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  • Engineering General  (9,884)
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  • 1
    Electronic Resource
    Electronic Resource
    New Syntheses of Flavones from Diels-Alder Reactions of 2-Styrylchromones with ortho-Benzoquinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 135-139 
    Details
    ISSN: 1434-193X
    Keywords: Flavones ; Chromones ; ortho-Benzoquinodimethanes ; Diels-Alder reactions ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first reported cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodimethane afforded 2-[2-(3-aryl-1,2,3,4-tetrahydronaphthyl)]chromones. These cycloadducts were converted into the corresponding 2-[2-(3-arylnaphthyl)]chromones (benzoflavone derivatives) by bromination/dehydrobromination processes. These benzoflavone derivatives were also obtained in one-pot cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodibromomethane.
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  • 2
    Electronic Resource
    Electronic Resource
    The Structures of a Tetracarba-nido-octaborane(8) and a Novel Spiro Derivative of a 2,3,5-Tricarba-nido-hexaborane(7) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 533-537 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Carboranes ; NMR ; X-ray analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroboration of bis(diethylboryl)ethyne (1) with tetraethyldiborane(6) leads to a B-ethyl-substituted tetracarba-nido-octaborane 2, a spiro-carborane 3, which belongs to the 2,3,5-tricarba-nido-carborane family, and a hexacarba-arachno-dodecaborane(12) 4, along with polymeric material. The X-ray structure analysis of carborane 2, determined here, is fully consistent with the structure deduced earlier from NMR data. The structure of 3 in solution was established by theoretical analysis of its NMR data. Ab initio calculations of the structures of 2b and 3b (b denotes the B-metyhl-substituted derivatives) and the comparison of calculated with experimental NMR data support the suggested structures of 2 and 3 in solution. The calculated structure of the carborane cage of 2a also agrees with the experimental geometry of 2.
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Stereodynamics of an N,N-Chiral “Proton Sponge” (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2501-2510 
    Details
    ISSN: 1434-193X
    Keywords: Proton Sponges ; N-Chirality ; Isotopic labelling ; Stereodynamics ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,8-Bis(N-benzyl-N-methylamino)naphthalene (2) and its hydrogen iodide salt [2H]+[I]- were synthesised from 1,8-diaminonaphthalene. The thermodynamic diastereomer ratios of (2) and [2H]+ in [D7]DMF are 73.4:26.6 and 89.7:10.3 respectively at 293 K. The solid state structures of the major dl-(RNRNSNSN) diastereomers were determined by single crystal X-ray diffraction. The minor diastereomers were shown to be the meso-(RNSN) forms by performing 1H-NMR NOE studies on isotopically desymmetrized 1-(N-benzyl-N-[13C]-methylamino)-8-(N′-benzyl-N′-methylamino)naphthalene [13C]-2 and the salt [13C]-[2H]+. In [D7]DMF at 298 K, the meso form of the free base 2 is 0.6 (± 0.07) kcal·mol-1 less stable than the dl form (ΔH° = -0.64 (±0.03) kcal·mol-1; ΔS° = -0.18 (±0.13) cal·K-1mol-1) and the activation barriers for interconversion are ca. 14.2 (±0.4) and 14.8 (±0.4) kcal·mol-1 respectively. The effect of solvent polarity on the entropy and enthalpy change on approach to the transition state was studied. An approximate correlation with the solvent dielectric constant was found for both ΔH# and ΔS# and this may be ascribed to the development of a net dipole in the transition state due to substantially different hybridisation and geometry at the two nitrogen centres.
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  • 4
    Electronic Resource
    Electronic Resource
    Structure analysis of a soluble polysiloxane-block-polyimide and kinetic analysis of the solution imidization of the relevant polyamic acid (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2237-2245 
    Details
    ISSN: 0887-624X
    Keywords: NMR ; polysiloxane, polysiloxane-block-polyimide ; solution imidization ; kinetic analysis ; structure analysis ; spin-lattice relaxation time ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of polysiloxane-block-polyimides were synthesized by solution imidization of the polyamic acids derived from the combination of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and diamino(polysiloxane) (PSX (Mw = 750)) in N-methyl-2-pyrrolidone (NMP). Their structures were analyzed by 1H-, 13C-, and 29Si-NMR spectra as well as by IR spectroscopy. The solid-state NMR spectrum was also measured to determine the spin-lattice relaxation time of the copolyimides. The observed relaxation times of both aromatic and polysiloxane segments were similar in the copolyimides having 10-30 wt % of PSX, while those in the copolyimide with 50 wt % of PSX was significantly different. This may be attributed to the morphology change due to the increase in PSX composition in the polymer backbone. The reduced viscosity of the copolyimides could be controlled by changing the monomer ratio in the feed or by adding an end-capping reagent such as phthalic anhydride into the polymerization system. The kinetic study of the solution imidization revealed that the imidization reaction obeyed second-order kinetics. The activation energy calculated for this imidization was 99.2 kJ/mol, being similar to that for the imidization of the DSDA-based aromatic polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2237-2245, 1998
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of the microstructure of metallocene-catalyzed norbornene-ethylene copolymers using NMR spectroscopy (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1633-1638 
    Details
    ISSN: 0887-624X
    Keywords: cyclic olefin copolymers ; norbornene ; metallocene catalysts ; NMR ; microstructure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Norbornene-ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with 1H-NMR and 13C-NMR methods. From a Cosy 1H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using 13C-1H correlations, hmqc for one-bond correlations, and hmbc for two- or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy 1H-NMR spectrum revealed a new crosspeak which, according to the corresponding 13C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1633-1638, 1998
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  • 6
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    Electronic Resource
    Stereochemical and compositional assignment of acrylonitrile/methyl methacrylate copolymers by DEPT and inverse HECTOR NMR spectroscopy (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1081-1092 
    Details
    ISSN: 0887-624X
    Keywords: NMR ; microstructure ; acrylonitrile/methyl methacrylate copolymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acrylonitrile/methyl methacrylate copolymers of different monomer concentration were prepared by photo polymerization using uranyl ion as initiator. The carbon 13 and proton spectra of these copolymers are overlapping and complex. The complete spectral assignment of the 13C- and 1H-NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and two dimensional 13C-1H Heteronuclear Single Quantum Correlation (HSQC) experiments. The methylene, methine and the methyl carbon resonances show both stereochemical (triad level) and compositional (dyad, triad, tetrad, pentad and hexad level) sensitivity. 2D Double Quantum Filtered Correlated Spectroscopy (DQFCOSY) experiment was used to ascertain the various geminal couplings between the methylene protons. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1081-1092, 1998
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis of novel polyaryl(ether-ketones) with tert-butyl pendent groupsDedicated to Prof. F. J. Baltaá Calleja on the occasion of his 60th birthday. (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1251-1256 
    Details
    ISSN: 0887-624X
    Keywords: ether ketones ; synthesis ; NMR ; thermal properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Linear polyaryl(ether ketones) containing tert-butyl pendent groups were prepared from aromatic hydrocarbons and aromatic diacid chlorides, both classes of monomers containing tert-butyl pendent groups. The polymers were prepared in high yield and high molecular weight by low-temperature precipitation polycondensation in 1,2-dichloroethane. The presence of meta-oriented moieties and bulky pendent groups played a beneficial role with regard to solubility, while the thermal transitions and thermal resistance were not greatly impaired relative to conventional all para-oriented polyaryl(ether-ketones). The current polyaryl(ether-ketones) showed glass transition temperatures in the range 170-240°C and decomposition temperatures, as measured by TGA, of about 500°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1251-1256, 1998
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  • 8
    Electronic Resource
    Electronic Resource
    NMR and semi-empirical study of the tautomerism of­2,2′-bisbenzimidazolyl (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 411-418 
    Details
    ISSN: 0894-3230
    Keywords: 2,2′-bisbenzimidazolyl ; tautomerism ; NMR ; semi-empirical calculations ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A dynamic NMR study of the tautomerism of 2,2′-bisbenzimidazolyl in DMSO-d6 and a mechanistic interpretation of the process, based on a stepwise, single-proton transfer and formation of a zwitterionic intermediate, are presented. This interpretation is substantiated by semi-empirical calculations of the postulated intermediate and transition state, that yield results which are compared with previous studies on related aliphatic systems. © 1998 John Wiley & Sons, Ltd.
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  • 9
    Electronic Resource
    Electronic Resource
    Enantioselective synthesis of α-aminophosphonic acid derivatives by hydrogenation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 564-572 
    Details
    ISSN: 0899-0042
    Keywords: asymmetric hydrogenation ; aminophosphine phosphinites ; rhodium complexes ; dehydro aminophosphonic acids ; NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral α-aminophosphonic acid derivatives are efficiently synthesized by asymmetric hydrogenation of the prochiral N-acyl-α,β-dehydroaminophosphonates. PROPRAPHOS-Rh-catalysts from readily available (S)- and (R)-Propranolol proved to be suitable in the homogenous reaction affording an enantiomeric excess of 87-92% with high rate. The aminophosphonic acid derivatives and precursors were fully characterized by 1H, 13C, and 31P NMR spectroscopy. Chirality 10:564-572, 1998. © 1998 Wiley-Liss, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    Stereochemistry of polycyclohexyl systems (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 159-168 
    Details
    ISSN: 0899-0042
    Keywords: symmetry ; conformation ; chirality ; stereochemistry ; NMR ; rotational barrier ; interconversion graph ; gear meshing ; molecular propellers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The static and dynamic stereochemistries of tricyclohexylmethane, tetracyclohexylmethane, and tetracyclohexylethene are reviewed. Chirality 10:159-168, 1998. © 1998 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/chir.25
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  • 11
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    Electronic Resource
    A New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal-Metal Bond - 3. Unusual Equilibria in Aqueous Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 565-570 
    Details
    ISSN: 1434-1948
    Keywords: Equilibrium ; Metal-metal bond ; Stability constants ; Platinum ; Thallium ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new series of four binuclear platinum-thallium cyano compounds containing a direct and unsupported by ligands metal-metal bond has been prepared in aqueous solution. These compounds are represented by the formula[(NC)5Pt-Tl(CN)n-1](n-1)- (n = 1-4 for compounds I, II, III IV, respectively) and [(NC)5Pt-Tl-Pt(CN)5]3- (for compound V). The oligonuclear complexes are synthesised according to the reaction mPt(CN)42- + Tl3+ + nCN- █[PtmTl(CN)4m+n]3-2-n. Thus, there occurs a change of the coordination number of the Pt center from four (square planar) to six (octahedral). Consequently, the formation of binuclear platinum-thallium cyano compounds involves at least two steps: (i) formation of metal-metal bond and (ii) formation of (NC)5Pt- unit by a cyanide transfer process. - The complexes exist in an equilibrium, which also includes the parent complexes Pt(CN)42- and Tl(CN)n3-n (n = 0-4), and can be controlled by varying the cyanide concentration and/or pH of the solution. The stability constants of the compounds βN =[PtmTl(CN)4m+n3-2m-n{[Pt(CN)42-]m · [Tl3+] · [CN-]n} have been determined by means of multinuclear NMR (195Pt, 205Tl): logβN = 19.9±0.4, 30.7±0.3, 38.6±0.3, and 44.8±0.2 for I, II, III and IV(m = 1, n = 1-4), and 32.1±0.3 for V(m = 2, n = 2), respectively, (in 1 M NaClO4 as ionic medium, at 25 oC). To our knowledge, the present work constitutes the first detailed equilibrium study of metal-metal bonded compounds; it indicates that also other cluster formation reactions described in the literature may represent real equilibria.
