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  • 2005-2009  (54)
  • 1990-1994  (1,025)
  • 2006  (54)
  • 1990  (1,025)
  • Organic Chemistry  (891)
  • Physical Chemistry  (232)
  • Electronic commerce, Management
  • composting
  • ddc:000
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  • 2005-2009  (54)
  • 1990-1994  (1,025)
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  • 1
    Unknown
    Managing business in a multi-channel world : success factors for E-business (2006)
    Hershey PA : Idea Group Pub
    Details
    Keywords: Electronic books ; Electronic commerce, Management ; Information technology, Management ; Technological innovations, Management
    Pages: 1 v. (various pagings)
    ISBN: 1-591-40631-5
    URL: http://www.netLibrary.com/urlapi.asp?action=summary&v=1&bookid=126097
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    E-Book (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Efforts to Explain and Control the Prolonged Thermophilic Period in Two-phase Olive Oil Mill Sludge Composting (2006)
    Springer
    Biodegradation 17 (2006), S. 285-292 
    Details
    ISSN: 1572-9729
    Keywords: composting ; crude oil ; olive mill wastewater ; olive oil mills ; olive tree branches ; olive tree leaves ; sludge ; woodchips
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The aim of this paper was to evaluate the use of different bulking agents in different ratios as a means to control, optimise and eventually reduce the duration of the thermophilic period in two-phase olive oil mill sludge (OOMS) composting. The bulking agents used were: (i) olive tree leaves (OTL), (ii) olive tree shredded branches (OTB) and (iii) woodchips (WDC). The selection of these materials was based on their abundance and availability on the island of Crete, the southernmost point of Greece. The ratios studied were: Pile 1, OOMS:OTL in 1:1 v/v; Pile 2, OOMS:WDC in 1:1.5 v/v; Pile 3, OOMS:OTL in 1:2 v/v; Pile 4, OOMS:OTL:OTB in 1:1:1 v/v; and Pile 5, OOMS:OTL:OTB in 1:1:2 v/v. The composting system used was that of windrows with the volume of each pile approximately 20–25 m3. The experiments took place over two consecutive years. A composting turner was used and turnings were performed at one and two week intervals. In each pile a variety of physiochemical parameters were monitored. Temperature remained high in all five trials. Piles 1, 2, 3, 4 and 5 temperatures recorded values of above 50 °C for 106, 158, 160, 175 and 183 days, respectively. Volumes were reduced by approximately 67%, 62%, 63%, 80% and 84%, respectively. Temperature remained high, mainly due to the presence in large amounts of oily substances which during their complete oxidation release important amounts of energy and aid the cometabolism of more stable molecules such as lignin. This process is better described as the slow “burning” of a “fuel” mixture in an “engine” than composting. This approach is based on the extensive similarities of this process to that of crude oil sludge or similar waste composting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s10532-005-7566-4
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Bioremediation by Composting of Heavy Oil Refinery Sludge in Semiarid Conditions (2006)
    Springer
    Biodegradation 17 (2006), S. 251-261 
    Details
    ISSN: 1572-9729
    Keywords: bioremediation ; composting ; ecotoxicity ; oil sludge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The present work attempts to ascertain the efficacy of low cost technology (in our case, composting) as a bioremediation technique for reducing the hydrocarbon content of oil refinery sludge with a large total hydrocarbon content (250–300 g kg−1), in semiarid conditions. The oil sludge was produced in a refinery sited in SE Spain The composting system designed, which involved open air piles turned periodically over a period of 3 months, proved to be inexpensive and reliable. The influence on hydrocarbon biodegradation of adding a bulking agent (wood shavings) and inoculation of the composting piles with pig slurry (a liquid organic fertiliser which adds nutrients and microbial biomass to the pile) was also studied. The most difficult part during the composting process was maintaining a suitable level of humidity in the piles. The most effective treatment was the one in which the bulking agent was added, where the initial hydrocarbon content was reduced by 60% in 3 months, compared with the 32% reduction achieved without the bulking agent. The introduction of the organic fertiliser did not significantly improve the degree of hydrocarbon degradation (56% hydrocarbon degraded). The composting process undoubtedly led to the biodegradation of toxic compounds, as was demonstrated by ecotoxicity tests using luminescent bacteria and tests on plants in Petri dishes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s10532-005-5020-2
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    Paper (German National Licenses)
    Fulltext
  • 4
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    Jahresbericht 2005 (2006)
    Details
    Publication Date: 2019-10-24
    Keywords: ddc:000
    Language: German
    Type: annualzib , doc-type:report
    Format: application/pdf
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    OPUS
  • 5
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    Convergence of the Control Reduced Interior Point Method for PDE Constrained Optimal Control with State Constraints (2006)
    Details
    Publication Date: 2014-02-26
    Description: We propose a variant of the control reduced interior point method for the solution of state constrained problems. We show convergence of the corresponding interior point pathfollowing algorithm in function space. Morever, we provide error bounds for the iterates.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 6
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    A Complex Mathematical Model of the Human Menstrual Cycle (2006)
    Details
    Publication Date: 2014-02-26
    Description: This paper aims at presenting the complex coupled network of the human menstrual cycle to the interested community. Beyond the presently popular smaller models, where important network components arise only as extremely simplified source terms, we add: the GnRH pulse generator in the hypothalamus, receptor binding, and the biosynthesis in the ovaries. Simulation and parameter identification are left to a forthcoming paper.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 7
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    A continuity result for Nemyckii Operators and some applications in PDE constrained optimal control (2006)
    Details
    Publication Date: 2014-02-26
    Description: This work explores two applications of a classical result on the continuity of Nemyckii operators to optimal control with PDEs. First, we present an alternative approach to the analysis of Newton's method for function space problems involving semi-smooth Nemyckii operators. A concise proof for superlinear convergence is presented, and sharpened bounds on the rate of convergence are derived. Second, we derive second order sufficient conditions for problems, where the underlying PDE has poor regularity properties. We point out that the analytical structure in both topics is essentially the same.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 8
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    Nash Equilibria in Online Sequential Routing Games (2006)
    Details
    Publication Date: 2014-02-26
    Description: In this paper, we study the efficiency of Nash equilibria for a sequence of nonatomic routing games. We assume that the games are played consecutively in time in an online fashion: by the time of playing game $i$, future games $i+1,\dots,n$ are not known, and, once players of game $i$ are in equilibrium, their corresponding strategies and costs remain fixed. Given a sequence of games, the cost for the sequence of Nash equilibria is defined as the sum of the cost of each game. We analyze the efficiency of a sequence of Nash equilibria in terms of competitive analysis arising in the online optimization field. Our main result states that the online algorithm $\sl {SeqNash}$ consisting of the sequence of Nash equilibria is $\frac{4n}{2+n}$-competitive for affine linear latency functions. For $n=1$, this result contains the bound on the price of anarchy of $\frac{4}{3}$ for affine linear latency functions of Roughgarden and Tardos [2002] as a special case. Furthermore, we analyze a problem variant with a modified cost function that reflects the total congestion cost, when all games have been played. In this case, we prove an upper bound of $\frac{4n}{2+n}$ on the competitive ratio of $\sl {SeqNash}$. We further prove a lower bound of $\frac{3n-2}{n}$ of $\sl {SeqNash}$ showing that for $n=2$ our upper bound is tight.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 9
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    Adaptive, Fast and Oblivious Convolution in Evolution Equations with Memory (2006)
    Details
    Publication Date: 2016-06-09
    Description: To approximate convolutions which occur in evolution equations with memory terms, a variable-stepsize algorithm is presented for which advancing $N$ steps requires only $O(N\log N)$ operations and $O(\log N)$ active memory, in place of $O(N^2)$ operations and $O(N)$ memory for a direct implementation. A basic feature of the fast algorithm is the reduction, via contour integral representations, to differential equations which are solved numerically with adaptive step sizes. Rather than the kernel itself, its Laplace transform is used in the algorithm. The algorithm is illustrated on three examples: a blow-up example originating from a Schrödinger equation with concentrated nonlinearity, chemical reactions with inhibited diffusion, and viscoelasticity with a fractional order constitutive law.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 10
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    Two-layer Network Design by Branch-and-Cut featuring MIP-based Heuristics (2006)
    Details
    Publication Date: 2020-11-13
    Description: This paper deals with MIP-based primal heuristics to be used within a branch-and-cut approach for solving multi-layer telecommunication network design problems. Based on a mixed-integer programming formulation for two network layers, we present three heuristics for solving important subproblems, two of which solve a sub-MIP. On multi-layer planning instances with many parallel logical links, we show the effectiveness of our heuristics in finding good solutions early in the branch-and-cut search tree.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 11
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    Adaptive Finite Element Simulation of Ventricular Fibrillation Dynamics (2006)
    Details
    Publication Date: 2019-05-10
    Description: The dynamics of ventricular fibrillation caused by irregular excitation is simulated in the frame of the monodomain model with an action potential model due to Aliev-Panfilov for a human 3D geometry. The numerical solution of this multiscale reaction-diffusion problem is attacked by algorithms which are fully adaptive in both space and time (code library {\sc Kardos}). The obtained results clearly demonstrate an accurate resolution of the cardiac potential during the excitation and the plateau phases (in the regular cycle) as well as after a reentrant excitation (in the irregular cycle).
