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  • 1
    Electronic Resource
    Electronic Resource
    Solid-State NMR characterization of a superactive supported ziegler-natta catalystThis is Part XXXI of the series on MgCl2-supported Ziegler-Natta catalyst. Part XXX was: J. Vizzini, F. Ciardelli, and J. C. W. Chien, “Stereoselective Polymerization of α-Olefins by Heterogeneous Chiral Ziegler-Natta Catalysts,” Macromolecules, 25, 3199 (1992). (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 2173-2179 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The formation of CH-type catalysts has been investigated by high-resolution and solid-state NMR. These catalysts are prepared from a soluble MgCl2 and 2-ethyl-1-hexanol adduct (MgCl2·3EH) by reaction with phthalic anhydride (PA) to form dioctylphthalate (DOP) and then with TiCl4 in the presence of di-i-butylphthalate (BP). In the model systems MgCl2·3EH/PA, MgCl2/BP, and MgCl2/TiCl4/BP, the ester is complexed with MgCl2 and /or TiCl4 in two or more states. Only single-ester C=O and OCH2 resonances are seen in TiCl4/BP, probably due to exchange of ester coordinations. CH-catalysts prepared by three different procedures exhibit a single mode of bonding for the ester. The chemical shift values are consistent for ester complexed with MgCl2. The most active and stereoselective catalyst has the most shielded chemical shift values for the C=O and  - OCH2 -  carbons, shortest TH1 and TH1p, and longest TCH relaxation times. These parameters change monotonically with the decrease of activity and stereoselectivity of the catalyst preparation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070481211
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  • 2
    Electronic Resource
    Electronic Resource
    The equilibrium pair distribution function of a gas: Aspects associated with the presence of bound states (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9111-9121 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: At thermal equilibrium the momentum distribution of atoms in a gas is an atom is bound in a diatomic molecule, the atom's momentum distribution is non-Maxwellian. This paper explores the consequent singlet and pair particle distribution functions in a gas having both unbound atoms and bound pairs of atoms. Comment is made on the range of behavior associated with whether the chemical equilibrium constant for diatom formation is small or large. Calculations of distribution functions and their moments for atoms which are members of dimers are presented for some specific model potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465526
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  • 3
    Electronic Resource
    Electronic Resource
    Silyl group internal rotation in S1 phenylsilane and phenylsilane cation: Experiments and ab initio calculations (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4247-4265 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonant two-photon ionization (R2PI) and pulsed field ionization (PFI) were used to measure S1–S0 and cation–S1 spectra of internally cold phenylsilane. We measure the adiabatic ionization potentials IP(phenylsilane)=73 680±5 cm−1, IP(phenylsilane ⋅Ar)=73 517±5 cm−1 and IP(phenylsilane ⋅Ar2)=73 359±5 cm−1. We assign many low lying torsion–vibration levels of the S1 (A˜ 1A1) state and of X˜ 2B1 of phenylsilane+. In both states, the pure torsional transitions are well fit by a simple sixfold hindered rotor Hamiltonian. The results for the rotor inertial constant B and internal rotation potential barrier V6 are, in S1, B=2.7±0.2 cm−1 and V6=−44±4 cm−1; in the cation, B=2.7±0.2 cm−1 and V6=+19±3 cm−1. The sign of V6 and the conformation of minimum energy are inferred from spectral intensities of bands terminating on the 3a‘1 and 3a‘2 torsional levels. In S1 the staggered conformation is most stable, while in the cation ground state the eclipsed conformation is most stable. For all sixfold potentials whose absolute phase is known experimentally, the most stable conformer is staggered in the neutral states (S0 and S1 p-fluorotoluene, S1 toluene, S1 p-fluorotoluene) and eclipsed in the cationic states (ground state toluene+ and phenylsilane+). In phenylsilane+ we estimate several potential energy coupling matrix elements between torsional and vibrational states.For small V6, the term PαPa in the rigid-frame model Hamiltonian strongly mixes the 6a'1 and 6a'2 torsional states, which mediates further torsion–vibrational coupling. In addition, the cation X˜ 2B1 vibrational structure is badly perturbed, apparently by strong vibronic coupling with the low-lying A˜ 2A2 state. Accordingly, ab initio calculations find a substantial in-plane distortion of the equilibrium geometry of the X˜ 2B1 state, while the A˜ 2A2 state is planar and symmetric. The calculations also correctly predict the lowest energy conformer for S0 states and for cation ground states. Finally, we adapt the natural resonance theory (NRT) of Glendening and Weinhold to suggest why sixfold barriers for methyl and silyl rotors are uniformly small, while some threefold barriers are quite large. The phase of the sixfold potential is apparently determined by a subtle competition between two types of rotor-ring potential terms: attractive donor–acceptor interactions and repulsive van der Waals interactions (steric effects).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466079
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  • 4
    Electronic Resource
    Electronic Resource
    Calculation of enthalpy and entropy differences of near-critical binary mixtures with the modified Leung–Griffiths model (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2298-2307 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In previous applications of the Leung–Griffiths model as modified by Moldover and Rainwater, many near-critical vapor–liquid equilibrium surfaces have been described successfully in the space of pressure, temperature, density, and composition, but calorimetric properties such as entropy and enthalpy have not been examined. Such calculations are difficult in general because of the need to determine a parameter that is usually unknown in the definition of an independent field variable (the fugacity fraction). However, a generalization for mixtures of the Clapeyron equation is available which allows for the calculation of differences in entropy, enthalpy, and free energies between a pair of (noncoexisting) dew and bubble points at the same temperature and composition. A calculation of entropy differences from a correlation of carbon dioxide+propylene agrees well with results inferred indirectly from experimental data. As a more direct check, calculation of enthalpy differences from a correlation of n-pentane+benzene agrees with an interpolation of enthalpy data provided by calorimetric measurements of Lenoir and Hipkin. The generalized Clapeyron equation appears to be singular at the maxcondentherm point, but it is shown that the singular terms cancel one another and that the leading-order finite term is consistent with a thermodynamic Maxwell relation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464211
