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231.
Amide-water mixtures are studied by all-atom molecular dynamics (MD) simulations and the relative temperature-dependent NMR experiment. The weak C-H...O contacts are found in the amide-water systems theoretically and experimentally. The statistical results of the average numbers of hydrogen bonds indicate that the methyl groups in amide molecules represent different capabilities in forming the weak C-H...O contacts. The statistics also imply that the C-H...O contacts are more obvious in the amide-rich region than those in the water-rich region. The temperature-dependent NMR spectra are also adopted to investigate the weak C-H...O contacts in the amide-water systems. The relative chemical shifts of the methyl groups are in good agreement with the MD simulations. 相似文献
232.
报道了一种新的L-氨基酸氧化酶电极,这种酶电极系由氨气敏电极和以氨基化玻璃布为载体的酶膜所组成;研究了固定化条件对酶膜活性的影响以及底物浓度、温度和pH对电极响应特性的影响。该电极在6.0×10^-5~4.0×10^-3mol/L的底物浓度范围内呈良好的线性关系,检测下限为5.0×10^-5mol/L。在最宜条件下,酶电极具有良好的稳定性。 相似文献
233.
含氰基侧基聚芳醚砜的合成与表征 总被引:1,自引:0,他引:1
汉2,6-二卤苯甲腈、4,4′-二氯二苯砜、4,4′-二羟基二苯砜、间苯二酚、对苯二酚、酚酞及双酚A为主要原料,合成了含不同结构单元和不同氰基含量的含氰基侧基的聚芳醚砜,并采用IR、^13CNMR等分析手段对其结构进行了表征,同时研究了结构单元和氰基含量对聚芳醚砜性能的影响。 相似文献
234.
微乳液介质—1—(2—吡啶偶氮)—2—萘酚光度法测定汽油中环烷酸铁的含量 总被引:8,自引:2,他引:8
本研究了微乳液为介质时,铁与1-(2-吡啶偶氮)-2-萘酚(PAN)的显色反应。选择730nm处为测定波长,ε为1.4×10^4L.mol^-^1.cm^-^1,铁量在0-50μg/25ml范围内符合比耳定律,该法适用于汽油中环烷酸铁的测定。 相似文献
235.
236.
本文用微分脉冲极谱法研究了多酚氧化酶的活性测定和酶的反应动力学。应用于马铃薯等10余种植物样品的酶活力测定,结果良好。方法简便快速,重现性好。 相似文献
237.
基团的电子效应与单取代苯对位1H、13C的化学位移*韩长日冯娇杨钟照平(海南师范学院化学系海口571158)关键词1H的化学位移13C的化学位移基团电负性共轭效应引言在1H、13C核磁共振谱中,化学位移值的大小主要取决于屏蔽作用的大小,而屏蔽作用的大... 相似文献
238.
Cai H Lam WH Yu X Liu X Wu ZZ Chen T Lin Z Chen XT You XZ Xue Z 《Inorganic chemistry》2003,42(9):3008-3015
Titanium and zirconium amido complexes containing a hydrotris(pyrazolyl)borate (Tp) or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) ligand TpM(NMe(2))(3) (M = Ti, 1; M = Zr, 2) and Tp*M(NMe(2))(3) (M = Ti, 3; M = Zr, 4) were prepared by the reactions of M(NMe(2))(3)Cl (M = Ti, Zr) with sodium hydridotris(pyrazol-1-yl)borate and potassium hydridotris(3,5-dimethylpyrazol-1-yl)borate, respectively. The structures of 1, 2, and 4.CH(2)Cl(2) were determined by X-ray diffraction and show octahedral coordination geometry around the metal centers. Density functional theory calculations at the B3PW91 level were performed to understand the orientations and the rotational behavior of amido ligands in these metal complexes. 相似文献
239.
Yan?Zhang Changchun?Wang Wuli?Yang Bin?Shi Shoukuan?FuEmail author 《Colloid and polymer science》2005,283(11):1246-1252
Biodegradable tri-component diblock copolymer was synthesized by bulk copolymerization of ε-caprolactone (CL) and D, L-lactide (LA) in the presence of methoxy poly(ethylene glycol) (MePEG), using stannous octoate as catalyst. Their chemical
structure and physical properties were investigated by GPC, NMR, DSC, TGAand XRD. The increase of CL/LA ratio in the diblock
copolymer leads to lower T
g, higher decomposition temperature and crystallinity. Nanoparticles formulated from MePEG–poly(CL-co-LA) (PCAE) possess spherical structure, which was characterized by dynamic light scattering (DLS) and transmission electron
microscopy (TEM). The DLS results indicate that the particle size increased with the increase of CL/LA ratio and the hydrophobic
fragment length in the copolymer. The drug encapsulation efficiency and the drug release behavior in vitro conditions of camptothecin
were measured by high performance liquid chromatography (HPLC). The encapsulation efficiency can be achieved as high as 84.4%
and the release behavior can be made well-controlled. MePEG–poly(CL-co-LA) nanoparticles might have a great potential as carriers for hydrophobic drugs. 相似文献
240.
A method has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in water by coupling gallic acid (GA) modified nanometer-sized alumina micro-column separation with inductively coupled plasma mass spectrometry (ICP-MS). The separation of Fe(II) and Fe(III) was achieved based on the obvious difference in reaction kinetics between Fe(II) and Fe(III) with GA. Fe(III) was selectively retained on the micro-column at pH 5.5-6.5, while Fe(II) could not be retained by the micro-column at the whole tested pH range of 1.0-6.5, and passed through the micro-column. The Fe(II) can be determined by ICP-MS directly without preconcentration/separation procedure, while Fe(III) retained on the micro-column was then eluted with 1.0 mL of 1 mol L(-1) HCl and determined by ICP-MS. The parameters affecting the separation of Fe(II) and Fe(III) were investigated systematically and the optimum separation conditions were established. Under the optimized conditions, the detection limits of 0.48 microg L(-1) and 0.24 microg L(-1) with relative standard deviation of 5.6% and 4.3%(C= 5 microg L(-1), n= 7) for Fe(II) and Fe(III) were found, respectively. No obvious effect on the speciation of Fe(II) and Fe(III) was found with the change of the ratio of Fe(II) and Fe(III) from 0 ratio 10 to 10 ratio 0. The proposed method was applied for the determination of trace Fe(II) and Fe(III) in environmental water and the recoveries for spiked samples were found to be in the range of 97-105%. 相似文献