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  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 709-722 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed.
    Additional Material: 4 Ill.
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configuration of several keto-cyclolignans related to podophyllotoxin has been reviewed. Under basic catalysis, the configuration at the C-atom in α-position to the lactone carbonyl group in podophyllotoxone is inverted instead of the C-atom in α-position to the ketone group, as it has been reported.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1039-1049 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Local and nonlocal density functional computations have been carried out to study the electronic structure and the equilibrium geometry of the isoelectronic series Cr(NC)4, Mn(NO)3(CO), Fe(NO)2(CO)2, and Co(NO)(CO)3 and model compounds Fe(NO)2L2 (L = Cl, HCN, NH3, PH3, and C2H4). The structure of Fe(NO)2(C4H6) is also described. The discussion is focused on structural modifications through a change of ligand, in particular those concerning the metal-nitrosyl conformation (linear vs. bent). Though this is a preliminary study of metal-nitrosyl properties by DFT methods and more computations are required to analyze the mechanism of homogeneous catalysis processes, our results support the hypothesis that structural reorganization from linear to bent metal-nitrosyl plays a key role in some reactions, such as in butadiene dimerization. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 4
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vibrational frequencies of NaN clusters (2 ≤ N ≤ 72) are calculated by direct diagonalization of the dynamical matrix. Density functional theory with a spherically averaged pseudopotential is used to compute the total energy. The geometry is optimized by the simulated annealing technique. Contributions to the Hessian matrix due to electron relaxation following the ionic displacements are calculated in linear response theory. The frequencies are in the range 0-220 cm-1 and the electron relaxation strongly modifies those of the modes dominated by radial oscillations, particularly the breathing mode frequencies that are proportional to N-1/3. The filling of atomic shells produces a stepwise behavior of the highest frequencies. The giant dipole resonance energies are obtained as a byproduct of the calculation. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1988 (1988), S. 737-742 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthese von Pyrimidin-Analoga des Nucleosid-Antibiotikums AscamycinVier Analoga des Ascamycins 〈5′-O′-O-[N-(L-alanyl)sulfamoyl]-2-chloradenosin〉(1), bei welchen der 2-Chloradenosinrest durch Uridin, Thymidin, Cytidin und 2′-Deoxy-5-methylcytidin ersetzt wurde, sind durch selektive Aminoacylierung der 5′-O-Sulfamoyl-Derivate 2, 9, 14 und 21 des 2′,3′-Di-O-acetyluridins, 3′-O-Acetylthymidins, 2′,3′-O-Isopropylidencytidins, bzw. des 3′-O-Acetyl-2′-deoxy-5-methylcytidins mit Boc-L-Ala-OSu in DMF und in Anwesenheit von DBU, mit nachfolgender Abspaltung der Schutzgruppen, erhalten worden. Ähnlich wurde 5′-O-[N-(D-Alanyl)sulfamoyl]uridin (8) ausgehend von Boc-D-Ala-OSu und 2 hergestellt. Die Verbindungen 14 und 21 wurden direkt durch Sulfamoylierung der 4-N-(Dimethylamino)methylen-Derivate 13 und 20 von 2′,3′-O-Isopropylidencytidin bzw. 3′-O-Acetyl-2′-deoxy-5-methylcytidin über die 5′-O-Tributylzinn-Zwischenverbindungen dargestellt. Verbindung 20 wurde aus 5′-O-Isopropylidencytidin bzw. 3′-O-Acetyl-2′-deoxy-5-methylcytidin über die 5′-O-Tributylzinn-Zwischenverbindungen dargestellt. Verbindung 20 wurde aus 5′-O-(tert-Bu-tyldimethylsilyl)thymidin (17) mittels Acetylierung und nachfolgende Überführung des Thymidinrestes in 5-Methylcytosin über das entsprechende Triazolylpyrimidinon unter Schutz der Amidingruppe erhalten.