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 12
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    Orbitopal Fixing (2006)
    Details
    Publication Date: 2020-12-15
    Description: The topic of this paper are integer programming models in which a subset of 0/1-variables encode a partitioning of a set of objects into disjoint subsets. Such models can be surprisingly hard to solve by branch-and-cut algorithms if the permutation of the subsets of the partition is irrelevant. This kind of symmetry unnecessarily blows up the branch-and-cut tree. We present a general tool, called orbitopal fixing, for enhancing the capabilities of branch-and-cut algorithms in solving this kind of symmetric integer programming models. We devise a linear time algorithm that, applied at each node of the branch-and-cut tree, removes redundant parts of the tree produced by the above mentioned permutations. The method relies on certain polyhedra, called orbitopes, which have been investigated in (Kaibel and Pfetsch (2006)). However, it does not add inequalities to the model, and thus, it does not increase the difficulty of solving the linear programming relaxations. We demonstrate the computational power of orbitopal fixing at the example of a graph partitioning problem motivated from frequency planning in mobile telecommunication networks.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 13
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    Approximability of Unsplittable Shortest Path Routing Problems (2006)
    Details
    Publication Date: 2014-11-10
    Description: In this paper, we discuss the relation of unsplittable shortest path routing (USPR) to other routing schemes and study the approximability of three USPR network planning problems. Given a digraph $D=(V,A)$ and a set $K$ of directed commodities, an USPR is a set of flow paths $\Phi_{(s,t)}$, $(s,t)\in K$, such that there exists a metric $\lambda=(\lambda_a)\in \mathbb{Z}^A_+$ with respect to which each $\Phi_{(s,t)}$ is the unique shortest $(s,t)$-path. In the \textsc{Min-Con-USPR} problem, we seek for an USPR that minimizes the maximum congestion over all arcs. We show that this problem is hard to approximate within a factor of $\mathcal{O}(|V|^{1-\epsilon})$, but easily approximable within min$(|A|,|K|)$ in general and within $\mathcal{O}(1)$ if the underlying graph is an undirected cycle or a bidirected ring. We also construct examples where the minimum congestion that can be obtained by USPR is a factor of $\Omega(|V|^2)$ larger than that achievable by unsplittable flow routing or by shortest multi-path routing, and a factor of $\Omega(|V|)$ larger than by unsplittable source-invariant routing. In the CAP-USPR problem, we seek for a minimum cost installation of integer arc capacities that admit an USPR of the given commodities. We prove that this problem is $\mathcal{NP}$-hard to approximate within $2-\epsilon$ (even in the undirected case), and we devise approximation algorithms for various special cases. The fixed charge network design problem \textsc{Cap-USPR}, where the task is to find a minimum cost subgraph of $D$ whose fixed arc capacities admit an USPR of the commodities, is shown to be $\mathcal{NPO}$-complete. All three problems are of great practical interest in the planning of telecommunication networks that are based on shortest path routing protocols. Our results indicate that they are harder than the corresponding unsplittable flow or shortest multi-path routing problems.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    OPUS
  • 14
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    Availability and Cost Based Evaluation of Demand-wise Shared Protection (2006)
    Details
    Publication Date: 2014-11-11
    Description: In this paper, we investigate the connection availabilities for the new protection scheme Demand-wise Shared Protection (DSP) and describe an appropriate approach for their computation. The exemplary case study on two realistic network scenarios shows that in most cases the availabilities for DSP are comparable with that for 1+1 path protection and better than in case of shared path protection.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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    OPUS
  • 15
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    THESEUS - Protein Structure Prediction at ZIB (2006)
    Details
    Publication Date: 2016-06-30
    Description: THESEUS, the ZIB threading environment, is a parallel implementation of a protein threading based on a multi-queued branch-and-bound optimal search algorithm to find the best sequence-to-structure alignment through a library of template structures. THESEUS uses a template core model based on secondary structure definition and a scoring function based on knowledge-based potentials reflecting pairwise interactions and the chemical environment, as well as pseudo energies for homology detection, loop alignment, and secondary structure matching. The threading core is implemented in C++ as a SPMD parallization architecture using MPI for communication. The environment is designed for generic testing of different scoring functions, e.g. different secondary structure prediction terms, different scoring matrices and information derived from multiple sequence alignments. A validaton of the structure prediction results has been done on the basis of standard threading benchmark sets. THESEUS successfully participated in the 6th Critical Assessment of Techniques for Protein Structure Prediction (CASP) 2004.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    OPUS
  • 16
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    On the stability of the multi-queue multi-server processor sharing with limited service (2006)
    Details
    Publication Date: 2014-02-26
    Description: We consider a multi-queue multi-server system with $n$ servers (processors) and $m$ queues. At the system there arrives a stationary and ergodic stream of $m$ different types of requests with service requirements which are served according to the following $k$-limited head of the line processor sharing discipline: The first $k$ requests at the head of the $m$ queues are served in processor sharing by the $n$ processors, where each request may receive at most the capacity of one processor. By means of sample path analysis and Loynes' monotonicity method, a stationary and ergodic state process is constructed, and a necessary as well as a sufficient condition for the stability of the $m$ separate queues are given, which are tight within the class of all stationary ergodic inputs. These conditions lead to tight necessary and sufficient conditions for the whole system, also in case of permanent customers, generalizing an earlier result by the authors for the case of $n$=$k$=1.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 17
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    ConfJump : a fast biomolecular sampling method which drills tunnels through high mountains (2006)
    Details
    Publication Date: 2014-02-26
    Description: In order to compute the thermodynamic weights of the different metastable conformations of a molecule, we want to approximate the molecule's Boltzmann distribution in a reasonable time. This is an essential issue in computational drug design. The energy landscape of active biomolecules is generally very rough with a lot of high barriers and low regions. Many of the algorithms that perform such samplings (e.g. the hybrid Monte Carlo method) have difficulties with such landscapes. They are trapped in low-energy regions for a very long time and cannot overcome high barriers. Moving from one low-energy region to another is a very rare event. For these reasons, the distribution of the generated sampling points converges very slowly against the thermodynamically correct distribution of the molecule. The idea of ConfJump is to use $a~priori$ knowledge of the localization of low-energy regions to enhance the sampling with artificial jumps between these low-energy regions. The artificial jumps are combined with the hybrid Monte Carlo method. This allows the computation of some dynamical properties of the molecule. In ConfJump, the detailed balance condition is satisfied and the mathematically correct molecular distribution is sampled.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 18
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    Mathematik für den Volkssport (2006)
    Details
    Publication Date: 2020-02-11
    Description: "`Volkssport Sudoku"' titelt der Stern in seiner Ausgabe vom 24. Mai2006. In der Tat traut sich derzeit kaum noch eine Zeitung, ohne Sudoku zu erscheinen. Die Begeisterung am Lösen dieser Zahlenrätsel offenbart eine unvermutete Freude am algorithmischen Arbeiten. Mathematisch kann man Sudokus als lineare diophantische Gleichungssysteme mit Nichtnegativitätsbedingungen formulieren. Solche ganzzahligen linearen Programme sind die wichtigsten Modellierungswerkzeuge in zahlreichen Anwendungsgebieten wie z.B. der Optimierung von Telekommunikations- und Verkehrsnetzen. Moderne Verfahren zur Lösung dieser Optimierungsprobleme sind durch Sudokus allerdings deutlich weniger zu beeindrucken als Zeitungsleser.
    Keywords: ddc:000
    Language: German
    Type: reportzib , doc-type:preprint
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  • 19
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    Mathematical Methods for Physical Layout of Printed Circuit Boards: An Overview (2006)
    Details
    Publication Date: 2020-02-11
    Description: This article surveys mathematical models and methods used for physical PCB layout, i.e., component placement and wire routing. The main concepts are briefly described together with relevant references.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 20
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    Competitive Online Multicommodity Routing (2006)
    Details
    Publication Date: 2020-12-15
    Description: We study online multicommodity minimum cost routing problems in networks, where commodities have to be routed sequentially. Arcs are equipped with load dependent price functions defining the routing weights. We discuss an online algorithm that routes each commodity by minimizing a convex cost function that depends on the demands that are previously routed. We present a competitive analysis of this algorithm showing that for affine linear price functions this algorithm is $4K/2+K$-competitive, where $K$ is the number of commodities. For the parallel arc case this algorithm is optimal. Without restrictions on the price functions and network, no algorithm is competitive. Finally, we investigate a variant in which the demands have to be routed unsplittably.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 21
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    The extreme points of QSTAB(G) and its implications (2006)
    Details
    Publication Date: 2021-03-16
    Description: Perfect graphs constitute a well-studied graph class with a rich structure, reflected by many characterizations w.r.t different concepts. Perfect graphs are, e.g., characterized as precisely those graphs $G$ where the stable set polytope STAB$(G)$ coincides with the clique constraint stable set polytope QSTAB$(G)$. For all imperfect graphs STAB$(G) \subset$ QSTAB$(G)$ holds and, therefore, it is natural to measure imperfection in terms of the difference between STAB$(G)$ and QSTAB$(G)$. Several concepts have been developed in this direction, for instance the dilation ratio of STAB$(G)$ and QSTAB$(G)$ which is equivalent to the imperfection ratio imp$(G)$ of $G$. To determine imp$(G)$, both knowledge on the facets of STAB$(G)$ and the extreme points of QSTAB$(G)$ is required. The anti-blocking theory of polyhedra yields all {\em dominating} extreme points of QSTAB$(G)$, provided a complete description of the facets of STAB$(\overline G)$ is known. As this is typically not the case, we extend the result on anti-blocking polyhedra to a {\em complete} characterization of the extreme points of QSTAB$(G)$ by establishing a 1-1 correspondence to the facet-defining subgraphs of $\overline G$. We discuss several consequences, in particular, we give alternative proofs of several famous results.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 22
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    On exact algorithms for treewidth (2006)
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    Publication Date: 2014-11-10
    Description: We give experimental and theoretical results on the problem of computing the treewidth of a graph by exact exponential time algorithms using exponential space or using only polynomial space. We first report on an implementation of a dynamic programming algorithm for computing the treewidth of a graph with running time $O^\ast(2^n)$. This algorithm is based on the old dynamic programming method introduced by Held and Karp for the {\sc Tra veling Salesman} problem. We use some optimizations that do not affect the worst case running time but improve on the running time on actual instances and can be seen to be practical for small instances. However, our experiments show that the space use d by the algorithm is an important factor to what input sizes the algorithm is effective. For this purpose, we settle the problem of computing treewidth under the restriction that the space used is only polynomial. In this direction we give a simple $O^\ast(4^n)$ al gorithm that requires {\em polynomial} space. We also show that with a more complicated algorithm, using balanced separators, {\sc Treewidth} can be computed in $O^\ast(2.9512^n)$ time and polynomial space.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 23
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    Coarse Grained Molecular Kinetics (2006)
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    Publication Date: 2014-03-10
    Description: The dynamic behavior of molecules can often be described by Markov processes. From computational molecular simulations one can derive transition rates or transition probabilities between subsets of the discretized conformational space. On the basis of this dynamic information, the spatial subsets are combined into a small number of so-called metastable molecular conformations. This is done by clustering methods like the Robust Perron Cluster Analysis (PCCA+). Up to now it is an open question how this coarse graining in space can be transformed to a coarse graining of the Markov chain while preserving the essential dynamic information. In the following article we aim at a consistent coarse graining of transition probabilities or rates on the basis of metastable conformations such that important physical and mathematical relations are preserved. This approach is new because PCCA+ computes molecular conformations as linear combinations of the dominant eigenvectors of the transition matrix which does not hold for other clustering methods.
    Keywords: ddc:000
    Language: English
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  • 24
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    RSWK/SWD und Faceted Browsing: neue Möglichkeiten einer inhaltlich-intuitiven Navigation (2006)
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    Publication Date: 2014-02-26
    Description: Das deutschsprachige Bibliothekswesen verfügt mit den \glqq Regeln für den Schlagwortkatalog \grqq (RSWK) unter Verwendung der \glqq Schlagwortnormdatei \grqq (SWD) über ein Instrumentarium, welches zusammen mit einem \glqq Faceted Browsing \grqq das bisher bestehende Angebot für ein Information Retrieval optimal ergänzen kann. Die Verbindung zwischen Standardvokabular (SWD) und Kettenbildung (RSWK) einerseits und eine nach Facetten-Eigenschaften gegliederte Navigation andererseits unterstützt bestmöglich eine inhaltlich bezogene Recherche. Die Stärken und Schwächen der RSWK/SWD werden erörtert und auch Klassifikationen (DDC und RVK) als mögliche Facetten diskutiert.
    Keywords: ddc:000
    Language: German
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  • 25
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    Accuracy, Stability, Convergence of Rigorous Thermodynamic Sampling Methods (2006)
    Details
    Publication Date: 2016-06-09
    Keywords: ddc:000
    Language: English
    Type: masterthesis , doc-type:masterThesis
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  • 26
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    Primal Heuristics for Mixed Integer Programs (2006)
    Details
    Publication Date: 2022-03-14
    Description: A lot of problems arising in Combinatorial Optimization and Operations Research can be formulated as Mixed Integer Programs (MIP). Although MIP-solving is an NP-hard optimization problem, many practically relevant instances can be solved in reasonable time. In modern MIP-solvers like the branch-cut-and-price-framework SCIP, primal heuristics play a major role in finding and improving feasible solutions at the early steps of the solution process. This helps to reduce the overall computational effort, guides the remaining search process, and proves the feasibility of the MIP model. Furthermore, a heuristic solution with a small gap to optimality often is sufficient in practice. We investigate 16 different heuristics, all of which are available in SCIP. Four of them arise from the literature of the last decade, nine are specific implementations of general heuristic ideas, three have been newly developed. We present an improved version of the feasibility pump heuristic by Fischetti et al., which in experiments produced solutions with only a third of the optimality gap compared to the original version. Furthermore, we introduce two new Large Neighborhood Search (LNS) heuristics. Crossover is an LNS improvement heuristic making use of similarities of diverse MIP solutions to generate new incumbent solutions. RENS is an LNS rounding heuristic which evaluates the space of all possible roundings of a fractional LP-solution. This heuristic makes it possible to determine whether a point can be rounded to an integer solution and which is the best possible rounding. We conclude with a computational comparison of all described heuristics. It points out that a single heuristic on its own has only a slight impact on the overall performance of SCIP, but the combination of all of them reduces the running time by a factor of two compared to a version without any heuristics.
