Chemistry Commons^™

Decarbonylation Reaction Of [Os3(Co)10(Μ-H)(Μ-Sn2C4H5)]: X-Ray Structures Of The Two Isomers Of [Os3(Co)9(Μ-H)(Μ3-Η2-Sn2C4H5)], Shishir Ghosh, Shariff E. Kabir, Mansura Khatun, Daniel T. Haworth, Sergey V. Lindeman, Tasneem Siddiquee, Dennis W. Bennett

Chemistry Faculty Research and Publications

The thermal reaction of [Os₃(CO)₁₀(μ-H)(μ-SN₂C₄H₅)] (1) at 110 °C afforded the new compound [Os₃(CO)₉(μ-H)(μ ₃-η ²-SN₂C₄H₅)] (2) in 84% yield. Compound 2 exists as two isomers, which differ in the disposition of the bridging hydride ligand. Both of the isomers of 2 have been characterized by a combination of elemental analysis, infrared and ¹H NMR spectroscopic data together with single crystal X-ray crystallography. The isomers …

Toward Charge-Neutral ‘Soft Scorpionates’: Coordination Chemistry And Lewis Acid Promoted Isomerization Of Tris(1-Organo-Imidazol-2-Ylthio)Methanes, Chengeto Gwengo, Rosalice M. Silva, Mark D. Smith, Sergey V. Lindeman, James R. Gardinier

Chemistry Faculty Research and Publications

Two tris(1-organo-imidazol-2-ylthio)methanes, HC(S-tim^R)₃ (R = organo = methyl, tert-butyl), have been prepared by a triphasic reaction between chloroform, the appropriate heterocycle, and saturated aqueous solutions of Na₂CO₃, in the presence of a phase transfer agent, (NBu₄)(Br). These ligands have been characterized both spectroscopically and by single crystal X-ray diffraction. The reaction chemistry of these potentially N,N,N-tripodal ligands with AgBF₄ was also explored where simple 1:1 coordination complexes could be isolated from reactions performed in THF solution at room temperature. The derivative {Ag[HC(S-tim^Me)₃]}(BF₄) was structurally …

Activation Of Tri(2-Furyl)Phosphine At A Dirhenium Centre: Formation Of Phosphido-Bridged Dirhenium Complexes, Shishir Ghosh, Mansura Khatun, 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 tri(2-furyl)phosphine (PFu₃) with [Re₂(CO)_10−n(NCMe)_n] (n = 1, 2) at 40 °C gave the substituted complexes [Re₂(CO)_10−n(PFu₃)_n] (1 and 2), the phosphines occupying axial position in all cases. Heating [Re₂(CO)₁₀] and PFu₃ in refluxing xylene also gives 1 and 2 together with four phosphido-bridged complexes; [Re₂(CO)_8−n(PFu₃)_n(μ-PFu₂)(μ-H)] (n = 0, 1, 2) (3–5) and [Re₂(CO)_{6 …}

Does Organic Modification Of Layered Double Hydroxides Improve The Fire Performance Of Pmma?, Calistor Nyambo, Dan Chen, Shengpei Shu, Charles A. Wilkie

Chemistry Faculty Research and Publications

The effect of modified layered double hydroxides (LDHs) on fire properties of poly(methyl methacrylate) is investigated. Organically-modified LDHs were prepared via rehydration of calcined hydrotalcite in a palmitate solution. Composites consisting of the organo-LDHs, unmodified hydrotalcite and calcined oxides were prepared with poly(methyl methacrylate) using melt blending. Thermal and fire properties of the (nano)composites were studied. The thermogravimetric analyses of the composites show an increase in thermal stability. Fire performance, evaluated using cone calorimetry, show that organically-modified LDHs composites give the best reductions in peak heat release rate, PHRR, i.e., 51% at 10% weight loading. Dispersion of the LDHs was …

Regioselective Intermolecular Coupling Reaction Of Arylketones And Alkenes Involving C-H Bond Activation Catalyzed By An In Situ Formed Cationic Ruthenium-Hydride Complex, Chae S. Yi, Do W. Lee

Chemistry Faculty Research and Publications

The cationic ruthenium hydride complex, formed in situ from the treatment of the tetranuclear ruthenium hydride complex {[(PCy₃)(CO)RuH]₄(μ₄-O)(μ₃-OH)(μ₂-OH)} with HBF₄·OEt₂, was found to be a highly effective catalyst for the intermolecular coupling reaction of arylketones and 1-alkenes to give the substituted indene and ortho-C−H insertion products. The formation of the indene products resulted from the initial alkene isomerization followed by regioselective ortho-C−H insertion of 2-alkene and dehydrative cyclization. The preliminary mechanistic studies revealed a rapid and reversible ortho-C−H bond activation followed by the …

