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61.
Sannomiya M Rodrigues CM Coelho RG dos Santos LC Hiruma-Lima CA Souza Brito AR Vilegas W 《Journal of chromatography. A》2004,1035(1):47-51
The methanolic extract of the leaves of the medicinal plant Byrsonima crassa (Malpighiaceae) contain flavonoids with antioxidant activity. They were separated in a preparative scale using high-speed counter-current chromatography. The optimum solvent system used was composed of a mixture of ethyl acetate-n-propanol-water (140:8:80 (v/v/v)) and led to a successful separation between monoglucosilated flavonoids (quercetin-3-O-alpha-L-arabinoside, quercetin-3-O-beta-D-galactoside) and the biflavonoid amentoflavone in only 3.5 h. The purities of quercetin-3-O-alpha-L-arabinoside (95 mg), quercetin-3-O-beta-D-galactoside (16 mg) and the biflavonoid amentoflavone (114 mg) were all isolated at purity over 95%. Identification was performed by 1H NMR, 13C NMR and UV analyses. 相似文献
62.
Alessandro D' Aprano Dorina Ines Donato Antonio Carrubba Doctor in Chemistry thesis of A. Carrubba 《Journal of solution chemistry》1983,12(3):209-220
Conductance measurements are reported for LiPi, NaPi, KPi, RbPi, CsPi, Bu4NPi, Bu4NBr, Bu4NClO4, Bu4NNO3, and Bu4NBBu4 at 25°C in -butyrolactone-sulfolane mixtures. In these mixtures of solvents that are practically homomorphous, isodielectic and with comparable dipole moments, the ion pair association and ionic mobilities of large ions conform to the expectations of the primitive model. Electrolytes containing lithium or sodium ions show anomalies indicating that other factors besides shape, dipole moment, and polarizability of the solvent molecules are involved in the association and transport processes of these ions. 相似文献
63.
Alessandro Boido Francesco Savelli Fernando Sancassan 《Journal of heterocyclic chemistry》1997,34(5):1643-1644
Following a previous experiment, an original heteropolycyclic structure 4 was obtained by a reaction of chloroacetyl chloride with compound 3 bearing a conjugated double bond system. The condensation develops with an initial NH-chloroacetylation and ring closure by quaternarization of the pyridine nitrogen. This is achieved through an 1,4 -cycloaddition of chloroketene to make a pyranone ring. 相似文献
64.
65.
S. Patzer N.L. Arthur P. Potzinger H.Gg. Wagner 《Journal of photochemistry and photobiology. A, Chemistry》1997,110(3):2543-227
The photolysis of Me6Si2 at 206 nm results in two main decomposition processes: simple Si---Si bond breaking with a quantum yield of Φ = 0.21 ± 0.03, and Me3SiH elimination with the concomitant formation of Me2SiCH2 with Φ = 0.18 ± 0.01. There is also a minor decomposition channel with a very small quantum yield, Φ = (5.6 ± 0.2) × 10−3, which results in the formation of Me4Si and Me2Si. The main fate of the excited Me6Si2 molecule produced during photolysis is stabilization by collisional deactivation. The end products observed indicate that the reaction pathways followed by the main intermediates, Me3Si and Me2SiCH2, are the same as those found in the photolysis of Me4Si (Ahmed et al., J. Photochem. Photobiol. A: Chem. 86 (1995) 33). 相似文献
66.
67.
A. Mandelis W. Lo R. E. Wagner 《Applied Physics A: Materials Science & Processing》1987,43(2):123-130
The electrical and dielectric properties of mercuric iodide were studied at room temperature under various intensities and colours of light in the frequency range 1 Hz–10 kHz. In the high-frequency region (>40 Hz), the real part of the dielectric constant () is almost constant with frequency (f), colour and intensity of light. At lower frequencies, varies nearly as 1/f and monotonically increases with intensity (I) of the yellow (or green) light, whereas it is almost constant with red light intensity. This behaviour is discussed in the view of the different polarization contributions. The imaginary part of the dielectric constant () was found to vary as 1/f over the frequency range studied. This behaviour was observed whether the crystal was in dark or illuminated implying that the roomtemperature ac dark- or photo-conductivity () is independent of frequency. The observed variation of with intensity of yellow (or green) light was found to follow anI
1/2 dependence and a weaker dependence for the red light. the red light. The conductivity behaviour is discussed in the view of the current theories. 相似文献
68.
