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  • 1
    ISSN: 1059-910X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The density of intramembranous protein particles was studied by freeze-fracture. Particle density on the fracture faces of the plasmalemma and the rough endoplasmic reticulum (RER), as well as the outer and inner membranes of the nucleus and the mitochondria in rat hepatocytes were quantified. Comparison among different age groups sampled days postcoitum (dpc), days postpartum (dpp), and months postpartum (mpp) shows age-related changes in particle density in each membrane system. With the exception of the RER, particle densities increased after the 16th dpc, reached a maximum at birth, and then decreased with increasing age. Simultaneously, the number nuclear pores shows a positive correlation with the particle density of the nuclear membranes. The particle density on the membranes of the RER shows a maximum on the 16th dpc, and on the 6th dpp. Thereafter, the density of the RER decreases slightly. In all membrane systems, the density of the particles on the external fracture faces is more variable than the density of the particles on the protoplasmic fracture faces.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Hydrogen transfer ; Photochemistry ; Solid-state chemistry ; Topochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Due to the matrix effect of the crystal lattice, irradiation of ketone 1 yields 2 diastereoselectively as the main product (97% de). Furthermore, the chiral crystal environment in single crystals of 1 (space group P212121) also renders the reaction enantioselective (86% ee). Both enantiomers of alcohol 2 could be produced, depending on which enantiomorphic form of the chiral crystal was irradiated. As the ketone 1 is achiral and the chiral induction is caused exclusively by physical influences, this reaction represents a further example of an absolute asymmetric synthesis.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-193X
    Keywords: Crystal engineering ; Diynes ; Photochemistry ; Solid-state chemistry ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diynes 4a-c were obtained from the corresponding 2,5-dimethoxybenzenes 1 by bromination followed by a copper-catalyzed Grignard reaction with 3-bromoprop-1-yne. Catalyzed coupling of the resulting 3-(2,5-dimethoxyphenyl)prop-1-ynes 3 under Hay conditions gave the hexa-2,4-diynes 4a-c in good yields. The molecular structures of the diynes 4a and 4b were determined by X-ray diffraction analysis. In each crystal structure, an unusual 1,6-synperiplanar conformation of the hexa-2,4-diyne unit is observed, with the 1,6-diphenyl substituents arranged in a coplanar orientation. According to the crystal structure data obtained, irradiation of diynes 4a and 4b afforded the deeply-colored, highly-ordered polymers 5a and 5b under topochemical control. Oxidation of 4a and 4b with cerium(IV) ammonium nitrate gave the corresponding 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diyne-1,6-diones 6a and 6b.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1647-1651 
    ISSN: 1434-193X
    Keywords: Fullerenes ; Anthracene ; Photooxidations ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Anthracene groups have been linked to [60]fullerene by the [3+2] cycloaddition of the corresponding nitrile oxides or by esterification with a [60]fullerenol. The anthryl groups of the fullerene derivatives 3, 7, and 10 react readily with singlet oxygen to form the 9,10-epidioxides 4, 8, and 12 under photooxidation. The anthryl moiety of the fullerenol ester 10 also reacts with the fullerene skeleton to form the stable intramolecular Diels-Alder adduct 11.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 595-604 
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Photochemistry ; Quinones ; Solid-state chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2,5-bisacrylate-substituted 1,4-benzoquinone bisketal 7a was synthesized by electrochemical oxidation of the corresponding dimethoxybenzene 6. The methyl ester 7a was transesterified to the corresponding ethyl, n-propyl and isopropyl esters 7b-7d by Ti(OEt)4 catalysis and to the corresponding n-butyl and benzyl esters 7e-7f by the Li alkoxides. The bisketals 7a-7f were hydrolyzed to the corresponding 2,5-bisacrylate-substituted 1,4-benzoquinones 1a-1f. The crystal structure of the ethyl ester 1b was determined by X-ray diffraction, which revealed short intermolecular contacts of 3.463 and 4.051 Å between vinyl groups and quinone double bonds, respectively, related by twofold symmetry. Because of the shorter distance and the smaller shift in projection (vinyl: 1.002; quinone: 2.107 Å), only the vinyl group is photoactive in the crystal. In the solid state, topochemically controlled [2+2] photocycloadditions take place at the vinylic groups of the bisvinyl quinones 1a-1f, to afford dimers and oligomers (nmax = 7), under topochemical control. The cyclobutane units generated from 1b and from 1c-1f have twofold and centric symmetry, respectively, as determined by 1H-NMR spectroscopy and simulation thereof. The twofold symmetry in the cycloaddition products of 1b is in agreement with the crystal structure of the monomers.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 605-626 
