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排序方式: 共有170条查询结果,搜索用时 484 毫秒
41.
Nicole Kunesch Yves Rolland Jacques Poisson P. L. Majumder R. Majumder A. Chatterjee Vincent C. Agwada Jorge Naranjo Manfred Hesse Hans Schmid 《Helvetica chimica acta》1977,60(8):2854-2859
The Structure of bis-indoline alkaloids of a novel type The structure of folicangine 4 , a bis-indoline alkaloid from the leaves of Voacanga africana, is obtained by correlation with voafolidine 3a and isovoafolidine 3b . It requires an ether bridge between the two parts of the molecule, as in subsessiline (amataine 5a ). Subsessiline-lactone, from the leaves of Voacanga thouarsii has structure 5b proved by correlation with 5a . The CD. curves of double-indole alkaloids of vobtusine type are given (Table 3). 相似文献
42.
Ha-Thi MH Shafizadeh N Poisson L Soep B 《Physical chemistry chemical physics : PCCP》2010,12(45):14985-14993
The time evolution of electronically excited heme (iron II protoporphyrin IX, [Fe(II) PP]) and its associated salt hemin (iron III protoporphyrin IX chloride, [Fe(III) PP-Cl]), has been investigated for the first time in the gas phase by femtosecond pump-probe spectroscopy. The porphyrins were excited at 400 nm in the S(2) state (Soret band) and their relaxation dynamics was probed by multiphoton ionization at 800 nm. This time evolution was compared with that of the excited state of zinc protoporphyrin IX [Zn PP] whose S(2) excited state likely decays to the long lived S(1) state through a conical intersection, in less than 100 fs. Instead, for [Fe(II) PP] and [Fe(III) PP-Cl], the key relaxation step from S(2) is interpreted as an ultrafast charge transfer from the porphyrin excited orbital π* to a vacant d orbital on the iron atom (ligand to metal charge transfer, LMCT). This intermediate LMCT state then relaxes to the ground state within 250 fs. Through this work a new, serendipitous, preparation step was found for Fe(II) porphyrins, in the gas phase. 相似文献
43.
Joël Poisson 《Journal of organometallic chemistry》2010,695(23):2557-2561
The biologically important heterocycles pyrrole, C4H4N, and indole, C8H6N, ought to be useful as reagents in organic synthesis. Unfortunately, working with them has proved to be difficult because they tend to self-polymerize in solution, especially in the presence of acid catalysts. When the self-polymerization can be controlled, however, the pyrrole and indole units should provide an important route to selective N-metal binding, particularly when these ligands are activated by alkyl-lithium reagents. Using this approach, a general synthesis of the group 14 pyrrolides and indolides, Ph3MX (M = Si, Ge, Sn; X = C4H4N, C8H6N), has been developed and the results are reported here. The compounds are formed as high-melting, white crystalline solids and have been characterized by 13C-, 29Si- and 119Sn-NMR, Raman and electron-impact mass spectroscopy as well as elemental analysis. A single-crystal X-ray study of Ph3Si(C4H4N) has shown that the compound is disordered in the tetragonal lattice, even at low temperature (100 K). 相似文献
44.
45.
46.
M. Sablier H. Mestdagh L. Poisson N. Leymarie C. Rolando 《Journal of the American Society for Mass Spectrometry》1997,8(6):587-593
Fragmentation of electron-impact-generated organic molecular cations, submitted to low-energy collisions with hydrogen in a MS/MS/MS multiquadrupole mass spectrometer, was promoted or significantly increased in the presence of atomic hydrogen generated from a microwave discharge. Loss of hydrogen alpha to a heteroatom and bond cleavage alpha to a carbonyl group are the major H-induced fragmentation pathways. 相似文献
47.
Green J Tyrrell Z Radosz M Hong K Mays JW 《The journal of physical chemistry. C, Nanomaterials and interfaces》2011,115(19):9465-9470
In contrast to incompressible liquid solutions, compressible near-critical solutions of block copolymers allow for controlling rapid structure transformations with pressure alone. For example, when dissolved in near-critical propane, polystyrene-block-polybutadiene can form a random molecular solution at high pressures, a micellar solution at moderate pressures, and a solvent-free precipitate at low pressures. In contrast to the unstructured virgin copolymer, such a propane-treated precipitate rapidly self assembles toward structures characteristic of equilibrated block copolymers, such as lamellae, spheres or cylinders, which depend on the block ratio rather than on the decompression rate or temperature, at least within the rate and temperature ranges investigated in this work. At lower temperatures, however, say below 40 °C, glass transition of the styrene-butadiene diblocks can inhibit independent structure formation while crystallization of their hydrogenated-butadiene analogs can preserve the micellar-solution structure. 相似文献
48.
