William A. Donaldson

Chemistry Faculty Research and Publications

The dicarbonyl(1,2-dimethylpentadienyl)triphenylphosphineiron(1+) cation (11) has been prepared from methyl 4-methyl-2E,4E-hexadienoate in four steps. The cation (11) reacts with hydride and carbon nucleophiles in a regiospecific fashion to afford (3-methyl-2E,4Z-diene)iron complexes. Dicarbonyl(3-methyl-7-nitro-2E,4Z-heptadiene)triphenylphosphineiron (15), the product from the reaction of 11 with nitromethane anion, has been utilized as a precursor for nitrile oxide–olefin cyclocondensations.

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Thermal Degradation Of Blends Of Polystyrene And Poly(Sodium 4-Styrenesulfonate) And The Copolymer, Poly(Styrene-Co-Sodium 4-Styrenesulfonate), Qiang Yao, Charles Wilkie Dec 1999

Thermal Degradation Of Blends Of Polystyrene And Poly(Sodium 4-Styrenesulfonate) And The Copolymer, Poly(Styrene-Co-Sodium 4-Styrenesulfonate), Qiang Yao, Charles Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of blends and copolymers of styrene with styrenesulfonic acid has been studied using thermogravimetric analysis, TGA/FTIR, and cone calorimetry. The blends have enhanced thermal stability relative to virgin polystyrene but there is no enhancement in thermal stability for the copolymers. Apparently, it is necessary to have adjacent sulfonic acid groups in order to permit the formation of a graphite-like char which can provide thermal protection to the polymer. It is necessary to have a good match in degradation temperatures of the two components if one is to have significantly enhanced thermal stability.

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Further Studies On Fire Retardant Polystyrene By Friedel–Crafts Chemistry, Zhitao Wang, David D. Jiang, Charles Wilkie, Jeffery W. Gilman Dec 1999

Further Studies On Fire Retardant Polystyrene By Friedel–Crafts Chemistry, Zhitao Wang, David D. Jiang, Charles Wilkie, Jeffery W. Gilman

Chemistry Faculty Research and Publications

The combination of a copolymer of 4-vinylbenzyl alcohol and styrene with 2-ethylhexyldiphenylphosphate (DPP) and with metal chlorides has been studied by TGA, radiative gasification, Cone Calorimetry, and oxygen index measurements. Evidence is presented in support of a cross-linking reaction with the additives and the copolymer, which proceeds through a Friedel–Crafts mechanism. This approach reduces the peak heat release rate (HRR) by 60% as measured in the Cone Calorimeter. There is a significant reduction in the mass loss rate during the thermal degradation, and evidence of char formation is observed in the radiative gasification experiments.

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Tga/Ftir: An Extremely Useful Technique For Studying Polymer Degradation, Charles A. Wilkie Dec 1999

Tga/Ftir: An Extremely Useful Technique For Studying Polymer Degradation, Charles A. Wilkie

Chemistry Faculty Research and Publications

Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy, TGA/FTIR, has been used to probe the degradation of several polymeric systems. These include poly(methyl methacrylate) in the presence of various additives, graft copolymers of acrylonitrile-butadiene-styrene and styrene-butadiene with sodium methacrylate and styrene with acrylonitrile, blends of styrene-butadiene block copolymers with poly(vinylphosphonic acid) and poly(vinylsulfonic acid), and cross-linked polystyrenes. Additives may interact with poly(methyl methacrylate) by coordination to the carbonyl oxygen to a Lewis acid and the subsequent transfer of an electron from the polymer chain to the metal atom or by the formation of a radical which can trap the degrading …

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Stabilization Of Polystyrene By Friedel-Crafts Chemistry: Effect Of Position Of Alcohol And The Catalyst, Jin Zhu, Michael A. Mckinney, Charles Wilkie Nov 1999

Stabilization Of Polystyrene By Friedel-Crafts Chemistry: Effect Of Position Of Alcohol And The Catalyst, Jin Zhu, Michael A. Mckinney, Charles Wilkie

