Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Keyword
-
- Nanocomposites (42)
- Polystyrene (25)
- Fire retardancy (22)
- Cone calorimetry (13)
- Spectroelectrochemistry (11)
-
- Poly(methyl methacrylate) (10)
- Thermal stability (10)
- Inelastic scattering (8)
- NMR (8)
- Nanocomposite (8)
- Thermal degradation (8)
- Cobalt (7)
- Fire Retardancy (7)
- Iron (7)
- X-ray structures (7)
- Cross-linking (6)
- Crystal structure (6)
- Cyclic voltammetry (6)
- Electrochemistry (6)
- Ionic liquid (6)
- Layered double hydroxide (6)
- Molecular data (6)
- Oxidation (6)
- Cytochrome P450 (5)
- Kinetics (5)
- Layered double hydroxides (5)
- Polyethylene (5)
- Wave functions (5)
- XPS (5)
- Zinc (5)
- Publication Year
Articles 451 - 480 of 690
Full-Text Articles in Chemistry
The Crystal And Molecular Structure Of A Trifluoroacetylacetonate Complex Of Scandium, Sc(Ch3Cochcocf3)3, Dennis W. Bennett, Tasneem Siddiquee, Daniel T. Haworth, Sergey V. Lindeman
The Crystal And Molecular Structure Of A Trifluoroacetylacetonate Complex Of Scandium, Sc(Ch3Cochcocf3)3, Dennis W. Bennett, Tasneem Siddiquee, Daniel T. Haworth, Sergey V. Lindeman
Chemistry Faculty Research and Publications
The crystal and molecular structure of Sc(CH3COCHCOCF3)3 has been determined by X-ray diffraction. The compound crystallizes as pure mer-isomer in the orthorhombic space group Pbca with lattice parameters a=15.166(8) Å, b=13.560(7) Å, c=19.327(10) Å, α=β=γ=90°, V=3974(4) Å3, Z=8. The complex at 100 K is partially disordered in the crystal structure in an approximate 5:1 ratio with 83% fluorine population at C-11 and 17% at C-15. NMR data is compared to that previously reported.
13C Nmr Analysis Of Biologically Produced Pyrene Residues By Mycobacterium Sp. Kms In The Presence Of Humic Acid, J. Karl C. Nieman, Richard C. Holz, Ronald C. Sims
13C Nmr Analysis Of Biologically Produced Pyrene Residues By Mycobacterium Sp. Kms In The Presence Of Humic Acid, J. Karl C. Nieman, Richard C. Holz, Ronald C. Sims
Chemistry Faculty Research and Publications
Cultures of the pyrene degrading Mycobacterium sp. KMS were incubated with [4-13C]pyrene or [4,5,9,10-14C]pyrene with and without a soil humic acid standard to characterize the chemical nature of the produced residues and evaluate the potential for bonding reactions with humic acid. Cultures were subjected to a “humic acid/humin” separation at acidic pH, a duplicate separation followed by solvent extraction of the humic acid/humin fraction, and a high pH separation. 13C NMR analysis was conducted on the resulting solid extracts. Results indicated that the activity associated with solid extracts did not depend on pH and that …
Conserved Amino Acids In Each Subunit Of The Heteroligomeric Trna M1A58 Mtase From Saccharomyces Cerevisiae Contribute To Trna Binding, Sarah G. Ozanick, Janusz M. Bujnicki, Daniel S. Sem, James T. Anderson
Conserved Amino Acids In Each Subunit Of The Heteroligomeric Trna M1A58 Mtase From Saccharomyces Cerevisiae Contribute To Trna Binding, Sarah G. Ozanick, Janusz M. Bujnicki, Daniel S. Sem, James T. Anderson
Chemistry Faculty Research and Publications
