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  • 1
    Electronic Resource
    Electronic Resource
    Conducting phenylenevinylene blends as electrode materials in LC amperometric detection (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 1197-1200 
    Details
    ISSN: 1040-0397
    Keywords: Conducting polymer ; Phenylenevinylene ; Flow detection ; Catecholamines ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel amperometric electrode based on a conducting polymer is presented and its properties are compared with those of a glassy carbon electrode. The electrode material was made by mixing 2,5-dimethoxy-1,4-bis[2-(3,4,5-trimethoxy-phenyl)ethenyl]benzene with iodine and polycarbonate. The blend was coated on a glassy carbon electrode by evaporation from a chloroform solution. Catecholamines were used as test substances in LC and FIA measurements. They were oxidized at a potential of +0.7 V (vs. SCE). The electrode exhibited a linear response for injected concentrations from 2.5 × 10-6M to 2.5 × 10-3M. It had a response time of 1.2 s and a coulometric efficiency of 0.74% at a linear flow rate of 1 mL/min. The electrode material is stable for several months under normal operating conditions. Hydrodynamic voltammograms showed E1/2 values shifted by approximately 100 mV as compared to glassy carbon. The novel redox-conducting coating is proposed as an alternative material for the development of enzyme electrodes and chemically modified electrodes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140091514
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio studies of crystal field effects. VII. Structure of 2,3-diketopiperazine using a 13-molecule cluster, a calculation involving 1092 basis functions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 73-80 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of 2,3-diketopiperazine in a crystal phase (P21/c), modeled by a 13-molecule cluster surrounded by point charges, was completely optimized using standard gradient procedures. The (ab initio) MIA approach was used to perform the SCF step, which using a 4-21G basis set, involves calculations using 1092 basis functions. Results are in very good agreement with experimental (X-ray) data, in contrast to a previous study in which a model was used consisting of only point charges. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560460107
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio studies of structural features not easily amenable to experiment. 30. Conformational analysis and molecular structures of propanal and butanal (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 122-128 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometries of several conformations of propanal and butanal have been refined by geometrically unconstrained ab initio gradient relaxation on the 4-21G level. Both compounds possess energy minima at O—C—C—C torsional angles of 0° and in the 120° region, and energy maxima in the 70° region and at 180°. The structure of the aldehyde functional group is found to be relatively invariant both when different systems or when different conformations of the same system are compared. Conformationally dependent geometrical trends in propanal and butanal are discussed and found to be subtle yet noticeable.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540050203
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  • 4
    Electronic Resource
    Electronic Resource
    Phenylene vinylene oligomers studied by theoretical methods: Joint analysis of computational and x-ray results of the configurational isomers of 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 1245-1257 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The configurational isomers of 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene have been investigated by ab initio and MOPAC-AM1 semiempirical methods. The calculations were guided by and compared with single crystal X-ray results of the trans, trans-isomer (taken from the literature) and of the cis,cis-isomer (reported here). Using 4-21G-based ab initio calculations, free state geometries, deviations from coplanarity, and barriers to rotation of the central and peripheral rings were evaluated. Such barriers were also enumerated for the solid state of the cis,cis- and trans,trans-isomers. A single-molecule cluster surrounded by point charges sufficed to rationalize observed solid state properties in the trans,trans-isomer, including the quasi-free rotation of the central ring. A multimolecule cluster, however, was required to rationalize the restricted rotation of the rings in the cis,cis-isomer. MOPAC-AM1 methods were used to calculate geometries and energies of rotameric forms on the singlet photoisomerization path cis,cis → cis,trans → trans,trans. Finally, UV absorption wavelengths and oscillator strengths were calculated and the electronic structure of the states discussed. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.5
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  • 5
    Electronic Resource
    Electronic Resource
    On the applicability of the MINDO/3 method in studies of molecular structures in the vapor phase. Geometries, conformational energies, and vibrational amplitudes of alkenes and chloroalkanes (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 2 (1981), S. 63-72 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometries and force fields of the different conformers of five alkenes and five chloroalkanes (17 conformers in total) were calculated in the MINDO/3 approximation and compared with the corresponding experimental values. The direct use of geometrical or vibrational parameters derived from MINDO/3 either as starting values or as a source of constraints in the analysis of gas-phase electron diffraction data presents great risks. After a scaling procedure in which the calculated values are fitted to the experimental ones for a small number of compounds, scale factors can be obtained which, with due caution, are transferable to other molecules in the same class. Scaled MINDO/3 produces geometries and force fields that fit to experiment considerably better than their unscaled counterparts. However, scaled MINDO/3 does not produce better results than molecular mechanics. Calculated energy differences between rotamers are generally too high.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540020112
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  • 6
    Electronic Resource
    Electronic Resource
    The gradient-optimized geometry of haloperidol at the 4-21G level (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 302-308 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The molecular structure of haloperidol as free base in its C(13) - C(14) trans form is optimized using Pulay's gradient method and a 4-21G basis set without any geometrical constraints. The resulting structure is compared with the experimental structure of the free base in the C(13) - C(14) gauche form and with the experimental structure of the HBr salt of haloperidol in the C(13) - C(14) trans form. Apart from the obvious differences, the two rotameric forms of the free base show many similarities. This, together with the manner in which the differences of the two experimental structures are distributed over the haloperidol molecule, leads to the conclusion that the conspicuous differences between the experimental structures are caused by inaccuracies in the X-ray determination of the HBr salt. Deviations of phenyl ring geometries from D6h symmetry and the asymmetry of the conformation around C(1) - C(9) could be rationalized by intramolecular effects.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100304
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  • 7
    Electronic Resource
    Electronic Resource
    2,5-Dimethoxy-1,4-bis[2-(2,4-dimethoxyphenyl) ethenyl]benzene studied by quantum chemical calculations and single crystal X-ray diffraction (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 1820-1835 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The configurational isomers of 2,5-dimethoxy-1,4-bis-[2-(2,4-dimethoxyphenyl)ethenyl]benzene have been investigated by ab initio (4-21G level) and MOPAC-AM1 semiempirical methods. The calculations were guided by and compared with single crystal X-ray results of the trans,trans-isomer determined at 298 K and 103 K. The barriers of rotation of the latter isomer in the free and the solid state were enumerated. A comparison with related molecules, in particular 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene, is made. The positioning of substituents is shown to be of importance for ring rotational movements and NMR shifts, as well as for UV /Vis spectroscopy. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.3
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  • 8
    Electronic Resource
    Electronic Resource
    Structural characterization of mono- and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry (1993)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 28 (1993), S. 71-82 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono- and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3-nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one-electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long-chain hydrocarbon alkyl group, high-energy collision-induced decomposition of the intact cation is needed to obtain unambiguous structural information.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210280204
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  • 9
    Electronic Resource
    Electronic Resource
    The Structure of Benzimidazole Cyanine Dyes, Their Spectroscopy and Their Performance in Photographic Emulsions (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 27-33 
    Details
    ISSN: 0947-3440
    Keywords: Sensitizing dyes ; Mass Spectrometry ; NMR Spectra ; Electron distribution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The multi-step synthesis of two benzimidazole trimethine cyanines as possible green sensitizing dyes (Gs3-1, Gs3-2) is reported. Compounds were characterized from UV-Vis, mass spectroscopic and NMR data. The charge density distributions of the two compounds, calculated using the semi-empirical MOPAC 93 package, are in agreement with assignments in NMR spectroscopy. Sensitizing properties of the cyanine dyes were evaluated in actual photographic T-grain emulsions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970107
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