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  • 12
    Electronic Resource
    Electronic Resource
    VTF to arrhenius crossover in temperature dependence of conductivity in (PEG)xNH4ClO4 polymer electrolyte (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1201-1209 
    Details
    ISSN: 0887-6266
    Keywords: polymer electrolytes ; NMR ; conductivity ; glasses ; Arrhenius and VTF dependences ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have studied the temperature variation of conductivity and 1H NMR linewidth of (PEG)xNH4ClO4 (x = 20, 30, 46, 100, 200, & 1000) polymer electrolyte systems. The temperature dependence of the conductivity shows two distinct behaviors, the low temperature VTF dependence crossing over to Arrhenius dependence at higher temperatures. The departure from the VTF behavior is found to be composition dependent. NMR spectra indicate the presence of large fractions of crystalline regions that start to melt around the crossover temperature. We understand the deviation from the VTF behavior as a consequence of this crystalline to elastomer transition. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1201-1209, 1998
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  • 13
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    Conformation and membrane activity of an analogue of the peptaibol antibiotic trichogin GA IV with a lipophilic amino acid at the N-terminus (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 389-399 
    Details
    ISSN: 1075-2617
    Keywords: conformational analysis ; lipo-amino acid ; membrane activity ; NMR ; peptide antibiotic ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have synthesized by solution-phase methods two analogues of the 11-residue lipopeptaibol antibiotic trichogin GA IV in which the N-terminal n-octanoyl group is replaced either by an N-acetylated 2-amino-2-methyl-l-undecanoic acid or by an N-acetylated α-aminoisobutyric acid. CD, FTIR absorption, and NMR analyses unequivocally show that the main structural features of trichogin GA IV are preserved in these analogues. Since only the peptide containing the lipophilic chain exhibits membrane-modifying properties, these results strongly support the view that moving the long acyl moiety from the Nα-blocking group to the side chain of the N-terminal extra-residue does not affect the conformational properties or the membrane activity of trichogin GA IV. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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  • 14
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    Conformational sampling of bioactive conformers: a low-temperature NMR study of 15N-Leu-enkephalin (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 253-265 
    Details
    ISSN: 1075-2617
    Keywords: Opioids ; enkephalin ; selectivity ; conformation ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational studies of enkephalins are hampered by their high flexibility which leads to mixtures of quasi-isoenergetic conformers in solution and makes NOEs very difficult to detect in NMR spectra. In order to improve the quality of the NMR data, Leu-enkephalin was synthesized with 15N-labelled uniformly on all amide nitrogens and examined in a viscous solvent medium at low temperature. HMQC NOESY spectra of the labelled Leu-enkephalin in a DMSOd6/H2O mixture at 275 K do show numerous NOEs, but these are not consistent with a single conformer and are only sufficient to describe the conformational state as a mixture of several conformers. Here a different approach to the structure-activity relationships of enkephalins is presented: it is possible to analyse the NMR data in terms of limiting canonical structures (i.e. β- and γ-turns) and finally to select only those consistent with the requirements of δ selective agonists and antagonists. This strategy results in the prediction of a family of conformers that may be useful in the design of new δ selective opioid peptides. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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  • 15
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    Effect of extracellular glutamine concentration on primary and secondary metabolism of a murine hybridoma: An in vivo 13C nuclear magnetic resonance study (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 172-186 
    Details
    ISSN: 0006-3592
    Keywords: hybridoma ; futile cycling ; hollow fiber bioreactor ; glutamine ; NMR ; C-13 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of changes in extracellular glutamine level on metabolism of a murine hybridoma was examined with in vivo nuclear magnetic resonance (NMR) spectroscopy. Cells were cultured in a hollow-fiber bioreactor at high cell density to allow intracellular metabolite levels to be determined on a metabolically relevant time scale. Steady infusions of [1-13C] glucose were used to label glycolytic and tricarboxylic acid cycle intermediates, which permitted continuous monitoring with NMR spectroscopy during changes in environmental glutamine level. Samples of the extracellular medium were also analyzed to determine the effect of glutamine on other metabolites associated with primary and secondary metabolism. The changes in glutamine concentration had several effects on primary and secondary metabolism, depending on the rate the changes were made. For a brief reduction in feed glutamine concentration from 4 to 0 mM (which produced a rapid change from 0.67 to ∼0 mM in residual glutamine), large changes were observed in the rate of consumption of metabolites normally associated with energy production. Antibody synthesis was strongly stimulated and nitrogen metabolism was significantly altered. For a more prolonged reduction from 2.4 to 1.2 mM (which produced a slower reduction from 0.30 to 0.08 mM in residual glutamine), much smaller changes were observed even though the concentration of glutamine at the reduced feed level was very low. Energy metabolism did not appear to be limited by glutamine at 0.08 mM, which suggests that significant futile cycling may occur in energy producing pathways when excess glucose and glutamine are available. However, this concentration of extracellular glutamine appeared to affect some anabolic pathways, which require amino groups from glutamine. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 172-186, 1998.
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  • 16
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    Characterization of the diffusive properties of biofilms using pulsed field gradient-nuclear magnetic resonance (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 60 (1998), S. 283-291 
    Details
    ISSN: 0006-3592
    Keywords: diffusion ; biofilms ; gels ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The mobility of water in intact biofilms was measured with pulsed field gradient nuclear magnetic resonance (PFG-NMR) and used to characterise their diffusive properties. The results obtained with several well-defined systems, viz. pure water, agar, and agar containing inert particles or active bacteria were compared to glucose diffusion coefficients measured with micro-electrodes and those calculated utilising theoretical diffusion models. A good correspondence was observed indicating that PFG-NMR should also enable the measurement of diffusion coefficients in heterogeneous biological systems. Diffusion coefficients of several types of natural biofilms were measured as well and these results were related to the physical biofilm characteristics. The values had a high accuracy and reflected the properties of a sample of ca. 100 biofilms, while non-uniformity or non-geometrical shapes did not negatively influence the results. The monitored PFG-NMR signal contains supplementary information on e.g. cell fraction or spatial organisation but quantitative analysis was not yet possible. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 283-291, 1998.
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  • 17
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    7Li and 23Na NMR studies of transmembrane cation transport mediated by ionophore lasalocid A (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 15-20 
    Details
    ISSN: 1075-2617
    Keywords: ion transport ; kinetics ; lithium ; NMR ; shift reagent ; vesicles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion transport across phospholipid vesicles was studied by 7Li and 23Na-NMR using an aqueous anionic paramagnetic shift reagent, dysprosium nitrilotriacetate [Dy(NTA)2]3-, mediated by ionophores, lasalocid A and A23187. The intra- and extracellular 7Li and 23Na-NMR signals were well separated (20 Hz) at mM concentration of the shift reagent. The observed data on the rate constant for lithium transport across DPPC vesicles at various concentrations of the ionophores indicated that lasalocid A is a more efficient carrier for lithium ion compared with the sodium ion transport by this ionophore, while A23187 was not specific to either of the ions (Li or Na). ©1998 European Peptide Society and John Wiley & Sons, Ltd.
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  • 18
    Electronic Resource
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    Solution conformation of an immunogenic peptide from HRV2: comparison with the conformation found in a complex with a Fab fragment of an anti-HRV2 neutralizing antibody (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 101-110 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; random coil ; rhinovirus ; synthetic vaccine ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of a [15]-peptide (H-VKAETRLNPDLQPTE-NH2) from VP2 of rhinovirus HRV2 complexed with a Fab fragment was previously shown by X-ray crystallographic studies to be similar to the one found in the corresponding region of HRV1A. Antibodies raised against this peptide bind to and neutralize HRV2. In order to identify structural features preserved in solution that may explain the ability of this short peptide to mimic the structure of the protein surface, the peptide has been studied by NMR in aqueous solution as well as under denaturing conditions.The peptide is shown to be a random coil in solution. However, the sequence forming a 310 helix in the complex is biased into a helical conformation according to NOE intensity data as well as from urea and pH titrations. This sequence adopts the same conformation in an unrelated protein. NOE data suggest that a β-turn found in the complex may be sampled in solution. Also, Glu4, interacting with Arg6 in the crystal, has a reduced pKa value in solution. It is concluded that the local structure present in the random coil state of VP2(156-170) contains enough information to direct the production of antibodies that bind to and neutralize HRV2. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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  • 19
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    A conformational study in solution of pro-somatostatin fragments by NMR and computational methods (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 305-318 
    Details
    ISSN: 1075-2617
    Keywords: pro-somatostatin ; β-turn ; NMR ; computational methods ; conformational analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of a conformational study by nuclear magnetic spectroscopy and computational methods on a series of point-mutated synthetic peptides, containing 14 amino acid residues and mimicking the region containing the Arg-Lys dibasic cleavage site of pro-somatostatin, have confirmed the possible role of a well defined secondary structure in the recognition phenomenon by processing enzymes.The importance of the residues located near the Arg-Lys dibasic site in the C-terminal region of the pro-hormone for the cleavage of the precursor into somatostatin-14 has been confirmed. The present structural analysis indicates the occurrence of two β-turns in the 4-7 and 11-14 regions, flanking the cleavage site, for all the peptides recognized as substrates by the processing enzyme.Interestingly, in the point-mutated analogue not processed by the enzyme and containing the replacement of proline by alanine in position 5 the first β-turn is displaced by one residue and involves the Ala5-Arg8 segment. This observation may explain the lack of recognition by the maturation enzyme. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
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    Synthesis and characterization of arsenobetaine and arsenocholine derivatives (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 635-641 
    Details
    ISSN: 0268-2605
    Keywords: arsenobetaine ; arsenocholine ; non-hygroscopic ; NMR ; FAB MS ; ICP MS ; synthesis ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multigram quantities of arsenobetaine bromide and arsenocholine iodide were synthesized from trimethylarsine using uncomplicated techniques. Arsenobetaine bromide and arsenocholine iodide are both non-hygroscopic. Arsenocholine iodide is, however, light-sensitive and should be used with actinic glassware. Both compounds were characterized by elemental and spectroscopic techniques and found to be suitable for use as primary analytical standards. © 1998 John Wiley & Sons, Ltd.
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    Synthesis and characterization of diorganotin(IV) complexes of N-(2-pyridylmethylene)arylamines and mutagenicity testing in vivo of Et2SnCl2·[L4=N-(2-pyridylmethylene)-4-toluidine] (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 503-513 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; N-(2-pyridylmethylene)arylamines ; IR ; NMR ; Mössbauer ; mutagenicity ; sister chromatid exchange ; cell cycle delay ; bone-marrow cells ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diorganotin(IV) dichloride complexes of the type R2SnCl2·L (R = methyl, ethyl, vinyl, t-butyl, n-butyl or phenyl; L = N-(2-pyridylmethylene)arylamine) have been synthesized and characterized on the basis of IR, NMR and 119Sn Mössbauer studies. Investigation of the complexes indicated that N-(2-pyridylmethylene)arylamines form distorted trans-octahedral complexes with R2SnCl2 similar to the well-known R2SnCl2·L. Cytogenetic toxicology testing has been performed for Et2SnCl2·L4 [L4 = N-(2-pyridylmethylene)-4-toluidine] in mouse bone-marrow cells in vivo since such testing is a regulatory requirement before new drugs are released. This tin compound induced delay in cell-cycle kinetics and sister chromatid exchanges (SCEs) significantly. The effect of Et2SnCl2·L4 was greater when endogenous glutathione (GSH) was depleted by buthionine sulphoximine (BSO). It seems that Et2SnCl2·L4 induces SCEs due to formation of adduct by binding on DNA which could interfere in DNA synthesis and cause delay in cell proliferation. Depletion of GSH could reduce the shielding effect of GSH on chromatin and allows more Et2SnCl2·L4 to bind on DNA. © 1998 John Wiley & Sons, Ltd.
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    Diorganotin(IV)-2-mercaptopyrimidine complexes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 12 (1998), S. 861-871 
    Details
    ISSN: 0268-2605
    Keywords: diorganotin ; Pyrimidine ; complex ; Mössbauer ; IR ; NMR ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes formed between the diorganotin(IV) moieties, R2Sn(IV), and the ligand 2-mercaptopyrimidine, (H)SPym, were investigated. Complexes R2SnHal(SPym) and R2Sn(SPym)2 [R = Me, iPr, nBu, iBu, tBu, cyclohexyl(Cy), Ph] were synthesized, and characterized by elemental analysis. In the solid state, chelation of SPym through S and N donors was established by IR spectroscopy, and the nature of the environment of tin centers was investigated by 119Sn Mössbauer spectroscopy. From the dynamics of 119Sn nuclei determined by variable-temperature measurements on representative compounds [Me2SnCl(SPym) and Cy2SnBr(SPym)], as well as by point-charge model treatment of nuclear quadrupole splitting parameters, it was inferred that Me2SnCl-­(SPym) may assume a trans-Me2 octahedral coordination geometry around tin in a monodimensional polymer, or a monomeric trigonal-bipyramidal structure (distorted). The latter type of structure was assigned to the other R2SnHal(SPym) species, while R2Sn(SPym)2 complexes assume a trans-octahedral, or skew trapezoidal, tin environment. In CHCl3-CDCl3 solutions, monomeric species occur (according to vapor-pressure osmometry), where 1H and 13C NMR spectroscopic parameters of SPym indicate the persistence of Sn chelation by S and N donor atoms. The Me2SnCl(SPym) species assume trigonal-bipyramidal structures with a chelating SPym ligand, in CDCl3 and C2H5OH solutions, according to the coupling constants 1J(119Sn,13C), as well as IR and 119Sn Mössbauer spectroscopic data. 119Sn NMR parameters fully correspond with data for the homologous complexes with 2-mercaptopyridine. Copyright © 1998 John Wiley & Sons, Ltd.