In Saccharomyces cerevisiae, a two-subunit methyltransferase (Mtase) encoded by the essential genes TRM6 and TRM61 is responsible for the formation of 1-methyladenosine, a modified nucleoside found at position 58 in tRNA that is critical for the stability of . The crystal structure of the homotetrameric m1A58 tRNA Mtase from Mycobacterium tuberculosis, TrmI, has been solved and was used as a template to build a model of the yeast m1A58 tRNA Mtase heterotetramer. We altered amino acids in TRM6 and TRM61 that were predicted to be important for the stability of the heteroligomer based on …
Use Of Factor Analysis In Multi‐Electron Spectroelectrochemistry, Michael D. Ryan, Robert L. Keesey
Use Of Factor Analysis In Multi‐Electron Spectroelectrochemistry, Michael D. Ryan, Robert L. Keesey
Chemistry Faculty Research and Publications
Spectroelectrochemistry and voltammetry contain both unique and complementary information. For multielectron transfers, information on each electron exchange is only directly accessible in the voltammetric data if the potentials are well separated so that two distinct waves can be observed. If the E°’s are close together, the voltammetric data will contain the sum of the two exchanges which can only be deconvoluted by modeling the system and solving the appropriate equations. On the other hand, the spectroscopic data contains direct information on each electron exchange even when the E°’s are close together. Unfortunately, this information cannot be readily extracted if the …
Practical Synthesis Of Unsymmetrical Tetraarylethylenes And Their Application For The Preparation Of [Triphenylethylene−Spacer−Triphenylethylene] Triads, Moloy Banerjee, Susanna J. Emond, Sergey V. Lindeman, Rajendra Rathore
Practical Synthesis Of Unsymmetrical Tetraarylethylenes And Their Application For The Preparation Of [Triphenylethylene−Spacer−Triphenylethylene] Triads, Moloy Banerjee, Susanna J. Emond, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
We have demonstrated that reactions of diphenylmethyllithium with a variety of substituted benzophenones produces corresponding tertiary alcohols that are easily dehydrated, without any need for purification, to produce various unsymmetrical and symmetrical tetraarylethylenes in excellent yields. The simplicity of the method allows for the preparation of a variety of ethylenic derivatives in multigram (10−50 g) quantities with great ease. The methodology was successfully employed for the preparation of various triphenylethylene (TPE)-based triads (i.e., TPE−spacer−TPE) containing polyphenylene and fluoranyl-based spacers. The ready availability of various substituted tetraarylethylenes allowed us to shed light on the effect of substituents on the oxidation potentials …
Hexabenzo[4.4.4]Propellane: A Helical Molecular Platform For The Construction Of Electroactive Materials, Paromita Debroy, Sergey V. Lindeman, Rajendra Rathore
Hexabenzo[4.4.4]Propellane: A Helical Molecular Platform For The Construction Of Electroactive Materials, Paromita Debroy, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
Helical hexabenzo[4.4.4]propellane (a relative of hexaphenylethane) and its derivatives are synthesized and their structures are established by X-ray crystallography. Isolation and X-ray crystallographic characterization of a robust trication-radical salt of hexamethoxypropellane derivative confirms that its framework is stable toward oxidative (aliphatic) C−C bond cleavage. It is also demonstrated that propellane can be easily brominated at the 4,4‘-positions of the biphenyl linkages for its usage as a molecular platform for the preparation of electroactive materials.
