The compositions and the microstructures of the copolymers formed by radical-initiated copolymerization of 2-vinyl pyridine and methyl methacrylate have been quantitatively studied using 250 MHz 1H NMR spectra. V-centered triad and M-centered triad distributions were quantitatively measured. These results confirmed that this copolymerization system belongs to the first order Markov chain model. Reactivity ratios for 2-vinyl pyridine and methyl methacrylate established are rv = 0.64 and rM = 0.31, respectively, agreeing very well with those calculated theoretically. 相似文献
An isostructural series of M(2)L(4) molecular capsules quantitatively self-assembled from two M(II) ions (M=Zn, Cu, Pt, Pd, Ni, Co, and Mn) and four bent ligands with embedded anthracene fluorophores. X-ray crystallographic analysis (for M=Zn, Cu, Ni, and Pd) confirmed the formation of closed-shell structures in which the large interior cavities inside the molecular capsules (about 1 nm) were shielded by eight anthracene panels. Analysis of the Zn(II) and Cu(II) structures showed the inclusion of an unusual triad guest cluster; four MeCN molecules, one water molecule, and one CF(3)SO(3)(-) ion were located inside the cavities. Full characterization by NMR spectroscopy and MS (ESI-TOF) demonstrated that the molecular capsules were quite stable and persist in solution. The fluorescence properties of the isostructural capsules were strongly dependent on the identity of the metal species: the Zn(II) capsule emitted strong blue fluorescence with a high quantum yield (Φ=0.8), in sharp contrast to the weakly emissive Ni(II) and Mn(II) capsules and the completely non-emissive Pd(II), Pt(II), and Co(II) capsules. On the other hand, the Cu(II) capsule exhibited solvatochromism and solvent-dependent emission behavior; blue emission of the capsule was "on" in DMSO but "off" in MeCN. 相似文献
A method for the preconcentration of gold in natural waters at the sampling site using tributyl phosphate as a solid extractant [Se(TBP)] was developed as a preliminary step prior to the determination of gold by neutron activation and γ-spectrometry. The SE(TBP) was saturated with gaseous chlorine for extracting all gold species. In batch experiments gold was quantitatively retained on the SE(TBP) in 10 min. After extraction and washing, the SE(TBP) was ashed or back-extracted. Gold was quantitatively eluted with hot, neutral 0.025 M thiourea. The gold content of residues of ashing or eluents after evaporation was determined by neutron activation and γ-spectrometry. The detection limit for the overall procedure was 0.2 ng 1?1. The efficiency was tested on ‘equilibrated’ solutions prepared from river water and tracer solutions of gold. For comparison, the gold content of natural water samples was determined using preconcentration on activated charcoal. 相似文献
A combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminium (MeAI(ODBP)2) was found to be an efficient initiator for heterotactic living polymerization of certain alkyl methacrylates in toluene at low temperatures. The polymerization of methyl methacrylate (MMA) with t-BuLi/MeAI(ODBP)2 (AI/Li=5 mol/mol) in toluene at −78°C gave heterotactic-rich poly(methyl methacrylate) (PMMA) with narrow molecular weight distributions (MWDs) (heterotactic triad fraction mr = 68%, ratio of weight- to number-average molecular weights M̄w/M̄n = 1.06-1.17). Other alkyl methacrylates also gave heterotactic polymers under the same conditions; in particular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% was obtained for the polymerization of ethyl methacrylate at −95°C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with other structural information of the polymer such as chain-end stereostructure and stereosequence distribution in the main chain. 相似文献
Neutron activation γ-spectrometry is sufficiently sensitive for the determination of traces of rare earth elements but quantitative separation from uranium is essential. The rare earth elements in 0.2 M ammonium carbonate medium are quantitatively retained on Chelex-100, and are quantitatively separated from uranium by recycling the eluate. When 10-g samples are used, neutron activation provides detection limits of 1–20 μg kg?1. Recoveries of rare earths, checked by spiking with radiotracers, are essentially complete. 相似文献
A simple solvent extraction procedure for the efficient separation of the radioactive tracers95Nb and182Ta from each other in a mixture using di-(2-ethylhexyl)phosphoric acid (HDEHP) as extractant is described. Tantalum was found to be quantitatively extracted from an aqueous madium, which is 1.6N in HCl and 10?2 M in oxalic acid, with a HDEHP solution of 0.1 M concentration. Extractabilities of both niobium and tantalum in mineral acids like HCl, H2SO4 and HNO3 and in some organic acids like oxalic, citric, etc., in HDEHP under the experimental conditions were also studied. The reliability of the separation procedure was verified further by γ-ray spectrometry. 相似文献
A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively. 相似文献
The γ-hydroxymetal hydrides OH (M = Si, Ge, Sn) were synthesized by reduction of γ-acetoxychloro- or γ-hydroxychloro-silanes, -germanes and -stannanes. These derivatives with MH bonds lead, by cyclisation at room- or higher temperatures, with or without catalyst, depending on the nature of the metal, to various oxametallacyclopentanes. The cyclisation proceeds by intramolecular dehydrocondensation between MH and OH bonds. These dehydrocondensation reactions are analysed and discussed according to the polarity of the MH bonds. Intramolecular addition of the MH bond into the unsaturated carboncarbon bonds of the corresponding non-cyclic compounds is also an excellent way of preparing the same heterocycles.The IR and NMR analyses of all new compounds are given. 相似文献