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Articles 391 - 420 of 690
Full-Text Articles in Chemistry
Comparative Study On The Flammability Of Polyethylene Modified With Commercial Fire Retardants And A Zinc Aluminum Oleate Layered Double Hydroxide, Charles Manzi-Nshuti, Jeanne Hossenlopp, Charles A. Wilkie
Comparative Study On The Flammability Of Polyethylene Modified With Commercial Fire Retardants And A Zinc Aluminum Oleate Layered Double Hydroxide, Charles Manzi-Nshuti, Jeanne Hossenlopp, Charles A. Wilkie
Chemistry Faculty Research and Publications
Polyethylene (PE) was modified by the addition of a layered hydroxide of zinc aluminum oleate (ZnAl) and/or commercial fire retardants. Commercial additives included: melamine polyphosphate (MPP), ammonium polyphosphate (APP), triphenol phosphate (TPP), resorcinol diphosphate (RDP), decabromophenyl oxide (DECA) and antimony oxide (AO). The thermal stability and the combustion behaviors of the new composite polymeric materials are evaluated in TGA experiments and cone calorimetry. At 20% total additive loading, APP and LDH enhance the thermal stability of the PE composites and favor char formation. ZnAl leads to the best reduction in the peak of heat release rate (PHRR), 72%, while the …
Variation Of Anions In Layered Double Hydroxides: Effects On Dispersion And Fire Properties, Linjiang Wang, Shengpei Shu, Dan Chen, Charles A. Wilkie
Variation Of Anions In Layered Double Hydroxides: Effects On Dispersion And Fire Properties, Linjiang Wang, Shengpei Shu, Dan Chen, Charles A. Wilkie
Chemistry Faculty Research and Publications
Layered double hydroxides (LDHs) are interesting materials for nanocomposite formation because one can vary the identity of the metals, the anions and the stoichiometry to see the effect of these on the ability of the nano-material to disperse in a polymer and to see what effect dispersion has on the properties of the polymer. In this study, the anions 2-ethylhexyl sulfate (SEHS), bis(2-ethylhexyl) phosphate (HDEHP) and dodecyl benzenesulfonate (SDBS) have been utilized as the charge balancing anions to synthesize organo-LDHs. Nanocomposites of poly(methyl methacrylate) (PMMA) and polystyrene (PS) with organo-LDHs were prepared both by melt blending and bulk polymerization. X-ray …
Subunit-Selective Interrogation Of Co Recombination In Carbonmonoxy Hemoglobin By Isotope-Edited Time-Resolved Resonance Raman Spectroscopy, Gurusamy Balakrishnan, Xiaojie Zhao, Edyta Podstawska, Leonard M. Proniewicz, James R. Kincaid, Thomas G. Spiro
Subunit-Selective Interrogation Of Co Recombination In Carbonmonoxy Hemoglobin By Isotope-Edited Time-Resolved Resonance Raman Spectroscopy, Gurusamy Balakrishnan, Xiaojie Zhao, Edyta Podstawska, Leonard M. Proniewicz, James R. Kincaid, Thomas G. Spiro
Chemistry Faculty Research and Publications
Hemoglobin (Hb) is an allosteric tetrameric protein made up of αβ heterodimers. The α and β chains are similar, but are chemically and structurally distinct. To investigate dynamical differences between the chains, we have prepared tetramers in which the chains are isotopically distinguishable, via reconstitution with 15N-heme. Ligand recombination and heme structural evolution, following HbCO dissociation, was monitored with chain selectivity by resonance Raman (RR) spectroscopy. For α but not for β chains, the frequency of the ν4 porphyrin breathing mode increased on the microsecond time scale. This increase is a manifestation of proximal tension in the Hb …
Material Properties Of Nanoclay Pvc Composites, Walid Awad, Gunter Beyer, Daphne Benderly, Wouter L. Ijdo, Ponusa Songtipya, Maria Del Mar Jimenez-Gasco, Evangelos Manias, Charles A. Wilkie
Material Properties Of Nanoclay Pvc Composites, Walid Awad, Gunter Beyer, Daphne Benderly, Wouter L. Ijdo, Ponusa Songtipya, Maria Del Mar Jimenez-Gasco, Evangelos Manias, Charles A. Wilkie
Chemistry Faculty Research and Publications