Borazans: Tunable Fluorophores Based On 2-(Pyrazolyl)Aniline Chelates Of Diphenylboron, Brendan J. Liddle, Rosalice M. Silva, Tyler James Morin, Felipe P. Macedo, Ruchi Shukla, Sergey V. Lindeman, James R. Gardinier
Borazans: Tunable Fluorophores Based On 2-(Pyrazolyl)Aniline Chelates Of Diphenylboron, Brendan J. Liddle, Rosalice M. Silva, Tyler James Morin, Felipe P. Macedo, Ruchi Shukla, Sergey V. Lindeman, James R. Gardinier
Chemistry Faculty Research and Publications
The reaction between 2-pyrazolyl-4-X-anilines, H(pzAnX), (X = para-OMe (L1), Me (L2), H (L3), Cl (L4), CO2Et (L5), CF3 (L6), CN (L7)) and triphenylboron in boiling toluene affords the respective, highly emissive N,N‘-boron chelate complexes, BPh2(pzAnX) (X = para-OMe (1), Me (2), H (3), Cl (4), CO2Et (5), CF3 (6), CN (7)) in high yield. The …
Electron Transfer Prompted Ejection Of A Tightly Bound K+ From The Ethereal Cavity Of A Hexaarylbenzene-Based Receptor, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Electron Transfer Prompted Ejection Of A Tightly Bound K+ From The Ethereal Cavity Of A Hexaarylbenzene-Based Receptor, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
Synthesis of a pair of rotamers (9u/9s) of a hexaarylbenzene derivative containing six (cofacially arranged) electroactive 2,5-dimethoxytolyl groups is described. The toroidal electronic stabilization due to the circular arrangement of aryl groups in 9u/9s leads to the observation of multiple (reversible) oxidation waves and lowering of their Eox1 by ∼250 mV relative to model compounds. The binding of K+ to symmetrical rotamer 9s was monitored by an electrochemical method and further confirmed by X-ray crystallography.
Chemistry And Biology Of Streptogramin A Antibiotics, Fahim Ahmed, William A. Donaldson
Chemistry And Biology Of Streptogramin A Antibiotics, Fahim Ahmed, William A. Donaldson
Chemistry Faculty Research and Publications
The streptogramin A antibiotics have proven to be highly active against Gram positive bacteria, particularly methicillin-resistant Staphylococcus aureus. Members of this group of compounds are characterized by a 23-membered macrocycles containing polyene, oxazole, amide and ester functionality. The chemistry and biology of these valuable antimicrobial agents is covered.
Preparation, Characterization And Reactivity Of (3-Methylpentadienyl)Iron(1+) Cations, Subhabrata Chaudhury, Shukun Li, Dennis W. Bennett, Tasneem Siddiquee, Daniel T. Haworth, William A. Donaldson
Preparation, Characterization And Reactivity Of (3-Methylpentadienyl)Iron(1+) Cations, Subhabrata Chaudhury, Shukun Li, Dennis W. Bennett, Tasneem Siddiquee, Daniel T. Haworth, William A. Donaldson
Chemistry Faculty Research and Publications
The title cations (9 and 12) were prepared by dehydration of (3-methyl-2,4-pentadien-1-ol)Fe(CO)2L+ complexes. The structure of the (CO)2PPh3-ligated 12 was determined by single-crystal X-ray analysis. Reaction of carbon and heteroatom nucleophiles to (3-methylpentadienyl)Fe(CO)3+ cations 9 and 12 proceeds either via attack at the dienyl terminus to give (3-methyl-1,3Z-diene)iron complexes or via attack at the internal carbon, followed by carbon monoxide insertion and reductive elimination to afford 3-methyl-4-substituted cyclohexenones. Cyclohexenone formation was found to be prevalent for addition of stabilized nucleophiles with strongly dissociated counterions to cation 9 …
Enhanced Fire Retardancy Of Vinyl Ester Resins By Combination Of Additives, Grace Chigwada, Charles A. Wilkie
Enhanced Fire Retardancy Of Vinyl Ester Resins By Combination Of Additives, Grace Chigwada, Charles A. Wilkie
Chemistry Faculty Research and Publications
In pursuit of fire-retardant materials, vinyl ester resins were combined with commercially available fire retardants at lower loadings than that at which they are usually effective when used alone. The thermal stability and flammability of the various combinations of fire retardants were evaluated by thermogravimetric analysis and cone calorimetric analysis. With some combinations, the 50% degradation temperature was improved by about 5-10ºC Different additives affected the flammability to varying extents and some combinations resulted in an enhanced fire retardancy compared to the additives used alone. The combinations that showed the best reductions in the peak heat release rate (PHRR) were …
A Thallium Mediated Route To Σ-Arylalkynyl Complexes Of Bipyridyltricarbonylrhenium(I), Brendan J. Liddle, Sergey V. Lindeman, Daniel L. Reger, James R. Gardinier
A Thallium Mediated Route To Σ-Arylalkynyl Complexes Of Bipyridyltricarbonylrhenium(I), Brendan J. Liddle, Sergey V. Lindeman, Daniel L. Reger, James R. Gardinier
Chemistry Faculty Research and Publications
A simple, one-pot preparation of rhenium(I) σ-arylalkynyl complexes is reported using thallium(I) hexafluorophosphate as a halogen abstraction agent. This new route to rhenium σ-alkynyls enjoys higher yields compared to analogous preparations using silver salts by eliminating potential electrochemical degradation pathways.
