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51.
Muller T Hulliger J Seichter W Weber E Weber T Wubbenhorst M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(1):54-61
A new type of dumb-bell-shaped host molecule (6-8) has been synthesised, of which 1,8-bis((1)-adamantyl)-1,3,5,7-octatetrayne (8 = BAOT) forms an open porous architecture when cocrystallised with a number of typical solvent molecules. Adamantyl substituents attached to a tetraalkyne spacer build up the walls of parallel channels wherein guest molecules are aligned. Surprisingly, the tetraalkyne unit is significantly bent. Desolvation experiments provide evidence for a reversible inclusion of guests. In the case of the inclusion of 2-butanone, a partial substitution by symmetrical and asymmetrical long-chain chromophores during crystallisation was possible. Stained crystals showed optical frequency doubling. The crystal structure analysis revealed a centric space group, although considerable translational and orientational disorder was present. Application of scanning pyroelectric microscopy revealed that the growth of inclusion compounds with 2-butanone produced polar ordering of guest molecules, which were aligned in two macro-domains of opposing polarity. The resulting orientation of the carbonyl dipoles is in agreement with the theoretical prediction of a Markov model of spontaneous polarity formation based on molecular recognition processes on growing crystal faces. The present case represents a new example of a property-driven supramolecular synthesis. 相似文献
52.
The study of reductive group actions on a normal surface singularityX is facilitated by the fact that the group Aut X of automorphismsof X has a maximal reductive algebraic subgroup G which containsevery reductive algebraic subgroup of Aut X up to conjugation.If X is not weighted homogeneous then this maximal group G isfinite (Scheja, Wiebe). It has been determined for cusp singularitiesby Wall. On the other hand, if X is weighted homogeneous butnot a cyclic quotient singularity then the connected componentG1 of the unit coincides with the C* defining the weighted homogeneousstructure (Scheja, Wiebe, Wahl). Thus the main interest liesin the finite group G/G1. Not much is known about G/G1. Ganterhas given a bound on its order valid for Gorenstein singularitieswhich are not log-canonical. Aumann-Körber has determinedG/G1 for all quotient singularities. We propose to study G/G1 through the action of G on the minimalgood resolution of X. If X is weightedhomogeneous but not a cyclic quotient singularity, let E0 bethe central curve of the exceptional divisor of . We show that the natural homomorphism GAut E0 haskernel C* and finite image. In particular, this re-proves therest of Scheja, Wiebe and Wahl mentioned above. Moreover, itallows us to view G/G1 as a subgroup of Aut E0. For simple ellipticsingularities it equals (ZbxZb)Aut0 E0 where b is theself-intersection number of E0, ZbxZb is the group of b-torsionpoints of the elliptic curve E0 acting by translations, andAut0 E0 is the group of automorphisms fixing the zero elementof E0. If E0 is rational then G/G1 is the group of automorphismsof E0 which permute the intersection points with the branchesof the exceptional divisor while preserving the Seifert invariantsof these branches. When there are exactly three branches weconclude that G/G1 is isomorphic to the group of automorphismsof the weighted resolution graph. This applies to all non-cyclicquotient singularities as well as to triangle singularities.We also investigate whether the maximal reductive automorphismgroup is a direct product GG1xG/G1. This is the case, for instance,if the central curve E0 is rational of even self-intersectionnumber or if X is Gorenstein such that its nowhere-zero 2-form has degree ±1. In the latter case there is a naturalsection G/G1G of GG/G1 given by the group of automorphisms inG which fix . For a simple elliptic singularity one has GG1xG/G1if and only if E0 · E0 = 1. 相似文献
53.
Marie-Paule Muller 《Topology》1980,19(2):199-201
54.
55.
The synthesis of three lipophilic n-dodecyl tetraazacycloalkanes is described. Extraction of Cu(II), Cd(II) and Pb(II) is related. 相似文献
56.
The superconducting transition temperature has been investigated as a function of composition and degree of long-range order in a number of binary and ternary A 15-type phases on Cr and Mo. It is concluded that these compounds are unlike the typical Nb- or V- based phases with the same structure. The maximum Tc does usually not occur at the ideal composition. Nevertheless, a correlation has been found between Tc and the degree of order. 相似文献
57.
The effect of polymer conformation, polymer concentration, and added salt concentration on the quantum yield ? of Auramine O (AuO) is discussed in connection with dialysis equilibrium data. The quantum yield per bound dye molecule (?/q) assumes different values which are related principally to solvation changes in the environment of the binding sites. Binding to globular compact a states results in high ?/q, whereas low ?/q (of the order of magnitude of ? of free AuO) are observed for the binding to expanded solvated b states. The quantum yield of bound AuO is therefore affected by the organic nature of the environment, but shows little or no relation to the amount of bound dye molecules. 相似文献
58.
R. Daniel Little George W. Muller Manuel G. Venegas Gary L. Carroll Ahmed Bukhari Larry Patton Keith Stone 《Tetrahedron》1981,37(25):4371-4383
A comparison of the inter- and intramolecular diyl trapping routes to linearly fused tricyclopentanoids is presented. In addition, several of the factors which are responsible for the stereoselectivity which is associated with the intramolecular process are examined and it is concluded that conformational rather than electronic (secondary orbital) factors play the dominant role. It is shown that gem methyl groups located on the acyclic chain which joins the diyl and diylophile (in reference to 32 and 35, but not to 47) have no practical effect upon the outcome of the trapping reaction. The intramolecular process is stereospecific with respect to diylophile geometry, and highly stereoselective with respect to the ring junction stereochemistry. Finally, an abortive attempt to synthesize the marine natural product Δ9(12)-capnellene (19) as well as a successful synthesis of the mold metabolite d,l- hirsutene (18) is presented. 相似文献
59.
P. Muller 《Journal of sound and vibration》1983,87(1):115-141
A one-dimensional theory is developed for coupled torsional-flexural waves in thin-walled elastic beams of arbitrary open cross-section. Complex kinematical effects are fully taken into account with an emphasis on consistency. Exact equations of motion are obtained in terms of generalized stresses and generalized displacements defined by an averaging procedure. Constitutive relations accounting for flexural-torsional couplings are proposed. They include and generalize the static laws of strength of materials. General features of the dispersion are analyzed. This theory is applied to the case of a standard angle-section of which the dispersion curves are given. 相似文献
60.