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981.
Bolm C Martin M Gescheidt G Palivan C Stanoeva T Bertagnolli H Feth M Schweiger A Mitrikas G Harmer J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(6):1842-1850
The initial steps of an enantioselective Diels-Alder reaction catalyzed by a CuII-bissulfoximine complex were followed by EXAFS (EXAFS=extended X-ray absorption fine structure), EPR (EPR=electron paramagnetic resonance) spectroscopy (CW-EPR, FID-detected EPR, pulse ENDOR, HYSCORE; CW=continuous wave; ENDOR=electron nuclear double resonance; HYSCORE=hyperfine sublevel correlation; FID=free induction decay), and UV-visible spectroscopy. The complexes formed between the parent CuX2 (X=Cl-, Br-, TfO-, SbF6-) salts, the chiral bissulfoximine ligand (S,S)-1, and N-(1-oxoprop-2-en-1-yl)oxazolidin-2-one (2) as the substrate in CH2Cl2 were investigated in frozen and fluid solution. In all cases, penta- or hexacoordinated CuII centers were established. The complexes with counterions indicating high stereoselectivity (TfO- and SbF6-) reveal one unique species in which substrate 2 binds to pseudoequatorial positions (via O atoms), shifting the counterions to axial locations. On the other hand, those lacking stereoselectivity (X=Cl- and Br-) form two species in which the parent halogen anions remain at equatorial positions preventing the formation of geometries compatible with those found for X=TfO- and SbF6-. 相似文献
982.
Handler N Jaeger W Puschacher H Leisser K Erker T 《Chemical & pharmaceutical bulletin》2007,55(1):64-71
Curcumin, a major yellow pigment and active component of turmeric, has been shown to possess anti-inflammatory and anti-cancer activities. Recent studies have indicated that cyclooxygenase-1 (COX-1) plays an important role in inflammation and carcinogenesis. In order to find more selective COX-1 inhibitors a series of novel curcumin derivatives was synthesized and evaluated for their ability to inhibit this enzyme using in vitro inhibition assays for COX-1 and COX-2 by measuring PGE(2) production. All curcumin analogues showed a higher rate of COX-1 inhibition. The most potent curcumin compounds were (1E,6E)-1,7-di-(2,3,4-trimethoxyphenyl)-1,6-heptadien-3,5-dione (4) (COX-1: IC(50) = 0.06 microM, COX-2: IC(50) > 100 microM, selectivity index>1666) and (1E,6E)-methyl 4-[7-(4-methoxycarbonyl)phenyl]-3,5-dioxo-1,6-heptadienyl]benzoate (6) (COX-1: IC(50) = 0.05 microM, COX-2: IC(50) > 100 microM, selectivity index > 2000). Curcumin analogues therefore represent a novel class of highly selective COX-1 inhibitors and promising candidates for in vivo studies. 相似文献
983.
Sigel R Łosik M Schlaad H 《Langmuir : the ACS journal of surfaces and colloids》2007,23(13):7196-7199
The aggregation behavior of polybutadiene165-block-poly(L-lysine)88 in saline solution was studied by combined static and dynamic light scattering analyses. Vesicles were observed if the polypeptide segment was in a 100% coil conformation (pH 7.0) or in an 80% alpha-helical conformation (pH 10.3). At the higher pH, aggregates were smaller in size (hydrodynamic radius: 364 nm --> 215 nm) and chains were more densely packed at the core-corona interface (interchain distance: 3.2 nm --> 2.4 nm). Changes in size and structure could be explained in basic terms of colloid stabilization without considering a secondary structure effect. 相似文献
984.
T. von Egidy P. Figuera J. Galin F. Goldenbaum Ye. S. Golubeva M. Hasinoff D. Hilscher A. S. Iljinov U. Jahnke M. Krause W. Kurcewicz X. Ledoux B. Lott L. Maier M. Manrique de Lara G. Pausch L. Pienkowski B. Quednau W. Schott W. U. Schröder J. Tõke 《The European Physical Journal A - Hadrons and Nuclei》2000,8(2):197-204
Inclusive neutron energy spectra were measured by time of flight using 1.22 GeV antiprotons from LEAR, CERN, as projectiles
and targets from natural Al, Cu, Ag, Ho, Ta, Au, Pb, Bi, U. The sum of two Maxwellian distributions was fitted to the spectra
obtained at several forward and backward angles yielding neutron multiplicities Mi and slope or temperature parameters T
i for the low-energy (evaporative, i=1) and high-energy (pre-equilibrium,i=2) parts, respectively. M
1 increases with A, proportional to the nuclear volume, and M
2 is growing with A
, proportional to the nuclear radius. The T parameters are nearly independent of A. The results are compared with previous multiplicity measurements with a neutron detector, intranuclear cascade calculations and neutron spectra from stopped antiproton annihilation on nuclei. With
the measured proton spectra also the ratio of emitted neutrons to protons was determined for Au.
Received: 25 February 2000 / Accepted: 19 May 2000 相似文献
985.
986.
G.M. Marshall T.A. Porcelli A. Adamczak J.M. Bailey G.A. Beer M.P. Faifman M.C. Fujiwara T.M. Huber R. Jacot-Guillarmod P. Kammel S.K. Kim P.E. Knowles A.R. Kunselman M. Maier V.E. Markushin G.R. Mason F. Mulhauser A. Olin C. Petitjean J. Zmeskal 《Hyperfine Interactions》1999,118(1-4):89-101
Solid hydrogen in the form of an inhomogeneous layered target offers several experimental advantages when compared with liquid
or gas. Beams of non-thermalized muonic hydrogen atoms allow us to explore resonant molecular ion formation processes near
eV kinetic energies. Isotopically specific layers make it possible to separate competing and confusing interactions and to
employ the time of flight for comparison with predictions based on theoretical energy dependences. Unambiguous charged fusion
product detection simplifies absolute intensity measurements.
The systematic uncertainties encountered in resonant molecular ion formation measurements, using solid hydrogen target layers,
are being investigated with simulations which use the many calculated energy-dependent rates and cross-sections which are
now available. The importance of the rates for processes such as muon transfer and elastic scattering are discussed, and results
of some recent analyses are presented.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
987.
Port controlled Hamiltonian systems with dissipation are a well known tool for the modeling and the controller design for plants, described by nonlinear ordinary differential equations. This contribution presents a possible extension to systems, described by partial differential equations, where the state manifold and the input space of the ODE case are replaced by new geometric structures. This approach takes dissipative effects into account and shows, how distributed ports can be introduced. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
988.
Dominique Collin Günter K. Auernhammer Odile Gavat Philippe Martinoty Helmut R. Brand 《Macromolecular rapid communications》2003,24(12):737-741
We describe the preparation and characterization of uniaxial magnetic gels. Fibril formation of the embedded magnetic particles generates easily detectable magnetic and optical anisotropies. A finite magnetization is frozen‐in and leads to a ferromagnetic‐like response in small homogeneous external magnetic fields. We present, for the first time, frequency dependent measurements of the shear modulus G′. Despite their optical and magnetic anisotropy, the gels are mechanically isotropic.
989.
990.