Chemistry Commons^™

Hydroxy Double Salt Anion Exchange Kinetics: Effects Of Precursor Structure And Anion Size, Everson Kandare, Jeanne Hossenlopp

Chemistry Faculty Research and Publications

H NMR spectroscopy and powder X-ray diffraction have been used to explore the details of anion exchange reactions of two layered hydroxy double salts (HDSs), zinc copper hydroxy acetate (ZCA), nickel zinc hydroxy acetate (NZA), and a related layered material, zinc hydroxy acetate (ZHA), at room temperature (21−22 °C). Reactions that followed Avrami−Erofe'ev kinetics with respect to temporal profiles for acetate release, ZCA with butyrate (k = 1.7 × 10^-3 s^-1), and octanoate (k = 0.79 × 10^-3 s^-1) anions, as well as ZHA with octanoate (k = 2.6 × 10 …

Isolation, X-Ray Structures, And Electronic Spectra Of Reactive Intermediates In Friedel−Crafts Acylations, M. G. Davlieva, Sergey V. Lindeman, I. S. Neretin, Jay K. Kochi

Chemistry Faculty Research and Publications

Reactive intermediates in the Friedel−Crafts acylation of aromatic donors are scrutinized upon their successful isolation and X-ray crystallography at very low temperatures. Detailed analyses of the X-ray parameters for the [1:1] complexes of different aliphatic and aromatic-acid chlorides with the Lewis acids antimony pentafluoride and pentachloride, gallium trichloride, titanium and zirconium tetrachlorides provide unexpected insight into the activation mechanism for the formation of the critical acylium carbocations. Likewise, the X-ray-structure examinations of aliphatic and aromatic acylium electrophiles also isolated as crystalline salts point to the origins of their electrophilic reactivity. Although the Wheland intermediates (as acylium adducts to arene donors) …

The Relationship Between The Solubility Parameter Of Polymers And The Clay-Dispersion In Polymer/Clay Nanocomposites And The Role Of The Surfactant, Bok Nam Jang, Dongyan Wang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites were prepared of polymers having different solubility parameters and pristine or organically modified clays, and the dispersion of clay in the polymer was evaluated using X-ray diffraction and transmission electron microscopy. The solubility parameters of both the polymers and surfactants of interest were calculated according to the group contribution method and correlated with the clay morphology. A close relationship between the solubility parameter of the polymer and the clay morphology was observed. The clay has a very polar group, so the higher is the solubility parameter of the polymer, the larger is the d spacing of the clay that …

Scope And Mechanistic Study Of The Ruthenium-Catalyzed Ortho-C−H Bond Activation And Cyclization Reactions Of Arylamines With Terminal Alkynes, Chae S. Yi, Young Yun

Chemistry Faculty Research and Publications

The cationic ruthenium hydride complex [(PCy₃)₂(CO)(CH₃CN)₂RuH]⁺BF₄^- was found to be a highly effective catalyst for the C−H bond activation reaction of arylamines and terminal alkynes. The regioselective catalytic synthesis of substituted quinoline and quinoxaline derivatives was achieved from the ortho-C−H bond activation reaction of arylamines and terminal alkynes by using the catalyst Ru₃(CO)₁₂/HBF₄·OEt₂. The normal isotope effect (k_CH/k_CD = 2.5) was observed for the reaction of C₆H₅NH₂ and C …

Isolation And X-Ray Structures Of Labile Benzoic- And Acetic-Acidium Carbocations, Sergey V. Lindeman, I. S. Neretin, M. G. Davlieva, Jay K. Kochi

Chemistry Faculty Research and Publications

New carbocationic salts (via O-protonation of substituted benzoic acids) are prepared for the first time by controlled hydration of the corresponding benzoylium salts and isolated in pure crystalline form. Precise X-ray structural analyses reveal the rather unexpected (electronic) structure of the carboxylic-acidium functionality.

The Thermal Degradation Of Bisphenol A Polycarbonate In Air, Bok Nam Jang, Charles A. Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of polycarbonate in air was studied as a function of mass loss using TGA/FTIR, GC/MS and LC/MS. In the main degradation region, 480–560 °C, the assigned structures of smaller molecules and linear molecules that evolved in air were very similar to those obtained from the degradation in nitrogen; the degradation of polycarbonate follows chain scission of the isopropylidene linkage, in agreement with the bond dissociation energies, and hydrolysis/alcoholysis of carbonate linkage. Compared to the degradation in nitrogen, some differences were observed primarily in the beginning stage of degradation. Oxygen may facilitate branching as well as radical formation …

Polyethylene And Polypropylene Nanocomposites Based Upon An Oligomerically-Modified Clay, Jinguo Zhang, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Montmorillonite clay was modified with an oligomeric surfactant, which was then melt blended with polyethylene and polypropylene in a Brabender mixer. The morphology was characterized by X-ray diffraction and transmission electron microscopy, while thermal stability was evaluated from thermogravimetric analysis and the fire properties by cone calorimetry. The nanocomposites are best described as mixed immiscible/intercalated/delaminated systems and the reduction in peak heat release rate is about 40% at 5% inorganic clay loading.

