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71.
Guan F Uboh CE Soma LR Luo Y Li R Birks EK Teleis D Rudy JA Tsang DS 《Rapid communications in mass spectrometry : RCM》2002,16(17):1642-1651
Clenbuterol (CBL) is a potent beta(2)-adrenoceptor agonist used for the management of respiratory disorders in the horse. The detection and quantification of CBL can pose a problem due to its potency, the relatively low dose administered to the horse, its slow clearance and low plasma concentrations. Thus, a sensitive method for the quantification and confirmation of CBL in racehorses is required to study its distribution and elimination. A sensitive and fast method was developed for quantification and confirmation of the presence of CBL in equine plasma, urine and tissue samples. The method involved liquid-liquid extraction (LLE), separation by liquid chromatography (LC) on a short cyano column, and pseudo multiple reaction monitoring (pseudo-MRM) by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS). At very low concentrations (picograms of CBL/mL), LLE produced better extraction efficiency and calibration curves than solid-phase extraction (SPE). The operating parameters for electrospray QTOF and yield of the product ion in MRM were optimized to enhance sensitivity for the detection and quantification of CBL. The quantification range of the method was 0.013-10 ng of CBL/mL plasma, 0.05-20 ng/0.1 mL of urine, and 0.025-10 ng/g tissue. The detection limit of the method was 13 pg/mL of plasma, 50 pg/0.1 mL of urine, and 25 pg/g of tissue. The method was successfully applied to the analysis of CBL in plasma, urine and various tissue samples, and in pharmacokinetic (PK) studies of CBL in the horse. CBL was quantified for 96 h in plasma and 288 h in urine post-administration of CLB (1.6 micro g/kg, 2 x daily x 7 days). This method is useful for the detection and quantification of very low concentrations of CBL in urine, plasma and tissue samples. 相似文献
72.
The complexes of poly(methacrylic acid-co-methyl methacrylate) network with poly(ethylene glycol) stabilized byhydrogen bonds were prepared. By introducing the poly(ethylene glycol), a large difference in storage modulus below andabove the glass transition temperature occurred and the complexes exhibited shape memory behaviors. The morphology ofcomplexes was studied by using DSC, WAXD, and DMA. The results indicate that the fixed phase of this kind of novelshape memory materials is the network, and the reversible phase is the amorphous state of PEG:PMAA complex phase. Theshape recoverability almost reaches 100%. This type of complexes can be regarded as a novel shape memory network. 相似文献
73.
离子交换树脂负载Ni—B无定形合金催化剂的制备与性能 总被引:2,自引:0,他引:2
制备了一种新型离子交换树脂负载的Ni-B无定形合金催化剂.用3种树脂作为催化剂载体,即弱酸型阳离子树脂D152,强酸型阳离子树脂D72及强碱型阴离子树脂D261.用XPS、TEM和ICP等技术对催化剂进行了表征.结果表明,催化剂上镍与带有功能基的载体树脂之间有着很强的相互作用,但其强度与所带的功能基有关.3种催化剂Ni2p3/2的XPS谱图上,NiB/D152催化剂的氧化态峰最小,而NiB/D261的氧化态峰最大.异丙醇脱氢反应活性实验证实了这一结果. 相似文献
74.
生物检材中乌头类生物碱的检验 总被引:2,自引:1,他引:2
用薄层 (TLC)、高效液相 光电二极管阵列检测器 (HPLC/DAD)、动物实验等方法对生物检材中乌头生物碱进行检验 ,并对这些方法进行比较。结果发现 ,TLC法为此类药物检验筛选的首选方法 ,最小检出量为 0 3μg。在进行HPLC检测时 ,以乌头生物碱的特征紫外吸收光谱和动物实验结果为重要的定性手段 ,其特征吸收波长为 (2 2 8± 2 )nm和 (2 75± 2 )nm。乌头生物碱在 2mg/L~ 5 0mg/L时其峰面积与质量浓度有很好的线性 ,相关系数为 0 9996。经实际案件证明 ,方法准确、灵敏 ,可用于生物检材中乌头类生物碱的检验。 相似文献
75.
76.
