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61.
Jinmao You Yanyan Fu Zhiwei Sun Yourui Suo 《Analytical and bioanalytical chemistry》2010,396(7):2657-2666
2-(5-Benzoacridine)ethyl-p-toluenesulfonate (BAETS), a dual-sensitive probe, was reacted with bile acids in the presence of K2CO3 catalyst in dimethyl sulfoxide (DMSO) solvent to give BAETS–bile acid derivatives. Derivatives exhibited intense fluorescence
(FL) with an excitation maximum at λ
ex 270 nm and an emission maximum at λ
em 510 nm. MS analysis using APCI-MS indicated that derivatives had excellent APCI-MS ionizability with percentage ionization
δ values changing from 0 to 88.83% in aqueous acetonitrile and from 0 to 89.15% in aqueous methanol. The collision induced
dissociation spectra of m/z [M + H]+ contained specific fragment ions at m/z [M + H−H2O]+, [M + H−2H2O]+, [M + H−3H2O]+, 347.3, and 290.1. Repeatability was good for LC separation of BAETS–bile acid derivatives with aqueous acetonitrile as mobile
phase. The relative standard deviations (RSDs) of retention time and peak area at 6.6 nmol mL−1 levels with fluorescence detection (FL) were from 0.045 to 0.072% and from 2.16 to 2.73%, respectively. Excellent linear
responses were observed, with regression coefficients >0.9995. The FL detection limits (S/N = 3) were in the range of 18.0–36.1 fmol. The online APCI-MS detection limits are in the range of 500–790 fmol (at a signal-to-noise
ratio of 3). 相似文献
62.
Multiconfiguration Dirac-Fock (MCDF) method was employed to calculate the first five ionization potentials, electron affinities, resonance excitation energies, oscillator strengths, and radii for the element Uus and its homologue At. Main valence correlation effects were taken into account. The Breit interaction and QED effects were also estimated. The uncertainties of calculated IPs, EAs, and IR for Uus and At were reduced through an extrapolation procedure. The good consistency with available experimental and other theoretical values demonstrates the validity of the present results. These theoretical data therefore can be used to predict some unknown physicochemical properties of element Uus, Astatine, and their compounds. 相似文献
63.
Two kinds of online preconcentration techniques including large-volume sample stacking-sweeping and selective-exhaustive injection-sweeping (SEI-S) were employed in CE to develop a rapid, simple and sensitive method for determination of melamine (MM) and its derivatives such as ammeline (AMN), ammelide (AMD) and cyanuric acid (CA) in liquid milk products. Though the sensitivity of large-volume sample stacking-sweeping is not particularly high, it can be used to detect all the four compounds simultaneously. However, it is very difficult to improve the sensitivity of these four compounds by using single SEI-S method directly, owing to their completely different extents of protonation or deprotonation. Grouping can solve this problem perfectly. After the four compounds are divided into two groups (MM/AMN and AMD/CA), cation-SEI-S or anion-SEI-S can be applied for their online stacking. In cation-SEI-S, the detection limits for MM and AMN were both 0.01 ng/mL based on the signal-to-noise ratio of 3. In anion-SEI-S, the detection limits were 0.05 and 0.02 ng/mL for CA and AMD, respectively. Results of this study show a great potential for the SEI-S method to be a useful tool for the rapid and sensitive determination of MM and its derivatives in liquid milk products. 相似文献
64.
An efficient palladium-catalyzed AAA reaction with a simple α-sulfonyl carbon anion as nucleophiles is presented for the first time. Allyl fluorides are used as superior precursors for the generation of π-allyl complexes that upon ionization liberate fluoride anions for activation of silylated nucleophiles. With the unique bidentate diamidophosphite ligand ligated palladium as catalyst, the in situ generated α-sulfonyl carbon anion was quickly captured by the allylic intermediates, affording a series of chiral homo-allylic sulfones with high efficiency and selectivity. This work provides a mild in situ desilylation strategy to reveal nucleophilic carbon centers that could be used to overcome the pKa limitation of “hard” nucleophiles in enantioselective transformations.A variety of “hard” α-sulfonyl carbanions of aryl, heteroaryl and alkyl sulfones were successfully employed as nucleophiles in palladium-catalyzed asymmetric allylic alkylation with excellent enantioselectivities. 相似文献
65.
66.
YANG Peizhi DENG Peizhen HUANG Guosong ZHAO Zhiwei CHEN Wei XU Jun 《Chinese Journal of Lasers》2000,9(1):91-96
1 Introduction Recently,withthedevelopmentofhighperformanceInGaAsdiodelasersinthewavelengthrangebetween0.9and1.1μm[1],greatatte... 相似文献
67.
68.
三线摆振动周期与角振幅的关系 总被引:2,自引:0,他引:2
本根据机械能守恒定律推出了三线摆的振动周期和角振幅的关系,并据该关系式讨论了角振幅对周期的影响以及角振幅的确定。 相似文献
69.
给出了三维回旋自共振微波放大器(CARM)的电于运动方程和光场演化方程,并在忽略束流空间电荷效应的前提下,编制了单模放大器程序。利用数值模拟详细考察了电子束束流质量对微波输出功率的影响,模拟结果与实验值符合得很好。 相似文献
70.
A facile way for preparing tin nanoparticles from bulk tin via ultrasound dispersion 总被引:3,自引:0,他引:3
In this paper, we reported a facile and rapid process to prepare tin nanoparticles from bulk tin via ultrasound dispersion. The morphology and structure of synthesized tin nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and thermogravimetric analysis (TGA). The results show that the morphology of tin nanoparticles is spherical and the structure of tin nanoparticles has the same crystal structure as the bulk tin. In addition, the tribological property of tin nanoparticles as additives in oil is evaluated on a four-ball tester and the results show that tin nanoparticles exhibit good performance in wear. 相似文献