The Effects Of Triphenylphosphate And Recorcinolbis(Diphenylphosphate) On The Thermal Degradation Of Polycarbonate In Air, Bok Nam Jang, Charles A. Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of polycarbonate/triphenylphosphate (PC/TPP) and PC/resocinolbis(diphenylphosphate) (PC/RDP) in air has been studied using TGA/FTIR and GC/MS. In PC/phosphate blends, the phosphate stabilizes the carbonate group of polycarbonate from alcoholysis between the alcohol products of polycarbonate degradation and the carbonate linkage. Thus, the evolution of bisphenol A, which is mainly produced via hydrolysis/alcoholysis of the carbonate linkage, is significantly reduced, while, the evolution of various alkylphenols and diarylcarbonates increases. The bonds that are broken first in the thermal degradation of both the carbonate and isopropylidene linkages of polycarbonate are the weakest bonds in each, when a phosphate is present. …

Polystyrene Nanocomposites Based On Carbazole-Containing Surfactants, Grace Chigwada, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

New organically-modified clays containing a carbazole unit were prepared and the number of long alkyl chains on the surfactant was varied. The clay was used to prepare polystyrene nanocomposites by both bulk polymerization and melt blending. The dispersion of these clays in the polymer matrix was evaluated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability of the clays and the nanocomposites were analyzed by thermogravimetric analysis (TGA) while the fire properties were evaluated by cone calorimetry. If more than two alkyl chains were present, the gallery spacing is apparently overcrowded, leading to poor dispersion. Bulk polymerization …

Synthesis Of Cyclopropanes Via Organoiron Methodology: Preparation Of The C9–C16 Alkenylcyclopropane Segment Of Ambruticin, Julie Lukesh, William A. Donaldson

Chemistry Faculty Research and Publications

A synthesis of the C9–C16 segment of ambruticin is described which relies on organoiron methodology to establish the 1,2,3-trisubstituted cyclopropane ring.

Methyl Methacrylate Oligomerically-Modified Clay And Its Poly (Methyl Methacrylate) Nanocomposites, Xiaoxia Zheng, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

A methyl methacrylate oligomerically-modified clay was used to prepare poly(methyl methacrylate) clay nanocomposites by melt blending and the effect of the clay loading level on the modified clay and corresponding nanocomposite was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed intercalated/delaminated morphology with good nanodispersion. The compatibility between the methylacrylate-subsituted clay and poly(methyl methacrylate) (PMMA) are greatly improved compared to other oligomerically-modified clays.

Cofactor Fingerprinting With Std Nmr To Characterize Proteins Of Unknown Function: Identification Of A Rare Ccmp Cofactor Preference, Huili Yao, Daniel Sem

Chemistry Faculty Research and Publications

Proteomics efforts have created a need for better strategies to functionally categorize newly discovered proteins. To this end, we have employed saturation transfer difference NMR with pools of closely related cofactors, to determine cofactor preferences. This approach works well for dehydrogenases and has also been applied to cyclic nucleotide‐binding proteins. In the latter application, a protein (radial spoke protein‐2, RSP2) that plays a central role in forming the radial spoke of Chlamydomonas reinhardtii flagella was shown to bind cCMP. cCMP‐binding proteins are rare, although previous reports of their presence in sperm and flagella suggest that cCMP may have a more …

A Tga/Ftir And Mass Spectral Study On The Thermal Degradation Of Bisphenol A Polycarbonate, Bok Nam Jang, Charles A. Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of polycarbonate under nitrogen was studied using TGA/FTIR, GC/MS and LC/MS as a function of mass loss. The gases evolved during degradation were inspected by in situ FTIR and then the evolved products were collected and analysed using FTIR, GC–MS and LC–MS. The structures of the evolved products are assigned on the basis of FTIR and GC/MS results. The main thermal degradation pathways follow chain scission of the isopropylidene linkage, and hydrolysis/alcoholysis and rearrangement of carbonate linkages. In the case of chain scission, it was proposed that methyl scission of isopropylidene occurs first, according to the bond …