Preparation Of Chiral Cholestanofluorene And Its Electron-Rich Derivatives For Isolation Of A Stable Cation−Radical Salt, Paromita Debroy, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Preparation Of Chiral Cholestanofluorene And Its Electron-Rich Derivatives For Isolation Of A Stable Cation−Radical Salt, Paromita Debroy, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
A simple and practical synthesis of a variety of chiral fluorene derivatives is described where a cholestane moiety is attached to the carbon 9 of the fluorene ring system from readily available starting materials. An appropriately substituted fluorene derivative (i.e., R = OMe) forms a highly colored (chiral) cation−radical that can be isolated as robust hexachloroantimonate salt. Interestingly, the simplest cholestanofluorene (i.e., R = H) can also be transformed into a dibromo derivative (i.e., R = Br), a precursor to the (poly)cholestanofluorenes where the cholestane moieties will serve not only as groups that impart chirality but also allow them to …
A ‘Metallic Tape’ Stabilized By An Unprecedented Μ5-Κ2,Κ2,Κ2,Κ1,Κ1-) Scorpionate Binding Mode, James R. Gardinier, Rosalice M. Silva, Chengeto Gwengo, Sergey V. Lindeman
A ‘Metallic Tape’ Stabilized By An Unprecedented Μ5-Κ2,Κ2,Κ2,Κ1,Κ1-) Scorpionate Binding Mode, James R. Gardinier, Rosalice M. Silva, Chengeto Gwengo, Sergey V. Lindeman
Chemistry Faculty Research and Publications
The Janus scorpionate ligand, tris(mercaptothiadiazolyl)borate, exhibits extraordinary coordination capacity and versatility, binding from two up to five metal cations as demonstrated by its thallium(I) salt, a compound that serves as a model for metal–surface binding.
Attachment Of Motile Bacterial Cells To Prealigned Holed Microarrays, Sergey Rozhok, Zhifang Fan, Dorjderem Nyamjav, Chang Liu, Chad A. Mirkin, Richard C. Holz
Attachment Of Motile Bacterial Cells To Prealigned Holed Microarrays, Sergey Rozhok, Zhifang Fan, Dorjderem Nyamjav, Chang Liu, Chad A. Mirkin, Richard C. Holz
Chemistry Faculty Research and Publications
Construction of biomotors is an exciting area of scientific research that holds great promise for the development of new technologies with broad potential applications in areas such as the energy industry and medicine. Herein, we demonstrate the fabrication of prealigned microarrays of motile Escherichia coli bacterial cells on SiOx substrates. To prepare these arrays, holed surfaces with a gold layer on the bottom of the holes were utilized. The attachment of bacteria to the holes was achieved via nonspecific interactions using poly-l-lysine hydrobromide (PLL). Our data suggest that a single motile bacterial cell can be selectively attached to an individual …
The Proteomics Of N-Terminal Methionine Cleavage, Frédéric Frottin, Aude Martinez, Philippe Peynot, Sanghamitra Mitra, Richard C. Holz, Carmela Giglione, Thierry Meinnel
The Proteomics Of N-Terminal Methionine Cleavage, Frédéric Frottin, Aude Martinez, Philippe Peynot, Sanghamitra Mitra, Richard C. Holz, Carmela Giglione, Thierry Meinnel
Chemistry Faculty Research and Publications
Methionine aminopeptidase (MAP) is a ubiquitous, essential enzyme involved in protein N-terminal methionine excision. According to the generally accepted cleavage rules for MAP, this enzyme cleaves all proteins with small side chains on the residue in the second position (P1′), but many exceptions are known. The substrate specificity of Escherichia coli MAP1 was studied in vitro with a large (>120) coherent array of peptides mimicking the natural substrates and kinetically analyzed in detail. Peptides with Val or Thr at P1′ were much less efficiently cleaved than those with Ala, Cys, Gly, Pro, or Ser in this position. Certain residues …
