Chemistry Commons^™

Preparation, Properties, And Reactivity Of Carbonylrhodium(I) Complexes Of Di(2-Pyrazolylaryl)Amido-Pincer Ligands, Sarath Wanniarachchi, Brendan J. Liddle, Sergey V. Lindeman, James R. Gardinier

Chemistry Faculty Research and Publications

A series of six carbonylrhodium(I) complexes of three new and three previously reported di(2-3R-pyrazolyl)-p-Z/X-aryl)amido pincer ligands, (^RZX)Rh(CO), (R is the substituent at the 3-pyrazolyl position proximal to the metal; Z and X are the aryl substituents para- to the arylamido nitrogen) were prepared. The metal complexes were studied to assess how their properties and reactivities can be tuned by varying the groups along the ligand periphery and how they compared to other known carbonylrhodium(I) pincer derivatives. This study was facilitated by the discovery of a new CuI-catalyzed coupling reaction between 2-(pyrazolyl)-4-X-anilines (X = Me or …

Removal Of 2,4-Dichlorophenoxyacetic Acid By Calcined Zn–Al–Zr Layered Double Hydroxide, Allen Chaparadza, Jeanne Hossenlopp

Chemistry Faculty Research and Publications

The adsorption equilibrium, kinetics, and thermodynamics of removal of 2,4-dichlorophenoxy-acetic acid (2,4-D) from aqueous solutions by a calcined Zn–Al layered double hydroxide incorporated with Zr⁴⁺ were studied with respect to time, temperature, pH, and initial 2,4-D concentration. Zr⁴⁺ incorporation into the LDH was used to enhance 2,4-D uptake by creating higher positive charges and surface/layer modification of the adsorbent. The LDH was capable of removing up to 98% of 2,4-D from 5 to 400 ppm aqueous at adsorbent dosages of 500 and 5000 mg L⁻¹. The adsorption was described by a Langmuir-type isotherm. The percentage 2,4-D …

Analysis Of Binding Site Hot Spots On The Surface Of Ras Gtpase, Greg Buhrman, Casey O'Connor, Brandon Zerbe, Bradley M. Kearney, Raeanne Napoleon, Elizaveta A. Kovrigina, Sandor Vajda, Dima Kozakov, Evgueni Kovriguine, Carla Mattos

Chemistry Faculty Research and Publications

We have recently discovered an allosteric switch in Ras, bringing an additional level of complexity to this GTPase whose mutants are involved in nearly 30% of cancers. Upon activation of the allosteric switch, there is a shift in helix 3/loop 7 associated with a disorder to order transition in the active site. Here, we use a combination of multiple solvent crystal structures and computational solvent mapping (FTMap) to determine binding site hot spots in the “off” and “on” allosteric states of the GTP-bound form of H-Ras. Thirteen sites are revealed, expanding possible target sites for ligand binding well beyond the …

Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Synthetic Studies Directed Toward The Frondosins, Do W. Lee, Rajesh K. Pandey, Sergey Lindeman, William Donaldson

Chemistry Faculty Research and Publications

A short, 4-step route to the scaffold of frondosin A and B is reported. The [1-methoxycarbonyl-5-(2′,5′-dimethoxyphenyl)pentadienyl]Fe(CO)₃⁺ cation was prepared in two steps from (methyl 6-oxo-2,4-hexadienoate)Fe(CO)₃. Reaction of this cation with isopropenyl Grignard or cyclohexenyllithium reagents affords (2-alkenyl-5-aryl-1-methoxycarbonyl-3-pentene-1,5-diyl)Fe(CO)₃ along with other addition products. Oxidative decomplexation of these (pentenediyl)iron complexes, utilizing CuCl₂, affords 6-aryl-3-methoxycarbonyl-1,4-cycloheptadienes via the presumed intermediacy of a cis-divinylcyclopropane.

Complete Determination Of The Pin1 Catalytic Domain Thermodynamic Cycle By Nmr Lineshape Analysis, Alexander I. Greenwood, Monique J. Rogals, Soumya De, Kun Ping Lu, Evgueni Kovriguine, Linda K. Nicholson

Chemistry Faculty Research and Publications

The phosphorylation-specific peptidyl-prolyl isomerase Pin1 catalyzes the isomerization of the peptide bond preceding a proline residue between cis and trans isomers. To best understand the mechanisms of Pin1 regulation, rigorous enzymatic assays of isomerization are required. However, most measures of isomerase activity require significant constraints on substrate sequence and only yield rate constants for the cis isomer, k^cis_catand apparent Michaelis constants, K^App_M . By contrast, NMR lineshape analysis is a powerful tool for determining microscopic rates and populations of each state in a complex binding scheme. The isolated catalytic domain of Pin1 was employed as …

An In Vitro Spectroscopic Analysis To Determine The Chemical Composition Of The Precipitate Formed By Mixing Sodium Hypochlorite And Chlorhexidine, James B. Nowicki, Daniel S. Sem

Chemistry Faculty Research and Publications

Introduction—The purpose of this in vitro study was to determine the chemical composition of the precipitate formed by mixing sodium hypochlorite (NaOCl) and Chlorhexidine (CHX), and relative molecular weight of the components.