Function Of The Signal Peptide And N- And C-Terminal Propeptides In The Leucine Aminopeptidase From Aeromonas Proteolytica, Krzysztof P. Bzymek, Ventris M. D'Souza, Guanjing Chen, Heidi Campbell, Alice Mitchell, Richard C. Holz

Chemistry Faculty Research and Publications

The leucine aminopeptidase from Aeromonas proteolytica (also known as Vibrio proteolyticus) (AAP) is a metalloenzyme with broad substrate specificity. The open reading frame (ORF) for AAP encodes a 54 kDa enzyme, however, the extracellular enzyme has a molecular weight of 43 kDa. This form of AAP is further processed to a mature, thermostable 32 kDa form but the exact nature of this process is unknown. Over-expression of different forms of AAP in Escherichia coli (with AAP's native leader sequence, with and without the N- and/or C-terminal propeptides, and as fusion protein) has allowed a model for the processing of …

Halide Recognition Through Diagnostic “Anion–Π” Interactions: Molecular Complexes Of CL−, Br−, And I− With Olefinic And Aromatic Π Receptors, Yaroslav S. Rosokha, Sergey V. Lindeman, Sergiy V. Rosokha, Jay K. Kochi

Chemistry Faculty Research and Publications

Intense colorations and new charge-transfer absorption bands are observed upon addition of a halide (Cl⁻, Br⁻, I⁻) to neutral organic π acceptors with electron-deficient olefinic and aromatic centers. These phenomena results from noncovalent anion–π interactions (shown schematically), which were confirmed by X-ray crystallography.

The Catalytic Role Of Glutamate 151 In The Leucine Aminopeptidase From Aeromonas Proteolytica, Krzysztof P. Bzymek, Richard C. Holz

Chemistry Faculty Research and Publications

Glutamate 151 has been proposed to act as the general acid/base during the peptide hydrolysis reaction catalyzed by the co-catalytic metallohydrolase from Aeromonas proteolytica (AAP). However, to date, no direct evidence has been reported for the role of Glu-151 during catalytic turnover by AAP. In order to elucidate the catalytic role of Glu-151, altered AAP enzymes have been prepared in which Glu-151 has been substituted with a glutamine, an alanine, and an aspartate. The Michaelis constant (K_m) does not change upon substitution to aspartate or glutamine, but the rate of the reaction changes drastically in the following …

Characterization Of Epoxy Resin (Su-8) Film Using Thickness-Shear Mode (Tsm) Resonator Under Various Conditions, Jeanne Hossenlopp, Lizhong Jiang, Richard Cernosek, Fabien Josse

Chemistry Faculty Research and Publications

Characterization of an epoxy resin film, commonly known as SU-8, is presented using thickness shear mode (TSM) quartz resonator. The impedance-admittance characteristics of the equivalent circuit models of the unperturbed and coated resonators are analyzed to extract the storage modulus and loss modulus (G' and G''). Those parameters are needed to establish SU-8 film as an effective wave-guiding layer in the implementation of guided shear-horizontal surface acoustic wave (SH-SAW) sensor platforms. Both cured and uncured polymer films are studied at the fundamental and third harmonic frequencies of the TSM resonators. The storage modulus (G') and loss …

Polystyrene Magadiite Nanocomposites, Dongyan Wang, David D. Jiang, Jaclyn Pabst, Zhidong Han, Jianqi Wang, Charles A. Wilkie

Chemistry Faculty Research and Publications

An organically modified magadiite has been prepared and used to make a mixed intercalated-exfoliated polystyrene nanocomposite by bulk polymerization. This system gives excellent improvement in mechanical properties, but the thermogravimetric analysis curves do not show any change in the onset of the degradation and the degradation pathway is not changed from that for virgin polystyrene, unlike the situation for an aluminosilicate clay, monlmorillonite. By cone calorimetry, the peak heat release rate is not changed, again unlike the results with the aluminosilicate. This suggests that not all clays exhibit the same behavior in nanocomposite formation.

Kinetic Analysis Of The Thermal Degradation Of Polystyrene-Montmorillonite Nanocomposite, Serge Bourbigot, Jeffery W. Gilman Sr., Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites exhibit a combination of unique properties, such as increased heat distortion temperature, reduced permeability, reduced flammability and improved mechanical properties. In this work, a polystyrene (PS) clay nanocomposite was prepared via bulk polymerization using a novel organically modified montmorillonite (MMT). The organic-modifier is the N,N-dimethyl-n-hexadecyl-(4-vinylbenzyl) ammonium chloride (VB16). The thermal stability of PS–VB16 compared to pure PS is examined in pyrolytic and thermo-oxidative conditions. It is then studied using a kinetic analysis. It is shown that the stability of PS is significantly increased in the presence of clay. The thermal behavior of PS and …

