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991.
Jun Cao Lifen Zhang Xiaowu Jiang Chun Tian Xiaoning Zhao Qi Ke Xiangqiang Pan Zhenping Cheng Xiulin Zhu 《Macromolecular rapid communications》2013,34(22):1747-1754
An iron‐mediated reverse ATRP of methyl methacrylate (MMA) is successfully carried out in water in the absence of any dispersants, using a water‐soluble 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (V‐50) as the initiator and the stabilizer, and using an oil‐soluble N,N‐butyldithiocarbamate ferrum (Fe(S2CN(C4H9)2)3) as the catalyst without adding any additional ligands. Micron‐sized PMMA particles with UV light‐sensitive ‐S2CN(C4H9)2 end group are obtained, and monomer droplet nucleation and suspension polymerization mechanism are proposed. Polymerization results demonstrated typical “living”/controlled characteristics of ATRP: first‐order polymerization kinetics, linear increase of molecular weights with monomer conversion and narrow molecular weight distributions for the resultant PMMA particles. NMR spectroscopy and chain‐extension experiments under UV light irradiation confirm the attachment and livingness of UV light‐sensitive ‐S2CN(C4H9)2 group in the chain end.
992.
We previously showed that in N,N‐dimethylformamide (DMF), poly(9‐anthracenylmethyl methacrylate) (PAMMA) and poly(2‐naphthylmethacrylate) selectively disperse semiconducting and metallic single‐walled carbon nanotubes (SWNTs), respectively. We have also proposed a new noncovalent polymer interaction based on photon induced dipole–dipole interaction to account for the metallicity‐based selectivity. In this article, we investigate two other polymethacrylates, that is, poly(benzyl methacrylate) (PBMA) and poly(methylmethacrylate)‐co‐(9‐anthracenylmethyl acrylate) (PMMA‐c‐PAMA) in the light of our previously proposed photon‐induced dipole–dipole interaction. We find that PBMA and PMM‐c‐PAMMA in DMF show no metallicity selectivity. The different selective behavior of the four polymers in DMF manifests the decisive influence of the side aromatic group in determining their metallicity selectivity. The nonpreferential energy transfer from PMMA‐c‐PAMA to SWNTs and the nonoverlap of PBMA fluorescence (in the ultraviolet range) with nanotube absorption account for their nonselectivity of specific nanotube species. Further, the parallel relationship between the diameters of extracted tube species and the affinity between polymers and solvents suggests the leading role of the polymeric conformation on the diameter selectivity. A sufficient (i.e., 2 weeks) standing time of the SWNTs solution after sonication, during which the polymers presumably optimize their conformation to the SWNTs, was found to be essential to the enrichment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
993.
A highly accurate method for measuring pentachlorophenol (PCP) concentrations in textile samples was developed. This highly accurate method for the analysis of textile samples is valuable, given the inherent challenges associated with the complexity of the sample matrix. This method can be applied to certify the concentration of pentachlorophenol in textile CRMs. A measurement procedure based on isotope dilution liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) was developed. Samples were pretreated with acid and then with n-hexane. Excellent precision was obtained. The validated concentration ranges for the method were 1.0-50 ng/g, the LOD was 1.0 ng/g, and the LOQ was 5.0 ng/g. The precision of this method is in the range of 0.80-1.40%. The method can trace to mass. 相似文献
994.
In this paper, the interactions of meso-Tetrakis (4-sulfonatophenyl) porphyrin (TPPS 4 ) and six cyclodextrins have been studied, respectively, by fluorescence spectroscopy, polarography and thin-layer chromatography. The inclusion constants of different methods are determined and the comparison of inclusion capacity of various cyclodextrins indicates that for the ionic cyclodextrins the charge interaction plays an important role in the inclusion procedure. The thermodynamic parameters of interaction imply that the inclusion process shows the enthalpy-entropy compensation effect. Cyclodextrin, being regarded as an artificial analogue of proteinoid of heme, provides a protective sheath for porphyrin. However, the TPPS 4 , encapsulated within this saccharid-coated barrier, its solubility is enhanced prominently, which exhibits that this interaction may modify the biological properties of TPPS 4 that owned the similar properties as hematoporphyrin. 相似文献
995.
The ability of β-cyclodextrin (β-CD), γ-CD, hydroxypropyl-β-CD (HP-β-CD), trimethyl-β-CD (TM-β-CD), sulfurbutylether-β-CD (SBE-β-CD) and carboxymethyl-β-cyclodextrin (CM-β-CD) to break the aggregate of the meso-tetrakis(4-N-trimethylaminobenzyl)porphyrin (TAPP) and to form 2:1 inclusion complexes has been studied by absorption and fluorescence spectroscopy. The formation constants are calculated, respectively, by fluorimetry, from which the inclusion capacity of different CDs is compared and the inclusion mechanism of charged-β-CD (SBE-β-CD and CM-β-CD) is quite different from that of the parent β-CD. At lower pH, the complexation between TM-β-CD and H2TAPP2+ (the form of the diprotonated TAPP) hampers the continuous protonation of the pyrrole nitrogen of TAPP and the hydrophobic cavity may prefer to bind an apolar neutral porphyrin molecule. 1HNMR data support the inclusion conformation of the porphyrin–cyclodextrin supramolecular system, indicating the interaction of the meso-phenyl groups of TAPP with the cavity of CDs. For this host–guest inclusion model, cyclodextrin being regarded as the protein component, which acts as a carrier enveloping the active site of heme prosthetic group within its hydrophobic environment, provides a protective sheath for the porphyrin, creating artificial analogues of heme-containing proteins. However, for TAPP, encapsulated within this saccharide-coated barrier, its photophysical and photochemical properties changed strongly. 相似文献
996.
997.
998.
Triterpenoids from the Roots and Stems of Rubus alceaefolius 总被引:1,自引:0,他引:1
999.
Lijin Zhang Shaowen Liu Xinyi Cui Canping Pan Ailin Zhang Fang Chen 《Central European Journal of Chemistry》2012,10(3):900-925
The pesticide residues in foods have received increasing attention as one of the most important food safety issues. Therefore,
more strict regulations on the maximum residue limits (MRLs) for pesticides in foods have been established in many countries
and health organizations, based on the sensitive and reliable analysis methods of pesticide residues. However, the analysis
of pesticide residues is a continuing challenge mainly because of the small quantities of analytes as well as the large amounts
of interfering substances which can be co-extracted with them, often leading to experimental errors and damage to the analytical
instruments. Thus, extensive sample preparation is often required for the pesticide residue analysis for the effective extraction
of the analytes and removal of the interferences. This paper focuses on reviewing the recent development in the sample preparation
methods for the pesticide residue analysis in foods since 2006. The methods include: liquid-liquid extraction (LLE), supercritical-fluid
extraction (SFE), pressurized-liquid extraction (PLE), microwave-assisted extraction (MAE), ultrasound-assisted extraction
(UAE), gel permeation chromatography (GPC), solid-phase extraction (SPE), molecularly imprinted polymers (MIPs), matrix solid-phase
dispersion (MSPD), solid-phase micro-extraction (SPME), QuEChERS, cloud point extraction (CPE) and liquid phase micro-extraction
(LPME), etc. Particularly their advantages, disadvantages and future perspectives will be discussed. 相似文献
1000.