Chemistry Commons^™

Double Carbon−Hydrogen Activation Of 2-Vinylpyridine: Synthesis Of Tri- And Pentanuclear Clusters Containing The Μ-Nc5H4Ch═C Ligand, Kazi A. Azam, Dennis W. Bennett, Mohammad R. Hassan, Daniel T. Haworth, Graeme Hogarth, Shariff E. Kabir, Sergey V. Lindeman, Luca Salassa, Sultana R. Simi, Tasneem Siddiquee

Chemistry Faculty Research and Publications

Reactions of 2-vinylpyridine with the triruthenium complexes [Ru₃(CO)₁₂] and [Ru₃(CO)₁₀(μ-dppm)] leads to a previously unknown double carbon−hydrogen bond activation of the β-carbon of the vinyl group to afford the pentaruthenium and triruthenium complexes [Ru₅(CO)₁₄(μ₄-C₅H₄CH═C)(μ-H)₂] (1) and [Ru₃Cl(CO)₅(μ-CO)(μ-dppm)(μ₃-NC₅H₄CH═C)(μ-H)] (2), respectively. Crystal structures reveal two different forms of bridging of the dimetalated 2-vinylpyridyl ligand, capping a square face in 1 and a triangular face in 2.

A Second-Generation Janus Scorpionate Ligand: Controlling Coordination Modes In Iron(Ii) Complexes By Steric Modulation, Rosalice M. Silva, Chengeto Gwengo, Sergey V. Lindeman, Mark D. Smith, Gary J. Long, Fernande Grandjean, James R. Gardinier

Chemistry Faculty Research and Publications

The second-generation Janus scorpionate ligand [HB(mtda^Me)₃⁻] containing methyl-mercaptothiadiazolyl (mtda^Me) heterocyclic rings and (N,N,N-) and (S,S,S-) binding pockets has been prepared. The effect of methyl substitution versus the unsubstituted first-generation Janus scorpionate [HB(mtda)₃]− on the coordination chemistry with alkali metals and on the binding preferences and on the ground spin state of iron(II) complexes has been studied structurally and by ⁵⁷Fe Mossbauer Spectroscopy.

Kinetic, Spectroscopic, And X-Ray Crystallographic Evidence For The Cooperative Mechanism Of The Hydration Of Nitriles Catalyzed By A Tetranuclear Ruthenium-Μ-Oxo-Μ-Hydroxo Complex, Chae S. Yi, Tonya N. Zeczycki, Sergey V. Lindeman

Chemistry Faculty Research and Publications

The tetranuclear ruthenium-oxo-hydroxo-hydride complex {[(PCy₃)(CO)RuH]₄(μ₄-O)(μ₃-OH)(μ₂-OH)} (1) was found to be a highly cooperative catalyst for the nitrile hydration reaction. The cooperative mechanism of the hydration of benzonitrile was established by Hill inhibition kinetics. The treatment of a nitrile substrate with complex 1 led to the catalytically relevant nitrile-coordinated tetraruthenium complex 3. The X-ray structure of the nitrile-coordinated complex 3 showed a considerably “relaxed” tetrameric core structure compared to that of 1. The hydration of para-substituted benzonitriles p-X-C₆H₄CN with an electron-withdrawing …

Isolation And X-Ray Structural Characterization Of Tetraisopropylpyrene Cation Radical, Moloy Banerjee, Vijay Vyas, Sergey V. Lindeman, Rajendra Rathore

Chemistry Faculty Research and Publications

A practical synthesis of 1,3,6,8-tetraisopropylpyrene and the isolation and X-ray structural characterization of its monomeric cation radical salt are described.

Synthesis Of Cyclopropanes Via Organoiron Methodology: Preparation Of Rac-Dysibetaine Cpa, Tasneem A. Siddiquee, Julie Lukesh, Sergey Sergey Lindeman, William A. Donaldson

Chemistry Faculty Research and Publications

The cyclopropane containing betaine, rac-dysibetaine CPa, was prepared from (1-methoxycarbonylpentadienyl)-Fe(CO)₂PPh₃⁺ by nucleophilic addition of nitromethane anion followed by oxidatively induced reductive elimination.

Benzimidazolium Surfactants For Modification Of Clays For Use With Styrenic Polymers, Marius C. Costache, Matthew Heidecker, Evangelos Manias, Rakesh K. Gupta, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites of polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays.

Generation Of Molecular Complexity From Cyclooctatetraene: Synthesis Of A Protected 2-(3′-Carboxy-2′-Benzoylcyclopentyl)Glycine, Subhabrata Chaudhury, Sergey V. Lindeman, William A. Donaldson

Chemistry Faculty Research and Publications

Synthesis of a protected 2-(3′-carboxycyclopentyl)glycine rac-11, possessing four contiguous chiral carbons, was accomplished in six steps (20% yield) from the hydrocarbon cyclooctatetraene.