Chemistry Faculty Research and Publications

Polystyrene has been copolymerized with 4-vinylbenzyl alcohol, 4-(2-hydroxyethyl)styrene, and 4-(3-hydroxypropyl)styrene and it has been shown that thermal cross-linking of these copolymers is dependent upon the alcohol content. When the alcohol content is low, no thermal cross-linking is observed. When various phosphate esters are present as catalysts with these low alcohol content copolymers, cross-linking is observed at temperatures of about 250°C but not at lower temperatures. Cross-linking enhances the thermal stability of the copolymers. Studies of the thermal stability of the copolymers and their blends with the catalysts have been performed using thermogravimetric analysis and thermogravimetric analysis coupled to Fourier transform …

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An Xps Study Of The Radiation-Induced Effect On The Thermal Degradation And Charring Of Butadiene And Its Copolymers, Jianwei Hao, Shaoli Wu, Charles Wilkie, Jianqi Wang Oct 1999

An Xps Study Of The Radiation-Induced Effect On The Thermal Degradation And Charring Of Butadiene And Its Copolymers, Jianwei Hao, Shaoli Wu, Charles Wilkie, Jianqi Wang

Chemistry Faculty Research and Publications

A pseudo-in-situ XPS approach shows that cross-linking induced by irradiation may lead to char formation even though it shows only a small or no effect on the onset temperature of degradation.

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Thermal Decomposition Of Cross-Linked Polybutadiene And Its Copolymers, David D. Jiang, Galina F. Levchik, Sergei V. Levchik, Charles Wilkie Sep 1999

Thermal Decomposition Of Cross-Linked Polybutadiene And Its Copolymers, David D. Jiang, Galina F. Levchik, Sergei V. Levchik, Charles Wilkie

Chemistry Faculty Research and Publications

Polybutadiene and two copolymers containing butadiene and styrene have been cross-linked by thermal processes, by the use of initiators in solution, and by intimately mixing an initiator with the polymer and then heating this blend. The most efficient cross-linking process is the use of an intimate blend of the initiator and polymer. Most cross-linking processes lower the onset temperature of degradation, presumably because chain scission reactions occur simultaneously with cross-linking, while also increasing the fraction of non-volatile residue which is produced. It is believed that the density of cross-links is responsible for the increased yield of non-volatile residue.

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1H Nmr Studies On The Cua Center Of Nitrous Oxide Reductase From Pseudomonas Stutzeri, Richard C. Holz, Marcela L. Alvarez, Walter G. Zumft, David M. Dooley Aug 1999

1H Nmr Studies On The Cua Center Of Nitrous Oxide Reductase From Pseudomonas Stutzeri, Richard C. Holz, Marcela L. Alvarez, Walter G. Zumft, David M. Dooley

Chemistry Faculty Research and Publications

1H NMR spectra of the CuA center of N2OR from Pseudomonas stutzeri, and a mutant enzyme that contains only CuA, were recorded in both H2O- and D2O-buffered solution at pH 7.5. Several sharp, well-resolved hyperfine-shifted 1H NMR signals were observed in the 60 to −10 ppm chemical shift range. Comparison of the native and mutant N2OR spectra recorded in H2O-buffered solutions indicated that several additional signals are present in the native protein spectrum. These signals are attributed to a dinuclear copper(II) center. At least …

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The Methionyl Aminopeptidase From Escherichia Coli Can Function As An Iron(Ii) Enzyme, Ventris M. D'Souza, Richard C. Holz Aug 1999

The Methionyl Aminopeptidase From Escherichia Coli Can Function As An Iron(Ii) Enzyme, Ventris M. D'Souza, Richard C. Holz

Chemistry Faculty Research and Publications

The identity of the physiologically relevant metal ions for the methionyl aminopeptidase (MetAP) from Escherichia coli was investigated and is suggested to be Fe(II). The metal content of whole cells in the absence and presence of expression of the type I MetAP from E. coli was determined by inductively coupled plasma (ICP) emission analysis. The observed change in whole cell concentrations of cobalt, cadmium, copper, nickel, strontium, titanium, and vanadium upon expression of MetAP was negligible. On the other hand, significant increases in the cellular metal ion concentrations of chromium, zinc, manganese, and iron were observed with the increase in …

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Models For Molybdenum Coordination During The Catalytic Cycle Of Periplasmic Nitrate Reductase From Paracoccus Denitrificans Derived From Epr And Exafs Spectroscopy, Clive S. Butler, John M. Charnock, Brian Bennett, Heather J. Sears, Ann J. Reilly, Stuart J. Ferguson, C. David Garner, David J. Lowe, Andrew J. Thomson, Ben C. Berks, David J. Richardson Jul 1999