Structure - Property Relationships Of New Polystyrene Nanocomposites Prepared From Initiator-Containing Layered Double Hydroxides Of Zinc Aluminum And Magnesium Aluminum, Charles Manzi-Nshuti, Dan Chen, Shengpei Shu, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polystyrene/layered double hydroxides (PS/LDHs) nanocomposites were prepared by free radical polymerization of styrene monomer in the presence of LDHs intercalated with 4,4′-azobis(4-cyanopentanoate) anions (LDH–ACPA). XRD and ATR-IR are used to confirm that the materials produced are layered and the presence of the azo-initiator anions in these LDHs. These LDHs were used successfully to polymerize styrene and both XRD and TEM images of the composites support the formation of a mixed exfoliated-intercalated nanocomposite for ZnAl–ACPA but a microcomposite for MgAl–ACPA. The magnesium-containing LDHs decreased the glass transition temperature (T_g) of the composites while ZnAl–ACPA did not affect T …

Investigations Of 2-Thiazoline-2-Thiol As A Ligand: Synthesis And X-Ray Structures Of [Mn2(Co)7(Μ-Ns2C3H4)2] And [Mn(Co)3(Pph3)(Κ2-Ns2C3H4)], Shishir Ghosh, Faruque Ahmed, Rafique Al-Mamun, Daniel T. Haworth, Sergey V. Lindeman, Tasneem Siddiquee, Dennis W. Bennett, Shariff E. Kabir

Chemistry Faculty Research and Publications

Treatment of Mn₂(CO)₁₀ with 2-thiazoline-2-thiol in the presence of Me₃NO at room temperature afforded the dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) in 51 and 34% yields, respectively. Compound 1 was quantitatively converted into 2 when reacted with one equiv of Me₃NO. Reaction of 1 with triphenylphosphine at room temperature furnished the mononuclear complex [Mn(CO)₃(PPh₃)(κ ^{2 …}

Recent Applications Of Acyclic (Diene)Iron Complexes And (Dienyl)Iron Cations In Organic Synthesis, William A. Donaldson, Subhabrata Chaudhury

Chemistry Faculty Research and Publications

Complexation of (tricarbonyl)iron to an acyclic diene serves to protect the ligand against oxidation, reduction, and cycloaddition reactions, whereas the steric bulk of this adjunct serves to direct the approaches of reagents to unsaturated groups attached to the diene onto the face opposite to iron. Furthermore, the Fe(CO)₃ moiety can serve to stabilize carbocation centers adjacent to the diene (i.e. pentadienyl-iron cations). Recent applications of these reactivities to the synthesis of polyene-, cyclopropane-, cycloheptadiene-, and cyclohexenone-containing natural products or analogues are presented.

Polymer Nanocomposites Using Zinc Aluminum And Magnesium Aluminum Oleate Layered Double Hydroxides: Effects Of Ldh Divalent Metals On Dispersion, Thermal, Mechanical And Fire Performance In Various Polymers, Charles Manzi-Nshuti, Ponusa Songtipya, Evangelos Manias, Maria Del Mar Jimenez-Gasco, Jeanne Hossenlopp, Charles Wilkie

Chemistry Faculty Research and Publications

Oleate-containing layered double hydroxides of zinc aluminum (ZnAl) and magnesium aluminum (MgAl) were used to prepare nanocomposites of polyethylene, poly(ethylene-co-butyl acrylate) and poly(methyl methacrylate). The additives and/or their polymer composites were characterized by X-ray diffraction, FTIR, elemental analysis, thermogravimetric analysis, mechanical testing, and cone calorimetry. The unusual packing of the monounsaturated oleate anions in the gallery of these LDHs facilitates the dispersion of these nanomaterials. The inorganic LDH protects the polymer from thermal oxidation, shown by enhancement of the thermal and fire properties of the corresponding polymer nanocomposites. There is a qualitative difference in the morphology of the …

Fire Retardancy Of Bis[2-(Methacryloyloxy)Ethyl] Phosphate Modified Poly(Methyl Methacrylate) Nanocomposites Containing Layered Double Hydroxide And Montmorillonite, Linjiang Wang, Shengpei Shu, Dan Chen, Charles A. Wilkie

