Preparation, characterization, and application of electrodes modified with electropolymerized one-dimensional Magnus' green salts: Pt(NH3)4 · PtCl4 and Pt(NH3)4 · PtCl6

We report the modification of various electrode surfaces with electropolymerized Magnus' green salts, [Pt(NH₃)₄ · PtCl₄] _n and [Pt(NH₃)₄ · PtCl₆] _n . The modified electrodes were prepared by cyclic scanning of the electrode potential in an aqueous solution containing Pt(NH₃)₄ ²⁺ and PtCl₄ ²⁻ or PtCl₆ ²⁻ and the supporting electrolyte. The conditions for the film deposition were studied in detail. Several surface analytical techniques, including micro-Raman scattering and X-ray diffraction, were employed to characterize the modifier film. The electrochemical behavior of the modified electrode was studied in detail and the modified electrodes display very good electrocatalytic activity in the oxidation of ascorbic acid, hydrogen peroxide, thiosulfate, and especially nitric oxide. Received: 22 April 1999 / Accepted: 30 June 1999     

Solid State Analysis with the New Leipzig High-Energy Ion Nanoprobe

 The high-energy ion nanoprobe LIPSION at the University of Leipzig has been operational since October 1998. The ultrastable single ended 3.5 MV SINLETRON^TM accelerator supplies the H⁺ or He⁺ ion beam. A magnetic scanning system moves the focused beam across the sample. At present, a resolution of 150 nm in the low current mode and 300 nm at 5 pA could be achieved. The UHV grade experimental chamber is equipped with electron-, energy dispersive X-ray-, and particle detectors. They can be used simultaneously to analyse the sample by means of PIXE (particle induced X-ray emission), RBS (Rutherford backscattering) and in the case of thin samples STIM (scanning transmission ion microscopy). A goniometer allows the application of channeling measurements in single crystals in combination with these methods. The detection limits depend on the elements to be analysed and range from (1000⋯1) μg/g relative and (1⋯0.01) pg absolute. The analysis is nondestructive, but the sample has to be vacuum resistant. Applications of the nanoprobe in the field of semiconductor research, biomedicine, and archaeology will be described.     

金属离子修饰的铂纳米金属簇催化2,3-戊二酮区域选择性氢化

近年来,α-二酮的不对称氢化引起了人们的极大兴趣[1～3].由于α-二酮分子内存在两个共轭的羰基,α-二酮的氢化包括两步反应,通过控制反应条件可以使反应停留在第一步氢化的阶段[3].在已往的文献报道中[1～3],氢化反应的底物均局限于对称的α-二酮,如2,3-丁二酮或3,4-己二酮.这类底物的第一步氢化并不涉及区域选择性的问题.以2,3-丁二酮为例,第一步氢化只生成3-羟基-2-丁酮一种产物.但是,象2,3-戊二酮之类的不对称α-二酮的氢化情况则复杂得多,因为在第一步反应中有2-羟基-3-戊酮和3-羟基-2-戊酮两种产物生成.因此,在研究不对称α-二酮的对映体选择性氢化时还必须顾及其区域选择性氢化.     

用于检测水环境中银离子浓度的荧光适体传感器研究

银凭借其独特的性能,在医疗材料、摄影、电子、成像等行业中应用广泛。然而,银离子被列为最具毒性的重金属离子之一,会对环境以及人类的生命健康造成严重威胁。为了灵敏、特异性的检测水环境中的银离子浓度,利用纳米金的优良光学猝灭性以及双链核酸适体捕获银离子能力更强的优点,结合荧光能量共振转移原理,提出一种用于检测水环境中银离子浓度的荧光适体传感器。将修饰SH键的核酸适体与纳米金混合形成稳定的纳米结构,并加入标记有FAM的核酸适体,形成检测银离子浓度的工作溶液。当不存在银离子时由于不匹配碱基C-C之间的排斥力导致两条核酸适体不结合,反应体系中具有较强的荧光;当存在银离子时,双链核酸适体中不匹配的C-C能与银离子通过金属离子-碱基的相互作用形成稳定的C-Ag+-C碱基对,这种复合结构的产生会拉近纳米金和荧光基团之间的距离,使得荧光信号随着银离子浓度的增加而逐渐减弱。根据加入银离子前后荧光强度的变化可实现银离子浓度的检测。同时,为了提高传感器的灵敏性和稳定性,实验优化了工作溶液中纳米金与核酸适体的浓度比、氯化钠浓度、缓冲液的pH以及培养温度等参数。结果表明,当浓度为0.012 5 g·L-1的纳米金与5 μmol·L-1核酸适体的体积比为5∶1,NaCl浓度为260 mmol·L-1,缓冲液pH 7,培养温度为30 ℃时,工作溶液初始荧光强度最强,银离子检出限为10 nmol·L-1,相关系数为R2=0.99。此外,该传感器对银离子的浓度检测表现出较好的特异性,且具有操作简单、灵敏和不引入有毒溶剂等优点,在水环境中的银离子浓度检测领域有较好的应用前景。     

ChemInform Abstract: Predicted Lithium—Boron Compounds under High Pressure.