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    Ab initio prediction of 15N-NMR chemical shift in α-boron nitride based on an analysis of connectivities (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 716-725 
    Details
    ISSN: 0192-8651
    Keywords: NMR ; boron nitride ; solid state ; theoretical chemistry ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Hydrogen-saturated cut-outs of hexagonal boron nitride have been used to model the solid state. Model compounds have been geometry optimized by means of density functional theory, whereas chemical shift calculations have been carried out at the coupled-perturbed Hartree-Fock level of theory employing gauge-including atomic orbital (GIAO) basis sets. The reliability of results has been tested against experimental values for chemical shifts in stable molecules with similar structural elements. With increasing cluster size, viz. a vanishing influence of the saturating hydrogens on the innermost nitrogen atoms, we find a convergence of 15N chemical shifts. A classification scheme for the chemical environment of a nitrogen atom has been set up according to its bonding graph including the second coordination sphere. For a given connectivity, chemical shifts vary within a few parts per million, thus enabling us to predict a 15N-NMR chemical shift of -285 ± 5 ppm for solid α-boron nitride.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 716-725, 1998
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    Determination of molecular weight distributions of novolac resins by gel permeation chromatography (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1399-1407 
    Details
    ISSN: 0887-624X
    Keywords: phenol-formaldehyde resin; ; novolac ; GPC ; molecular weight averages ; NMR ; hydrodynamic volume ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The number- and weight-average molecular weights of several statistical and high ortho novolac resins were determined using gel permeation chromatography (GPC). The standards used were pure compounds having between 2 and 12 phenol units bridged via methylene linkages. Three series of compounds were studied: (i) those with methylene linkages substituted in only the ortho positions relative to the phenolic hydroxyl group; (ii) those in which all para positions, together with sufficient ortho positions, were used to synthesize the compounds; and (iii) those in which the methylene linkages were substituted at a mixture of ortho and para positions. Such compounds, having known molecular architecture and units similar to the segments of industrial novolac resins, provide for a more exact measurement of the molecular weight than do the commonly used poly(styrene) standards. Using these new standards the number average molecular weights of the resins determined by GPC were in good agreement with the average molecular weight obtained by 1H-NMR spectra of the resins, particularly for low molecular weight resins. GPC analysis of higher molecular weight resins tends to underestimate the molecular weights because of complications introduced by hydrogen bonding. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1399-1407, 1997
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    Chemistry of novolac resins. II. Reaction of model phenols with hexamethylenetetramine (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1389-1398 
    Details
    ISSN: 0887-624X
    Keywords: benzylamines ; benzoxazines ; curving ; HMTA ; NMR ; novolac resins ; xylenols ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is proposed that the reactions of hexamethylenetetramine (HMTA) with 2,4-xylenol and with 2,6-xylenol occur by different pathways. The rate of reaction and the final product distribution depend on the initial xylenol : HMTA ratio and are different in the two systems. Measured by HMTA consumption, with 2,4-xylenol the reaction rate increased with increasing xylenol : HMTA ratios, whereas with 2,6-xylenol the rate of reaction decreased with increasing 2,6-xylenol : HMTA ratio. In systems which contain both 2,4- and 2,6-xylenol, a strong preference for reaction of the HMTA with the ortho site of 2,4-xylenol was noted. This preference was apparent even in mixtures in which 2,6-xylenol was present in greater amounts than 2,4-xylenol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1389-1398, 1997
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    Influence of the stoichiometry of epoxy-cyanate systems (non-catalyzed and catalyzed) on molten state reactivity (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3101-3115 
    Details
    ISSN: 0887-624X
    Keywords: molten state reactivity cyanate esters ; epoxy resins ; NMR ; 13C (liquid and solid) ; FTIR ; DSC ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on an FT-IR and 13C-NMR spectroscopic study using model compounds, we previously proposed an epoxy-cyanate coreaction path in the molten state, by identifying all chemical species and their role in the reaction mixture. These data were then applied to difunctional systems involving diglycidyl ether of bisphenol A (DGEBA) and bisphenol A dicyanate (BADCy), with mixtures prepared in different epoxy/cyanate ratios. Using FT-IR and solid state 13C-NMR spectroscopic analyses, we show the effect of epoxy group concentration on the final structure of the system. We were able to show that epoxy functions react on the triazine rings formed in the first step of homopolymerization of cyanates, and that the structure of the final system depends on their initial concentration. In addition, a study of difunctional systems for identical cyanate-epoxy stoichiometry was undertaken in the presence of anionic (imidazole) and metallic (AcAcCu and AcAcCr) catalysts in order to determine their effect on the reactivity of the two monomers and on the structure of the final system. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3101-3115, 1997
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    NMR study of the structure and properties of poly(MMA-co-VP) crosslinked hydrogels (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3619-3625 
    Details
    ISSN: 0887-624X
    Keywords: NMR ; structure ; porperties ; poly(MMA-co-VP) ; hydrogels ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H- and 13C-NMR techniques were used to study the microscopic structure of NMA/VP copolymer hydrogels. Evidence was obtained for a plasticization effect of MMA chains by VP. An original 1H-NMR approach revealed the existence of several types of water with various degree of bounding to the polymer network, a conclusion that is corroborated by a complementary 13C-NMR study. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3619-3625, 1997
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    Novel emulsion graft copolymerization onto the silylmethyl group of poly(dimethylsiloxane) (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2607-2617 
    Details
    ISSN: 0887-624X
    Keywords: poly(dimethylsiloxane) ; emulsion graft copolymerization ; hydrogen abstraction reaction ; peroxide ; NMR ; lubricity ; MOPAC ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of radical initiators upon the emulsion graft copolymerization of styrene and acrylonitrile onto poly(dimethylsiloxane) (PDMS) was studied. As initiators, a series of peroxides and hydroperoxides were coupled with ferrous sulfate, among which the tert-butyl peroxylaurate system gave the highest grafting efficiency (30%). The tert-butyl peroxylaurate initiator fulfills the criteria for efficient radical grafting by generating only the tert-butoxy radical, which is reluctant to form a carbon radical via β-scission, being highly hydrophobic, and not carrying a tertiary hydrogen that may be abstracted by a radical. 13C-NMR analysis of the products showed that the grafting occurred on the silylmethyl groups of PDMS to give 10-25 grafts per polymer and graft ratio in the range 44-140%. The PDMS graft copolymers thus obtained could be used as surface-modifying agents to improve the lubricity and water-repellency of ABS [poly(styrene-co-acrylonitrile)-graft-polybutadiene]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2607-2617, 1997
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    Aggregation kinetics and precipitation phenomena in poly(phenylisocyanide) (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 439-446 
    Details
    ISSN: 0887-624X
    Keywords: poly(phenylisocyanide) ; NMR ; GPC ; light-scattering techniques ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of N-phenyl-substituted poly(isocyanide) (N-φ-PIM) utilizing a Ni(II) catalyst in methanol yields a brown material having a number average molecular weight of about 2000. Analysis of this “as prepared” polymer indicates that a rigid rod structure is present in the derived solid. Dissolution of this “as prepared” N-φ-PIM in halocarbon solvents or THF apparently leads to unraveling of the helical polymer with subsequent aggregation and precipitation of materials that have different properties from the original. These processes have been investigated by NMR, GPC, and light-scattering techniques in THF and other solvents. UV spectroscopy has been utilized to follow the kinetics of the aggregation process in solution. X-ray diffraction (XRD) measurements have been employed to investigate the changes attendant with precipitation. An explanation of these observations is offered that implicates the uncoiling of the rigid rod helix as the most important step in defining subsequent physical and chemical properties of the ultimate amorphous polymer. © 1997 John Wiley & Sons, Inc.
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    Allyl endcapped polyethylene oxide crosslinkers and their use in superabsorbents (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 799-806 
    Details
    ISSN: 0887-624X
    Keywords: allyl crosslinkers ; poly(acrylic acid) ; NMR ; superabsorbent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new crosslinkers have been synthesized for evaluation in superabsorbent polymers. These crosslinkers are allyl endcapped polyethylene glycols (PEG) of 200, 600, and 3400 molecular weight. A branched polyethylene oxide of 600 molecular weight, initiated with glycerin, was also synthesized as a trifunctional crosslinker. The allyl functionality was chosen because it is less reactive during radical polymerization than acrylate crosslinkers, an attribute that was necessary to achieve a more uniform gel network. A synthesis route was devised to make the crosslinkers in high purity and yield. The purity of the crosslinkers was determined by 13C NMR, liquid chromatography, and size exclusion chromatography. Gels that were produced with the allyl crosslinkers gave excellent soluble polymer levels and swelling characteristics. The mechanism of incorporation of the allyl functionality was determined to be exclusively vinyl polymerization rather than through hydrogen abstraction. This was determined using NMR spectroscopy, monitoring the polymerization of a model system consisting of acrylic acid and allylacetate. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 799-806, 1997
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    Identifying crosslinks in polyethylene following gamma-irradiation in acetylene: A model compound study (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1549-1562 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; γ-irradiation ; crosslinking ; NMR ; alkanes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Long-chain linear alkanes have been used as model compounds for polyethylene in an attempt to identify the chemical nature of crosslinks formed in polyethylene when it undergoes γ-irradiation in the presence of acetylene. IR and UV spectral analysis of alkanes and polyethylene following acetylene-sensitized irradiation shows the formation of vinyl, trans-vinylene, and diene groups. A correlation of the conditions of formation suggests that in polyethylene the vinyl groups are restricted to amorphous regions, diene groups are restricted to the crystalline regions, and trans-vinylene groups are formed in both regions. There is no information on the nature of crosslinks. 13C-NMR analysis of alkanes following irradiation of molten alkanes in the presence of 13C-enriched acetylene has shown that a range of saturated alphatic structures are formed by inclusion of acetylene molecules in the alkane structure. They include ethyl branches, γ-branches,—CH(CH3)—, and —CH2—CH2— branches as the major species; the latter two are potential crosslink sites in the irradiation of polyethylene. In addition, the NMR analysis confirmed that the C atoms of the vinyl groups come from acetylene molecules and those of the trans-vinylene groups come from alkane molecules. Data on irradiation of the alkanes in the crystalline state showed that acetylene inclusion in the alkane structure is minimal under these conditions. The principal finding of this work is that acetylene can be incorporated as saturated aliphatic crosslinks in the amorphous regions of polyethylene during high-energy irradiation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1549-1561, 1997
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    O-nitromandelic acid: A chiral solvating agent for the NMR determination of chiral diamine enantiomeric purity (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 556-562 
    Details
    ISSN: 0899-0042
    Keywords: O-nitromandelic acid ; chiral solvating agent ; NMR ; enantiomeric purity ; mandelic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: O-Nitromandelic acid, easily prepared from either enantiomer of mandelic acid, has been used as a chiral solvating agent for the determination of enantiomeric purity of several diamine derivatives and other compounds using 1H NMR spectroscopy. Chirality 9:556-562, 1997. © 1997 Wiley-Liss, Inc.
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    Application of phenylglycine methyl ester (PGME) to determination of the absolute configuration of carboxylic acids having phenylalkyl group (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 550-555 
    Details
    ISSN: 0899-0042
    Keywords: NMR ; chiral anisotropic reagent ; long-chain carboxylic acid ; Mosher's method ; absolute configuration ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (R)- and (S)-phenylglycine methyl ester (PGME) was applied to elucidate the absolute configuration of a series of aliphatic carboxylic acids, 2a and 2b (n = 1-6), which possess a phenyl group on the chain, by the process similar to the modified Mosher's method. (S)-PGME was condensed with rac-2a and 2b, and the resulting diastereomeric pair was separated for each of 2a and 2b. Δδ values were calculated from the 1H-NMR chemical shifts of (R)-2a-(or 2b)-(S)-PGME and (R)-2a-(or 2b)-PGME amides. By analyzing the positive and negative distribution patterns for each compound, it was concluded that this new method was successful to predict the absolute configuration of such type of acids, and that no significant interaction between the two phenyl groups, one in the chain and the other in the PGME, was present. Chirality 9:550-555, 1997. © 1997 Wiley-Liss, Inc.
