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  • 1995-1999  (2.633)
  • 1955-1959
  • 1996  (2.633)
  • General Chemistry  (1.786)
  • Engineering  (847)
  • Nuclear reactions
  • 1
    Digitale Medien
    Digitale Medien
    Computation of 3-D electromagnetic field using differential forms based elements and dual formulations (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 81-98 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The vector and scalar variables describing electromagnetic fields with different requirements of continuity can be identified to four different degrees of differential forms. The association of differential forms with finite elements leads to a set of differential forms based elements (Whitney elements); they are naturally adapted to the discretization of different vector and scalar variables. With the help of a Tonti diagram, Maxwell equations can be classified by two dual sequences together with the constitutive laws of materials. The application of Whitney elements to the two dual sequences leads to two dual approximation schemes. As an example, two dual formulations for eddy current computation using potential variables and the hybrid finite element - boundary element method are derived, where Whitney 3-D and 2-D elements are employed. A numerical application is given at the end of the paper, where the dual features of the two formulations are reported.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Finite element iterative solution of skin effect problems in open boundaries (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 125-143 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The paper proposes an iterative procedure, called current iteration, for the finite element solution of two-dimensional steady-state skin effect problems in open boundaries. In the procedure a fictitious boundary is introduced enclosing all the conductors. On it, the magnetic vector potential is first guessed and then iteratively updated according to the current density computed in the conductors. Conditions are obtained implying convergence to the exact solution of the unbounded problem whatever the initial guess. The choice of the fictitious boundary and the selection of the relaxation parameter in such a way that computational efficiency is obtained are discussed. The greatest advantage of the procedure is its ease of implementation in a pre-existing finite element code for bounded problems. An axisymmetric version of the procedure is also described since implementation only involves minor changes as compared with the 2-D one. Examples are provided in order to clarify and validate the procedure and compare it with other techniques.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    AN FFT-BASED FORMULATION FOR THE COMPUTATION OF ELECTROMAGNETIC SCATTERING FROM 3-D, PERFECTLY CONDUCTING BODIES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 225-236 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An FFT-based formulation for the computation of electromagnetic scattering from 3-D, perfectly conducting objects is presented. The formulation solves the EFIE iteratively via a conjugate gradient scheme and has the major advantage of a low storage requirement for scatterers in the resonance region. This factor, coupled with the low run-times resulting from use of the FFT to compute the associated matrices, makes the formulation a particularly efficient one. Numerical results encompassing current distributions and far-field radar cross-sections are presented for PEC cubes of resonant size. It is shown that the computed results yield good agreement compared with other numerical techniques and experimental data.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    THREE-DIMENSIONAL FULL-VECTOR ANALYSIS OF OPTICAL WAVEGUIDES BY FINITE-INTEGRATION BEAM-PROPAGATION METHOD (FIBPM) (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 249-258 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In the paper a novel finite-integration beam-propagation method (FIBPM) is presented. This method is especially suited for the simulation of optical waveguides containing extremely thin layers of complex permittivity. For calculating the propagating optical field an efficient algorithm based on expansion of the matrix exponential in Chebyshev polynomials is applied. The derivation of the propagation algorithm is given, also detailing the convergence criteria. A code for a massively parallel computer has been developed and applied successfully to complex waveguide structures used for high-power laser diodes
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Report. Final report on the First International Workshop on Transmission Line Matrix (TLM) Modeling  -  Theory and Applications (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 167-170 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: No Abstract
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    A MODIFIED FINITE DIFFERENCE METHOD FOR MODELLING DIFFUSION PROCESSES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 215-223 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A time domain unconditionally stable explicit method is presented which may be used to model processes governed by the diffusion equation such as transient heat flow. Unlike the explicit finite difference routine, the method models the diffusion process within the time step (MPWT). Being explicit, the method (MPWT) may easily account for non-linear physical parmeters and may be compared with the transmission line matrix (TLM) method of diffusion modelling in terms of its utility. Unlike the TLM model, however, the equivalent circuit does not contain inductive components which have no clear physical meaning. The MPWT method is based on a simple resistive and capacitive circuit model, which for short time steps reduces to the explicit finite difference formulation but is stable for large time steps. Good agreement has been found when results obtained using this algorithm are compared with other numerical methods and analytical results.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    TENSOR-AIDED GEARBOX MODELLING (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 181-190 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper develops an electrical analogue for a gearbox suitable for use in the time-domain modelling of many electromechanical systems, with tensor methods being used to define the changing conditions in the gearbox brought about by backlash. Unlike most existing models it is compatible with the time-varying and discontinuous models often used to describe the electrical items of a typical system, and it allows for the effects of these items of mechanical non-linearities and discontinuities such as friction and backlash.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    A METHOD FOR INCORPORATING CHARGED PARTICLE MOTION WITHIN A 2-D TLM FIELD CODE (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 201-214 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Charged particle motion is incorporated within a transmission line modelling (TLM) field code to establish a new model which allows the investigation of field-particle interactions. The model is validated by using it to predict the trajectory of moving particles and the field and potential distributions inside a planar diode for which analytical solutions are available. The effect of space charge on the operation of the diode is also investigated. The model is then applied to study in detail a practical electron gun design.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996) 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090301
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  • 10
    Digitale Medien
    Digitale Medien
    Neuromagnetic field computation using the multiple multipole method (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 145-158 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: For the interpretation of human neuromagnetic data it is necessary to compute the magnetic field of a source (e.g. a dipole) in a volume conductor (e.g. a homogeneous conducting sphere or a homogeneous head model). The Multiple Multipole (MMP) method, which is a semianalytical field calculation method, is applied to neuromagnetic field calculation for the first time. The unique feature of the MMP method is that multipole expansions are used for the description of the electromagnetic field. First a validation of the MMP method is done with the help of a spherical model and an analytical solution. Then the MMP method is applied to a realistically shaped one compartment head model. The results are compared to results obtained with the Boundary Element Method (BEM). The results suggest that it is possible to solve the neuromagnetic forward problem faster with the help of the MMP method than with the conventional numerical field calculation methods for realistic shaped volume conductor models. Further investigations are necessary to tackle the inverse problem of biomagnetism with the MMP method.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    FAST S-PARAMETER COMPUTATION OF A MICROSTRIP INTERDIGITAL FILTER USING TLM, PRONY'S AND DIGITAL FILTERING TECHNIQUES (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 237-248 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A spectral estimation technique based on Prony's method has been used to analyse a five section microstrip interdigital filter with the TLM method. The time response of the filter is expressed as the sum of only five damped sinusoids, yielding an analytical expression for the time response. Furthermore, since an analytical Fourier transform exists for this expression, the frequency response is obtained without applying the fast Fourier or discrete Fourier transform. This typically reduces the time required for a TLM analysis by a factor of five. The approximation agrees very well with a full TLM time response. It is also shown that the numerical noise due to single precision computation of the absorbing boundary algorithm can be eliminated by digital filtering techniques. The effect of the via holes used for grounding the quarter-wave resonators of the filter has been included by discretizing them along with the rest of the circuit. Scattering parameters for the filter compare well with measurements published by Swanson.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    DISCRETE SIMULATION OF UNIFORM TRANSMISSION LINES BY MULTIDIMENSIONAL DIGITAL FILTERS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 271-294 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Recently, a new method has been presented for the discrete simulation of multidimensional systems, which are described by linear partial differential equations with constant coefficients. It is based on methods customary in linear systems theory and digital signal processing and uses a frequency-domain representation of the continuous system to be simulated. A proper choice of functional transformations for each independent variable allows us to treat the influence of initial conditions, boundary conditions and excitation functions separately by suitable transfer functions. From these, corresponding discrete transfer functions and the structure of a discrete system for the simulation of the continuous problem are derived. The application of this method to wave propagation problems on uniform transmission lines is presented here. At first, the continuous problem is characterized by transfer functions; then the derivation of a discrete system is shown, and finally, some simulation results and a comparison with other methods are given.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Forthcoming papers (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 325-325 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090402
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  • 14
    Digitale Medien
    Digitale Medien
    OPTIMIZATION ISSUES IN FINITE ELEMENT CODES FOR SOLVING OPEN DOMAIN 3D ELECTROMAGNETIC SCATTERING AND CONFORMAL ANTENNA PROBLEMS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 335-344 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The first part of the paper presents the implementation and performance of a new absorbing boundary condition (ABC) for truncating finite element meshes. This ABC can be applied conformally to the surface of the structure for scattering and antenna radiation calculations. Consequently, the computational domain is reduced dramatically, thus allowing the simulation of much larger structures, and results are presented for three-dimensional bodies. The latter part of the paper discusses optimization issues relating to the solver's CPU speed on parallel and vector processors. It is shown that a jagged diagonal storage scheme leads to a four-fold increase in the FLOP rate of the code, and a standard matrix profile reduction algorithm substantially reduces the inter-processor communication.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996) 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090501
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  • 16
    Digitale Medien
    Digitale Medien
    A COMBINED FINE-COARSE MESH METHOD FOR THE TRANSMISSION LINE MODELLING OF DIFFUSION (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 405-415 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An improved combined fine-coarse mesh (CFCM) method for two transmission line models of diffusion is described. The method allows regular cells of different sizes to be connected and solved simultaneously. The CFCM method is applied to (a) a finite difference algorithm, (b) a conventional transmission line model and (c) a lossy transmission line model. The latter model is shown to be the most accurate. The proposed CFCM method is also compared with the graded mesh and the multigrid techniques.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    DISCRETE MODELS OF HEAT FLOW IN LAYERED MATERIALS USING SIMPLE AND CORRELATED RANDOM WALKS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 445-457 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The paper reviews some discrete probabilistic numerical techniques with particular emphasis on heat flow in inhomogeneous materials. The effects of different nodal configurations on the development of suitable algorithms are outlined and we suggest a new and consistent description for the discrete apparent effusivity. Our approach is then discussed in the context of TLM, and analogues are presented for flux relaxation time and effusivity.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    LETTER TO THE EDITOR. A GENERAL EXPRESSION OF BOUNDARY CONDITIONS IN TLM DIFFUSION MODELLING (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 459-461 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We show that the general boundary condition D∂Φ/∂x + αΦ = 0 (D is the diffusion coefficient and α is a constant) in TLM diffusion modelling can be expressed accurately in terms of a voltage reflection coefficient ρ = (Δx - αΔt)/(Δx + αΔt), where Δx is the spatial resolution and Δt is the time step. Based on this general expression, the special cases of short-circuit (ρ = -1), open-circuit (ρ = 1) and matched-load (ρ = 0) boundaries can be described succinctly by α → ∞, α → 0 and α = Δx/Δt, respectively. This formulation allows for straightforward treatment of mixed boundary conditions found, for example, in diffusion-drift systems.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Synthesis, inverse problems and optimization in computational electromagnetics (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 45-57 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The paper gives an overview on mathematical optimization techniques specially suited to problems in electromagnetism. It is described how efficient optimization procedures consist of decision making, treatment of non-linear constraints, and an algorithm for minimizing the objective function. The optimization of a rectangular waveguide branching, a permanent magnet synchronous machine, and the iron cross-section of a superconducting magnet are given as examples. Optimization routines are used for the tracing of manufacturing errors in the production of superconducting coils. Finally the application of a genetic algorithm to a dipole coil design is discussed as an example for field synthesis.
    Zusätzliches Material: 6 Ill.
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  • 20
    Digitale Medien
    Digitale Medien
    Numerical differentiation in magnetic field postprocessing (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 99-113 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Postprocessing encompasses graphic display and numerical computation. The critical process in this work is numerical differentiation. Methods of numerical differentiation of approximate solutions may be divided into three groups: direct numerical differentiation, smoothing methods based on superconvergence properties, and methods that exploit properties the solution is known to possess though the numerical approximation does not. The choice of method is determined by the problem, as well as the use to which derivatives are put: graphical display, local field calculation, mesh refinement or a a posteriori error estimation. The paper compares current derivative extraction methods and reviews progress in this field, with particular attention to superconvergent patch recovery and methods based on Green's second identity. A new modification of the method based on Green's second identity is presented, to include inhomogeneous and discontinuous materials.