    Keywords: ddc:000
    Language: English
    Type: masterthesis , doc-type:masterThesis
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    A cartesian grid finite volume method for the solution of the Poisson equation with variable coefficients and embedded interfaces (2006)
    Details
    Publication Date: 2014-02-26
    Description: We present a finite volume method for the solution of the two-dimensional Poisson equation $ \nabla\cdot( \beta( {\mbox{\boldmath $x$}}) \nabla u({\mbox{\boldmath $x$}})) = f(\mbox{\boldmath $x$}) $ with variable, discontinuous coefficients and solution discontinuities on irregular domains. The method uses bilinear ansatz functions on Cartesian grids for the solution $u({\mbox{\boldmath $x$})$ resulting in a compact nine-point stencil. The resulting linear problem has been solved with a standard multigrid solver. Singularities associated with vanishing partial volumes of intersected grid cells or the dual bilinear ansatz itself are removed by a two-step asymptotic approach. The method achieves second order of accuracy in the $L^\infty$ and $L^2$ norm.
    Keywords: ddc:000
    Language: English
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    Efficient Sampling of the Stationary Distribution of Metastable Dynamical Systems (2006)
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    Publication Date: 2014-11-11
    Description: In this article we aim at an efficient sampling of the stationary distribution of dynamical systems in the presence of metastabilities. In the past decade many sophisticated algorithms have been inven ted in this field. We do not want to simply add a further one. We address the problem that one has applied a sampling algorithm for a dynamical system many times. This leads to different samplings which more or less represent the stationary distribution partially very well, but which are still far away from ergodicity or from the global stationary distribution. We will show how these samplings can be joined together in order to get one global sampling of the stationary distribution.
    Keywords: ddc:000
    Language: English
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    Polynomial-Time Algorithms for Linear and Convex Optimization on Jump Systems (2006)
    Details
    Publication Date: 2014-02-26
    Description: The concept of jump system, introduced by Buchet and Cunningham (1995), is a set of integer points with a certain exchange property. In this paper, we discuss several linear and convex optimization problems on jump systems and show that these problems can be solved in polynomial time under the assumption that a membership oracle for a jump system is available. We firstly present a polynomial-time implementation of the greedy algorithm for the minimization of a linear function. We then consider the minimization of a separable-convex function on a jump system, and propose the first polynomial-time algorithm for this problem. The algorithm is based on the domain reduction approach developed in Shioura (1998). We finally consider the concept of M-convex functions on constant-parity jump systems which has been recently proposed by Murota (2006). It is shown that the minimization of an M-convex function can be solved in polynomial time by the domain reduction approach.
    Keywords: ddc:000
    Language: English
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    Packing and Partitioning Orbitopes (2006)
    Details
    Publication Date: 2020-12-15
    Description: We introduce orbitopes as the convex hulls of 0/1-matrices that are lexicographically maximal subject to a group acting on the columns. Special cases are packing and partitioning orbitopes, which arise from restrictions to matrices with at most or exactly one 1-entry in each row, respectively. The goal of investigating these polytopes is to gain insight into ways of breaking certain symmetries in integer programs by adding constraints, e.g., for a well-known formulation of the graph coloring problem. We provide a thorough polyhedral investigation of packing and partitioning orbitopes for the cases in which the group acting on the columns is the cyclic group or the symmetric group. Our main results are complete linear inequality descriptions of these polytopes by facet-defining inequalities. For the cyclic group case, the descriptions turn out to be totally unimodular, while for the symmetric group case, both the description and the proof are more involved. The associated separation problems can be solved in linear time.
    Keywords: ddc:000
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    LP-Based Local Approximation for Markov Decision Problems (2006)
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    Publication Date: 2014-11-21
    Description: The standard computational methods for computing the optimal value functions of Markov Decision Problems (MDP) require the exploration of the entire state space. This is practically infeasible for applications with huge numbers of states as they arise, e.\,g., from modeling the decisions in online optimization problems by MDPs. Exploiting column generation techniques, we propose and apply an LP-based method to determine an $\varepsilon$-approximation of the optimal value function at a given state by inspecting only states in a small neighborhood. In the context of online optimization problems, we use these methods in order to evaluate the quality of concrete policies with respect to given initial states. Moreover, the tools can also be used to obtain evidence of the impact of single decisions. This way, they can be utilized in the design of policies.
    Keywords: ddc:000
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    Ein gemischt-ganzzahliges lineares Optimierungsmodell für ein Laserschweißproblem im Karosseriebau (2006)
    Details
    Publication Date: 2014-11-21
    Description: Wir beschäftigen uns mit dem Problem der Betriebsplanung von Laserschweißrobotern im Karosseriebau. Gegeben ist eine Menge von Schweißnähten, die innerhalb einer Fertigungszelle an einem Karosserieteil gefertigt werden müssen. Die Schweißnähte werden durch mehrere parallel betriebene Roboter bearbeitet. Die Aufgabe besteht darin, für jeden Roboter eine Reihenfolge und eine zeitliche Koordinierung seiner Bewegungen zu finden, so dass alle Schweißnähte innerhalb der Taktzeit der Fertigungszelle bearbeitet werden und so wenig Laserquellen wie möglich eingesetzt werden. Dabei müssen einige Nebenbedingungen berücksichtigt werden. Für dieses spezielle Schweißproblem haben wir eine Formulierung als gemischt-ganzzahliges lineares Programm entwickelt, welches sich für die untersuchten praktischen Fälle sehr schnell lösen lässt.
    Keywords: ddc:000
    Language: German
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    Software for Teaching Modeling of Integer Programming Problems (2006)
    Details
    Publication Date: 2021-08-05
    Description: Modern applications of mathematical programming must take into account a multitude of technical details, business demands, and legal requirements. Teaching the mathematical modeling of such issues and their interrelations requires real-world examples that are well beyond the toy sizes that can be tackled with the student editions of most commercial software packages. We present a new tool, which is freely available for academic use including complete source code. It consists of an algebraic modeling language and a linear mixed integer programming solver. The performance and features of the tool are in the range of current state-of-the-art commercial tools, though not in all aspects as good as the best ones. Our tool does allow the execution and analysis of large real-world instances in the classroom and can therefore enhance the teaching of problem solving issues. Teaching experience has been gathered and practical usability was tested in classes at several universities and a two week intensive block course at TU Berlin. The feedback from students and teachers has been very positive.
    Keywords: ddc:000
    Language: English
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    On the Bottleneck Shortest Path Problem (2006)
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    Publication Date: 2014-11-21
    Description: The Bottleneck Shortest Path Problem is a basic problem in network optimization. The goal is to determine the limiting capacity of any path between two specified vertices of the network. This is equivalent to determining the unsplittable maximum flow between the two vertices. In this note we analyze the complexity of the problem, its relation to the Shortest Path Problem, and the impact of the underlying machine/computation model.
    Keywords: ddc:000
    Language: English
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    Graph Coloring Manifolds (2006)
    Details
    Publication Date: 2014-02-26
    Description: We introduce a new and rich class of graph coloring manifolds via the Hom complex construction of Lov\´{a}sz. The class comprises examples of Stiefel manifolds, series of spheres and products of spheres, cubical surfaces, as well as examples of Seifert manifolds. Asymptotically, graph coloring manifolds provide examples of highly connected, highly symmetric manifolds.
    Keywords: ddc:000
    Language: English
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    Polyhedra of Genus 3 with 10 Vertices and Minimal Coordinates (2006)
    Details
    Publication Date: 2014-02-26
    Description: We give coordinate-minimal geometric realizations in general position for 17 of the 20 vertex-minimal triangulations of the orientable surface of genus 3 in the 5x5x5-cube.
    Keywords: ddc:000
    Language: English
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    ConFlow? A new space-based Application for complete Conformational Analysis of Molecules (2006)
    Details
    Publication Date: 2014-02-26
    Description: Biochemical interactions are determined by the 3D-structure of the involved components - thus the identification of conformations is a key for many applications in rational drug design. {\sf ConFlow} is a new multilevel approach to conformational analysis with main focus on completeness in investigation of conformational space. In contrast to known conformational analysis, the starting point for design is a space-based description of conformational areas. A tight integration of sampling and analysis leads to an identification of conformational areas simultaneously during sampling. An incremental decomposition of high-dimensional conformational space is used to guide the analysis. A new concept for the description of conformations and their path connected components based on convex hulls and {\em Hypercubes}is developed. The first results of the {\sf ConFlow} application constitute a 'proof of concept' and are further more highly encouraging. In comparison to conventional industrial applications, {\sf ConFlow} achieves higher accuracy and a specified degree of completeness with comparable effort.
    Keywords: ddc:000
    Language: English
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    Iteratively Solving Linear Inverse Problems under General Convex Contraints (2006)
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    Publication Date: 2014-02-26
    Description: We consider linear inverse problems where the solution is assumed to fulfill some general homogeneous convex constraint. We develop an algorithm that amounts to a projected Landweber iteration and that provides and iterative approach to the solution of this inverse problem. For relatively moderate assumptions on the constraint we can always prove weak convergence of the iterative scheme. In certain cases, i.e. for special families of convex constraints, weak convergence implies norm convergence. The presented approach covers a wide range of problems, e.g. Besov- or BV-restoration for which we present also numerical experiments in the context of image processing.
    Keywords: ddc:000
    Language: English
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    Stable computation of probability densities for metastable dynamical systems (2006)
    Details
    Publication Date: 2014-03-10
    Description: Whenever the invariant stationary density of metastable dynamical systems decomposes into almost invariant partial densities, its computation as eigenvector of some transition probability matrix is an ill-conditioned problem. In order to avoid this computational difficulty, we suggest to apply an aggregation/disaggregation method which only addresses wellconditioned sub-problems and thus results in a stable algorithm. In contrast to existing methods, the aggregation step is done via a sampling algorithm which covers only small patches of the sampling space. Finally, the theoretical analysis is illustrated by two biomolecular examples.
    Keywords: ddc:000
    Language: English
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    Facets of the (s,t)-p-path polytope (2006)
    Details
    Publication Date: 2016-02-29
    Description: \noindent We give a partial description of the $(s,t)-p$-path polytope of a directed graph $D$ which is the convex hull of the incidence vectors of simple directed $(s,t)$-paths in $D$ of length $p$. First, we point out how the $(s,t)-p$-path polytope is located in the family of path and cycle polyhedra. Next, we give some classes of valid inequalities which are very similar to inequalities which are valid for the $p$-cycle polytope, that is, the convex hull of the incidence vectors of simple cycles of length $p$ in $D$. We give necessary and sufficient conditions for these inequalities to be facet defining. Furthermore, we consider a class of inequalities that has been identifie d to be valid for $(s,t)$-paths of cardinality at most $p$. Finally, we transfer the results to related polytopes, in particular, the undirected counterpart of the $(s,t)-p$-path polytope.