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    Bidirectional reaction steps in metabolic networks: I. Modeling and simulation of carbon isotope labeling experiments (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 101-117 
    Details
    ISSN: 0006-3592
    Keywords: stationary flux analysis ; metabolite flux balancing ; 13C isotope labeling experiments ; NMR ; metabolic engineering ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The extension of metabolite balancing with carbon labeling experiments, as described by Marx et al. (Biotechnol. Bioeng. 49: 11-29), results in a much more detailed stationary metabolic flux analysis. As opposed to basic metabolite flux balancing alone, this method enables both flux directions of bidirectional reaction steps to be quantitated. However, the mathematical treatment of carbon labeling systems is much more complicated, because it requires the solution of numerous balance equations that are bilinear with respect to fluxes and fractional labeling. In this study, a universal modeling framework is presented for describing the metabolite and carbon atom flux in a metabolic network. Bidirectional reaction steps are extensively treated and their impact on the system's labeling state is investigated. Various kinds of modeling assumptions, as usually made for metabolic fluxes, are expressed by linear constraint equations. A numerical algorithm for the solution of the resulting linear constrained set of nonlinear equations is developed. The numerical stability problems caused by large bidirectional fluxes are solved by a specially developed transformation method. Finally, the simulation of carbon labeling experiments is facilitated by a flexible software tool for network synthesis. An illustrative simulation study on flux identifiability from available flux and labeling measurements in the cyclic pentose phosphate pathway of a recombinant strain of Zymomonas mobilis concludes this contribution. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 101-117, 1997.
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    Lipopeptides with Improved Properties: Structure by NMR, Purification by HPLC and Structure-Activity Relationships of New Isoleucyl-rich Surfactins (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 145-154 
    Details
    ISSN: 1075-2617
    Keywords: biosurfactant ; lipopeptide ; surfactins ; Bacillus subtilis ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biosynthesis of bacterial isoleucyl-rich surfactins was controlled by supplementation of L-isoleucine to the culture medium. Two new variants, the [Ile4,7]- and [Ile2,4,7]surfactins, were thus produced by Bacillus subtilis and their separation was achieved by reverse-phase HPLC. Amino acids of the heptapeptide moiety were analysed by chemical methods, and the lipid moiety was identified to β-hydroxy anteiso pentadecanoic acid by combined GC/MS. Sequences were established on the basis of two-dimensional NMR data. Because conformational parameters issuing from NMR spectra suggested that the cyclic backbone fold was globally conserved in the new variants, structure-activity relationships were discussed in details on the basis of the three-dimensional model of surfactin in solution. Indeed, both variants have increased surface properties compared with that of surfactin, and this improvement is assigned to an increase of the hydrophobicity of the apolar domain favouring micellization. Furthermore, the additional Leu-to-Ile substitution at position 2 in the [Ile2,4,7]surfactin leads to a substantial increase of its affinity for calcium, when compared with that of [Ile4,7]surfactin or surfactin. This effect is assigned, from the model, to an increase in the accessibility of the acidic side chains constituting the calcium binding site. Thus, the propensities of such active lipopeptides for both hydrophobic and electrostatic interactions were improved, further substantiating that they can be rationally designed. © 1997 European Peptide Society and John Wiley & Sons, Ltd
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    3D structure of kaliotoxin: is residue 34 a key for channel selectivity? (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 314-319 
    Details
    ISSN: 1075-2617
    Keywords: kaliotoxin ; NMR ; K+ channel blockers ; scorpion toxin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kaliotoxin (KTX) is a natural peptide blocker of voltage-dependent K+ channels. The 3D structure of a truncated analogue of KTX (Fernández et al. (1994) Biochemistry 33, 14256-14263) was determined by NMR spectroscopy and showed significant differences from structures established for other related scorpion toxins. A recent publication with the structure of the complete toxin (Aiyar et al. (1995) Neuron 15, 1169-1181) did not confirm these differences. In this communication we report NMR data for KTX at pH 3.0, 5.5 and 7.2 and the 3D structure obtained from data at pH=5.5. Complete KTX displays a folding similar to that of other toxins with an α-helix and a β-sheet linked by two disulphide bonds. The pKa of His 34 is anomalously low (4.7-5.2 depending on the buffer) owing to its interaction with two Lys residues (including the essential Lys 27), the charged N-terminus and the side chain of Met 29. Charged residues are placed symmetrically with respect to an axis that approximately coincides with one of the principal components of the moment of inertia of the toxin. His 34, which occupies a well-defined position between two conserved Cys, is located on the centre of a layer of charged groups. Positively and negatively charged residues are found at the same position in related toxins. It is suggested that electrostatic effects modulate the distances between positive charges in flexible side chains, contributing to the fine tuning of the selectivity toward different channel subclasses and that the approximate coincidence between the moment of inertia and the charge axis facilitate the approach of the toxin to the channel. The very low pKa of His 34 implies that it will be completely unprotonated at physiological pH. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
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    Proton NMR investigation of the local dynamics of PEO in PEO/PMMA blends (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1095-1105 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; dynamics ; polyethylene oxide (PEO) ; polymethyl methacrylate (PMMA) ; polymer blend ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Longitudinal relaxation of proton magnetisation was used to characterize the molecular motions of PEO chains in compatible PEO (hydrogenated)/PMMA (deuterated) blends. Both the temperature and the PEO concentration, Φ, were varied. A maximum in the spin-lattice relaxation rate was observed and its properties were analyzed as a function of Φ. For Φ ≤ 0.50, the maximum is observed below the glass transition temperature of the blend; this shows that PEO chains dispersed in a matrix of PMMA remain highly mobile on a local scale even below Tg(Φ). A frequency-temperature correspondence procedure, applied to the measurements performed at two Larmor frequencies, 32 and 60 MHz, leads to a characteristic correlation time for PEO molecular motions. Its temperature dependence obeys a WLF free volume relation above the glass transition of the blends. The PEO free volume fraction and its thermal expansion are strongly reduced by the presence of the PMMA chains. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1095-1105, 1997
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    Characterization of mechanically sheared ethylene-propylene copolymers by high resolution NMR (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1955-1961 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; EPM ; EPDM ; polyolefin ; mechanochemistry ; chain ends ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We report high-resolution solution-state NMR experiments on chain ends generated in ethylene-propylene copolymers by mechanical shearing in an extruder. The use of the higher resolution of the 13C-NMR spectrum, in a two-dimensional 1H-13C chemical shift correlation experiment, has allowed the complete resolution and assignment of the olefinic chain-end region of the 1H-NMR spectrum. Simultaneously, the assignments of the 13C olefinic resonances, previously identified [A. C. Kolbert, J. G. Didier, and L. Xu, Macromolecules, 29, 8591 (1996)] are confirmed. An iterative method for calculating the average molecular weight, based on quantitative measurements of the olefinic 1H-NMR peak intensities is introduced and these results are compared with measurements from 13C-NMR and size exclusion chromatography and correlated to reduced viscosities. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1955-1961, 1997
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    Nanoheterogeneity in PEO/PMMA blends probed by 129Xe-NMR (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2681-2688 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; 129Xe ; blends ; PEO ; PMMA ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Xenon has been used as a structural probe of solid poly(ethylene oxide)/atactic poly(methyl methacrylate) (PEO/PMMA) blends of concentrations 10/90 to 75/25. 129Xe-NMR spectra at 293 K show significant changes in line width and chemical shift as the blend composition is varied. The 129Xe spectra are interpreted in terms of exchange between amorphous single-phase PEO and PMMA domains. It is shown that a simple two-site exchange model can be used to calculate spectra which fit the experimental data over the whole concentration range. Xe exchange between blend subregions is demonstrated also by a two-dimensional NMR experiment. The PEO/PMMA results are compared to previously published poly(vinylidene fluoride)/PMMA 129Xe spectra. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2681-2688, 1997
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    An NMR and vibrational study of 5-bromouridine and its base pairing with guanosine and adenosine (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 3 (1997), S. 241-249 
    Details
    ISSN: 1075-4261
    Keywords: NMR ; vibrational spectroscopy ; 5-bromouridine ; base pairing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A multinuclear magnetic resonance and vibrational study on 5-bromouridine and its base pairing with guanosine and adenosine in deuterated dimethyl sulfoxide at different concentrations is reported. A dicarbonylic non-self-associated form is suggested for 5-bromouridine on the basis of the 1H-, 15N-NMR, and Raman data. When guanosine is added in equimolar amounts, a downfield shift of the (N3)H proton of 5-bromouridine and of the (N1)H and NH2 protons of guanosine is observed; these results can be interpreted, according to the Raman ones, considering that only a fraction of guanosine is “wobble base paired” with 5-bromouridine, whereas the remaining part is self-associated. When 5-bromouridine is mixed with adenosine, the proton chemical shift of the aminic NH2 of adenosine increases and the (N3)H iminic of 5-bromouridine moves downfield at a value higher than that observed for the 5-bromouridine-guanosine mixture. This behavior supports the hypothesis that 5-bromouridine interacts more with adenosine than with guanosine, but the results obtained are not able to establish which type of pairing (Watson-Crick or Hoogsteen) is present. Finally, the infrared spectrum of the solid 5-bromouridine: adenosine adduct, for which X-ray measurements of other authors suggested a Hoogsteen pairing, is reported and the observed bands are discussed. © 1997 John Wiley & Sons, Inc. Biospect 3: 241-249, 1997
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    Constrained Refinement Based on NOE and Chemical Shift Information: The Monomer Form of Arginine-Vasopressin-like Insect Factor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 133-140 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; chemical shift estimation ; restrained refinement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Via the refinement process of the monomer form of an arginine-vasopressin-like insect factor, the paper analyses the most relevant NMR information to define the solution structure of a flexible peptide. The relative importance of the different NOE constraints is discussed. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
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    The design of a specific ligand of HIV gp120 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 383-390 
    Details
    ISSN: 1075-2617
    Keywords: CD4 ; gp120 ; NMR ; structure ; peptides ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of CD4 suggested that the C/G38 and C/L44 replacements with the consequent cystine bridge formation are compatible with the native structure of that molecular moiety. As the NQGSF sequence, corresponding to the 39-43 fragment of human CD4 protein, was found to be involved in the HIV gp120 interaction, it has been synthesized in a cyclic form by adding two cysteine residues at the amino and carboxy termini. 1H-NMR studies show that the predominant solution conformation of cyclo-[CNQGSFC] is a type II β-turn centred on the NQGS segment. Structural and dynamic properties of the peptide are also analysed in relation to the in vitro activity. © 1997 European Peptide Society and John Wiley & Sons, Ltd.J. Pep. Sci. 3: 383-390No. of Figures: 7. No. of Tables: 1. No. of References: 33.