Revealing Nano-Confinement In Degradation And Relaxation Studies Of Two Structurally Different Polystyrene-Clay Systems, Kai Chen, Charles A. Wilkie, Sergey Vyazovkin

Chemistry Faculty Research and Publications

Degradation and relaxation studies have been performed on two polystyrene (PS)−montmorillonite clay nanocomposites, one of which has an intercalated PS−clay structure and the other an exfoliated PS−clay brush structure. Compared to virgin PS, both nanostructured materials have demonstrated the following similarities: (a) a high yield of α-methylstyrene in the degradation products as measured by infrared spectroscopy; (b) larger values of the activation energy of the thermal degradation as determined by isoconversional kinetic analysis of thermogravimetric data; and (c) larger values of the activation energy for the glass transition as found from the frequency dependence of the glass transition temperature measured …

Ferrocene And Ferrocenium Modified Clays And Their Styrene And Eva Composites, Charles Manzi-Nshuti, Charles A. Wilkie

Chemistry Faculty Research and Publications

In this work, ferrocene- and ferrocenium-containing salts were employed to modify montmorillonite. X-ray measurements show an increase in the interlayer spacing upon clay modification, which means that the larger and more organophilic cations were inserted into the gallery space of montmorillonite. Attempts to prepare nanocomposites of polystyrene and ethylene vinyl acetate copolymers lead to immiscible systems; the morphology of these systems was elucidated with TEM, XRD and cone calorimetry. The thermal stability of the composites is greater than that of the virgin polymer.

Reactivity Of [Re2(Co)8(Mecn)2] With Thiazoles: Hydrido Bridged Dirhenium Compounds Bearing Thiazoles In Different Coordination Modes, Shariff E. Kabir, Faruque Ahmed, Anamika Das, Mohammad R. Hassan, Daniel T. Haworth, Sergey V. Lindeman, G. M. Golzar Hossain, Tasneem Siddiquee, Dennis W. Bennett

Chemistry Faculty Research and Publications

Reactions of the labile compound [Re₂(CO)₈(MeCN)₂] with thiazole and 4-methylthiazole in refluxing benzene afforded the new compounds [Re₂(CO)₇{μ-2,3-η²-C₃H(R)NS}{η¹-NC₃H₂(4-R)S}(μ-H)] (1, R = H; 2, R = CH₃), [Re₂(CO)₆{μ-2,3-η²-C₃H(R)NS}{η¹-NC₃H₂(4-R)S}₂(μ-H)] (3, R = H; 4, R = CH₃) and fac-[Re(CO)₃(Cl){η¹-NC₃H₂(4-R)S}₂] (5, R = H; …

P–C And C–H Bond Cleavages Of Dppm In The Thermal Reaction Of [Ru3(Co)10(Μ-Dppm)] With Benzothiophene: X-Ray Structures Of [Ru6(Μ-Co)(Co)13{Μ4-Php(C6H4)Pph}(Μ6-C)] And [Ru4(Co)9(Μ3-Η2-Phpch2Pph2)(Μ4-Η6:Η1:Η1-C6H4)(Μ-H)], Shariff E. Kabir, Mohammad R. Hassan, Daniel T. Haworth, Sergey V. Lindeman, Tasneem Siddiquee, Dennis W. Bennett

Chemistry Faculty Research and Publications

The thermal reaction of [Ru₃(CO)₁₀(μ-dppm)] (1) with benzothiophene in refluxing toluene gives a complex mixture of products. These include the known compounds [Ru₂(CO)₆{μ-CH₂PPh(C₆H₄)PPh}] (2), [Ru₂(CO)₆{μ-C₆H₄PPh(CH₂)PPh}] (3), [Ru₃(CO)₉{μ₃-η³-(Ph)PCH₂P(Ph)C₆H₄}] (4) and [Ru₃(CO)₁₀{μ-η²-PPh(CH₂)(C₆H₄)PPh}] (6), as well as the new clusters [Ru₆(μ-CO)(CO) …

Spectral Data For "Synthesis Of Cyclopropanes Via Organoiron Methodology: Stereoselective Preparation Of Bi(Cyclopropyl)S", Rajesh K. Pandey, Sergey V. Lindeman, William A. Donaldson

Natural Products Synthesis via Organoiron Methodology

Spectral data created in the course of the research project. Supports specific findings in "Synthesis of Cyclopropanes via Organoiron Methodology: Stereoselective Preparation of Bi(cyclopropyl)s".