Styrenic Polymer Nanocomposites Based On An Oligomerically-Modified Clay With High Inorganic Content, Jinguo Zhang, David D. Jiang, Dongyan Wang, Charles A. Wilkie
Styrenic Polymer Nanocomposites Based On An Oligomerically-Modified Clay With High Inorganic Content, Jinguo Zhang, David D. Jiang, Dongyan Wang, Charles A. Wilkie
Chemistry Faculty Research and Publications
Clay was modified with an oligomeric surfactant containing styrene and lauryl acrylate units along with a small amount of vinylbenzyl chloride to permit the formation of an ammonium salt so that this can be attached to a clay. The oligomerically-modified clay contains 50% inorganic clay, and styrenic polymer nanocomposites, including those of polystyrene (PS), high-impact polystyrene (HIPS), styrene–acrylonitrile copolymer (SAN) and acrylonitrile–butadiene–styrene (ABS), were prepared by melt blending. The morphologies of the nanocomposites were evaluated by X-ray diffraction and transmission electron microscopy. Mixed intercalated/delaminated nanocomposites were formed for SAN and ABS while largely immiscible nanocomposites were formed for PS and …
Additional Evidence For The Migration Of Clay Upon Heating Of Clay–Polypropylene Nanocomposites From X-Ray Photoelectron Spectroscopy (Xps), Jianwei Hao, Menachem Lewin, Charles A. Wilkie, Jiangqi Wang
Additional Evidence For The Migration Of Clay Upon Heating Of Clay–Polypropylene Nanocomposites From X-Ray Photoelectron Spectroscopy (Xps), Jianwei Hao, Menachem Lewin, Charles A. Wilkie, Jiangqi Wang
Chemistry Faculty Research and Publications
The explanation for reduction in the peak heat release rate of polymer–clay nanocomposites which is normally accepted is that clay accumulates at the surface, forming a thermal shield which is also a barrier to mass transport. The process by which this clay arrives at the surface has never been described in print but the common assumption is that pyrolysis is required for clay accumulation to occur. In this work, X-ray photoelectron spectroscopy, a tool much more sensitive in surface analysis than conventional techniques, is used to probe the surface of polypropylene–clay nanocomposites that have been annealed at relatively low temperatures, …
A New Colorimetric Assay For Methionyl Aminopeptidases: Examination Of The Binding Of A New Class Of Pseudopeptide Analog Inhibitors, Sanghamitra Mitra, Anna M. Dygas-Holz, Jiri Jiracek, Miroslava Zertova, Lenka Zakova, Richard C. Holz
A New Colorimetric Assay For Methionyl Aminopeptidases: Examination Of The Binding Of A New Class Of Pseudopeptide Analog Inhibitors, Sanghamitra Mitra, Anna M. Dygas-Holz, Jiri Jiracek, Miroslava Zertova, Lenka Zakova, Richard C. Holz
Chemistry Faculty Research and Publications
A direct and convenient spectrophotometric assay has been developed for methionine aminopeptidases (MetAPs). The method employs the hydrolysis of a substrate that is a methionyl analogue of p-nitroaniline (l-Met-p-NA), which releases the chromogenic product p-nitroaniline. This chromogenic product can be monitored continuously using a UV–Vis spectrophotometer set at 405 nm. The assay was tested with the type I MetAP from Escherichia coli (EcMetAP-I) and the type II MetAP from Pyrococcus furiosus (PfMetAP-II). Using l-Met-p-NA, the kinetic constants kcat and Km were determined for EcMetAP-I and PfMetAP-II …
Crystal And Molecular Structure Of Bis(8-Phenylmenthyl) 2-(2-Methyl-5-Oxo-3-Cyclohexen-1-Yl)Propandioate, C42H54O5• Ch3Cn, Dennis W. Bennett, Tasneem A. Siddiquee, Daniel T. Haworth, Subhabrata Chaudhury, William A. Donaldson