    Keywords: ddc:000
    Language: English
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    A Contact-Stabilized Newmark Method for Dynamical Contact Problems (2006)
    Details
    Publication Date: 2020-11-13
    Description: The numerical integration of dynamical contact problems often leads to instabilities at contact boundaries caused by the non-penetration condition between bodies in contact. Even a recent energy dissipative modification due to Kane et al. (1999), which discretizes the non-penetration constraints implicitly, is not able to circumvent artificial oscillations. For this reason, the present paper suggests a contact stabilization which avoids artificial oscillations at contact interfaces and is also energy dissipative. The key idea of this contact stabilization is an additional $L^2$-projection at contact interfaces, which can easily be added to any existing time integration scheme. In case of a lumped mass matrix, this projection can be carried out completely locally, thus creating only negligible additional numerical cost. For the new scheme, an elementary analysis is given, which is confirmed by numerical findings in an illustrative test example (Hertzian two body contact).
    Keywords: ddc:000
    Language: English
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    Implementation eines Resourcebrokers im Kontext eines Grid-Datenmanagement-Systems (2006)
    Details
    Publication Date: 2016-06-30
    Keywords: ddc:000
    Language: German
    Type: masterthesis , doc-type:masterThesis
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    Enumeration and Random Realization of Triangulated Surfaces (2006)
    Details
    Publication Date: 2014-02-26
    Description: We discuss different approaches for the enumeration of triangulated surfaces. In particular, we enumerate all triangulated surfaces with 9 and 10 vertices. We also show how geometric realizations of orientable surfaces with few vertices can be obtained by choosing coordinates randomly.
    Keywords: ddc:000
    Language: English
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    Note on L#-convex Function Minimization Algorithms: Comparison of Murota's and Kolmogorov's Algorithms (2006)
    Details
    Publication Date: 2014-02-26
    Description: The concept of L##-convexity is introduced by Fujishige--Murota (2000) as a discrete convexity for functions defined over the integer lattice. The main aim of this note is to understand the difference of the two algorithms for L##-convex function minimization: Murota's steepest descent algorithm (2003) and Kolmogorov's primal algorithm (2005).
    Keywords: ddc:000
    Language: English
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    Triangulated Manifolds with Few Vertices: Combinatorial Manifolds (2006)
    Details
    Publication Date: 2014-02-26
    Description: In this survey on combinatorial properties of triangulated manifolds we discuss various lower bounds on the number of vertices of simplicial and combinatorial manifolds. Moreover, we give a list of all known examples of vertex-minimal triangulations.
    Keywords: ddc:000
    Language: English
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    Optimizing the Landside Operation of a Container Terminal (2006)
    Details
    Publication Date: 2020-02-11
    Description: This paper concerns the problem of operating a landside container exchange area that is serviced by multiple semi-automated rail mounted gantry cranes (RMGs) that are moving on a single bi-directional traveling lane. Such a facility is being built by Patrick Corporation at the Port Botany terminal in Sydney. The gantry cranes are a scarce resource and handle the bulk of container movements. Thus, they require a sophisticated analysis to achieve near optimal utilization. We present a three stage algorithm to manage the container exchange facility, including the scheduling of cranes, the control of associated short-term container stacking, and the allocation of delivery locations for trucks and other container transporters. The key components of our approach are a time scale decomposition, whereby an integer program controls decisions across a long time horizon to produce a balanced plan that is fed to a series of short time scale online subproblems, and a highly efficient space-time divisioning of short term storage areas. A computational evaluation shows that our heuristic can find effective solutions for the planning problem; on real-world data it yields a solution at most~8\% above a lower bound on optimal RMG utilization.
    Keywords: ddc:000
    Language: English
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    Triangulated Manifolds with Few Vertices: Vertex-Transitive Triangulations I (2006)
    Details
    Publication Date: 2014-02-26
    Description: We describe an algorithm for the enumeration of (candidates of) vertex-transitive combinatorial $d$-manifolds. With an implementation of our algorithm, we determine, up to combinatorial equivalence, all combinatorial manifolds with a vertex-transitive automorphism group on $n\leq 13$ vertices. With the exception of actions of groups of small order, the enumeration is extended to 14 and 15 vertices.
    Keywords: ddc:000
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    Polyhedra of Genus 2 with 10 Vertices and Minimal Coordinates (2006)
    Details
    Publication Date: 2014-02-26
    Description: We give coordinate-minimal geometric realizations in general position of all 865 vertex-minimal triangulations of the orientable surface of genus 2 in the 4x4x4-cube.
    Keywords: ddc:000
    Language: English
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    Combinatorial 3-Manifolds with 10 Vertices (2006)
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    Publication Date: 2014-02-26
    Description: We give a complete enumeration of combinatorial 3-manifolds with 10 vertices: There are precisely 247882 triangulated 3-spheres with 10 vertices as well as 518 vertex-minimal triangulations of the sphere product $S^2 x S^1$ and 615 triangulations of the twisted sphere product $S^2 \underline{x} S^1$. An analysis of the 3-spheres with up to 10 vertices shows that all these spheres are shellable, but that there are 29 vertex-minimal non-shellable 3-balls with 9 vertices.
    Keywords: ddc:000
    Language: English
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    Adaptive Linearly Implicit Methods for Linear Poroelastic Equations (2006)
    Details
    Publication Date: 2019-05-10
    Description: Adaptive numerical methods in time and space are introduced and studied for linear poroelastic models in two and three space dimensions. We present equivalent models for linear poroelasticity and choose both the {\em displacement--pressure} and the {\em stress--pressure} formulation for our computations. Their discretizations are provided by means of linearly implicit schemes in time and linear finite elements in space. Our concept of adaptivity opens a way to a fast and reliable simulation of different loading cases defined by corresponding boundary conditions. We present some examples using our code {\sf Kardos} and show that the method works efficiently. In particular, it could be used in the simulation of some bone healing models.
    Keywords: ddc:000
    Language: English
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    A computational approach to microRNA detection (2006)
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    Publication Date: 2016-06-30
    Description: During the last few years more and more functionalities of RNA have been discovered that were previously thought of being carried out by proteins alone. One of the most striking discoveries was the de tection of microRNAs, a class of noncoding RNAs that play an important role in post-transcriptional gene regulation. Large-scale analyses are needed for the still increasingly growing amount of sequen ce data derived from new experimental technologies. In this paper we present a framework for the detection of the distinctive precursor structure of microRNAS that is based on the well-known Smith-Wat erman algorithm and various filtering steps. We conducted experiments on real genomic data and we found several new putative hits for microRNA precursor structures.
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    Neustart für Bibliotheken ins Informationszeitalter (2006)
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    Publication Date: 2014-02-26
    Description: Wir erleben zu Beginn des aufkommenden Informationszeitalters mit dem Siegeszug von Google und anderen Internet-Technologien einen Wandel im Verhalten von Wissenschaftlern und Studenten, der mit dem Einsatz von {\sl Google Scholar} und {\sl Google Book Search} einen Paradigmenwechsel für Bibliotheken und Informationsversorger gleichkommt. Der Artikel untersucht die technischen Hintergründe für den Erfolg dieser besonderen Art des Information Retrievals: Fulltext Indexing und Citation Ranking als besondere Form des Information Minig. Er diskutiert Stärken und auch Schwächen des Google-Ansatzes. Der Autor stellt sich auch der Frage, unter welchen Bedingungen es möglich ist, ein zu {\sl Google Scholar} und der {\sl Google Book Search} konkurrenzfähiges Retrieval in der Landschaft der Bibliotheken und Bibliotheksverbünde zu entrichten. Die These ist, dass dieses unter Einsatz des {\sl Open Source} Indexierers {\sl Lucene} und des Web-Robots {\sl Nutch} möglich ist. Bibliotheken können durch gezielten Einsatz solcher Internet-Technologien dem Nutzer die Leistungen, welche Google uns mit seinen Tools im {\sl Visible Web} und mit Referenzen auf {\sl Citations} in der Welt der Literatur zur Verfügung stellt, in vergleichbarer Art auch für ihre eigenen durch Lizenzen geschützten digitalen Journale und ihre speziellen lokal verfügbaren Ressourcen, auf die Internet-Suchmaschinen keine Zugriff haben, anbieten. Es besteht die Hoffnung, dass Nutzer dann nicht - wie in einer kürzlichen Studie des OCLC konstatiert - überwiegend im Internet verbleiben, sondern bei ihrer Suche auch den Weg zu den Angeboten der örtlichen Bibliothek attraktiv finden.
    Keywords: ddc:000
    Language: German
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    Waiting times for M/M systems under generalized processor sharing (2006)
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    Publication Date: 2014-02-26
    Description: We consider a system where the arrivals form a Poisson process and the required service times of the requests are exponentially distributed. According to the generalized processor sharing discipline, each request in the system receives a fraction of the capacity of one processor which depends on the actual number of requests in the system. We derive systems of ordinary differential equations for the LST and for the moments of the conditional waiting time of a request with given required service time as well as a stable and fast recursive algorithm for the LST of the second moment of the conditional waiting time, which in particular yields the second moment of the unconditional waiting time. Moreover, asymptotically tight upper bounds for the moments of the conditional waiting time are given. The presented numerical results for the first two moments of the sojourn times in the $M/M/m-PS$ system show that the proposed algorithms work well.