    ISSN: 1434-193X
    Keywords: Crystal engineering ; Cycloadditions ; Photochemistry ; Quinones ; Solid-state reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the course of topochemical investigations of substituted quinones the 2-monovinyl-substituted 1,4-benzoquinones 1 were synthesized by electrochemical oxidation of the corresponding 1,4-dimethoxybenzene derivatives 3 to the quinone bisketals 4 and subsequent hydrolysis. In solution, the aryl-substituted vinylquinones 1a-1t underwent unexpected Diels-Alder additions. The stereochemically unique course of the reaction was proved spectroscopically and by X-ray structure analysis of the dimer 8k. As a basic requirement for the topochemical studies, the crystal structures of eight quinones 1 were determined by X-ray diffraction. In the crystals of 1a, 1c, 1e, 1f, 1i and 1n with an α-type packing arrangement, the vinylic double bonds have short contacts (〈 4.4 Å) across a centre of symmetry. The quinone 1k crystallizes in a β arrangement with short distances (〈 4.0 Å) between molecules related by translation and in a γ arrangement without suitable contacts. The crystals of all quinones 1 were irradiated with UV light to perform [2+2] cycloadditions. The photoreactive quinones dimerized exclusively at the vinylic double bonds, resulting in the corresponding cyclobutanes 9. Topochemically controlled the dimers 9a-9c, 9e, 9l-9n, 9q, 9r and 9u with molecular Ci symmetry were formed whereas the dimers 9k and 9t have Cs symmetry. The structures of the cyclobutanes were determined by spectroscopical investigations and in the case of 9b, 9e and 9r additionally by X-ray analysis. Despite short contacts, crystals of 1f and 1i were photostable. This is probably because of insufficient lattice flexibility indicated by relatively high densities.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 137 (1988), S. 421-429 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cumene hydroperoxide (Chp), a lipophilic peroxide, and hydroxy-nonenal (HNE), a breakdown product of lipid peroxides, were used as model compounds to assess the effects of lipid peroxidation upon cell proliferation. Amniotic fluid fibroblastlike (AFFL) cells and human diploid skin-derived (HDFL) cells were cultured with the two model compounds and cell proliferation was assayed via bromodeoxyuridine-Hoechst flow cytometry. At low doses Chp elicited an accumulation of cells in the S and G2 phase, while at higher doses the fraction of nonproliferating cells increased as well. Low doses of HNE caused an accumulation of cells in the G1 and G2 phase, whereas an additional increase of cells in S phase and in the nonproliferating fraction was found at an elevated concentration. A delay of onset of proliferation was obtained with both Chp and HNE. Permanent arrests in the S, G2, and G1 compartment are provoked by Chp only when Chp was applied together with serum. HNE, to the contrary, elicited a permanent arrest in the G2 and the G1 compartment even if added to quiescent cell cultures. Additionally, HNE caused a combination of a prolongation of the G1 phase of the cell cycle and an arrest in this compartment, which is reminiscent of cell differentiation. HDFL cells were much more sensitive toward Chp than were AFFL cells, but both cell types showed similar sensitivities toward HNE. We conclude that lipophilic peroxides exert toxic effects upon cell proliferation distinct from the pattern elicited by aldehydic breakdown products of lipid peroxides. The pattern of cell cycle arrest induced by Chp and HNE makes it unlikely that Chp and HNE, or related products of lipid peroxidation, are responsible for the limitation of the proliferative life span of human fibroblasts in culture.
    Additional Material: 4 Ill.
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  • 10
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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