    Zusätzliches Material: 3 Ill.
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  • 21
    Digitale Medien
    Digitale Medien
    Verification of computational electromagnetic programs (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 159-165 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Although software testing comprises a large body of knowledge and is extensively used in verification and validation (V&V) of software and software systems, the need to verify engineering software posses unique challenges. Electromagnetic programs fall under the category of so-called non-testable programs, a group that includes numerical computation and most other programs that use floating point operations. There are, however, certain techniques that can be used to check for program correctness in the context of expected behaviour and results. The approach to testing by multiple methods, multiple codes and multiple algorithms is well known as an effective tool in testing of scientific software. In addition, testing against canonical and known solutions, evaluation of programs based on properties of the computation performed and error analysis are all common techniques used to verify computer programs. Their use in the context of the TEAM series of problems and workshop is used as an example for a unique method of verification of programs and to underscore the needs of both users and program developers in this important issue of code validation.
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  • 22
    Digitale Medien
    Digitale Medien
    EFFICIENT STABILITY ANALYSIS OF FREE RUNNING MICROWAVE OSCILLATORS IN THE FREQUENCY DOMAIN (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 171-179 
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    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A stability analysis of free running oscillators in the frequency domain is presented. By insertion of a simple damping subnetwork, depending on one parameter, a global stability analysis starting in a Hopf bifurcation is performed. Near the bifurcation, stability of a periodic orbit is determined by studying stability of the stationary solutions. Provided turning and bifurcation points are detected, stability is thus known on the whole path connecting the Hopf bifurcation and the solution of the undamped oscillator network. It is shown that for the generation of starting values for the signal analysis by homotopy and for the stability analysis the same solution path can be utilized. Thus coupling of large-signal and stability analysis leads to an efficient algorithm where stability of oscillatory solutions is computed as a by-product of signal analysis with hardly any additional cost. The presented method is applied to a microwave oscillator at 15 GHz and to an oscillator model which has several coexisting large-signal solutions. Our method may be combined with any large-signal analysis program based on a piecewise network description. It may be fully automated and requires no sophisticated knowledge of the program user about stability analysis or bifurcation theory.
    Zusätzliches Material: 7 Ill.
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  • 23
    Digitale Medien
    Digitale Medien
    Forthcoming papers (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. ii 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090302
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  • 24
    Digitale Medien
    Digitale Medien
    TRANSIENT ANALYSIS OF n-TIER GaAs MESFET MATRIX AMPLIFIERS BY THE TLM METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 259-270 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The performances of n-tier GaAs MESFET matrix amplifiers are studied in the time domain. The model is developed incorporating the parasitic resistive loss and internal coupling capacitance of the active device. Techniques are contemplated to transform the matrix amplifier into a set of coupled multi-conductor transmission lines. The resultant model is analysed by the TLM method. Impulse responses of 2 × 4 and 3 × 3 matrix amplifiers are investigated. The frequency responses of the amplifiers are obtained through a Fourier transform. Agreement is observed between results obtained by the TLM model and those obtained by other analytical methods or a complicated circuit analysis program. A 5 × 7 matrix amplifier is also analysed to show the advantage of the developed method.
    Zusätzliches Material: 11 Ill.
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  • 25
    Digitale Medien
    Digitale Medien
    CAN THE TRANSMISSION LINE MATRIX METHOD YIELD STATIONARY SOLUTIONS OF THE TIME-DEPENDENT SCHRÖDINGER EQUATION? (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 321-323 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: By virtue of the success of the transmission line matrix method (TLM) in solving heat and matter diffusion problems, it should also be applicable to the time-dependent Schrödinger equation. The occurrence of complex-valued circuit elements does notdestroy the unconditional stability of the routine. But it seems to be impossible to obtain stationary (eigen)solutions to this equation as well as separable solutions to the diffusion equation. It is suggested that this is due to the non-dissipativity of the TLM routine.
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  • 26
    Digitale Medien
    Digitale Medien
    TIME DOMAIN ELECTROMAGNETIC FIELD COMPUTATION WITH FINITE DIFFERENCE METHODS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 295-319 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The solution of Maxwell's equations in the time domain has now been in use for almost three decades and has had great success in many different applications. The main attraction of the time domain approach, originating in a paper by Yee (1966), is its simplicity. Compared with conventional frequency domain methods it takes only marginal effort to write a computer code for solving a simple scattering problem. However, when applying the time domain approach in a general way to arbitrarily complex problems, many seemingly simple additional problems add up. We describe a theoretical framework for solving Maxwell's equations in integral form, resulting in a set of matrix equations, each of which is the discrete analogue to one of the original Maxwell equations. This approach is called Finite Integration Theory and was first developed for frequency domain problems starting about two decades ago. The key point in this formulation is that it can be applied to static, harmonic and time dependent fields, mainly because it is nothing but a computer-compatible reformulation of Maxwell's equations in integral form. When specialised to time domain fields, the method actualy contains Yee's algorithm as a subset. Further additions include lossy materials and fields of moving charges, even including fully relativistic analysis.For amny practical problems the pure time domain algorithm is not sufficient. For instance a waveguide transition analysis requires knowledge of the incoming and outgoing mode patterns for proper excitation in the time domain. This is a typical example where both frequency and time domian analysis are essential and only the combinatin yields the successful result. Typical engineers may wonder why at all one should apply time domain analysis to basically monochromatic field problems. The answer is simple: it is much faster, needs less computer memory, is more general nad typically more accurate. Speed-up factors of over 200 have been reached for realistic problems in filter and waveguide design. The small core space requirement makes time domain methods applicable on desktop computers using milions of cells, and six unknowns per cell - a dimension that has not yet been reached by frequency domain approaches. This enormous amount of mesh cells is absolutely neceesary when complex structures or structures with spacial dimensions of many wavelengths are to be studied. Our personal recod so far is a waveguide problem in which we used 72,000,000 unknowns.
    Zusätzliches Material: 15 Ill.
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  • 27
    Digitale Medien
    Digitale Medien
    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996) 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090401
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  • 28
    Digitale Medien
    Digitale Medien
    TLM TREATMENT OF A GENERAL DIFFUSION FLUX BOUNDARY CONDITION (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 327-333 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An approach of using a current-controlled voltage source analogy to account for a general boundary condition of particle or thermal flux in transmission-line matrix (TLM) diffusion modelling has been developed. For mass diffusion, this boundary condition is expressed as D ∂C/∂x + αC = 0, where C is the concentration, D is the diffusion coefficient, and α is a parameter characterizing the out-diffusion mobility across the boundary of interest. Confirmation of the TLM numerical treatment through comparison with analytical solutions is presented. Besides the open-circuit and short-circuit boundaries, the matched-load boundary is also found to be a special case of the present boundary condition. This extension of the boundary treatment allows the highly flexible TLM method to be applied to a greater variety of diffusion problems.
    Zusätzliches Material: 5 Ill.
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  • 29
    Digitale Medien
    Digitale Medien
    Forthcoming papers (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 395-395 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090502
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  • 30
    Digitale Medien
    Digitale Medien
    CORRECT MACROMODELLING OF THE COMMON MODE AND POWER SUPPLY REJECTIONS OF OPERATIONAL AMPLIFIERS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 397-404 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The relationship between common mode rejection and positive and negative power supply rejections of operational amplifiers is derived and compared with symmetrical power supply rejection. The results are used to develop a macromodel which provides a correct representation of the terminal voltages at the op amp pins. The performance of the new macromodel is illustrated comparing simulation results with those of the device level model for the standard integrated circuit op amp uA741.
    Zusätzliches Material: 7 Ill.
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  • 31
    Digitale Medien
    Digitale Medien
    A TLM MODEL OF TRANSIENT, 2-DIMENSIONAL STRESS PROPAGATION (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 429-443 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A TLM nodal structure suitable for modelling the propagation of transient stresses is described. The nodal structure is analysed algebraically using the analogy between TLM and discrete state space control theory. A numerical implementation based on this nodal structure is validated by comparing results generated using the TLM model with those produced using the finite difference approach for the case of pressure applied to a semi-infinite plate.
    Zusätzliches Material: 7 Ill.
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  • 32
    Digitale Medien
    Digitale Medien
    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996) 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090601
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  • 33
    Digitale Medien
    Digitale Medien
    Integral equations in electromagnetics (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 3-17 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Algorithms for the numerical solution of continuum electromagnetic field problems are based either on differential or integral formulations. The most common approach, at least for low frequency problems, has been the former, using the finite element method. The paper examines the special advantages of integral equations over differential equations, explores some of the difficulties involved and suggests that, in the context of more advanced problems, i.e. optimization and moving systems, the integral equation approach may be particularly effective.
    Zusätzliches Material: 9 Ill.
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  • 34
    Digitale Medien
    Digitale Medien
    Edge elements for magnetostatics (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 19-34 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Edge-elements are introduced and discussed in the context of complementarity, a desirable characteristic of numerical methods, by which solutions which are equally satisfactory as regards both fields b and h are obtained. By making the vector potential approach easier than with standard nodal elements, edge-elements enhance complementarity. Comparative merits of both kinds of elements are discussed.
    Zusätzliches Material: 9 Ill.
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  • 35
    Digitale Medien
    Digitale Medien
    Automated design and optimization of electromechanical actuators (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 59-69 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The paper investigates various optimization techniques and their suitability for the magnetic design of electromechanical actuators. Selected algorithms, including Gauss-Newton, Levenberg-Marquardt and Trust region, are examined and compared using 18 test functions. The Levenberg-Marquardt method is chosen for its robustness and fast convergence, and incorporated into an automated CAD optimization system (EAMON), which interfaces an external optimizer to a general purpose finite element package. The EAMON program, which is user friendly with pull-down menus, searches for constrained shape design variables that fulfil prescribed performance criteria. The electromagnetic field analysis forms part of the optimization iterative cycle. Finally, two application examples are described. First, a DC solenoid actuator with truncated cone pole face is optimized to produce a user specified force-displacement characteristic. Secondly, an actuator solenoid is optimized to produce maximum energy per stroke.
    Zusätzliches Material: 9 Ill.
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  • 36
    Digitale Medien
    Digitale Medien
    Adaptive methods in computational magnetics (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 71-80 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A review of adaptive methods in 2-D and 3-D for the efficient solution of electromagnetic problems with the finite element method, developed by the authors, is presented in the paper. The adaptive methods presented consist mainly of two processes: mesh refinement and error estimation. A highly efficient technique for the refinement of arbitrary unstructured triangular and tetrahedral meshes, based on Delaunay triangulation, directly applicable and suitable in an automatic adaptive procedure, is described. The use of various error estimation criteria for electromagnetic problems is presented. The implementation of an automatic adaptive procedure with the finite element method, incorporating the above techniques, is provided and applied to the efficient solution of various 2-D and 3-D electromagnetic field problems.
    Zusätzliches Material: 11 Ill.
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  • 37
    Digitale Medien
    Digitale Medien
    Pushing the limits of 2-D boundary element eddy current codes - connectivity (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 115-124 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The serious electromechanical designer is faced with optimizing the shape of a device for a number of conflicting criteria. If the design involves eddy currents with saturable media, a true optimization will take a long time, since it requires a lot of information as input with multiple variable variations. If the analyses must be performed in three dimensions, an inordinate amount of computer time is required even for the simplest of problems. No small advantage is accrued if the problem can be approached in two dimensions. The paper outlines a technique for examining eddy currents induced in complex series wound coils for which the connections must be specified to ensure solution accuracy. A boundary element formulation is adopted in which an arbitrary constant vector potential is assigned to each conductor. The connection of the coils can be specified by placing additional constraints on these vector potentials. The technique is tested against two experiments involving forces imposed on flux eliminating coils.
    Zusätzliches Material: 12 Ill.
