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991.
Małgorzata Olejnik Teresa Szprengier-Juszkiewicz Piotr Jedziniak Jan Żmudzki 《Accreditation and quality assurance》2007,12(12):637-641
In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the
data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole
and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical
approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole
in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted.
Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in
PT 0270 are questionable. 相似文献
992.
Single-armed, 15- and 18-membered lariat ether receptor systems having indolylethyl side arms bind Na+ and K+ in the ring. The indole residue serves as a pi-donor to the ring-bound cation. Whether the five- or six-membered ring interacts most directly with Na+ or K+ depends on whether the sidearm is attached to indole's 3- or 5-position. This suggests that structural as well as electronic factors are important in pi-complexation of alkali metal cations. 相似文献
993.
研究了水溶性钌-膦配合物催化肉桂醛选择加氢反应中,相转移剂和表面活性剂对反应转化率和选择性的影响,考察了表面活性剂CTAB(十六烷基三甲溴化铵)浓度以及影响两相界面性质的因素—水相和有机相体积比、有机溶剂的改变等的影响.结果表明,相转移剂可以促进反应进行,其中以季铵盐相转移剂最好;表面活性剂能够显著地加快反应,其中以阳离子表面活性剂的效果最佳,且分子中含有长链烷基者(如CTAB)效果更好,非离子和阴离子表面活性剂的效果较差;对于CTAB,其浓度的增加导致反应速度的明显加快,但CTAB浓度达到1.65×10-2mol/L之后,反应体系乳化严重,反应完成后,两相分离变得困难.而增加水相体积和加入适当的有机溶剂,有利于转化率和选择性的提高. 相似文献
994.
Desorption/ionization on silicon mass spectrometry (DIOS-MS) is a matrix-free technique that allows for the direct desorption/ionization of low-molecular-weight compounds with little or no fragmentation of analytes. This technique has a relatively high tolerance for contaminants commonly found in biological samples. DIOS-MS has been applied to determine the activity of immobilized enzymes on the porous silicon surface. Enzyme activities were also monitored with the addition of a competitive inhibitor in the substrate solution. It is demonstrated that this method can be applied to the screening of enzyme inhibitors. Furthermore, a method for peptide mapping analysis by in situ digestion of proteins on the porous silicon surface modified by trypsin, combined with matrix-assisted laser desorption/ionization-time of flight-MS has been developed. 相似文献
995.
Wang M Wang BM Shi L Tu YQ Fan CA Wang SH Hu XD Zhang SY 《Chemical communications (Cambridge, England)》2005,(44):5580-5582
A quinine/Selectfluor combination inducing rearrangement reaction of allylic alcohols was discovered, which involved a moderate yield with good enantioselective construction of alpha-quaternary carbon center and beta-fluoro aldehyde under base condition. 相似文献
996.
Hu D Croutxé-Barghorn C Feuillade M Carré C 《The journal of physical chemistry. B》2005,109(32):15214-15220
Hybrid sol-gel materials have been prepared by hydrolytic polycondensation of an alkoxysilane. The sol-gel process of methacryloxypropyltrimethoxysilane (MAPTMS) has been followed by fluorescence spectroscopy with 2-naphthol as a probe. The experimental results showed that this photoprobe was dramatically sensitive to the microenvironment polarity. Spectroscopic studies revealed fluctuations of the maximum emission intensity and wavelength as a function of time. These fluctuations were attributed to the amphiphilic behavior of the hydrolyzed precursor. The maximum emission wavelength of the probe corresponding to its protonated form was higher than in pure water. All the results suggest that the presence of water molecules, tightly bonded to the polar head of the silanols, increased locally the sol polarity and induced a red-shifted emission. Fluorescence spectroscopy emphasized the reversibility of monomeric silanol aggregates and the changes in hydroxy group number of the silica network during the sol maturation. The behavior of this system upon shaking confirmed this statement. 相似文献
997.
The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal
bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test
cases, including the bis-ethoxy bridged cluster Os3(μ-OEt)2(CO)10, 1b, and some of its group 15 derivatives Os3(μ-OEt)2(CO)9(EPh3), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic
studies.
In honour of Professor Dieter Fenske on his 65th birthday. 相似文献
998.
Madhushaw RJ Li CL Su HL Hu CC Lush SF Liu RS 《The Journal of organic chemistry》2003,68(5):1872-1877
In the presence of BF3*Et2O, alkynyltungsten complexes underwent [3 + 2] cycloaddition with tethered epoxides to give bicyclic -lactones efficiently. Only one diastereomeric product was formed despite the presence of three stereogenic centers. A mechanism is proposed that involves formation of a tungsten-vinylidenium species via an SN2 attack of the epoxide carbon by an alkynyltungsten group to give a tungsten-enol ether species via counterattack at the central tungsten-vinylidenium carbon by the OBF3- terminus. Most of the tungsten enol ether species were too unstable for isolation and underwent hydrolysis to give only cis-fused -bicyclic lactones. This cyclization works for both cis- and trans-epoxides and tolerates various functional groups. In the case of trans-phenyl epoxide, the reaction led to an addition product via a 6-endo attack of epoxide by the tungsten fragment. This method provides a simple enantiospecific synthesis of complex bicyclic lactones if a chiral epoxide is used in the cyclization. It is also applicable to the one-pot synthesis of bicyclic unsaturated gamma-lactones if a suitable alkynyltungsten functionality is used. 相似文献
999.
利用电荷迁移反应测定头孢羟氨苄 总被引:4,自引:0,他引:4
提出一种基于电荷迁移反应简便可靠地测定头孢羟氨苄的分光光度法。在甲醇-乙醇介质中,头孢羟氨苄与氯冉酸于50℃反应15min能够形成稳定的1:1络合物,其λmax=528nm,线性范围为20 ̄400mg/L。用拟定的方法测定原粉和胶囊,结果与药典法一致。对浓度100mg/L的药物10次测定相对标准偏差为1.4%,样品的标准加入回收率为99.0% ̄100.8%。 相似文献
1000.
The evidence for the stabilizing nature of the H–H bonding in planar biphenyl is succinctly reviewed. The stabilizing nature
of the H–H bonding is revealed through a comparison of the atomic energy of every atom in planar biphenyl with the same atom
in the twisted equilibrium structure. It is shown that the barrier to rotation via the planar transition state is the net
resultant of a stabilisation of the four ortho-hydrogen atoms (by 8 kcal/mol each), a stabilisation of the two para-carbon atoms (by 3 kcal/mol each) and by the dominant destabilisation of the two carbon atoms joining the two rings—the two
junction carbon atoms—(by 22 kcal/mol each). The energetic stabilisation of the four ortho-hydrogen atoms is further shown to be in large proportion due to the formation of the hydrogen–hydrogen interatomic surface.
Furthermore, neither the “bond order” between the two junction carbon atoms nor the total electron delocalisation between
the two rings exhibit a significant change in going from the planar to the twisted equilibrium geometry. These findings are
in contrast with the classical view of a balance between “steric non-bonded repulsion” and better electron delocalisation
as a function of the twist dihedral angle. Similar conclusions have been recently reached by Pacios and Gómez through a study
of the electrostatic potential at the position of the hydrogen nuclei.
We dedicate this article to Professor TM Krygowski on the occasion of his 70th birthday wishing him a long and productive
life. 相似文献