Nanocomposites of poly(vinyl chloride) have been prepared using both hectorite- and bentonite-based organically-modified clays. The organic modification used is tallow-triethanol-ammonium ion. The morphology of the systems was investigated using X-ray diffraction and transmission electron microscopy and these systems show that true nanocomposites, both intercalated and exfoliated systems, are produced. The mechanical properties have been evaluated and the modulus increases upon nanocomposite formation without a significant decrease in tensile strength or elongation at break. Thermal analysis studies using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were conducted. Thermal stability of the PVC systems was assessed using a standard thermal …
Aqueous Phase C-H Bond Oxidation Reaction Of Arylalkanes Catalyzed By A Water-Soluble Cationic Ru(Iii) Complex [(Pymox-Me2)2Rucl2]+Bf4-, Chae S. Yi, Ki Hyeok Kwon, Do W. Lee
Aqueous Phase C-H Bond Oxidation Reaction Of Arylalkanes Catalyzed By A Water-Soluble Cationic Ru(Iii) Complex [(Pymox-Me2)2Rucl2]+Bf4-, Chae S. Yi, Ki Hyeok Kwon, Do W. Lee
Chemistry Faculty Research and Publications
The cationic complex [(pymox-Me2)RuCl2]+BF4− was found to be a highly effective catalyst for the C−H bond oxidation reaction of arylalkanes in water. For example, the treatment of ethylbenzene (1.0 mmol) with t-BuOOH (3.0 mmol) and 1.0 mol % of the Ru catalyst in water (3 mL) cleanly produced PhCOCH3 at room temperature. Both a large kinetic isotope effect (kH/kD = 14) and a relatively large Hammett value (ρ = −1.1) suggest a solvent-caged oxygen rebounding mechanism via a Ru(IV)-oxo intermediate species.
Variation Of Benzyl Anions In Mgal-Layered Double Hydroxides: Fire And Thermal Properties In Pmma, Calistor Nyambo, Dan Chen, Shengpei Shu, Charles A. Wilkie
Variation Of Benzyl Anions In Mgal-Layered Double Hydroxides: Fire And Thermal Properties In Pmma, Calistor Nyambo, Dan Chen, Shengpei Shu, Charles A. Wilkie
Chemistry Faculty Research and Publications
Magnesium aluminum layered double hydroxides (MgAl-LDHs) intercalated with a range of benzyl anions were prepared using the coprecipitation method. The benzyl anions differ in functionality (i.e. carboxylate, sulfonate, and phosphonate) and presence or absence of an amino substituent. Various methods for preparing LDHs (i.e. ion exchange, coprecipitation and rehydration of the calcined LDH methods) have been compared with the MgAl-benzene phosphonate and their effect on fire and thermal properties was studied. After characterization, the MgAl-LDHs were melt-blended with poly(methyl methacrylate) (PMMA) at loadings of 3 and 10% by weight to prepare composites. Characterization of the LDHs and the PMMA composites …
Layered Double Hydroxides Intercalated With Borate Anions: Fire And Thermal Properties In Ethylene Vinyl Acetate Copolymer, Calistor Nyambo, Charles A. Wilkie
Layered Double Hydroxides Intercalated With Borate Anions: Fire And Thermal Properties In Ethylene Vinyl Acetate Copolymer, Calistor Nyambo, Charles A. Wilkie
Chemistry Faculty Research and Publications
Fire and thermal properties of ethylene vinyl acetate (EVA) composites prepared by melt blending with layered double hydroxides (LDH) have been studied. Two types of LDHs intercalated with borate anion were prepared using the coprecipitation method and the metals Mg2+, Zn2+ and Al3+. Characterization of the LDHs and the EVA composites was performed using X-ray diffraction, thermogravimetric analysis, and cone calorimetry. Thermal analyses show that the addition of LDHs improves the thermal stability of EVA. Fire properties evaluated using the cone calorimeter were significantly improved in the EVA/LDH composites. The peak heat release rate was …
The Role Of The Trivalent Metal In An Ldh: Synthesis, Characterization And Fire Properties Of Thermally Stable Pmma/Ldh Systems, Charles Manzi-Nshuti, Dongyan Wang, Jeanne Hossenlopp, Charles A. Wilkie
The Role Of The Trivalent Metal In An Ldh: Synthesis, Characterization And Fire Properties Of Thermally Stable Pmma/Ldh Systems, Charles Manzi-Nshuti, Dongyan Wang, Jeanne Hossenlopp, Charles A. Wilkie
Chemistry Faculty Research and Publications
Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca3Al) and calcium iron undecenoate (Ca3Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.
