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651.
The synthesis of five steroid-oligo(ethyleneglycol) conjugates (1-5) has been accomplished starting from commercially available epi-androsterone (8) and known 3β-[(tert-butyldiphenylsilyl)oxy]-5α-23,24-bisnorchol-16-en-6α,7β,22-triol (27). The synthetic strategy was based on a convergent approach including stereoselective C-17 side chains construction and standard coupling reactions. The activities of the head-to-tail amphiphiles, once incorporated in 95:5 egg PC/PG vesicular membranes, have been assessed by direct determination of transported species by NMR techniques (23Na+) and fluorescence spectroscopy (H+). The sodium and proton transmembrane transport was compared to those evaluated for the polyene macrolide antibiotic amphotericin B and those shown by the known related C2-symmetric sterol-polyether conjugates 6 and 7. 相似文献
652.
Jing Hua ZHAO Tai Gang LIANG Qing Shan LI* Armando J.L. Pombeiro School of Pharmaceutical Science Shanxi Medical University Taiyuan Complexo I Instituto Superior T閏nico Av. Rovisco Pais - Lisbon Portugal 《中国化学快报》2003,14(8)
Diorganotin (IV) complexes constitute a class of potential antitumor agents, which were active against P388 lymphocytic leukaemia and MCF-7 mammary tumor1. Hydroxamic acids such as arylhydroxamic acid are strong bidentate O-donors with bioactivity2. A few years ago, we initiated an investigation on the interactions between diorganotin (IV) acceptors and benzohydroxamic acid and its derivatives3, 4, hoping that a synergic effect would occur. We found most of this type of diorganotin (IV) … 相似文献
653.
[reaction: see text] One-pot asymmetric Mannich-hydrocyanation reactions are described. Reaction of unmodified aldehydes with N-PMP-protected alpha-imino ethyl glyoxylate in the presence of catalytic amounts of L-proline followed by the addition of Et(2)AlCN provided highly enantiomerically pure beta-cyanohydroxymethyl alpha-amino acid derivatives possessing three contiguous stereogenic centers as single diastereomers (93-99% ee). Control of reaction temperature during the cyanation step directed whether cyclization of the products to lactones occurred. 相似文献
654.
(S)-selective kinetic resolution and chemoenzymatic dynamic kinetic resolution of secondary alcohols
Borén L Martín-Matute B Xu Y Córdova A Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):225-232
(S)-Selective kinetic resolution was achieved through the use of a commercially available protease, which was activated with a combination of two different surfactants. The kinetic resolution (KR) process was optimized with respect to activation of the protease and to the acyl donor. The KR proved to be compatible with a range of functionalized sec-alcohols, giving good to high enantiomeric ratio values (up to >200). The enzymatic resolution was combined with a ruthenium-catalyzed racemization to give an (S)-selective dynamic kinetic resolution (DKR) of sec-alcohols. The DKR process works under very mild reaction conditions to give the corresponding esters in high yields and with excellent enantioselectivities. 相似文献
655.
Summary By limiting equations, we prove some asymptotic stability theorems for the origin ofR
n with respect to the solutions of a differential equation
, also when the functionf is not defined forx=0. Further we examine similar problems concerning the asymptotic stability of a setM ofR
n that can be unbounded.
Work performed under the auspices of the Italian Council of Research (G.N.F.M. del C.N.R.). 相似文献
Riassunto Mediante le equazioni limiti, si dimostrano alcuni teoremi di stabilità asintotica per l'origine diR n rispetto alle soluzioni di un'equazione differenziale , anche quando la funzionef non è definita perx=0. Vengono inoltre esaminati analoghi problemi relativi alla stabilità asintotica di un insiemeM diR n anche non limitato.
Work performed under the auspices of the Italian Council of Research (G.N.F.M. del C.N.R.). 相似文献
656.
Armando Vieira Marta Brajczewska Carlos Fiolhais 《International journal of quantum chemistry》1995,56(4):239-246
The stabilized jellium model is a simple modification of the jellium model, which more realistically describes simple metals of high density, such as Al, Ga, Pb, etc. We analyzed the fragmentation processes of charged spherical Al clusters in the framework of the stabilized jellium model. Kohn-Sham calculations of the parents and daughters, using the local density approximation, have been made. We evaluated the dissociation energies of Al, Al, and Al, with N=1-30 atoms, in all possible decay channels. We discuss the most favorable decay channels, which are ruled by the shell structure (magic numbers of valence electrons in the parents and the daughters) oscillations around an average trend given by a liquid drop model. We compare our calculations with others and with the available experimental data. © 1995 John Wiley & Sons, Inc. 相似文献
657.
Armando Marzotto Dore Augusto Clemente Antonella Ciccarese Giovanni Valle 《Journal of chemical crystallography》1993,23(2):119-131
With the aim to obtain further insight into the nature of the Ni(II)-nitrogen bond in complexes with nucleobases, we have synthesized two novel Ni(II) ternary complexes constituted by Ni(II), tris(2-aminoethyl)amine (tren) and neutral adenine (AdH) or imidazole (ImH). The reaction of NiCl2·6H2O with tren and imidazole yields the ternary [Ni(tren)(ImH)(H2O)]Cl2·H2O complex and the same reaction with adenine instead of imidazole gives the ternary [Ni(tren)(AdH)Cl]Cl complex. The complexes have been studied by spectrophotometric and spectroscopic measurements and by X-ray diffraction. The ternary complex of adenine is monoclinic, space groupC2/c, and exhibits a pseudo-octahedral geometry, being Ni(II) coordinated to the four nitrogen atoms of the tetradentate tren ligand, to a Cl– ion and to the pyrimidine N3 site of a neutral adenine. Such an exclusive Ni-N3 bonding [2.081(4)Å] is now reported for the first time. The ternary complex of imidazole is monoclinic, space groupP21/n. Its pseudo-octahedral geometry is similar to that found in the above adenine complex although a water molecule instead of a Cl– ion is now present in the coordination sphere. In fact, Ni(II) is coordinated to tetradentate tren, to the imidazole N1 nitrogen and to a water molecule. Electronic and1H NMR spectra in solution indicate that the octahedral structures found in the solid state are substantially maintained in solution. Furthermore, the present investigation suggests that the adenine Ni-N3 and imidazole Ni-N1 bonds have the same chemical nature, involving mainly - and only partially-bonding. The Ni-N3 bonding is discussed in connection with biological implications and possible applications. 相似文献
658.
659.
Jin An Wang Gabliela González Lifang Chen Miguel A. Valenzuela Maria Moran-Pineda Armando Vázquez Salvador Castillo 《Reaction Kinetics and Catalysis Letters》2007,90(2):381-387
Ceria-zirconia nanophase with structural defects and high thermal stability was synthesized by a surfactant-templated method.
The 0.5 wt.% Rh/ceria-zirconia catalyst shows high activity for NO reduction by CO under an oxygen-rich condition, and the
selectivity to 100% N2 below 200°C was achieved. 相似文献
660.