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  • 38
    Digitale Medien
    Digitale Medien
    Masthead (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996) 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jnm.1660090101
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  • 39
    Digitale Medien
    Digitale Medien
    HORIZONTAL WIRE ANTENNA ABOVE LOSSY HALF-SPACE: SIMPLE ACCURATE IMAGE SOLUTION (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 191-199 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A simple, approximate, but highly accurate, method is proposed for the analysis of horizontal thin-wire antennas above a lossy half-space. In the first step, the contribution of the lossy half-space to the field of a horizontal Hertzian dipole above the interface, both in the half-space above and in that below the interface, is approximated by the field of few (typically six) equivalent sources (images). The relative image intensities are obtained by enforcing the boundary conditions for the tangential components of the electric and magnetic field at a number of points at the interface. The field of the images is introduced into the Hallén equation; current distribution is approximated by polynomials and determined by point-matching. The results for the impedance of horizontal dipoles obtained by the present method are in excellent agreement with the exact results (obtained from the Sommerfeld theory), although the proposed method is conceptually much simpler and requires at least an order of magnitude less computing time than the exact method.
    Zusätzliches Material: 8 Ill.
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  • 40
    Digitale Medien
    Digitale Medien
    BOOK REVIEW. GENETIC ALGORITHMS IN ENGINEERING AND COMPUTER SCIENCE, edited by G. Winter, J. Péiaux, M. Galán and P. Cuesta, Wiley, Chichester, 1995. ISBN 0-471-95859-X. No of pages: 464. Price: £45.00 (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 324-324 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: No Abstract
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  • 41
    Digitale Medien
    Digitale Medien
    FAST SIMULATION OF MICROSTRIP STRUCTURES USING THE FAST MULTIPOLE METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 345-357 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We apply a new method of reducing the computational effort required for solution of the Electric Field Integral Equation used for modelling microstrip structures. The Fast Multipole Method is used to compute the radiation pattern and input impedance of single layer microstrip antennas.
    Zusätzliches Material: 9 Ill.
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  • 42
    Digitale Medien
    Digitale Medien
    A CONSISTENT SUBGRIDDING SCHEME FOR THE FINITE DIFFERENCE TIME DOMAIN METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 359-374 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Recently, the simulation of high frequency devices has become of increasing importance due to the demand for faster development processes. The Finite Difference Time Domain (FDTD) method has been proved to be an efficient tool for the simulation of electromagnetic phenomena. In the paper we derive a new consistent three-dimensional subgridding scheme for the Finite Integration Technique. In the time domain the latter method reduces to FDTD when only cubical cells are used. The subgridding extension can help to achieve accurate models of small structure details without heavily decreasing numerical efficiency while the properties of continuous Maxwell equations are still conserved in the grid space. After studying numerical dispersion and stability, the applicability of the method is demonstrated by regarding an example studying scattering at a small post in a rectangular waveguide.
    Zusätzliches Material: 18 Ill.
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  • 43
    Digitale Medien
    Digitale Medien
    NEW INTEGRATED SIMULATION TECHNIQUES FOR THE ELECTROMAGNETIC ANALYSIS OF MICROWAVE CIRCUITS USING THE TLM METHOD (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 375-393 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A new methodology is presented which allows the integration of lumped elements into electromagnetic simulations, using the TLM method. It is shown that the new method retains the symmetrical condensed node algorithm structure, with the potential to be applied to all lumped elements. A new and accurate method for the extraction of circuit parameters from the impulse response of the TLM method is also presented. The method is simple and can be used for waveguide and planar structures. A study is carried out on the applications of various data windowing techniques during the postprocessing stages of an electromagnetic analysis. This has resulted in the realization of the need for careful selection of a particular window profile, according to the application and the nature of the required results.
    Zusätzliches Material: 21 Ill.
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  • 44
    Digitale Medien
    Digitale Medien
    AUTOMATIC TIME STEP CONTROL IN TLM DIFFUSION MODELLING FOR PROBLEMS WITH TIME-VARYING LOAD CONDITIONS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 417-428 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Existing methods for time step control in TLM diffusion modelling that are based on the ‘m’ parameter introduced by Pulko are shown to be inappropriate for problems where the load conditions are arbitrarily time-varying. A new parameter is proposed for monitoring the error in the TLM diffusion model arising from the hyperbolic component of the lossy wave equation. This parameter is used as the controlling variable in a general purpose time step control algorithm and its suitability is demonstrated by applying this algorithm to a number of test cases in which the load conditions are time-varying.
    Zusätzliches Material: 13 Ill.
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  • 45
    Digitale Medien
    Digitale Medien
    BOOK REVIEW. MICROWAVE AND OPTICAL WAVEGUIDE ANALYSIS BY THE FINITE ELEMENT METHOD by F. Anibal Fernandez and Yilong Lu, Research Studies Press, ISBN 0-86380-182-X, 1996, 205 pp, $40.00. (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 462-462 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: No Abstract
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  • 46
    Digitale Medien
    Digitale Medien
    Editorial: Special issue of International Journal of Numerical Modelling: Electronic Networks, Devices and Fields on Computational Magnetics (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 1-1 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: No Abstract
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  • 47
    Digitale Medien
    Digitale Medien
    Knowledge-based and numerical optimization techniques for the design of electromagnetic devices (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 9 (1996), S. 35-44 
    Details
    ISSN: 0894-3370
    Schlagwort(e): Engineering ; Electrical and Electronics Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Automatic electromagnetic device design is now becoming possible. Advances in numerical methods, knowledge-based techniques and database structures are helping to solve the problem of synthesis. The paper discusses the major problems of design and reviews techniques which have been developed for solving them. An architecture for a design system is proposed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 48
    Digitale Medien
    Digitale Medien
    Thianthrene 5-Oxide as a Mechanistic Probe in Oxygen Transfer Reactions: The Case of Carbonyl Oxides versus Dioxiranes Revisited (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 255-258 
    Details
    ISSN: 0947-6539
    Schlagwort(e): carbonyl oxides ; dioxiranes ; mechanistic studies ; oxidations ; thianthrene 5-oxide ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Thianthrene 5-oxide (SSO) constitutes a useful mechanistic tool for the assessment of the electronic character of oxygen transfer agents by means of their Xso values, which reflect the extent of nucleophilic oxidation at the SO site in SSO. Treatment of dioxiranes 1 a-d with the SSO probe confirms that these are electrophilic oxidants (Xso 〈 0.15). Dioxirane sulfoxidation is sensitive to protic solvents and acids, which implies a polar mechanism (SN2) with nucleophilic attack of the sulfide electron pair on the dioxirane peroxide bond. In contrast, the carbonyl oxides 2 a and b, diethyl persulfoxide (3), and adamantylideneadamantane perepoxide (4) are nucleophilic oxidants (Xso 〉 0.85). However, the cyclopentadienone carbonyl oxides 2 c and d show low Xso values typical for electrophilic oxygen transfer agents. For these carbonyl oxides, photoisomerization to the respective dioxiranes is proposed under the photooxidation conditions of the diazoalkanes. Additionally, the trans/cis ratio of bissulfoxides (SOSO) formed provides valuable information on the stereochemical course of the oxygen-transfer process due to the steric requirements of the oxidant. Thus, the electrophilic dioxiranes preferentially attack the axial lone pair of SSO because of repulsion by the peri hydrogen atoms to afford trans-SO-SO.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020304
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  • 49
    Digitale Medien
    Digitale Medien
    Polysaccharides of Intracrystalline Glycoproteins Modulate Calcite Crystal Growth In Vitro (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 278-284 
    Details
    ISSN: 0947-6539
    Schlagwort(e): biomineralization ; calcite ; crystal morphology ; glycoproteins ; polysaccharides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Assemblies of glycoproteins from within the mineralized tissues of sea urchins and mollusks both interact in vitro in a similar manner with growing calcite crystals. A protein-rich fraction, a polysaccharide-rich fraction, and a fraction composed of densely glycosylated peptide cores were obtained by chemical and enzymatic treatment of the glycoproteins from sea-urchin spines. Each fraction was partially purified and characterized (amino acid composition, FTIR and NMR spectroscopy). A comparison of the interactions of these fractions with growing calcite crystals in vitro shows that the polysaccharide moieties of these glycoproteins are intimately involved in the interaction with growing calcite crystals on planes approximately parallel to the c crystallographic axis. Presumably the polysaccharides in the mollusk-shell glycoproteins are likewise responsible for the similar interactions of these macromolecules with calcite. We suggest that structured polysaccharide moieties of glycoproteins are important in controlling aspects of crystal growth in vivo as well.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020308
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  • 50
    Digitale Medien
    Digitale Medien
    Aryloxycarbonylcarbene Complexes of Bis(oxazolinyl)pyridineruthenium as Active Intermediates in Asymmetric Catalytic CyclopropanationsDedicated to Professor Henri Brunner on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 303-306 
    Details
    ISSN: 0947-6539
    Schlagwort(e): asymmetric syntheses ; carbene complexes ; cyclopropanations ; diazoacetates ; ruthenium complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of [RuCl2(pybox)-(C2H4)] (1) (pybox = 2,6-bis[4′S)-isopropyloxazolin-2′-yl]pyridine) and 2,6-di-tert-butyltolyl diazoacetate (4) (DBT-DA) in benzene at 50°C gave a stable 2,6-di-tert-butyltolylcarbonylcarbene-ruthenium complex 5 in 94% yield. The structure of 5 was characterized by NMR spectroscopy. 2,6-Diisopropylphenyl diazoacetate (6) and 2,4,6-trimethylphenyl diazoacetate (7) also gave the corresponding carbene complexes 9 and 10, respectively. Asymmetric carbene transfer from the carbene complexes to styrene resulted in formation of the trans isomer of phenylcyclopropanecarboxylates 2 with high enantioselectivity: 2 was obtained as the sole product in 80% yield (55% ee) from 5 at 80 °C and in 82% yield (97% ee) from 9 at 60°C; from 10 at 40°C, a mixture of 2 and 3 in a ratio of 97:3 was formed in 91% yield (97% ee for 2 and 99% ee for 3). After the carbene transfer reaction, the ethylene complex 1 could be regenerated and isolated by treatment of the reaction mixture under an ethylene atmosphere. The carbene complexes 9 and 10 (2 mol%) exhibited catalytic activity in the asymmetric cyclopropanation of styrene with the corresponding diazoacetates.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020311
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  • 51
    Digitale Medien
    Digitale Medien
    The photochemical Formation of Fulvene from Benzene via Prefulvene-a Theoretical StudyDedicated to Professor Roy McWeeny on the occasion of his 70th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 335-341 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; benzene ; fulvene ; isomerization ; photochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Results of semiempirical MN-DOC-CI and ab initio CASSCF calculations reveal that fulvene is a primary product of the photolysis of benzene. The photochemical step is assumed to lead to prefulvene, and both a synchronous conversion and a two-step process via bicyclo[3.1.0]hexa-1,3-diene (isofulvene) could be ruled out as possible pathways from prefulvene to benzene. The most probable mechanism for the photochemical isomerization of benzene to fulvene involves the intermediate structures prefulvene and 1,3-cyclopentadienylcarbene and has to compete with the almost barrierless formation of benzvalene and rearomatization to benzene. The short-lived intermediates are rather flexible structures with negligible barriers to inversion at the radical center in the threemembered ring of prefulvene and prebenzvalene and to rotation around the exocyclic single bond in 1,3-cyclopentadienylcarbene.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020315
