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21.
Evgen V. Govor Andrey B. Lysenko Alexander N. Chernega Judith A.K. Howard Andriy A. Mokhir Joachim Sieler Konstantin V. Domasevitch 《Polyhedron》2008
Reaction of copper(II) acetate, lanthanium(III) or gadolinium(III) nitrate (1/5 equiv.) with pyrazinohydroxamic acid (H2Pyzha) in DMF led to a series of new heterobimetallic 15-metallacrown-5 complexes. In a MeOH/H2O solution the complexes exist as molecular unassociated metallacrowns. In solid state their structures are more complicated as it has been confirmed by X-ray analysis: discrete molecular metallacrowns [Gd(NO3)2{Cu(pyzha)}5(DMF)4(NO3)] · 0.5C6H6 · H2O (1), [Gd(NO3)2{Cu(pyzha)}5(DMF)5](NO3) · 1.5DMF · 0.5H2O (2), [La(NO3)2{Cu(pyzha)}5(DMF)5]NO3 · 1.5DMF · 2C6H6 (3) are solvates, whereas compound [{La(NO3)2{Cu(pyzha)}5(DMF)5}2(μ2-NO3)](NO3) · 3DMF (4) is a dimer, where μ-bridged nitrate links two copper centres of the adjacent metallamacrocycles. Complex [Gd(NO3)2{Cu(pyzha)}5(DMF)2(H2O)(NO3)] · CH2Cl2 · DMF (5) self-associates into a polymer chain by means of one pyrazine moiety and the copper ring atom. Reaction of the molecular metallacrowns with excess of inorganic salts CdBr2 or Cu(OAc)2 proceeds as anion methathesis process affording heteroanionic metallacrowns: molecular [Gd(NO3)2{Cu(pyzha)}5(DMF)5] [Gd(NO3)2{Cu(pyzha)}5(DMF)4(H2O)][CdBr4] · 1.5DMF (6), and 3D hydrogen bonded polymer [La(μ2-OAc)(H2O)3{Cu(pyzha)}5 (H2O)4(NO3)](NO3) · 4H2O (7). 相似文献
22.
Ritesh Raju Oleksandr Gromyko Viktor Fedorenko Andriy Luzhetskyy Rolf Müller 《Tetrahedron letters》2012,53(24):3009-3011
A Streptomyces sp. Lv3-13, isolated from the rhizosphere soil of the plant Mespilus germanica, has yielded three new pimprinine derivatives, named pimprinols A–C (1–3) and the unknown (2-aminophenyl)(2-ethyloxazol-5-yl) methanone (4) along with the known compounds 2-ethyl oxazole pimprinine and 2-propyl oxazole pimprinine. The structures of the compounds were elucidated based on spectroscopic methods including UV, HR-ESIMS and 1D, 2D NMR data. Compounds 1–4 were screened for antimicrobial and cytotoxic activities. 相似文献
23.
Andriy Romanyuk Viktor Melnik Yaroslav Olikh Johannes Biskupek Ute Kaiser Martin Feneberg Klaus Thonke Peter Oelhafen 《Journal of luminescence》2010,130(1):87-91
Silicon clusters embedded in a silicon dioxide matrix were prepared by ultrasound-assisted implantation resulting in a modified concentration of suboxide states as revealed by high-resolution photoelectron spectroscopy. It is suggested that ultrasound treatment results in formation of different interface structure between silicon cluster and silicon dioxide matrix which is characterized by a distinctly reduced concentration of the suboxide states. It is observed that photoluminescence properties are strongly correlated with the concentration of the suboxide states thereby providing an evidence that besides a quantum confinement effect a closer look at the chemical composition of the nc-Si/SiO2 system is important. 相似文献
24.
We construct non-tight frames in finite-dimensional spaces consisting of periodic functions. In order for these frames to
be useful in practice one needs to calculate a dual frame; while the canonical dual frame might be cumbersome to work with,
the setup presented here enables us to obtain explicit constructions of some particularly convenient oblique duals. We also
provide explicit oblique duals belonging to prescribed spaces different from the space where we obtain the expansion. In particular
this leads to oblique duals that are trigonometric polynomials. 相似文献
25.
26.
We propose a self-consistent molecular theory of conformational properties of flexible polymers in melts and solutions. The method employs the polymer reference interaction site model for the intermolecular correlations and the Green function technique for the intramolecular correlations. We demonstrate this method on n-alkane molecules in different environments: water, hexane, and in melt, corresponding to poor, good, and theta condition, respectively. The numerical results of the intramolecular correlation function, the radius of gyration, and the characteristic ratio of a polymer chain are indicative of conformational changes from one environment to another and are in agreement with other findings in the literature. Scaling laws for the chain size with respect to the number of monomers are discussed. We show results for the intra- and intermolecular correlation functions and the medium-induced potential. We also extract the Kuhn length and the characteristic ratio for the infinite chain limit for melts. The latter is compared to the experimental results and computer simulation. The conformational free energy per monomer in different solvents is calculated. Our treatment can be generalized readily to other polymer-solvent systems, for example, those containing branched copolymers and polar solvents. 相似文献
27.
Nevidomskyy AH 《Physical review letters》2005,94(9):097003
A microscopic mean-field theory of the phase coexistence between ferromagnetism and superconductivity in the weakly ferromagnetic itinerant electron system is constructed, while incorporating a realistic mechanism for superconducting pairing due to the exchange of critical spin fluctuations. The self-consistent solution of the resulting equations determines the superconducting transition temperature which is shown to depend strongly on the exchange splitting. The effect of phase crossover from isotropic (Heisenberg-like) to uniaxial (Ising-like) spin fluctuations near the quantum phase transition is analyzed and the generic phase diagram is obtained. This scenario is then applied to the case of itinerant ferromagnet ZrZn2, which sheds light on the proposed phase diagram of this compound. A possible explanation of superconductivity in UGe2 is also discussed. 相似文献
28.
Let G/K be a semisimple orbit of the adjoint representation of a real connected
reductive Lie group G. Let K1 be any closed subgroup of K containing the commutant of
the identity component of K. We prove that the geodesic flow on the symplectic manifold
T*(G/K1), corresponding to a G-invariant pseudo-Riemannian metric on G/K1 which is induced
by a bi-invariant pseudo-Riemannian metric on G, is completely integrable in the class
of real analytic functions, polynomial in momenta. To this end we study the Poisson geometry
of the space of G-invariant functions on T*(G/K) using a one-parameter family of moment
maps. 相似文献
29.
Alencar Raymundo; Aron Richard; Galindo Pablo; Zagorodnyuk Andriy 《Bulletin London Mathematical Society》2003,35(1):55-64
The authors study the algebra of uniformly continuous holomorphicsymmetric functions on the ball of lp, investigating in particularthe spectrum of such algebras. To do so, they examine the algebraof symmetric polynomials on lp-spaces, as well as finitely generatedsymmetric algebras of holomorphic functions. Such symmetricpolynomials determine the points in lp up to a permutation. 相似文献
30.
We address the problem of correlating the observed FID and T1ρ components in wideline 1H relaxation measurements of motionally heterogeneous polymers, and show that different methods of data treatment can highlight different aspects of the correlations present. For a sample of polypropylene we find that the T1ρ relaxation behaviour is driven by relaxation associated with the intermediate FID component, which strongly suggests a motionally inhomogeneous amorphous region in the sample. 相似文献