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  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pentacyclic triterpenes 1a, b and 2a, b are isolated from extracts of Euphorbia mellifera Arr. Their structures, determined by X-ray analysis, are supported in part by MS, NMR, and IR data. The skeleton differs from that of representatives of the lupane or hopane class by (i) an unusual arrangement of the substituents in the cyclopentane ring E, the Me group being on C(19) and the i-Pr group in an angular position on C(17), and (ii) a cis D/E ring junction. We propose to name Die unknown pentacyclic parent ‘madeirane’, thus 1a, b and 2a, b are D-friedomadeir-14-ene and D:C-friedomadeir-7-ene derivatives. The biosynthesis of these compounds may be rationalized via ‘spirodammaranol’-cation intermediates 5 and 5′ and madeiranol cation 6, as outlined in Scheme 2.
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 411-418 
    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: A theoretical prediction of the absorption spectra in n-doped semiconductors due to donor pairs is extended further to investigate its contribution to the refractive index of phosphorus-doped silicon. Such a contribution yields a polarization catastrophe at the metal-nonmetal transition. The alternant molecular orbital with a many-valley character of the host material is used in the calculation. The results show good agreement with experiments.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 41 (1992), S. 517-524 
    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 density of states is calculated for a random distribution of donor-pairs of hydrogenlike impurities in three- and two-dimensional systems. Recent investigations of the hydrogen molecule in the alternant-molecular-orbital approximation are here extended. We found that the lowest excited state 1Σu (i.e., H+H-), which is optically connected to the ground state, plays a relevant role in the absorption spectra of semiconductor systems.
    Additional Material: 8 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1137-1147 
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalysts ; propylene polymerization ; catalysts characterization ; supported catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article we present the results of the preparation and characterization of two Ziegler-Natta precatalysts: MgCl2/Ethyl benzoate (EB)/TiCl4 and MgCl2/2,2,6,6 tetramethylpiperidine (TMPiP)/TiCl4 by means of FTIR, X-ray diffraction, SEM, BET surface area measurements, and other techniques applied at different steps of their preparation procedures.The precatalysts were prepared by impregnating with TiCl4 a given amount of MgCl2, which was previously ball-milled with the electron donor chosen.Prior to impregnation, the ball-milled material presented different surface compounds depending on the electron donor used: [(MgCl2)2] · 2EB, MgCl2 · EB, or a salt of the amine. The solid milled with EB is more homogeneous than the one milled with the TMPiP.Titanium is better retained in the solid milled with EB. This precatalyst has better morphological properties and larger BET surface area. By means of FTIR, we found evidences that an adequate surface structure for the formation of stereospecific sites in MgCl2/TMPiP/TiCl4 was formed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 25 (1993), S. 336-344 
    ISSN: 0886-1544
    Keywords: MTOC ; dendrites ; neurite extension ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Centrosomes are unique cytoplasmic structures which serve as microtubule organizing centers (MTOC). In most animal cells centrosomes consist of one or more pair of centrioles surrounded by electron dense amorphous pericentriolar material (PCM) responsible for nucleation of microtubules. In the present study we analyzed the pattern of induction and localization of proteins of the PCM at different stages of neuronal development in cell cultures prepared from the embryonic hippocampus. For this purpose we used a human polyclonal antibody that recognizes two proteins of the PCM (100 kd and 60 kd, respectively). The results indicate that in mature neurons, pericentriolar immunoreactive material is preferentially localized in dendritic processes, and that throughout the course of neurite development and differentiation it is systematically excluded from the neuron's axon. Western blot analysis showed that during neuronal development in situ, there is an increase in he immunoreactivity for both proteins recognized by this antibody. In contrast, in hippocampal pyramidal neurons that develop in culture, there is an increase in the 60 kd polypeptide, while the 100 kd one is not detected after 7 days in vitro. © 1993 Wiley-Liss, Inc.