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  • 52
    Digitale Medien
    Digitale Medien
    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020401
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  • 53
    Digitale Medien
    Digitale Medien
    NMR Chemical-Shift Anomaly and Bonding in Piano-Stool Carbonyl and Related Complexes-an Ab Initio ECP/DFT StudyDedicated to Professor Hans Georg von Schnering on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 348-358 
    Details
    ISSN: 0947-6539
    Schlagwort(e): carbonyl complexes ; density-functional theory ; NMR chemical shifts ; pseudopotentials ; transition-metal complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The origin of the unusually large carbonyl 13C shifts and of unusual periodic trends in four-legged piano-stool complexes [M(n5-C5H5)(CO)4]- (M=Ti, Zr, Hf) and in related species has been investigated by using a combination of ab initio effective-core potentials (ECPs) and density-functional theory (DFT). The ECP/SOS-DFPT(IGLO) calculations indicate a considerable reduction in the anisotropy of the 13C(CO) chemical shift tensors compared to terminal carbonyl ligands in “normal” complexes. This is due to large paramagnetic contributions from metal d AO type (dz2, dxy) orbitals to the parallel component, σ33, of the shielding tensors of the carbonyl carbon atoms. The neutral d4 Group 5 and 6 complexes [M(n5-C5H5)(CO)4] (M=V, Nb, Ta) and [M(n5-C5H5)(CO)3CH3] (M=Cr, Mo, W) exhibit successively smaller but still significant paramagnetic d-orbital contributions to σ33, consistent with the observed less dramatic deshielding. The three-legged d6 piano-stool complexes [M(n5-C5H5)(CO)3] (M=Mn, Tc, Re) do not exhibit these reductions of the shielding anisotropy, but have carbonyl 13C shift tensors comparable to regular octahedral carbonyl complexes. The special situation for the four-legged complexes is related to the presence of high-lying occupied metal d orbitals, and particularly to the favorable spatial arrangement of these d orbitals with respect to the carbonyl ligands. Bent-sandwich d2 complexes like [Zr(n5-C5H5)2(CO)2] exhibit comparable deshielding contributions from an occupied metal d orbital. For similar reasons, the 17O resonances for these piano-stool and bent-sandwich complexes are also predicted to be at unusually high frequencies, with low shift anisotropy. NMR shifts for the (n5-C5H5)-ligand atoms and the structures of the complexes are also discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020317
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  • 54
    Digitale Medien
    Digitale Medien
    A bis(diimidazole)copper complex possessing a reversible CuII/CuI couple with a high redox potential (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 685-693 
    Details
    ISSN: 0947-6539
    Schlagwort(e): copper complexes ; imidazole ligands ; redox systems ; structure elucidation ; enzyme models ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The new diimidazole ligand, bis (1-methyl-4,5-diphenylimidazol-2-yl)ke-tone (BIMDPK), has been synthesised, characterised and shown to form four-coordinate bis(diimidazole) CuII and CuI complexes in the salts [Cu(bimdpk)2]-[BF4]2 and [Cu(bimdpk)2][PF6], the structures of which have been determined by X-ray crystallography. The cations of these salts have a very similar geometry with CuII-Nav = 1.949 and CuI-Nav = 1.999 Å; the N-Cu-N interbond angles are constrained by 1) the bite angle of the BIMDPK ligand to 94 ± 2° and 2) the interligand steric interactions, which lead to the dihedral angle of the intraligand CuN2 planes of 68.2° for CuII and 74.9° for CuI-that is, a CuN4 geometry intermediate between tetrahedral and square planar. The X-band EPR spectrum for the powdered CuII compound is typical of an approximately D2 CuN4 centre possessing a dxy ground state (gx = 2.080, gy = 2.075, gz = 2.291; Az = 112.3 × 10-4 cm-1). The UV/vis spectra are dominated by charge-transfer bands, and both the CuII and CuI systems are intensely coloured. The EPR and electronic spectra indicate that these cations have a very similar structure in the solid state and in solution; the potential of the [Cu(bimdpk)2]2+/[Cu(bimdpk)2]+ couple is 0.59 V vs. SCE in MeCN and 0.80 V vs. SCE in CH2Cl2, and the electron self-exchange constant in MeCN is 1.9 × 104M-1S-1. Comparisons are made between the properties of the [Cu(bimdpk)2]2+/+ centres and related Cu centres in chmical and biological systems; the results of this study reinforce the view that a [Cu(His)4] centre should not be precluded from consideration in biological electron transport.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020611
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  • 55
    Digitale Medien
    Digitale Medien
    On the definition of chirality (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 743-744 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020617
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  • 56
    Digitale Medien
    Digitale Medien
    Self-assembling [2]- and [3]rotaxanes from secondary dialkylammonium salts and crown ethersMolecular Meccano, Part 7: for Part 6; see the preceding paper in this issue (ref. [14]). (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 729-736 
    Details
    ISSN: 0947-6539
    Schlagwort(e): interlocking moleucles ; molecular recognition ; pseudorotaxanes ; rotaxanes ; template syntheses ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The self-assembly of three new rotaxanes - two [2]rotaxanes and a [3]rotaxane - formed by a “threading followed by stoppering” approach is described. These template-directed syntheses rely on the formation of pseudorotaxane intermediates, which self-assemble in solution from functionalized secondary dialkylammonium hexafluorophosphate threads and macrocyclic polyether rings (either dibenzo-[24]crown-8 or its asymmetric constitutional isomer). The stoppers - substituted 1,2,3-triazoles-were created by thermally allowed 1,3-dipolar cycloadditions between azido groups, which terminate the threads, and di-tert-butyl acetylenedicarboxylate.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020615
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  • 57
    Digitale Medien
    Digitale Medien
    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 613-616 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020619
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  • 58
    Digitale Medien
    Digitale Medien
    Notice to authors 1996 (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 757-758 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020703
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  • 59
    Digitale Medien
    Digitale Medien
    Structure and conductivity of an electrocrystallized ruthenium [1,8]binaphthyridine complex (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 781-788 
    Details
    ISSN: 0947-6539
    Schlagwort(e): chelate ligands ; intermolecular interactions ; reductions ; ruthenium complexes ; semiconductors ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: For the first time, the crystal structure of a RuII binaphthyridine complex and that of its corresponding oneelectron reduced product are reported. Reductive electrocrystallization of [Ru-(binap-2)3](PF6)2 (1, where binap-2 = 3,3′-dimethylene -2,2′ - bi [1, 8] naphthyridine) from an acetonitrile solution resulted in the formation of dark blue crystals of the one-electron reduction product, [Ru-(binap-2)3](PF6) (2) having one fewer PF-6 per formula unit. X-ray analysis reveals that the reduced complex retains the three-ligand d6 coordination around the central RuII. Based on electrostatic considerations and the positions of the PF-6 anions in the lattice, the added electron appears to be delocalized over two nearly equivalent binap-2 ligands in 2, in marked contrast to monoreduced and electrocrystallized [Na ⊂ (trisbipyridyl cryptand)]0, in which the electron is localized on only one of the bipyridyl subunits. However, based on the available data, alternative interpretations are possible. The crystal packing diagram of 2 shows several intermolecular π-π interactions, with 12 of these being shorter than 3.5 Å. In contrast, there are no intermolecular distances shorter than 3.5 Å in the crystals of 1. Two-probe electrical conductivity measurements under anaerobic conditions indicate that the crystals of 2 behave as semiconductors with a band gap of 0.53 eV, while those of the unreduced compound are insulating. This represents the first molecular semiconducting material with the potential for bidimensional behavior of its kind.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020707
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  • 60
    Digitale Medien
    Digitale Medien
    In Situ 13C Solid-State NMR and Ex Situ GC-MS Analysis of the Products of tert-Butyl Alcohol Dehydration on H-ZSM-5 Zeolite Catalyst (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 157-167 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alcohols ; cracking ; dehydrations ; isomerizations ; NMR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The hydrocarbon products that are formed upon dehydration at 296-673 K of tert-butyl alcohol (tBuOH), adsorbed on H-ZSM-5 zeolite in concentrations equal to that to active Al—OH—Si sites in the catalyst, have been analyzed by 13C solid-state MAS NMR and GC-MS. To facilitate 13C NMR analysis, the alcohol selectively labeled with 13C isotope in the COH group was used. It was found that tBuOH transforms to the adsorbed C8 butene dimers plus a trace amount of alkanes at 296 K. Butene dimers exist inside H—ZSM-5 pores in the form of interconverting adsorbed octene, octyl silyl ether, and octyl carbenium ion; octyl silyl ether is the main adsorption state. Fluxionality of the carbenium ion form provides a pathway for isomerization of the highly branched hydrocarbon skeleton of the intial alcohol to the predominantly linear one in the adsorbed butene dimer. The driving force for the isomerization into the linear structure is the shape selectivity induced by the small size of the zeolite channels. At 373 K the adsorbed butene dimers further crack into species that contain an average of about 6.5 carbon atoms, in addition to further alkanes. At 448 K the adsorbed C3-C7+ paraffins become the predominant hydrocarbon products observed with both in situ 13C NMR and ex situ GC-MS. Simultaneously, a mixture of adsorbed polyenes is formed. According to 13C CP/MAS NMR, polyenes exist in the zeolite pores in the form of rather stable cyclopentenyl cations. At 573-673 K adsorbed cyclopentenyl cations further transform into a mixture of condensed and simple aromatics and then into xylenes and toluene. Simultaneously, paraffins crack further to give mainly C3-C4 paraffinic species at 573 K and propane at 673 K.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020207
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  • 61
    Digitale Medien
    Digitale Medien
    A stereoselective synthesis of (E)-α, β-unsaturated ketones involving the reactions of organocerium reagents with secondary β-enamino ketones (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 913-918 
    Details
    ISSN: 0947-6539
    Schlagwort(e): assymetric substitution ; cerium reagents ; enamino ketones ; regioselectivity ; synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stereoselective construction of trisubstituted alkenes has wide applicability to the synthesis of many natual products Specifically, β-disubstituted enones are important functionalized trisubstituted alkene targets. The reaction of organocerium reagents with secondary β-enamino ketones affords β=disubsituted α,β-unsaturated ketones in fairly good yields. This process shows considerable stereoselectivity, and α,β-unsaturated ketones of (E) configuration are predominantly observed. Organolithium-derived cerium reagents display better stereoselectivity than organomagnesium-based ones. The mechanism of the reaction varies with nitrogen substitution: N-phenyl groups give 1,2-addition products, whereas substitution products are observed with N-alkyl groups. When organocerium reagents were used with β-enamino ketones bearing secondary alkyl groups at the nitrogen atom, a lack of reactivity was observed.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020802
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  • 62
    Digitale Medien
    Digitale Medien
    Synthesis of 4-silylcyclobut-2-enethiones and their use in cyclobutadiene generation (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 949-956 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkynyl sulfides ; cyclobutadienes ; cyclobutenethiones ; desilylation ; ynamines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Alkynyl silyl sulfides 2 reacted with ynamines 3 to give 1:1 adducts. The structure of 4-silylcyclobut-2-enethiones 4 was confirmed by X-ray analysis of 4a. A cyclobutadiene intermediate is probably not involved in this reaction; we think that it is initiated by a silyl transfer from 2 to 3, and that this is followed by a combination of the resulting ions to give the unsaturated thioketene 7, which undergoes an electrocyclization to give products 4. In the reaction of thiones 4 with trimethyloxonium tetrafluoroborate (Meerrwein salt) selective methylation at sulfur was observed to give cyclobutenethionium ions 16. Ions 16 underwent fluoride-induced desilylation with various fluoride sources to give cyclobutadienes 17, which could not be isolated, but trapping of 17 a-c was possible with dimethyl acetylenedicarboxylate yielding regioisomeric benzene derivatives 20-23. Similarly, 17 a and bis(methylthio)methylene malononitrile (24) led to hexatriene derivative 27 by a sequence of cycloaddition and two ring-opening reactions. In contrast, silyl-substituted cyclobutadienes 17d,e dimerized even in the presence of trapping agents to anti-tricyclo-[4.2.0.02,5]octadienes 29; this suggests that a two-step cycloaddition is taking place, rather than a concerted Diels-Alder reaction. Attempts to intercept 17d, e, generated from 16d,e with cyclopentadiene (30), gave deprotonation of 30 leading to substitution of the methylthio group in 16 and finally to formation of cyclobutenes 33 through a hydrogen shift.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020807