Crystal And Molecular Structure Of Bis(8-Phenylmenthyl) 2-(2-Methyl-5-Oxo-3-Cyclohexen-1-Yl)Propandioate, C42H54O5• Ch3Cn, Dennis W. Bennett, Tasneem A. Siddiquee, Daniel T. Haworth, Subhabrata Chaudhury, William A. Donaldson
Chemistry Faculty Research and Publications
The X-ray crystal structure of the title compound, as crystallized from acetonitrile-water was determined. The relative stereochemistry of the cyclohexenone ring with respect to the 8-phenylmenthyl esters was determined. The title compound crystallizes in the noncentrosymmetric space group P21, with a=8.9850(10) Å, b=15.575(3) Å, c=14.478(2) Å, β=94.61(2)°, and D calc=1.118 g cm−3 for Z=2.
Nanostructured Layered Copper Hydroxy Dodecyl Sulfate: A Potential Fire Retardant For Poly(Vinyl Ester) (Pve), Everson Kandare, Grace Chigwada, Dongyan Wang, Charles A. Wilkie, Jeanne Hossenlopp
Nanostructured Layered Copper Hydroxy Dodecyl Sulfate: A Potential Fire Retardant For Poly(Vinyl Ester) (Pve), Everson Kandare, Grace Chigwada, Dongyan Wang, Charles A. Wilkie, Jeanne Hossenlopp
Chemistry Faculty Research and Publications
Composites of poly(vinyl ester) (PVE) with copper hydroxy dodecyl sulfate (CHDS) were prepared by thermal curing. The efficiency of the additive, CHDS, in reducing flammability is demonstrated via cone calorimetry and thermogravimetric analysis (TGA). The addition of 1-10% by mass of the CHDS additive resulted in significant increments in char formation (~4-11%) from thermogravimetric analysis (TGA). Incorporation of the CHDS into the polymer matrix at these low concentrations leads to substantial reductions in the total heat release (~20-30%) but no significant change in the peak heat release rate. The composite materials generally ignite more quickly, however, the flame extinguishes faster …
Polyethylene And Polypropylene Nanocomposites Based On Polymerically - Modified Clay Containing Alkylstyrene Units, Jinguo Zhang, Charles A. Wilkie
Polyethylene And Polypropylene Nanocomposites Based On Polymerically - Modified Clay Containing Alkylstyrene Units, Jinguo Zhang, Charles A. Wilkie
Chemistry Faculty Research and Publications
Sodium montmorillonite was modified with a new polymeric surfactant. The high molecular weight of the surfactant appears to have led to incomplete cation exchange of the clays, but did promote nanocomposite formation with polyethylene and polypropylene. X-ray diffraction combined with transmission electron microscopy revealed a mixed nanocomposite morphology. The thermal stability of the nanocomposites was evaluated by thermogravimetric analysis, while flammability of the nanocomposites was evaluated by cone calorimetry. A significant 40% reduction in peak heat release rate was observed at 10% organo-clay (3% inorganic clay) loading with an even higher 50% reduction at a loading level of 16% modified …
Novel Potentiometric And Optical Silver Ion-Selective Sensors With Subnanomolar Detection Limits, Zsófia Szigeti, Adam Malon, Tamás Vigassy, Viktor Csokai, Alajos Grün, Katarzyna Wygladacz, Nan Ye, Chao Xu, Vincent J. Chebny, István Bitter, Rajendra Rathore, Eric Bakker, Ernö Pretsch
Novel Potentiometric And Optical Silver Ion-Selective Sensors With Subnanomolar Detection Limits, Zsófia Szigeti, Adam Malon, Tamás Vigassy, Viktor Csokai, Alajos Grün, Katarzyna Wygladacz, Nan Ye, Chao Xu, Vincent J. Chebny, István Bitter, Rajendra Rathore, Eric Bakker, Ernö Pretsch
Chemistry Faculty Research and Publications
Ten Ag+-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag+ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10−11 M (potentiometrically) and 2 × 10−11 …