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  • 5
    Electronic Resource
    Electronic Resource
    High Activities of Glutamine Transaminase K (Dichlorovinylcysteine β-Lyase) and ω-Amidase in the Choroid Plexus of Rat Brain (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Certain halogenated hydrocarbons, e.g., dichlo-roacetylene, are nephrotoxic to experimental animals and neurotoxic to humans; cysteine-S-conjugate β-lyases may play a role in the nephrotoxicity. We now show that with dichlorovinylcysteine as substrate the only detectable cysteine-S-conjugate β-lyase in rat brain homogenates is identical to glutamine transaminase K. The predominant (mitochondrial) form of glutamine transaminase K in rat brain was shown to be immunologically distinct from the predominant (cytosolic) form of the enzyme in rat kidney. Glutamine transaminase K and ω-amidase (constituents of the glutaminase II pathway) activities were shown to be widespread throughout the rat brain. However, the highest specific activities of these enzymes were found in the choroid plexus. The high activity of glutamine transaminase K in choroid plexus was also demonstrated by means of an immunohistochemical staining procedure. Glutamine transaminase K has a broad specificity toward amino acid and α-keto acid substrates. The ω-amidase also has a broad specificity; presumably, however, the natural substrates are α-ketoglutaramate and α-ketosuccinamate, the α-keto acid analogues of glutamine and aspara-gine, respectively. The high activities of both glutamine transaminase K and ω-amidase in the choroid plexus suggest that the two enzymes are linked metabolically and perhaps are coordinately expressed in that organ. The data suggest that the natural substrate of glutamine transaminase K in rat brain is indeed glutamine and that the metabolism of glutamine through the glutaminase II pathway (i.e., l-glutamine and α-keto acid α-ketoglutarate and l-amino acid + ammonia) is an important function of the choroid plexus. Moreover, the present findings also suggest that any explanation of the neurotoxicity of halogenated xenobiotics must take into account the role of glutamine transaminase K and its presence in the choroid plexus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb09810.x
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  • 6
    Electronic Resource
    Electronic Resource
    Complexities of Junctional Tachycardias (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 4 (1993), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Complexities of functional Tachycardias. The atrioventricular junction is a compact area in which most of the known electrophysiologic substrates and mechanisms play a role in the genesis and maintenance of tachyarrhythmias. The purpose of this review is to summarize the data on normal atrioventricular junction anatomy and electrophysiologic function and correlate that information with surface electrocardiographic recordings, intracardiac electrophysiologic data, and interventional data from surgical and catheter techniques. Models of tachycardia mechanisms are proposed for typical and atypical atrioventricular nodal reentrant tachycardia, permanent Junctional reciprocating tachycardia, and orthodromic supraventricular tachycardias utilizing “intermediate septal” accessory connections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1993.tb01226.x
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  • 7
    Electronic Resource
    Electronic Resource
    Double Balloon Mitral Valvuloplasty Through Dual Femoral Vein Punctures and a Single Atrial Septal Puncture (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of interventional cardiology 6 (1993), S. 0 
    Details
    ISSN: 1540-8183
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: A modification of a previously described double balloon mitral valvuloplasty procedure is described. This involves dual femoral vein punctures with a single atrial septal puncture. After initial transseptal catheterization and predilatation of the interatrial septum with an 8-mm balloon, a second catheter is advanced through the resulting atrial septal defect allowing access to the left atrium and left ventricle through the mitral valve via two separate femoral vein puncture sites. In comparison with the previously described technique using two balloon catheters inserted through a single femoral vein puncture site, this modification has reduced the amount of bleeding from the femoral vein and the need for transfusion. Furthermore, the potential for subsequent interatrial shunting is less than with the alternative previously described technique utilizing two femoral vein punctures with two separate punctures in the interatrial septum. In utilizing two separate femoral vein punctures with only one atrial septal puncture this technique combines advantages of the two previously described techniques. (J Interven Cardiol 1993; 6:219–222)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8183.1993.tb00859.x
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  • 8
    Electronic Resource
    Electronic Resource
    Complexes containing heteronuclear and homonuclear quadruple bonds. Preparation and characterization of bis[bis(dimethylphosphino)methane]tetrachloromolybdenumtungsten and Mo2X4(dmpm)2 (X = bromide, iodide) (1993)
    s.l. : American Chemical Society
    Inorganic chemistry 32 (1993), S. 5183-5187 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00075a040
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  • 9
    Electronic Resource
    Electronic Resource
    Advances in metabolic control analysis (1993)
    s.l. : American Chemical Society
    Biotechnology progress 9 (1993), S. 221-233 
    Details
    ISSN: 1520-6033
    Source: ACS Legacy Archives
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bp00021a001
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular cloning of testicular 20.alpha.-hydroxysteroid dehydrogenase: Identity with aldose reductase (1993)
    s.l. : American Chemical Society
    Biochemistry 32 (1993), S. 1401-1406 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00057a003
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