The phase transition of tungsten(W)under high pressures was investigated with molecular dynamics simulation.The structure was characterized in terms of the pair distribution function and the largest standard cluster a...The phase transition of tungsten(W)under high pressures was investigated with molecular dynamics simulation.The structure was characterized in terms of the pair distribution function and the largest standard cluster analysis(LSCA).It is found that under 40−100 GPa at a cooling rate of 0.1 K/ps a pure W melt first crystallizes into the body-centred cubic(BCC)crystal,and then transfers into the hexagonal close-packed(HCP)crystal through a series of BCC−HCP coexisting states.The dynamic factors may induce intermediate stages during the liquid−solid transition and the criss-cross grain boundaries cause lots of indistinguishable intermediate states,making the first-order BCC−HCP transition appear to be continuous.Furthermore,LSCA is shown to be a parameter-free method that can effectively analyze both ordered and disordered structures.Therefore,LSCA can detect more details about the evolution of the structure in such structure transition processes with rich intermediate structures.展开更多
[ Objective] The research aimed to develop a new molecular imprinting solid-phase extraction column for the separation and enrichment of melamine in feed. [ Method] The molecular imprinting polymer of melamine was pre...[ Objective] The research aimed to develop a new molecular imprinting solid-phase extraction column for the separation and enrichment of melamine in feed. [ Method] The molecular imprinting polymer of melamine was prepared by mass polymerization method. This polymer was used as filler to prepare molecular imprinting polymer solid-phase extraction（MIP-SPE） column of melamine. The solid-phase extraction conditions were optimized and melamine content in concentrated solution was determined by using HPLC. [ Result] Melamine eould be separated selectively from feed and enriehed by self-made MIP-SPE column. It could wipe off complex matrix from feed and the addition recovery rate was 95%. The contrast experiment between MIP-SPE column and NMIP-SPE （ non-imprinted polymer- solid phase extraction） column showed that the extraction efficiency of the former was obviously higher than the latter. [ Conclusion] The home-made MIP- SPE column could be used to separate and enrich melamine in feed efficiently, with a broad application prospect.展开更多
A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were ...A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity.展开更多
Chitosan was prepared with stressing method by blending chitin and solid alkali in a single-screw extruder at given temperature and characterized by potentiometric titration, gel permeation chromatography (GPC), infra...Chitosan was prepared with stressing method by blending chitin and solid alkali in a single-screw extruder at given temperature and characterized by potentiometric titration, gel permeation chromatography (GPC), infrared spectrum (IR) and carbon-13 magnetic resonance sperctroscopy ( 13 C NMR) . Chitosan with a deacetylation degree (DD) of 76.1% was obtained at a mass ratio 0.2∶1∶1 for H_ 2 O/chitin/NaOH at 160 ℃ for 12 min. Compared to conventional solution method(usually 1∶10 for chitin/NaOH), the alkali assumption greatly decreased. Molecular weight of chitosan obtained by solid-phase method(S3,M_w1.54×10 5 ) was lower than that obtained by suspension method(Y2,M_w3.34×10 5 ). During deacetylation, molecular weight decreased with high reaction temperature and long reaction time but remained same at different initial ratios of NaOH/chitin. It might be concluded that degradation of chitosan was caused by breakout of the main chain of the oxidized chitosan catalyzed by alkali during the deactylation. IR and 13 C NMR showed that structures of chitosans prepared by solid-phase method were not changed.展开更多
Ecteinascidin 743 from sea squirt is one of the most original anti-tumoral activity compounds, as proven by the Natural Cancer Institute. Ecteinascidin 743 could be obtained with traditional liquid extraction, but it ...Ecteinascidin 743 from sea squirt is one of the most original anti-tumoral activity compounds, as proven by the Natural Cancer Institute. Ecteinascidin 743 could be obtained with traditional liquid extraction, but it should be purified and separated from the extract. A molecularly imprinted solid-phase extraction procedure was developed for the selective separation. Ecteinascidin 743 was used as the template and the polymer was synthesized in a methanol environment. Water and n-hexane as the washing solvents can eliminate most of the interference. Good linearity and low relative standard deviations （less than 4.39%）justify its continuing development.展开更多
Surface molecularly imprinted polymers （SMIPs） have been synthesized to selectively determine （-）-epigallocatechin gallate in aqueous media. SMIPs were prepared using a surface grafting copolymerization method on ...Surface molecularly imprinted polymers （SMIPs） have been synthesized to selectively determine （-）-epigallocatechin gallate in aqueous media. SMIPs were prepared using a surface grafting copolymerization method on a functionalized silica gel modified with β-cyclodextrin and vinyl groups. The morphology and composition of the SMIPs were investigated by scanning electron microscopy, Fourier transform-infrared spectroscopy and thermogravimetric analysis. In addition, the molecular binding capacity, recognition properties and selectivity of the SMIPs were evaluated. The imprinted polymers were found to have a highly specific recognition and binding capacity for aqueous media which is （-）-epigallocatechin gallate in the result of the hydrophobic properties of the β-cyclodextrin and the hydrogen-bonding interactions of methacrylic acid. The SMIPs were successfully employed as solid-phase extraction adsor- bents prior to the HPLC determination of （-）-epigallocatechin gallate in toothpaste. The HPLC analysis had a linear dynamic range of 0.5-50.0 μg·mL^-1 with a correlation coefficient of 0.9998 and the recoveries ranged from 89.4% to 97.0% with relative standard deviations less than 4.8%. The limit of detection and limit of quantification were 0.17 and 0.33 μg·mL^-1, respectively. The method provides a promising approach for the preparation of selective materials for the purification and determination of complex samples.展开更多
基金Projects(51661005,U1612442)supported by the National Natural Science Foundation of ChinaProject(QKHJC[2017]1025)supported by the Natural Science Foundation of Guizhou Province,ChinaProject(2018JJ3560)supported by the Natural Science Foundation of Hunan Province,China。
文摘The phase transition of tungsten(W)under high pressures was investigated with molecular dynamics simulation.The structure was characterized in terms of the pair distribution function and the largest standard cluster analysis(LSCA).It is found that under 40−100 GPa at a cooling rate of 0.1 K/ps a pure W melt first crystallizes into the body-centred cubic(BCC)crystal,and then transfers into the hexagonal close-packed(HCP)crystal through a series of BCC−HCP coexisting states.The dynamic factors may induce intermediate stages during the liquid−solid transition and the criss-cross grain boundaries cause lots of indistinguishable intermediate states,making the first-order BCC−HCP transition appear to be continuous.Furthermore,LSCA is shown to be a parameter-free method that can effectively analyze both ordered and disordered structures.Therefore,LSCA can detect more details about the evolution of the structure in such structure transition processes with rich intermediate structures.