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  • 63
    Digitale Medien
    Digitale Medien
    Molecular structure of the chloroiron(III) derivative of the meso-unsubstituted 2,7,12,17-tetramethyl-3,8,13,18-tetramesitylporphyrin and weak ferromagnetic exchange interactions in the Alu oxoiron(iv) porphyrin π radical cation complex (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1159-1163 
    Details
    ISSN: 0947-6539
    Schlagwort(e): electronic structure ; exchange coupling ; heme proteins ; iron complexes ; porhyrins ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The molecular structure of the chloroiron(III) porphyrinate [FeIIICl- (tmtmp)] (1) is described. The doming off the bifacially encumbered tmtmp dianionic ligand present in 1 is characterized by a separation of 0.09 (1) Å between the mean plane of the four pyrrole nitrogens (4NP) and that of the porphyrin core. The coordination polyhedron of the five-coordinate iron atom is a square pyramid of C4v symmetry. The metal is displaced by 0.44 (1) Å from the 4Np mean plane towards the axial chloro ligand. The Fe-Np and Fe-Cl bond lengths are 2.057 (6) and 2.223(5) Å, respectively. Upon treatment of [FeIIITf(tmtmp)] (2) with m-chloroperoxybenzoic acid, the green oxoferryl π radical cation complex [FeIV=O(tmtmp)]+ (3) is obtained. It has been studied by EPR, Mössbauer, and resonance Raman spectroscopy. It exhibits an EPR spectrum strikingly similar to those of compounds I of Micrococcus lysodeikticus catalase (APX-I) and ascorbate peroxidase (APX-I) The exchange interactions between the spins of the radical cation and the ferryl iron are of the ferromagnetic type and are the weakest ever found for a synthetic compound I model. The shift of + 22 cm-1 in the radical marker band v2 in the resonance Raman spectra upon oxidation of 2 to 3 confirms that the electronic state of the porphyrin π radical cation is predominantly 2Alu in this tmtmp compound 1 model.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020917
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  • 64
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    Digitale Medien
    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021001
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  • 65
    Digitale Medien
    Digitale Medien
    Homochiral and heterochiral dimers of the methylzinc alkoxide formed from dimethylzinc and enantiomeric 3-exo-(dimethylamino)isoborneol - origin of the distinct differences in solution-phase behavior and crystal structures (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1173-1181 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; asymmetric alkylations ; catalysis ; structure ; elucidation ; zinc complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dimethylzinc reacts with (2S)-or (2R)-3-exo-(dimethylamino)isoborneol [(2S)- or (2R)-DAIB] to eliminate methane and produce a tricoordinate methylzinc aminoalkoxide, which forms a dimeric structure. The homochiral dimerization of the enantiomeric compound leads to the chiral, (S,S) or (R,R) dinuclear Zn complex, while the heterochiral interaction forms the meso (S,R) dinuclear compound. In both solution and crystalline state, the heterochiral dimer is more stable than the homochiral dimer. This stability difference in solution is the origin of the chirality amplification observed in the amino alcohol promoted asymmetric addition of dimethylzinc to benzaldehyde. In toluene, the homochiral dimer dissociates more readily into the monomer than the heterchiral isomer and also undergoes dissociation of the N-Zn dative bond making the two N-methyl groups equivalent. The differences in solution behavior between the diastereomers can be understood by comparing their crystal structures. X-ray analysis indicates that the labile Zn-O and Zn-N bonds in the (S,S) dimer are longer than those in the (S,R) isomer. Skeletal congestion caused by the polycyclic framework is the prime factor determining the properties of the dinuclear Zn complexes, with both steric and electronic factors governing their geometries. The distances between the C-2 proton and N-CH3 of the other DAIB moiety in the homochiral dimer are close to the sum of the van der Waals radii. A significant nuclear Overhauser effect is seen between these protons in the homochiral dimer. The tetrahedral Zn atoms in the dinuclear complexes are linked covalently to the methyl group, to two oxygen atoms through covalent/electrostatic hybrid bonds, and to the dimethylamino group through electrostatic interaction. The repulsive interaction of the 1, 3-synoriented Zn-CH3 bonds significantly contributes to the lower stability of the homochiral dimeric complex. The N-Zn interaction in the homochiral dimer is labile, owing to the increase in the electrostatic interaction between the Zn atom and the neighboring oxygen atoms. This view is supported by the ab initio molecular orbital calculations of the model systems.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020919
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  • 66
    Digitale Medien
    Digitale Medien
    Stereoselective Preparation of Polyfunctional Cyclopentane Derivatives by Radical Nickel- or Palladium-Catalyzed Carbozincations (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1204-1220 
    Details
    ISSN: 0947-6539
    Schlagwort(e): asymmetric cyclization ; catalysis ; cyclopentane ; natural products ; palladium complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of 5-hexenyl iodides with diethylzinc (2 equiv) and catalytic amounts of a PdII or NiII complex like PdCl2(dppf), PdCl2(MeCN)2, or Ni(acac)2 results in an efficient ring closure (THF, RT, 2-12 h) affording cyclopentylmethylzinc iodides, which, after transmetalation with CuCN·2LiCl, can be further functionalized by treatment with a range of electrophiles like allylic halides, acyl chlorides, enones, nitroolefins, ethyl propynoate, and alkynyl halides to yield polyfunctional cyclopentane derivatives. The ring closures occur via radical intermediates, and the stereochemistry of the products can be explained according to the rules for radical cyclizations developed by Beckwith. The preparation of several di- and trisubstituted cyclopentanes has been achieved with high stereoselectivity. Tandem ring closures can be performed to construct bicyclic or tricyclic ring systems. Cyclizations of iodo-ethylenic and acetylenic esters and ketones can be accomplished, although the high reactivity of acetylenic ketones leads to unexpected cyclization products. The synthetic utility of this method has been demonstrated by an enantioselective synthesis of (+)-methyl epijasmonate and (-)-methyl cucurbate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021006
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  • 67
    Digitale Medien
    Digitale Medien
    Gas-Phase Experiments Aimed at Probing the Existence of the Elusive Water Oxide MoleculeFirst reported at the 44th Conference on Mass Spectrometry and Allied Topics, Portland (Oregon, USA), 13 May, 1996.Dedicated to Professor Gerhard Ertl on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1235-1242 
    Details
    ISSN: 0947-6539
    Schlagwort(e): computer chemistry ; electron transfer ; hydrogen peroxide ; mass spectrometry ; water oxide ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Collisional activation, charge reversal, and six different neutralization - reionization mass spectrometric experiments with [H2,O2]·+ radical cations and [H2,O2]·- radical anions were performed in order to probe the predicated existence of neutral water oxide, H2OO, the long sought after tautomer of hydrogen peroxide, HOOH. The experiments together with ab initio calculations indicate that H2OO is a local minimum on the [H2,O2] potential-energy surface, and the elusive molecule seems to be formed as a transient upon neutralization of the corresponding radical cation H2OO·+ in the gas phase.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021009
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  • 68
    Digitale Medien
    Digitale Medien
    Alkali-Metal Cation Binding by Self-Assembled Cryptand-Type Supermolecules (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1264-1268 
    Details
    ISSN: 0947-6539
    Schlagwort(e): catechols ; cryptates ; helicates ; NMR spectroscopy ; titanium complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of three equivalents of alkyl-bridged biscatechol ligands (1-3)-H4 with two equivalents of [(acac)2TiO] in the presence of two equivalents of alkalimetal carbonate (M = Na, K) affords helicate- or meso-helicate-type supramolecular coordination compounds by spontaneous self-assembly processes. The cryptand-type structure of the binuclear tetraanions [(1)3Ti2]4- or [(2)3Ti2]4- permits inclusion of sodium cations; this was observed by 23Na NMR spectroscopy in solution. Competition experiments with potassium or lithium cations revealed that potassium but not lithium easily displaces the sodium ions from the cavity. Titration experiments indicated that the binding constant for potassium is significantly higher than for sodium. On the other hand, for the large tetraanion [(3)3Ti2]4- with hexamethylene spacers, no binding of alkali-metal ions could be observed by NMR spectroscopy in solution. In the solid state, however, two potassium ions could be incorporated in the interior of the cryptand-type helicate.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021013
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  • 69
    Digitale Medien
    Digitale Medien
    Cesium Fluoride-Bromine Intercalation Compounds (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1303-1307 
    Details
    ISSN: 0947-6539
    Schlagwort(e): bromine compounds ; cesium compounds ; crystal structure ; fluorides ; intercalation compounds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: CsF reacts with Br2 to form the two intercalation compounds CsF·Br2 and 2CsF·Br2. The former consists of layers of CsF squares separated by layers of Br2 molecules oriented perpendicular to the CsF layers. 2CsF·Br2 is a second-stage compound, composed of two layers of CsF followed by one layer of bromine molecules. Iodine cannot replace bromine; instead, it reacts with CsF to form Cs2I8, and probably CsIF6 between 0° and 120 °C. Chlorine does not react at all with CsF. Bromine reacts with RbF only superficially, and after a long time some RbBr3 is observed; RbF and I2 give RbI3.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021018
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  • 70
    Digitale Medien
    Digitale Medien
    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021102
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  • 71
    Digitale Medien
    Digitale Medien
    Anionic Glucophospholipids - A New Family of Tubule-Forming Amphiphiles (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1335-1339 
    Details
    ISSN: 0947-6539
    Schlagwort(e): amphiphiles ; glucophospholipids ; self-assembly ; tubules ; vesicles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new family of amphiphiles that form tubules (i.e., hollow cylindrical bilayer-based microstructures) by self-aggregation has been identified, namely, anionic glucophospholipids of type 1, in which a double-tailed hydrophobe is grafted through a phosphate linkage to the O-6 position of a polar glucose head group. Compounds 1a-c self-assemble into stable, hollow tubular microstructures when dispersed in water and cooled below the temperature at which the transition between crystal and liquid-crystal phases takes place (estimated from change in turbidity). The diameter of the microstructures appears to depend on the nature of the hydrophobic tail, significantly smaller diameters being obtained for fluorinated tails. No tubules were obtained when galactose (2a-c, pH〈11) or mannose (3a-c) derivatives were used instead of glucose derivatives, or when glucose was derivatized at the O-3 (4b) rather than O-6 position; in these cases only vesicles were formed. Tubules made of 1 converted rapidly into giant vesicles when heated; they spontaneously formed again upon cooling. The presence of a fluorinated chain, as in 1b and 1c, increased the temperature at which the tubule-vesicle interconversion occurred to above room temperature. Because the amphiphiles are negatively charged, the formation of tubules is pH-dependent and is favored at higher pH. These findings support the view that hydration of and hydrogen bonds between polar heads play a major role in tubule formation. Hydration of the sugar-derived head groups decreases as the number of intermolecular hydrogen bonds increases; this favors membrane crystallization and tubule formation.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021022
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  • 72
    Digitale Medien
    Digitale Medien