    Keywords: ddc:000
    Language: English
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    Domain Decomposition Method for Maxwell's Equations: Scattering off Periodic Structures (2006)
    Details
    Publication Date: 2022-07-07
    Description: We present a domain decomposition approach for the computation of the electromagnetic field within periodic structures. We use a Schwarz method with transparent boundary conditions at the interfaces of the domains. Transparent boundary conditions are approximated by the perfectly matched layer method (PML). To cope with Wood anomalies appearing in periodic structures an adaptive strategy to determine optimal PML parameters is developed. We focus on the application to typical EUV lithography line masks. Light propagation within the multi-layer stack of the EUV mask is treated analytically. This results in a drastic reduction of the computational costs and allows for the simulation of next generation lithography masks on a standard personal computer.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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    Format: application/postscript
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  • 55
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    Evaluation of methods of measurement of nitrogen in poultry and animal manures (1990)
    Springer
    Nutrient cycling in agroecosystems 24 (1990), S. 141-148 
    Details
    ISSN: 1573-0867
    Keywords: Ammonia volatilization ; animal manures ; composting ; forms of nitrogen ; Kjeldahl nitrogen ; poultry ; total nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Kjeldahl nitrogen (N), total N and forms of inorganic N (ammoniacal (NH4)-N, nitrate (NO3)-N and nitrite (NO2)-N) were measured in a range of animal manures. The manures include fresh samples of poultry manure, sheep manure, horse manure, dairy slurry and pig slurry and composted poultry manure. Kjeldahl N was measured by standard micro-Kjeldahl digestion. For total N measurements, NO3-N and NO2-N were recovered during Kjeldahl digestion by pretreatments with various oxidizing and reducing agents. Inorganic forms of N were measured by extraction with 2M KCl solution. Kjeldahl digestion alone allowed measurement only of organic N and NH4-N. Amongst various modifications to the Kjeldahl, pretreatment with either acidified (H2SO4) Zn-CrK(SO4)2 or acidified (H2SO4) reduced Fe achieved complete recovery of NO3-N. Nitrite N was only recovered by first oxidising the NO 2 - to NO 3 - with KMnO4 followed by reduction to NH4-N with acidified (H2SO4) reduced Fe. More than 95% of the total N in fresh animal manure was present as organic N and NH4-N which were recovered by the standard Kjeldahl digestion. In the case of fresh manures there was no difference between the amount of total N measured by the Kjeldahl digestion and its modified methods. However composting of poultry manure or drying of poultry manure, pig slurry and dairy slurry resulted in an increase in NO3-N which was not recovered during Kjeldahl digestion alone. Under these conditions the total N could be measured by pretreating the samples with KMnO4 and reduced Fe prior to Kjeldahl digestion. Drying of animal manures caused a decrease in organic N and NH4-N, especially in poultry, pig and dairy manures. There was a slight increase in NO3-N; but most of the decrease in N content with drying was attributed to the volatilization loss of ammonia (NH3). Amongst various drying methods examined air drying caused maximum loss of N as NH3 whereas freeze drying caused minimum loss of N. This suggests that fresh animal manures can be freeze dried for analysis of N which causes minimum loss of N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073582
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  • 56
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    European bioconversion projects and realizations for macroalgal biomass : Saint-Cast-Le-Guildo (France) experiment (1990)
    Springer
    Hydrobiologia 204-205 (1990), S. 301-308 
    Details
    ISSN: 1573-5117
    Keywords: digester ; composting ; Europe ; methanization ; phycocolloid extraction ; residues ; seaweed ; stranded macroalgae ; Ulva
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Proliferation of macroalgae is a world-wide problem with 50,000 m3 of drift Ulva harvested per year in Brittany and about 1.0 to 1.2 million tons growing in the Venice lagoon. This biomass may be treated by bioconversion (aerobic or anaerobic fermentation) to give useful products (gas, fertilizers or others) and to remove a source of environmental pollution. Such a treatment also may be applied to cultivated or harvested seaweds and to seaweed industry residues. Studies of seaweed methanization showed Laminaria an especially good substrate and Ulva a possible substrate. Research led to a defined way of treating drift algae, encompassing natural hydrolysis and pressing with methanization of the juices. The most advanced full-scale realization for algal biomass utilization is the C.A.T.-Quatre-Vaulx composting plant in Saint-Cast-Le-Guildo (Brittany, France). It produced from seaweed, wood and animal dung a biological quality compost that is competitive with the traditional market products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00040249
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  • 57
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    Regiochemical Trends in Intramolecular [2 + 2] Photocycloadditions of 6-(prop-2-enyl)cyclohex-2-enones and 5-(prop-2-enyl)cyclopent-2-enonesDedicated to Prof. H. F. Mark, Brooklyn, in admiration and reverence on the occasion of his 95th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 288-297 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of substituents (X = H, Me, or F at C(6), R = H or Me at C(2′) of the allyl side chain) on the photoisomerization (λ = 350 nm) of 6-allylcyclohex-2-enones 1 in MeCN is studied. Substituents X control the overall efficiency of intramolecular [2 + 2] photocycloadduct formation (Φ: Me 〉 F 〉 H) but do not exercise an influence on the orientation of addition of the exocyclic double bond to the enone C=C bond. In contrast, replacement of the prop-2-enyl (R = H) by a 2-methylprop-2-enyl (R = Me) side chain causes a change in the tricyclo[3.3.1.02,7]nonan-6-one 4 vs. tricyclo[4.2,1.03,8]nonan-7-one (5) product ratio from 100:0 (R = H) to roughly 2:1 (R = Me) but has almost no bearing on the relative rates of conversion of 1 to products. For C(6)-unsubstituted enones 1aa and 1ba (X = H), the efficiency of cyclization becomes low enough so that lumiketone rearrangement to bicyclohexanones 6 and 3-isopropylcyclopent-2-enones 9 becomes competitive. Enones 9 undergo consecutive intramolecular [2 + 2] photocycloaddition to tricyclo[3.2.1.03,6]octan-2-ones 7 and to tricyclo[3.2.1.03,6]octan-7-ones 8, compounds 8 only being formed when R = Me.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730208
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  • 58
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    Effets de substituant, d'hétéroatome et de solvant sur les cinétiques de décoloration thermique et les spectres d'absorption de photomérocyanines en série spiro[indoline-oxazine] (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 303-315 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent, Heteroatom, and Solvent Effects on the Thermal-Bleaching Kinetics and Absorption Spectra of Photomerocyanines Issued from Spiro[indoline-oxazines]Quantitative information useful for the development of new photochromic systems is obtained from the study of heteroatom and substituent effects on the thermal-bleaching kinetics and the absorption spectra of the photomerocyanines issued from spiro[indoline-oxazines]. The effect on photochromic properties of the presence of N-atoms either in the dimethine bridge or in the aromatic rings has been investigated through the comparison of spiro[indoline-naphthopyrans] C with spiro[indoline-naphthoxazines] A and with spiro[indoline-quinolinoxazines] B. Besides the occurrence of biexponential thermal-bleaching kinetics in non-polar solvents is observed: a tentative explanation for this observation is given which involves the formation, in either sequential or parallel steps, of energetically distinct stereoisomers of the opened form.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730210
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  • 59
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    Stereoselectivity and Chiral Recognition in the Electron-Transfer Reaction between Spinach Ferredoxin and Optically Active Cobalt(III) ComplexesPart XIII of the series ‘Stereoselectivity in Reactions of Metal Complexes’. For Part XII, see [1]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 346-352 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the electron transfer between reduced spinach [2Fe-2S]-ferredoxin and the optically active complexes [Co((R,R)- or (S,S)-alamp)py]+ (I), [Co((R,R)- or (S,S)-promp)H2O]+ (IIa), and [Co((R,R)- or (S,S)-promp)py]+ (IIb) have been investigated. The reactions are stereoselective, and for I and IIa, the Stereoselectivity strongly depends on temperature due to large differences in the activation enthalpy between enantiomeric reagents. Isokinetic behaviour is observed between enantiomers, the ΔΔHΔ-Λ# values being largely compensated by the ΔΔSΔ-Λ# values. The compensation behaviour is explained by the combination of stereochemical interactions and desolvation processes on formation of the precursor complex or the transition state.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730214
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  • 60
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    A Facile Synthesis of Optically Pure (-)-(S)-Ipsenol Using a Chiral Titanium ComplexPart 6 of ‘Enantioselective Syntheses with Titanium-Carbohydrate Complexes’; part 5, see [1]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 353-358 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A stereocontrolled synthetic route to optically pure (-)-(S)-ipsenol (1), the pheromone of Pityokteines curvidens and various other bark-beetle species is described. Key step of the synthesis is an enantioselective aldol reaction using a chiral titanium-carbohydrate complex (Scheme 1). The carboxylate function of the optically pure β-hydroxy acid 5 thus obtained in mol quantities is then elaborated to the diene moiety by standard methodology (Scheme 2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730215
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  • 61
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    Synthese von 2-Oxo-2H-pyran-5-Carboxylat-Derivaten (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 411-416 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 2-Oxo-2H-pyran-5-carboxylate Derivatives3-Substituted diethyl pent-2-enedioates are easily formylated by means of ethyl formate/TiCl4/4-methylmorpholine to produce the ethoxymethylene derivatives, which are smoothly cyclized either with HCOOH or PPA to corresponding 2-oxo-2H-pyran-5-carboxylate derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730220
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  • 62
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    Potential antipsychotic agents. Part 8Part 7: [1].. Antidopaminergic properties of a potent series of 5-substituted (-)-(S)-N-[(1-ethylpyrrolidin-2-yl)methyl]-2,3-dimethoxybcnzaimides. Synthesis via common lithio intermediates (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 417-425 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of 5-substituted (-)-(S)-N-[(1-ethylpyrrolidin-2-yl)methyl]-2,3-diniethoxybenzanndes were made by reaction of the corresponding benzoyl chlorides with (S)-1-ethylpyrrolidine-2-methylaruine (→ 14-16, 18-21). The acids required were prepared in a regiospecific manner from 5-bromo-2,3-dimethoxybenzoic acid which was protected as dihydrooxazole (→ 4-8), metalated, reacted with various electrophiles (MeI, EtI, BuBr, CC13CCl3 or MeSSMe), and hydrolyzed (→9-13). Alternatively, (-)-(S)-5-bromo-N-[(1-ethylpyrrolidin-2-yl)methyl]-2,3-di-methoxybenzamide was treated with KH followed by BuLi and an electrophile (I2 or Me3SiCl) to give the 5-iodo and 5-(trimethylsilyl) derivatives 17 and 22, respectively. All 5-substituted amides were highly potent inhibitors of [3H]spiperone binding in rat striatal membranes with IC50 values of 0.5 to 5 nM (Table 3). Thus, a relatively large steric bulk can be accomodated in the position para to the 2-MeO group. This work also supports the notion that a positive as well as negative electrostatic potential can be located in this position. A selected number of derivatives were also investigated in vivo and found to inhibit apomorphine-induced behavioural responses in the same dose range as haloperidol and raclopride (Table 4). This new group of benzamides is suitable for investigations of dopamine D-2 receptors in labelled or unlabelled form.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730221
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  • 63
