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41.
Hans-Dietrich Stachel K. Klaus Harigel Hermann Poschenrieder Hans Burghard 《Journal of heterocyclic chemistry》1980,17(6):1195-1199
Alkyl cyanoacetate, malonate, acetoacetate and methylsulfonyl acetic acid ethyl ester are acylated by alkylidenazlactones. The acyl compounds easily form alkylideneteramic acids by condensations. The acylcyanoacetates 2 isomerize into aminopyrrolinones 3 via acid catalysis. 相似文献
42.
Klaus Burger Elisabeth Windeisen Elisabeth Heistracher Torsten Lange Abdel-Aleem H. Abdel-Aleem 《Monatshefte für Chemie / Chemical Monthly》2002,2(3):41-58
The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building
blocks for peptide and depsipeptide modification. 相似文献
43.
Photo-extrusion of nitrogen from the azoalkane 1 in the presence of molecular oxygen gave besides the hydrocarbons 3 and 5, the endoperoxide 10 and hydroperoxide 11, the former via trapping of the 1,4-diradical 4 by triplet oxygen, the latter by ene-reaction-6f hydrocarbon 5 with singlet oxygen. 相似文献
44.
Klaus Helfrich 《Theoretical chemistry accounts》1971,21(4):381-397
If χ i (χ k ) is an exact generalized diatomic orbital (solution of Eq. (1) of text), a sequence of functions χ i (N) converging to χ i may be constructed so that matrix elements of frequently occurring operators between χ i (N) and χ k (N) may be computed without any numerical integration. Exact expectation values are given for kinetic and potential energy, dipole moment, θ 2=x 2+y 2, and quadrupole moment 3z 2?r 2, for various ratios of nuclear charges Z 1,Z 2 and for several distances R. Special subjects discussed in terms of computed expectation values are:
- R-dependence of the contributions to total energy of HeH2+ in state 2pσ and of LiH3+ in state 3dσ
- RZ-and λ-dependence of dipole and quadrupole moment functions in state 1sσ
- Some properties of those generalized diatomic orbitals which approach, for R going to 0, Slater-type atomic functions.
45.
Boström J Böhm M Gundertofte K Klebe G 《Journal of chemical information and computer sciences》2003,43(3):1020-1027
The molecular alignments obtained from a previously reported pharmacophore model have been employed in a three-dimensional quantitative structure-activity relationship (3D QSAR) study, to obtain a more detailed insight into the structure-activity relationships for D(2) and D(4) receptor antagonists. The frequently applied CoMFA method and the related CoMSIA method were used. Statistically significant models have been derived with these two methods, based on a set of 32 structurally diverse D(2) and D(4) receptor antagonists. The CoMSIA and the CoMFA methods produced equally good models expressed in terms of q(2) values. The predictive power of the derived models were demonstrated to be high. Graphical interpretation of the results, provided by the CoMSIA method, brings to light important structural features of the compounds related to either low- or high-affinity D(2) or D(4) antagonism. The results of the 3D QSAR studies indicate that bulky N-substituents decrease D(2) binding, whereas D(4) binding is enhanced. Electrostatically favorable and unfavorable regions exclusive to D(2) receptor binding were identified. Likewise, certain hydrogen-bond acceptors can be used to lower D(2) affinity. These observations may be exploited for the design of novel dopamine D(4) selective antagonists. 相似文献
46.
Abstract— When log phase cells of wild-type E. coli K-12 were maintained in growth medium after X irradiation, they became progressively more resistant to a subsequent exposure to UV or X radiation. The time to achieve maximum resistance was about 60 min. The uvrB, uvrD, polA and certain exrA strains (W3110 background) also demonstrated this X ray-induced resistance to subsequent UV or X irradiation but recA, recB, lex (AB1157 or W3110 backgrounds) and other exrA strains (AB1157 background) did not. The resistance induced in wild-type, uvrB and uvrD cells was characterized by the production or enhancement of a shoulder on the survival curves obtained for the second irradiation, while the resistance induced in the W3110 exrA strains was expressed only as a change in slope. The induction of resistance in the W3110 exrA strain was not inhibited by the presence of chloramphenicol, but that in the wild-type cells appeared to be. The production or enhancement of a shoulder on the survival curves of the rec + lex + exr + cells is consistent with the concept of the radiation induction of repair enzymes. Alternative explanations, however, are discussed. 相似文献
47.
Klaus Ziegler 《Zeitschrift für Physik B Condensed Matter》1981,43(3):275-280
A chain of interacting vectors (, ) withn components subject to the hyperbolic conditions 2–2=1 is considered. The interaction possesses a global non-compactO(1, n–1)/O(1)×O(n–1) symmetry. Symmetries of this kind are known from the study of disordered electronic systems. The non-compactness of the symmetry group causes divergencies such that a symmetry breaking term is necessary. Asymptotic behaviour of the expectation values and long-ranged correlation functions are calculated for a small symmetry breaking field.Supported in part by the Deutsche Forschungsgemeinschaft through the Sonderforschungsbereich 123 at the University of Heidelberg 相似文献
48.
Klaus Thews 《manuscripta mathematica》1981,33(3-4):327-338
We are discussing existence and multiplicity of T-periodic solutions of the time dependent Hamiltonian system
= U(x, t) under the assumption that U(x, t) approaches 0 for large |x| meaning that the force U is concentrated in a finite region. Our method is variational and it is shown how the difficulties with the Palais-Smale condition can be overcome in this case. 相似文献
49.
One considers m-dimensional Riemannian manifoldsM with tangent spaces Tp(M), p M that are a direct sum of a spacelike m-2 planeR
p and a 2-planeH
p. It is supposed that onM there exists a connection whose space-like components are parallel conformal flat (pkf). These components are generated by a vector field X. Assuming that X belongs to a pair X,Y of reciprocal quasi-cocircular vector fields and that the Pfaffian of this pair is the 1-form associated with the connection, the following results are derived: 1. X and Y are of equal constant length (This is true for all Riemannian manifolds). 2. The immersion of the integral manifold ofH
p intoM is cylindrical and the normal connection is flat. 3. The immersion of any space-like submanifold intoM is cylindrical with respect to the sections inH
p and umbilical with respect to all spacelike sections. 4. If m 4, the integral manifoldP
p is flat.
Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca 相似文献
Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca 相似文献
50.
Klaus Potthoff 《Archive for Mathematical Logic》1977,18(1):67-71
We prove a tree lemma on perfect trees to obtain an ultrafilter of definable subsets of , which is Ramsey but not conservative (see [Phi 2]). 相似文献