Models For Molybdenum Coordination During The Catalytic Cycle Of Periplasmic Nitrate Reductase From Paracoccus Denitrificans Derived From Epr And Exafs Spectroscopy, Clive S. Butler, John M. Charnock, Brian Bennett, Heather J. Sears, Ann J. Reilly, Stuart J. Ferguson, C. David Garner, David J. Lowe, Andrew J. Thomson, Ben C. Berks, David J. Richardson

Physics Faculty Research and Publications

The periplasmic nitrate reductase from Paracoccus denitrificans is a soluble two-subunit enzyme which binds two hemes (c-type), a [4Fe-4S] center, and a bis molybdopterin guanine dinucleotide cofactor (bis-MGD). A catalytic cycle for this enzyme is presented based on a study of these redox centers using electron paramagnetic resonance (EPR) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The Mo(V) EPR signal of resting NAP (High g [resting]) has gav = 1.9898 is rhombic, exhibits low anisotropy, and is split by two weakly interacting protons which are not solvent-exchangeable. Addition of exogenous ligands to this resting …

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Cross-Linking Of Polystyrene By Friedel–Crafts Chemistry To Improve Thermal Stability, Zhitao Wang, David D. Jiang, Michael A. Mckinney, Charles Wilkie Jun 1999

Cross-Linking Of Polystyrene By Friedel–Crafts Chemistry To Improve Thermal Stability, Zhitao Wang, David D. Jiang, Michael A. Mckinney, Charles Wilkie

Chemistry Faculty Research and Publications

Copolymers which contain either alcohol or chloride functionalized polystyrene units have been prepared and they participate in Friedel–Crafts chemistry to give cross-linked polymers by the evolution of either hydrogen chloride or water. Proof of cross-linking comes from the identification of the evolved gas, the insolubility of the product, and the thermal resistance of the newly formed polymer. The onset temperature for the degradation is raised by about 100°C relative to that of polystyrene and the fraction which is not volatile at 800°C ranges from 10% for the alcohol copolymers to 20% for the chloride copolymers.

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Thermal Decomposition And Combustion Of Γ-Irradiated Polyamide 6 Containing Phosphorus Oxynitride Or Phospham, A. I. Balabanovich, Sergei V. Levchik, Galina F. Levchik, W. Schnabel, Charles Wilkie May 1999

Thermal Decomposition And Combustion Of Γ-Irradiated Polyamide 6 Containing Phosphorus Oxynitride Or Phospham, A. I. Balabanovich, Sergei V. Levchik, Galina F. Levchik, W. Schnabel, Charles Wilkie

Chemistry Faculty Research and Publications

Polyamide 6 (PA-6) containing the fire retardants phosphorus oxynitride ((PON)m) or phospham ((PN2H)n) was exposed to 60Co-γ-rays (absorbed dose: 1.0–4.0 MGy). The irradiation led to crosslinking of the polymer which caused an increase in the char yield and a decrease in the flammability of the polymer. The combustion behavior was strongly affected by irradiation: dripping was totally prevented in the case of system PA-6/(PN2H)n and strongly retarded in the case of system PA-6/(PON)m. The thermal stability of the system PA-6/(PN2H)n decreased with increasing absorbed dose …

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Thermal Degradation Of Polystyrene, Poly(1,4-Butadiene) And Copolymers Of Styrene And 1,4-Butadiene Irradiated Under Air Or Argon With 60co-Γ-Rays, W. Schnabel, Galina F. Levchik, Charles Wilkie, David D. Jiang, Sergei V. Levchik May 1999

Thermal Degradation Of Polystyrene, Poly(1,4-Butadiene) And Copolymers Of Styrene And 1,4-Butadiene Irradiated Under Air Or Argon With 60co-Γ-Rays, W. Schnabel, Galina F. Levchik, Charles Wilkie, David D. Jiang, Sergei V. Levchik

