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  • Wiley  (41)
  • Wiley-Blackwell  (31)
  • 1995-1999  (64)
  • 1955-1959  (8)
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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 methanolysis of the epimeric 7-chloro-7H-yohimbine derivatives 2 and 3 was reinvestigated. In case of the 7α-epimer 2, the reaction was uneventful and conformed with earlier observations, i.e., under sufficiently mild conditions, only the imino ether 4 (= imino ether A) was produced. Under the same conditions, the less reactive β-isomer 3 furnished a mixture of both imino ethers 4 and 5, accompanied by the elimination product 11, and by equal amounts of yohimbine (1) and 3,4,5,6-tetradehydroyohimbine (12), which are believed to arise through a disproportionation process of the putative intermediate 5,6-didehydroyhimbine (23). The nature of this divergent reactivity and of the ready equilibration of 4 and 5 was investigated by means of extensive force-field and semi-empirical calculations (AM1 and PM3) of various conformers of the compounds 2-5 and of some possible reaction intermediates.
    Additional Material: 7 Tab.
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  • 2
    ISSN: 0947-3440
    Keywords: Conformational analysis ; Force field calculations ; MM3 ; Polyketide natural products ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4-Dimethylpentane (1) is a typical biconformational backbone segment. When one methyl group in 1 is replaced by a sp2 bound residue (vinyl, formyl, phenyl), as in compounds 3-6, a small preference for conformer 2b ensues, in which the sp2 bound group resides in the sterically more hindered position. Oxygen substituents in the 3-position do not change this conformational preference, but in concert with bulkier sp2-hybridized groups in the 2-position, a preference for the 2a backbone conformation may be induced, in which the sp2-hybridized group is in the less sterically hindered end-of-chain position, cf. compounds 20 and 23.
    Additional Material: 3 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 869-876 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; silaguanidinium cations ; silylium cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantium mechanical calculations at the MP2/6-31 G(d) level are reported for the silaguanidinium cation Si(NH2)3+ (1) and derivatives thereof. The equilibrium structure 1a has D3 symmetry with planar amino groups rotated out of the SiN3 plane by 19.60. The Si-N bond length of 1 a (1.658 Å) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation 1 a by the amino groups (63.5 kcal mol-1) is about 40% of the resonance stabilization of the guanidinium cation (159.3 kcal mol-1), but 1 a is clearly better stabilized than alkyl-substituted silylium cations. The electronic stabilization of 1 a by the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6- 31 G(d) is markedly lower for Si(NH2)3-(H2O)+ (6) (28.8 kcal mol-1) than for SiMe3(H2O)+ (40.6 kcal mol-1). The tris(dimethylamino) silylium cation Si(N-Me2)3+ (8) is even more stable than 1 a. The complexation energy of Si(NMe2)3-(H2O)+ (10) is only 17.3 kcal mol-1. IGLO calculations of the 29Si N M R chemical shifts predict that 1 a and 8 should not show the same extremely low shielding that is calculated for alkyl-sub-stituted silylium ions. The calculated 29Si resonances for 8 are in reasonable agreement with the experimental N M R spectrum of (Me2N)3 SiB(C6F5)4. AM 1 calculations predict that the substituted tripyrrolidino silylium cation 12 would be an even better candidate for a stable tricoordinate silylium cation in condensed phases. One of the pyrrolidine rings of 12 has tert-butyl groups in the 2 and 5 positions, which serve as a steric fence around the silicon atom.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 732-746 
    ISSN: 0006-3592
    Keywords: Desulfovibrio vulgaris ; hydrogen cycling ; kinetics ; thermodynamics ; modeling ; anaerobic ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A unified model for the growth of Desulfovibrio vulgaris under different environmental conditions is presented. The model assumes the existence of two electron transport mechanisms functioning simultaneously. One mechanism results in the evolution and consumption of hydrogen, as in the hydrogen-cycling model. The second mechanism assumes a direct transport of electrons from the donor to the acceptor, without the participation of H2. A combination of kinetic and thermodynamic conditions control the flow of electrons through each pathway. The model was calibrated using batch experiments with D. vulgaris grown on lactate, in the presence and absence of sulfate, and was verified using additional batch experiments under different conditions. The model captured the general trends of consumption of substrates and accumulation of products, including the transient accumulation and consumption of H2. Furthermore, the model estimated that 48% of the electrons transported from lactate to sulfate involved H2 production, indicating that hydrogen cycling is a fundamental process in D. vulgaris. The presence of simultaneous electron transport mechanisms might provide D. vulgaris with important ecological advantages, because it facilitates a rapid response to changes in environmental conditions. This model increases our ability to study the microbial ecology of anaerobic environments and the role of Desulfovibrio species in a variety of environments. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:732-746, 1998.
    Additional Material: 6 Ill.
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  • 5
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 89 (1956), S. 2424-2429 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxydiacetyl liegt praktisch vollständig als Diketon vor, gibt aber in polaren Lösungsmitteln Reduktonreaktionen. Es unterscheidet sich hierin vom Hydroxybrenztraubenaldehyd.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 67 (1995), S. 1486-1489 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 63-72 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Dithienium and 1,3-Dithiolenium Salts. IX. Reactions of 1,3-Dithiane-2-ylium Tetrafluoroborates with C-Nucleophiles1,3-Dithian-2-ylium tetrafluoroborates (1), which can be easily obtained by variable methods, react in good to excellent yields with variable C-nucleophiles to new geminal disubstituted 1,3-dithianes. The latter compounds are potential precursors of interesting synthetic building blocks. Reactions are described with 2-lithio-1,3-dithianes 2, sodium cyanide 4, sodium salts of the nitro alkanes 7 and CH-acids of the type of the 1,3-dicarbonyl compounds 9. The reduction of 3-oxo-2-(2-phenyl-1,3-dithian-2-yl)-ethoxybutanoat-following a diastereoselective pathway - leads to the Cram product 11. Further presented is the crystal structure of 2-phenyl-1,3-dithiane-2-ylium tetrafluoroborate (1b).
    Additional Material: 1 Ill.
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  • 9
    ISSN: 0947-3440
    Keywords: Carotenoids ; Isonorastacene synthesis ; Singlet oxygen ; Effective chain length ; Second-order quenching rate constants ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bimolecular rate constants kq for quenching of singlet oxygen (1Δg state) by 26 different natural and novel synthetic carotenoids were determined at 37 °C in a mixture of chloroform and ethanol. The steady-state technique used involves the generation of 1O2 by thermal decomposition of disodium 3,3′-naphtalene-1,4-diyl-dipropionate endoperoxide (NDPO2) and the detection of its luminescence intensity at 1270 nm. Excitation energies (π,π*, 11Ag → 11Bu) and absorption maxima (430-590 nm) vary in the broadest range. Deeply coloured blue carotenoids are also included in the studies for the first time. An empirical correlation between the π,π* (11Ag → 11Bu) excitation energy and carotenoid structure (effective chain length Neff) was found: E(S) = 12642 cm-1 + 92027 cm-1 × 1/Neff. The quenching ability of the investigated carotenoids depends on the excitation energy of their transition at long wavelengths in a characteristic way showing as limiting factors either the thermal Arrhenius activation or the diffusion-controlled rate. This dependence and the suspected relationship between singlet E(S) and triplet E(T) energies, respectively, are discussed.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 337 (1995), S. 441-445 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regioselective sulfation of a Lex-trisaccharide having free hydroxyl groups in 2-, 3- and 4- position of the galactose elucidated their different reactivities and gave mono- and disulfated Lex derivatives.
    Additional Material: 2 Ill.
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