Thermal Stability And Flammability Characteristics Of Ethylene Vinyl Acetate (Eva) Composites Blended With A Phenyl Phosphonate-Intercalated Layered Double Hydroxide (Ldh), Melamine Polyphosphate And/Or Boric Acid, Calistor Nyambo, Everson Kandare, Charles A. Wilkie
Thermal Stability And Flammability Characteristics Of Ethylene Vinyl Acetate (Eva) Composites Blended With A Phenyl Phosphonate-Intercalated Layered Double Hydroxide (Ldh), Melamine Polyphosphate And/Or Boric Acid, Calistor Nyambo, Everson Kandare, Charles A. Wilkie
Chemistry Faculty Research and Publications
A phenyl phosphonate-intercalated MgAl–LDH (MgAl–PPh), melamine polyphosphate (MP), and boric acid (BA) were independently and concomitantly added to neat ethylene vinyl acetate (EVA) copolymer at loading fractions of 10% (w/w). The structural morphology of MgAl–PPh was established via powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) while the presence of phenyl phosphonate in the galleries was confirmed by Fourier transform infrared (FTIR). Thermogravimetric analysis (TGA) and cone calorimetry were used to evaluate the thermal stability and flammability behavior of EVA and its composites. While time-to-ignition is greatly reduced for EVA composites compared to the virgin polymer, there are remarkable …
Synthetic Studies Directed Toward Guianolides: An Organoiron Route To The 5,7,5 Tricyclic Ring System, Jayapal Reddy Gone, Nathaniel J Wallock, Sergey V. Lindeman, William A. Donaldson
Synthetic Studies Directed Toward Guianolides: An Organoiron Route To The 5,7,5 Tricyclic Ring System, Jayapal Reddy Gone, Nathaniel J Wallock, Sergey V. Lindeman, William A. Donaldson
Chemistry Faculty Research and Publications
A diastereoselective route to the 5,7,5-tricyclic core of the guianolides is presented. This route relies on Cope rearrangement of a divinylcyclopropane prepared by alkenyl Grignard addition to a (pentadienyl)iron(+1) cation, followed by oxidative decomplexation. An additional key reaction involves oxidative rearrangement of a 3,4-epoxy-1,7-diol to generate a γ-lactone. The relative stereochemistry of this product was established by X-ray crystallography.
