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221.
Sauviat MP Benoit AG Debitus C Pouny I Laurent D 《Photochemistry and photobiology》2001,74(2):115-119
The effects of gymnochrome A were tested on the electrical activity of the frog atrial heart muscle. Gymnochrome A (1-5 microM) did not alter the resting potential. Gymnochrome A (5 microM) slowed the initial depolarizing phase of the spontaneously beating action potential. Under voltage-clamp conditions gymnochrome A (5 microM) did not affect the electrical constant of the membrane and the kinetic parameters of the peak Na+ current (INa) recorded in the Ringer solution containing tetraethylammonium (2 mM) and Cd2+ (1 mM) but shifted the membrane potential at which the current both activated and reached its maximal value toward more negative membrane potentials. It did not alter the reversal potential for INa, indicating that the selectivity of the Na+ channels had not changed. These observations suggest that gymnochrome A binds to the membrane and shifts the activation of INa on the voltage axis by modifying the free negative fixed charges present at the membrane surface rather than by occupying a specific site on the Na+ channel. Photoexcited gymnochrome A transiently triggered an early outward current which lengthened the time-to-peak of INa and decreased its amplitude. In addition, photoexcited gymnochrome A blocked the background K+ current. This is, to our knowledge, the first time that such effects are reported on the cardiac muscle. These observations suggest that the photoexcitation of gymnochrome produces physico-chemical effects which lead to intracellular changes. Further experiments are required to determine their nature. 相似文献
222.
Loss S Magistrato A Cataldo L Hoffmann S Geoffroy M Röthlisberger U Grützmacher H 《Angewandte Chemie (International ed. in English)》2001,40(7):1143
The cover picture shows the metalloporphyrin heterodimer [(tpp)Mo$\rm{\mathop{-}^{4}}$Re(oep)](+) with the novel [Mo$\rm{\mathop{-}^{4}}$Re](5+) core. The core represents the first example of a quadruple bond between elements of different triads, thus proving that heterometallic quadruple bonds are not limited to the Group 6 metals. From the space-filling model it is clear that there is no interaction between the stabilizing porphyrin ligands. The ORTEP plot in a projection along the Re-Mo axis emphasizes the perfectly eclipsed geometry of the porphyrins, which is unambiguous proof of the existence of the quadruple bond in the solid state. The diamagnetism and large magnetic anisotropy of the cation, as determined by (1)H NMR spectroscopy, indicate that the quadruple bond is retained in solution. A logical and well-defined synthetic route was used to synthesize the dimer, and can be extended to other metalloporphyrins to generate further novel quadruple bonds (the picture was generated by Marina Boulan, St. Petersburg, Russia), full details are reported by J. P. Collman et al. on p. 1271 ff. 相似文献
223.
224.
The optimizer developed for the Mining Minima algorithm, which uses ideas from Genetic Algorithms, the Global Underestimator Method, and Poling, has been adapted for use in ligand-receptor docking. The present study describes the resulting methodology and evaluates its accuracy and speed for 27 test systems. The performance of the new docking algorithm appears to be competitive with that of previously published methods. The energy model, an empirical force field with a distance-dependent dielectric treatment of solvation, is adequate for a number of test cases, although incorrect low-energy conformations begin to compete with the correct conformation for larger sampling volumes and for highly solvent-exposed binding sites that impose little steric constraint on the ligand. 相似文献
225.
Labiche M Orr NA Marqués FM Angélique JC Axelsson L Benoit B Bergmann UC Borge MJ Catford WN Chappell SP Clarke NM Costa G Curtis N D'Arrigo A de Góes Brennand E Dorvaux O Fazio G Freer M Fulton BR Giardina G Grévy S Guillemaud-Mueller D Hanappe F Heusch B Jones KL Jonson B Le Brun C Leenhardt S Lewitowicz M Lopez MJ Markenroth K Mueller AC Nilsson T Ninane A Nyman G de Oliveira F Piqueras I Riisager K Saint Laurent MG Sarazin F Singer SM Sorlin O Stuttgé L 《Physical review letters》2001,86(4):600-603
The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation. 相似文献
226.
