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203.
Mingxiao Deng Xuesi Chen Longhai Piao Xuefei Zhang Zhongli Dai Xiabin Jing 《Journal of polymer science. Part A, Polymer chemistry》2004,42(4):950-959
Biodegradable, amphiphilic, four‐armed poly(?‐caprolactone)‐block‐poly(ethylene oxide) (PCL‐b‐PEO) copolymers were synthesized by ring‐opening polymerization of ethylene oxide in the presence of four‐armed poly(?‐caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt2) as a catalyst. The chemical structure of PCL‐b‐PEO copolymer was confirmed by 1H NMR and 13C NMR. The hydroxyl end groups of the four‐armed PCL were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four‐armed architecture of the copolymer. Physicochemical properties of the four‐armed block copolymers differed from their starting four‐armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four‐armed block copolymer increased with PEO length and PEO content. The micelle formation of the four‐armed block copolymer was examined by a fluorescent probe technique, and the existence of the critical micelle concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. The cmc value increased with increasing PEO length. The absolute cmc values were higher than those for linear amphiphilic block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 950–959, 2004 相似文献
204.
M. Nakayama T. Nakanishi Z. S. Piao H. Nishimura M. Takahashi N. Egami 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We have investigated the excitonic properties of In0.15Ga0.85As/GaAs strained single quantum wells by using photoreflectance spectroscopy and a variational calculation method. We clearly detected the photoreflectance signal of the type-II light-hole exciton, which consists of an electron confined in the InGaAs layer and a light hole located in the thick GaAs layer, in addition to the type-I heavy-hole exciton confined in the InGaAs layer. The calculated results of the overlap integral of the envelope function in the type-II light-hole exciton predict that the oscillator strength is remarkably enhanced with decreasing the InGaAs-layer thickness. This is demonstrated by the layer-thickness dependence of the photoreflectance intensity of the type-II light-hole exciton. 相似文献
205.
在非完备的拓扑线性空间值锥度量空间上得到了新的满足某种Lipschitz型条件的四个映射的唯一公共不动点定理并给出了一些推论.所得结果推广和改进了文献中一些已知结论. 相似文献
206.
Ji Won Cha Mei Jing Piao Ki Cheon Kim Jian Zheng Cheng Wen Yao Chang Lim Hyun Hee Kyoung Kang Eun Sook Yoo Young Sang Koh Nam Ho Lee Mi Hee Ko Jin Won Hyun 《Applied biochemistry and biotechnology》2014,172(5):2582-2592
The aim of the present study was to elucidate the protective properties of 3,4-dihydroxybenzoic acid (DBA) isolated from Cladophora wrightiana Harvey (a green alga) against ultraviolet B (UVB)-induced damage to human HaCaT keratinocytes. DBA exhibited scavenging actions against the 1,1-diphenyl-2-picrylhydrazyl radical, the superoxide anion, and the hydroxyl radical. Furthermore, DBA decreased the levels of intracellular reactive oxygen species generated by hydrogen peroxide or UVB treatment of the cells. DBA also decreased the UVB-augmented levels of phospho-histone H2A.X and the extent of comet tail formation, which are both indications of DNA damage. In addition, the compound safeguarded keratinocytes from UVB-induced injury by reversing the production of apoptotic bodies, overturning the disruption of mitochondrial membrane potential, increasing the expression of the anti-apoptotic protein, B-cell lymphoma 2, and decreasing the expression of the pro-apoptotic proteins, Bcl-2-associated X and cleaved caspase-3. Taken together, these results demonstrate that DBA isolated from a green alga protects human keratinocytes against UVB-induced oxidative stress and apoptosis. 相似文献
207.
Ying Li Zhenrui Gao Chunlan Piao Kaiwen Lu Zhiping Wang Min-Long Cui 《Applied biochemistry and biotechnology》2014,172(4):1807-1817
In this study, we developed a rapid and efficient method for in vitro propagation and Agrobacterium tumefaciens-mediated transformation of Digitalis purpurea L. (syn. foxglove), an important medicinal plant. Mature leaf explants of D. purpurea were used for 100 % adventitious shoot regeneration on Murashige and Skoog (MS) medium supplemented with 1 mg L?1 thidiazuron (TDZ) (a cytokine) and 0.1 mg L?1 1-naphthaleneacetic acid (NAA) (an auxin). Transformation was achieved by inoculating leaf explants with the A. tumefaciens strains GV2260/pBI121 or GV3101/pBI121. The binary vector pBI121 contained the reporter β-glucuronidase gene (GUS) and kanamycin selection marker nptII. Kanamycin-resistant shoots were regenerated directly on the selection medium 4–6 weeks after co-cultivation. Approximately, 52.2 and 60 % of kanamycin-resistant shoots transformed with Agrobacterium strains GV2260 and GV3101, respectively, showed strong GUS staining by histochemical assay. Furthermore, PCR and Southern blot analysis confirmed the presence of nptII and GUS on the chromosome of the transformed D. purpurea plants, and stable GUS expression was detected in the transformants by RT-PCR analysis. This efficient method of shoot regeneration and genetic transformation of D. purpurea will provide a powerful tool to increase and produce valuable components such as digitoxin, digoxin, and digoxigenin in D. purpurea through improved secondary metabolic pathways via a biotechnological approach. 相似文献
208.
Yongjie Piao 《分析论及其应用》2015,(2):167-175
A class Φ of 5-dimensional functions was introduced and an existence and uniqueness of common fixed points for a family of non-self mappings satisfying a φiquasi-contractive condition and a certain boundary condition was given on complete metrically convex metric spaces, and from which, more general unique common fixed point theorems were obtained. Our main results generalize and improve many same type common fixed point theorems in references. 相似文献
209.
Monodisperse hollow carbon nanocapsules (<200 nm) with mesoporous shells were synthesized by coating their outer shells with silica to prevent aggregation during their high‐temperature annealing. Monodispersed silica nanoparticles were used as starting materials and octadecyltrimethoxysilane (C18TMS) was used as a carbon source to create core–shell nanostructures. These core–shell nanoparticles were coated with silica on their outer shell to form a second shell layer. This outer silica shell prevented aggregation during calcination. The samples were characterized by TEM, SEM, dynamic light scattering (DLS), UV/Vis spectroscopy, and by using the Brunauer–Emmett–Teller (BET) method. The as‐synthesized hollow carbon nanoparticles exhibited a high surface area (1123 m2 g?1) and formed stable dispersions in water after the pegylation process. The drug‐loading and drug‐release properties of these hollow carbon nanocapsules were also investigated. 相似文献
210.
建立了超高效液相色谱-串联质谱(UPLC-MS/MS)同时测定化妆品中73种糖皮质激素的分析方法。样品采用饱和氯化钠分散,乙腈超声提取,经PRiME HLB固相萃取柱(60 mg/3 mL)净化,采用Waters Cortecs C_(18)色谱柱(150 mm×2.1 mm,2.7μm)分离,以0.1%乙酸溶液-乙腈为流动相梯度洗脱。在电喷雾离子源正离子模式下,采用多反应监测(MRM)扫描方式测定,外标法定量。结果表明,73种糖皮质激素在各自的质量浓度范围内均呈良好线性关系,相关系数(r)均大于0.99,定量下限(LOQ)为0.1~0.3μg/g。在1LOQ、2LOQ、5LOQ 3个加标水平下,73种糖皮质激素的回收率为73.3%~119%,相对标准偏差(RSD)为0.40%~18%。该方法快速、准确、高效,可作为化妆品中73种糖皮质激素的筛查方法。 相似文献