Arenediazonium Salts As Versatile (Meso-Ionic) Tectons. Charge-Transfer Intercalates And Clathrates In Unusual Crystalline Networks Self-Assembled With Neutral Aromatic Π-Donors, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Synopsis

Arenediazonium salts as tectonic building elements for crystal engineering possess a unique array of binding properties, including (a) strong acceptor affinity toward electronegative or neutral σ-donors; (b) enhanced C−H acidity for extensive formation of C−H···X bonds; and (c) π-acceptor properties of the electron-deficient arene substituent for charge-transfer complex formation with appropriate aromatic π-donors. Shown: Donor/acceptor intercalate in the layered structure of 3,5(NO₂)C₆H₃N₂⁺ BF₄^- with naphthalene.

Abstract

The surprisingly uniform crystal packings of various arenediazonium salts (ArN₂⁺X^-) largely consist of two-dimensional ionic layers from …

Study On The Thermal Stability Of Polystyryl Surfactants And Its Modified Clay Nanocomposites, Shengpei Su, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Five oligomeric styrene surfactants, N,N,N-trimethylpolystyrylammonium, N,N-dimethyl-N-benzylpolystyrylammonium, N,N-dimethyl-N-hexadecylpolystyrylammonium, 1,2-dimethyl-3-polystyrylimidazolium, and triphenylpolystyrylphosphonium chlorides were synthesized and used to prepare organically modified clays. Both styrene and methyl methacrylate nanocomposites were prepared by melt blending and the type of nanocomposite was evaluated by X-ray diffraction and transmission electron microscopy. The thermal stability of the organically modified clays and the nanocomposites were studied by thermogravimetric analysis; these systems do give clays which have good thermal stability and may be useful for melt blending with polymers that must be processed at …

Preparation Of Nanocomposites From Styrene And Modified Graphite Oxides, Fawn Marie Uhl, Charles A. Wilkie

Chemistry Faculty Research and Publications

Graphite oxide was prepared and modified with several ammonium salts and these modified graphite oxides were used to prepare nanocomposites with polystyrene by in situ polymerization of styrene monomer and by melt blending with polystyrene. Nanocomposites were characterized by X-ray diffraction, cone calorimetry, thermogravimetric analysis and the evaluation of mechanical properties. Nanocomposites are formed by in situ polymerization but not by melt blending; the graphite oxide undergoes thermal degradation at the temperature of melt blending so nanocomposite formation would be unlikely. Mechanical properties of the melt blended nanocomposites are improved relative to the virgin polystyrene while those prepared by in …

Synthesis And Reactivity Of Tricarbonyl(1-Methoxycarbonyl-5-Phenylpentadienyl)Iron(1+) Cation, Subhabrata Chaudhury, William A. Donaldson, Dennis W. Bennett, Daniel T. Haworth, Tasneem Siddiquee, Jennifer M. Kloss

Chemistry Faculty Research and Publications

Tricarbonyl(1-methoxycarbonyl-5-phenylpentadienyl)iron(1+) hexafluorophosphate (7) was prepared in two steps from tricarbonyl(methyl 6-oxo-2,4-hexadienoate)iron. While addition of carbon and heteroatom nucleophiles to 7 generally occurs at the phenyl-substituted dienyl carbon to afford (2,4-dienoate)iron products, the addition of phthalimide proceeded at C2 to afford a (pentenediyl)iron product (18). Complex 18 was structurally characterized by X-ray diffraction analysis.

The reaction of the title cation with carbon and heteroatom nucleophiles was examined. In general, the products arise from nucleophilic attack at C5 to give E,E- or E,Z-dienoate iron complexes. Addition of phthalimide anion proceeds at C2 …

Polybutadiene Modified Clay And Its Nanocomposites, Shengpei Su, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

A butadiene-modified clay was prepared by ionic exchange between sodium montmorillonite and a butadiene surfactant; the butadiene surfactant was obtained from the reaction of vinylbenzyl chloride grafted polybutadiene with a tertiary amine. Nanocomposites of polystyrene, high impact polystyrene, acrylonitrile–butadiene–styrene terpolymer, poly(methyl methacrylate), polypropylene and polyethylene were prepared by melt blending this modified clay with the virgin polymers. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the evaluation of mechanical properties. A morphological study of PBD-modified clay–polymer nanocomposites shows that all the composites are immiscible micro-composites. The consistency of the result from XRD and …

Fighting Antibiotic Resistance: The Dape-Encoded N-Succinyl-L, L-Diaminopimelic Acid Desuccinylase From Haemophilus Influenzae In A Dinuclear Metallohydrolase, Nathaniel J. Cosper, David L. Bienvenue, Jacob E. Shokes, Danuta M. Gilner, Takashi Tsukamoto, Robert A. Scott, Richard C. Holz

Chemistry Faculty Research and Publications

No abstract provided.