Chemistry Faculty Research and Publications

Copolymer nanocomposites were prepared by suspension copolymerization of bis[2-(methacryloyloxy)ethyl] phosphate and methyl methacrylate, together with bis(2-ethylhexyl) phosphate layered double hydroxide and a montmorillonite, Cloisite 93A. X-ray diffraction and transmission electron microscopy were used to characterize the morphology of nanocomposites and the dispersion of additives in the polymer. The thermal stability of the nanocomposites has been assessed by thermogravimetric analysis and cone calorimetry has been used to study the fire properties. Bis[2-(methacryloyloxy)ethyl] phosphate not only copolymerized with MMA, but also aids in the dispersion of additives in PMMA. The copolymer nanocomposites have better dispersion and higher degradation temperature and more char …

X-Ray Structural Characterization Of Charge Delocalization Onto The Three Equivalent Benzenoid Rings In Hexamethoxytriptycene Cation Radical, Vincent J. Chebny, Tushar S. Navale, Ruchi Shukla, Sergey V. Lindeman, Rajendra Rathore

Chemistry Faculty Research and Publications

Definitive X-ray crystallographic evidence is obtained for a single hole (or a polaron) to be uniformly distributed on the three equivalent 1,2-dimethoxybenzenoid (or veratrole) rings in the hexamethoxytriptycene cation radical. This conclusion is further supported by electrochemical analysis and by the observation of an intense near-IR transition in its electronic spectrum, as well as by comparison of the spectral and electrochemical characteristics with the model compounds containing one and two dimethoxybenzene rings.

Linking Conformation Change To Hemoglobin Activation Via Chain-Selective Time-Resolved Resonance Raman Spectroscopy On Protoheme/Mesoheme Hybrids, Gurusamy Balakrishnan, Mohammed Ibrahim, Piotr J. Mak, Jessica Hata, James R. Kincaid, Thomas G. Spiro

Chemistry Faculty Research and Publications

Time-resolved Resonance Raman spectra are reported for Hb tetramers, in which the αand β chains are selectively substituted with mesoheme. The Soret absorption band shift in meso- relative to protoheme permits chain-selective excitation of heme RR spectra. The evolution of these spectra following HbCO photolysis show that geminate recombination rates and yields are the same for the two chains, consistent with recent results on 15N-heme isotopomer hybrids. The spectra also reveal systematic shifts in the deoxy-heme ν4 and νFe-His) RR bands, which are anti-correlated. These shifts are resolved for the successive intermediates in the protein structure, which have previously been …

Analyzing The Binding Of Co(Ii)-Specific Inhibitors To The Methionyl Aminopeptidases From Escherichia Coli And Pyrococcus Furiosus, Sanghamitra Mitra, George Sheppard, Jieyi Wang, Brian Bennett, Richard C. Holz

Chemistry Faculty Research and Publications

Methionine aminopeptidases (MetAPs) represent a unique class of protease that is capable of the hydrolytic removal of an N-terminal methionine residue from nascent polypeptide chains. MetAPs are physiologically important enzymes; hence, there is considerable interest in developing inhibitors that can be used as antiangiogenic and antimicrobial agents. A detailed kinetic and spectroscopic study has been performed to probe the binding of a triazole-based inhibitor and a bestatin-based inhibitor to both Mn(II)- and Co(II)-loaded type-I (Escherichia coli) and type-II (Pyrococcus furiosus) MetAPs. Both inhibitors were found to be moderate competitive inhibitors. The triazole-type inhibitor was found to …

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

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

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

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

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 (k_H/k_D = 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

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 …

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

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 …

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 …

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

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 …

Design, Synthesis And Study Of The Bridged And Cofacially-Arrayed Poly-P-Phenylene Molecular Wires, Matthew J. Modjewski

Master's Theses (2009 -)

Two novel series of bridged and cofacially-arrayed poly-p-phenylenes have been designed synthesized and studied. The bridged poly-p-phenylenes have been synthesized from a readily available diacetylenic precursor utilizing three high yielding steps, and their structures were determined by 1H/13C NMR spectroscopy as well as X-ray crystallography. The racemization barrier between the two atropoisomers was found to be ~12 Kcal mol-1; the versatility of the synthesis employed was extended to synthesis a triply bridged tetra-p-phenylene and a quadruply bridged penta-p-phenylene.

The cofacially-arrayed poly-p-phenylenes have shown that the X-ray crystal structures of the neutral compounds are largely dominated by C-H--π-interactions interactions while the …

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.

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 …

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.

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⁻).

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 …