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21.
22.
Schneider MJ Vazquez-Moreno L Bermudez-Almada Mdel C Guardado RB Ortega-Nieblas M 《Journal of AOAC International》2005,88(4):1160-1166
An efficient multiresidue method for analysis of fluoroquinolones in shrimp has been developed in which quantitation by fluorescence and confirmation by Multiple Stage Mass Spectrometry (MS) is achieved simultaneously. In this method, shrimp tissue is extracted with ammoniacal acetonitrile and the extract is defatted and then evaporated. After dissolution in basic phosphate buffer, fluoroquinolones in the extract are separated by liquid chromatography and quantitated, taking advantage of their intense fluorescence. Eluate from the fluorescence detector enters the MS, which allows for confirmation by monitoring ratios of 2 prominent product ions in the MS3 or MS2 spectrum. Using this method, 8 fluoroquinolones have been analyzed in shrimp samples fortified at 10, 25, 50, or 100 ppb levels. Recoveries for desethyleneciprofloxacin, norfloxacin, ciprofloxacin, danofloxacin, enrofloxacin, orbifloxacin, sarafloxacin, and difloxacin ranged from 75 to 92%, with relative standard deviation values of <6%. The limits of quantitation ranged from 0.1 to 1 ng/g. Enrofloxacin and ciprofloxacin were also successfully determined in enrofloxacin-incurred shrimp using this method. 相似文献
23.
The aim of this research was to investigate new bulky electron donors (EDs) generating hindered active species in the cationic polymerization of 1,3-pentadiene initiated by AlCl3 in pentane, in order to avoid or strongly reduce the reaction between the active species and the double bonds of the polymer which are responsible for side reactions. At room temperature, the polymerization in the presence of new ED, such as OPh2, N(PhBr)3, NPh3 and SPh2, allowed to obtain higher conversions and lower insoluble fractions than without electron donor. The formation of a complex ED/AlCl3 was shown for each electron donor. However, in the case of NPh3 and SPh2, variations of the polymer microstructure demonstrated an interaction between active species and these EDs. Similar results were obtained at lower temperature (−10 °C). The beneficial effect of the presence of electron donors such as NPh3 and SPh2 demonstrated the validity of the concept of sterically hindered active species, but the polymerization was still uncontrolled. 相似文献
24.
[reaction: see text] Double phosphinylation of propargylic alcohols with diphenylphosphine oxide in the presence of a thiolate-bridged diruthenium complex as catalyst gives the corresponding 2,3-bis(diphenylphosphinyl)-1-propenes in high yields with a complete selectivity. 相似文献
25.
The effect of isocyanides as axial ligands on the formation and stability of verdoheme by oxidation has been examined. The reaction of [Fe(III)(OEPO)]2 with t-butyl isocyanide under dioxygen-free conditions results in the formation of (t-BuNC)2Fe(II)(OEPO*) with an electron paramagnetic resonance at g=2.009 with a peak-to-peak separation of 23.5 G at 4 K. (OEPO is the trianion of octaethyloxophlorin and OEPO* is the radical dianion obtained from OEPO by one-electron oxidation.) Exposure of chloroform solutions of either (2,6-xylylNC)2Fe(II)(OEPO*) or (t-BuNC)2Fe(II)(OEPO*) to dioxygen followed by the addition of ammonium hexafluorophosphate results in their transformation into the diamagnetic verdohemes, [(2,6-xylylNC)2Fe(II)(OEOP)](PF6) and [(t-BuNC)2Fe(II)(OEOP)](PF6), yields 68 and 70%, respectively. (OEOP is the anion of octaethyl-5-oxaporphyrin.) The oxidation reactions of (2,6-xylylNC)2Fe(II)(OEPO*) and (t-BuNC)2Fe(II)(OEPO*) have also been monitored by 1H NMR spectroscopy. No resonances due to paramagnetic products could be detected, the reactions appear to result only in the formation of the diamagnetic verdohemes, and the products are not susceptible to further oxidation. 相似文献
26.
Harrop TC Olmstead MM Mascharak PK 《Journal of the American Chemical Society》2004,126(45):14714-14715
The Ni(II)-dicarboxamido-dithiolato complexes (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) were used as Nid metallosynthons in the construction of higher nuclearity dinuclear Ni-Cu and Ni-Ni species to model the bimetallic Mp-Nid site of the A-cluster of acetyl coenzyme A synthase/CO dehydrogenase (ACS/CODH). Reaction of 1 with [Cu(neo)Cl] and [Ni(terpy)Cl2] in MeCN affords the dinuclear complexes (Et4N)[Cu(neo)Ni(NpPepS)] (3) and [Ni(terpy)Ni(NpPepS)] (4), respectively. Reaction of 2 with [Ni(dppe)Cl2] in MeCN yields [Ni(dppe)Ni(PhPepS)] (6). The Ni-Cu complex 3 exhibits no redox chemistry at the Nid site and no reaction with CO. In contrast, the Nip sites in 4 and 6 are readily reduced (characterized by their Ni(I) EPR spectra) and bind CO, exhibiting nuco bands at 2044 and 1997 cm-1, respectively, indicating terminal CO binding. The present Ni-Ni systems replicate the structural and chemical properties of the A-cluster site in ACS/CODH and support the presence of Ni at Mp in the catalytically active enzyme. 相似文献
27.