Wagner F Gruber O Lackner K Murmann HD Speth E Becker G Bosch HS Brocken H Cattanei G Dorst D Eberhagen A Elsner A Erckmann V Fussmann G Gehre O Gernhardt J Gierke Gv Glock E Grieger G Grigull P Haas G Hacker H Hartfuss HJ Jäckel H Jaenicke R Janeschitz G Junker J Karger F Kasparek W Keilhacker M Kick M Klüber O Kornherr M Kroiss H Kuehner M Lenoci M Lisitano G Maassberg M Mahn C Marlier S Mayer HM McCormick K Meisel D Mertens V Müller ER Müller Müller G Niedermeyer H Ohlendorf W 《Physical review letters》1986,56(20):2187-2190
69.
Summary In this paper we employ equivariant singularity theory to study the postbuckling behavior of a cylindrical shell under axial compression, obtaining some results about the existence of secondary bifurcations and how they are connected to each other. The basic idea, first employed by Bauer, Keller and Reiss in [1], and then coupled with singularity theory by Schaeffer and Golubitsky in [16] and [17] and by Buzano in [4], consists in unfolding a multiple eigenvalue, obtained by forcing two eigenvalues to coalesce by varying the geometric parameters of the shell. This approah is made possible by a general analysis of bifurcation problems invariant with respect to the symmetries of the cylinder i.e. with respect to the group O(2)Z
2. 相似文献
70.
Elisa Brivio Alessandro Ceriotti Roberto Della Pergola Luigi Garlaschelli Mario Manassero Mirella Sansoni 《Journal of Cluster Science》1995,6(2):271-287
Redox condensation of [Ru3H(CO)11]- with Ni(CO)4, in tetrahydrofuran solution, under a nitrogen atmosphere, yields the tetranuclear anion [NiRuH(CO)11)-. Subsequent deprotonation with Bu'OK in acetonitrile solution leads to the formation of the related dianion. Both anions have been characterized by spectroscopic techniques, elemental analysis and single crystal X-ray diffraction. [PPh4][NiRu3H(CO)12] crystallizes in the triclinic space group PI with unit cell dimensionsof a = 11.842(2) Å,b = 12.335(3) Å, c = 13.3080) Å,a = 91.89(2)°, = 93.35(1)°,y = 96.41(2)°, Z = 2, V= 1926.9(7) Å'. The NiRu3, metal core of the molecule defines a distorted tetrahedron with nine terminal and three edge bridging carbonyl groups. The hydrido ligand was located by difference Fourier techniques and was found to bridge the NiRu2 basal triangle at a distance of 0.88(6) A from this plane. Selected average distances and angles are: Ru-Ru = 2.839 Å, Ru-Ni = 2.640 Å, Ru-C, = 1.910 A,Ru-C
b
= 2.084 Å, Ni-C
b
= 2.022 Å, Ru-H = 1.77 Å, C-0, = 1.135 Å, C-O
b
= 1.159 Å, M-C-O, = 176.3°,M-C--O
b
= 139.3°;other distances are: Ni-C1 = l.758(7) Å, Ni-H= 1.85(7) Å. [NEt4]2[NiRu3(CO)12] crystallizes in the orthorhombic space group Pnma (no. 62) with unit cell dimensions ofa=20.247(5) Å,b = 15.038(4)Å,c = 12.079(3) Å, Z=4, V=3678(2) A'. The molecule contains a tetrahedral NiRu3 core with eight terminal and four edge bridging carbon monoxide groups which bridge the three Ni-Ru and one Ru-Ru bond. Average distances and angles are: Ru -Ru =2.3050A Ru-Ni 2.648 Å, Ru-C
t
= 1.878 Å, Ru-C
b
2.045 Å, Ni-C
b
= 2.055 Å, C-O
t
= 1.145 Å, C-01,=1.157 Å, M-C-O,= 176.9°, M-C-O
b
= 138.6°; other distance is: Ni-C
t
= 1.754(10) Å,t = terminal,b = bridging. 相似文献