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  • 6
    ISSN: 0003-3146
    Keywords: polyethylene ; photo-oxidation ; weathering ; mechanism ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the natural and accelerated photo-oxidation of low-denisty polyethylene (LDPE) films have been studied; different geographical locations have been selected for the natural tests, and a range of temperatures used in the accelerated experiments in a specially built temperature-controlled ultraviolet radiation enclosure. A meaningful correlation between natural and accelerated weathering results was established, by means of an adequate superposition of the effects of UV radiation exposure and temperature. Reasonably detailed and accurate, lumped-parameter, kinetic models of the photo-oxidation process have also been developed, to interpret and predict the results of measurements of carbonyl, hydroperoxide and vinyl absorbances as functions of time and temperature; the models predict the general experimental behaviour, and also that both the formation of hydroperoxides and carbonyl Norrish-I reactions are important initiation steps. More complex models have the potential of interpreting other fine details of the degradation behaviour, namely the generation of other chemical species, and the chain scission and cross-linking process which are directly related to changes in the mechanical properties.
    Additional Material: 10 Ill.
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  • 7
    ISSN: 0730-2312
    Keywords: Hps47 ; 78 procollagen ; molecular chaperones ; metabolic stress ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Hps47, Grp78, have been implicated with procellagen maturation events. In particular Hps47 has been shown to blind to nascent procellagen α1(I) chains in the course of synthesis and/or translocation into the endoplasmic reticulum (ER). Although, Hsp47 binding to gelatin and collgen has previsously been suggested to mechanism. The early association of Hps47 with procollagen and its relatively late relese suggested that other chaperones, Grp78 and Grp94, interact successively or concurrently with Hps47. Herein, we examined how these events occurs in cells metabolically stressed by depletion of ATP. In cells depleted of ATP, the releses of Hps47, Grp78, and Grp94 from maturing procollange is delayed. Thus, in cell experiencing metabolic stress, newly synthesized procollagen unable to property fold became stable bound to a complex of molecular chaperones. In that Hps47, Grp78, and Grp98 could be recovered with nascent procollagen and as oligomer in ATP depleted cells suggests that these chaperones function in a series of coupled or successive reactions.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The partial decomposition of PF6- during pyrrole electropolymerization in methanol and acetonitrile on Fe and Pt electrodes is demonstrated using XPS analysis. A complex mixture of PF6-, fluorides of phosphorus and metal oxides is shown to exist in the interfacial region, probably resulting in a weak cohesive layer unfavourable to the adhesion of polymer films.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 885-890 
    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 use of principal components as a basis for a graphical procedure to analyze polar tensor data is proposed. Molecular orbital and experimental polar tensor data for all possible sign combinations of the ∂p/∂Qj of CHCl3 and CDCl3 are represented graphically as principal component scores facilitating sign selection for the ∂p/∂Qj. The graphs are particularly useful in analyzing an apparent conflict in ∂p/∂Qj sign choices based on the isotopic invariance criterion and molecular orbital results for the A1 symmetry species of these molecules. The numerical impacts of individual sign ambiguities for the ∂p/∂Qj on the polar tensor data are measured by the variances associated with the principal components. Assuming the ∂p/∂Qj sign sets with indeterminate signs provide replicated results for the polar tensor elements, their errors are estimated and compared with errors obtained previously by propagating intensity uncertainties through the polar tensor equations.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 1114-1120 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A mass spectrometric study of eight new carbohydrate derivatives has been carried out to determine the influence of structure on the fragmentation mechanisms of stereoisomers. Results indicate that the relative intensities of peaks due to fragment ions of each pair of isomers are sometimes very different, especially those observed in the collision-induced decomposition mass spectra of [MH]+ ions. Metastable decompositions related to identical fragmentation processes of two isomers release different amounts of kinetic energy, however. It is usually observed that the kinetic energy released is larger for the S-configuration than for the R-configuration of the two epimers of a particular species.
    Additional Material: 6 Ill.
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