Prof. Dr. Skye Fortier José Veleta Dr. Amélie Pialat Jennifer Le Roy Kamran B. Ghiassi Prof. Dr. Marilyn M. Olmstead Dr. Alejandro Metta‐Magaña Prof. Dr. Muralee Murugesu Prof. Dr. Dino Villagrán 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):1931-1936
After more than 50 years, the synthesis and electronic structure of the first and only reported “U0 complex” [U(bipy)4] ( 1 ) has been reinvestigated. Additionally, its one‐electron reduced product [Na(THF)6][U(bipy)4] ( 2 ) has been newly discovered. High resolution crystallographic analyses combined with magnetic and computational data show that 1 and its derivative 2 are best described as highly reduced species containing mid‐to‐high‐valent uranium ligated by redox non‐innocent ligands. 相似文献
28.
The synthesis, characterization and in situ catalytic performance of new unsymmetric N,N′‐disubstituted imidazolium‐based dicationic salts in Mizoroki–Heck coupling of acrylates with aryl bromides under aerobic conditions are described. A series of flexible dicationic salts with varying steric and electronic properties were synthesized in good to excellent yields. All the salts were well characterized using spectroscopic techniques. X‐ray diffraction analysis of two salts with the same dicationic backbone and different counter anions shows that the ligand adopts two different conformations which are influenced by the nature of the anion. Thus, the ligand is capable of changing its conformation according to the change in environment due to its flexible nature. All the synthesized imidazolium salts were found to be active in in situ palladium‐catalysed Mizoroki–Heck coupling under aerobic conditions. Amongst the salts, the hydroxyl‐functionalized imidazolium salt, incorporating the features of both bidentate chelating O,O ligand and carbene, shows the maximum catalytic activity. A variety of aryl and heteroaryl methyl and ethyl cinnamates were synthesized using these imidazolium salts as preligands. In addition, NMR studies confirm in situ generation of normal N‐heterocyclic carbenes from the C‐2 position of imidazol‐2‐ylidene ring. The mercury poisoning test was also performed to ascertain the nature of catalytically active palladium species. Aerobic conditions, low catalytic loading (0.5 mol%), shorter reaction times, broad functional group tolerance and good to excellent isolated yields are some of the significant features of the novel catalytic systems described here. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
29.
30.
Dr. Amineh Aghabali Sharon Jun Prof. Dr. Marilyn M. Olmstead Prof. Dr. Alan L. Balch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18908-18915
The photochemical reaction of piperazine with C70 produces a mono‐adduct (N(CH2CH2)2NC70) in high yield (67 %) along with three bis‐adducts. These piperazine adducts can combine with various Lewis acids to form crystalline supramolecular aggregates suitable for X‐ray diffraction. The structure of the mono‐adduct was determined from examination of the adduct I2N(CH2CH2)2NI2C70 that was formed by reaction of N(CH2CH2)2NC70 with I2. Crystals of polymeric {Rh2(O2CCF3)4N(CH2CH2)2NC70}n?nC6H6 that formed from reaction of the mono‐adduct with Rh2(O2CCF3)4 contain a sinusoidal strand of alternating molecules of N(CH2CH2)2NC70 and Rh2(O2CCF3)4 connected through Rh?N bonds. Silver nitrate reacts with N(CH2CH2)2NC70 to form black crystals of {(Ag(NO3))4(N(CH2CH2)2NC70)4}n?7nCH2Cl2 that contain parallel, nearly linear chains of alternating (N(CH2CH2)2NC70 molecules and silver ions. Four of these {Ag(NO3)N(CH2CH2)2NC70}n chains adopt a structure that resembles a columnar micelle with the ionic silver nitrate portion in the center and the nearly non‐polar C70 cages encircling that core. Of the three bis‐adducts, one was definitively identified through crystallization in the presence of I2 as 12{N(CH2CH2)2N}2C70 with addends on opposite poles of the C70 cage and a structure with C2v symmetry. In 12{I2N(CH2CH2)2N}2C70, individual 12{I2N(CH2CH2)2N}2C70 units are further connected by secondary I2???N2 interactions to form chains that occur in layers within the crystal. Halogen bond formation between a Lewis base such as a tertiary amine and I2 is suggested as a method to produce ordered crystals with complex supramolecular structures from substances that are otherwise difficult to crystallize. 相似文献