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    Structural comparison in solution of a native and retro peptide derived from the third helix of Staphylococcus aureus protein A, domain B: retro peptides, a useful tool for the discrimination of helix stabilization factors dependent on the peptide chain orientation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 299-313 
    Details
    ISSN: 1075-2617
    Keywords: NMR ; retro-enantio ; helix ; macrodipole ; protein A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A peptide fragment corresponding to the third helix of Staphylococcus Aureus protein A, domain B, was chosen to study the effect of the main-chain direction upon secondary structure formation and stability, applying the retro-enantio concept. For this purpose, two peptides consisting of the native (Ln) and reversed (Lr) sequences were synthesized and their conformational preferences analysed by CD and NMR spectroscopy. A combination of CD and NMR data, such as molar ellipcitity, NOE connectivities, Hα and NH chemical shifts, 3JαN coupling constants and amide temperature coefficients indicated the presence of nascent helices for both Ln and Lr in water, stabilized upon addition of the fluorinated solvents TFE and HFIP. Helix formation and stabilization appeared to be very similar in both normal and retro peptides, despite the unfavourable charge-macrodipole interactions and bad N-capping in the retro peptide. Thus, these helix stabilization factors are not a secondary structure as determined for this specific peptide. In general, the synthesis and confirmational analysis of peptide pairs with opposite main-chain directions, normal and retro peptides, could be useful in the determination of secondary structure stabilization factors dependent on the direction. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
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    Characterization of silane-modified ZrO2 powder surfaces (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 917-923 
    Details
    ISSN: 0142-2421
    Keywords: x-ray photoelectron spectroscopy ; infrared spectroscopy ; NMR ; silane, γ-MPS ; zirconia ; zircon ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Polymerizable organic silane molecules such as 3-(trimethoxysilyl)propylmethacrylate (γ-MPS) have been grafted onto the surface of ZrO2 powders, via hydroxyl groups, to obtain hybrid ‘macromonomers’. A combination of x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and 29Si nuclear magnetic resonance (NMR) spectroscopy have been employed to study the interaction between organic silane molecules and the surface of the ZrO2 powders. The core-level XPS regions, Zr3d, O1s, C1s and Si2p, have been studied to determine the nature of chemical bonding between the organic grafted monomer and inorganic phase and correlated with NMR results. Based upon the results obtained, it is proposed that grafting results in γ-MPS bonded to the ZrO2 powder surface via Zr—O—Si bonds accompanied by interlinkage of γ-MPS molecules through Si—O—Si bonding. © 1997 John Wiley & Sons, Ltd.
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    Synthesen und Eigenschaften von Tris(perfluoralkyl)arsen- und -antimon(III, V)-VerbindungenProfessor Hans Bürger zum 60. Geburtstag gewidmet (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 1183-1189 
    Details
    ISSN: 0044-2313
    Keywords: Tris(perfluoroalkyl) arsenic and antimony ; tris(pentafluoroethyl) arsenic and antimony(V) halides ; synthesis ; NMR ; mass spectra ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparations and Properties of Tris(perfluoroalkyl) Arsenic and Antimony(III, V) CompoundsAs(Rf)3 and Sb(Rf)3 (Rf=C2F5, C4F9, C6F13) are prepared in good yields by the polar reactions of AsCl3 and SbCl3 with bis(perfluoroalkyl) cadmium compounds as colourless liquids or solids. The oxidation of As(C2F5)3 and Sb(C2F5)3 with XeF2 gives the difluorides M(C2F5)3F2 (M=As, Sb). As(C2F5)3Cl2 is prepared by chlorination of As(C2F5)3 in the presence of AlCl3, while Sb(C2F5)3Cl2 is formed in the reaction of Sb(C2F5)3F2 with (CH3)3SiCl. During the reaction of M(C2F5)3F2 with (CH3)3SiBr 19F-NMR spectroscopic evidence is found for M(C2F5)3 Br2. The thermal decompositions of M(C2F5)3F2 mainly yield C4F10 and M(C2F5)F2, while the thermal decompositions of M(C2F5)3Cl2 yield M(C2F5)2Cl and C2F5Cl. The properties and spectroscopic data of the new compounds are described.
    Notes: As(Rf)3 und Sb(Rf)3 (Rf=C2F5, C4F9, C6F13) werden durch Umsetzungen von AsCl3 und SbCl3 mit Bis(perfluoralkyl)cadmium-Verbindungen unter polaren Bedingungen in guten Ausbeuten als farblose Flüssigkeiten bzw. Festkörper dargestellt. Durch Oxidation von As(C2F5)3 und Sb(C2F5)3 mit XeF2 entstehen die Difluoride M(C2F5)3F2 (M=As, Sb). Die Darstellung von As(C2F5)3Cl2 gelingt durch Chlorierung von As(C2F5)3 in Gegenwart von AlCl3; die Darstellung von Sb(C2F5)3Cl2 durch Reaktion von Sb(C2F5)3F2 mit (CH3)3SiCl. Die Dibromide M(C2F5)3Br2 sind nur 19F-NMR-spektroskopisch bei der Reaktion von M(C2F5)3F2 mit (CH3)3SiBr nachweisbar. Bei der thermischen Zersetzung von M(C2F5)3F2 entstehen hauptsächlich C4F10 und M(C2F5)F2, während die thermische Zersetzung von M(C2F5)3Cl2 unter Bildung von M(C2F5)2Cl und C2F5Cl verläuft. Eigenschaften und spektroskopische Daten der neuen Verbindungen werden beschrieben.
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    Synthese, NMR-spektroskopische Charakterisierung und Struktur von Bis(1,2-dimethoxyethan-O,O′)barium-bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenid] (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 1237-1242 
    Details
    ISSN: 0044-2313
    Keywords: Barium 1-Aza-3-phosphapropenide ; 1,3-Azaphosphaallyl Anion ; NMR ; X-ray Structure Determination ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis, NMR Spectroscopic Characterization and Structure of Bis(1,2-dimethoxyethane-O,O′)barium Bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenide]Barium-bis[bis(trimethylsilyl)phosphanide] 1 reacts with two equivalents of benzonitrile to give barium bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenide]; the choice of the solvent determines whether a tris-(tetrahydrofuran)- or a bis(1,2-dimethoxyethane)-complex 2 can be isolated. 2 crystallizes from DME as red cuboids (monoclinic, C2/c, a = 1627.0(3), b = 1836.6(3), c = 1602.5(2) pm; β = 96.071(12)°; V = 4761.7(12); Z = 4; wR2 = 0.0851). The phosphorus atom displays a pyramidal surrounding in contrast to the planar coordination sphere of the nitrogen atom. In addition a twist within the P—C—N skeleton of the heteroallyl anion is observed.
    Notes: Barium-bis[bis(trimethylsilyl)phosphanid] 1 reagiert mit zwei Äquivalenten Benzonitril zu Barium-bis[1,3-bis(trimethylsilyl)-2-phenyl-1-aza-3-phosphapropenid]; durch die Wahl des Lösungsmittels läßt sich entweder der Tris(tetrahydrofuran)- oder der Bis(1,2-dimethoxyethan)-Komplex 2 isolieren. Verbindung 2 kristallisiert aus DME in Form roter Würfel aus (monoklin. C2/c, a = 1627,0(3), b = 1836,6(3), c = 1602,5(2) pm; β = 96,071(12)°; V = 4761,7(12); Z = 4; wR2 = 0,0851). Während die Koordinationssphäre des Stickstoffatoms planar ist, befindet sich das Phosphoratom in einer pyramidalen Umgebung. Zusätzlich beobachtet man im 1-Aza-3-phosphapropenid-Anion eine leichte Verdrillung.
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    Eigenschaften und Reaktionen von Tris(2,6-difluorphenyl)bismut(III)- und Tris(2,6-difluorphenyl)bismut(V)-Verbindungen (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 122-128 
    Details
    ISSN: 0044-2313
    Keywords: tris(2,6-difluorophenyl)bismuth dihalides ; tris(2,6-difluorophenyl)bismuth bis(trifluoromethanesulfonate) ; tris(2,6-difluorophenyl)bismuth bis(trifluoroacetate) ; 2,6-difluorophenyliodine tetrafluoride ; synthesis ; NMR ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Properties and Reactions of Tris(2,6-difluorophenyl)bismuth(III) and Tris(2,6-difluorophenyl)bismuth(V) Derivatives(2,6-F2C6H3)3BiF2 and (2,6-F2C6H3)3BiCl2 are prepared oxidizing (2,6-F2C6H3)3Bi with XeF2 or Cl2 respectively, while direct fluorination effect the oxidation of the aromatic system. The reaction of (2,6-F2C6H3)3BiCl2 With (CH3)3SiCl yields (2,6-F2C6H3)3BiCl2. Attempts to oxidize (2,6-F2C6H3)3Bi with Br2, I2 and ICl give (2,6-F2C6H3)X and BiX′3 (X = Br, I; X′ = Cl, Br, I). The rection of (2,6-F2C6H3)3Bi with IF5 gives BiF3 and (2,6-F2C6H3)IF4. (2,6-F2C6H3)3Bi(OCOCF3)2 and (2,6-F2C6H3)3Bi(OSO2CF3)2 are formed via ligand exchange rection of (2,6-F2C6H3)3BiF2 with (CH3)3SiOR or of (2,6-F2C6H3)3BiCl2 with AgOR (R = COCF3, SO2CF3). The preparations and properties of the new compounds are described. (2,6-F2C6H3)3Sb and (2,6-F2C6H3)2Te are prepared by the transmetalation reactions of (2,6-F2C6H3)3Bi with Sb and Te.
    Notes: (2,6-F2C6H3)3 BiF2und(2,6-F2C6H3)3BiCl2 werden durch Oxidation von (2,6-F2C6H3)3 Bi mit XeF2 bzw. Cl2 dargestellt, während die Direktfluorierung zu einer Oxidation des aromatischen Systems führt, (2,6-F2C6H3)3BiCl2 wird auch durch die Umsetzung von (2,6-F2C6H3)3 BiF2 mit (CH3)3SiCl erhalten. Oxidationsversuche von (2,6-F2C6H3)3Bi mit Br2, I2 und ICl ergeben (2,6-F2C6H3)X und BiX′3 (X = Br, I; X′ = Cl, Br, I). Die Umsetzung von (2,6-F2C6H3)3Bi mit IF5 führt zur Bildung von BiF3 und (2,6-F2C6H3)IF4. (2,6-F2C6H3)3Bi(OCOCF3)2 bzw. (2,6-F2C6H3)3Bi(OSO2CF3)2 werden durch Ligandenaustauschreaktionen von (2,6-F2C6H3)3BiF2 mit (CH3)3SiOR oder von (2,6-F2C6H3)3BiCl2 mit AgOR gebildet (R COCF3, SO2CF3). Die Syntheseverfahren und Eigenschaften der neuen Verbindungen werden beschrieben. Durch Transmetallierungsreaktionen von (2,6-F2C6H3)3Bi mit Te und Sb werden (2,6-F2C6H3)3Sb und (2,6-F2C6H3)2Te dargestellt.
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    Organometallic Complexes with Biological Molecules: VII. Dialkyl- and Trialkyl-tin (IV)[meso-tetra(4-carboxyphenyl)porphinate] Derivatives: Solid-state, Solution-phase Structural Aspects and In Vivo Effects (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 499-511 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; porphyrin ; structures ; Mössbauer ; infrared ; NMR ; biologial activity ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, the structural features and the in vivo biological activity of diorganotin(IV) and triorganotin(IV) derivatives of [meso-tetra(4-carboxyphenyl)porphine] (H4TPPC) are reported. Derivatives with general formula (R2Sn)2TPPC and (R3Sn)4TPPC (R=Me, Bu, and Ph) were obtained, and the main information extracted from the infrared and Mössbauer spectral data, in the solid state, was in favor of the occurrence of five-coordinated tin(IV) atoms, in a polymeric trigonal-bipyramidal configuration, attained through two differently coordinated, ester-type and chelating respectively, carboxylate anions in [R2Sn]2TPPC, while in [Alk3Sn]4TPPC five-coordination of the tin(IV) atom is reached through bridging carboxylate groups.1H and 13C NMR spectra, in DMSO-d6 or CDCl3 suggested that the soluble derivatives, at room temperature or at 342 K, were present in solution as simple monomers.The interactions of (trimethyltin)4[meso-tetra(4-carboxyphenyl)porphinate] (TMTPPC) and (tributyltin)4[meso-tetra(4-carboxyphenyl)porphinate] (TBTPPC) with Bluescript KS(+) plasmid and cultured 3T3 fibroblasts were studied.Both compounds have a clear inhibitory effect on the growth of cultured mouse embryonal fibroblasts (NIH-3T3), TBTPPC being much more active. No evidence was found, however, for DNA cleavage by the compounds at molar ratios as high as 1:10 (TMTPPC, TBTPPC/DNA base pairs).According to our observations, the cytotoxicity of TBTPPC and TMTPPC does not seem to be based on direct interaction with DNA. © 1997 John Wiley & Sons, Ltd.
