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251.
252.
Preparation and properties of reversible hydrogels based on triblock poly(amino acid)s with tunable pH‐responsivity across a broad range
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253.
Wenling Zhang Jinlin He Zhuang Liu Peihong Ni Xiulin Zhu 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1079-1091
A series of well‐defined amphiphilic triblock copolymers [polyethylene glycol monomethyl ether]‐block‐poly(ε‐caprolactone)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] (mPEG‐b‐PCL‐b‐PDMAEMA or abbreviated as mPEG‐b‐PCL‐b‐PDMA) were prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization. The chemical structures and compositions of these copolymers have been characterized by Fourier transform infrared spectroscopy, 1H NMR, and thermogravimetric analysis. The molecular weights of the triblock copolymers were obtained by calculating from 1H NMR spectra and gel permeation chromatography measurements. Subsequently, the self‐assembly behavior of these copolymers was investigated by fluorescence probe method and transmission electron microscopy, which indicated that these amphiphilic triblock copolymers possess distinct pH‐dependent critical aggregation concentrations and can self‐assemble into micelles or vesicles in PBS buffer solution, depending on the length of PDMA in the copolymer. Agarose gel retardation assays demonstrated that these cationic nanoparticles can effectively condense plasmid DNA. Cell toxicity tests indicated that these triblock copolymers displayed lower cytotoxicity than that of branched polyethylenimine with molecular weight of 25 kDa. In addition, in vitro release of Naproxen from these nanoparticles in pH buffer solutions was conducted, demonstrating that higher PCL content would result in the higher drug loading content and lower release rate. These biodegradable and biocompatible cationic copolymers have potential applications in drug and gene delivery. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1079–1091, 2010 相似文献
254.
Superparamagnetic pH‐sensitive multilayer hybrid hollow microspheres for targeted controlled release
Bin Mu Peng Liu Yun Dong Chunyin Lu Xueli Wu 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):3135-3144
The superparamagnetic multilayer hybrid hollow microspheres have been fabricated using the layer‐by‐layer assembly technique by the electrostatic interaction between the polyelectrolyte cation chitosan (CS) and the hybrid anion citrate modified ferroferric oxide nanoparticles (Fe3O4‐CA) onto the sacrificial polystyrene sulfonate microspheres templates after etching the templates by dialysis. The saturation magnetization and magnetite contents of the superparamagnetic multilayer hybrid hollow microspheres were 32.46 emu/g and 51.3%, respectively. The hybrid hollow microspheres showed pH‐sensitive characteristics. The adsorption and release of the basic dye (methylene blue) were applied to investigate the interaction between the amino groups of CS and the carboxyl groups of the Fe3O4‐CA nanoparticles in different pH media. The superparamagnetic pH‐sensitive multilayer hybrid hollow microspheres are expected to be used for the targeted controlled release of drugs or in diagnostics. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3135–3144, 2010 相似文献
255.
Shiun-Sheng JanJung-Lung Chiang Ying-Chung Chen Jung-Chuan ChouChien-Chuan Cheng 《Analytica chimica acta》2002,469(2):205-216
The sol-gel-derived lead titanate (PbTiO3) membrane has been successfully applied as a pH sensitive layer to form the PbTiO3 gate ion-sensitive field-effect transistor (ISFET). There exhibit the excellent quasi-Nernstian response of 56-59 mV pH−1, good surface adsorption and anticorrosion characteristics via the C-V measurement of the EIS structure. At a specific pH concentration, the output and transfer characteristics are very similar to the behaviours of MOSFETs, and the ISFET model can be derived by the modified MOSFET model. As it operated in the nonsaturation region, there exhibits a linear pH response of about 56-59 mV pH−1. On the other hand, as it operated in the saturation region, the pH response and linearity can be controlled by adjusting the VGS values, e.g. the pH responses of −4.2, −24.8 and −31.3 μA pH−1 and the correlation coefficients of 0.9491, 0.9995 and 0.9996 at VGS=1, 3 and 5 V can be obtained, respectively. Besides, in order to get the best pH response and the minimized leakage current, the heat treatment temperature of the PbTiO3 membrane must be limited between 350 and 450 °C. 相似文献
256.
