磁共振方法研究12-钨磷酸水合物中水分子的运动状态

本文使用以Cu(Ⅱ)为顺磁探针的ESR以及宽谱线~1H-NMR等磁共振方法,研究了12-钨磷酸水合物中水分子的运动状态,结果表明水合水的活动性不仅取决于温度,而且还与12-钨磷酸水合物中的含水量有关。     

极性介质中醋酸乙烯酯的辐照引发分散聚合

用钴 60γ射线引发醋酸乙烯酯的分散聚合 ,通过选择各种极性溶剂体系 ,确立了醋酸乙烯酯在极性介质中稳定的分散聚合体系 .对异丙醇 水体系 ,聚合物分子量随剂量率的降低、稳定剂含量的增加、单体浓度的增大、反应温度的升高以及醇水比的降低而增加 .运用XPS、元素分析等表征聚合物粒子 ,及通过辐射接枝理论的分析 ,可以判断稳定剂所起的稳定作用主要是以物理吸附为主     

凤仙花不同提取物中山奈酚的测定

为寻求有效的山奈酚分离、纯化条件,并从凤仙花中提取山奈酚;分别采用不同溶剂和不同方法对凤仙花红色花瓣进行了提取,并利用高效液相色谱法对其主成分进行了测定;实验结果表明: 9种提取物中均含有山奈酚,乙酸乙酯提取物中山奈酚的含量最高: 1 g凤仙花红色花瓣的乙酸乙酯提取液中含有8.1 mg的山奈酚.     

液晶的激光拉曼光谱研究——Ⅰ.十九种液晶的固相激光拉曼光谱

本文报道联苯、联苯酯、单酯、双酯、Schiff碱和氧化偶氮苯型十九种液晶化合物的固相激光拉曼光谱,讨论了2300～400 cm~(-1)范围内基团的特征谱带归属以及光谱与结构之间的关系.     

可逆与不可逆吸附氢在合成甲醇反应中的作用

在自行设计和建立的加压动态分析装置上研究了合成甲醇催化剂上氢的吸附和反应行为。结果表明:在反应条件下催化剂上吸附的氢可分为可逆吸附氢和不可逆吸附氢;不可逆吸附氢又可分为能被CO顶替出来的和不能被CO顶替出来的两部分;能被CO顶替出来的不可逆吸附氢对CO的吸附起促进作用,不能被CO顶替出来的不可逆吸附氢是合成甲醇催化剂必不可少的“组分”或称“促进剂”;同时甲醇的生成是可逆吸附氢与一氧化碳作用的结果。     

ROOM-TEMPERATURE FLUORESCENCE PROPERTIES OF THE POLYNUCLEOTIDE POLYdA POLYdT

The room-temperature fluorescence spectrum of the non-alternating polynucleotide polydA.polydT is found to have its maximum at about 325 nm and, when exciting in the spectral region where both adenine (A) and thymine (T) absorb, to coincide with that obtained for excitation at 293 nm where thymine is selectively excited. The fluorescence anisotropy is found to be equal to 0.18 and independent of the excitation and emission wavelengths. These observations are consistent with: (i) emission stemming from T; and (ii) transfer of electronic energy from A to T being not efficient. These inferences are also supported by the observed dependence of the fluorescence quantum yield on the excitation wavelength.     

Thermal Decomposition Kinetics of the Zn(II) Complex with Norfloxacin in Static Air Atmosphere

The thermal decomposition of Zn[NFA]₂5H₂O (NFA=C₁₆H₁₈FN₃O₃, norfloxacin) and its kinetics were studied under non-isothermal conditions in air by TG-DTG and DTA methods. The intermediate and residue for each decomposition were identified from the TG curve. The non-isothermal kinetic data were analyzed by means of the Achar method and the Madhusudanan-Krishnan-Ninan (MKN) method. The possible reaction mechanisms were investigated by comparing the kinetic parameters. The kinetic equation for the second stage can be expressed as d/dt=Aexp(–E/RT)(1–).This revised version was published online in November 2005 with corrections to the Cover Date.     