Chemistry Faculty Research and Publications

60Co-γ-irradiated samples of polystyrene (PSt), poly(1,4-butadiene), (PBD), and two poly(styrene-co-butadiene)s containing 25 and 75% BD were subjected to thermogravimetric analysis (TGA), in the presence and absence of O2. In the case of PSt the irradiation caused a significant shift in Tonset, the onset temperature for mass loss, to higher temperatures, whereas in the cases of the BD-containing polymers irradiation caused a decrease in Tonset (oxic irradiation) or had little or no effect on Tonset (anoxic irradiation). The amount of non-volatile residue formed in the cases of BD-containing polymers was augmented by …

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Use Of Evolutionary Factor Analysis In The Spectroelectrochemistry Of Escherichia Coli Sulfite Reductase Hemoprotein And A Mo/Fe/S Cluster, Robert L. Keesey, Michael D. Ryan May 1999

Use Of Evolutionary Factor Analysis In The Spectroelectrochemistry Of Escherichia Coli Sulfite Reductase Hemoprotein And A Mo/Fe/S Cluster, Robert L. Keesey, Michael D. Ryan

Chemistry Faculty Research and Publications

The deconvolution of spectroelectrochemical data is often quite difficult if the spectra of intermediates are not known. Factor analysis, however, has been shown to be a powerful technique which can make it possible to deconvolute overlapping spectra. In this work, evolving factor analysis will be used to determine the number of intermediates and the spectra of those species for two typical spectroelectrochemical experiments:  linear scan voltammetry and chronoabsorptometry in a thin-layer cell. The first system was the reduction of E. coli sulfite reductase hemoprotein (SiR-HP). Principal factor analysis indicated that three species were present. By using evolving factor analysis, …

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Visible And Resonance Raman Spectra Of Low Valent Iron Porphyrins, Chathra De Silva, Kazimierz Czarnecki, Michael D. Ryan Apr 1999

Visible And Resonance Raman Spectra Of Low Valent Iron Porphyrins, Chathra De Silva, Kazimierz Czarnecki, Michael D. Ryan

Chemistry Faculty Research and Publications

The resonance Raman spectrum of Fe(TPP)2− was obtained after the three-electron electrochemical reduction of Fe(TPP)(Cl). The coulometric reduction was carried out in the presence of bis(triphenylphosphoanylidine)ammonium chloride in DMF in order to avoid the formation of iron–σ-alkyl complexes. The resonance Raman spectrum of the intermediate oxidation states (Fe(TPP) and Fe(TPP)−) were consistent with previous work. The spectrum of the three-electron product, Fe(TPP)2−, obtained at 442 nm, was qualitatively similar to the two-electron reduced product, Fe(TPP)−, with an intense ν2 band at 1537 cm−1. The high frequency bands generally decreased in …

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Tga/Ftir Studies On The Thermal Degradation Of Some Polymeric Sulfonic And Phosphonic Acids And Their Sodium Salts, David D. Jiang, Qiang Yao, Michael A. Mckinney, Charles Wilkie Mar 1999

Tga/Ftir Studies On The Thermal Degradation Of Some Polymeric Sulfonic And Phosphonic Acids And Their Sodium Salts, David D. Jiang, Qiang Yao, Michael A. Mckinney, Charles Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of poly(vinyl sulfonic acid) and its sodium salt, poly(4-styrenesulfonic acid) and its sodium salt, and poly(vinylphosphonic acid) was studied by a combination of techniques, including TGA/FTIR, to identify the volatile products which were evolved during the degradation as well as analysis of the residues which were obtained in order to propose a mechanism for the degradation. The motivation for the work was to attempt to identify new monomers which could be graft copolymerized onto a polymer in order to improve the thermal stability of that polymer.

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X-Ray Crystal Structures And The Facile Oxidative (Au−C) Cleavage Of The Dimethylaurate(I) And Tetramethylaurate(Iii) Homologues, Dunming Zhu, Sergey V. Lindeman, Jay K. Kochi Jan 1999

X-Ray Crystal Structures And The Facile Oxidative (Au−C) Cleavage Of The Dimethylaurate(I) And Tetramethylaurate(Iii) Homologues, Dunming Zhu, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Dimethylaurate(I) has been prepared as the crystalline tetrabutylammonium salt for comparison with the known tetramethylaurate(III) analogue. The linear structure of dimethylaurate(I) and the square-planar structure of tetramethylaurate(III) have both been confirmed by X-ray crystallography. One-electron oxidation of dimethylaurate(I) by either ferrocenium or arenediazonium cations produces the metastable dimethylgold(II) intermediate, which can be trapped as the paramagnetic 9,10-phenanthrenequinone (PQ) adduct. Otherwise, dimethylgold(II) is subject to rapid reductive elimination of ethane and affords metallic gold (mirror). The analogous oxidation of tetramethylaurate(III) by ferrocenium, arenediazonium, or nitrosonium cations also proceeds via electron transfer to generate the putative tetramethylgold(IV) intermediate. The highly unstable (CH …

