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  • Chemistry  (143)
  • Atomic, Molecular and Optical Physics  (5)
  • 42.75
  • Wiley-Blackwell  (148)
  • 1995-1999  (102)
  • 1975-1979  (46)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 337 (1995), S. 245-249 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spectroscopic Investigations on the Acidity of O,O′-Dithiophosphoric Acid Esters in Nonpolar Aprotic Solvents
    Additional Material: 3 Tab.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 1735-1745 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Infrared spectroscopy was used for the determination of the base-pairing content of four specific tRNAs in deuterium oxide solution. Infrared spectra were obtained in the 1750-1550 cm-1 region at various temperatures ranging from about 15 to 90°C. Melting curves were constructed by plotting the molar extinction coefficient at ν = 1657 cm-1 versus temperature. These transition curves enabled us to determine the ranges of temperature which correspond to the ordered (partially double-stranded) or randomly coiled structure of the tRNA. For a set of wavenumbers the extinction coefficients at these temperatures were used for the calculation of the base-pairing content. The procedure employed here is based on a method described earlier by Thomas [(1969) Biopolymers 7, 325-334]. For the conditions selected for this investigation (Mg2+-free D2O-buffer; 0.01M tris-DCl, 0.015M NaCl, pD 7.5) the results of this determination agree within the limits of errors with the number of base pairs predicted by the cloverleaf model.
    Additional Material: 7 Ill.
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Macrocyclic [4n + 2]-Hückel Aromatic Systems up to n = 9 and [4n] Antiaromatic Systems up to n = 10: Homologous Sequences from Tetraepoxy[24]annulene(2.0.2.0) to Tetraepoxy[40]annulene(12.0.12.0) and from the ‘Tetraoxa[22]porphyrin(2.0.2.0)-’ to the ‘Tetraoxa[38]porphyrin(12.0.12.0’-Dication1)2)Tetraepoxy[32]annulene(8.0.8.0) 3, tetraepoxy[36]annulene(10.0.10.0) 4, and tetraepoxy[40]annulene(12.0.12.0) 5 are synthesized and oxidized to give the ‘tetraoxa[30]-’, ‘tetraoxa[34]-’, and ‘tetraoxa[38]porphyrin’ dications 8-10. The annulenes as well as the ‘porphyrins’ are mixtures of at least two different configurational isomers, which can be analyzed by 1H-NMR techniques. Together with systems described already earlier, a complete homologous sequence from tetraepoxy[24]annulene(2.0.2.0) to tetraepoxy[40]annulene(12.1.12.0) and from ‘tetraoxa[22]porphyrin(2.0.2.0)’ to ‘tetraoxa[38]porphyrin(12.0.12.0)’ dications are available for the first time. The UV/VIS-absorptionmaxima in the annulene series are shifted to longer wavelengths with an increment of 12 nm per additional C=C bonds, and the Δδ values of the 1H-NMR spectra demonstrate a decreasing paratropic character (Δδ = 5.97 (1), 2.80 (3), and 4.23 ppm (4). The averaged λmax values of the Soret bands of the ‘tetraoxaporphyrin’ dications show a linear bathochromic shift with an increment Δδ of 58 nm per two additional double bonds, the absorptions of the most intensive Q-bands also increase linearly with an increment of ca. 160 nm. The Δδ values of the 1H-NMR spectra of the ‘tetraoxaporphyrin’ dications are increasing with the ring size (Δδ = 24.04 (7a) to 25.17 (9a) ppm), respectively, decreasing (Δδ = 21.55 (6) to 21.50 (9b) ppm) with a small maximum of 22.60 ppm for 7b, depending on the configuration of the isomers. The results confirm the antiaromatic character of the annulenes with up to 40π electrons and the aromatic character of the ‘tetraoxaporphyrin’ dications with up to 38π electrons.
    Additional Material: 18 Ill.
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  • 4
    ISSN: 0009-2940
    Keywords: Organotungsten selenolates ; 77Se NMR ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organotungsten-selenolato complexes were prepared in moderate yields by insertion of selenium into the alkali metaltungsten bonds of MSeW(CO)3cp (M = Li, Na) and subsequent reactions with the organohalides o-, m-, and p- C6H4(CH2Br)2, C6H5CHBr2, m-C6H4(CHBr2)2 and C6H5CCl3. The 77Se-NMR data of the new complexes are discussed and compared with those of related complexes derived from organomonohalides. Moreover, the X-ray crystal structures of C6H5CH2W(CO)3cp (1), μ-[m-C6H4{CH2SeW(CO)3cp}2] (3), μ-[p-C6H4{CH2SeW(CO)3cp}2] (4), and C6H5CH[SeW-(CO)3cp]2 (5) were determined. In complex (1), the W-CH2 bond length is 2.374 Å; the W-Se bond lengths in the complexes 3, 4 and 5 are all in the range 2.625-2.655 Å, corresponding to W-Se single bonds.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 12 (1977), S. 805-811 
    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 PCILO method was used to study systems with the following types of intermolecular hydrogen bonds, involving 2nd row atoms: N…H—S, S…H—S, N…H—Cl, Cl…H—F, Cl…H—Cl, P…H—N, P…H—P, P…H—F, S…H—F.In all the cases calculated, the PCILO method yields an accurate qualitative description of the stabilization energies and to some extent quantitatively good agreement with reliable ab initio and experimental results. The corresponding equilibrium distances are in almost all cases smaller (up to 0.6 Å) than the ab initio values of the same compounds.
    Additional Material: 2 Ill.