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    Organometallic Complexes with Biological Molecules: VIII. Synthesis, Solid State and in vivo Investigation of Triorganotin(IV) Derivatives of L-Homocysteic Acid (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 601-616 
    Details
    ISSN: 0268-2605
    Keywords: triorganotin(IV) ; L-homocysteic acid ; infrared ; Mössbauer ; NMR ; sea urchin ; Paracentrotus lividus (Echinodermata) ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new triorganotin(IV) derivatives of L-homocysteic acid (L-HCAH) with formula R3Sn(L-HCA) (R=Me, nBu, Ph) have been synthesized. Their solid-state configurations were determined by IR and Mössbauer spectroscopy. The tin(IV) atom is five-coordinated in all the complexes, with the L-homocysteic acid behaving as a monoanionic bidentate ligand coordinating the tin(IV) atom through a chelating or bridging carboxylate group. The sulfonate (SO3-) and NH3+ groups of L-homocysteic acid maintain their free acid configuration and hence do not participate to the coordination of the tin(IV) atom. Coordination hypotheses have been checked through the correlation between the Mössbauer parameter isomer shift, δ, and partial atomic charge on the tin atoms, QSn, performed, for all the new organotin(IV) compounds, on the basis of an equalization procedure applied to idealized trigonal-bipyramidal structures for R3Sn(L-HCA).1H and 13C NMR spectra of the complexes show that pentacoordination of the tin atom, with R groups in the equatorial plane of a trigonal bipyramid, is retained in DMSO solution. The NMR data confirm also that the uncoordinated NH3+ group of the ligand is still present in solution.Results gathered after exposure of two- to four-cell embryos of the sea urchin Paracentrotus lividus (Echinodermata) to the triorganotin(IV) L-homocysteate derivatives as well as to the parent triorganotin(IV) chlorides document cytotoxicity of the complexes, while free L-homocysteic acid exerts no significant toxic activity. The trimethyltin(IV) L-homocysteate derivative seems to exert a lower cytotoxicity than the tributyl- and triphenyl-tin(IV) ones. Different structural lesions have been identified by comparative analysis of mitotic chromosomes from untreated embryos (negative controls) and embryos treated with triorganotin(IV) L-homocysteate derivatives, such as (1) suppression of the stretch among sister chromatids at the beginning of anaphase stage; (2) deeply stained zones mainly located at the telomeric regions of chromosomes; (3) arm breakages; and (4) chromosome bridges among daughter chromosomes at anaphase stage. A colchicine-like effect of triorganotin(IV) L-homocysteate derivatives was observed. © 1997 John Wiley & Sons, Ltd.
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    The Effect of Organotin Compounds on the Permeability of Model Biological Membranes (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 369-379 
    Details
    ISSN: 0268-2605
    Keywords: efflux ; liposomes ; dimethylarsinic acid ; membrane modification ; egg phosphatidylcholine ; bilayer ; tributyltin chloride ; monobutyltin trichloride ; facilitated diffusion ; NMR ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The efflux of dimethylarsinic acid (DMA) from liposomes formed from egg phosphatidylcholine (EPC) is increased when tributyltin chloride (TBT) is added to the extraliposomal compartment; however the addition of monobutyltin trichloride (MBT) slows down the efflux. When the liposomes are prepared from EPC and organotin compounds, different mechanisms for DMA efflux seem to operate: TBT-EPC liposomes show a mixture of facilitated and passive diffusion; MBT-EPC liposomes show only passive diffusion. The facilitated diffusion of DMA- seems to be stopped by the addition of TBT to the extraliposomal compartment. © 1997 by John Wiley & Sons, Ltd.
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    Organometallic complexes with biological molecules. IX. Diorgano- and triorgano-tin(IV)[meso-tetra (4-sulfonatophenyl)porphinate] derivatives: solid-state and solution-phase structural aspects and in vivo effects (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 707-719 
    Details
    ISSN: 0268-2605
    Keywords: organotin(IV) ; porphine ; Mössbauer ; NMR ; development ; Ascidiaceae ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diorgano- and triorgano-tin(IV) derivatives of meso-tetra(4-sulfonatophenyl)porphine (H4TPPS) with general formula (R2Sn)2TPPS and (R3Sn)4TPPS (TPPS4-=[meso-tetra(4-sulfonatophenyl)porphinate]4-, R=Me, Bu, Ph) have been obtained and their solid-state configuration inferred on the basis of IR and Mössbauer spectroscopy, while solution-phase studies have been carried out by 1H and 13C NMR in DMSO-d6, together with determination of the in vivo cytotoxicity of the new derivatives towards embryonic development of Ciona intestinalis. In particular, octahedral and trigonal-bipyramidal eq-R3Sn polymeric configurations are proposed, in the solid state, respectively for (R2Sn)2TPPS and (R3Sn)4TPPS complexes, with the arylsulfonate groups behaving as monoanionic bidentate bridging ligands.The 1H and 13C NMR data lead to the conclusion that the metal-to-ligand ratio (2:1 or 4:1), binding site (the sulfonato-group oxygens), and the coordination polyhedron around the metal (trans-octahedral or trigonal-bipyramidal) found in the solid state are preserved in solution. © 1997 John Wiley & Sons, Ltd.
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    Synthesis, characterization and cytotoxic activity of complexes of diorganotin(IV) halides with N-methyl-2,2′-bisimidazole (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 963-968 
    Details
    ISSN: 0268-2605
    Keywords: diorganotin(IV) halides ; N-methyl-2,2′-bisimidazole ; Mössbauer ; IR ; NMR ; cytostatic activity ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The compounds [SnR2X2(MBIm)] (MBIm=N-methyl-2,2′-bisimidazole; R=Me, Et, Bu, Ph; X=Cl or Br) have been synthesized and characterized by IR, Raman, Mössbauer and NMR spectroscopy, and their capacity to inhibit tumour cell division has been assayed. Measurements of conductivity in acetonitrile show the adducts to behave as non-ionogens in this solvent. The IR, Raman and Mössbauer data suggest that all the complexes have analogous pseudo-octahedral coordination geometries, with the R groups trans and MBIm bidentate. The 1H NMR spectra show the MBIm ligand to be partially dissociated in CDCl3. The most active compounds against the established cell line KB were the butyl derivatives. © 1997 John Wiley & Sons, Ltd.
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    Mono-organotin(IV) and tin(IV) derivatives of 2-mercaptopyridine and 2-mercaptopyrimidine: X-ray structures of methyl-tris(2-pyridinethiolato)tin(IV) and phenyl-tris(2-pyridinethiolato)tin(IV)·1.5CHCl3 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 11 (1997), S. 869-888 
    Details
    ISSN: 0268-2605
    Keywords: organotin ; pyridine-2-thiolate complexes ; pyrimidine-2-thiolate complexes ; crystal structure ; Mössbauer ; IR ; NMR ; Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mono-organotin(IV) and tin(IV) derivatives of 2-mercaptopyridine (HSPy) and 2-mercaptopyrimidine (HSPym), RSnL3 (R=Me, n-Bu, Ph; L=SPy, SPym; R=Bz=benzyl, o-ClBz, o-ClC6H4, p-ClC6H4, o-tolyl, p-tolyl; L=SPy), RSnClL2 (R=Me, n-Bu, Ph; L=SPy, SPym), RSnCl2L (R=Me, n-Bu; L=SPy, SPym) and SnCl4-nLn (L=SPy, SPym; n=2, 4) were obtained from RSnCl3 or SnCl4 and NaL or by neutralization (R=Ph, p-tolyl; L=SPy, SPym). RSnClL2 and RSnCl2L were better prepared by comproportionation of RSnCl3 and RSnL3.MeSn(SPy)3 and PhSn(SPy)3·1.5CHCl3 crystals, as determined by single-crystal X-ray diffraction, are monoclinic. In the discrete monomeric RSn(SPy)3 units, three bidentate SPy ligands together with R form a distorted pentagonal bipyramid around tin. One S and the C(R) atom are in the axial positions. Two S atoms and three N atoms form the pentagonal plane.From 119Sn Mössbauer and IR data, analogous structures are inferred for the other solid RSnL3 compounds, except for R=Bz, o-ClBz, o-ClC6H4 and o-tolyl, in which tin would be hexacoordinated. In the compounds RSnClL2 and RSnCl2L, tin is at the center of an octahedron or a trigonal bipyramid, respectively. For Sn(SPym)4 and SnCl2(SPym)2, the same type of octahedral structure as was previously found for Sn(SPy)4·HSPy and SnCl2(SPy)2 is proposed.According to IR and 1H, 13C and 119Sn NMR data, the solid-state molecular structures are retained in chloroform and dimethyl sulfoxide solution. © 1997 John Wiley & Sons, Ltd.
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    Aliphatic-aromatic poly(ether amide)s containing oxyethylene units. Synthesis and characterization (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 659-667 
    Details
    ISSN: 0887-624X
    Keywords: condensation monomers ; amide-ether copolymers ; solution and interfacial polycondensation ; NMR ; GPC ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of aromatic polyamides containing oxyethylene units is reported, and the differences observed in polycondensation yields, molecular weights, and molecular weight distributions, as a function of the method of synthesis, are discussed. Four diamines containing oxyethylene units and aromatic rings, meta and para oriented, and their corresponding hydrochlorides were prepared as condensation monomers to be combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC). High molecular weight polyamides were obtained by interfacial and low-temperature solution methods. Values of (OVERLINE)M(/OVERLINE)n up to 6 × 104 g/mol and (OVERLINE)M(/OVERLINE)w up to 2 × 105 g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of (OVERLINE)M(/OVERLINE)n up to 2 × 105 g/mol and (OVERLINE)M(/OVERLINE)w up to 5 × 105 g/mol by using polystyrene standards. © 1996 John Wiley & Sons, Inc.
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    An investigation of radiation-induced structural changes in nitrile rubber (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2439-2454 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; nitrile rubber ; NMR ; ESR ; radicals ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of radiation-induced structural changes in nitrile rubber with different acrylonitrile contents were investigated by ESR, NMR, and FTIR. To investigate new structures solid-state NMR methods had to be used due to crosslinking of the irradiated rubbers, and higher probe temperatures were used to obtain better resolution. The radicals generated on the acrylonitrile groups were found to abstract hydrogen from the adjacent butadiene units resulting in the formation of allylic radicals. These allylic radicals reacted to form intermolecular crosslinks and cyclisation. Cyclisation of the butadiene units were found to occur in the initial stages of the irradiation. Radiation yields of radicals increased with acrylonitrile content from 1.42, 1.58, to 2.42 for 18, 30, and 45% acrylonitrile rubbers. The radiation yields for intermolecular crosslinking were higher in rubbers with higher acrylonitrile contents, giving G values of 17.8, 21.3, and 24.5 for 18, 30, and 45% acrylonitrile rubbers, respectively. However, the crosslink clustering was found to be less in the rubbers with a higher acrylonitrile content. © 1996 John Wiley & Sons, Inc.
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    End group chemistry of fluoro-oligomers: Highly selective syntheses of diepoxy, diallyl, and tetraol derivatives (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 3263-3275 
    Details
    ISSN: 0887-624X
    Keywords: end group chemistry ; chemical modification ; fluoropolyether ; oligomer ; allyl ; epoxide ; polyol ; tetraol ; oxidation ; etherification ; NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different synthetic methods for the preparation of polyfunctional fluorinated oligomers were explored and the results compared. Fluoropolyether macromonomers bearing epoxy, allyl, and polyhydroxy end groups were synthesized and spectroscopically characterized. For obtaining a polyol (namely tetraol) functionality, a highly selective route was the reaction of the fluoropolyether macrodiol ZDOL with allylic halides and subsequent oxidation reaction at the C=C double bond by means of peroxyacids. This approach made it possible to obtain a segmented structure RH-RF-RH in which the molecular body RF consisted of a perfluoropolyether block endcapped by two hydrogenated segments RH, where RH = - CH2OCH2CH(OH)CH2OH. Unlike other more conventional syntheses, which always produce byproducts and higher molecular weight species such as RH-(RF-RH)n-RF-RH or RH-RF-(RH)n-, the described method offers high yields and selectivity. The fluoropolyether polyfunctional derivatives offer the possibility to prepare a variety of highly crosslinked fluorinated materials and, owing to their well defined regularly segmented structures, they also constitute interesting models for the understanding of basic structure-property relations of fluoro-oligomers and their copolymers. © 1996 John Wiley & Sons, Inc.