Ling Chen Dr. Thi Minh Thi Le Prof. Dr. Jean-Philippe Bouillon Prof. Dr. Thomas Poisson Prof. Dr. Philippe Jubault 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(42):e202201254
The catalytic asymmetric synthesis of highly functionalized cyclopropanes from α-substituted allyl sulfones and silanes is reported. The reaction, using α-aryl diazoacetates or diacceptor diazo reagents, catalyzed by a chiral rhodium complex (Rh2((S)-BTPCP)4), furnished the corresponding cyclopropanes in moderate to high yields (27–97 %), high diastereoselectivities (68 : 32 to 20 : 1 d.r.) and moderate to excellent ee (40–99 %). This methodology offers a privileged access to an underexplored class of enantioenriched cyclopropanes with a high level of functionality, an asset for further post-functionalization and their incorporation into more complex structure. 相似文献
49.
Comprehension of wall-injection flow in a channel in the presence of different geometric discontinuities is necessary as part of the general investigations concerning combustion instabilities of solid propellant rocket motors. In order to characterise the aerodynamic flow field and to evaluate the influence of an obstacle inside a porous channel in such a case, experimental studies were conducted on a 1/40 scale model of the new ARIANE V motor. In fact, the flow is only induced by wall-injection and the presence of an obstacle creates a particular shear layer development in the obstacle wake. Particular attention was given to the unstable dynamic conditions of the shear layer. A thermal seeding of the shear layer was made in order to qualify the heat transfer therein, and especially to emphasise the turbulent structure development. Transverse and longitudinal spatial correlations were measured to characterise turbulence scales in the shear layer. At the origin of the shear layer, the decay of turbulence memory is found to be similar to that observed in a forced flow boundary layer, but the injecting wall modifies the change in structures. The wall flow is found to preserve the turbulent structures in such a way that the turbulence memory predominates in a longitudinal direction.List of Symbols
f
frequency (Hz)
-
h
channel height (m)
-
h
v
obstacle height (m)
-
L
mean dimension of large structures (m)
-
P
pressure (Pa)
-
m
mass flow rate (kg/s)
-
r
distance between probes in X direction (m)
-
r
+(–)
distance between probes in Y direction (m)
-
u
longitudinal velocity in X direction (m/s)
-
v
transversal velocity in Y direction (m/s)
-
T
temperature (K)
-
x,y,z
axis system (m)
-
t
= T-T
amb
(K)
-
v
kinematic viscosity (mVs)
-
density (kg/m3)
-
characteristic porous size (urn)
-
u
longitudinal rms (m/s)
-
I
u
dynamic turbulence intensity
u
/u
max
-
I
T
thermal turbulence intensity
-
M
Mach number u/a
-
Re
w
wall Reynolds number v
w
h/v
-
Re
c
longitudinal Reynolds number u
c
h/v
-
R
uT
thermal dynamic correlation coefficient
-
St
Strouhal number fh/u
-
X,Y,Z
axis system normalised by the channel height h
-
X
S
longitudinal position of the obstacle
-
X
X-X
S
- amb
ambient reference
-
c
flowing cavity
- fav
head end
-
l
lateral direction
-
g
longitudinal direction max maximum at a longitudinal position
-
w
wall
The authors thank the CNES for its financial support, and in particular E. Robert and R. Bee. 相似文献
50.
Samuel A. Meek Antonin Poisson Guy Guelachvili Theodor W. Hänsch Nathalie Picqué 《Applied physics. B, Lasers and optics》2014,114(4):573-578
We characterize a new mid-infrared frequency comb generator based on difference frequency generation around 3.1 μm. High power per comb mode (>10?7 W/mode) is obtained over a broad spectral span (>750 nm, >790 cm?1). The source is used for direct absorption spectroscopy with a Michelson-based Fourier transform interferometer. 相似文献