    Self-Assembly of Heterobimetallic Complexes and Reactive Nucleophiles: A General Strategy for the Activation of Asymmetric Reactions Promoted by Heterobimetallic Catalysts (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1368-1372 
    Details
    ISSN: 0947-6539
    Schlagwort(e): heterobimetallic catalysts ; Michael additions ; multifunctional catalysts ; nitroaldol reactions ; self-assembly ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Heterobimetallic asymmetric catalysts, such as the lanthanum-lithium-binaphthol complex (La Li-BINOL), the aluminum-lithium-binaphthol complex (AlLi-BINOL), and a newly prepared gallium-sodium-binaphthol complex (Ga Na-BINOL), have been self-assembled with reactive nucleophiles, such as lithium nitronates and sodium malonates, to generate more efficient catalysts than the parent heterobimetallic catalysts. For example, by the combined use of La Li-BINOL (1 mol%; contains one H2O molecule) and BuLi (0.9 mol%) as the catalyst system, asymmetric nitroaldol reactions are greatly accelerated in all cases without a decrease in the optical purity of the nitroaldol products. Kinetic analyses have also been carried out on the Ga Na-BINOL-catalyzed Michael reaction of dibenzyl malonate with cyclohexenone, with or without NaOtBu. The calculated rate constants show that the combined use of Ga Na-BINOL and NaOtBu as the catalyst gives reaction rates that are about 50 times faster than with Ga Na-BINOL alone. This activation method should be useful for other asymmetric reactions catalyzed by heterobimetallic complexes.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021107
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  • 73
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    Digitale Medien
    Photochemistry of N-Phthaloylcysteine Derivatives: Multiplicity-Directed Regioselective CH Activation (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1388-1394 
    Details
    ISSN: 0947-6539
    Schlagwort(e): amino acids ; C-H activation ; electron transfer ; photochemistry ; state selectivity ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The photochemistry of the methyl esters of N-phthaloylcysteine derivatives 1b-5b was studied. The results are remarkable, because they prove a pronounced, multiplicity-controlled regioselectivity of the initial CH activation step. From substrates 1b-4b the benzazepine-1,5-dione 6 was produced exclusively by the singlet path. The formation of compound 6 is initiated by a γ-H abstraction; this was demonstrated by deuterium labeling experiments. The penicillamine derivative 5b was unreactive in the singlet manifold. From substrates 1b-3b and 5b the thiazinoisoindoles 7-9 and 11 were produced exclusively by the triplet path. The sterically hindered S-isopropylcysteine derivative 4b also furnished this product type (10) as a proportion of the products in the singlet manifold. These annulation products result from a primary photoinduced electron-transfer (PET) step followed by heterolytic ∊-H activation. The mechanistic scenario was elucidated by quenching and sensitization experiments. An interplay of CH activation steps and electron back-transfer is probably responsible for this type of spin selectivity.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021110
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  • 74
    Digitale Medien
    Digitale Medien
    Synthesis, Crystal Structure, Magnetism, and Magnetic Anisotropy of Cyclic Clusters Comprising six Iron(III) Ions and Entrapping Alkaline Ions (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1379-1387 
    Details
    ISSN: 0947-6539
    Schlagwort(e): aggregates ; clusters ; host-guest chemistry ; iron complexes ; magnetic anisotropy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of ferric chloride and β-diketones (HL) in alkaline methanol solution represents a good synthetic route to hexairon(III) clusters [MFe6-(OCH3)12(L)6]+ (M = Na, Li), which exhibit an unusual sixfold molecular symmetry. Single-crystal X-ray diffraction showed that the six octahedrally coordinated iron(III) ions define a ring and are linked by twelve bridging methoxide ligands. The resulting [Fe6(OCH3)12] skeleton has the remarkable property of acting as a host for an alkali-metal ion both in the solid state and in organic solution, as demonstrated by 23Na and 7Li NMR experiments. The magnetic behavior of these systems is consistent with the presence of a nonmagnetic S = 0 ground state and of antiferromagnetic exchange interactions between the high-spin ferric ions. The energy of the excited states was studied in detail by high-field DC and pulsed-field differential magnetization experiments at 0.7 and 1.5 K. Single-crystal susceptibility measurements at variable temperature revealed a sizeable magnetic anisotropy, which has been successfully analyzed in terms of single-ion and dipolar contributions. The results are relevant to research into the origin of superparamagnetic-type behavior in transition-metal clusters.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021109
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  • 75
    Digitale Medien
    Digitale Medien
    Photoswitched and Functionalized Oligothiophenes: Synthesis and Photochemical and Electrochemical Properties (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1399-1406 
    Details
    ISSN: 0947-6539
    Schlagwort(e): electrochromes ; fluorescence ; molecular devices ; oligothiophenes ; photochromes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The extended dithienylethene compounds 1-3 have been synthesized. They undergo photochromic and electrochemical changes by photoinduced interconversion between open and closed forms of type A and B. In addition, both forms of the N-methylated derivatives 1b and 2b have absorption bands in which excitation results in very large differences in fluorescence between the two forms with very little effect on the opening/closing state, a feature of interest for optical memory data systems. The compounds 2 and 3 contain six and eight conjugated thiophene units in the closed forms, respectively, and thus represent oligothiophenes endowed with a photoactivated switch; they are of special interest in this respect in view of the potential use of switched oligothiophenes in molecular electronic devices.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021112
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  • 76
    Digitale Medien
    Digitale Medien
    Synthesis of a Pentasaccharide-Oligonucleotide Conjugate: A Novel Antithrombotic Agent (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1572-1577 
    Details
    ISSN: 0947-6539
    Schlagwort(e): antithrombotics ; enzyme inhibitors ; oligonucleotides ; oligosaccharides ; protecting groups ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Derivatization of the octadecathymidylate derivative 18 (T18 ODN) containing a free amine function with sulfo-SIAB® gave the corresponding iodoacetyl ODN 21. Conjugation of the latter with the thiol-containing pentasaccharide 17c gave pentasaccharide-ODN conjugate III, which exhibited anti-Xa and antithrombin activities of 173 U mg-1 and 5 U mg-1, respectively.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021216
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  • 77
    Digitale Medien
    Digitale Medien
    Concave Hydrocarbons (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1585-1595 
    Details
    ISSN: 0947-6539
    Schlagwort(e): concave hydrocarbons ; cyclophanes ; host/guest chemistry ; ion-selective electrodes ; prismands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Concave hydrocarbons, such as 1 (C36H36), 4 (C60H60), 5 (C54H48), and 6 (C60H52), represent three-dimensionally clamped analogues of π-prismands. They encapsulate small metal ions and accomplish metal-ion extraction from aqueous solution. Their remarkable selectivity allows applications such as incorporation in ion-selective electrodes. The synthetic route is based on well-established cyclophane methodology and, thus, offers a general approach to a whole family of concave hydrocarbons.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021218
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  • 78
    Digitale Medien
    Digitale Medien
    Covalent Bonding of Crown Ethers to γ-Zirconium Phosphate - New Layered Ion Exchangers Showing Selective Recognition (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1578-1584 
    Details
    ISSN: 0947-6539
    Schlagwort(e): crown ethers ; layered materials ; molecular recognition ; zirconium phosphate ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The topotactic exchange reactions of γ-zirconium phosphate and γ-zirconium phosphate/methylphosphonate with phosphonic acids derived from azacrown ethers of different sizes was examined. Prior intercalation of hexylamine was necessary in most cases to attain the maximum exchange level predicted by molecular modeling. Materials with imbricated or nonimbricated layers were obtained depending on crown size and exchange level. Exchange of methylphosphonates in γ-zirconium phosphate/methylphosphonate was only observed when hexylamine had previously been intercalated. The exchange with the bisphosphonic acid derived from 1,10-diaza[18]-crown-6 gave a material with an interlayer distance compatible with pillaring of the γ-phase. The materials obtained from the exchange reactions of γ-zirconium phosphate with phosphonic acids derived from [12]crown-4 and [18]crown-6 showed thermodynamic selectivities towards Na+ and K+, respectively, that were much higher than those observed for the simple crowns in solution. This observation suggests that the inorganic molecular framework enhances molecular recognition by minimization of solvation effects.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021217
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  • 79
    Digitale Medien
    Digitale Medien
    Resolution of the Absorbance and CD Spectra and Formation Constants of the Complexes between Human Serum Albumin and Methyl OrangeA preliminary communication has been presented at the 12th Conference on Physical Organic Chemistry (IUPAC), Padua (Italy), 1994, Abstracts, p. 82. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 149-156 
    Details
    ISSN: 0947-6539
    Schlagwort(e): azo dyes ; circular dichroism ; data fitting ; formation constants ; protein complexation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Difference absorbance and circular dichroism techniques show that two complexes are formed between human serum albumin (HSA) and Methyl Orange (MO). The stoichiometries of the two HSA-MO complexes (1:1 (C1) and 1:2 (C2)), their association constants (K1, 1 = 2.32 (0.18) × 105 M-1 and K1, 2 = 1.12 (0.15) × 1011 M-2), and both absorbance and dichroic spectra have been determined by a computational approach. Nearly 900 experimental points, consisting of absorbance and CD measurements registered in the 340-550 nm interval and over a wide range of concentrations of protein and ligand, have been included in a unique fitting procedure. The Scatchard plot indicates the existence of a unique binding site which can accommodate up to two molecules of MO in a positive co-operative process. Calculation of the CD spectrum for the C2 complex according to the DeVoe method reproduces the fitted dichroic spectrum for the same complex. The shapes of the fitted absorbance and dichroic spectra, as well as the influence of concentrated NaCl or ethylene glycol on the absorbances of both free MO and HSA-MO mixtures are consistent with the presence of dominant electrostatic interactions in C1. The C2 complex can be envisaged as a unique chromophore, consisting of two MO units associated in a stacking process into the same binding site of HSA, leading to a well-defined chirality. The general validity of this multitechnique, multiwavelength approach in the investigation of protein-ligand complexes is discussed.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020206
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  • 80
    Digitale Medien
    Digitale Medien
    Tricarbonyl(η6-1,2-dioxobenzocyclobutene)chromium(0): Preparation, Nucleophilic Addition Studies and Syntheses of cmplex Polycyclic Systems by Dianionic Oxy-Cope Rearrangement (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 182-190 
    Details
    ISSN: 0947-6539
    Schlagwort(e): asymmetric syntheses ; chromium complexes ; diones ; oxy-Cope rearrangements ; polycycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The tricarbonylchromium complex 3 of 1,2-dioxobenzocyclobutene (1) is easily prepared by hydrolysis of diacetal 4. Complex 3 stereoselectively undergoes both single and double nucleophilic addition reactions at the keto groups. As a consequence, addition of excess alkenyllithium to 3 gives rise to a dianionic oxy-Cope rearrangement yielding benzocyclooctenedione complexes with good diastereoselectivity. Trapping of the bis(enolate) intermediate with chlorotrimethylsilane gives bis(enolether) 23. Subsequent addition of two different alkenyllithium derivatives yields the asymmetrically substituted rearrangement product 15. To some extent, dependent on the method of hydrolysis, an intramolecular aldol addition follows the dianionic oxy-Cope rearrangement. This results in the formation of benzoanellated bicyclo[3.3.0]octane derivatives and, in the case of 1-cyclopentenyllithium as the alkenylmetal, in the tetraquinane system 19. The trans-anellation of one of the cyclopentane rings in trans-20 has been verified by an X-ray structural analysis. The highly substituted rearrangement product 21/22 is formed only in small yield; in solution the bis(enol) tautomeric form 22 is favored over diketone 21.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020210
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  • 81