    Notes: Four analogues of ascamycin 〈5′-O-[N-(L-alanyl)sulfamoyl]-2-chloroadenosine〉 (1) in which the 2-chloroadenosine moiety has been replaced by uridine, thymidine, cytidine, and 2′-deoxy-5-methylcytidine have been synthesized by selective aminoacylation of the 5′-O-sulfamoyl derivatives 2, 9, 14, and 21 of 2′,3′-di-O-acetyluridine, 3′-O-acetylthymidine, 2′,3′-O-isopropylidenecytidine, and 3′-O-acetyl-2′-deoxy-5-methylcytidine, respectively, with Boc-L-Ala-OSu in DMF and in the presence of DBU, followed by removal of the protecting groups. Similarly, 5′-O-[N-(D-alanyl)sulfamoyl]uridine (8) has been prepared from Boc-D-Ala-OSu and 2. Compounds 14 and 21 were directly prepared by sulfamoylation of the 4-N-(dimethylamino)methylene derivatives 13 and 20 of 2′,3′-O-isopropylidenecytidine and 3′-O-acetyl-2′-deoxy-5-methylcytidine, respectively, via the intermediate 5′-O-tributyltin derivatives. Compound 20 was obtained from 5′-O-(tert-butyldimethylsilyl)thymidine (17) by a route involving acetylation, conversion of the thymidine moiety into 5-methylcytosine through the corresponding triazolylpyrimidinone, and amidine protection.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1675-1688 
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We have carried out theoretical calculations to analyze molecular interactions and proton transfer mechanisms in the formate-imidazole-water system, which may be considered the simplest model of catalytic triads in serine proteases. Computations were carried out at the density functional theory level. The effect of a dielectric environment on energy surfaces is considered using a polarizable continuum model and the self-consistent reaction field approach. The role played by inertial and noninertial polarization of this environment is emphasized. Nonequilibrium solvation effects have been estimated. The results show that there are different reaction mechanisms, concerted or stepwise, that may be competitive, depending on the nature of the molecular environment.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1675-1688, 1998
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 19-29 
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A theoretical model to investigate chemical processes in solution is described. It is based on the use of a coupled density functional/molecular mechanics Hamiltonian. The most interesting feature of the method is that it allows a detailed study of the solute's electronic distribution and of its fluctuations. We present the results for isothermal-isobaric constant-NPT Monte Carlo simulation of a water molecule in liquid water. The quantum subsystem is described using a double-zeta quality basis set with polarization orbitals and nonlocal exchange-correlation corrections. The classical system is constituted by 128 classical TIP3P or Simple Point Charge (SPC) water molecules. The atom-atom radial distribution functions present a good agreement with the experimental curves. Differences with respect to the classical simulation are discussed. The instantaneous and the averaged polarization of the quantum molecule are also analyzed. © 1996 by John Wiley & Sons, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Gamete Research 18 (1987), S. 319-332 
    ISSN: 0148-7280
    Keywords: sperm membrane ; stallion spermatozoa ; spermatic maturation ; ultrastructural cytochemistry ; cellular microelectrophoresis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The structure, relative density, and distribution of anionic sites on the surface of epididymal and ejaculated spermatozoa were studied using polycationic ferritin (CF), colloidal iron hydroxide (CIH), various enzymatic treatments, methylation, and de-acetylation. Macro-molecules containing sugar residues, probably sialic acid, are part of the sperm membrane and show a characteristic distribution and density that is dependent of the sperm region and of its origin. Unlike the spermatozoa of other eutheria examined, the exposure of the stallion spermatozoa to neuraminidase treatment did not produce significant changes in the density of the negative charge of the sperm surface. The ability of purified neuraminidase to act only after saponification suggests that sialic acid may be present in the acetylated form. When CIH was used it is seen that the density of the negative charge is rather uniform within a particular segment of the spermatozoa and abruptly changes at the junction of morphologically distinct segments (Between the acrosomal and post acrosomal region of the sperm head and between the post acrosomal region and middle piece of the flagellum). The acrosome presented more negative groups dissociated at pH 1.8 than the postacrosomal region. A greater concentration of anionic sites over the flagellum was also observed when CIH and CF were used. This assymetry probably represents different domains that may be related to specific functions.The cytochemical observations and the cellular electrophoretic mobility measurements did not show striking differences on the negative charge of sperm obtained from different regions of epididymis and ejaculates in contrast to previous results in other species. The spermatozoa collected from caput epididymidis bind CIH but not all population present equal response. In corpus and cauda region of epididymis the population displaying the capacity to bind CIH or CF significantly over the head and tail surface was the majority.This study corroborates that the distribution and density of terminal oligosaccharide residues on the sperm plasma membrane has species specific characteristics. The surface charge of the spermatozoa obtained either during the breeding or nonbreeding season, determined by measurements of cellular electrophoretic mobility and by the binding pattern of CIH and CF, does not show significant differences.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 15 (1994), S. 479-487 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The effect of correlation energy, basis set size, zero-point energy (ZPE) correction, and solvation on the reaction mechanism of the ketene-imine cycloaddition reaction has been investigated. The electrostatic solvent effect was studied with a self-consistent reaction field method in which the solvation energy is obtained using a multipole expansion of the molecular charge distribution. The ab initio results have been analyzed by means of a theoretical method based on the expansion of the MOs of the supermolecule in terms of those of the reactants and the performance of the configuration analysis. In gas phase, due to the correlation energy and/or the ZPE corrections, the reaction is predicted to be a one-step process. In solution, the stabilization of the charge-transferred configurations results in the occurrence of a very stable, Zwitterionic intermediate giving a two-step mechanism. © 1994 by John Wiley & Sons, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1826-1833 
    ISSN: 0192-8651
    Keywords: quantum-chemical computations ; β-lactams ; ester enolate-imine condensation ; solvent effect ; stepwise process ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The condensation reaction of the enolate of methyl acetate with formaldimine to afford a β-lactam was studied using the MP2-FC/6-31+G* level of theory taking into account the electrostatic effect of the solvent by means of a self-consistent reaction field continuum model. The reaction is a stepwise process with three main steps: the formation of the C3(SINGLE BOND)C4 bond, the closure of the β-lactam ring, and the elimination of the methoxide ion. The formation of the C3(SINGLE BOND)C4 bond is rate determining and according to our calculations is not a reversible step.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1826-1833, 1998
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