《Magnetic resonance in chemistry : MRC》2002,40(10):666-671
The effect of pH on the rotational conformations of 1,3‐diamino‐2‐hydroxypropane in aqueous solution was investigated by proton NMR. Both the observed chemical shifts and coupling constants were used to calculate experimental pKa values. The observed couplings were correlated with the expected couplings for the various possible staggered conformations to try to determine the pattern of conformations for the diamine and its conjugate acids. The best fits suggested a modest preference for the gauche–gauche conformation, especially at low pH, where the diprotonated hydroxydiamine predominates. In methanol, dimethyl sulfoxide and trichloromethane solutions, it was only possible to evaluate the conformational equilibria of the diamine. Slow proton exchange, which caused uncertainties in both chemical shifts and couplings for the monoprotonated and unprotonated diamine, nullified efforts to determine whether or not hydrogen bonding was important for these species in less polar solvents. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
257.
Summary The retention behaviour of an homologous series of phosphorylated oligodeoxythymidylic acid (pd(T)5–18) oligonucleotides was studied using reversed-phase ion-pair chromatography with isocratic elution conditions. The effects
of temperature, pH, eluent ionic strength, percentage organic modifier, concentration and alkyl chain length of the ion-pairing
reagent were investigated. The retention behaviour was generally explicable by current theoretical models of ion-pair chromatography.
However, the marked effect of mobile phase pH on the retention of the oligonucleotides was unexpected, and this was ascribed
to the presence of ionisable residual silanols on the surface of the reversed-phase packing material. 相似文献
258.
A new cell engineering technique (L. B. technique) was established in our Lab. At first, the physical and chemical methods were used to facilitate the reestablishment of intercellular contacts and plasmodesma channels between different parents, thus forcing cytoplasm and chromatin to pass the cell wall with different qualities and quantities from one cell to others, through the enlarged intercellular plasmodesma channels or the vulnerable regions and the holes on the cell wall formed differently in growth and thickness in the process of cell wall formation to introduce external genetic substances or gene groups into plant cells. There are different ways, frequencies and strengths for the migration between the cells in different growth and development regions or the same growth and development region. In this paper we advance the mechanism of cytoplasm and chromatin migration through the cell wall: There are a large number of plasmodesma channels or vulnerable regions and holes different in growth and th 相似文献
259.
Lightly crosslinked nitrated poly(4-hydroxystyrene) microspheres were prepared for pH sensing. The first step is to prepare poly(4-acetoxystyrene) microspheres using porous glass membrane emulsification followed by suspension polymerization. The resulting microspheres have diameters between 1 and 2 μm. They hydrolyzed to poly(4-hydroxystyrene) by exposing them to base. This is followed by nitration to nitric acid. The percentage of nitrogen depends on the nitration conditions. Percentages greater than the theoretical percentage for mononitro poly(4-hydroxystyrene) can be obtained at elevated temperatures indicating partial dinitration. These microspheres were cast into hydrogel membranes for use as pH sensors. The membrane is turbid because the refractive index of the microspheres is higher than the hydrogel refractive index. At high pH, deprotonation of the hydroxyl group introduces a negative charge onto the polymer backbone causing it to swell. Swelling is accompanied by a decrease in microsphere refractive index, which is detected as a decrease in membrane turbidity. 相似文献
260.
Optimization of separations of alkyl-substituted phenolate anions by capillary zone electrophoresis 总被引:1,自引:0,他引:1
Anions of alkylphenols have very similar electrophoretic mobilities in CZE owing to their very small differences in size and the narrow range of their pKa values. By studying electrophoretic mobility as a function both of pH and of the amount of acetonitrile in the electrolyte solution, optimum separation conditions were determined. It was possible to separate a group of methyl-substituted phenols, including several positional isomers. Mixtures containing n-propyl and isopropyl phenols and 1°, 2°, and 3° butylphenols could be resolved. 相似文献