Yaouanc A Dalmas De Reotier P Gygax FN Schenck A Amato A Baines C Gubbens PC Kaiser CT de Visser A Keizer RJ Huxley A Menovsky AA 《Physical review letters》2000,84(12):2702-2705
The magnetic response of the heavy fermion superconductor UPt3 has been investigated on a microscopic scale by muon Knight shift studies. Two distinct and isotropic Knight shifts have been found for the field in the basal plane. While the volume fractions associated with the two Knight shifts are approximately equal at low and high temperatures, they show a dramatic and opposite temperature dependence around T(N). Our results are independent on the precise muon localization site. We conclude that UPt3 is characterized by a two component magnetic response. 相似文献
227.
Niering M Holzwarth R Reichert J Pokasov P Udem T Weitz M Hansch TW Lemonde P Santarelli G Abgrall M Laurent P Salomon C Clairon A 《Physical review letters》2000,84(24):5496-5499
We report on an absolute frequency measurement of the hydrogen 1S-2S two-photon transition in a cold atomic beam with an accuracy of 1.8 parts in 10(14). Our experimental result of 2 466 061 413 187 103(46) Hz has been obtained by phase coherent comparison of the hydrogen transition frequency with an atomic cesium fountain clock. Both frequencies are linked with a comb of laser frequencies emitted by a mode locked laser. 相似文献
228.
Tracking susceptibility effects is a convenient way to detect small inclusions in a bulk tissue matrix by MRI. We propose a quantitative assessment of these susceptibility effects by simultaneously mapping T(2)* and magnetic field from the time course of magnitude and phase using a multiple GE sequence at 4.7 T. A high-pass scheme is also introduced to highlight the mesoscopic magnetic field variations due to local susceptibility differences specifically in the magnetic field map. Applying this method to muscle tissue, we demonstrate that connective tissue generates detectable susceptibility effects through concomitant local magnetic field variation and T(2)* shortening. 相似文献
229.
Olivier Lagrille Jacques Taillades Laurent Boiteau Auguste Commeyras 《Journal of Physical Organic Chemistry》2007,20(4):271-284
Nitrosation of N‐carbamoylamino acids (CAA) by gaseous NO + O2, an interesting synthetic pathway to amino acid N‐carboxyanhydrides (NCA), alternative to the phosgene route, was investigated on N‐carbamoyl‐valine either in acetonitrile suspension or solventless conditions, and compared to the classical nitrosating system NaNO2 + CF3COOH (TFA), the latter being quite less efficient in terms of either rate, stoichiometric demand, or further tractability of the product. The rate and efficiency of the NO + O2 reaction mainly depends on the O2/NO ratio. Evaluation of the contribution of various nitrosating species (N2O3, N2O4, HNO2) through stoichiometric balance showed the reaction to be effected mostly by N2O3 for O2/NO ratios below 0.3, and by N2O4 for O2/NO ratios above 0.4. The relative contribution of (subsequently formed) HNO2 always remains minor. Differential scanning calorimetry (DSC) monitoring of the reaction in the solid phase by either HNO2 (from NaNO2 + TFA), gaseous N2O4 or gaseous N2O3, provides the associated rate constants (ca. 0.1, 2 and 108 s?1 at 25°C, respectively), showing that N2O3 is by far the most reactive of these nitrosating species. From the DSC measurement, the latent heat of fusion of N2O3, 2.74 kJ · mol?1 at ?105 °C is also obtained for the first time. The kinetics was investigated under solventless conditions at 0°C, by either quenching experiments or less tedious, rough calorimetric techniques. Auto‐accelerated, parabolic‐shaped kinetics was observed in the first half of the reaction course, together with substantial heat release (temperature increase of ca. 20°C within 1–2 min in a 20‐mg sample), followed by pseudo‐zero‐order kinetics after a sudden, important decrease in apparent rate. This kinetic break is possibly due to the transition between the initial solid‐gas system and a solid‐liquid‐gas system resulting from water formation. Overall rate constants increased with parameters such as the specific surface of the solid, the O2/NO ratio, or the presence of moisture (or equivalently the hydrophilicity of the involved CAA), however without precise relationship, while the last two parameters may directly correlate to the increasing acidity of the medium. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
230.
Thanh Nam Nguyen Monique Thual Laurent Provino Nick Traynor 《Optics Communications》2007,278(1):60-65
We present a novel and simple method to measure both the value of the second-order dispersion coefficient and the nonlinear coefficient in optical fibers. This method is based on the higher-order soliton-effect pulse compression phenomenon and is valid for dispersion values greater than 0.5 ps/km/nm. A non-zero dispersion-shifted fiber, a standard single-mode fiber and a highly-dispersive highly-nonlinear fiber have been measured using this method. 相似文献