    Digitale Medien
    Digitale Medien
    Effect of the Position and Number of Chiral Carbons on Ferroelectric Liquid Crystals from Multichain Mononuclear ortho-Palladated Complexes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 214-220 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ferroelectrics ; liquid crystals ; metallomesogens ; palladium complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of twelve mononuclear ortho-palladated complexes incorporating a Schiff base and a β-diketone ligand have been synthesised. These compounds have four nonequivalent terminal chain positions and differ in the number and position(s) of chiral chains [(R)-2-methylheptyl] in the structure. A study of the ferroelectric properties of the compounds has been performed. It is found that the spontaneous polarisation is highly dependent not only on the number of chiral carbons present, but also on the position within the molecular core.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020214
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  • 82
    Digitale Medien
    Digitale Medien
    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020301
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  • 83
    Digitale Medien
    Digitale Medien
    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 251-254 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020303
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  • 84
    Digitale Medien
    Digitale Medien
    The Pre-Reactive Complex of H2S and BrCl; Observation and Characterisation by Rotational Spectroscopy (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 265-270 
    Details
    ISSN: 0947-6539
    Schlagwort(e): cyclic compounds ; medium-sized ; rings ; tetraketones ; transannular interactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: By using a fast-mixing nozzle in a Fourier transform microwave spectrometer, any chemical reaction accompanying mixing of H2S and BrCl was prevented, thus allowing the observation of the pre-reactive complex H2S ··· BrCl. The rotational spectra of eight isotopomers of the complex were recorded. The analysis of the determined spectroscopic constants shows that the atoms S ··· Br—Cl are collinear or nearly so and that the H2S plane is approximately perpendicular to the S ··· Br—Cl axis with r(S ··· Br) = 3.094 (7) Å. This geometry is in agreement with previously stated rules for B ··· XY complexes, where B is a Lewis base and XY is an (inter)halogen molecule. The intermolecular interaction is shown to be relatively weak, both in terms of the intermolecular stretching force constant kσ and the intramolecular electric change redistribution δ within the BrCl subunit that accompanies formation of H2S ··· BrCl.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020306
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  • 85
    Digitale Medien
    Digitale Medien
    Synthesis, Conformational Analysis and Comparative Protein Binding of a Galabioside and Its Thioglycoside Analogues (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 295-302 
    Details
    ISSN: 0947-6539
    Schlagwort(e): conformational analysis ; galabioside ; hydrogen bonds ; protein recognition ; thioglycosides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The two thio analogues (2 and 3) of TMSEt galabioside [2-(trimethylsilyl)ethyl 4-O-(α-D-galactopyranosyl)-β-D-galactopyranoside, 1], having anomeric sulfur instead of anomeric oxygen atoms, were synthesized and their conformations investigated by NMR and computational (MM 3) methods. A spacer galabioside was covalently coupled to aminated microtiter plates, and binding of a bacterial pilus adhesin (PapG) to the plates was inhibited by the soluble ligands 1, 2 and 3. The ligand 2, which has an intersaccharidic sulfur linkage, was a much less efficient inhibitor than 1, which has the natural oxygen linkage. The inhibitory power of ligand 3 was only slightly less than that of 1. An NMR experiment with 1 and 2, in which hydroxyl-group hydrogens had been partially (50%) substituted by deuterium, demonstrated the presence (in 1) and absence (in 2) of an intramolecular (HO 2′ - HO 6) hydrogen bond. This result indicates that the conformations of 1 and 2 are different and that the difference is sufficient to cause the observed (≈ 30 times) reduction of the saccharide-protein binding strength.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020310
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  • 86
    Digitale Medien
    Digitale Medien
    X-ray structural studies of highly enantioselective Mn(salen) epoxidation catalysts (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 974-980 
    Details
    ISSN: 0947-6539
    Schlagwort(e): asymmetric eponidations ; Cstalysis ; manganese complexes ; structure elucidation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relationship between catalyst structure and enantioselectivity in the asymmetric epoxidation of unfunctionalized olefins by a series of chiral Mn(sa1en) complexes (1 - 10) was examined. The X-ray structures of 5-coordinate complexes 5, 8, of 6-coordinate 9 ([6,6′= -tBu; 4,4 = -tBu]+ClO4-), and 10 (6,6′= -tBu; 4,4′=-Br) were determined. Catalysts 1 - 9 were derived from (R,R)-1, tdiaminocyclohexane and catalyst 10 from (S,S)-1,2-diphenylethyIenediamine. Catalysts 1-9 differ in the stereoelectronic substitution of the orfho (6,6) and para (4,4) positions of the salicylidene moiety. A comparison between structures 5, 8, and 9 reveals that the ligand geometry around the metal center and the chiral diimine backbone remains remarkably constant in both five- and six-coordinate cyclohexanediamine-derived complexes; in contrast, the salicylidene regions of the complexes display a wide range of conformations. The asymmetric epoxidation of indene and 6-cyano-2,2-dimethylchromene with NaOCl catalyzed by complexes 1 - 10 was effected. Systematically increasing the steric bulk on the ortho and then the para position in the order 1 (6,6′ = -H; 4,4′ = -H),2(6,6′ = -CH3; 4,4′ = -CH3),3(6,6′=-tBu;4,4′=-H),4(6,6′=-tBu; 4,4′ =-CH3), 5 (6,6′=-tBu; 4,4′=-tBu), and 6 (6,6′=-tBu; 4,4′= -trityl), and electronically modifying the para substituents in 7 (6,6 = -tBu; 4,4 =-OMe) and 8 (6.6′ = -tBu; 4,4′=-OTIPS) resulted in enhanced enantioselectivities of the desired epoxides. The conformational variations observed in the solid state are likely to reflect accessible solution conformations and may help explain the high levels of stereoinduction obtained with these catalysts in the asymmetric epoxidation of unfunctionalized olefins.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020810
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  • 87
    Digitale Medien
    Digitale Medien
    Effects of nitrogen substitution in poly(pyrazolyl)borato ligands: From orbital energy levels to C-H ⃛ O hydrogen bondingDedicated to Professor Max Herberhold on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 992-1000 
    Details
    ISSN: 0947-6539
    Schlagwort(e): cyclovoltammetry ; electronic effects ; photoelectron spectroscopy ; pyrazole ligands ; Mössbauer spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electronic effect of substituting CH with N in poly(pyrazolyl)-borato ligands and their transition-metal complexes is shown to be a decrease in energy of the filled metal and ligand orbitals. This conclusion is based on the cyclovoltammograms and photoelectron spectra of bis(hydrotris(azolyl)borato)-iron(II) and -cobalt(II) complexes (azolyl = pyrazolyl and 1,2,4-triazolyl) and on MO calculations. 57Fe Mössbauer spectra of bis(hydrotris(1,2,4-triazolyl)-borato)iron(II) show that there is a fine-tuning of the HOMO-LUMO gap by a shift in transition temperature for the spin equilibrium. 15N NMR spectroscopy supports the assignment of a higher negative charge to the exodentate N-4 nitrogen than to the endodentate N-2 or N-3 positions in the poly(azolyl)borato anions, where azolyl is 1,2,4-triazolyl or tetrazolyl. The electron withdrawing effect of the additional nitrogen atoms and the in-corporation of water of crystallization by O-H ⃛ N bonding both assist in the formation of (azolyl)C-H ⃛ O bonds.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020813
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  • 88
    Digitale Medien
    Digitale Medien
    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 909-912 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020819
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  • 89
    Digitale Medien
    Digitale Medien
    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020820
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  • 90
    Digitale Medien
    Digitale Medien
    A novel catalytic cycle for the synthesis of epoxides using sulfur ylides (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1024-1030 
    Details
    ISSN: 0947-6539
    Schlagwort(e): catalysis ; diazo compounds ; epoxidations ; sulfur ylides ; synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel, neutral catalytic cycle for the synthesis of epoxides from carbonyl compounds and diazo compounds using catalytic quantities of transition metal salts and sulfides has been developed. In this catalytic cycle, the diazo compound is decomposed by the transition metal salt to give a metallocarbene, and this is picked up by the sulfide to give a sulfur ylide, which then reacts with the aldehyde to give an epoxide and returns the sulfide back into the catalytic cycle. To obtain good yields of epoxides it is necessary to maintain a low concentration of the diazo compound (by slow addition), otherwise dimerisation of the diazo compound is the dominant reaction. Factors affecting the outcome of the reaction were studied. The reactions are relatively insensitive to solvent, but are sensitive to the structure of the sulfide, the metal salt and the concentration. Unhindered sulfides give good yields of epoxides with any metal salt, but with hindered sulfides higher yields are obtained with Cu(acac)2 than with Rh2(OAc)4. The yields of epoxides are sensitive to sulfide concentration especially when using substoichiometric amounts of sulfides. Higher concentration leads to faster rates of formation and subsequent reaction of the sulfur ylides, and consequently to higher yields. This novel catalytic cycle has also been applied to base-sensitive aldehydes. We found that our new catalytic cycle for epoxidation gives much improved yields of epoxides compared to those obtained by traditional sulfur ylide chemistry and is tolerant to a wide variety of sensitive functional groups. Ketones also participate in the catalytic cycle, although they give reduced yields of epoxides compared to aldehydes and require a slightly elevated temperature.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020817
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  • 91
    Digitale Medien
    Digitale Medien
    TiIV-BINOLate-catalyzed highly enantioselective additions of β-substituted allylstannanes to aldehydesFirst presented at the „15th Regiosymposium of the Universities Basel, Freiburg, and Mulhouse“ in Falkau, September 27-29, 1995. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1077-1084 
    Details
    ISSN: 0947-6539
    Schlagwort(e): allylstannanes ; asymmetric allylations ; catalysis ; C-C bond formation ; homoallylic alcohols ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Enantiomerically pure homoallyl alcohols were prepared from aldehydes R1-CH=O (R1 = Ph, pentyl, Ph-CH=CH-, iPr) and β-substituted allyl-stannanes H2C=CR2-CH2-SnBu3 (R2 = pentyl, tBuPh2SiO-CH2-, tBuPh2SiO-CH2-CH2-, PhS-CH2-CH2-). These reactions were catalyzed by the same additives - Ti(OR)4 (10 mol%) and (R)-BINOL (20 mol%) - that Keck et al. used in analogous reactions with methallyl-and allyltributylstannane. To attain optimum ee values (96.4-99.2% in the reaction with hexanal) these additives had to be premixed for 2 h at room temperature. Ti(OEt)4 and Ti(OiPr)4 gave equally good results, while Ti(OMe)4, Ti(OCHEt2)4, and Ti(OtBu)4 were inferior. Our procedure works in the absence of molecular sieves [which were previously found to give rather unreliable results in reactions catalyzed by Ti(OiPr)4/(R)-BINOL] and can be extended to enantioselective addition reactions with allyl- and methallyltributylstannane, too (+ hexanal: 97.4 and 97.0% ee, respectively).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020905
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  • 92
    Digitale Medien
    Digitale Medien
    Catalytic properties of layered gold-palladium colloidsDedicated to Professor Max Herberhold on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1099-1103 
    Details
    ISSN: 0947-6539
    Schlagwort(e): catalysis ; colloids ; gold-palladium colloids ; HRTEM ; hydrogenations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Layered bimetallic gold-palladium colloids in the size range of 20-56 nm have been synthesized by the seed=growth method: gold seeds were convered by palladium layers of various thickness and vice vaers. The outer metal was coordinated by trisulfonated triphenylphosphine and sodium sulfanilate ligands to stabilize the bimetallic particles to such an extent that they could be isolated in the solid state. Owing to the hydrophilic ligand shell, redispersion in water was posible in any concentration. High-resolution transmission electronn microscopy and energy-dispersive X-ray analysis was used to characterized the colloids. Stabilized and nonstabilized gold-palladium and palladium-gold systems on a TiO2 support were used as heterogeneous catalysts for the hydrogenation of hex-2-yne to cis-hex-2-ene. Both the palladium-plated gold seeds and the gold-plated palladium particles showed considerably increased activities compared with the pure metals. The ligand shell seems not to influence the catalytic behavior because protected and unprotected colloids behave very similarly.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020908