Methods—Using commercially available chlorhexidine gluconate (CHXg), a 2% solution was formed and mixed in a 1:1 ratio with commercially available NaOCl producing a brown precipitate. The precipitate as well as a mixture of precipitate and pure chlorhexidine diacetate (CHXa) was then analyzed using 1D and 2D NMR spectroscopy.

Results—The 1D and 2D NMR spectra were fully assigned, in terms of chemical shifts of all proton …

Calcium Carbonate And Ammonium Polyphosphate-Based Flame Retardant Composition For Polypropylene, Sarang Deodhar, Kadhiravan Shanmuganathan, Qinguo Fan, Charles A. Wilkie, Maurius C. Costache, Nicholas A. Dembsey, Prabir K. Patra

Chemistry Faculty Research and Publications

The chemical mode of action as a flame retardant of calcium carbonate nanoparticles combined with ammonium polyphosphate in polypropylene was investigated. Reduction in burning rates for 0.5 mm thick samples were observed without appreciable char formation up to 30 wt % loading of additives. Thermogravimetric analysis (TGA) of the mixture of CaCO₃ and ammonium polyphosphate (APP) showed that calcium carbonate nanoparticles react with ammonium polyphosphate before the degradation of the phosphate chains. TGA–FTIR studies of the polymer composite samples and powder mixtures of the additives confirmed the evolution of ammonia and carbon dioxide due to interaction between the additives. …

Eva-Layered Double Hydroxide (Nano)Composites: Mechanism Of Fire Retardancy, Xiaolan Wang, Rajendra Rathore, Ponusa Songtipya, Maria Del Mar Jimenez-Gasco, Evangelos Manias, Charles A. Wilkie

Chemistry Faculty Research and Publications

Composites of ethylene-vinyl acetate copolymer with two different layered double hydroxides have been obtained by melt blending and these have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, thermogravimetric analysis connected to mass spectroscopy and cone calorimetry. There is some small difference in dispersion between the zinc-containing and the magnesium-containing layered double hydroxides in EVA, but both these are microcomposites with good dispersion at the micrometer level and relatively poor dispersion at the nanometer level. There is a good reduction in the peak heat release rate at 10% LDH loading. In addition to chain stripping, which involves the …

Synthesis Of Hydroxy- And Polyhydroxy-Substituted 1,3-Diaminocyclohexanes, Anobick Sar, Sergey Lindeman, William Donaldson

Chemistry Faculty Research and Publications

The synthesis of hydroxy-trans-1,3-diaminocyclo­hexanes based on nitroso-Diels-Alder cycloaddition of (cyclohexadienyl)phthalimide is reported.

Recent Advances In The Synthetic And Mechanistic Aspects Of The Ruthenium-Catalyzed Carbon-Heteroatom Bond Forming Reactions Of Alkenes And Alkynes, Chae S. Yi

Chemistry Faculty Research and Publications

The group’s recent advances in catalytic carbon-to-heteroatom bond forming reactions of alkenes and alkynes are described. For the C–O bond formation reaction, a well-defined bifunctional ruthenium-amido catalyst has been successfully employed for the conjugate addition of alcohols to acrylic compounds. The ruthenium-hydride complex (PCy₃)₂(CO)RuHCl was found to be a highly effective catalyst for the regioselective alkyne-to-carboxylic acid coupling reaction in yielding synthetically useful enol ester products. Cationic ruthenium-hydride catalyst generated in-situ from (PCy₃)₂(CO)RuHCl/HBF₄·OEt₂ was successfully utilized for both the hydroamination and related C–N bond forming reactions of alkenes. For …

Alteration Of Hydrogen Bonding In The Vicinity Of Histidine 48 Disrupts Millisecond Motions In Rnase A, Nicolet Doucet, Gennady Khirich, Evgueni Kovriguine, J. Patrick Loria

Chemistry Faculty Research and Publications

The motion of amino acid residues on the millisecond (ms) time scale is involved in the tight regulation of catalytic function in numerous enzyme systems. Using a combination of mutational, enzymological, and relaxation-compensated ¹⁵N Carr−Purcell−Meiboom−Gill (CPMG) methods, we have previously established the conformational significance of the distant His48 residue and the neighboring loop 1 in RNase A function. These studies suggested that RNase A relies on an intricate network of hydrogen bonding interactions involved in propagating functionally relevant, long-range ms motions to the catalytic site of the enzyme. To further investigate the dynamic importance of this H-bonding network, this …

Direct Patterning Of A Cyclotriveratrylene Derivative For Directed Self-Assembly Of C60, Zachary R. Osner, Dorjderem Nyamjav, Richard C. Holz, Daniel P. Becker

Chemistry Faculty Research and Publications

A novel apex-modified cyclotriveratrylene (CTV) derivative with an attached thiolane-containing lipoic acid linker was directly patterned onto gold substrates via dip-pen nanolithography (DPN). The addition of a dithiolane-containing linker to the apex of CTV provides a molecule that can adhere to a gold surface with its bowl-shaped cavity directed away from the surface, thereby providing a surface-bound CTV host that can be used for the directed assembly of guest molecules. Subsequent exposure of these CTV microarrays to C₆₀ in toluene resulted in the directed assembly of predesigned, spatially controlled, high-density microarrays of C₆₀. The molecular recognition capabilities …