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Adventures In Fire Retardancy, Charles A. Wilkie Jan 1999

Adventures In Fire Retardancy, Charles A. Wilkie

Chemistry Faculty Research and Publications

The work of the author's research group on fire retardancy over the past twenty years is reviewed.

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Synthetic Studies Directed Toward Streptenol D: Enantioselective Preparation Of The 3,5-Diacetoxy-6E,8E-Decadiene Segment, Bireshwar Dasgupta, William A. Donaldson Nov 1998

Synthetic Studies Directed Toward Streptenol D: Enantioselective Preparation Of The 3,5-Diacetoxy-6E,8E-Decadiene Segment, Bireshwar Dasgupta, William A. Donaldson

Chemistry Faculty Research and Publications

The enantioselective preparation of 2-(3′R,5′R-diacetoxy-6E,8E-decadienyl)-1,3-dioxane, (+)-13, is described. This synthesis of the skeleton of streptenol D utilizes the ability of a diene-complexed (tricarbonyl)iron unit to serve as a protecting and stereodirecting functionality.

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Tga–Fti.R. Investigation Of The Thermal Degradation Of Nafion® And Nafion®/[Silicon Oxide]-Based Nanocomposites, Q. Deng, Charles Wilkie, R. B. Moore, Kenneth A. Mauritz Nov 1998

Tga–Fti.R. Investigation Of The Thermal Degradation Of Nafion® And Nafion®/[Silicon Oxide]-Based Nanocomposites, Q. Deng, Charles Wilkie, R. B. Moore, Kenneth A. Mauritz

Chemistry Faculty Research and Publications

The integrated TGA–FTi.r. technique probed the thermal degradation of: (1) a Nafion®–H+ membrane; (2) this membrane as modified by incorporation of a SiO2[1-x/4] (OH)x phase via in situ sol–gel reactions for tetraethoxysilane; and (3) this modified membrane as further modified, organically, via post-reaction with diethoxydimethylsilane. Gravimetric loss is multistep for (1) and (2), but occurs in a single step for (3) which has the greatest thermal degradative stability. The considerable inhibition of SO2 evolution for (2) and (3) is rationalized in terms of side-chains that are immobilized within silicon oxide cages …

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Direct Voltammetric Observation Of Redox Driven Changes In Axial Coordination And Intramolecular Rearrangement Of The Phenylalanine-82-Histidine Variant Of Yeast Iso-1-Cytochrome C, Benjamin A. Feinberg, Xiangjun Liu, Michael D. Ryan, Abel Schejter, Chongyao Zhang, Emanuel Margoliash Sep 1998

Direct Voltammetric Observation Of Redox Driven Changes In Axial Coordination And Intramolecular Rearrangement Of The Phenylalanine-82-Histidine Variant Of Yeast Iso-1-Cytochrome C, Benjamin A. Feinberg, Xiangjun Liu, Michael D. Ryan, Abel Schejter, Chongyao Zhang, Emanuel Margoliash

Chemistry Faculty Research and Publications

Direct square-wave and cyclic voltammetric electrochemical examination of the yeast iso-1-cytochrome c Phe82His/Cys102Ser variant revealed the intricacies of redox driven changes in axial coordination, concomitant with intramolecular rearrangement. Electrochemical methods are ideally suited for such a redox study, since they provide a direct and quantitative visualization of specific dynamic events. For the iso-1-cytochrome c Phe82His/Cys102Ser variant, square-wave voltammetry showed that the primary species in the reduced state is the Met80-Fe2+-His18 coordination form, while in the oxidized state the His82-Fe3+-His18 form predominates. The addition or removal of an electron to the …

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Synthesis And Characterization Of Large Stereoregular Organosiloxane Cycles, O. I. Schchegolikhina, V. A. Igonin, Yulia A. Molodtsova, Yu. A. Pozdniakova, Alexandr A. Zhdanov, T. V. Strelkova, Sergey V. Lindeman Jul 1998

