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31.
ABSTRACT Improved syntheses for the 3-β-D-glucuronides of the steroidal sex hormones 17β-estradiol, 17α-ethynylestradiol and estrone are reported employing boron trifluoride diethyl etherate catalysis with tetraacetylated glucuronic acid or the corresponding imidate. 相似文献
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35.
Dipl.‐Chem. Alexander Zhdanko Dr. Markus Ströbele Prof. Dr. Martin E. Maier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(46):14732-14744
Coordination chemistry of gold catalysts bearing eight different ligands [L=PPh3, JohnPhos (L2), Xphos (L3), DTBP, IMes, IPr, dppf, S‐tolBINAP (L8)] has been studied by NMR spectroscopy in solution at room temperature. Cationic or neutral mononuclear complexes LAuX (L=L2, L3, IMes, IPr; X=charged or neutral ligand) underwent simple ligand exchange without giving any higher coordinate complexes. For L2AuX the following ligand strength series was determined: MeOH?hex‐3‐yne <MeCN≈OTf??Me2S<2,6‐lutidine<4‐picoline<CF3CO2?≈DMAP<TMTU<PPh3<OH?≈Cl?. Some heteroligand complexes DTBPAuX exist in solution in equilibrium with the corresponding symmetrical species. Binuclear complexes dppf(AuOTf)2 and S‐tolBINAP(AuOTf)2 showed different behavior in exchange reactions with ligands depending on the ligand strength. Thus, PPh3 causes abstraction of one gold atom to give mononuclear complexes LLAuPPh3+ and (Ph3P)nAu+, but other N and S ligands give ordinary dicationic species LL(AuNu)22+. In reactions with different bases, LAu+ provided new oxonium ions whose chemistry was also studied: (DTBPAu)3O+, (L2Au)2OH+, (L2Au)3O+, (L3Au)2OH+, and (IMesAu)2OH+. Ultimately, formation of gold hydroxide LAuOH (L=L2, L3, IMes) was studied. Ligand‐ or base‐assisted interconversions between (L2Au)2OH+, (L2Au)3O+, and L2AuOH are described. Reactions of dppf(AuOTf)2 and S‐tolBINAP(AuOTf)2 with bases provided more interesting oxonium ions, whose molecular composition was found to be [dppf(Au)2]3O22+, L8(Au)2OH+, and [L8(Au)2]3O22+, but their exact structure was not established. Several reactions between different oxonium species were conducted to observe mixed heteroligand oxonium species. Reaction of L2AuNCMe+ with S2? was studied; several new complexes with sulfide are described. For many reversible reactions the corresponding equilibrium constants were determined. 相似文献
36.
Charles K. Chui Wenjie He Joachim Stöckler Qiyu Sun 《Advances in Computational Mathematics》2003,18(2-4):159-187
When a cardinal B-spline of order greater than 1 is used as the scaling function to generate a multiresolution approximation of L
2=L
2(R) with dilation integer factor M2, the standard matrix extension approach for constructing compactly supported tight frames has the limitation that at least one of the tight frame generators does not annihilate any polynomial except the constant. The notion of vanishing moment recovery (VMR) was introduced in our earlier work (and independently by Daubechies et al.) for dilation M=2 to increase the order of vanishing moments. This present paper extends the tight frame results in the above mentioned papers from dilation M=2 to arbitrary integer M2 for any compactly supported M-dilation scaling functions. It is shown, in particular, that M compactly supported tight frame generators suffice, but not M–1 in general. A complete characterization of the M-dilation polynomial symbol is derived for the existence of M–1 such frame generators. Linear spline examples are given for M=3,4 to demonstrate our constructive approach. 相似文献
37.
Joachim Käschel 《Proceedings Mathematical Sciences》1992,102(2):155-158
In Venkaiah [1] an algorithm for solving linear optimization problems based on the idea of the projective algorithm of Karmarkar,
is proposed. The essential simplification in the new algorithm is the use of a fixed projection operator. In this way the
algorithm requires onlyO(n
2
) operations to obtain a sufficient exact solution. In this note it is shown that in some special cases the algorithm of Venkaiah
yields a feasible solution that is far from the optimal one. 相似文献
38.
Excitation functions of the analyzing power in elastic proton-proton scattering from 0.45 to 2.5 GeV
M. Altmeier F. Bauer J. Bisplinghoff K. Büßer M. Busch T. Colberg L. Demirörs H. P. Engelhardt P. D. Eversheim K. O. Eyser O. Felden R. Gebel M. Glende J. Greiff F. Hinterberger E. Jonas H. Krause T. Lindemann J. Lindlein B. Lorentz R. Maier R. Maschuw A. Meinerzhagen D. Prasuhn H. Rohdjeß D. Rosendaal P. von Rossen N. Schirm V. Schwarz W. Scobel H. -J. Trelle K. Ulbrich E. Weise A. Wellinghausen R. Ziegler 《The European Physical Journal A - Hadrons and Nuclei》2005,23(2):351-364
Excitation functions AN(plab,c.m.) of the analyzing power in elastic proton-proton scattering have been measured in an internal target experiment at the Cooler Synchrotron COSY with an unpolarized proton beam and a polarized atomic hydrogen target. Data were taken continuously during the acceleration and deceleration for proton kinetic energies Tlab (momenta plab) between 0.45 and 2.5 GeV (1.0 and 3.3 GeV/c) and scattering angles 30 ° c.m. 90°. The results provide excitation functions and angular distributions of high precision and internal consistency. The data can be used as calibration standard between 0.45 and 2.5 GeV. They have significant impact on phase shift solutions, in particular on the spin triplet phase shifts between 1.0 and 1.8 GeV. 相似文献
39.
Hans‐Joachim Schmid Susanne Veith Heinz Umhauer 《Particle & Particle Systems Characterization》2002,19(3):203-215
An optical measuring technique is presented allowing the exact in‐situ measurement of local particle flux densities in a confined channel flow by counting single particles penetrating an optically well defined measuring volume. This enables a precise flux determination up to the direct vicinity of planar walls. The measurement set‐up and its calibration as well as the whole test facility are described in detail. This measurement technique is used to study the particle transport in electrostatic precipitators. Exemplarily, results of particle flux profiles as well as precipitation, as gained from balances of parts of the precipitator channel, are presented. Furthermore, the possibility to determine particle velocity fluctuations is demonstrated. 相似文献
40.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献