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排序方式: 共有689条查询结果,搜索用时 15 毫秒
1.
2.
Gerhard Laus Johannes Schütz Herwig Schottenberger Max Andre Klaus Wurst Mariana Spetea Karl‐Hans Ongania AdrianG. Müller Helmut Schmidhammer 《Helvetica chimica acta》2003,86(10):3274-3280
The two diastereoisomeric ferrocenyl‐substituted orvinols 2 and 3 were prepared. The modified alkaloids are still able to interact with opioid receptors (see Table). The ferrocene moiety allows highly selective and sensitive electrochemical detection. The X‐ray crystal structure of the major isomer 2 was determined. The combination of a metallocene and a morphinan alkaloid holds promise for useful antitumor activity. 相似文献
3.
Carette M Zerega Y March RE Perrier P Andre J 《Rapid communications in mass spectrometry : RCM》2000,14(11):979-986
The coupling of a Rydberg electron capture ion source with a Nermag R10-10H quadrupole mass filter is described. Details are given of the addition to this instrument of a creation cell for atoms excited in Rydberg states. Within the Nermag ion source, such atoms allow attachment of electrons of well-defined thermal energy. SF(6) was used for optimization of the main experimental parameters (gas pressures and voltages applied to the electrodes). The procedure by which Rydberg electron attachment was confirmed is described. A polychlorobiphenyl compound was used to illustrate the performance of this ionization technique. Ion formation was observed in the absence of fragmentation. 相似文献
4.
A. Bouchy J. C. Andre F. Baros M. Bouchy-Noirel 《Reaction Kinetics and Catalysis Letters》1989,39(1):199-205
Starting from a uniform distribution and knowing the space dependent rate constant, it is possible to express the fluorescence quenching effect. In the case of long distance energy transfer (Forster), we show that the introduction of radial distribution functions and of non-uniform repartition of quenchers has only small effects on the kinetics of such reactions.
. (Forster) , .相似文献
5.
Andre Rosowsky Ronald A. Forsch Richard G. Moran 《Journal of heterocyclic chemistry》1996,33(4):1355-1361
Nα-[4-[[(4-Aminopteridin-6-yl)methyl]amino]benzoyl]-L-ornithine (dAPA-Orn) was synthesized, and its ability to inhibit folylpolyglutamate synthetase from mouse liver was compared with that of the corresponding 2,4-diamino analogue APA-Orn. Also compared were the inhibitory activities of the deaza analogues 5-deazaAPA-Orn, 8-deazaAPA-Orn, and 5,8-dideazaAPA-Orn, as well as those of Nα-pteroyl-L-ornithine (PteOrn) and its deaza analogues 5-deazaPteOrn and 5,8-dideazaPteOrn. The inhibition constant Ki of dAPA-Orn was 7-fold greater than that of APA-Orn, indicating that the 2-amino group plays a role in binding to the active site. The binding affinity of the 2,4-diamino compounds increased in the order 5-deazaAPA < APA-Orn <5,8-dideazaAPA-Orn < 8-deazaAPA-Orn, and that of the 2-amino-4(3H)-oxo compounds increased in the order 5-deazaPteOrn < PteOrn < 5,8-dideazaPteOrn. The most potent inhibitor of both groups was 8-deazaAPA-Orn, with a Ki of 0.018 μM, coresponding to an 8-fold and 15-fold increase in affinity relative to APA-Orn and 5-deazaAPA-Orn, respectively. The results suggest (a) that the binding of Orn-containing folylpolyglutamate synthetase inhibitors is affected to a greater degree by replacement of N8 by a carbon atom than it is by the corresponding change at N5, (b) that the effect of carbon for nitrogen replacement is greater in the 2,4-diamino derivatives than in the 2-amino-4(3H)-oxo compounds, and (c) that the 2,4-diamines are the better inhibitors. Comparison of the Ki values of the Orn-containing inhibitors with the Km values of the corresponding glutamate-containing substrates revealed that Km/Ki ratio can vary as much as 100-fold depending on the nature of the heterocyclic moiety, suggesting that caution should be exercised in using Km values of known substrates to predict Ki values of putative inhibitors. 相似文献
6.
J. M. Andre J. Delhalle J. G. Fripiat G. Leroy 《International journal of quantum chemistry》1971,5(1):67-84
The LCAO form of the Hartree–Fock method is discussed in its application to crystals. General formulae are given for obtaining Fourier coefficient of electronic density (in direct space) as well as of the band structure (in momentum space). Finally, it is shown that in its LCAO form, Slater–Hartree–Fock equations are very simple and that this method is of interest for numerical applications. Special integrals occurring in this formalism are evaluated for a Gaussian basis in the last part of this paper. 相似文献
7.
Galan MC Venot AP Glushka J Imberty A Boons GJ 《Journal of the American Chemical Society》2002,124(21):5964-5973
It is demonstrated that conformationally restricted oligosaccharides can act as acceptors for glycosyltransferases. Correlation of the conformational properties of N-acetyl lactosamine (Galbeta(1-4)GlcNAc, LacNAc) and several preorganized derivatives with the corresponding apparent kinetic parameters of rat liver alpha-(2,6)-sialyltransferase-catalyzed sialylations revealed that this enzyme recognizes LacNAc in a low energy conformation. Furthermore, small variations in the conformational properties of the acceptors resulted in large differences in catalytic efficiency. Collectively, our data suggest that preorganization of acceptors in conformations that are favorable for recognition by a transferase may improve catalytic efficiencies. 相似文献
8.
9.
Liposomes encapsulating monomeric actin (G-actin) were produced via extrusion through 400 and 600 nm pore diameter polycarbonate membranes in low ionic strength buffer (G-buffer). After actin-containing liposomes were subjected to high ionic strength polymerization buffer (F-buffer), morphological changes in the structure of actin-containing liposomes were studied using asymmetric flow field-flow fractionation (AFFF) coupled with multiangle static light scattering (MASLS). The general shape of these liposomes was initially determined by fitting three form factors, which describe the angular distribution of scattered light from a spherical thin shell, thin disk, and thin rod, to the experimentally measured light scattering spectra to regress the dimensions of the liposomes corresponding to the proposed geometry. Light scattering spectra that yielded a best fit to the thin disk model were analyzed further and fit to the ellipsoidal of revolution form factor to regress both the major and minor axis dimensions. The results of this analysis showed that actin-containing liposomes extruded through 400 and 600 nm pore diameter membranes in F-buffer, at a low actin concentration (0.1 mg/mL), assumed a spherical shape, which is also the case for plain liposomes (no actin present) in G-buffer and F-buffer. When the actin concentration was increased to 1 mg/mL, the polymerizing actin filaments stretched the initially spherical liposome into a disklike shape. However, when the actin concentration was further increased to 5 mg/mL, the liposomes reverted back to a spherical shape. 相似文献
10.
Charles Merritt Gary W. Scott Amitava Gupta Andre Yavrouian 《Chemical physics letters》1980,69(1):169-173
Transient absorption spectra (400–600 nm) of 2-hydroxybenzophenone and the methyl methacrylate copolymer of 2-hydroxy, 3-allyl, 4,4'-dimethoxybenzophenone following 355 nm excitation (7–480 ps delay) are reported. A short-lived, 435 nm transient (τ ≈ 10 ps in CH2Cl2) for both molecules is assigned to the lowest excited singlet before internal proton transfer. Weaker, broad T-T absorption is observed after 480 ps. 相似文献