Reactivity Of (Bicyclo[5.1.0]Octadienyl)Iron(1+) Cations: Application To The Synthesis Of Cis-2-(2’-Carboxycyclopropyl)Glycines, Nathaniel J. Wallock, William A. Donaldson

Chemistry Faculty Research and Publications

The addition of carbon and heteroatom nucleophiles to (bicyclo[5.1.0]octadienyl)Fe(CO)₂L⁺ cations 5 or 8 (L = CO, PPh₃) generally proceeds via attack at the dienyl terminus on the face of the ligand opposite to iron to generate 6-substituted (bicyclo[5.1.0]octa-2,4-diene)iron complexes (11 or 13). In certain cases, these products are unstable with respect to elimination of a proton and the nucleophilic substituent to afford (cyclooctatetraene)Fe(CO)₂L (4 or 7). Decomplexation of 13f, arising from addition of phthalimide to 8, gave N-(bicyclo[5.1.0]octa-3,5-dien-2-yl)phthalimide (19). Oxidative cleavage of 19 (RuCl …

Poly(Methyl Methacrylate), Polypropylene And Polyethylene Nanocomposite Formation By Melt Blending Using Novel Polymerically-Modified Clays, Shengpei Su, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Two new organically-modified clays that contain an oligomeric styrene or methacrylate have been prepared and used to produce nanocomposites of poly(methyl methacryate), polypropylene and polyethylene. Intercalated nanocomposites and, in some cases, exfoliated or mixed intercalated/exfoliated nanocomposites of all of these polymers have been produced by melt blending in a Brabender mixer. The use of the styrene-containing clay permits the direct blending of the clay with polypropylene, without the usual need for maleation, to produce the nanocomposites. The systems have all been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the measurement of mechanical properties. These novel …

Systems-Based Design Of Bi-Ligand Inhibitors Of Oxidoreductases: Filling The Chemical Proteomic Toolbox, Daniel S. Sem, Bonnie Bertolaet, Brian Baker, Edcon Chang, Aurora Demertrina Costache, Stephen Coutts, Qing Dong, Mark Hansen, Victor Hong, Xuemei Huang, Richard M. Jack, Richard Kho, Henk Lang, Chen-Ting Ma, David Meininger, Maurizio Pellacchia, Fabrice Pierre, Hugo Villar, Lin Yu

Chemistry Faculty Research and Publications

Genomics-driven growth in the number of enzymes of unknown function has created a need for better strategies to characterize them. Since enzyme inhibitors have traditionally served this purpose, we present here an efficient systems-based inhibitor design strategy, enabled by bioinformatic and NMR structural developments. First, we parse the oxidoreductase gene family into structural subfamilies termed pharmacofamilies, which share pharmacophore features in their cofactor binding sites. Then we identify a ligand for this site and use NMR-based binding site mapping (NMR SOLVE) to determine where to extend a combinatorial library, such that diversity elements are directed into the adjacent substrate site. …

The Thermal Degradation Of Nanocomposites That Contain An Oligomeric Ammonium Cation On The Clay, Shengpei Su, Charles A. Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of polystyrene, high-impact polystyrene, ABS terpolymer, poly(methyl methacrylate), polypropylene and polyethylene nanocomposites has been studied using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy, TGA/FT-IR. The nanocomposites that have been studied include immiscible, intercalated and exfoliated systems and the evolved gases do not depend upon the type of nanocomposite and are qualitatively similar to those of the virgin polymer. In the case of the styrenics, the presence of clay promotes the production of oligomer, rather than monomer. It is suggested that this change in evolved products may offer an explanation for why some polymers give large reduction …

Novel Polymerically-Modified Clays Permit The Preparation Of Intercalated And Exfoliated Nanocomposites Of Styrene And Its Copolymers By Melt Blending, Shengpei Su, David D. Jiang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Two new organically-modified clays have been made and used to produce nanocomposites of polystyrene, high impact polystyrene and acrylonitrile–butadiene–styrene terploymer. At a minimum, intercalated nanocomposites of all of these polymers have been produced by melt blending in a Brabender mixer and, in some cases, exfoliated nanocomposites have been obtained. The systems have all been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the measurement of mechanical properties. These novel new clays open new opportunities for melt blending of polymers with clays to obtain nanocomposites with important properties.