Supramolecular Complexation Of N-Alkyl- And N,N′-Dialkylpiperazines With Cucurbit[6]Uril In Aqueous Solution And In The Solid State, Mikhail V. Rekharsky, Hatsuo Yamamura, Tadashi Mori, Akihiro Sato, Motoo Shiro, Sergey V. Lindeman, Rajendra Rathore, Kouhei Shiba, Young Ho Ko, Narayanan Selvapalam, Kimoon Kim, Yoshihisa Inoue
Supramolecular Complexation Of N-Alkyl- And N,N′-Dialkylpiperazines With Cucurbit[6]Uril In Aqueous Solution And In The Solid State, Mikhail V. Rekharsky, Hatsuo Yamamura, Tadashi Mori, Akihiro Sato, Motoo Shiro, Sergey V. Lindeman, Rajendra Rathore, Kouhei Shiba, Young Ho Ko, Narayanan Selvapalam, Kimoon Kim, Yoshihisa Inoue
Chemistry Faculty Research and Publications
Water seeds: Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. It was found that the complex stability and the degree of oligomerization increase with elongating the alkyl chain attached …
A Versatile Synthesis Of Electroactive Stilbenoprismands For Effective Binding Of Metal Cations, Sergey V. Lindeman, Rajendra Rathore, Paromita Debroy
A Versatile Synthesis Of Electroactive Stilbenoprismands For Effective Binding Of Metal Cations, Sergey V. Lindeman, Rajendra Rathore, Paromita Debroy
Chemistry Faculty Research and Publications
A versatile synthesis of a new class of polyaromatic receptors (stilbenoprismands) containing a Δ-shaped cavity similar to that of the π-prismand together with an intimately coupled electroactive stilbenoid moiety was accomplished via an efficient intramolecular McMurry coupling reaction. The presence of the Δ-shaped cavity in stilbenoprismands allows an efficient binding of a single silver cation as probed by 1H NMR spectroscopy. Electron-rich stilbenoprismands undergo a ready oxidation to their highly robust cation−radical and dicationic salts. X-ray structure determination of a representative dicationic stilbenoprismand showed that the charges were largely localized on the tetraarylethylene moiety, which results in a twisting …
Substrate Induced Structural And Dynamics Changes In Human Phosphomevalonate Iinase And Implications For Mechanism, Andrew Lawrence Olson, Huili Yao, Timothy J. Herdendorf, Henry M. Miziorko, Supa Hannongbua, Patchareenat Saparpakom, Sheng Cai, Daniel S. Sem
Substrate Induced Structural And Dynamics Changes In Human Phosphomevalonate Iinase And Implications For Mechanism, Andrew Lawrence Olson, Huili Yao, Timothy J. Herdendorf, Henry M. Miziorko, Supa Hannongbua, Patchareenat Saparpakom, Sheng Cai, Daniel S. Sem
Chemistry Faculty Research and Publications
Phosphomevalonate kinase (PMK) catalyzes an essential step in the mevalonate pathway, which is the only pathway for synthesis of isoprenoids and steroids in humans. PMK catalyzes transfer of the γ-phosphate of ATP to mevalonate 5-phosphate (M5P) to form mevalonate 5-diphosphate. Bringing these phosphate groups in proximity to react is especially challenging, given the high negative charge density on the four phosphate groups in the active site. As such, conformational and dynamics changes needed to form the Michaelis complex are of mechanistic interest. Herein, we report the characterization of substrate induced changes (Mg-ADP, M5P, and the ternary complex) in PMK using …
Mutation Of H63 And Its Catalytic Affect On The Methionine Aminopeptidase From Escherichia Coli, Sanghamitra Mitra, Brian Bennett, Richard C. Holz
Mutation Of H63 And Its Catalytic Affect On The Methionine Aminopeptidase From Escherichia Coli, Sanghamitra Mitra, Brian Bennett, Richard C. Holz
Chemistry Faculty Research and Publications
