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61.
Baki B. Sadi Chunsheng Li Gary H. Kramer Cassandra L. Johnson Queenie Ko Edward P. C. Lai 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(2):415-425
A new radioanalytical method was developed for rapid determination of 226Ra in drinking water samples. The method is based on extraction and preconcentration of 226Ra from a water sample to an organic solvent using a dispersive liquid-liquid microextraction (DLLME) technique followed by
radiometric measurement using liquid scintillation counting. In DLLME for 226Ra, a mixture of an organic extractant (toluene doped with dibenzo-21-crown-7 and 2-theonyltrifluoroacetone) and a disperser
solvent (acetonitrile) is rapidly injected into the water sample resulting in the formation of an emulsion. Within the emulsion,
226Ra reacts with dibenzo-21-crown-7 and 2-theonyltrifluoroacetone and partitions into the fine droplets of toluene. The water/toluene
phases were separated by addition of acetonitrile as a de-emulsifier solvent. The toluene phase containing 226Ra was then measured by liquid scintillation counting. Several parameters were studied to optimize the extraction efficiency
of 226Ra, including water immiscible organic solvent, disperser and de-emulsifier solvent type and their volume, chelating ligands
for 226Ra and their concentrations, inorganic salt additive and its concentration, and equilibrium pH. With the optimized DLLME conditions,
the accuracy (expressed as relative bias, B
r
) and method repeatability (expressed as relative precision, S
B
) were determined by spiking 226Ra at the maximum acceptable concentration level (0.5 Bq L−1) according to the Guidelines for Canadian Drinking Water Quality. Accuracy and repeatability were found to be less than −5%
(B
r
) and less than 6% (S
B
), respectively, for both tap water and bottled natural spring water samples. The minimum detectable activity and sample turnaround
time for determination of 226Ra was 33 mBq L−1 and less than 3 h, respectively. The DLLME technique is selective for extraction of 226Ra from its decay progenies. 相似文献
62.
Fourteen conformers of 3-amino-1-propanol as the minima on the potential energy surface are examined at the MP2/6-311++G** level. Their relative energies calculated at B3LYP, MP3 and MP4 levels of theory indicated that two most stable conformers display the in-tramolecular OH…N hydrogen bonds. The vertical ionization energies of these conformers calculated with ab initio electron propagator theory in the P3/aug-cc-pVTZ approximation are in agreement with experimental data from photoelectron spectroscopy. Natural bond orbital analyses were used to explain the differences of IEs of the highest occupied molec-ular ortibal of conformers. Combined with statistical mechanics principles, conformational distributions at various temperatures are obtained and the temperature dependence of pho-toelectron spectra is interpreted. 相似文献
63.
[reaction: see text] The preparation of pyrazoline and isoxazoline derivatives with traceless solid-phase sulfone linker strategy is described. Key steps involved in the solid-phase synthetic procedure include (i) sulfinate S-alkylation, (ii) sulfone anion alkylation, (iii) gamma-hydroxy sulfone --> gamma-ketosulfone oxidation, and (iv) traceless product release via elimination-cyclization. A library of 12 pyrazolines and isoxazolines was synthesized. 相似文献
64.
3, 4′-Bipyridine was synthesized from 6-methoxy-3, 4′-bipyridine or 6-benzyloxy-3, 4′-bipyridine via 6-chloro-3, 4′-bipyridine. The chloro derivative was catalytically dechlorinated into the corresponding 3, 4′ -bipyridine. 相似文献
65.
Lu Lai Ping Mei Xiao-Mei Wu Cong Hou Yan-Cheng Zheng Yi Liu 《Colloid and polymer science》2014,292(11):2821-2830
A series of anionic gemini surfactants have been synthesized. The surface properties and micellization process of as-prepared sulfonate gemini surfactants (SGS) and carboxylate gemini surfactant (CGS) have been studied by surface tension measurement and isothermal titration microcalorimetry. Meanwhile, the interaction of these five surfactants with polyacrylamide (PAM) was investigated using surface tension, steady-state fluorescence measurement, and isothermal titration microcalorimetry. The results show that the critical micelle concentrations (CMCs) of above-mentioned surfactants are more than 1 order of magnitude lower than those of corresponding single chain surfactants. Moreover, the enthalpy of micelle formation (ΔH mic) for the investigated gemini surfactants is negative. In the surfactant–PAM systems, the thermodynamic parameters of binding have also been determined. The conclusion may be drawn that the binding strength of SGS onto PAM is stronger than that of CGS, resulting from more compact structure of SGS aggregates. With increasing surfactant hydrophobicity, the values of ΔH agg become more exothermic and a ΔS agg decrease was observed. Therefore, the interaction between SGS and PAM is enthalpy-driven. 相似文献
66.