Synthesis And Characterization Of Large Stereoregular Organosiloxane Cycles, O. I. Schchegolikhina, V. A. Igonin, Yulia A. Molodtsova, Yu. A. Pozdniakova, Alexandr A. Zhdanov, T. V. Strelkova, Sergey V. Lindeman

Chemistry Faculty Research and Publications

The large stereoregular phenyltrimethylsiloxysiloxane macrocycles of general formula [PhSi(OSiMe3)O]n (n=6 and 12) have been selectively obtained with high yields by trimethylsilylation of cage-like oligophenylmetallasiloxanes (OPMS) which we described earlier. The compounds 3 (n=6) and 4 (n=12) have been characterized by NMR-spectroscopy method and by single crystal X-ray analysis. This investigation showed unambiguously that the siloxane macrocycles keep their size and configuration (the same as in the initial OPMS) during the trimethylsilylation. Thus a synthetic route for obtaining large stereoregular siloxane macrocycles has been developed.

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Folding Under Inequilibrium Conditions As A Possible Reason For Partial Irreversibility Of Heat-Denatured Proteins: Computer Simulation Study, Sergey A. Potekhin, Evgenii L. Kovrigin Jul 1998

Folding Under Inequilibrium Conditions As A Possible Reason For Partial Irreversibility Of Heat-Denatured Proteins: Computer Simulation Study, Sergey A. Potekhin, Evgenii L. Kovrigin

Chemistry Faculty Research and Publications

Using computer simulations we have studied possible effects of heating and cooling at different scan rates on unfolding and refolding of macromolecules. We have shown that even the simplest two-state reversible transition can behave irreversibly when an unfavorable combination of cooling rate, relaxation time and activation energy of refolding occurs. On the basis of this finding we suppose that apparent irreversibility of some proteins denatured by heat may result from slow relaxation on cooling rather than thermodynamic instability and/or irreversible alterations of the polypeptide chain. Using this kinetic reversible two-state model, we estimated the effects of the scan rate and …

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Graft Copolymerization Of Methacrylic Acid, Acrylic Acid And Methyl Acrylate Onto Styrene–Butadiene Block Copolymer, David D. Jiang, Charles Wilkie Jul 1998

Graft Copolymerization Of Methacrylic Acid, Acrylic Acid And Methyl Acrylate Onto Styrene–Butadiene Block Copolymer, David D. Jiang, Charles Wilkie

Chemistry Faculty Research and Publications

Methyl acrylate, methacrylic acid, and acrylic acid have been graft copolymerized onto styrene–butadiene block copolymer. All three monomers react through the macroradical interacting with the double bond of butadiene. The site of reaction has been established by infrared spectroscopy. For methyl acrylate every unit of the styrene–butadiene block copolymer is grafted but only a small fraction is grafted when the acids are used. The difference apparently lies in the fact that the reaction with the ester is homogeneous while with the acids the reactions are heterogeneous.

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Structure Of 5-Nitro-2-Tosylaminobenzaldehyde Di(Morpholin-4-Yl)Aminal Complex With Carbon Tetrachloride, V. N. Khrustalev, Sergey V. Lindeman, L. Yu Ukhin, G. I. Orlova, T. N. Gribanova, O. V. Shishkin May 1998

Structure Of 5-Nitro-2-Tosylaminobenzaldehyde Di(Morpholin-4-Yl)Aminal Complex With Carbon Tetrachloride, V. N. Khrustalev, Sergey V. Lindeman, L. Yu Ukhin, G. I. Orlova, T. N. Gribanova, O. V. Shishkin

Chemistry Faculty Research and Publications

The 5-nitro-2-tosylaminobenzaldehyde di(morpholin-4-yl)aminal forms a stable complex with carbon tetrachloride in the crystal phase. X-ray structural study of this complex indicates an essentially shortened intermolecular contact of 2.89 Å between the oxygen atom of the nitro group and one of the chlorine atom of the CCI4 molecule. Quantum-chemical calculations by semiempirical AMI method showed that the formation of such complex did not cause considerable decrease of system energy or change of charge distribution in molecules. It was supposed that this associate has van der Waals character.

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