In order to gain insight into the mechanistic role of a flexible exterior loop near the active site, made up of Y62, H63, G64, and Y65, that has been proposed to play an important role in substrate binding and recognition in the methionyl aminopeptidase from Escherichia coli (EcMetAP-I), the H63A enzyme was prepared. Mutation of H63 to alanine does not affect the ability of the enzyme to bind divalent metal ions. The specific activity of H63A EcMetAP-I was determined using four different substrates of varying lengths, namely, l-Met-p-NA, MAS, MGMM and MSSHRWDW. For the smallest/shortest …
Molecular Motion And Performance Enhancement Of Borazan Fluorescent Dyes, Tyler James Morin, Sergey V. Lindeman, James R. Gardinier
Molecular Motion And Performance Enhancement Of Borazan Fluorescent Dyes, Tyler James Morin, Sergey V. Lindeman, James R. Gardinier
Chemistry Faculty Research and Publications
The preparation of three 2,6-dipyrazolyl-4-X-anilines, H(pz2AnX) (X = p-CF3, Cl, tBu) using CuI-catalyzed amination is described. Subsequent reactions of H(pz2AnX) with triphenylboron proceeds with benzene elimination to give the corresponding Ph2B(pz2AnX) compounds in high yields. The Ph2B(pz2AnX) are more highly emissive in the solid state than the previously reported BORAZAN fluorophores, Ph2B(pzAnX), their monopyrazolyl counterparts. As with the Ph2B(pzAnX), the color of emission in Ph2B(pz2 …
Carbon−Phosphorus Bond Activation Of Tri(2-Thienyl)Phosphine At Dirhenium And Dimanganese Centers, Md. Nazim Uddin, M. Abdul Mottalib, Noorjahan Begum, Shishir Ghosh, Arun K. Raha, Daniel T. Haworth, Sergey V. Lindeman, Tasneem Siddiquee, Dennis W. Bennett, Graeme Hogarth, Ebbe Nordlander, Shariff E. Kabir
Carbon−Phosphorus Bond Activation Of Tri(2-Thienyl)Phosphine At Dirhenium And Dimanganese Centers, Md. Nazim Uddin, M. Abdul Mottalib, Noorjahan Begum, Shishir Ghosh, Arun K. Raha, Daniel T. Haworth, Sergey V. Lindeman, Tasneem Siddiquee, Dennis W. Bennett, Graeme Hogarth, Ebbe Nordlander, Shariff E. Kabir
Chemistry Faculty Research and Publications
Reaction of [Re2(CO)9(NCMe)] with tri(2-thienyl)phosphine (PTh3) in refluxing cyclohexane affords three substituted dirhenium complexes: [Re2(CO)9(PTh3)] (1), [Re2(CO)8(NCMe)(PTh3)] (2), and [Re2(CO)8(PTh3)2] (3). Complex 2 was also obtained from the room-temperature reaction of [Re2(CO)8(NCMe)2] with PTh3 and is an unusual example in which the acetonitrile and phosphine ligands are coordinated to the same rhenium atom. Thermolysis of 1 and 3 in refluxing xylene …
Octamethoxydibenzochrysene: Isolation And X-Ray Crystallographic Characterization Of A Twisted Polyaromatic Cation Radical, Tushar Navale, Linyi Zhai, Sergey V. Lindeman, Rajendra Rathore
Octamethoxydibenzochrysene: Isolation And X-Ray Crystallographic Characterization Of A Twisted Polyaromatic Cation Radical, Tushar Navale, Linyi Zhai, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
The isolation and X-ray crystal structure determination of octamethoxydibenzochrysene (3) cation radical together with DFT calculations allow us to delineate evidence that the complex structural changes (i.e. elongation and shortening of various bonds) in a polyaromatic hydrocarbon can be predicted based on the positioning of the largest bonding and antibonding character of the HOMO.
Terphenyl Crowns: A New Family Of Receptors Containing Ethereal Canopies That Direct Potassium Cation Onto Benzenoid Platforms For Cation–Π Interactions, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Terphenyl Crowns: A New Family Of Receptors Containing Ethereal Canopies That Direct Potassium Cation Onto Benzenoid Platforms For Cation–Π Interactions, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
We have synthesized three simple and versatile terphenyl crowns (TC) receptors containing ethereal canopies that direct a potassium cation for efficient cation–π interactions as established by 1H NMR spectroscopy and by isolation and X-ray crystallography of their K+ salts.
