Fluorescent Triphenyl Substituted Maleimide Derivatives: Synthesis,Spectroscopy and Quantum Chemical Calculations

In this paper we describe a semi-empirical quantum method for predicting the wavelength of maximum fluorescence excitation and emission for several known and new maleimide derivatives. All new maleimides, containing a N-Benzyl attachment, were successfully synthesised via a tandem Suzuki reaction with aryl boronic acids containing either an electron donating, electron withdrawing functional groups. Absorption and emission spectra calculated using the semi-empirical AM1 method with excited state ZINDO calculations proved more reliable than either Hartree-Fock Configuration interaction or time dependent density functional methods. Calculated absorption and emission wavelengths were compared with 26 experimental spectra from known or newly synthesised maleimides and found to have provide reasonable predictions, with an average deviation of less the 6% for absorption maxima and less than 4% for emission peaks. The described method provides a strong benchmark for the accuracy that can be expected from theoretical predictions of fluorescence spectra.     

Nickel(II) complexes bearing pyrazolylimine ligand: synthesis,structure, and catalytic properties for vinyl‐type polymerization of norbornene

Two nickel(II) complexes of {2‐[C₃HN₂(R₁)₂‐3,5]}[C(R₂)?N(C₆H₃ⁱPr₂‐2,6)]NiBr₂ (complex 1 : R₁ = CH₃, R₂ = 2,4,6‐trimethylphenyl; complex 2 : R₁ = R₂ = Ph) were synthesized and characterized. The solid‐state structure of complex 1 has been confirmed by X‐ray single‐crystal analysis. Activated by methylaluminoxane (MAO), complexes 1 and 2 are capable of catalyzing the polymerization of norbornene with moderate activities [up to 10.56 × 10⁵ gPNBE (mol Ni h)^?1] with high molecular weights (M_w?13.56 × 10⁵ g mol^?1) and molecular weight distributions were around 2. The influences of polymerization parameters such as reaction temperature and Al–Ni molar ratio on catalytic activity and molecular weight of the polynorbornene were investigated in detail. The obtained polynorbornenes were characterized by means of ¹H‐NMR and FTIR techniques. The analytical results of polymer structures indicated that the norbornene polymerization is vinyl‐type polymerization rather than ROMP. Copyright © 2009 John Wiley & Sons, Ltd.     

介孔钯-硼合金纳米颗粒的制备和甲醇氧化电催化性能北大核心CSCD

合金化可以调节贵金属纳米材料的物理化学性质,从而显著提升它们的电催化性能。尽管合金化在过去的20多年里已取得诸多成果,但是如何充分发挥纳米合金的组分优势仍需深入的探究。本研究通过一步溶液相合成法实现了类金属硼(B)合金化的钯基介孔纳米催化剂材料的合成,同时探究了B原子的组分优势和介孔形貌的结构优势在碱性介质中电化学甲醇氧化反应(MOR)的协同作用。最优PdCuB介孔纳米催化剂表现出优异的电化学MOR活性和稳定性。机理研究表明,优异的催化活性源于B原子在Pd基介孔纳米催化剂中的积极协同作用;该协同作用通过电子效应(改变Pd的表面电子结构从而减弱CO基中间体的吸附)和双功能效应(促进OH_(2)的吸附从而氧化CO基中间体)在动力学上加速了有毒CO基中间体的去除(提高甲醇氧化的决速步骤)。同时,B原子的间隙插入和介孔结构抑制了物理奥斯特瓦尔德(Ostwald)熟化过程,显著增加了催化剂的稳定性。     

Fast Fabrication and Judgement of Tip-Enhanced Raman Spectroscopy-Active Tips

The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy (TERS) experiments towards large signal enhancement and high spatial resolution. In this work, we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale, and propose two important criteria to in-situ judge the tip's TERS activity for tip-enhanced Raman measurements. One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon; the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field. This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials, which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.     

基于ZIF-8/PAN复合薄膜的柔性丙酮气体传感器

ZIF-8是一种Zn基金属有机骨架材料, 可以吸附丙酮气体从而作为电容式丙酮传感器的气敏材料, 然而ZIF-8的传统使用形式为粉末态, 这导致其不能成为具备柔性的整体, 从而限制了传感器的柔性. 结合包埋种子和二次生长法将ZIF-8与纳米纤维结合成纤维型柔性材料, 并将其作为气敏层制备了柔性电容式丙酮气体传感器. 该传感器在9种常见挥发性有机化合物中表现出良好的选择性, 对250~2000 cm³/m³的丙酮气体具有灵敏的响应、良好的循环响应及长期稳定性. 值得注意的是该柔性传感器不仅在室温下进行传感, 而且在弯折180°的状态下对丙酮气体的响应值与不弯折(0°)状态下几乎一致, 在200次以内的180°弯折-恢复后同样表现出了传感性能的稳定, 表明了其在柔性传感器方面的潜力.     