The existence of Li₃B₂, Li₂B, Li₄B, and Li₆B that might be experimentally synthesizable over a wide range of pressures is predicted by an unbiased structure search method based on particle‐swarm optimization algorithms in combination with DFT calculations.     

核物质对称能和重离子碰撞中径向流阈能的同位旋效应

基于同位旋相关的量子分子动力学模型，采用三种不同形式的对称势，研究了¹²⁴Sn+¹²⁴Sn和¹²⁴Ba+¹²⁴Ba对心碰撞时在三种不同对称势下的径向膨胀流，发现径向膨胀流阈能与所采用的对称能形式密切相关，表现出明显同位旋效应，预示着径向膨胀流阈能的同位旋相关性可作为对称能的灵敏探针. 关键词： 径向膨胀流阈能 同位旋效应 重离子碰撞 同位旋相关的量子分子动力学模型     

Mechanism of relaxation enhancement of spin labels in membranes by paramagnetic ion salts: dependence on 3d and 4f ions and on the anions

Progressive saturation EPR measurements and EPR linewidth determinations have been performed on spin-labeled lipids in fluid phospholipid bilayer membranes to elucidate the mechanisms of relaxation enhancement by different paramagnetic ion salts. Such paramagnetic relaxation agents are widely used for structural EPR studies in biological systems, particularly with membranes. Metal ions of the 3d and 4f series were used as their chloride, sulfate, and perchlorate salts. For a given anion, the efficiency of relaxation enhancement is in the order Mn(2+) > or = Cu(2+) > Ni(2+) > Co(2+) approximately Dy(3+). A pronounced dependence of the paramagnetic relaxation enhancement on the anion is found in the order ClO(-)(4) > Cl(-) > SO(2-)(4). This is in the order of the octanol partition coefficients multiplied by spin exchange rate constants that were determined for the different paramagnetic salts in methanol. Detailed studies coupled with theoretical estimates reveal that, for the chlorides and perchlorates of Ni(2+) (and Co(2+)), the relaxation enhancements are dominated by Heisenberg spin exchange interactions with paramagnetic ions dissolved in fluid membranes. The dependence on membrane composition of the relaxation enhancement by intramembrane Heisenberg exchange indicates that the diffusion of the ions within the membrane takes place via water-filled defects. For the corresponding Cu(2+) salts, additional relaxation enhancements arise from dipolar interactions with ions within the membrane. For the case of Mn(2+) salts, static dipolar interactions with paramagnetic ions in the aqueous phase also make a further appreciable contribution to the spin-label relaxation enhancement. On this basis, different paramagnetic agents may be chosen to optimize sensitivity to different structurally correlated interactions. These results therefore will aid further spin-label EPR studies in structural biology.     

Preparation and Characterization of Electroactive Anion‐Exchange Acrylic Polymer–Gold Composites

The characteristics and performance of an ionic polymer–metal composite (IPMC), prepared with an anion‐exchange acrylic copolymer, was examined. The acrylic copolymer was synthesized by the radical copolymerization of fluoroalkyl methacrylate and 2‐(dimethyl amino)ethyl methacrylate(AMA). Effects of the AMA repeating unit's content in the copolymer and effects of the anion type present on the actuation of the IPMC were observed. The optimal content of 19.4 wt% AMA in the IPMC copolymer yielded the best actuation. The actuation also improved according to the type of anion present in the composite, in the following order: Br^???4 ^?.     

Influence of cooperativity on the frequency shift of the Ar–H stretch vibration in HArF complexes

CH₃Li–FArH–X (X?=?H₂, OC, N₂, P₂, CO₂, CO, BeH₂) trimers have been investigated using quantum chemical calculations at the QCISD/6-311++G(2d,2p) level. The results show that the lithium bonding has a prominent effect on the strength and properties of the hydrogen bonding. The hydrogen-bonding interaction energy is increased by 160–340% due to the presence of lithium bonding. The Ar–H stretch vibration shows a blue shift in the FArH–X (X?=?H₂, OC, N₂, CO₂, CO) dimer, but a red shift in the FArH–X (X?=?P₂, BeH₂) dimer. The red shift is increased in the corresponding trimer, while the blue shift shows a different change. The blue shift is also increased in CH₃Li–FArH–X (X?=?H₂, OC, N₂, CO₂) trimers, but it changes to a red shift in the CH₃Li–FArH–CO trimer. The shift change is consistent with the explanation given by Joseph and Jemmis.