Nano-crystalline FeOOH particles(5~10 nm) have been uniformly mixed with electric matrix of single-walled carbon nanotubes(SWNTs)for forming FeOOH/SWNT composite via a facile ultrasonication method. Directly using the FeOOH/SWNT composite(containing 15 wt%SWNTs) as anode material for lithium battery enhances kinetics of the Li+insertion/extraction processes, thereby effectively improving reversible capacity and cycle performance, which delivers a high reversible capacity of 758 mAh g-1under a current density of 400 mA g-1even after 180 cycles, being comparable with previous reports in terms of electrochemical performance for FeOOH anode. The good electrochemical performance should be ascribed to the small particle size and nano-crystalline of FeOOH, as well as the good electronic conductivity of SWNT matrix. 相似文献
67.
The effect of antimony concentration (C(Sb)/mass%) on the surface tension of molten silicon has been determined with the sessile drop method in the temperature range from 1693 to 1773 K and in the range of the oxygen partial pressure, Po(2), in an Ar atmosphere from 10(-23) to 10(-21) MPa. The results show that the surface tension of molten silicon decreases with increasing Sb concentration in the range of C(Sb)<0.9 mass%, which indicates positive adsorption of Sb in molten silicon and can be fairly described with the Szyszkowski's equation. The maximum decrease rate of surface tension is about 65 mN m(-1) (mass% C(Sb))(-1), and the temperature coefficient of surface tension, (partial differential sigma/ partial differential T)C(Sb), increases with increasing C(Sb). The evaporation of the systems was only observed between the melting points of antimony (904 K) and silicon (1683 K), and the surface tension presents no dependence on measuring time above the melting point of silicon. 相似文献
68.
Lin C Wang Y Lai Y Yang W Jiao F Zhang H Ye S Zhang Q 《Colloids and surfaces. B, Biointerfaces》2011,83(2):285-375
Biodegradable poly(lactic-co-glycolic acid) (PLGA)/carboxyl-functionalized multi-walled carbon nanotube (c-MWCNT) nanocomposites were successfully prepared via solvent casting technique. Rat bone marrow-derived mesenchymal stem cells (MSCs) were employed to assess the biocompatibility of the nanocomposites in vitro. Scanning electron microscopy (SEM) observations revealed that c-MWCNTs gave a better dispersion than unmodified MWCNTs in the PLGA matrix. Surface properties were determined by means of static contact angle, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis. The presence of c-MWCNTs increased the mechanical properties of the nanocomposites. Seven-week period in vitro degradation test showed the addition of c-MWCNTs accelerated the hydrolytic degradation of PLGA. In addition, SEM proved that the cells could adhere to and spread on films via cytoplasmic processes. Compared with control groups, MSCs cultured onto PLGA/c-MWCNT nanocomposites exhibited better adhesion and viability and also displayed significantly higher production levels of alkaline phosphatase (ALP) over 21 days culture. These results demonstrated that c-MWCNTs modified PLGA films were beneficial for promoting cell growth and inducing MSCs to differentiate into osteoblasts. This work presented here had potential applications in the development of 3-D scaffolds for bone tissue engineering. 相似文献
69.
[formula: see text] The preparation of the first library of imidazo[1,2-a]pyridine derivatives on a solid support is described. A sulfone linker strategy was applied in the synthesis. Key steps involved in the solid-phase synthetic procedure include (i) alpha-haloketone resin formation by sulfinate-->sulfone alkylation, (ii) imidazo[1,2-a]pyridine ring formation by treatment with 2-aminopyridine, (iii) sulfone anion alkylation, and (iv) traceless product release by oxidation-elimination. A library of 12 imidazo[1,2-a]pyridines was synthesized. 相似文献
70.