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    Stereoselective Coordination to Chiral Matrices. Cobalt(III). Chemistry of Simple Facially Coordinating Chiral Triamines (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 874-882 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral ligands coordinated to metal ions exert a selectivity towards the additional coordination of racemic substrates. Experimentally determined equilibria distributions of [Co(L3)2]3+ and [Co(L3)(L2)(X)]n+ are compared with calculated data based on strain-energy minimization (L3: trap = propane-1,2,3-triamine; 1,2,4-trab = butane-1,2,4-triamine; 1,2,3-trab = butane-1,2,3-triamine; 1,3,4-trpe = pentane-1,3,4-triamine; 1,3,4-tmeb = 2-methylbutane-1,3,4-triamine; 1,2,4-trpe = pentane-1,2,4-triamine; L2: en = ethane-1,2-diamine; pn = propane-1,2-diamine; X: NH3, OH2, OH-). Equilibration of Co(III) complexes was achieved by oxygenation of aqueous solutions of Co(II) salts in presence of the ligands. Quantitative isomer distribution was investigated with HPLC, and quantitative analysis of the enantiomeric excess (ee) of the racemic substrate (present in a two-fold excess) was studied, after chromatographical recovery, by 1H-NMR analysis of its Mosher-acid derivative. There is good agreement between calculated and experimental data. Systems with L = 1,2,4-trab are, as expected, relatively poorly discriminating (ee([Co(1,2,4-trab)2]3+) ∼ 5%; ee([Co(1,2,4-trab)(pn)(X)]n+) ∼ 10%). Calculations indicate that Me substitution of the ligand backbone of 1,2,4-trab (and trap) leads to an increased enantioselectivity (with practically constant isomer selectivity), and at the optimum site for substitution ∼ 90% ee is predicted.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730413
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  • 64
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    Reaction of 3-Amino-2H-azirines with 2-Amino-4,6-dinitrophenol (Picramic Acid): Synthesis of Quinazoline- and 1,3-Benzoxazole DerivativesPresented (H. H.) at the ‘International Symposium über Stickstoff-Ringe und -Ketten’, Heidelberg, March 19-21, 1990. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 959-974 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 3-(dimethylamino)-2H-azirines 1a-c and 2-amino-4,6-dinitrophenol (picramic acid, 2) in MeCN at 0° to room temperature leads to a mixture of the corresponding 1,2,3,4-tetrahydroquinazoline-2-one 5, 3-(dimethylamino)-1,2-dihydroquinazoline 6, 2-(1-aminoalkyl)-1,3-benzoxazole 7, and N-[2-(dimethylamino)phenyl]-α-aminocarboxamide 8 (Scheme 3). Under the same conditions, 3-(N-methyl-N-phenyl-amino)-2H-azirines 1d and 1e react with 2 to give exclusively the 1,3-benzoxazole derivative 7. The structure of the products has been established by X-ray crystallography. Two different reaction mechanisms for the formation of 7 are discussed in Scheme 6. Treatment of 7 with phenyl isocyanate, 4-nitrobenzoyl chloride, tosyl chloride, and HCl leads to a derivatization of the NH2-group of 7 (Scheme 4). With NaOH or NaOMe as well as with morpholine, 7 is transformed into quinazoline derivatives 5, 14, and 15, respectively, via ring expansion (Scheme 5). In case of the reaction with morpholine, a second product 16, corresponding to structure 8, is isolated. With these results, the reaction of 1 and 2 is interpreted as the primary formation of 7, which, under the reaction conditions, reacts with Me2NH to yield the secondary products 5, 6, and 8 (Scheme 7).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730423
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    Analogues of Sialic Acids as Potential Sialidase Inhibitors Synthesis of 2-C-Hydroxymethyl Derivatives of N-Acetyl-6-amino-2,6-dideoxy-neuraminic Acid (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 940-958 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intramolecular cycloaddition of the previously described azidoalkene 16, the related diacetates 7 and 13, and the monoacetate 8 led diastereoselectivity to the (2R)- and (2S)-configurated hydropyridotriazoles 17, 9 and 11, 14 and 15, and 10 and 12, respectively (Scheme 1). Thermolysis of 16 gave also the aziridine 18, its proportion increasing with reaction time. The diastereoselectivity of the cycloaddition- is rationalized on the basis of steric interactions and of H—bonds in the transition state. Photolysis in benzene partially transformed 9 into the aziridine 19. Treatment of 9 with aqueous AcOH gave 19 and the tetrahydrofuran 20, with AcOH in benzene 20 and the triacetate 23, and with aqueous H2SO4 in THF, the primary alcohol 22 (room temperature) or 19 and 22 (0°). Deacetylation of 9 followed by reaction with pyridinium hydrochloride led to the tetrahydrofuran 21 and the chloride 24 (Scheme 2). The diacetate 22 and the triacetate 23 gave the tripl 25 which was deprotected to 26. Reduction of the keto-aziridine 18 (NaBH4) gave the alcohols 27 and 29 which were acetylated to give 28 and 19, respectively (Scheme 3). Treatment of the aziridine 28 with AcOH in benzene followed by deacetylation gave 30 and hence 31. AcOH in benzene transformed the triazoline 15 first into the aziridine 32 and hence into 33, which was deprotected to give the triol 34 and hence 35. The 2-(hydroxymethyl)piperidines 26, 31, and 35 inhibited Vibrio cholerae sialidase with K1 = 3.8 · 10-2 M, 3.4 · 10-3 M, and 1.5 · 10-4 M, respectively. The conformation of the glycerol side chain of these compounds and of the unbranched piperidines 2-4 deviates from the one of Neu5Ac (and Neu2en5Ac). This finding is rationalized by an H-bond between OH—C(8) and NH—C(6). The conformations and the K1 values of 26, 31, and 35 correlate with each other.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19900730422
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    Synthesis of IH-Cyclopropal[g]quinoline via Trapping of an ortho-Quinodimethane (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1228-1232 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-Cyclopropa[g]quinoline (3-aza-lH-cyclopropa[b]naphthalene; 17) was synthesized via interception of the heterocyclic ortho -quinodimethane 15 with l-bromo-2-chlorocyclopropene, followed by aromatization of the adduct 16 with t-BuOK.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730512
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    Isolation and Characterization of s̰-Adducts upon Attempted Vicarious Nucleophilic Substitution with Cationic Arene-Iron Complexes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1242-1249 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the carbanions derived from chloromethyl phenyl sulfone or 1 -chloroethyl phenyl sulfone with the cationic [Fe(arene)Cp] complexes 8 or 9 produced isolable c-adducts 10-12. Attempted base induced elimination of the s̰-adducts, which would have led to products of vicarious nucleophilic substitution (VNS reaction), failed. Similarly, no VNS products were obtained, when the (arene)tricarbonylchromium complexes 4 were reacted with the anion of chloromethyl phenyl sulfone.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730514
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    A New Convergent Synthesis of Thiamine HydrochlorideDedicated to Dr. Otto Isler on the occasion of his 80th birthday (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1300-1305 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thiamine hydrochloride (1a; 3-[(4-amino-2-methylpyrimidin-5-yl)methyl]-5-(2-hydroxyethyl)-4-methylthia-zolium chloride hydrochloride; vitamin B1) has been synthesized in excellent yield by condensation of 3-mercapto-4-oxopentyl acetate (5a) with 3, 4-dihydro-7-methylpyrimido[4, 5-d]pyrimidine (4) in formic acid. The two intermediates 5a and 4 are prepared from 3-chloro-4-oxopentyl acetate (3) and 4-amino-2-methyl-5-(aminomethyl)-pyrimidine (Grewe diamine; 2a), respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730518
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    Ringerweiterungen und Ringverengungen bei der Umsetzung von 1, 3-Oxazolidin-2, 4-dionen und 1, 3-Thiazoiidin-2, 4-dion mit 3-Amino-2H-azirinen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1314-1328 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ring Enlargements and Ring Contractions in the Reaction of 1, 3-Oxazolidine-2, 4-diones and l, 3-Thiazolidine-2, 4-dione with 3-Amino-2H-azirinesThe reaction of 3-amino-2H-azirines 1 and 1, 3-oxazolidine-2, 4-diones 2 in MeCN at room temperature leads to 3, 4-dihydro-3-(2-hydroxyacetyl)-2H-imidazol-2-ones 3 in good yield (Scheme 2, Table 1). A reaction mechanism proceeding via ring enlargement of the bicyclic zwitterion A to give B, followed by transannular ring contraction to C, is proposed for the formation of 3. This mechanism is in accordance with the result of the reaction of 2a and the 15N-labelled 1a*: in the isolated product 3a*, only N(3) is labelled (Scheme 1). The analogous reaction of 1 and 1, 3-thiazolidine-2, 4-dione (5) is more complex (Schemes 4 and 5, Table 2). Besides the expected 3, 4-dihydro-3-(2-mercaptoacetyl)-2H-imidazol-2-ones 7, 5-amino-3, 4-dihydro-2H-imidazol-2-ones of type 8 and/or N-(1, 4-thiazin-2-ylidene)ureas 9 are formed. In the case of 2-(dimethylamino)-1-azaspiro[2. 3]hex-1-ene (1d), the postulated eight-membered intermediate 6d could be isolated. Its structure as well as that of 9f has been determined by X-ray structure analysis. A reaction mechanism for the formation of the 1, 4-thiazine derivatives of type 9 is proposed in Scheme 6.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19900730520
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    Synthesis of Potential Glucosidase-Inhibitors: D-Xylopyranoside-5-spiro-l′-cyclopropanesTaken in part from the thesis of L.P.M. [1] (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1329-1337 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the D-xylopyranose-5-spiro-1′-cyclopropane 5, its methyl α-D-glycoside 7 and its benzyl β-D-glycoside 13 from D-glucose is described, and their conformation in solution is discussed. A Königs-Knorr glycosidation of 10 reveals the ionic intermediate of a 1, 1-(dibromocyclopropyl)carboxonium ion type to be stable against opening of the cyclopropane ring. Very weak inhibition of saccharase was observed for the α-D-configurated methyl glycoside 7, whereas the β-D-configurated benzyl glycoside 13 did not inhibit emulsin.
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    Chemie von α-Aminonitrilen.2. Mitteilung über die Chemie von α-Aminonitrilen. 1. Mitteilung:[1]. Aziridin-2-carbonitril photochemische Bildung aus 2-AminopropennitrilOtto Isler gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1373-1390 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 2-Aminopropenenitrile in solvents such as MeCN, MeOH, or H2O is photoisomerized by UV light to racemic aziridine-2-carbonitrile (rac-2); the larger part of the starting material, however, fragments to HCN and MeCN. The observed photocyclization constitutes a structural connection within an ensemble of C3H4N2 compounds considered to be potentially relevant to prebiotic chemistry.
    Notes: No Abstract.The English Footnotes (*) referring to Schemes 1-6 are intended to provide an extension of this summary. In the Footnote (*) to Scheme 5, a definition of the term ‘chirogenic reaction step’ is given.
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  • 72
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    Elektrophile Substitutionsreaktionen des 1,1-Difluoro-1H-cyclopropabenzolsHerrn Prof. Dr. Dr. h. c. mult. Rolf Huisgen zum 70. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1497-1503 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrophilic Substitution Reactions of 1,1-;Difluoro-1H-cyclopropabenzene1,1-Difluoro-1H-cyclopropabenzene (1) can be deprotonated with strong bases at C(2). The resulting 1,1-di-fluoro-2-lithio-1H-cyclopropabenzene (2) reacts with electrophiles to form C(2)-substituted derivatives of 1. The Diels-Alder reactions with electron-poor dienes, characteristic for 1H-cyclopropabenzene, do not occur with the 1,1-difluoro analogue 1.
    Additional Material: 1 Tab.
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  • 73
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    Eine Synthese methylierter Epoxyhydroazulenone durch intramolekulare [4 + 3]-Cycloaddition einer aus 1,1-Dichloro-6-(3-methylfur-2-yl)hexan-2-on erzeugten Oxyallyl-ZwischenstufeAus der Dissertation von R. K[1].Diese Arbeit Wurde erstmals auf dem ‘6th European Symposium on Organic Chemistry, ESOC 6’, vom 10-15.9.1989 in Belgrad, Jugoslawien, vorgestellt; Book of Abstracts A-O 022, S,40. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1504-1514 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthesis of Methylated Epoxyhydroazulenones by Intramolecular [4 + 3] Cycloaddition of an Oxyallyl Intermediate, Generated from 1,1-Dichloro-6-(3-methyl-2-furyl)hexan-2-one(Z)-3-Methylpent-2-en-4-yn-1-ol (7) was transformed to 2-(4-chlorobutyl)-3-methylfuran (4b) and 2-(but-3-enyl)-3-methylfuran (10a) by C-alkylation and 5-exo-dig cyclization. The Grignard derivative formed from 4b gave 1,1-dichloro-6-(3-methylfur-2-yl)hexan-2-onc (1b) on reaction with dichloroacetyl chloride. This dichloromethyl ketone undergoes a base-induced cyclization to form diastereoisomeric 7-chloro-1,2,3,6,7,8a-hexahydro-4-methyl-8H-3a,6-epoxyazulen-8-ones (3bα and 3bβ) by way of an intramolecular [4+3] cycloaddition of an oxyallyl intermediate 2b. By dechlorination and hydrogenation of 3bβ, the tricyclic hydroepoxyazulenones 18 and 19 have been synthesized.
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  • 74
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    Rogiolol Acetate: A Novel β-Chamigrene-Type Sesquiterpene Isolated from a Marine SpongeWe use the chamigrene numbering for the structural formulae and spectroscopic data; IUPAC nomenclature and numbering are used for retrieval purposes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1612-1620 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The marine sponge Spongia zimocca SCHMIDT, 1862, collected in front of the torrent II Rogiolo, south of Livorno, contains the sesquiterpene rogiolol acetate (= (+)-(2R,3S,6R,8R,9R)-2,8-dibromo-9-chloro-1,1,9-trimethyl-5-methylidenespiro[5.5]undec-3-yl acetate; (+)-3a), which represents the first chamigrane isolated from a sponge. Although compounds of this class are common in red seaweeds of the genus Laurencia, and our sponge actually contains 9-bromochamigrene and a variety of other metabolites of nearby growing Laurencia sp., (+)-3a is unique to our sponge.