Probing Synergism, Antagonism, And Additive Effects In Poly(Vinyl Ester) (Pve) Composites With Fire Retardants, Everson Kandare, Grace Chigwada, Dongyan Wang, Charles Wilkie, Jeanne Hossenlopp
Probing Synergism, Antagonism, And Additive Effects In Poly(Vinyl Ester) (Pve) Composites With Fire Retardants, Everson Kandare, Grace Chigwada, Dongyan Wang, Charles Wilkie, Jeanne Hossenlopp
Chemistry Faculty Research and Publications
Potential fire retardants, including copper hydroxy dodecyl sulfate (CHDS), organically-modified montmorillonite (Cloisite 15A), and resorcinol di-phosphate (RDP), were added to pure poly(vinyl ester) (PVE) individually or in combinations at low concentration formulations. Thermogravimetric analysis and cone calorimetry were used to study the thermal stability and fire performance of the composites. Synergistic, antagonistic, and additive effects were observed depending on the specific formulation. Time to self-sustained combustion is greatly reduced, but the flame extinguishes faster, for the composites containing CROS alone or in combination with either RDP or Cloisite 15A compared to the virgin polymer. The presence of copper in PVE …
Characterization Of The Transition State Of Functional Enzyme Dynamics, Evgenii L. Kovrigin, J. Patrick Loria
Characterization Of The Transition State Of Functional Enzyme Dynamics, Evgenii L. Kovrigin, J. Patrick Loria
Chemistry Faculty Research and Publications
Through characterization of the solvent isotope effect on protein dynamics, we have examined determinants of the rate limitation to enzyme catalysis. A global conformational change in Ribonuclease A limits the overall rate of catalytic turnover. Here we show that this motion is sensitive to solvent deuterium content; the isotope effect is 2.2, a value equivalent to the isotope effect on the catalytic rate constant. We further demonstrate that the protein motion possesses a linear proton inventory plot, indicating that a single proton is transferred in the transition state. These results provide compelling evidence for close coupling between enzyme dynamics and …
Faithful Estimation Of Dynamics Parameters From Cpmg Relaxation Dispersion Measurements, Evgenii L. Kovrigin, James G. Kempf, Michael J. Grey, J. Patrick Loria
Faithful Estimation Of Dynamics Parameters From Cpmg Relaxation Dispersion Measurements, Evgenii L. Kovrigin, James G. Kempf, Michael J. Grey, J. Patrick Loria
Chemistry Faculty Research and Publications
This work examines the robustness of fitting of parameters describing conformational exchange (kex, pa/b, and Δω) processes from CPMG relaxation dispersion data. We have analyzed the equations describing conformational exchange processes for the intrinsic inter-dependence of their parameters that leads to the existence of multiple equivalent solutions, which equally satisfy the experimental data. We have used Monte-Carlo simulations and fitting to the synthetic data sets as well as the direct 3-D mapping of the parameter space of kex, pa/b, and Δω to quantitatively assess …
Thermal Degradation Of Acetate-Intercalated Hydroxy Double And Layered Hydroxy Salts, Everson Kandare, Jeanne Hossenlopp
Thermal Degradation Of Acetate-Intercalated Hydroxy Double And Layered Hydroxy Salts, Everson Kandare, Jeanne Hossenlopp
Chemistry Faculty Research and Publications
