Syntheses and Studies of PEG-b-PNIPA Block Polymers

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Structure and Magnetic Properties of Nickel–Zinc Ferrite Nanoparticles Prepared by Glass Crystallization Method

Summary. The magnetic and microstructure properties of Fe₂O₃–0.4NiO–0.6ZnO–B₂O₃ glass system, which was subjected to heat treatment in order to induce a magnetic crystalline phase (Ni_0.4Zn_0.6-Fe₂O₄ crystals) within the glass matrix, were investigated. DSC measurement was performed to reveal the crystallization temperature of the prepared glass sample. The obtained samples, produced by heat treatment at 765°C for various times (1, 1.5, 2, and 3 h), were characterized by X-ray diffraction, IR spectra, transmission electron microscopy, and vibrating sample magnetometer. The results indicated the formation of spinel Ni–Zn ferrite in the glass matrix. Particles of the ferrite with sizes ranging from 28 to 120 nm depending on the sintering time were observed. The coercivity values for different heat-treatment samples were found to be in the range from 15.2 to 100 Oe. The combination of zinc content and sintering times leads to samples with saturation magnetization ranging from 12.25 to 17.82 emu/g.     

High-vacuum pyrolysis of 1,1,1-trifluoro-2-bromo-2-chloroethane. IR spectrum of 1,1,1-trifluoro-2-chloroethyl radical in an argon matrix

The products of high-vacuum pyrolysis of 1,1,1-trifluoro-2-bromo-2-chloroethane were studied by matrix IR spectroscopy. The decomposition of 1,1,1-trifluoro-2-bromo-2-chloroethane was shown to occur predominantlyvia two directions: to form the 1,1,1-trifluoro-2-chloroethyl radical and trifluoromethylcarbene isomerizing to trifluoroethylene. The CF₃CHCl radical has been detected in the matrix for the first time. The bands observed in the IR spectrum were calculated by the quantum-chemical B3LYP/6-311 G(d,p) method and assigned to normal vibrations of the radical. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2085–2088, October, 1998.     

高分辨等离子体质谱法直接测定高纯镓中的痕量元素

建立高分辨电感耦合等离子体质谱法(HR-ICP-MS)测定高纯镓样品中Be、Mg、A l、S i、Ti、V、Cr、Mn、Fe、Co、N i、Cu、Zn、Ge、As、Mo、Ag、Cd、In、Sb、Ba、Pb、B i等痕量元素的方法。样品用HNO3 HC l经微波消解后,试液直接进样用HR-ICP-MS法同时测定上述元素,在高分辨质谱测量模式下避免了大量的质谱干扰,详细地研究了HC l和高纯镓所产生的基体效应,以Sc、Rh、Tl作为内标元素校正了基体效应,讨论和确定了实验的最佳测定条件。结果表明,23种痕量元素的检出限在0.001~0.21μg/L之间;回收率在89.8%~111.6%之间,相对标准偏差(RSD)小于3.3%。     

A simple scheme for calculating the energy levels and the spectra of molecular crystals

A simple matrix method for calculating the vibrational and electron energy levels and spectra in molecular crystals is proposed.     

A Closed-Form Relation for Dimension-Dependent Two-Electron Matrix Elements of the Interelectronic Distance

The evaluation of matrix elements of two electron atoms is fundamental for the study of the electronic properties of those systems. We add to this knowledge by presenting an explicit expression for the matrix elements of the inverse of the interelectronic distance of two-electron atoms in any spatial dimension D. The basis functions used are the D-dependent hydrogenic wavefunctions {1s ²,2p ²,3d ²,4f ²,5g ²,...,21y ²,...}, extending and including, in this way, the results of the previous basis set {1s ²,2p ²,3d ²,4f ²}. The methodology used does not employ Fourier integral transforms as in previous works but hypergeometric transformation formulas.     

Protein secondary structure and stability determined by combining exoproteolysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In the post-genomic era, several projects focused on the massive experimental resolution of the three-dimensional structures of all the proteins of different organisms have been initiated. Simultaneously, significant progress has been made in the ab initio prediction of protein three-dimensional structure. One of the keys to the success of such a prediction is the use of local information (i.e. secondary structure). Here we describe a new limited proteolysis methodology, based on the use of unspecific exoproteases coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), to map quickly secondary structure elements of a protein from both ends, the N- and C-termini. We show that the proteolytic patterns (mass spectra series) obtained can be interpreted in the light of the conformation and local stability of the analyzed proteins, a direct correlation being observed between the predicted and the experimentally derived protein secondary structure. Further, this methodology can be easily applied to check rapidly the folding state of a protein and characterize mutational effects on protein conformation and stability. Moreover, given global stability information, this methodology allows one to locate the protein regions of increased or decreased conformational stability. All of this can be done with a small fraction of the amount of protein required by most of the other methods for conformational analysis. Thus limited exoproteolysis, together with MALDI-TOF MS, can be a useful tool to achieve quickly the elucidation of protein structure and stability.     

生物体系中电子转移机理的研究Ⅱ: 分子间电子转移及 电子供、受体间不同基 团的影响

利用自编程序MOPAC-ET中AM1方法,及KT(Koopman'sTheorem)法,研究了二苯负离子体系的分子间电子转移现象,计算了其电子供、受体在不同距离下的V~A~B及它们之间的相关性,另外,还对两苯环间不同介入基团对电子转移的影响做了初步研究,发现不同的介入基团存在着较大的差异。     

苯乙烯-异戊二烯两嵌段共聚物溶液的dn/dc和紫外吸收光谱

本文研究了苯乙烯-异戊二烯两嵌段共聚物在CHCl_3中的折光指数浓度增量(dn/dc)和紫外吸收光谱。嵌段共聚物dn/dc具有很好的加和性,可以测定嵌段共聚物的组成。紫外吸收光谱的结果表明,除低苯乙烯含量的样品外,其它嵌段共聚物都显示明显的紫外增色性(UV hyperchromism)。因此UV和UV-RI双检测GPC不会得到可靠的嵌段共聚物组成数据。这种增色现象与其特征的紫外吸收谱图紧密关联     

SYNTHESIS OF BLOCK COPOLYMER FROM 5,6 -BENZO-2-METHYLENE-1,3-DIOXEPANE AND METHYL ACRYLATE VIA ATOM TRANSFER RADICAL POLYMERIZATION

Poly(methyl acrylate)-b-poly(5,6-benzo-2-methylene-1, 3-dioxepane) (PMA-b-PBMDO) was synthesized by two-step atom transfer radical polymerization (ATRP). Firstly, ATRP of methyl acrylate (MA) was realized using ethyl α-bromobutyrate (EBrB) as initiator in the presence of CuBr/2,2'-bipyridine. After isolation, poly(methyl acrylate) withterminal bromine (PMA-Br) was synthesized. Secondly, the resulting PMA-Br was used as a macromolecular initiator in theATRP of BMDO. The Structure of block copolymer was characterized by ~1H-NMR spectroscopy. Molecular weight andmolecular weight distribution were determined on a gel permeation chromatograph (GPC).