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  • Articles  (88)
  • Wiley  (41)
  • Wiley-Blackwell  (31)
  • Springer Nature  (10)
  • International Union of Crystallography (IUCr)  (6)
  • 1995-1999  (80)
  • 1955-1959  (8)
Collection
  • Articles  (88)
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Year
Journal
  • 1
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 0-0 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 2179-2182 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 383-387 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Single crystals of caesium titanyl arsenate (CTA, CsTiOAsO4), with space group Pna21 and isomorphous with potassium titanyl phosphate (KTP, KTiOPO4), have been studied using high-resolution synchrotron X-rays. During the experiments, an electric field was applied along the polar axis [001]. Single-crystal plates, between 300 and 450 μm thick along [001], were polarized by a variable square wave of frequency 20 Hz alternately applied to each side of the plate. A field-induced splitting of the + /− peaks for reflections hkl with l ≠ 0 was observed. This splitting provides information about the coercive field, polarizability and the piezoelectric strain tensor. Two of the piezoelectric coefficients of CTA could be estimated as d31 ∼ 1 and d33 ∼ 27 pm V−1. Whereas the coercive fields were estimated at 2300 V mm−1, the field necessary to reverse the domains just once in CTA was found to be either 560 or 1550 V mm−1, depending on the polarity of the reversed domain in relation to the polarity of the nonswitched part of the crystal.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 514-519 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Trirutiles are AB2O6 crystal structures with a tripled c-axis repeat compared to the rutile type, owing to ABBABBA metal ordering. Partially disordered trirutiles, space group P42/mnm, are here described by addition of a sinusoidal scattering density wave along c to the basic rutile structure. As a result of this approach, an infinite number of crystal structures can be envisaged, which pairwise exhibit identical X-ray diffraction patterns, i.e. this is a case where the expected one-to-one relationship between crystal structure and diffraction intensity distribution is replaced by a two-to-one relationship
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 717-720 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The icosahedral nucleocapsid of human hepatitis B virus is a homopolymer of the dimeric capsid protein also known as hepatitis B core antigen or HBcAg. Purified capsid protein obtained from an Escherichia coli expression system was reassembled into a mixture of T = 3 and T = 4 icosahedral particles consisting of 90 and 120 dimers, respectively. The two types of capsid were separated on a preparative scale by centrifugation through a sucrose gradient. In addition to this heterogeneity, the capsid protein has three cysteines, one of which has a great propensity for forming disulfide bonds between the two subunits, forming a dimer. To eliminate heterogeneity arising from oxidation, alanines were substituted for the cysteines. T = 3 and T = 4 capsids crystallized under similar conditions. Crystals of T = 3 capsids diffracted to ∼8 Å resolution; crystals of T = 4 capsids diffracted to 4 Å resolution.
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  • 6
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 221-230 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of Sb0.9V1.1O4, antimony vanadium oxide, has been studied by powder X-ray diffraction, electron diffraction and high-resolution electron microscopy (HREM). The X-ray powder diffraction pattern showed only basic rutile reflections [ar = 4.6085 (1), cr = 3.0867 (1) Å] and the basic rutile structure was refined using the Rietveld method. A rutile superstructure was revealed when the sample was studied by electron diffraction. The electron diffraction patterns were indexed on the unit cell a = 21/2ar, b = 21/2br, c = 2cr. Its space group, I41md, was determined by means of convergent-beam electron diffraction (CBED). A structural model based on alternating cation ordering along c in the chains of edge-sharing octahedra is proposed and its electron diffraction patterns and HREM image are calculated and matched with the experimental ones.
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    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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