V-Ag-Ni系氧化物的表面氧性质与甲苯选择性氧化的催化性能

制备了一系列Ｖ，Ａｇ，Ｎｉ原子比不同的三元氧化物，应用ＴＰＤ－ＭＳ技术研究了样品表面氧的性质，并测定了甲苯选择性氧化生成苯甲醛的催化活性。实验结果表明，样品表面存在有多种吸附的氧物种。在脱附温度＜９００℃：当Ｎｉ含量对Ａｇ（或Ｖ）的原子比为０．２５或０．５０时，仅在低温处出现有表面的Ｏ＾－和Ｏ＾２＾－两种氧物种的脱附峰；当Ｎｉ含量对Ａｇ（或Ｖ）的原子比增高到＞０．７５时，除有表面的Ｏ＾－和Ｏ＾２＾     

Affinity enrichment of plasma membrane for proteomics analysis

Proteomics analysis of plasma membranes from cells exposed to different extracellular environments is potentially a powerful approach for the identification of membrane-associated proteins responding to these environments. Preparation of high concentration plasma membrane fractions with low contamination from cellular organelles is essential for such studies. Here, we describe an affinity enrichment method, which combines cell surface biotinylation with affinity enrichment by immobilized streptavidin beads, for the isolation of plasma membranes. This method results in a 400-fold enrichment of plasma membrane relative to endoplasmic reticulum, a major contaminant in standard plasma membrane preparations, and dramatically reduces contamination from other cellular organelles. The biotinylation reaction did not interfere with ligand-dependent activation of receptor tyrosine kinases or G-protein coupled receptors, suggesting cell-surface signal transduction machinery remains functional. Membrane fractions prepared by this method should provide excellent starting materials for membrane proteomics analysis such as studies of dynamic trafficking and regulation of signaling molecules or identification of disease-specific membrane markers.     

High-frequency (140-GHz) time domain EPR and ENDOR spectroscopy: the tyrosyl radical-diiron cofactor in ribonucleotide reductase from yeast

High-frequency pulsed EPR and ENDOR have been employed to characterize the tyrosyl radical (Y*)-diiron cofactor in the Y2-containing R2 subunit of ribonucleotide reductase (RNR) from yeast. The present work represents the first use of 140-GHz time domain EPR and ENDOR to examine this system and demonstrates the capabilities of the method to elucidate the electronic structure and the chemical environment of protein radicals. Low-temperature spin-echo-detected EPR spectra of yeast Y* reveal an EPR line shape typical of a tyrosyl radical; however, when compared with the EPR spectra of Y* from E. coli RNR, a substantial upfield shift of the g(1)-value is observed. The origin of the shift in g(1) was investigated by 140-GHz (1)H and (2)H pulsed ENDOR experiments of the Y2-containing subunit in protonated and D(2)O-exchanged buffer. (2)H ENDOR spectra and simulations provide unambiguous evidence for one strongly coupled (2)H arising from a bond between the radical and an exchangeable proton of an adjacent residue or a water molecule. Orientation-selective 140-GHz ENDOR spectra indicate the direction of the hydrogen bond with respect to the molecular symmetry axes and the bond length (1.81 A). Finally, we have performed saturation recovery experiments and observed enhanced spin lattice relaxation rates of the Y* above 10 K. At temperatures higher than 20 K, the relaxation rates are isotropic across the EPR line, a phenomenon that we attribute to isotropic exchange interaction between Y* and the first excited paramagnetic state of the diiron cluster adjacent to it. From the activation energy of the rates, we determine the exchange interaction between the two irons of the cluster, J(exc) = -85 cm(-)(1). The relaxation mechanism and the presence of the hydrogen bond are discussed in terms of the differences in the structure of the Y*-diiron cofactor in yeast Y2 and other class I R2s.