    Additional Material: 1 Ill.
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  • 75
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    Stereochemistry of the Robinson Anellation: Studies on the Mode of Formation of the Intermediate Hydroxy Ketones (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1621-1636 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical outcome of the base-catalyzed cyclization of diketones 5-8 has been investigated under protic conditions (Scheme 3). The more stable trans-fused ketols are preferentially formed in kinetically controlled aldol reactions, when the incipient angular substituent R = H (6 → 10a) or CN (7 → 11a, 8a → 12a). For R = Me (as in 5), axial attack of the side-chain enolate double bond on the ring C≡O group results in the rather selective formation of cis-9b. It is assumed that these cyclizations are controlled by relative product stabilities (product-like transition state) and steric effects. The competition between fused (e.g. 9) and bridged ketol (e.g. 13) formation in these cyclizations is discussed. The cis-fused (‘steroid’) ketols were readily equilibrated with their trans-counterparts (9b ⇄ 9a, 10b ⇄ 10a, 11b ⇄ 11a) under aprotic conditions (5 mol-% of LDA, THF, 0°), thus, allowing assessments of relative stabilities.
    Additional Material: 6 Tab.
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  • 76
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    The Reaction of Singlet Oxygen with Adamantylideneadamantane Mediated by Rose Bengal (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1653-1658 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photo-oxygenation of adamantylideneadamantane (1) on siliceous supports using admixed granules of ion-exchange resin fixed to methylene blue (MB) and rose bengal (RB) gave exclusively the corresponding dioxetane derivative 2 for the former sensitizer, while the latter gave 2 and traces of the epoxide 3. RB and the charge-transfer complex produced from N-ethylcarbazole and 2,4,5,6-tetranitrofluoren-9-one both reacted with chemically generated singlet oxygen to give superoxide radical anion. Trapping of the latter with 5,5-dimethyl-1-pyrroline 1-oxide gave an adduct exhibiting a characteristic ESR spectrum. The treatment of 1 in MeOH with 30% aqueous H2O2 for 22 h at 60° gave 3 in 100% yield. Repetition of this experiment in the presence of 2,6-di(tert-butyl)-p-cresol caused no significant change. These results indicate that singlet oxygen reacts with 1, in the presence of RB, by two different processes. The first leads to dioxetane formation. The second process involves conversion of singlet oxygen by RB to superoxide radical anion which subsequently gives H2O2 so producing epoxide 3 from 1.
    Additional Material: 1 Ill.
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  • 77
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    Synthesis and Properties of a New Dihydroflavin: Reduction of a Flavinium Salt by BorocyanohydridePreliminary results were reported at the ‘Fifth International Symposium on Flavins and Flavoproteins’; San Francisco, March 31-April 3 1975. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1669-1678 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of 6 by borocyanohydride yielded the new dihydroflavin 7. The intermediate product 8 could only be observed in solution by 1H-NMR. The chemical and physical properties of 7 are reported. UV/VIS, 1H- and 13C-NMR, and luminescence techniques were used.
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  • 78
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    The Photoreversible Addition of Sulfur Dioxide to Benzobenzvalene: A new Approach to the Benzoprefulvene Biradical (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1724-1729 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Benzobenzvalene (naphthvalene; 1) is shown to add SO2 to a lateral bicyclobutane bond with formation of a sulfone 2 and a ‘γ-sultine’ 3. The structure of the latter is unambiguously established by X-ray diffraction. Both adducts extrude SO2 upon direct photolysis at 254 nm and regenerate 1 accompanied by naphthalene in a 1:3 ratio. This result is interpreted in terms of a reversible homolytic cleavage leading, for both, 2 and 3, to the same sulfinyloxy biradical 5, which by loss of SO2 gives the benzoprefulvene biradical 6. The latter in its singlet state undergoes ring closure to 1, or it opens to give naphthalene.
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  • 79
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    Glycosylidene Carbenes. Part 2. Synthesis of O-Aryl Glycosides (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1764-1778 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenol, 4-methoxyphenol, 4-nitrophenol, methyl orsellinate (1), and 2,6-di(tert-butyl)-4-methylphenol (BHT; 2) have been glycosylated by thermal reaction (20-60°) with various glycosylidene-derived diazirines.4-Methoxyphenol reacted with the D-glucosylidene-derived diazirine 3 to give O-glucosides (4 and 5, 69%, 3:1) and C-glucosides (6 and 7, 16%, 1:1). Similarly, phenol yielded O-glucosides (10 and 11, 70%, 4:1) and C-glucosides (12 and 13, 13%, 1:1). 4-Nitrophenol gave only O-glycosides, 3 leading to 14 and 15 (75%, 3:2; Scheme 1), and the D-galactosylidene-derived diazirine 17 to 22 and 23 (52% (from 16), 65:35; Scheme 2). The reaction of phenol with 17 yielded 58% (from 16) of the O-galactosides 18 and 19 (4:1) and 14% of the C-galactosides 20 and 21 (1:1). From the D-mannosylidene-derived diazirine 25, we predominantly obtained the α-D-configurated 26 (38 % from 24). These results are interpreted by assuming that an intermediate (presumably a glycosylidene carbene) first deprotonates the phenol to generate an ion pair which combines to give O- and - with electron-rich phenolates - also C-glycosides. A competition experiment of 3 with 4-nitro- and 4-methoxyphenol gave the products from the former (14 and 15) and the latter phenol (4-7) in almost equal amounts. Differences in the kinetic acidity of OH groups, however, may form the basis of a regioselective glycosidation, as evidenced by the reaction of 3 with methyl orsellinate (1) yielding exclusively the 4-O-monoglycosylated products 27 and 28 (78%, 85:15), although diglycosidation is possible (27→ 31 and 32; 67%, 4:3; Scheme 3). Steric hindrance does not affect this type of glycosidation; 3 reacted with the hindered BHT (2) to afford 33 and 34 (81 %, 4:1). The predominant formation of 1,2-trans -configurated O-aryl glycosides is rationalized by a neighbouring-group participation of the 2-benzyloxy group.
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  • 80
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    Anion Selectivity of Tetravalent Tin Compounds in Membranes Studied by 119Sn-, 13C- and 1H-NMR (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1894-1904 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fundamental molecular aspects of trialkyltin compounds of the type R3SnY have been investigated in view of their applicability as ion-selective components in solvent polymeric membranes. The interaction between these compounds and anions has been studied using 119Sn- and 13C-NMR. Neutral tetracoordinated trialkyltin compounds form a negatively charged pentacoordinated complex upon interaction with Cl-ions in homogeneous organic phases as well as in membranes in contact with aqueous solutions. Although in a homogeneous phase, the electronegative substituent Y determines the complex-formation constant, it has no influence on the potentiometric anion selectivity in liquid membranes containing trialkyltin carriers R3SnY with different Y. The observed selectivity pattern is not given by the magnitude of the stability constants in a homogeneous phase but is dictated by the prevailing association-dissociation process leading to tetracoordinated compounds which change in constitution due to varying sample composition, The results obtained from equilibrium studies of tetravalent mono tin compounds with anions in both homogeneous phase and in two-phase systems confirm the earlier hypothesis that trialkyltin compounds incorporated in solvent polymeric membranes act as electrically neutral carriers for anions.
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  • 81
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    Stereoelectronic Aspects of the Anomeric Effect in Fluoromethylamine (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1805-1817 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-level ab initio calculations have been made for fluoromethylamine to study structural and energetic effects of the relative orientation of the N lone pair to the C—F bond. The anti-conformer (N lone pair anti-planar to the C—F bond) corresponds to the global energy minimum. It has the longest C—F distance, the shortest C—N distance, and is 7.5 kcal·mol-1 more stable than the related perpendicular conformation (lone pair perpendicular to the C—F bond). The syn-conformation also shows hallmarks of the anomeric effect: long C—F bond, short C—N bond, and energetic stability when allowance is made for the two pairs of eclipsed hydrogens. The transition state for N inversion is close to the syn-structure; rotation about the C—N bond is strongly coupled with this inversion process. Small bond distance changes of ca. 0.02 Å between parallel and perpendicular conformations are associated with dissociation energy differences of ca. 30 kcal·mol-1. Various criteria for assessing the strength of the anomeric effect are discussed.
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  • 82
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    Enzyme-Mediated Regioselective Acylations of Flavonoid Disaccharide Monoglycosides (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1837-1844 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Flavonoid disaccharide monoglycosides have been acylated by the catalytic action of the protease subtilisin in anhydrous pyridine. The effects of the nature of the sugars and of the interglycosidic bonds on the regioselectivity of the reactions have been analyzed. The selectivity was excellent with rutin (1), hesperidin (2), naringin (6), and quercetin 3-O-[O-(β-D-glucopyranosyl)-(1→4)-α-L-rhamnoside] (9), giving single monoesters on their glucose moieties (see la, 2a, 6a, and 9b, resp.); quite interestingly, in the last compound, acylation did not occur at the free primary OH group but at the secondary OH—C(3‴). On the other hand, a mixture of mono- and diesters was obtained with the flavonoid peltatoside (7).
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    The chemistry of coumarin derivatives, part 2.Part 1, see [1a] Reaction of 4-hydroxycoumarin with α,β-unsaturated aldehydes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1865-1878 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Hydroxycoumarin (= 4-hydroxy-2H-1-benzopyran-2-one) reacts with enals to give 1,2- or 1,4-addition products, depending on the nature and relative location of the substituents on the olefinic double bond (Scheme 2). The resulting adducts further react intra- or intermolecularly, affording dimeric coumarins or pyranocoumarins in the case of 1,2-addition and acetalic pyranocoumarins in the case of 1,4-addition. With enals bearing alkyl groups at C(β), 2H-pyrano[3,2-c]coumarins are the only products formed, and the reaction represents an easy and straightforward entry into this class of recently described biologically active natural products.
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    Synthesis and Configuration of Some Hydroxymilbemycin Derivatives Including 22,23-Dihydroavermectin B1b AglyconeDedicated to Prof. Oskar Jeger (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1905-1917 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of several configurationally defined hydroxymilbemycin derivatives is described. One of these allylic alcohols is the known 5-O-[(tert-butyl)dimethylsilyl]-13α-hydroxymilbemycin D (= 5-O-[(tert-butyl)-dimethylsilyl]-22,23-dihydroavermectin B1b, aglycone; 15D), the synthesis of which represents LI conversion of the milbemycin to the avermectin series of natural products. The configurations at C(13), C(14), and C(15) of the new milbemycin derivatives were determined by NMR experiments and force-field calculations.
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    Configuration-Odor Relationships in 5β-Ambrox (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1935-1947 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The four possible A/B cis-fused diastereoisomers of Ambrox® have been synthesized and their configurations and conformations established by X-ray and NMR analysis. Only 5β-ambrox (= 1,2,3a,4,5,5β,6,7,8,9,9a,9bα-dodecahydro-3aβ,6,6,9aβ-tetramethylnaphtho[2,1-b]furan; 5) has an odor quality comparable to Ambrox®. The 1,3-synperiplanar/diaxial conformation of the substituents at C(8) ( = C(3a)) and C(10) (= C(9a)) has thus been confirmed to be a compulsory structure element for the particular odor.
