4,4′‐Bis(2,2,2‐trifluoroethoxymethyl)‐2,2′‐bipyridine

As part of a homologous series of novel polyfluorinated bipyridyl (bpy) ligands, the title compound, C₁₆H₁₄F₆N₂O₂, contains the smallest fluorinated group, viz. CF₃. The molecule resides on a crystallographic inversion centre at the mid‐point of the pyridine C_ipso—C_ipso bond. Therefore, the bpy skeleton lies in an anti conformation to avoid repulsion between the two pyridyl N atoms. Weak intramolecular C—H...N and C—H...O interactions are observed, similar to those in related polyfluorinated bpy–metal complexes. A π–π interaction is observed between the bpy rings of adjacent molecules and this is probably a primary driving force in crystallization. Weak intermolecular C—H...N hydrogen bonding is present between one of the CF₃CH₂– methylene H atoms and a pyridyl N atom related by translation along the [010] direction, in addition to weak benzyl‐type C—H...F interactions to atoms of the terminal CF₃ group. It is of note that the O—CH₂CF₃ bond is almost perpendicular to the bpy plane.     

In silico prediction and screening of γ‐secretase inhibitors by molecular descriptors and machine learning methods

γ‐Secretase inhibitors have been explored for the prevention and treatment of Alzheimer's disease (AD). Methods for prediction and screening of γ‐secretase inhibitors are highly desired for facilitating the design of novel therapeutic agents against AD, especially when incomplete knowledge about the mechanism and three‐dimensional structure of γ‐secretase. We explored two machine learning methods, support vector machine (SVM) and random forest (RF), to develop models for predicting γ‐secretase inhibitors of diverse structures. Quantitative analysis of the receiver operating characteristic (ROC) curve was performed to further examine and optimize the models. Especially, the Youden index (YI) was initially introduced into the ROC curve of RF so as to obtain an optimal threshold of probability for prediction. The developed models were validated by an external testing set with the prediction accuracies of SVM and RF 96.48 and 98.83% for γ‐secretase inhibitors and 98.18 and 99.27% for noninhibitors, respectively. The different feature selection methods were used to extract the physicochemical features most relevant to γ‐secretase inhibition. To the best of our knowledge, the RF model developed in this work is the first model with a broad applicability domain, based on which the virtual screening of γ‐secretase inhibitors against the ZINC database was performed, resulting in 368 potential hit candidates. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

高效液相色谱法同时测定肉制品中的6种食品添加剂

建立了同时测定肉制品中化学性质差异较大的6种常用食品添加剂的高效液相色谱(HPLC)分析方法。根据6种添加剂(苯甲酸(钠)、山梨酸(钾)、糖精钠、安赛蜜、诱惑红和胭脂红)的化学性质,对HPLC分析条件进行了详细的优化。结果表明:以ZORBAX Eclipse Plus C18柱(150mm×4.6mm,5μm)为分析柱,以甲醇和20mmol/L醋酸铵溶液(pH为6.9)为流动相进行梯度洗脱,在235nm波长下进行检测,可以在18min内完成6种添加剂的同时测定。在高、低两个加标浓度下,样品的回收率为80.7%～94.4%,相对标准偏差(n=3)为2.0%～7.1%。结果表明,该方法快速、准确,能够同时分析测定肉制品中上述6种食品添加剂。     

A New Strategy to Identify and Eliminate the Inner Filter Effects by Outer Filter Technique

To identify and eliminate the inner filter effects (IFEs), prepositive and side cells containing absorbents are fixed beside the fluorescer contained cell. In this way, excitation and emission lights can be quenched by primary and secondary outer filter effects respectively, depending on absorbent concentration and cell length. Herein the quenching of emission fluorescence caused by IFEs can be equally reduced by outer filter effects (OFEs) and the interference of IFEs was eliminated. This approach was experimentally used for identifying the interaction mode and mechanism between BSA and nanoAg. Results showed that the quenching of BSA fluorescence and synchronous fluorescence mainly attributes to IFEs, instead of static/dynamic fluorescent quenching. In view of the above, the elimination of the interference of IFEs by the design of OFEs plays an important part in the precise application of fluorescence detector.     

求解波束波导中激励-传输-辐射问题的积分方程方法

针对波束波导系统结构和馈电特性,应用体面积分方程建立了任意结构波束波导中电磁波的激励、传输和辐射问题所对应的物理模型.在激励端,采用模式展开方法描述输入口面场分布,并利用模式匹配方法精确模拟波束波导馈电端的匹配状况.通过对波束波导内部的实际结构的精确拟合,基于积分方程建立了激励-传输-辐射的电磁模型,并以高效数值解法给...     

