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991.
Treatment of various anilides with 1.5 equiv. of phenyliodine bis(trifluoroacetate) (PIFA) and 1.0 equiv. of BF(3)·OEt(2) in AcOH at room temperature afforded the corresponding para-acetoxylated products with high regioselectivity. In addition, this reaction could be expanded to the etherification of anilides. In the presence of 2.0 equiv. of PIFA and 2.0 equiv. of BF(3)·OEt(2), the reaction of anilides with alcohols provided the corresponding para-etherified products in good yields. 相似文献
992.
993.
A method was developed for the determination of rare earth impurities in high purity Gd(2)O(3) by inductively coupled plasma mass spectrometry (ICP-MS). The matrix suppression effect of Gd(2)O(3) on signals of rare earth impurities was compensated for by Re internal standardization. The spectra overlap interferences from GdH, GdO, GdOH(n) (n=1-3) on Tb, Tm, Yb and Lu were eliminated by 2-thylhexylhydrogen-2-ethylhexy phosphonate (EHEHP) extraction chromatographic separation. The detection limits for REEs were 0.005-0.017 ng ml(-1) in solution and 0.002-0.05 mug g(-1) in solid. Recoveries of spiked sample for REEs were from 88 to 121% with the precision of 1.0-7.5% RSD. Determination of trace REEs in two Gd(2)O(3) samples were performed. The method can be applied to analysis of 99.99-99.9999% high purity Gd(2)O(3). 相似文献
994.
Multirod and hierarchically spherical 3D Co(1-x)Mn(x)O (2/3 < or = x < or = 1) nanostructures have been successfully synthesized by the decomposition of acetylacetonate precursors. Their morphologies could be controlled through tuning the heat rating which affects the nucleation. The rods grew along [110] directions to reduce the appearance of high-energy crystallographic {110} planes. The hierarchically spherical superstructures were formed by a three-dimensional oriented-attachment mechanism. Magnetic measurement indicates that the MnO nanomaterials with hierarchically spherical superstructures show an antiferromagnetic transition temperature at 121 K, similar to that of bulk, and a ferromagnetic ordering exists at low temperature. Such anomalous magnetic properties arise plausibly from their microstructure characteristics. 相似文献
995.
为了探索生物基乙二醇中的1,2-丁二醇(1,2-BDO)作为共聚单体对生物基聚对苯二甲酸乙二醇酯(PET)的结晶行为和力学性能的影响。 本文合成了生物基PET均聚物和不同1,2-BDO共聚单元摩尔分数的系列生物基PET共聚物(共聚单体摩尔分数分别为2.0%、2.7%和5.6%),并采用傅里叶变换红外光谱仪(FTIR)、差示扫描量热仪(DSC)和力学测试等技术手段研究了其结晶行为和力学性能。 结果表明,随着1,2-BDO共聚单元摩尔分数的增加,PET共聚物的熔融温度、结晶速率及结晶度均明显降低,表明1,2-BDO共聚单体的引入破坏了PET分子链的规整性,阻碍了PET链段的结晶。 PET材料的拉伸强度随着1,2-BDO共聚单元摩尔分数的增加而降低,而弯曲强度和弯曲模量略有升高。 相似文献
996.
以异溴丁酸羟乙酯为引发剂、溴化亚铜和2,2′-联吡啶为催化剂和配体,引发丙烯酸琥珀酰胺酯(NAS)进行原子转移自由基聚合,得到的聚丙烯酸琥珀酰胺酯(PNAS)的分子量可以通过配比和转化率预测.进一步与单端氨基苯胺四聚体(TA)在50℃下反应,得到的聚合物用1H-NMR和FT-IR的测试,结果表明,当TA/NAS的摩尔比为3∶1时,PNAS上的琥珀酰胺酯可以完全被取代,从而得到侧链为苯胺四聚体的导电高分子.聚合物的结构和分子量以及分布用核磁共振氢谱、FT-IR和GPC进行表征;电化学性质用循环伏安法进行了测试. 相似文献
997.
在242-260nm波氏范围通过CS2分子的共振增强多光子电离(REMPI)获得了母体离子CS和碎片离子的分质量激发谱.在λ<246.4nm区间,CS激发谱上呈现出来源于CS2双光子电离的弥散谱带,碎片离子激发谱的归属强烈提示多光子过程中有中性基电子态的CS和S(经由CS2的光解离)产生:(1)CS 的谱带主要来源于中性CS碎片经由单光子跃迁产生的(1+1)共振增强电离,(2)除了部分S 的谱峰来自CS 的光解外,多数S 的锐谱峰来自中性S原子经由3p3(2D0)4p,3p3(4S0)np(n=6,7,8)←3p43pJ(J=2,1,0)双光子跃迁产生的(2+1)共振增强电离. 相似文献
998.
ZHAN Ru-Juan ZHU Xiao-Dong CHEN Ji-FongDepartment of Modem Physics. Structure Research Laboratory University of Science Technology of China Hefei Anhui 《天然气化学杂志》1995,(4)
The predeposition method for mereasing CH_4 concentration ininitial stage of diamond synthesis by plasma chemical vapor deposition.isused to enhance nucleated density of diamond films.The plasma parametersare diagnosed in situ using the Langmuir double probe.The relation betweenplasma ion density and nucleated densitv of diamond is revealed Increasingplasma ion density results in enhancement of nucleated density of diamondobviously 相似文献
999.
1000.
The determination of reaction paths for enzyme systems remains a great challenge for current computational methods. In this paper we present an efficient method for the determination of minimum energy reaction paths with the ab initio quantum mechanical/molecular mechanical approach. Our method is based on an adaptation of the path optimization procedure by Ayala and Schlegel for small molecules in gas phase, the iterative quantum mechanical/molecular mechanical (QM/MM) optimization method developed earlier in our laboratory and the introduction of a new metric defining the distance between different structures in the configuration space. In this method we represent the reaction path by a discrete set of structures. For each structure we partition the atoms into a core set that usually includes the QM subsystem and an environment set that usually includes the MM subsystem. These two sets are optimized iteratively: the core set is optimized to approximate the reaction path while the environment set is optimized to the corresponding energy minimum. In the optimization of the core set of atoms for the reaction path, we introduce a new metric to define the distances between the points on the reaction path, which excludes the soft degrees of freedom from the environment set and includes extra weights on coordinates describing chemical changes. Because the reaction path is represented by discrete structures and the optimization for each can be performed individually with very limited coupling, our method can be executed in a natural and efficient parallelization, with each processor handling one of the structures. We demonstrate the applicability and efficiency of our method by testing it on two systems previously studied by our group, triosephosphate isomerase and 4-oxalocrotonate tautomerase. In both cases the minimum energy paths for both enzymes agree with the previously reported paths. 相似文献