13c-Methyl Isocyanide As An Nmr Probe For Cytochrome P450 Active Site, Christopher R Mccullough, Phani Kumar Pullela, Sang-Choul Im, Lucy Waskell, Daniel S. Sem
13c-Methyl Isocyanide As An Nmr Probe For Cytochrome P450 Active Site, Christopher R Mccullough, Phani Kumar Pullela, Sang-Choul Im, Lucy Waskell, Daniel S. Sem
Chemistry Faculty Research and Publications
The cytochromes P450 (CYPs) play a central role in many biologically important oxidation reactions, including the metabolism of drugs and other xenobiotic compounds. Because they are often assayed as both drug targets and anti-targets, any tools that provide: (a) confirmation of active site binding and (b) structural data, would be of great utility, especially if data could be obtained in reasonably high throughput. To this end, we have developed an analog of the promiscuous heme ligand, cyanide,with a 13CH3-reporter attached. This 13C-methyl isocyanide ligand binds to bacterial (P450cam) and membrane-bound mammalian (CYP2B4) CYPs. It can be …
A Versatile Preparation Of Geländer-Type P-Terphenyls From A Readily Available Diacetylenic Precursor, Matthew J. Modjewski, Sergey V. Lindeman, Rajendra Rathore
A Versatile Preparation Of Geländer-Type P-Terphenyls From A Readily Available Diacetylenic Precursor, Matthew J. Modjewski, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
A series of doubly bridged p-terphenyls (4) have been synthesized utilizing a facile three-step synthesis starting from the readily available diacetylenic precursor (1) in excellent overall yields, and their structures were confirmed by 1H/13C NMR spectroscopy as well as by X-ray crystallography. The racemization barrier between the meso and chiral atropisomers of one of the derivatives of 4 was found to be ∼12 kcal/mol by variable-temperature NMR spectroscopy. The versatility of the protocol developed herein was further demonstrated by the preparation of a quadruply bridged penta-p-phenylene derivative.
Tetranuclear Group 7/8 Mixed-Metal And Open Trinuclear Group 7 Metal Carbonyl Clusters Bearing Bridging 2-Mercapto-1-Methylimidazole Ligands, Shishir Ghosh, Shariff E. Kabir, Salina Pervin, Arun K. Raha, G. M. Golzar Hossain, Daniel T. Haworth, Sergey V. Lindeman, Dennis W. Bennett, Tasneem Siddiquee, Luca Salassa, Herbert W. Roesky
Tetranuclear Group 7/8 Mixed-Metal And Open Trinuclear Group 7 Metal Carbonyl Clusters Bearing Bridging 2-Mercapto-1-Methylimidazole Ligands, Shishir Ghosh, Shariff E. Kabir, Salina Pervin, Arun K. Raha, G. M. Golzar Hossain, Daniel T. Haworth, Sergey V. Lindeman, Dennis W. Bennett, Tasneem Siddiquee, Luca Salassa, Herbert W. Roesky
Chemistry Faculty Research and Publications
The reactivity of group 7 metal dinuclear carbonyl complexes [M2(CO)6(μ-SN2C4H5)2] (1, M = Re; 2, M = Mn) toward group 8 metal trinuclear carbonyl clusters were examined. Reactions of 1 and 2 with [Os3(CO)10(NCMe)2] in refluxing benzene furnished the tetranuclear mixed-metal clusters [Os3Re(CO)13(μ3-SN2C4H5)] (3) and [Os3Mn(CO)13(μ3-SN2C4H5)] (4), respectively. Similar treatment of …
Molecular Actuator: Redox-Controlled Clam-Like Motion In A Bichromophoric Electron Donor, Vincent J. Chebny, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Molecular Actuator: Redox-Controlled Clam-Like Motion In A Bichromophoric Electron Donor, Vincent J. Chebny, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore
Chemistry Faculty Research and Publications
The one-electron oxidation of tetramethoxydibenzobicyclo[4.4.1]undecane (4) prompts it to undergo a clam-like electromechanical actuation into a cofacially π-stacked conformer as established by (i) electrochemical analysis, (ii) by the observation of the intense charge-resonance transition in the near IR region in its cation radical spectrum, and (iii) by X-ray crystallographic characterization of the isolated cation radical salt (4+• SbCl6−).