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    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2070-2070 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730727
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    Metal Complexes with Macrocyclic Ligands. Part XXXIPart XXX: see [1].. Protonation studies and complexation properties of tetraazamacrocyclic methylenephosphonates with earth-alkali ions (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 140-148 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The three ligands 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonic acid) (1), 1,4,7,11-tetraazacyclotridecane-1,4,7,11-tetrakis(methylenephosphonic acid) (2), and 1,4,8,11-tetraazacyclotetradecane-1,4,8,1 1-tetrakis(methylenephosphonic acid) (3) have been synthesized by condensation of the corresponding macrocycles with formaldehyde and phosphorous acid. The protonation and stability constants with the earth-alkali ions have been determined at 25° and I = 0.1 M (Me4)N(NO3) by potentiometric titrations. Because of the high values of the first two protonation constants, 1H-NMR measurements were necessary to determine them. Titrations in different supporting electrolytes (NaNO3, KNO3, RbNO3, CsNO3, and Me4N(NO3)) show that their choice is of paramount importance, as the above ligands can form complexes with alkali-metal ions. The potentiometric results for the earth-alkali ions show that beside mononuclear complexes of different degrees of protonation ([MLHn], n = 0-4), also binuclear species are formed ([M2LHm], m = 0-2). It is interesting that 1 with the smallest macrocyclic ring has the greatest tendency to form binuclear complexes, which are so stable that they partially prevent the formation of the corresponding mononuclear species. For [ML], [MLH], [M2L], and [M2LH], the stability sequence is Mg2+ 〈 Ca2+ 〉 Sr2+ 〉 Ba2+, whereas for [MLH2], [MLH3], and [MLH4], the stability steadily decreases from Mg2+ to Ba2+.
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    URL: http://dx.doi.org/10.1002/hlca.19900730115
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    Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IIIPart I and II: see[8]. Crystallographic and dynamic evidence for the intermediate of the ‘merry-go-round’ process in nonacarbonyl-μ3-(1,3,5-trithiane)-tetrairidium (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 154-160 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title complex crystallises in two C3v, isomeric forms differing in carbonyl-ligand arrangement. In solution, the isomer 1b with three edge-bridging carbonyls on a common face of the metal tetrahedron converts via an endothermic equilibrium into the isomer 1u with no bridging carbonyls. The latter was shown by 13C-NMR to be the intermediate of the ‘merry-go-round’ process which exchanges the sites of the basal CO's.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730117
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  • 89
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    Total Syntheses of (-)-Conduritol B ((-)-1L-Cyclohex-5-ene-1,3/2,4-tetrol) and of (+)-Conduritol F((+)-1D-Cyclohex-5-ene-1,2,4/3-tetrol). Determination of the Absolute Configuration of (+)-LeucanthemitoEnantiomerically pure 7-oxabicyclo [2.2.1]hept-5-en-2-yl derivatives (‘naked sugars’[1]) as synthetic intermediates, Part XI. Part X, see[2];Part IX, see[3]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 161-168 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ‘naked sugar’ (+)-(1R,2R4R)-2-endo-cyano-7-oxabicyclo[2.2.1]hept-5-sn-2-exo-yl acetate ((+)-4) was converted (7 steps, 45% overall) with high stereoselectivity into (-)-(4R,5S,6R)-4,5,6-tris{[(tert-butyl)dimethylsilyl]oxy}cyclohex-2-en-1-one ((-)-11). Reduction of (-)-1 with NaBH4- CeCl3 · 7 H2O, followed by deprotection of the silyl ether moieties gave (+)-conduritol F ((+)-1; 47%) whose characteristics were identical to those of natural (+)-leucanthemitol. Reduction of (-)-11 with DIBAH, followed by deprotection of the silyl ether moiety led to (-)-conduritol B ((-)-3; 51 %).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730118
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  • 90
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    A Novel Nitrone Cycloaddition/Rearrangement (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 169-173 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Adamantanone-derived nitrone 4 and some other keto-nitrones, when reacted with aromatic and aliphatic aldehydes in refluxing toluene or tetrahydrofuran, formed the corresponding aldonitrones (Z)-10, the latter arising from the fragmentation of an initially formed 1,4,2-dioxazolidine 6 to adamantan-2-one and an oxaziridine intermediate 11, which then rearranges to (Z)-10.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730119
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  • 91
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    Synthesis of Derivatives of (1R*,10aR*)-1-Azido-10-benzylidene-4-(diethylphosphono)-1,2,10,10a-tetrahydro-2-oxo-4H-azeto[1,2-a]pyrido[1,2-d]pyrazin-9-ylium Bromide (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 180-184 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of some derivatives of the title compound VI is described. Bromination of diethyl (cis-3-azido-2-oxo-4-styrylazetidin-1-yl)(pyridin-2-yl)methylphosphonate (6) in MeOH gave tricyclic β-lactam 7, while similar bromination of diethyl (cis-3-azido-2-oxo-4-vinylazetidin-1-yl)(pyridin-2-yl)methylphosphonate (9) afforded tri-cyclic β-lactam 10. Mechanisms for these transformations are proposed (Schemes 1 and 2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730121
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  • 92
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    Synthesis and Complexation of 1,2-Bis[(monoaza[15]crown-5)-N-yl]glyoxime. Crystal Structure of (1,2-Bis[(monoaza[15]crown-5)-N-yl]glyoximato)palladium(II) (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 174-179 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new vicinal dioxime ligand with two crown-ether groups, 1,2-bis[(monoaza[15]crown-5)-N-Yl]-glyoxime(LH2), has been prepared from cyanogen di-N-oxide and monoaza[15]crown-5. Ni(II), Pd(II), and Pt(IV) complexes of LH2 with or without alkali-metal ions bound to macrocyclic groups have been isolated. The high affinity of [Pd(LH)2] and [Ni(LH)2] for the K+ ion is observed in solvent extraction experiments. A single-crystal X-ray structure confirms the postulated geometry of [Pd(LH)2]- The Pd-atom of the centro-symmetric molecule has square-planar PdN4 coordination where Pd-N distances range from 1.978(3) to 1.970(3) Å. The N-Pd-N intraligand angle is 79.9(1)°.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730120
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  • 93
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    Synthesis, Reactivity Studies, and X-ray Crystal Structure of (11R)-25-O-Deacetyl-11-deoxo-11-hydroxy-21,23-O-isopropylidenerifamycin S (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 185-198 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protected intermediate (11R)-25-O-deacetyl-11-deoxo-11-hydroxy-21,23-O-isopropylidenerifamycin S (7) has been synthesized starting from rifamicin S (2; Scheme 2), the former being a potential substrate for the preparation of new types of rifamicin-S derivatives modified at C(11) and/or C(25). The reactivity of 7 toward acylations has been studied under both base- and acid-catalyzed conditions. The compound either did not react or nr underwent unexpected reactions, and no acylation products could be isolated. The X-ray crystal structure of 7 reveals that both OH groups at C(11) and C(25) are hindered, and this is probably the reason, why other take place faster than acylation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730122
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  • 94
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    A Variable-Pressure 2D 1H-NMR Study of the Mechanism of Trimethyl Phosphate Intermolecular Exchange and cis/trains-Isomerisation of Tetrachlorobis(trimethyl phosphate)zirconium(IV)Part 45 of the series ‘High-Pressure NMR Kinetics’; for part 44, see[1]. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 199-202 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In chloroform, [ZrCl4·2(MeO)3PO] exists in both cis- and trans-isomeric forms. Three reactions can be envisaged in the presence of excess (MeO)3PO = L: (1) cis-[ZrCl4·2L] + *L⇆cis-[ZrCl4·L*L]+ L; (2) trans-[ZrCl4·2L] + *L ⇆ trans-[ZrCl4·L*L] + L; (3) cis-[ZrCl4·2L]⇆ trans-[ZrCl4·2L]. To distinguish between these possible reaction pathways, we have used 2D 1H-NMR spectroscopy. For the first time, variable-pressure 2D exchange spectra were used for mechanistic assignments. cis/trans-Isomerisation was found to be the fastest reaction (in CHCl3/CDCl3), with a small acceleration at higher pressure: it is concluded to be an intramolecular process with a slightly contracted six-coordinate transition state. The intermolecular (MeO)3PO exchange on the cis- and trans-isomer are second-order processes and are strongly accelerated by increased pressure: Ia mechanisms are suggested without ruling out limiting A mechanisms.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730123
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  • 95
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    Catalysis of Ion Transfer by Tetraphenylborates in Neutral Carrier-Based Ion-Selective Electrodes (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 203-212 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For certain ionophores of extremely high lipophilicity, kinetic limitations of the carrier-induced ion transfer between aqueous and membrane phase may heavily disturb the electromotive behaviour of the ion-selective membrane electrode. These limitations may be overcome by adding tetraphenylborates to the membrane phase. Membranes prepared with different 3,6-dioxaoctanediamide homologues and potassium tetrakis(P-chlorophenyl)borate as phase-transfer catalyst all exhibit the same ion selectivity as well as theoretical electrode response. This behaviour is corroborated by a theoretical description of the ion-transfer process.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730124
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  • 96
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    Blockcopolymers in microemulsions differential heats of solution and shift of the percolation temperature in W/O microemulsions (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 213-220 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solutions of blockcopolymers (POE-b-PI-b-POE) in fluids of interacting aqueous nanodroplets (W/O microemulsions) are studied. The interaction strength between the (pseudo) two components is measured by the shift of the percolation temperature relative to that of the pure microemulsion. A quantitative measure of the interaction, the differential heat of solution, is thermodynamically related to the slopes of the equilibrium temperature of the system with varying monomeric nanodroplet concentration and the experimental percolation line in the presence of copolymer.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730125
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  • 97
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    Mitteilungen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 229-232 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730127
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  • 98
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    Synthese cyclischer Depsipeptide durch direkte Amid-Cyclisierung: 12gliedrige Depsipeptide mit alternierender Sequenz von α-Hydroxy- und α-Aminosäuren (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 221-228 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Cyclic Depsipeptides via Direct Amide Cyclization: Cyclic Depsipeptides with 12-Ring Atoms and Alternating Sequence of α-Hydroxy and α-Amino AddsThe reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine (1; R1 = R2 = R3 = R4 = Me) with α-hydroxy-carboxylic acids, followed by selective hydrolysis of the terminal dimethylamide group yields the dipeptide analogues 15a and 18b (Schemes 3 and 4). After protection of the OH group (→ 16a and 19, resp.), coupling with the C-terminus-protected derivatives 14 and 18a, respectively, by a modified 1,1′-carbonyldiimidazole procedure followed by hydrolysis gives the linear depsipeptides 17c and 20, respectively. Treatment with HCl gas in toluene at 100° leads to the cyclic depsipeptides 21 and 22 in very good yield. The two model reactions show that the ‘azirine/oxazolone-method’, combined with the ‘direct amide cyclization’, is a versatile procedure for the synthesis of cyclic depsipeptides containing α,α-disubstituted α-amino acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730126
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  • 99
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    Masthead (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730201
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  • 100
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    A Study on the Odour/Structure Relationship of Patchoulol and NorpatchoulenolPresented in part at the ‘11th Congress of Essential Oils, Fragrances and Flavours’, New Delhi, 12-16th November, 1989. (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1730-1733 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In continuation of studying structure/activity relationships of odorous compounds, the influence of the bridgehead-bonded Me group of (+)-norpatchoulenol (1) and (-)-patchoulol (2) and the olfactory properties of the corresponding unsaturated and saturated derivatives (±)-3, (±)-4 and (±)-5, (±)-6, respectively, are studied. The key odour descriptors-wood, earth, and camphor-are used for classification.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730618
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