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Organic radicals were produced in the tensides C16H33(OCH2CH2)21OH and C14H29(OCH2CH2)3-SO3Na in aqueous solutions using a short pulse of high energy electrons. The radicals were formed by OH attack on the (OCH2CH2)x-parts of the tensides. The decay of the 250nm absorption of the radicals was recorded at different initial radical concentrations and tenside concentrations. Several radicals could be produced in one micelle. Radicals formed in the same micelle decay within microseconds or faster. The half life time τ1 in a micelle carrying two radicals is 2,0·10-6 s for C16H33(OCH2CH2)21 OH and less than 6·10-7 s for C14H29(OCH2CH2)3SO3Na. A model for intramicellar radical-radical reactions is proposed according to which the rate is faster in tensides of high critical micelle concentration. Single radicals in micelles of C16H33(OCH2CH2)21OH can deactivate each other without leaving the micelles. This intermicellar reaction is discussed in terms of the rate of diffusion-controlled micelle-micelle encounters, an encounter time of 7·10-8s, and the above time τ1 for intramicellar reaction. The observed rate constant 2k of intermicellar reaction is 3,5·106 mol-1·l·s-1. At low tenside concentrations, the bimolecular rate constant increases since more single tenside radicals are present in solution. They react rapidly (ca. 108 mol-1·l·s-1) with radicals in micelles. Single radicals in C14H33(OCH2CH2)3-SO3Na micelles cannot directly react with each other because of the Coulombic repulsion between two anionic micelles. Reaction occurs after the exit of a tenside radical from its micelle, the rate of which depends on the micellar equilibrium Mn⇄Mn-1+M (M: tenside molecule; n: agglomeration number of micelle). A single radical in solution reacts with a single radical in a micelle with 2k = 1,0·108 mol-1·l·s-1 and with another single radical in solution with 4,0·107 mol-1·l·s-1.γ-Irradiation of both tensides in aqueous solution leads to slight increases in viscosity, followed by turbidity beyond the “gel dose” and phase separation. These effects are explained in terms of crosslinking of tenside molecules. Formation of a large network requires bridges between all participating tenside molecules (not only bridges between micelles).
    Additional Material: 11 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 81-87 
    ISSN: 0887-624X
    Keywords: 2-methylene-1,3-dioxolanes, benzoyl peroxide reaction of ; 2-methylene-1,3-oxazolidines, benzoyl peroxide reaction of ; polyacetals ; charge-transfer polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 2-methylene-1,3-dioxolanes and 2-methylene-1,3-oxazolidines with benzoyl peroxide (acceptor radical) and with N-ethylmaleimide (acceptor) was investigated. It was shown that benzoyl peroxide adds to monomers 1a and 1b, giving the corresponding linear diester amides 1a and 1b respectively. The oxazolidine 1c adds benzoyl peroxide, without ring opening, by addition to the exomethylene group. Together with N-ethylmaleimide the oxazolidines 1a or 1b produce deep-colored charge transfer complexes, resulting in high molecular poly-N-ethylmaleimides probably via a radical mechanism. The 1,3-dioxolanes 2a and 2b were radically polymerized to produce polyacetals by vinyl polymerization. 2c was polymerized to produce randomly containing acetal units and ester units. The mechanism of polymerization of 2e is complex, affording polymers of nonuniform character. 2-Methylene-4-phenyl-1,3-dioxolane polymerization leads to polyester as the main structure, and to a lesser degree polyacetal structures. The chemical structures of the polymers were confirmed by NMR spectra and elemental analysis. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 49-54 
    ISSN: 0887-624X
    Keywords: polymer membranes ; poly(vinyl pyrrolidone) ; hypochlorite ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sodium hypochlorite solutions are used to treat membranes prepared from a polymeric blend containing poly(vinyl pyrrolidone) (PVP) to increase their water permeability. Sodium hypochlorite affects the membrane material in such a way that PVP is selectively removed from the membrane matrix. The mechanism of the reaction between hypochlorite and PVP is investigated by several chemical analysis techniques of the reaction products. Strong indications are found that the reaction involves chain scission of PVP according to a radical mechanism. © 1995 John Wiley & Sons, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 577-587 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Complex mixing flows and mixing parameters are calculated to evaluate mixing quality on the basis of kinematic parameters together with a statistical analysis. The results allow for a comparative evaluation in terms of geometry and flow parameters. The evaluation is limited to two-dimensional flows with moving boundaries in periodic motion such as the flow in the cross section of a twin-cam mixer. The finite-element calculation requires a remeshing procedure for every time step with special techniques to upgrade mixing variables from one time step to the next. The relative mixing quality of single cam and co: or counterrotating cam devices are compared by evaluating segregation scale, length stretch, and efficiency. The numerical results exhibit a good correspondence with their experimental counterpart.
    Additional Material: 15 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 588-597 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Numerical tools for the analysis of complex 3-D mixing devices were developed. Calculations are based on the finite-element method. The flow calculation is combined with that of pathlines for a fairly large number of material points; along these pathlines, relevant kinematic variables, which are then subjected to a statistical treatment, are evaluated. These numerical techniques are applied to the analysis of a Kenics mixer. It is assumed that the geometry is periodic in the axial direction, that is, that the mixer contains an infinite number of blades; the finite-element analysis may then be completed on a single wavelength of the geometry. To test the accuracy of the three-dimensional calculation, a Kenics device was mounted in order to mix clays of different colors, and photographs of experimental cross-sections were compared with numerical results showing concentration maps. A statistical treatment was performed on some 8,000 material points crossing the entry section to evaluate mixing quality.
    Additional Material: 16 Ill.
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