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11.
12.
L. I. Alekseeva V. V. Volodin V. G. Luksha R. Lafont 《Chemistry of Natural Compounds》1999,35(5):532-534
The compounds 20-hydroxyecdysone-22-acetate and viticosterone E (20-hydroxyecdysone-25-acetate) are observed for the first
time inAjuga reptans L. growing at the northern limit of its range in a middle taiga subzone of European northeastern Russia.
Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 607–610, September–October, 1999. 相似文献
13.
Blandine Destrez Gaud Pinel Emmanuelle Bichon Fabrice Monteau Ren Lafont Bruno Le Bizec 《Rapid communications in mass spectrometry : RCM》2008,22(24):4073-4080
Ecdysteroids, which are steroid hormones in invertebrates, but which are also present in plants, could potentially be used as anabolic agents in food‐producing animals. The control of ecdysteroid misuse in cattle relies on the development of an efficient method for their detection in biological matrices at trace levels (µg L−1). In order to propose an analytical procedure dedicated to the identification of excreted 20‐hydroxyecdysone (20E) in urine and faecal samples of breeding animals, a comparative study of the spectrometric behaviour of these compounds was carried out both by LC/(ESI‐)/HRMSn (hybrid linear ion trap – orbital trap) and by LC/(ESI+)/MS/MS (triple quadrupole). This study revealed the formation of a large number of product ions both in positive and negative ion mode, corresponding to losses of water molecules and specific cleavages on the side chain. The sample preparation consisted of sequential purification on two solid‐phase extraction cartridges (SPE octadecylsilyl and SPE silica). The detection limits were around 0.5 µg L−1 in the selected reaction monitoring (SRM) mode and recoveries above 60% were obtained. The method was successfully applied to the analysis of real samples collected from calves treated with 60 mg 20E over 4 days. Analysis of the samples allowed the investigation of the kinetics of elimination of 20E in calf urine and determination of the time‐frame for the control of potential abuse. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
14.
Dominique Simon Olivier Lafont Claude Combet Farnoux Marcel Miocque 《Journal of heterocyclic chemistry》1985,22(6):1551-1557
Reactivity of 2-susbituted chalcones against diaza binucleophiles (hydrazines, thiourea, guanidine) has been studied. Various heterocycles (pyrazoles, pyrazolines, pyrimidines) or substituted hydrazines were obtained. A general interpretation is given according to the substituent of the enone system, R, the nature of binucleophile and the medium. 相似文献
15.
16.
The product distributions from bifunctional conversion ofn-decane over Pt/SAPO-5 and Pt/SAPO-11 catalysts are compared in detail. Selectivities in decane reaction vary largely with
the catalyst employed: Pt/SAPO-11 produces high yields of feed isomers, whereas Pt/SAPO-5 gives high yields of cracked products
and only under mild reaction conditions are isodecanes the main products obtained. These selectivities seem to be determined
by the structure of the catalyst. 相似文献
17.
N. S. Tabrizi Q. Xu N. M. van der Pers U. Lafont A. Schmidt-Ott 《Journal of nanoparticle research》2009,11(5):1209-1218
Short spark discharges (2 μs) were successfully applied to generate mixed particles a few nanometres in diameter by fast quenching.
Alloyed Cr–Co electrodes were applied to demonstrate this. Further it was shown that if the anode and the cathode are different
materials, the discharge process mixes the vapour of both materials, forming mixed nanoparticles. Electron microscopy (TEM,
SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses were performed on the collected particles
to study their size, morphology, composition and structure. The average compositions of the particles were measured by inductively
coupled plasma (ICP). In addition, online measurements of the particle size distribution by mobility analysis were carried
out. In the case of alloyed electrodes (Cr–Co), the relative concentration of the elements in the nanoparticulate sample was
consistent with the electrode composition. When using electrodes of different metals (Au–Pd and Ag–Pd) the individual nanoparticles
showed a range of mixing ratios. No surface segregation was observed in these mixed noble metal particles. Crystalline nanoparticulate
mixed phases were found in all cases. 相似文献
18.
N. S. Tabrizi M. Ullmann V. A. Vons U. Lafont A. Schmidt-Ott 《Journal of nanoparticle research》2009,11(2):315-332
The production of nanoparticles by microsecond spark discharge evaporation in inert gas is studied systematically applying
transmission electron microscopy, mobility analysis and BET surface area measurement. The method of spark discharge is of
special interest, because it is continuous, clean, extremely flexible with respect to material, and scale-up is possible.
The particle size distributions are narrow and the mean primary particle size can be controlled via the energy per spark.
Separated, unagglomerated particles, 3–12 nm in size, or agglomerates can be obtained depending on the flow rate. The nanoparticulate
mass produced is typically 5 g/kWh. A formula is given, which estimates the mass production rate via thermal conductivity,
evaporation enthalpy and the boiling point of the material used. We showed that with gas purified at the spot, the method
produced gold particles that were so clean that sintering of agglomerated particles occurred at room temperature. The influence
of a number of parameters on the primary particle size and mass production rate was studied and qualitatively understood with
a model of Lehtinen and Zachariah (J Aerosol Sci 33:357–368, 2002). Surprisingly high charging probabilities for one polarity
were obtained. Spark generation is therefore of special interest for producing monodisperse aerosols or particles of uniform
size via electrical mobility analysis. Qualitative observations in the present study include the phenomenon of material exchange
between the electrodes by the spark, which opens the possibility of producing arbitrary mixtures of materials on a nanoscale.
If spark generation of nanoparticles is performed in a standing or almost standing gas, an aerogel of a web-like structure
forms between surfaces of different electrical potential. 相似文献
19.
Gerard Descotes Dominique Lafont Denis Sinou 《Journal of organometallic chemistry》1978,150(1):C14-C16
High optical yields are obtained in the hydrogenation of α-amino acid precursors rising [Rh(COD)dioxop] + ClO4? in presence of triethylamine as catalyst. 相似文献
20.
N. Z. Mamadalieva L. N. Zibareva Z. Saatov R. Lafont 《Chemistry of Natural Compounds》2003,39(2):199-203
The known ecdysteroids polipodin B, 2-deoxyecdysterone, ecdysterone, 26-hydroxypolipodin B, integristerone A, and sileneosides A and D were observed in the aerial part of Silene viridiflora L. (Caryophyllaceae). 26-Hydroxypolipodin B was observed in this species for the first time. 相似文献