Efficient Dehydrogenation Of Amines And Carbonyl Compounds Catalyzed By A Tetranuclear Ruthenium-Μ-Oxo-Μ-Hydroxo-Hydride Complex, Chae S. Yi, Do W. Lee
Efficient Dehydrogenation Of Amines And Carbonyl Compounds Catalyzed By A Tetranuclear Ruthenium-Μ-Oxo-Μ-Hydroxo-Hydride Complex, Chae S. Yi, Do W. Lee
Chemistry Faculty Research and Publications
The tetranuclear ruthenium-μ-oxo-μ-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was found to be a highly effective catalyst for the transfer dehydrogenation of amines and carbonyl compounds. For example, the initial turnover rate of the dehydrogenation of 2-methylindoline was measured to be 1.9 s−1 with a TON of 7950 after 1 h at 200 °C. The extensive H/D scrambling patterns observed from the dehydrogenation reaction of indoline-N-d1 and indoline-α-d2 suggest a monohydride mechanistic pathway with the C−H bond activation rate-limiting step.
Resonance Raman Characterization Of The Peroxo And Hydroperoxo Intermediates In Cytochrome P450, Ilia G. Denisov, Piotr J. Mak, Thomas M. Makris, Stephen G. Sligar, James R. Kincaid
Resonance Raman Characterization Of The Peroxo And Hydroperoxo Intermediates In Cytochrome P450, Ilia G. Denisov, Piotr J. Mak, Thomas M. Makris, Stephen G. Sligar, James R. Kincaid
Chemistry Faculty Research and Publications
Resonance Raman (RR) studies of intermediates generated by cryoreduction of the oxyferrous complex of the D251N mutant of cytochrome P450cam (CYP101) are reported. Owing to the fact that proton delivery to the active site is hindered in this mutant, the unprotonated peroxo-ferric intermediate is observed as the primary species after radiolytic reduction of the oxy-complex in frozen solutions at 77 K. In as much as previous EPR and ENDOR studies have shown that annealing of this species to ∼180 K results in protonation of the distal oxygen atom to form the hydroperoxo intermediate, this system has been exploited to …
Resonance Raman Interrogation Of The Consequences Of Heme Rotational Disorder In Myoglobin And Its Ligated Derivatives, Freeborn Rwere, Piotr J. Mak, James R. Kincaid
Resonance Raman Interrogation Of The Consequences Of Heme Rotational Disorder In Myoglobin And Its Ligated Derivatives, Freeborn Rwere, Piotr J. Mak, James R. Kincaid
Chemistry Faculty Research and Publications
Resonance Raman spectroscopy is employed to characterize heme site structural changes arising from conformational heterogeneity in deoxyMb and ligated derivatives, i.e., the ferrous CO (MbCO) and ferric cyanide (MbCN) complexes. The spectra for the reversed forms of these derivatives have been extracted from the spectra of reconstituted samples. Dramatic changes in the low-frequency spectra are observed, where newly observed RR modes of the reversed forms are assigned using protohemes that are selectively deuterated at the four methyl groups or at the four methine carbons. Interestingly, while substantial changes in the disposition of the peripheral vinyl and propionate groups can be …
Analyzing The Catalytic Mechanism Of The Fe-Type Nitrile Hydratase From Comamonas Testosteroni Ni1, Saroja Rao, Richard C. Holz
Analyzing The Catalytic Mechanism Of The Fe-Type Nitrile Hydratase From Comamonas Testosteroni Ni1, Saroja Rao, Richard C. Holz
Chemistry Faculty Research and Publications
In order to gain insight into the catalytic mechanism of Fe-type nitrile hydratases (NHase), the pH and temperature dependence of the kinetic parameters kcat, Km, and kcat/Km along with the solvent isotope effect were examined for the Fe-type NHase from Comamonas testosteroni Ni1 (CtNHase). CtNHase was found to exhibit a bell-shaped curve for plots of relative activity vs pH over pH values 4−10 for the hydration of acrylonitrile and was found to display maximal activity at pH ∼7.2. Fits of these data provided a pKES1 value of …