Effects of doping on the surface energies of nanocrystals and evidence from studies at high pressure

Zn_1−XMn_XS (X=0.85% and 1.26%) nanoparticles have been synthesized using a specially designed equipment and we have studied the influence of doping Mn²⁺ on the surface energy of ZnS. The high pressure behaviors of ZnS nanocrystals with different dopant contents have been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. Theoretical calculations show that doping with Mn²⁺ increases the surface energy of the nanocrystals. The theoretical result has been further corroborated by our experimental observation of an increase in the phase transition pressure of Mn²⁺ doped ZnS nanocrystals in diamond-anvil-cell studies.     

High-power 880-nm diode-directly-pumped passively mode-locked Nd:YVO₄ laser at 1342 nm with a semiconductor saturable absorber mirror

A high-power 880-nm diode-directly-pumped passively mode-locked 1342 nm Nd:YVO? laser was demonstrated with a semiconductor saturable absorber mirror (SESAM). The laser mode radii in the laser crystal and on the SESAM were optimized carefully using the ABCD matrix formalism. An average output power of 2.3 W was obtained with a repetition rate of 76 MHz and a pulse width of 29.2 ps under an absorbed pump power of 12.1 W, corresponding to an optical-optical efficiency of 19.0% and a slope efficiency of 23.9%, respectively.     

Ultrafast Optical Kerr Effect of ConjugatedSilver Phenylacetylide Complex Oligomer

Conjugatedpolymerswithlargethird-orderopticalnonlinearityhavebeedfocusedfortheirpromisingpotentialsforadvancedmaterialsapplications'.Recently,investigationsoftransitionmetalwithorganicligandsystemshavebeengreatlyintensifiedduetothedelectronsincorporatedintheconjugatedsystem,whichareexpectedtoellhancethehyperpolarizability.Phenylacetyleneandthemetalphenylacetylidesplayimportantrolesinformationofuniquecoordinatedc-lusters',butitseamsthatthestudyofmetalphenylacetylides,particularlyofthesilverphen…     

Some results on difference Riccati equations

Some properties of solutions for the difference Riccati equations are obtained. The existence and forms of rational solutions, and the Borel exceptional value, zeros, poles and fixed points of transcendental solutions are researched.     

EAST快速极紫外光谱仪绝对强度的原位标定

磁约束等离子体中杂质(特别是高Z杂质)的存在将大大增强等离子体辐射功率损失，破坏等离子体的约束性能。杂质行为的定量研究首先要求对杂质测量的光谱诊断系统进行绝对强度标定，获得灵敏度响应曲线。介绍了EAST托卡马克上的快速极紫外光谱仪系统绝对强度的原位标定方法。在波长范围20～150Å内，通过对比极紫外(EUV)波段连续轫致辐射强度的计算值和测量值得到光谱仪的绝对强度标定。在此过程中，首先由(523±1) nm范围内可见连续轫致辐射强度的绝对测量值计算出有效电荷数Z_eff，进而结合电子温度和密度分布计算EUV波段连续轫致辐射强度；EUV波段连续轫致辐射强度的测量值即为不同波长处探测器的连续本底计数扣除背景噪声计数值。对于较长波段范围130～280Å，通过对比等离子体中类锂杂质离子(Fe23+，Cr21+，Ar15+)和类钠杂质离子(Mo31+，Fe15+)发出的共振谱线对(跃迁分别为1s22s 2S_1/2-1s22p 2P_{1/2, 3/2}及2p63s 2S_1/2-2p63p 2P_{1/2, 3/2})强度比的理论和实验值进行相对强度标定。其中共振谱线对强度比的理论值由辐射碰撞模型计算得到，模型中处在各个能级的离子数主要由电子碰撞激发，去激发以及辐射衰变三个过程决定。两种方法相结合，实现了光谱仪20～280Å范围的绝对强度标定。考虑轫致辐射、电子温度及电子密度的测量误差，绝对标定误差约为30%。在绝对标定的基础上，我们对杂质特征谱线强度进行绝对测量，并将测量结果与杂质输运程序结合ADAS(Atomic Data and Analysis Structure)原子数据库计算得到的模拟值进行比较，进而估算等离子体中的杂质浓度。