用WAXD和SAXS研究辐照聚酰胺1010结构

用ＷＡＸＤ和ＳＡＸＳ方法研究了聚酰胺１０１０的聚集态结构和结晶结构的辐射损伤过程和机理。辐射交联与裂解主要在非晶区和结晶表面或中间相发生；辐射损伤并从这里开始，随辐射剂量增大，非晶化逐渐向晶区伸展，有氢键的（０１０）晶面损伤几率高于（１００）晶面；辐射后效应导致新的交联与裂解生成，主要影响（０１０）晶面的形成与完善，使Ｌ１００及Ｗｃ变小。     

K对Mn—Co—O的结构及氧化活性的影响

利用XRD,TPD,TFD-MS及催化氧化反应等实验技术,研究了K对Mn-Co-O的结构及氧化活性的影响。XRD结果表明,Mn-Co-O系已形成反尖晶石型的MnCo_2O_4结构;K-Mn-Co-O系中除MnCo_2O_4型结构外,还有新相KMnO_2存在。根据O_2的TPD-MS及吡啶的TPD结果,Mn-Co-O中添加适量的K能提高供氧活性和增加供氧数目,但酸中心数目减少,强度降低。K对Mn-Co—O催化剂氧化活性的影响随反应物分子结构的不同而异,对乙酸乙脂、苯甲酰氯等极性有机物的完全氧化反应,K能提高氧化活性,但对苯、正己烷等非极性有机物的完全氧化反应,K使其活性降低。     

Synthesis and electrochemical properties of Zn3V3O8 as novel anode material

Zn₃V₃O₈ two-dimensional micro sheets are successfully synthesized by combination of solvothermal method and heat treatment. The Zn₃V₃O₈ has better electrochemical performances after calcinations.     

Solution-phase preparation of a 560-compound library of individual pure mappicine analogues by fluorous mixture synthesis

Solution-phase mixture synthesis has efficiency advantages and favorable reaction kinetics. Applications of this technique, however, have been discouraged by the difficulty in obtaining individual, pure final products by using conventional separation and identification processes. Introduced here is a new strategy for mixture synthesis that addresses the separation and identification problems. Members of a series of organic substrates are paired with a series of fluorous tags of different chain lengths. The tagged starting materials are then mixed and taken through a multistep reaction process. Fluorous chromatography is used to demix the tagged product mixtures on the basis of the fluorine content of the tags to provide the individual pure components of the mixture, which are detagged to release the final products. The utility of fluorous mixture synthesis is demonstrated by the preparation of a 560-membered library of analogues of the natural product mappicine. A seven-component mixture is carried through a four-step mixture synthesis (two one-pot and two parallel steps) to incorporate two additional points of diversity onto the tetracyclic core. Methods for analysis and purification of the intermediates are established for the quality control of the mixture synthesis.     

Synthesis and Electrochemical Studies of Spinel LiNi1−xMnxVO4

Spinel compound LiNi_1−xMn_xVO₄ (0≤x≤0.4) had been prepared by using the moist chemical method. X-ray diffraction spectra showed that the lattice constant increased with x in the LiNi_1−xMn_xVO₄, XPS spectra indicating that Li1s had a chemical shift towards lesser binding energy, and manganese in LiNi_1−xMn_xVO₄ existing as the mixed valence of Mn²⁺ and Mn³⁺. The electrochemical charge and discharge testing at a current density of 0.1 mA/cm² between the potentials of 4.0 and 3.0 V vs Li/Li⁺ in 1 mol/dm³ LiPF₆/EC+DEC (1:1 by volume) at 25°C showed that LiNi_1−xMn_xVO₄ cell has a better rechargeability, but a lower cell voltage of 4.0 V vs Li/Li⁺ than that without the doping sample, and the capacity and the cycle efficiency of the Li/LiNi_1−xMn_xVO₄ cells increased with x in the LiNi_1−xMn_xVO₄.     

Synthetic and mechanistic studies of the retro-Claisen rearrangement. 4. An application to the total synthesis of (+)-Laurenyne

[formula: see text] A novel asymmetric total synthesis of marine natural product (+)-Laurenyne has been achieved. The key elements of the strategy are the sequential metal ion-templated SN2' cyclization affording a highly functionalized chiral vinyl cyclobutane and a retro-Claisen rearrangement for the construction of an eight-membered ring ether.     

Temperature dependence of the distribution of the first passage time: results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Gō-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T(opt). The optimal folding temperature T(opt) is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T(opt) and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T(opt) and start to diverge when the temperature is lower than T(opt). The distribution of FPT is close to a log-normal-like distribution at T > or = T(opt). At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.     

Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.     

Shape control and associated magnetic properties of spinel cobalt ferrite nanocrystals

By combining nonhydrolytic reaction with seed-mediated growth, high-quality and monodisperse spinel cobalt ferrite, CoFe(2)O(4), nanocrystals can be synthesized with a highly controllable shape of nearly spherical or almost perfectly cubic. The shape of the nanocrystals can also be reversibly interchanged between spherical and cubic morphology through controlling nanocrystal growth rate. Furthermore, the magnetic studies show that the blocking temperature, saturation, and remanent magnetization of nanocrystals are solely determined by the size regardless the spherical or cubic shape. However, the shape of the nanocrystals is a dominating factor for the coercivity of nanocrystals due to the effect of surface anisotropy. Such magnetic nanocrystals with distinct shapes possess tremendous potentials in fundamental understanding of magnetism and in technological applications of magnetic nanocrystals for high-density information storage.     

An ab initio study on luminescent properties and aurophilic attraction of binuclear gold(I) complexes with phosphinothioether ligands

Electronic structures and spectroscopic properties of the binuclear head-to-tail [Au(2)(PH(2)CH(2)SH)(2)](2+) (1) complex were investigated by ab initio calculations. The solvent effect of the complex in the acetonitrile solution was taken into account by the weakly solvated [Au(2)(PH(2)CH(2)SH)(2)](2+).(MeCN)(2) (2) moiety in the calculations. The ground-state geometries of 1 and 2 were fully optimized by the MP2 method, while their excited-state structures were optimized by the CIS method. Aurophilic attraction apparently exists between the two Au(I) atoms in the ground state and is strongly enhanced in the excited state. A high-energy phosphorescent emission was calculated at 337 nm for 1 in the absence of the interactions with solvent molecules and/or counteranion in solid state; however the lowest-energy emission of 2 was obtained at 614 nm with the nature of (3)A(u)(s(sigma)) --> (1)A(g)(d(sigma)) (metal-centered, MC) transition. The coordination of acetonitrile to the gold atom in solution results in a dramatic red shift of emission wavelength. The investigations on the head-to-tail [Au(2)(PH(2)CH(2)SCH(3))(2)](2+) (5) and [Au(2)(PH(2)CH(2)SCH(3))(2)](2+).(MeCN)(2) (6) moieties indicate that the CH(3) substituent on the S atom causes blue shifts of emission wavelength for 5 and 6 with respect to 1 and 2. By comparison between Au(I) thioether 1 and head-to-tail Au(I) thiolate [Au(2)(PH(2)CH(2)S)(2)] (7), it is concluded that the S-->Au dative bonding results in evidently different transition characteristics from the S-Au covalent bonding in the Au(I) thioether/thiolate complexes.