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  • 93
    Digitale Medien
    Digitale Medien
    A Convergent synthesis of carbohydrate-containing dendrimersThis paper should be regarded as Part 1 of a series on Synthetic Carbohydrate Dendrimers. A list of abbreviations used in this paper is given in ref. [40]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1115-1128 
    Details
    ISSN: 0947-6539
    Schlagwort(e): carbohydrates ; cluster glucosides ; convergent syntheses ; dendrimers ; neoglycoconjugates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of carbohydratecontaining dendrimers has been achieved by a convergent growth approach. The synthetic strategy involves: 1) the synthesis of the triglucosylated derivative of tris(hydroxymethyl)methylamine (TRIS), 2) the introduction of a glycine-derived spacer and 3,3′-iminodipropionic acid derived branching units on to the TRIS derivative by amide bond formation, 3) condensation of the above saccharidecontaining dendrons with a trifunctional 1,3,5-benzenetricarbonyl derivative, used as the core, by formation of amide bonds, and 4) deprotection of the saccharide units. A 9-mer and an 18-mer, carrying nine and eighteen saccharide units at the periphery, respectively, have been synthesized, in high yields at each step, by this synthetic strategy. By a variety of chromatographic and spectroscopic techniques, the dendrimers were shown to be structurally homogeneous, monodisperse, and error-free at all steps in their growth. These investigations were complemented by molecular modeling studies on the dendrimers. The presence of slightly distorted C3 symmetry was noted in both the 9-mer and the 18-mer.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020911
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  • 94
    Digitale Medien
    Digitale Medien
    The unimolecular chemistry of protonated glycinamide and the proton affinity of glycinamid - mass spectrometric experiments and theoretical model (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1143-1149 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; glycinamide ; mass spectrometry ; protonations ; quantum chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The potential energy hypersurface of protonated glycinamide (GAH+) has been investigated experimentally and theoretically. The calculated G2(MP2) value for the proton affinity of glycinamide, PAcalcd = 919 kJ mol-1, is in good agreement with the measured value of 908PAexp〈914kJ mol-1. The fact that the amide group is a better hydrogenbond acceptor explains why glycinamide has a higher PA than glycine. Proton transfer experiments with glycinamide performed in a Fourier transform mass spectrometer and analysis of metastable GAH+ ions in a four-sector mass spectrometer show that the lowest-energy unimolecular reactions are two distinct processes: 1) loss of CO, which has a substantial barrier for the reverse reaction, and 2) loss of CO plus NH3, which has no barrier for the reverse reaction. Ab initio quantum chemical calculations give a reaction model that is consistent with the observed fragmentation pattern.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.1460020915
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  • 95
    Digitale Medien
    Digitale Medien
    Stabilization of Octahedral Thorium Clusters by Interstitial Hydrogen (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 511-515 
    Details
    ISSN: 0947-6539
    Schlagwort(e): chemical bonding ; hydrides ; interstitial atoms ; magnetic properties ; thorium clusters ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis, structure, and characterization of the cluster compounds Th6HxBr15 (x = 5 and 7) are reported. The compounds can be prepared by a reversible hydrogenation/dehydrogenation process; their structures have been determined by X-ray and neutron diffraction methods. Both compounds form a body-centered cubic structure of octahedral cluster units with five or seven hydrogen atoms in eight disordered positions above the faces of the octahedron. The chemical bonding in these diamagnetic compounds has been analyzed: the simple counting rules for octahedral cluster compounds are fulfilled, and MO and band structure calculations confirm the hydridic nature of the bonding.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020509
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  • 96
    Digitale Medien
    Digitale Medien
    Conformers of Saturated Chains: Matrix Isolation, Structure, IR and UV Spectra of n-Si4Me10Dedicated to Professor H.-D. Scharf on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 529-538 
    Details
    ISSN: 0947-6539
    Schlagwort(e): ab initio calculations ; conformation ; sigma conjugation ; matrix isolation ; oligosilanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Infrared and ultraviolet spectra of the gauche and anti conformers of matrix-isolated permethyl-n-tetrasilane have been obtained separately by taking advantage of thermally induced gauche-to-anti conversion and of wavelength-selective photochemical destruction of either conformer. The resolved UV spectrum of the gauche conformer provides the first piece of experimental evidence in favor of the recently proposed reinterpretation of conformational effects on tetrasilane electronic states. According to this, it is not the energy but the intensity of the lowest singlet excitation that changes dramatically as the SiSiSiSi dihedral angle is varied, as a result of an avoided crossing between s̰s̰* and s̰π* states. Implications for the general understanding of sigma conjugation in simple terms are discussed. Unconstrained MP2/6-31 G* optimization predicts the existence of a third backbone conformer (ortho), with a dihedral angle of about 90°. Its predicted (HF/3-21 G*) mid-IR spectrum is indistinguishable from that of the gauche conformer, and the matrix-isolation spectra thus provide no evidence for or against its presence.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020512
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  • 97
    Digitale Medien
    Digitale Medien
    Coordination and Coupling of OH-Functionalized C2 Units at a Single Metal Center: The Synthesis of Alkynyl(Vinylidene), Alkynyl(Enyne), Bis(Alkynyl)Hydrido, Enynyl, and Hexapentaene Rhodium Complexes from Propargylic Alcohols as PrecursorsDedicated to Professor Martin A. Bennett on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 561-569 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkyne complexes ; carbon-carbon coupling ; pentaenes ; rhodium complexes ; vinylidene complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of [Rh(η3-C3H5)-(PiPr3)2] (1) with HC≡C—CH(Ph)OH yields the alkynyl(vinylidene) complex trans-[Rh{C≡C—CH(Ph)OH}{=C=CH-CH(Ph)OH}(PiPr3)2] (2), while from 1 and HC≡C—CPh2OH the alkynyl-(enyne)metal derivative trans-[Rh(C≡C—CPh2OH){n2-(E)-Ph2(OH)C—C≡C—CH=CH-CPh2OH} (PiPr3)2] (3) is obtained. On treatment with 1-alkyn-3-ols HC≡C—CR2OH (R = Me, Ph, iPr), the highly reactive π-benzyl compound [Rh(n3-CH2Ph)(PiPr3)2] (4) yields the five-coordinate complexes [RhH(C≡C—CR2OH)2(PiPr3)2] (5-7) of which those with R = Me and Ph can be converted to the alkynyl(vinylidene)metal isomers trans-[Rh(C≡C—CR2OH)(=C=CH-CR2OH)-(PiPr3)2] (8, 9). Compounds 8 and 9 react with L′ = CO and isocyanides by migration of the alkynyl ligand to the vinylidene unit to give the enynylrhodium(I) complexes trans-[Rh{n1-(Z)-C(C≡C—CR2—OH)=CH-CR2OH}(L′)(PiPr3)2] (10, 11: L′ = CO; 12-15: L′ = CNR′). Cleavage of the Rh-C s̰-bond of 10 with CF3-CO2H affords trans-[Rh(n1-O2CCF3)-(CO)(PiPr3)2] (16) and the enyne (E)-Me2(OH)C—C≡C—CH=CH-CMe2OH (17). Compounds 5-7 react with L′ = CO and isocyanides to give the octahedral 1:1 adducts [RhH(C≡C—CR2OH)2(L′)(P-iPr3)2] (18-20 and 24-27), of which the CO derivatives 18-20 readily eliminate HC≡C—CR2OH to yield trans-[Rh-(C≡C—CR2OH)(CO)(PiPr3)2] (21-23). On treatment of 6 or 9 (R = Ph) with Al2O3 in the presence of chloride ions, besides trans-[RhCl(=C=C=CPh2)(P-iPr3)2] (28) the hexapentaenerhodium(I) complex trans-[RhCl(n2-Ph2C=C=C=C=C=CPh2)(PiPr3)2] (29) is formed. The kinetically preferred isomer trans-[RhCl(n2-Ph2C=C=C=C=C=CPh2)(P-iPr3)2] (33) has been prepared from [RhCl(PiPr3)2]2 and Ph2C=C=C=C=C=CPh2; it rearranges smoothly at room temperature to the thermodynamically more stable isomer 29. The molecular structures of 7 and 29 have been determined.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960020516
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  • 98
    Digitale Medien
    Digitale Medien
    Preparation, Characterization, and Reactivity of a Diamagnetic Vanadium Nitride (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1258-1263 
    Details
    ISSN: 0947-6539
    Schlagwort(e): dinitrogen activation ; nitrides ; structure elucidation ; vanadium complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactions of (Ph2N)3V-(THF) (1) with [(CH3)3Si]N3 and [(CH3)3Si]CHN2 proceed at room temperature to afford the corresponding derivatives (Ph2N)3V[N-Si(CH3)3] (2a) and (Ph2N)3V[N2CHSi(CH3)3] (3). Reactions of both 2a and 3 with lithium isopropylamide provide the unprecedented anionic vanadium nitride species [(Ph2N)3V(μ-N)Li(THF)3]·(THF)0.5 (4), which displays moderate nucleophilicity. It reacts with (CH3)3SiCl and Mel to reform the complex (Ph2N)3V(N-R) [R = Si(CH3)3 (2a), Me (2b)]. Reactions with Cp2ZrCl2 and CpTiCl3 lead to the formation of the heterodinuclear bridged nitride complexes [(Ph2N)3V(μ-N)ZrClCp]2] [Cp = Cp]=Cp (6a), CH3C5H4 (6b)] and [{(Ph2N)3V(μ-N)}2TiClCp] (8).
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021012
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  • 99
    Digitale Medien
    Digitale Medien
    Kinetic Analysis of the Stepwise Platination of Single- and Double-Stranded GG Oligonucleotides with Cisplatin and cis-[PtCl(H2O)(NH3)2]+ (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1283-1291 
    Details
    ISSN: 0947-6539
    Schlagwort(e): antitumour agents ; DNA ; kinetics ; nucleotides ; platinum complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We report the first direct comparison of the kinetics of platination of defined single- and double-stranded DNA with the anticancer drug cisplatin. The courses of the reactions of the 14-mer duplex d(A-T-A-C-A-T-G-G-T-A-C-A-T-A)·d(T-A-T-G-T-A-C-C-A-T-G-T-A-T) with [15N]cisplatin and cis-[PtCl(H2O)-(15NH3)2]+ and of each of the single strands with [15N]cisplatin have been studied at 298 K, pH 6, by [1H, 15N] NMR spectroscopy. As expected the reactions of cisplatin proceed via cis-[PtCl(H2O)(NH3)2]+, and lead to two monofunctional adducts on the duplex and two on the GG single strand. In both the GG single strand and the duplex, one of the two G's is platinated faster than the other (by a factor of ca. 4). Remarkably, ring closure on the duplex to form the GG chelate occurs about an order of magnitude faster for one monofunctional adduct than for the other. The latter monofunctional adduct has distinctive 1H and 15N NMR chemical shifts for Pt-NH3, and is very long-lived (persists for 〉5 d). The Pt-Cl bond in this monofunctional adduct is protected from hydrolysis by the duplex. In contrast, the two monofunctional adducts on the GG single strand undergo ring closure at about the same rate. Equilibria between kinked and distorted forms of the GG platinated duplex, the platination of G's on the complementary strand, and the potential biological significance of long-lived monofunctional adducts of platinum drugs with DNA are discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021016
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  • 100
    Digitale Medien
    Digitale Medien
    Me3TTF-PO3H2, a Redox Phosphonic Acid and Its Monoanilinium Salt [PhNH+3][Me3TTF-PO(OH)O-], the Electrocrystallized Neutral (Zwitterionic) π Radical [Me3TTF-PO(OH)O-]·+, and Their Associated Lamellar Constructions in the Solid State (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1275-1282 
    Details
    ISSN: 0947-6539
    Schlagwort(e): crystal engineering ; hydrogen bonds ; phosphonates ; radical cations ; tetrathia fulvalenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of Me3TTFLi (TTF = tetrathiafulvalene) with ClP(O)-(OEt)2 followed by hydrolysis with Me3SiBr affords the novel π-donor molecule trimethyltetrathiafulvalenylphosphonic acid (Me3TTF-PO3H2) in a partially oxidized form. Subsequent reduction and neutralization with aniline gives the corresponding phosphonate monoanilinium salt. A unique hydrogen-bonded hexagonal net is identified within the lamellar structure of [PhNH+3][Me3TTF-PO(OH)O-], which is described by analogy with the anti-CaSi2 structure type. Electrocrystallization of the former salt yields single crystals of a neutral (zwitterionic) π radical, formulated as [Me3TTF-PO(OH)O-]·+. Their structure reveals the presence of hydrogen-bonded molecular ribbons whose association creates a novel layered architecture similar to that obtained within radical cation salts of π-donor molecules of larger spatial extension. The analysis of the calculated HO-MO-HOMO intermolecular interaction energies demonstrates that these slabs contain strong π-π intermolecular interactions despite the nonexistence of any 2D network of short S ⃛S contacts. The spin susceptibility of [Me3TTF-PO-(OH)O-]·+, determined by single-crystal ESR measurements, is characteristic of triplet excitons, the origin of which may be understood from the electronic structure of the compound.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19960021015
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