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  • 1
    ISSN: 0947-3440
    Keywords: Phenazin-5(10H)-yl radicals ; Radical pairs ; π-π-Interactions ; Pimerization ; Dimer absorption ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unit cell of 10-ethylphenazin-5(10H)yl · H2O consists of eight phenazin-5(10H)-yls that are arranged in four independent radical pairs A-D. All pairs show close interplanar distances (3.28-3.36 Å). Furthermore, A, B, and D are characterized by short intermolecular contacts between atoms with significant spin populations. This is not valid for the pair C with the closest interplanar distance of 3.28 Å. Magnetic susceptibility measurements as a function of temperature indicate complete spin pairing (“pimerization”) between 20 and 100 K. Therefore, the radical pair C provides evidence that unspecific close interplanar contacts together with a reasonable overlap of the π systems are sufficient to lead to pimerization.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-193X
    Keywords: 1,4-Benzoquinones ; [2.2]Paracyclophanes ; 1,4,8,11-Pentacenetetrones ; Cyclic voltammetry ; Radical anions ; ESR/ENDOR spectroscopy ; Intramolecular electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three types of tetrone radical anions in which two 1,4-benzoquinone units are connected by ethano (1·-, 2·-), [2.2]paracyclophane (3·-, 4·-), and anthracene bridges (5·-, 6·-) have been studied by ESR and ENDOR spectroscopy. The displacement of the unpaired electron over the two π moieties in the [2.2]cyclophane radical anions 1·--4·- and the marked difference between the first and second reduction potentials, ΔE = |E20 - E10| ≥ 0.20 V, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Similar ΔE data for the syn- (3) and anti-naphthalenophanes (4) indicate that most of the intramolecular electronic interaction takes place through the [2.2]paracyclophane bridge. When ion pairing is inhibited by complexation of the cation, the unpaired electron in 5·- and 6·- is also delocalized over the whole pentacenetetrone system at temperatures as low as 160 K.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-193X
    Keywords: Paracyclophanes ; Cyclic voltammetry ; Radical cations ; ESR/ENDOR spectroscopy ; Intramolecular electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A range of [n.n]paracyclophane radical cations (4·+-12·+), in which two 2,5-dimethoxy-1,4-phenylene units are connected by alkano bridges of varying length, have been studied by ESR and ENDOR spectroscopy. In the [2.2]- and [3.3]paracyclophane radical cations 4·+-6·+, 10·+ and 11·+ the delocalization of the unpaired electron over both π-moieties and the distinct difference between the first and second oxidation potentials, ΔE = E20 - E10, are evidence for a strong intramolecular electronic interaction between the two electrophores. The [5.5] and [7.7] species (8·+ and 9·+) are localized radical cations at low temperature (ca. 220 K). At room temperature, the higher molecular flexibility leads to a significant increase in the number of internal collisions between the electrophores, resulting in a fast (ESR time scale) intramolecular electron transfer. The intermediate [4.4]paracyclophane radical cations 7·+ and 12·+ are apparently also localized radical cations. The close interplanar distance between the two π-moieties, however, facilitates their mutual contacts. In 7·+, the intramolecular electron transfer becomes fast on the ESR time scale at room temperature; in 12·+ the transfer is fast over the temperature range 200-300 K.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1615-1623 
    ISSN: 1434-193X
    Keywords: Homoconjugation ; Cyclovoltammetry ; ESR spectroscopy ; Diketones ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclovoltammetric investigations have been carried out on 3,3,6,6-tetramethylcyclohexane-1,2,4,5-tetrone (4), bicyclo-[3.2.2]nonane-6,7,8,9-tetrone (5), and several of their congeners, such as 6,13-dihydro-6,6,13,13-tetramethylquin-oxalino[2.3-b]phenazine (13), 5,10-dihydro-5,5,10,10-tetra-methylpyrazino[2,3-g]quinoxaline (17), and 6,13-dihydro-6,13-propanoquinoxalino[2,3-b]phenazine (20). For 5 and 20 a large difference (ΔE° ≥400 mV) between the first and second reduction potentials was found. The ESR results of the radical anion 20•- are in support of a strong homoconjugation. ESR studies of 4•-, 13•-, and 17•- also reveal a symmetrical displacement of the unpaired electron over both acceptor groups on the ESR time scale which, however, based on the small potential difference ΔE° ≤ 200 mV can be most likely described to a fast electron exchange.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-193X
    Keywords: [2.2](1,4)Naphthalenophanes ; [2.2](1,4)Anthracenophane ; Pentacene ; Cyclic voltammetry ; Radical cations ; ESR/ENDOR spectroscopy ; Intramolecular electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various radical cations, in which two terminal 1,4-dimethoxybenzene units are anellated to [2.2]paracyclophane (2b•+, 3b•+), [2.2](1,4)naphthalenophane (4d•+), and anthracene bridges (5•+), have been studied by ESR and ENDOR spectroscopy. In the syn- and anti-naphthalenophane radical cations 2b•+ and 3b•+ the delocalization of the unpaired electron over both π-moieties and the distinct difference between the first and second oxidation potentials, ΔE = E20 - E10, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Extension of the bridge in 4d•+ and 5 by benzo anellation results in a localized radical cation. Strong intramolecular electronic interaction between the two electrophores is found in the 1,4,8,11-tetramethoxy-pentacene radical cation (5•+). The syntheses of 4d are described.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0947-3440
