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641.
(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
642.
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
643.
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
644.
645.
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
646.
647.
Paneque Armando Fernández-Bertran José Reguera Edilso Yee-Madeira Hernani 《Transition Metal Chemistry》2001,26(1-2):76-80
Solid state reactions of hemin and imidazole were performed by milling the crystalline materials in an agate mortar. The process was monitored by i.r., x.r.d. and Mössbauer spectroscopies. Samples with different hemin to imidazole molar ratios were studied. The interactions of imidazole with the central Fe atom and with the propionic acid groups in the periphery of the hemin molecule were detected. The latter interactions are suppressed by washing with MeOH. Complexes with 1:2 and 1:4 hemin-to-imidazole molar ratios were identified. 相似文献
648.
Adriana García Forero Diego Armando Villamizar Mantilla Luis A. Núez Raquel Elvira Ocazionez Elena E. Stashenko Jorge Luis Fuentes 《Photochemistry and photobiology》2019,95(4):1010-1018
This work evaluated the photoprotective and antigenotoxic effects against ultraviolet B (UVB) radiation of flavonoid compounds apigenin, naringenin and pinocembrin. The photoprotective efficacy of these compounds was estimated using in vitro photoprotection indices, and the antigenotoxicity against UVB radiation was evaluated using the SOS chromotest and an enzymatic (proteinase K/T4 endonuclease V enzyme) comet assay in UV‐treated Escherichia coli and human (HEK‐293) cells, respectively. Naringenin and pinocembrin showed maximum UV‐absorption peak in UVC and UVB zones, while apigenin showed UV‐absorption capability from UVC to UVA range. These compounds acted as UV filters reducing UV‐induced genotoxicity, both in bacteria and in human cells. The enzymatic comet assay resulted highly sensitive for detection of UVB‐induced DNA damage in HEK‐293 cells. In this work, the photoprotective potential of these flavonoids was widely discussed. 相似文献
649.
650.
The isolation and the structure determination of an unusual xyloside from the plant Chenopodium album is reported. The structure has been attributed by means of its spectral data. 相似文献