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  • 1
    Electronic Resource
    Electronic Resource
    A conformational analysis of mono and dialkyl ethers of 2,2′-dihydroxy-1,1′-binaphthalene by circular dichroism spectroscopy and cholesteric induction in nematic liquid crystals (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 353-358 
    Details
    ISSN: 0899-0042
    Keywords: circular dichroism ; liquid crystal conformational analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coupling of the analysis of the absorption and circular dichroism (CD) spectra with that of the cholesteric mesophases induced in nematic liquid crystals indicated some interesting conformational features of bridged and nonbridged mono- and dialkylethers of optically active 2,2′-dihydroxy-1,1′-binaphthalene. Bridged derivatives are characterized by relatively small dihedral angles. Simple monoalkyl ethers are characterized by larger dihedral angles but they all assume an s-cis conformation, owing to the existence of intramolecular hydrogen bonds. Nonbridged dialkylethers prefer even larger dihedral angles and, depending on the bulkiness of the alkyl groups, the s-trans conformation can be found. Interestingly, the conformation of dialkylethers is strongly dependent on the structure of the liquid crystal solvent, because the intramolecular hydrogen bond is not possible there. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070508
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  • 2
    Electronic Resource
    Electronic Resource
    The Self-Recognition and Self-Assembly of Folic Acid Salts in Isotropic Water Solution (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 220-234 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of alkaline folates in isotropic water solutions, with or without added salts, has been investigated by small-angle neutron-scattering, circular-dichroism, and NMR techniques. The assembled species are chiral, cylindrical aggregates of finite length, composed of stacked tetramers; each tetramer is formed by Hoogsteen-bonded folate residues. The assembly process is more efficient in the presence of an excess of NaI ions, leading to longer aggregates with stronger tetramer-tetramer-tetramer interaction. In pure water, the rods are shorter and the tetramer-tetramer interaction weaker. Association between folates can be detected by circular-dichroism spectroscopy starting from a concentration of 6· 10-4 mol l-1, well below the critical concentration for the formation of the cholesteric mesophase (ca. 0.5 mol l-1).
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790123
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  • 3
    Electronic Resource
    Electronic Resource
    Self-assembly of dideoxyguanosine (3′,3′) and (5′,5′)-monophosphates (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 734-741 
    Details
    ISSN: 0899-0042
    Keywords: liquid crystals ; circular dichroism ; X-ray diffraction ; self-recognition ; salt ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds show a pronounced cation-directed ability to self-assemble in water and to gives columnar structures similar to four-stranded helices; for compound (5′→5′)-d(GpG), this leads to the formation of cholesteric and hexagonal liquid crystalline phases. Both phases are columnar and the cholesteric phase is left-handed. This behaviour is a further confirmation of the tendency of guanine derivatives to self-assemble to give stacked columnar structures whenever not impossible for structural reasons. The CD spectra of the aggregates in isotropic solutions are dominated by a negative exciton couplet centred around 250 nm associated to a left-handed columnar chirality. The shapes of the profiles, in the 220-300-nm region, for (5′→5′)-d(GpG) (in water or in saline solutions) and for (3′→3′)-d(GpG) (in KCl solution) are quasi-mirror images of those of poly(G) and (3′→5′)-d(GpG). The appearance of relatively intense CD signals around 280-300 nm in solution of (3′→3′)-d(GpG) in the presence of NaCl resembles that of (3′→5′)-d(GpG) in the presence of Rb+ or Na+. In the compounds investigated in this work, which present two equivalent ends, one observes the two CD features that have been associated, in the current literature, with the signature of four-stranded parallel and antiparallel structures: hence the origin of these CD bands cannot be found in the polarity of the strands. Self-assembly is favoured by the addition of extra salt and the stabilising effect of K+ is greater than that of Na+, in the case of (3′→3′)-d(GpG), an assembled species could be detected by CD only in the presence of extra salt. Chirality 10:734-741, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of ethidium bromide on the liquid crystalline phases of aqueous DNA (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 227-232 
    Details
    ISSN: 0899-0042
    Keywords: DNA ; liquid crystal ; ethidium ; circular dichroism ; X-ray diffraction ; optical microscopy ; intercalation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of the intercalation of ethidium bromide (EB) on the characteristics of the DNA cholesteric and hexagonal mesophases is studied by optical microscopy, circular dichroism, and X-ray diffraction. The distance between DNA rods in the hexagonal phase is not modified by the presence of EB whereas the pitch of the cholesteric mesophase is considerably shortened by the dye. This seems to be related to the stereochemical effect of the intercalation rather than to the presence of a random distribution of the positive charge of the dye.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030404
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis and Characterization of New Enantiopure 7,7′-Disubstituted 2,2′-Dihydroxy-1,1′-binaphthyls: Useful Ligands for the Asymmetric Allylation Reaction of Aldehydes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 491-497 
    Details
    ISSN: 1434-193X
    Keywords: Binaphthol ; Absolute configuration ; Chiroptical properties ; Enantioselective catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---As an extension of our interest in developing new enantioselective reactions based on the binaphthol privileged ligand, we report a simple approach to the synthesis of 7,7′-disubstituted binaphthols. The commercially available 1,7-dihydroxynaphthalene (1) was used as starting material for the preparation of the bromoderivatives 2, which were oxidatively coupled to afford 3, a key intermediate for the preparation of a variety of enantiopure substituted binaphthols (8, 10). The absolute configuration of the new compounds was established by chiroptical analysis and by cholesteric induction. The optically active catalysts derived from the ligands 3, 8, 10, 16 and 17, complexed with Ti(OiPr)2Cl2, Zr(OiPr)4 and ZrCl4(THF)2, were employed for the enantioselective addition of allyltributyltin to aldehydes. Finally, the influence of the substituents of the binaphthyl core on the transmission of the chiral information was also investigated.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    A Liquid-Crystal Study of Heptalene (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 430-435 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral structure of heptalene is characterised, for a given configuration, by helicities, which are opposite in the direction (x) of the central C(5a)-C(10a) bond and in the direction (y) of a line perpendicular to it, passing through the C(3)-and C(8)-atoms. These two helicities can be experimentally established and differentiated by the handedness of the cholesteric mesophases induced in a biphenyl-type liquid crystal (LC) by chiral heptalenes with substituents favouring the x or y orientation along the nematic director of the LC.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700222
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