基金Supported by Xiamen Science and Technology Plan Project(3502Z20123046)A-class Plan Project of Education Department of Fujian Province(JA12465)
文摘[ Objective] The research aimed to develop a new molecular imprinting solid-phase extraction column for the separation and enrichment of melamine in feed. [ Method] The molecular imprinting polymer of melamine was prepared by mass polymerization method. This polymer was used as filler to prepare molecular imprinting polymer solid-phase extraction（MIP-SPE） column of melamine. The solid-phase extraction conditions were optimized and melamine content in concentrated solution was determined by using HPLC. [ Result] Melamine eould be separated selectively from feed and enriehed by self-made MIP-SPE column. It could wipe off complex matrix from feed and the addition recovery rate was 95%. The contrast experiment between MIP-SPE column and NMIP-SPE （ non-imprinted polymer- solid phase extraction） column showed that the extraction efficiency of the former was obviously higher than the latter. [ Conclusion] The home-made MIP- SPE column could be used to separate and enrich melamine in feed efficiently, with a broad application prospect.
文摘A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity.
文摘Chitosan was prepared with stressing method by blending chitin and solid alkali in a single-screw extruder at given temperature and characterized by potentiometric titration, gel permeation chromatography (GPC), infrared spectrum (IR) and carbon-13 magnetic resonance sperctroscopy ( 13 C NMR) . Chitosan with a deacetylation degree (DD) of 76.1% was obtained at a mass ratio 0.2∶1∶1 for H_ 2 O/chitin/NaOH at 160 ℃ for 12 min. Compared to conventional solution method(usually 1∶10 for chitin/NaOH), the alkali assumption greatly decreased. Molecular weight of chitosan obtained by solid-phase method(S3,M_w1.54×10 5 ) was lower than that obtained by suspension method(Y2,M_w3.34×10 5 ). During deacetylation, molecular weight decreased with high reaction temperature and long reaction time but remained same at different initial ratios of NaOH/chitin. It might be concluded that degradation of chitosan was caused by breakout of the main chain of the oxidized chitosan catalyzed by alkali during the deactylation. IR and 13 C NMR showed that structures of chitosans prepared by solid-phase method were not changed.
文摘Ecteinascidin 743 from sea squirt is one of the most original anti-tumoral activity compounds, as proven by the Natural Cancer Institute. Ecteinascidin 743 could be obtained with traditional liquid extraction, but it should be purified and separated from the extract. A molecularly imprinted solid-phase extraction procedure was developed for the selective separation. Ecteinascidin 743 was used as the template and the polymer was synthesized in a methanol environment. Water and n-hexane as the washing solvents can eliminate most of the interference. Good linearity and low relative standard deviations （less than 4.39%）justify its continuing development.
基金Acknowledgements This work was supported by Zhejiang Provincial Natural Science Foundation of China （Grant No. LY 12B07010） and National Natural Science Foundation of China （Grant No.20807037）.
文摘Surface molecularly imprinted polymers （SMIPs） have been synthesized to selectively determine （-）-epigallocatechin gallate in aqueous media. SMIPs were prepared using a surface grafting copolymerization method on a functionalized silica gel modified with β-cyclodextrin and vinyl groups. The morphology and composition of the SMIPs were investigated by scanning electron microscopy, Fourier transform-infrared spectroscopy and thermogravimetric analysis. In addition, the molecular binding capacity, recognition properties and selectivity of the SMIPs were evaluated. The imprinted polymers were found to have a highly specific recognition and binding capacity for aqueous media which is （-）-epigallocatechin gallate in the result of the hydrophobic properties of the β-cyclodextrin and the hydrogen-bonding interactions of methacrylic acid. The SMIPs were successfully employed as solid-phase extraction adsor- bents prior to the HPLC determination of （-）-epigallocatechin gallate in toothpaste. The HPLC analysis had a linear dynamic range of 0.5-50.0 μg·mL^-1 with a correlation coefficient of 0.9998 and the recoveries ranged from 89.4% to 97.0% with relative standard deviations less than 4.8%. The limit of detection and limit of quantification were 0.17 and 0.33 μg·mL^-1, respectively. The method provides a promising approach for the preparation of selective materials for the purification and determination of complex samples.