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    Mechanism of radiation degradation of polyisobutylene (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 971-984 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; polyisobutylene ; NMR ; GC/MS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GC, GC/MS, GPC, and Solution NMR spectra were used to study the γ radiolysis of polyisobutylene (PIB) in vacuum to different total doses (0-900 kGy) and at different temperatures (77-423 K). NMR spectra show a large number of new resonances with relatively narrow line widths, and a variety of NMR techniques have been employed to determine and quantify the structures associated with these new resonances. Chemical shift assignments were made by comparison with those for small molecule model compounds and predictions based upon calculations according to several different schemes. Chain-end structures have been proposed that account well for the majority of the new resonances, all being the result of an initial chain scission reaction initiated by the radiation. These assignments support some previous proposals for the mechanism of radiation degradation of polyisobutylene and exclude others. For example, NMR provides no evidence for the formation of ethyl chain ends and some of the main chain unsaturated structures previously proposed. NMR also indicate that at higher doses the chain end products formed during initial stages undergo secondary reactions. GC/MS data show the formation of oligomers during irradiation, which may be due to a backbitting mechanism. © 1996 John Wiley & Sons, Inc.
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    An efficient Riemann solver for open channel flows (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 13-20 
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    ISSN: 1069-8299
    Keywords: open channel flows ; Riemann solver ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient numerical method is developed for the one-dimensional open channel flow equations. The scheme is a modification of one presented recently, but with an improvement in the efficiency made through the use of the arithmetic mean as an average of flow variables across the interface between adjacent states. Numerical results are shown for two problems, and an indication of the efficiency gained is given.
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    An explicit sparse unsymmetric finite element solver (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 21-29 
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    ISSN: 1069-8299
    Keywords: finite element systems ; elliptic partial differential equations ; approximate LU factorization ; explicit matrix inversion ; preconditioning ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new class of explicit generalized approximate inverse finite element matrix algorithmic methods, based on the concept of LU-sparse factorization procedures, without inverting the decomposition factors, has recently been introduced. The large sparse unsymmetric coefficient matrix of irregular structure is factorized approximately and, in conjunction with approximate inverse matrix techniques, yields explicit preconditioned methods for the finite element (FE) and finite difference (FD) method. The numerical implementation of these algorithms is presented and Fortran subroutines for the efficient solution of the sparse unsymmetric linear systems are given.
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    Conference diary (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 147-148 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640120202
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    Annoucement (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 149-150 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640120203
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    An asymptotic formula for correcting finite element predicted natural frequencies of membrane vibration problems (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 63-73 
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    ISSN: 1069-8299
    Keywords: asymptotic solution ; natural frequencies ; membrane vibrations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper an asymptotic formula has been developed to correct the discretization error for the finite element predicted natural frequencies of membrane transverse vibration problems. The general idea behind deriving this asymptotic formula is that, when the finite element size approaches zero, a discretized finite element system approaches a continuous system and the predicted natural frequencies of the system from the finite element analysis therefore approach the exact solutions of the system. Without losing generality, several different finite element mesh patterns have been considered and the same asymptotic formula for correcting the finite element predicted natural frequency has been obtained for all the different mesh patterns because of the uniqueness of the exact solution to the natural frequency of a real structure. The usefulness, effectiveness and efficiency of the present asymptotic formula have been assessed by a simple but critical problem, for which the exact solution is available for comparison. In order to investigate the applicability of the asymptotic formula to practical engineering problems, two challenging membrane vibration problems of irregular shapes, an L-shape and a tapered shape with a circular hole in the centre, have also been analysed. The related numerical results have demonstrated that the asymptotic formula provides a very useful post-processing error corrector for the finite element predicted natural frequencies of membrane transverse vibration problems, even though the problem domains are of irregular shape. The greatest advantage in using the present asymptotic formula is that it yields a solution of higher accuracy, by simply using the formula to correct the rough solution obtained from a much coarser finite element mesh with fewer degrees of freedom, without any further finite element calculation.
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    Vibration of continuous beams using modified beam vibration functions (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 107-114 
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    ISSN: 1069-8299
    Keywords: beam ; vibration ; trial functions ; Ritz method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Free vibration of beams with intermediate point supports is studied by the classical Ritz method within the context of Euler beam theory. For the Ritz method, the displacement of a beam is approximated by a set of admissible trial functions which must satisfy the kinematic conditions at the ends and intermediate supports of the beam. To this end, a polynomial is superimposed on the conventional single-span beam vibration functions to form continuous-span or modified beam vibration functions. These modified beam functions are taken as the admissible trial functions for subsequent formulation. Stiffness and mass matrices are formulated using the conventional procedure and the resulting linear eigen-equation can be solved easily. A number of numerical examples are given to demonstrate the accuracy and efficiency of the present method.
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    A symbolic computation procedure for the generation of Gauss quadrature rules with a user-defined weight function (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 141-145 
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    ISSN: 1069-8299
    Keywords: numerical integration ; Gauss quadrature rules ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The advance of powerful software for symbolic and numerical computations such as Mathematica sheds a new light on a paper by Golub and Welsch from 1969. Based on this paper the author describes a Mathematica procedure for determining the weights and abscissae of a Gauss quadrature rule with a user-defined weight function. After a brief description of the algorithm and its implementation examples demonstrate the usefulness of the procedure. The procedure is extremely useful if one has to compute many integrals with the same, possibly weakly singular, weight function. This might happen, for example, in the boundary element method.
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    A singular function boundary integral method for the Laplace equation (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 127-134 
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    ISSN: 1069-8299
    Keywords: Laplace equation ; singularities ; boundary integral method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The authors present a new singular function boundary integral method for the numerical solution of problems with singularities which is based on approximation of the solution by the leading terms of the local asymptotic expansion. The essential boundary conditions are weakly enforced by means of appropriate Lagrange multipliers. The method is applied to a benchmark Laplace-equation problem, the Motz problem, giving extremely accurate estimates for the leading singular coefficients. The method converges exponentially with the number of singular functions and requires a low computational cost. Comparisons are made to the analytical solution and other numerical methods.
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    On dependent variables and instrumental errors in filtering of experimental data (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 115-125 
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    ISSN: 1069-8299
    Keywords: experimental measurements ; filtering ; dynamics ; structures ; models ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents a filtering algorithm which corrects the results of measurements of certain physical quantities if some information about the model of the system is known. The results of measurements are not only obtained in an explicit form for the considered variable but also in a form of dependent variables which are related to the measured quantity by certain mathematical relations. Combining the information obtained from different measurements, much better accuracy can be reached. It is proved that the proposed algorithm is able not only to enhance the measured data but also to detect the errors of the instruments.
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996) 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640120301
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    Conference diary (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 221-222 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640120302
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    On a direct inversion of the impedance matrix in response reanalysis (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 151-159 
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    ISSN: 1069-8299
    Keywords: response reanalysis ; structural modifications ; matrix partitioning ; Sherman-Morrison formula ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper lays out an exact method, using the receptance strategy, to calculate the frequency response of a modified structure. A direct inversion of the modified impedance matrix is proposed, which reduces the computation time for successive calculations of an evolving design of the structure.
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    On permanent capillar-heavy waves in circular shaped channels (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 175-180 
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    ISSN: 1069-8299
    Keywords: permanent capillar-heavy waves ; conformal mapping ; circular shaped channels ; Zeidler's method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: E. Zeidler gave an existence and uniqueness proof for permanent heavy and capillar-heavy waves in circular shaped channels. Based on this proof and on a general computational method for constructing the solutions numerically given by the author (1991), the case of permanent heavy waves in circular shaped channels was recently computed by the author. In this work the case of permanent capillar-heavy waves in circular shaped channels is considered.
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    An inverse solution procedure for material parameters identification in large plastic deformations (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 161-173 
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    ISSN: 1069-8299
    Keywords: inverse identification ; non-linear behaviour ; material parameters ; sensitivity analysis ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The identification of materials rheological behaviour in the non-linear range is based on experimental tests. When using direct identification methods, one faces the problem of the interpretation of the experimental tests, which requires the assumption of deformation homogeneity and therefore the use of approximation methods. Since this assumption is often not satisfied in the case of non-linear behaviour, material parameters are not assessed precisely. In the paper, an inverse identification method is proposed to avoid the problems raised by interpretation of the experimental tests and to determine material parameters more accurately. The algorithm developed consists of both an optimization method and a finite element method. This method is applied to the inverse identification of viscoplastic parameters of an aluminium alloy, with an investigation on the effect of the initial guess and errors in experimental data on the identified values.
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    Revised mapping functions for three-dimensional serendipity infinite elements (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 181-184 
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    ISSN: 1069-8299
    Keywords: finite elements ; infinite elements ; mapping functions ; unbounded domains ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A few of the published three-dimensional Serendipity infinite element mapping functions have been discovered to be in error. The paper gives corrected versions of the defective mapping functions. The problems only relate to three-dimensional elements of the Serendipity type, when they extend to infinity in two or more directions. The new version of the mapping functions have been tested and appear to be robust.
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    A direct method to derive the boundary conditions of the homogenization equation for symmetric cells (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 185-196 
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    ISSN: 1069-8299
    Keywords: homogenization ; boundary conditions ; periodicity ; finite element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The numerical solution of homogenization equations by the finite element (FE) method is explained briefly. The issue of extracting boundary conditions from the periodicity assumption is addressed and a direct method utilizing symmetry is presented. Using this method, the computation of the elements of the constitutive matrix of a composite material is reduced to a very conventional boundary value problem with known forces and boundary conditions which can be carried out with any FE code. Two examples are presented.
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996) 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120401
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    Conference diary (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 269-270 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120402
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    A dual reciprocity formulation for elasticity problems with body forces using augmented thin plate splines (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 209-220 
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    ISSN: 1069-8299
    Keywords: boundary element method ; dual reciprocity ; radial basis functions ; augmented thin plate splines ; body forces ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a novel dual reciprocity formulation for elasticity problems with body forces in which the approximating functions are given in terms of augmented thin plate splines (ATPS). It is shown that the ATPS approximation is capable of correctly representing gravitational and centrifugal body forces, and provides superior accuracy for general load cases.
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    Automatic triangular mesh generation scheme for curved surfaces (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 197-208 
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    ISSN: 1069-8299
    Keywords: curved surface ; triangular mesh ; automatic generation ; Bézier patches ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper deals with the discretization of any given multi-connected curved surface into triangular elements with straight sides. The method evolves from an initial rough triangular mesh generated from a set of input points which describe the geometry of the problem domain. Interior nodes are distributed according to user-established node-spacing functions of pre-specified spacing control parameters, and they are linked using the advancing front technique. Particular attention is paid to obtaining good distribution of interior nodes in the vicinity of the domain limits. Surface geometry representation is established using triangular Bézier patches with G1 continuity. This approach ensures a geometrically well-defined working platform for the subsequent discretization of the problem domain. The proposed method requires minimum input from the user and allows mesh gradation and remeshing to be carried out in a straightforward manner. Furthermore, problems associated with variations in the domain geometry as a result of local remeshing are eliminated with the aid of the geometrically pre-defined discretization platform. Results are presented for a range of both curved and planar surfaces, typical of those which might be encountered in hydrodynamics modelling involving flows with a free surface. The presented results demonstrate the flexibility and power of the technique.
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    Best-fit stress performance of a higher-order beam element (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 229-234 
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    ISSN: 1069-8299
    Keywords: higher-order beam element ; best-fit stress prediction ; a priori error analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: It is known that finite elements try to capture stresses within each discretized local region in a ‘best-fit’ sense. In the paper we examine the performance of a beam element based on a higher-order shear deformation theory and show that the best-fit paradigm accounts for the manner in which through-the-thickness displacement and stresses are modelled. An a priori prediction derived from the paradigm is confirmed by a carefully chosen numerical experiment. This provides a measure of the quality of approximation as well as another ‘falsification’ of the best-fit paradigm.
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    A different approach to discretization for the numerical simulation of three-dimensional heat conduction in irregularly shaped materials (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 223-228 
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    ISSN: 1069-8299
    Keywords: Discretization ; heat conduction ; simulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A different approach to discretization is described with which complicated three-dimensional heat transfer problems can be solved with a finite volume approach on a general curvilinear grid. It represents an improvement on the existing methods in that it can easily be expanded to three-dimensional problems. A concise explanation of the transformation process is given, together with a discussion of the discretization procedure. The method is evaluated by solving two simple test problems and comparing the results with those of existing methods and the analytical solution. In conclusion it is found that this method yields equally or more accurate results than the existing methods, with the additional advantage of being easily expandable to three-dimensional problems.