    Keywords: Phenazin-5(10H)-yl ; ESR spectroscopy ; Radical pairs ; π Interactions ; Dimer absorption ; Magnetic susceptibility ; Nitrogen heterocycles ; Radicals ; Magnetic properties ; Solid-state chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Introduction of tert-butyl groups into the phenazine frame-work was accomplished by treatment of 5-acetyl-5,10-dihydrophenazine (2a) with tert-butyl chloride in the presence of AlCl3. Starting from the 2,8- or 3,7-di-tert-butyl-substituted derivatives 2c and 2b, a series of phenazin-5(10H)-yl radicals (1c-i) was synthesized and characterized by ESR and EN-DOR spectroscopy. With the exception of 1c, all phenazin-5(10H)-yls were obtained in crystalline form, and for 1d-f the long-wavelength absorption band at λ ≈ 870 nm indicates intermolecular π-π interactions in the solid state. For 1d, 1e and 1h the crystal structure could be determined. The unit cell of 1d consists of eight phenazin-5(10H)-yls. Surprisingly, four of them are arranged in radical pairs, whereas the other four lie independently in the lattice. In agreement with this structure, the magnetic susceptibility results correspond to a content of 50% monoradical and an almost complete spinpairing in the radical pairs up to T = 220 K. In 1e, the four phenazin-5(10H)-yls in the unit cell are arranged in two independent radical pairs, A and B, which are characterized by close interplanar distances and short intermolecular contacts between atoms with significant spin populations. Accordingly, the susceptibility data indicate strong spin-pairing at low temperature. Due to extensive steric shielding of the phenazin-5(10H)-yl framework, the crystal structure of 1h gives no evidence of any π-π interactions between adjacent radicals. As expected, the magnetic susceptibility of 1h corresponds to that of an ordinary monoradical.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1434-1948
    Keywords: Bridging ligands ; Manganese ; Azido bridge ; Alternating chain ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligands 3-ethyl-4-methylpyridine (3-Et,4-Mepy) and azide coordinate to MnII forming an alternating chain with the formula [Mn(3-Et,4-Mepy)2(μ-N3)2]n. This compound crystallizes in the space group P-1. The compound consists of chains of octahedrally coordinated manganese atoms alternately bridged by double end-to-end (μ1,3) and double end-on (μ1,1) azido bridges, which results in a structurally and magnetically alternating chain. The 3-ethyl-4-methylpyridine ligands are arranged trans, completing the six-fold coordination spheres of the manganese atoms. The Mn-Mn distances are distinctly different: Mn(1)-Mn(1A) = 5.149(3) Å (double end-to-end azido bridge) and Mn(1)-Mn(1B) = 3.402(2) Å (double end-on azido bridge). The magnetic properties of the compound, as studied in the temperature range 300-4 K, show bulk antiferromagnetic interaction. Fitting of the magnetic data by using an equation for alternating ferro-antiferromagnetic S = 5/2 1-D systems gives the parameters JAF = -13.7(1) cm-1, JF = 2.4(1) cm-1, g = 2.036(2).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0021-9304
    Keywords: basophils ; mast cells ; metal ions ; toxic histamine release ; apoptosis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Recent data suggest that distinct metal ions can be released from dental alloys or other biomaterials, and may cause toxic effects on various cells. In this study, the effects of 14 metal ions on histamine release from human blood basophils (n = 4), isolated tissue mast cells (lung n = 8, uterus n = 2, skin n = 1, gingiva n = 1), the basophil cell line KU-812, and the mast cell line HMC-1 were analyzed. Of the 14 metal ions, Ag+ (0.33 mM) and Hg2+ (0.33 mM) were found to induce release of histamine in blood basophils, KU-812, mast cells, and HMC-1. The effects of Ag+ and Hg2+ were dose dependent and were observed within 60 min of incubation. In primary mast cells and basophils, Au3+ (0.33 mM) also induced histamine release, whereas no effects of Au3+ on HMC-1 or KU-812 cells were seen. The other metal ions showed no effects on primary or immortal cells within 60 min. However, Pt4+ (0.33 mM) induced histamine liberation in HMC-1 and lung mast cells after 12 h. The Ag+- and Hg2+-induced rapid release of histamine from HMC-1 was associated with ultrastructural signs of necrosis, but not apoptosis. In contrast, prolonged exposure to Pt4+ (0.33 mM, 14 h) induced apoptotic cell death in HMC-1 cells, as assessed by electron microscopy and DNA analysis. Together, certain metal ions induce distinct cytopathogenic effects in mast cells and basophils. Whereas Ag+, Hg2+, and Au3+ cause direct toxicity, Pt4+ causes cell death through induction of apoptosis. Whether such effects contribute to local adverse reactions to metal-containing biomaterials in vivo remains to be determined. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 560-567, 1998.
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0044-8249
    Keywords: Azide ; Festkörperstrukturen ; Magnetische Eigenschaften ; Manganverbindungen ; Perowskite ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0570-0833
    Keywords: azides ; magnetic properties ; maganese compounds ; perovskites ; solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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