Cyclopropanation of [2-(alkenyl)pentenediyl]Fe(CO)₃ complexes (4) proceeds in a diastereoselective fashion to afford [2-(cyclopropyl)pentenediyl]Fe(CO)₃. The relative stereochemistry of the products was established by X-ray crystallography. The diastereoselectivity is rationalized on approach of the cyclopropanation reagent on the sterically more exposed face of 4. Oxidatively induced reductive elimination afforded stereodefined bi(cyclopropyl)s.

Mechanism Of Rate-Limiting Motions In Enzyme Function, Eric D. Watt, Hiroko Shimada, Evgenii L. Kovrigin, J. Patrick Loria

Chemistry Faculty Research and Publications

The ability to use conformational flexibility is a hallmark of enzyme function. Here we show that protein motions and catalytic activity in a RNase are coupled and display identical solvent isotope effects. Solution NMR relaxation experiments identify a cluster of residues, some distant from the active site, that are integral to this motion. These studies implicate a single residue, histidine-48, as the key modulator in coupling protein motion with enzyme function. Mutation of H48 to alanine results in loss of protein motion in the isotope-sensitive region of the enzyme. In addition, k _cat decreases for this mutant and the kinetic …

The Voltammetric Study Of The Reduction Of Tetraalkylammonium Perchlorate By Fe(Tpp)2-, Chathra Shirani De Silva, Michael D. Ryan

Chemistry Faculty Research and Publications

Tetraalkylammonium ions react with Fe(TPP)²⁻ to form Fe(TPP)(R)⁻ and trialkylamine. The tetrabutylammonium cation was verified to be the source of the alkyl group in the product, Fe(TPP)(R)⁻, by using (¹H₅C₂)₃(2H₅C₂)N⁻ as the cation and ²H NMR. The reaction of Fe(TPP)²⁻ with Bu₄N⁻ was monitored by cyclic voltammetry and thin layer spectroelectrochemistry. The activation parameters were measured, and were most consistent with an electron transfer (ET) mechanism. The rate of the reaction of tetramethyl and tetraethylammonium ions with Fe(TPP) …

Characterization Of The Catalytically Active Mn(Ii)-Loaded Arge-Encoded N-Acetyl-L-Ornithine Deacetylase From Escherichia Coli, Wade C. Mcgregor, Sabina I. Swierczek, Brian Bennett, Richard C. Holz

Physics Faculty Research and Publications

The catalytically competent Mn(II)-loaded form of the argE-encoded N-acetyl-l-ornithine deacetylase from Escherichia coli (ArgE) was characterized by kinetic, thermodynamic, and spectroscopic methods. Maximum N-acetyl-l-ornithine (NAO) hydrolytic activity was observed in the presence of one Mn(II) ion with k _cat and K _m values of 550 s⁻¹ and 0.8 mM, respectively, providing a catalytic efficiency (k _cat/K _m) of 6.9 × 10⁵ M⁻¹ s⁻¹. The ArgE dissociation constant (K _d) for Mn(II) was determined to be 0.18 μM, correlating well with a value obtained by isothermal titration …

Synthesis And Characterization Of Platinum – Selenium Derivatives: X-Ray Structure Of Trans-Pt(Pet3)2(Seph)2, Martin D. Rudd, Sergey V. Lindeman

Chemistry Faculty Research and Publications

The crystal structure of trans-[((bis)triethylphosphine)(bis(phenylselenato))platinum (II)] has been determined by single crystal X-ray diffraction. Crystallization occurs in the triclinic space group P-1 (No. 2) with a = 8.9964(2) Å, b = 11.5103(2) Å, c = 14.9335(3) Å; α = 85.8750(10)°, β = 72.5350(10)°, γ = 68.4450(10)°. Details of the structure and spectroscopic results are presented and discussed and comparisons are made with related square planar platinum (II) structures.

Unraveling The Catalytic Mechanism Of Nitrile Hydratases, Sanghamitra Mitra, Richard C. Holz

Chemistry Faculty Research and Publications

To elucidate a detailed catalytic mechanism for nitrile hydratases (NHases), the pH and temperature dependence of the kinetic constants k_cat and K_m for the cobalt-type NHase from Pseudonocardia thermophila JCM 3095 (PtNHase) were examined. PtNHase was found to exhibit a bell-shaped curve for plots of relative activity versus pH at pH 3.2–11 and was found to display maximal activity between pH 7.2 and 7.8. Fits of these data provided pK_ES1 and pK_ES2 values of 5.9 ± 0.1 and 9.2 ± 0.1 (k_cat′ = 130 ± 1 …

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) ų, 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

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 …

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

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 …

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(pzAn^X), (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(pzAn^X) (X = para-OMe (1), Me (2), H (3), Cl (4), CO₂Et (5), CF₃ (6), CN (7)) in high yield. The …

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

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 …

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 …

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

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

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 …

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.

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 E_ox1 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.