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    Automatic nodes generation in N-dimensional space (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 243-248 
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    ISSN: 1069-8299
    Keywords: finite elements ; automatic generation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Finite element generation methods, such as Delaunay, allow the meshing of shapes from a set of nodes. These nodes must previously exist. The authors present a simple, fast and reliable method to generate them in an unstructured way in N-dimensional space. Its main characteristic is to easily allow variation of the node density by introducing a density function, either analytical or discretized. This function can also be anisotropic. Some nodes can have a pre-fixed position. Inner lines and holes can also be specified in the domain to be meshed. Generated nodes are to be connected according to triangles in 2D and tetrahedrals in 3D.
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    A modified non-linear member element allowing large loading and displacement increments (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 235-242 
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    ISSN: 1069-8299
    Keywords: finite member element ; modified theory ; geometrical non-linearity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper a modified non-linear member element is derived which can lead to satisfactory computed results even for large loading and displacement increments from pre-instability to post-instability of structures. The high accuracy of this element is proved by numerical examples.
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    Masthead (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996) 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120501
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    Quadratic programming algorithms for obstacle problems (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 249-256 
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    ISSN: 1069-8299
    Keywords: obstacle problems ; quadratic programming ; finite element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The numerical solution of problems involving frictionless contact between an elastic body and a rigid obstacle is considered. The elastic body may undergo small or large deformation. Finite element discretization and repetitive linearization lead to a sequence of quadratic programming (QP) problems for incremental displacement. The performances of several QP algorithms, including two new versions of a modified steepest descent algorithm, are compared in this context. Numerical examples include a string, a membrane and an Euler-Bernoulli beam, in contact with flat and non-flat rigid obstacles.
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    Conference diary (1996)
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    Communications in Numerical Methods in Engineering 12 (1996), S. 317-319 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120502
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    Optimal design for minimum weight in a cracked pressure vessel of a turboshaft (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 271-280 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The authors study the shape optimization of a complex cracked shell under complex criteria. The shell is one of various cases of a turboshaft, and optimization criteria are associated to the cost, the technology, and above all the working conditions for the turboshaft. The optimization criteria involved are of course the weight of the structure, but also the plastic instability and critical stress intensity factor. All computations have been made with the Ansys finite element program in which an optimization module exists.
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    FE mode-matching schemes for the exterior Helmholtz problem and their relationship to the FE-DtN approach (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 257-267 
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    ISSN: 1069-8299
    Keywords: mode-matching ; Helmholtz' equation ; DtN ; finite element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Finite element (FE) mode-matching procedures for the solution of Helmholtz' equation on an unbounded domain are reviewed and a symmetric general formulation is presented. This is a formal restatement of procedures applied previously to computations involving scattering of shallow water waves, acoustic transmission in non-uniform ducts and acoustic radiation from prismatic sheet metal ducts. An essential feature of the method is the use of a Galerkin procedure, rather than collocation, to match a finite computational model to a truncated modal expansion with the desired radiation characteristics. The method produces a symmetric set of linear equations which can be solved to give the unknown nodal values of the dependent variable and the modal coefficients of an outer expansion. Either of these sets of variables can be eliminated prior to solution to yield a reduced set of equations in the remaining parameters. The reduced equations obtained by eliminating the modal coefficients are shown to be identical to those obtained by applying a truncated Dirichlet-to-Neumann (DtN) boundary condition. If applied in this form, mode-matching can therefore be regarded as an alternative to the DtN method for generating this common set of discrete equations while permitting simultaneous solution for the modal coefficients in the outer region.
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    On the conditioning of numerical boundary measures in wavelet Galerkin methods (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 281-294 
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    ISSN: 1069-8299
    Keywords: wavelets ; measures ; stability ; domains ; differential equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper investigates the accuracy and numerical stability of a class of wavelet Galerkin formulations on irregular domains. The method of numerical boundary measures is based upon a domain embedding strategy in which the irregular domain of interest is embedded in a larger domain having regular geometry. One advantage of the domain embedding method is that the boundary conditions on the larger, regular domain can be enforced in a straightforward manner, and the solution procedure can exploit the highly structured form of the resulting governing equations. The defining characteristic of this method is that the calculation of integrals along the irregular boundary are carried out using recently derived numerical boundary measures. In addition, the coercive bilinear forms characterizing the boundary value problem of interest must be calculated when restricted to the actual domain. In the case of wavelet Galerkin formulations, this calculation is accomplished with the three term connection coefficients that characterize the numerical boundary measure. The numerical stability and accuracy of the domain embedding procedure is compared to a newly developed wavelet-based finite element formulation.
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    Conference diary (1996)
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    Communications in Numerical Methods in Engineering 12 (1996), S. 371-372 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120601
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    The fractal behaviour of triangular refined/derefined meshes (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 295-302 
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    ISSN: 1069-8299
    Keywords: mesh generation ; adaptivity ; iterated fractal systems ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the author presents a novel point of view for the refinement and derefinement algorithms of triangular nested meshes using fractal concepts and iterated function systems (IFS). The fractal behaviour can be understood in the sense that these meshes feature a remarkable amplifying invariance under changes of magnification. Here we compare the meshes obtained by the combination of these algorithms with those presented by Bova and Carey (1992). Although both of the meshes are very similar, the current algorithms automatically build and manage sequences of nested irregular discretizations of the domain. The author illustrates here how the application of IFS families is equivalent to the use of an adaptive strategy that combines the refinement procedure with the derefinement one.
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    One-dimensional stretching functions for Cn patched grids, and associated truncation errors in finite-difference calculations (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 303-316 
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    ISSN: 1069-8299
    Keywords: stretching functions ; mesh refinement ; finite differences ; truncation error ; composite grids ; regularity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this work the truncation-error criteria of Thompson and Mastin (1985) are combined with conditions of vanishing second and higher derivatives at both endpoints for the purpose of deriving new classes of one-dimensional stretching functions for mesh refinement in finite-difference numerics. With these elementary stretching functions, matching of the slopes between adjacent grid patches then automatically confers Cn regularity upon the composite stretching function. Formulated with reference to two conceptions of truncation order (fixed relative distribution against fixed number of nodes) the resulting mappings are shown to provide particularly advantageous node distributions at both ends simultaneously (with concomitantly higher truncation error in between). Viewed overall, the truncation-error functions compare favourably with those for sinh, tanh and erf - mappings whose utility for mesh refinement was established by Thompson and Mastin. The numerical labour of implementing the new stretching functions is only slightly greater than that required for the error function. An illustrative derivation involving Cn patching leads to two-sided stretching functions, which allow the slopes at both ends to be prescribed arbitrarily. This formulation differs from a previous approach described by Vinokur (1983).
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    Finite element strategy for glass sheet manufacture by creep forming (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 331-341 
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    ISSN: 1069-8299
    Keywords: glass ; finite element ; strategy's creep forming ; sheet ; manufacture ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An original optimization strategy for creep forming is carried out by finite element thermodependent viscoplastic models. For reference design glass products, an optimum forming database is developed in two steps: the first step analyses feasibility, with elastic and viscoplastic finite element models, with regard to initial manufacture choices. With thermodependent viscoplastic finite element models, the second step leads to optimum forming parameters, concerning skeleton bending radii and/or non-homogeneous heating adjustments.
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    A DOF expanding method for connecting solid and shell element (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 321-330 
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    ISSN: 1069-8299
    Keywords: solid-shell structure ; 3D solid element ; degenerated shell element ; DOF expanding ; multipoint constraint equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents a degree of freedom expanding method for dealing with the connections of 3D isoparametric solid elements and the degenerated shell elements. By introducing two degrees of freedom to describe the elongation in the normal direction of the shell node linked with solid elements, a series of multipoint constraint equations which provide proper connections of solid and shell nodes are raised. The method gives a complete solution to the problem of connection between 3D isoparametric solid elements and degenerated shell elements even for the thermal elasto-plastic problem. It can adapt to complex junctions and simplify programming. Numerical examples are also presented to demonstrate the accuracy and feasibility in thermal elasto-plastic analysis.
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    Shape-derived anisotropy directions in quadrangle and brick finite elements (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 351-357 
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    ISSN: 1069-8299
    Keywords: anisotropy ; finite elements ; layers ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A modification of the usual quadrangle (2D) and brick (3D) finite element for field problems is proposed. It allows the principal directions of the conductivity tensor (anisotropy directions) to be derived from the geometrical shape of the finite element and to change within it. An internal layering is assumed which is parallel to the boundary at two opposite faces (top and bottom) of the element. Without an explicit computation of angles the anisotropy directions are parallel and perpendicular to this layering. An application is the modelling of pore fluid flow in sedimentary basins.
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    A combined octant/Delaunay method for fully automatic 3D mesh generation with multiple level octant differences (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 343-349 
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    ISSN: 1069-8299
    Keywords: mesh generation ; Delaunay mesh ; Watsens method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Automated mesh generation using a combined octree/Delaunay approach typically requires that rectangular elements be bounded by other rectangular elements which are not more that one division smaller (i.e. 1/8 the volume in 3D). This limitation is sometimes referred to as the 2 : 1 rule. This paper presents a modification which allows for any level of difference.
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    Masthead (1996)
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    Communications in Numerical Methods in Engineering 12 (1996) 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120701
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    Application of an artificial compressibility methodology for the incompressible flow through a wavy channel (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 359-369 
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    ISSN: 1069-8299
    Keywords: Navier-Stokes ; artificial compressibility methodology ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper considers the problem of laminar incompressible viscous flow through a wavy channel. An artificial compressibility method using the approximate factorization technique is applied to solve the velocity-pressure formulation of the Navier-Stokes equations written in curvilinear non-orthogonal coordinates. The physical domain used was one wavelength of the channel in which appropriate periodicity conditions were applied in order to find a solution independent of entry effects. Flow separation was observed for high Re numbers and/or large wave amplitudes of the channel. The effect of inertia to the velocity profiles was observed, and pressure and shear stress were calculated along the length of the channel. These flows have great interest in industry and medicine such as for the extracorporeal membrane oxygenator.
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    Conference diary (1996)
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    Communications in Numerical Methods in Engineering 12 (1996), S. 445-446 
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    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    URL: http://dx.doi.org/10.1002/cnm.1640120702
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    Fundamental solutions and boundary integral equations of moderately thick symmetrically laminated anisotropic plates (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 383-394 
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    ISSN: 1069-8299
    Keywords: symmetrically laminated plates ; anisotropy ; fundamental solutions ; boundary integral equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the bending problem of moderately thick symmetrically laminated anisotropic plates is considered, based on the first-order transverse shear deformation plate theory. Using the method of plane wave decomposition and Hörmander's operator method, the fundamental solution of the plates is presented. The boundary integral equation of the plates is formulated by taking the fundamental solution presented as the weighted function and using the method of weighted residuals. The numerical calculation of the boundary integral equation presented is discussed in detail. Some examples are presented and compared with the exact solutions and the numerical solutions available in the literature. The numerical results show that the present method has a satisfactory rate of convergence and acceptable accuracy with a reasonable boundary mesh.
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    Comparison of several mesh refinement strategies near edges (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 373-381 
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    ISSN: 1069-8299
    Keywords: finite element method ; mesh refinement ; adaptivity ; singularities near edges ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper is concerned with several refinement techniques of finite element meshes for treating elliptic boundary value problems in domains with re-entrant edges and corners. A priori mesh grading is explained, and it is combined with the well-known adaptive finite element method. For two representative examples the numerically determined error norms are recorded, and the different strategies are compared.
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    A comparison of second order convection discretization schemes for incompressible fluid flow (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 395-411 
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    ISSN: 1069-8299
    Keywords: finite volume ; high-order discretization ; non-oscillatory schemes ; pressure interpolation ; non-staggered grid ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper addresses the problem of convection discretization by extension and application of numerical schemes used in compressible flows: SONIC-A, SONIC-B, UNO2, MUSCL and MINMOD to predict steady incompressible recirculating convection dominated flows. A new scheme, SONIC-Q, is proposed together with a third-order non-oscillatory practice for pressure interpolation in non-staggered grids. Finite-volume calculations of the Navier-Stokes equations of a standard 2D driven square cavity standard test case and the laminar flow over a fence using primitive variables and non-staggered grid systems have shown that the schemes are alternatives to the conventional ones used in general algorithms for incompressible recirculating flows. In general these composite high-order schemes have proved to be good candidates to overcome the problems of false-diffusion and unboundedness encountered in non-composite high-order upwind schemes used in incompressible flows.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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