Two hydroxy double salts (HDSs), zinc copper hydroxy acetate (ZCA) and zinc nickel hydroxy acetate (ZNA), and an analogous layered compound, zinc hydroxy acetate (ZHA), have been prepared by a coprecipitation method. The thermal degradation of these materials was characterized via thermogravimetric analysis (TGA), differential thermal analysis (DTA), and TGA coupled with Fourier transform infrared spectroscopy of gas-phase products, TGA-FTIR. Loss of physisorbed and interlayer H2O was observed between 50 and 150 °C for all compounds. Acetic acid, acetone, water, and CO2 were released at high temperatures with relative acetone yields found to be dependent on precursor identity, with very …
The High-Resolution Structures Of The Neutral And The Low Ph Crystals Of Aminopeptidase From Aeromonas Proteolytica, William Desmarais, David L. Bienvenue, Krzysztof P. Bzymek, Gregory A. Petsko, Dagmar Ringe, Richard C. Holz
The High-Resolution Structures Of The Neutral And The Low Ph Crystals Of Aminopeptidase From Aeromonas Proteolytica, William Desmarais, David L. Bienvenue, Krzysztof P. Bzymek, Gregory A. Petsko, Dagmar Ringe, Richard C. Holz
Chemistry Faculty Research and Publications
The aminopeptidase from Aeromonas proteolytica (AAP) contains two zinc ions in the active site and catalyzes the degradation of peptides. Herein we report the crystal structures of AAP at 0.95-Å resolution at neutral pH and at 1.24-Å resolution at low pH. The combination of these structures allowed the precise modeling of atomic positions, the identification of the metal bridging oxygen species, and insight into the physical properties of the metal ions. On the basis of these structures, a new putative catalytic mechanism is proposed for AAP that is likely relevant to all binuclear metalloproteases.
Styrenic Nanocomposites Prepared Using A Novel Biphenyl-Containing Clay, Grace Chigwada, Dongyan Wang, David D. Jiang, Charles A. Wilkie
Styrenic Nanocomposites Prepared Using A Novel Biphenyl-Containing Clay, Grace Chigwada, Dongyan Wang, David D. Jiang, Charles A. Wilkie
Chemistry Faculty Research and Publications
Montmorillonite was organically modified using an ammonium salt containing 4-acetylbiphenyl. This clay (BPNC16 clay) was used to prepare polystyrene (PS), acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS) nanocomposites. Polystyrene nanocomposites were prepared both by in situ bulk polymerisation and melt blending processes, while the ABS and HIPS nanocomposites were prepared only by melt blending. X-ray diffraction and transmission electron microscopy were used to confirm nanocomposite formation. Thermogravimetric analysis was used to evaluate thermal stability and the flammability properties were evaluated using cone calorimetry. By thermogravimetry, BPNC16 clay was found to show high thermal stability, and by cone calorimetry, …
Polyethylene And Polypropylene Nanocomposites Based On A Three Component Oligomerically-Modified Clay, Jinguo Zhang, David D. Jiang, Charles A. Wilkie
Polyethylene And Polypropylene Nanocomposites Based On A Three Component Oligomerically-Modified Clay, Jinguo Zhang, David D. Jiang, Charles A. Wilkie
Chemistry Faculty Research and Publications
Polyethylene and polypropylene nanocomposites were prepared using a novel oligomerically-modified clay that contains three components, styrene, lauryl acrylate and vinylbenzyl chloride. The nanocomposites were prepared by directly melt blending the polymers with the clay and they were characterized by X-ray diffraction and transmission electron microscopy, to understand their morphology, and their thermal stability, flammability and mechanical properties were evaluated using thermogravimetric analysis, cone calorimetry and mechanical testing, respectively. The reduction in peak heat release rate is about 60% at 5% inorganic clay loading and 70% at 8% inorganic clay loading.