Defining Resonance Raman Spectral Responses To Substrate Binding By Cytochrome P450 From Pseudomonas Putida, Piotr J. Mak, Daniel Kaluka, Munyaradzi Edith Manyumwa, Haiqing Zhang, Tianjing Deng, James R. Kincaid
Defining Resonance Raman Spectral Responses To Substrate Binding By Cytochrome P450 From Pseudomonas Putida, Piotr J. Mak, Daniel Kaluka, Munyaradzi Edith Manyumwa, Haiqing Zhang, Tianjing Deng, James R. Kincaid
Chemistry Faculty Research and Publications
Resonance Raman spectra are reported for substrate-free and camphor-bound cytochrome P450cam and its isotopically labeled analogues that have been reconstituted with protoheme derivatives that bear -CD3 groups at the 1, 3, 5, and 8-positions (d12-protoheme) or deuterated methine carbons (d4-protoheme). In agreement with previous studies of this and similar enzymes, substrate binding induces changes in the high frequency and low frequency spectral regions, with the most dramatic effect in the low frequency region being activation of a new mode near 367 cm−1. This substrate-activated mode had been previously assigned as a second “propionate bending” mode (Chen et …
Synthetic Studies Directed Toward Amphidinol 2: Elucidation Of The Relative Configuration Of The C1–C10 Fragment, Praveen Kommana, Seung Won Chung, William A. Donaldson
Synthetic Studies Directed Toward Amphidinol 2: Elucidation Of The Relative Configuration Of The C1–C10 Fragment, Praveen Kommana, Seung Won Chung, William A. Donaldson
Chemistry Faculty Research and Publications
Model compounds (11 and 12) for the C1–C10 tetrahydropyran fragment of amphidinol 2 were prepared from (2S)-benzyloxypropanal in 9 steps. The synthetic route relied on diastereoselective diene-aldehyde cycloaddition, stereoselective C-allylation, and reagent based enantioselective aldehyde allylation. Comparison of the NMR spectra for models 11 and 12 with that for amphidinol 2 indicated that the C1–C10 segment of the natural product possesses the 2R*,4R*,6R*,7S*,8R*,10S* relative configuration.
Fire Retardancy Of Melamine And Zinc Aluminum Layered Double Hydroxide In Poly(Methyl Methacrylate), Charles Manzi-Nshuti, Jeanne Hossenlopp, Charles Wilkie
Fire Retardancy Of Melamine And Zinc Aluminum Layered Double Hydroxide In Poly(Methyl Methacrylate), Charles Manzi-Nshuti, Jeanne Hossenlopp, Charles Wilkie
Chemistry Faculty Research and Publications
The thermal and fire properties of PMMA modified with various loadings of melamine or zinc aluminum undecenoate LDH were evaluated using TGA, DTA and cone calorimetry. The additives were characterized by X-ray diffraction, TGA, FT-IR and elemental analysis. While the two additives are very effective with this polymer, a higher loading of melamine (30%) is required to reach a good reduction in PHRR (47%) relative to the pure polymer, while with the LDH, 10% loading is enough to obtain a similar reduction. The combinations of these additives in PMMA reveal that the time to PHRR and the amount of smoke …
Resonance Raman Spectroscopic Studies Of Hydroperoxo Derivatives Of Cobalt-Substituted Myoglobin, Piotr J. Mak, James R. Kincaid
Resonance Raman Spectroscopic Studies Of Hydroperoxo Derivatives Of Cobalt-Substituted Myoglobin, Piotr J. Mak, James R. Kincaid
Chemistry Faculty Research and Publications
Recent progress in generating and stabilizing reactive heme protein enzymatic intermediates by cryoradiolytic reduction has prompted application of a range of spectroscopic approaches to effectively interrogate these species. The impressive potential of resonance Raman spectroscopy for characterizing such samples has been recently demonstrated in a number of studies of peroxo- and hydroperoxo-intermediates. While it is anticipated that this approach can be productively applied to the wide range of heme proteins whose reaction cycles naturally involve these peroxo- and hydroperoxo-intermediates, one limitation that sometimes arises is the lack of enhancement of the key intraligand ν(O–O) stretching mode in the native …