Ab initio molecular orbital theory and density functional theory have been employed to study N14 cluster with low spin at the HF/6-31G*, B3LYP/6-31G*, B3PW91/6-31G*, BP86/6-31G*, and BHLYP/6-31G* levels of theory. Twelve isomers were studied, including one previously investigated cage molecule. The most stable isomer of N14 is a C
2h
-symmetric molecule that contains two separated five-membered nitrogen rings connected by a —N=N—N=N— bridge. The second, third, and fifth most stable isomers each have one five-membered nitrogen ring. The theoretical results suggest that the five-membered nitrogen ring gives rise to a particularly stable structural unit, and the more side chains that the five-membered nitrogen ring links with, the less stable the structure will become. 相似文献
77.
Bing Guan 《Tetrahedron letters》2005,46(36):6041-6044
p-tert-Calix[6]-1,4-2,5-biscrown-4 was subjected to functionalization by benzyl bromide or ethyl bromoacetate. Two pairs of disubstituted calix[6]biscrown stereoisomers were obtained. Their structures had been deduced from 1H NMR and ESI-MS (electrospray ionization mass spectroscopy). One of the bisethyloxycarbonylmethylated derivatives 3a was further investigated by X-ray crystallographic analysis. Two-phase extraction experiments indicated that bisethyloxycarbonylmethylated derivatives exhibited high Cs+/Na+ selectivity. By ESI-MS and 1H NMR experiments it was confirmed that 3a formed 1:1 complex with Cs+. 相似文献
78.
79.
A new fluorinated polystyrene bearing a p-sulbstiuted perfluoro[1-(2-fluorosulfonylethoxy)]ethyl group was synthesized via one-electron oxidation of polystyrene by perfluoro[2-(2-fluorosulfonylethoxy)]propionyl peroxide at different peroxide to polystyrene molar ratios.The yield of perfluoroalkylation decreases with the increase of the reactant molar ratio.The modified polymer has been characterized by various techniques:the ring pefluoro[1-(2-fluorosulfonylethoxy)]ethylation has been proved by FT-IR and ^19FNMR;the X-ray photoelectron spectra(XPS) show the maximum binding energy of F18,O18,C18(two kinds of carbon atoms,namely C-H and C-F)and S2p,respectively; desulfonylation of the fluorinated polystyrene appearing at 217℃ has been found by its thermogravimetric analysis (TGA).The determinations of contact angle,refractive index and glass transition temperature of the modified polymer have disclosed that when the contact angle increases with the increase of the molar ratio,the refractive index and glass transition temperature decrease.The polydispersity values indicate that the degradation of the polymer chains did not occur during the reaction. 相似文献
80.
Unsaturated nucleoside analogues 21, 22, 46, and 54, comprising four- and six-membered rings, were synthesized using two different approaches. The 2-benzyloxycycloalkanones 23a and 23b served as starting materials for both methods. Conversion to methylenecyclobutanes 29a and 29b was followed by addition of bromine via pyridinium perbromide to give vicinal dibromides 30a and 30b. Reaction of 29a with Br2 gave a ring-contracted cyclopropane derivative 31. Alkylation-elimination of adenine with 30a gave bromoalkene 32 as the major product and adenine-containing unsaturated derivatives 33, 34, and 35 as minor components. Vicinal dibromide 30b gave the Zaitsev cyclohexene 45 as the only product. Epoxidation of 29a and 29b afforded oxiranes 36a and 36b which were used in alkylation of adenine to furnish hydroxy derivatives 37a, 37b, 38a, and 38b. Beta-elimination via mesylates 39a and 40a using tBuOK/DMF gave Z- and E-methylenecyclobutanes 34 and 35. With an excess of base the E-bis-methylenecyclobutane 41 was obtained. Mesylation of cyclohexane derivatives 37b and 38b gave the Z- and E-N6-mesylated product 48. By contrast, the N6-benzoyl derivatives 49 and 50 afforded O-mesyl intermediates 51 and 52. Beta-elimination gave both Hofmann and Zaitsev products 53 and 45. O-Debenzylation of 34 and 35, 45, and 53 afforded analogues 21, 22, 46, and 54. The E-isomer 22 was also obtained by hydroboration procedure from E-bis-methylenecyclobutane 41. 相似文献