A rapid heating and high magnetic field thermal analysis technique

Journal of Thermal Analysis and Calorimetry - A new thermal analysis technique is described that allows measurements to be performed on bulk samples at extreme heating and cooling rates and in high...     

Electrokinetic characterization of hybrid NOA 81-glass microchips: Application to protein microchip electrophoresis with indirect fluorescence detection

A low-cost and straightforward hybrid NOA (Norland optical adhesive) 81-glass microchip electrophoresis device was designed and developed for protein separation using indirect fluorescence detection. This new microchip was first characterized in terms of surface charge density via electroosmotic mobility measurement and stability over time. A systematic determination of the electroosmotic mobility (μ_eo) over a wide pH range (2–10) and at various ionic strengths (20–50 mM) was developed for the first time via the neutral marker approach in an original simple frontal methodology. The evolution of μ_eo was proved consistent with the silanol and thiol functions arising from the glass and the NOA materials, respectively. The repeatability and reproducibility of the measurements on different microchips (RSD < 14%) and within 15 days (less than 5% decrease) were successfully demonstrated. The microchip was then applied for the efficient electrophoretic separation of proteins in a zonal mode coupled with indirect fluorescence detection, which is, to our knowledge, the first proof of concept of capillary zone electrophoresis in this hybrid microsystem.     

Development of ultra-high-performance supercritical fluid chromatography-mass spectrometry assays to analyze potential biomarkers in sweat

Liquid chromatography-mass spectrometry methods were required to afford the rapid separation and detection of purines and small organic acids. These compounds are found in sweat and sebum and are potential biomarkers for the early detection of pressures sores. Two ultra-high-performance supercritical fluid chromatography-mass spectrometry assays have been successfully developed for both classes of compounds. Separation for purines was achieved using a gradient of supercritical carbon dioxide and methanol with a 1-aminoanthracene sub 2 μm particle size column followed by positive ion electrospray ionization. Separation for organic acids was achieved using a gradient of supercritical carbon dioxide and methanol (50 mM ammonium acetate 2% water) with a Diol sub 2 μm particle size column followed by negative ion electrospray ionization. Calibration curves were created in the absence of internal standards and R² values > 0.96 were achieved using single ion monitoring methods for the protonated purines and the deprotonated acids. The two new assays afford rapid analytical methods for the separation and detection of potential biomarkers in human sweat leading to the early detection and prevention of pressure sores.     

Chiral Compounds Synthesized by Biocatalytic Reductions [New Synthetic Methods (51)]

It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H₂ and hydrogenase-containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen-dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10- to 100-fold higher than those of substances obtained by conventional techniques.     

超高效液相色谱-四极杆飞行时间质谱法同时测定食品接触用塑料中50种添加剂的迁移量

为评估食品接触用塑料中添加剂的迁移风险,采用超高效液相色谱－四极杆飞行时间质谱（UPLC－QTOF MS）建立了同时测定食品接触用塑料中50种添加剂迁移量的方法。以甲醇和0.01%（体积分数）甲酸－5 mmol/L乙酸铵溶液为流动相进行洗脱,采用目标离子采集（Target MS/MS）模式对目标物的一级离子与二级离子进行监测。结果表明,各物质在0.02～5 mg/L质量浓度范围内线性关系良好,方法检出限为0.01～0.1 mg/kg,加标回收率为92.6%～104%,相对标准偏差（RSD）为0.60%～8.4%。在20款实际样品中有12个样品检出塑料添加剂,其中2个样品检出壬基酚,迁移量为0.033～0.071 mg/kg;6个样品检出抗氧化剂1076和抗氧化剂168,迁移量为0.12～3.3 mg/kg;4个样品检出光引发剂369、光引发剂ITX和光引发剂TPO,迁移量为0.054～4.0 mg/kg。该方法简单、灵敏、准确,适用于食品接触用塑料中50种添加剂迁移量的检测。