关键词： luminescence   photochemistry   redox chemistry   self-assembly   self-complexation   template syntheses  

摘要： Photochemical control of a self-assembled supramolecular 1:1 pseudorotaxane (formed between a tetracationic cyclophane, namely the tetrachloride salt of cyclobis(paraquat-p-phenylene), and 1,5-bis[2-(2-(2-hydroxy)ethoxy)ethoxy]naphthalene) has been achieved in aqueous solution, The photochemical one-electron reduction of the cyclophane to the radical trication weakens the noncovalent bonding interactions between the cyclophane and the naphthalene guest-pi-pi interactions between the pi-electron-rich and pi-electron-poor aromatic systems, and hydrogen-bonding interactions between the acidic alpha-bipyridinium hydrogen atoms of the cyclophane and the polyether oxygen atoms of the naphthalene derivative-sufficiently to allow the guest to dethread from the cavity;the process can be monitored by the appearance of naphthalene fluorescence. The radical tricationic cyclophane can be oxidized back to the tetracation in the dark by allowing oxygen gas into the system. This reversible process is marked by the disappearance of naphthalene fluorescence as the molecule is recomplexed by the tetracationic cyclophane. This supramolecular system can be chemically modified such that the pi-electron-rich unit, either a naphthalene derivative or a hydroquinone ring, and the tetracationic cyclophane are covalently linked, We have demonstrated that the pi-electron-rich residue in this system is totally ''self-complexed'' by the cyclophane to which it is covalently attached. Additionally, the self-complexation can be switched ''off'' and ''ion'' by electrochemical two-electron reductions and oxidations, respectively, of the tetracationic cyclophane component, Thus, we have achieved the construction of two switches at the nanoscale level, one driven by photons and the other by electrons.

关键词： in situ STM   adsorbates   three-level processes   cytochrome c   azurin  

摘要： The electronic tunnel factor in homogeneous long-range electron transfer (ET) systems has been characterized experimentally and theoretically in great detail. Outstanding questions, however, remain, for example interference in multiple ET routes and environmentally induced barrier fluctuations. Well characterized electrochemical long-range ET systems have also become available where the tunnel factor can be accurately deconvoluted from the total current. Intriguing new effects here are associated with the electrode charge or overpotential effects on the tunnel factor and with the feasibility of observation of critical current behaviour near phase transitions in thin films across which electron tunnelling occurs. In situ scanning tunnel microscopy (STM) offers a conceptual and technical new frame for mapping of molecular ET routes through large adsorbate molecules with low-lying local fluctuating levels. Such a configuration would be representative of large transition metal complexes or redox metalloproteins. High-resolution images and new theoretical approaches to STM mapping of large adsorbates are, moreover reported. The independent in situ electrode potential control provides new, non-monotonous features in the current-voltage relations which differ from electrochemical ET behaviour at a single interface. Copyright (C) 1996 Elsevier Science Ltd.

关键词： 电气化县   议案   进程  

摘要： The investigation of mechanisms of electrochemical processes often requires the comparison of experiemntal current-voltage dependence and a theoretical wave shape corresponding to an assumed model. Theoretical relationships between an electrochemical observable and the electrode potential are obtained by solving the mass-transport equations with appropriate initial and boundary conditions. Complicated reaction schemes often lead to nonlinear equations that can only be treated by simulation techniques. Here, we focus on these techniques in the cases of irregular and fractal surfaces.

关键词： ELECTROCHEMICAL KINETICS   PHOTOSTIMULATED ELECTRODES   ELECTROCATALYSIS   ELECTRODE MODIFICATION   SPIROPYRAN DERIVATIVES   PYRROLOQUINOLINOQUINONE   NAD(P)H   OPTICAL MEMORY   PHOTOSWITCHABLE ELECTRODES  

摘要： Photoisomerizable self-assembled spiropyran (SP) monolayers on Au electrodes provide a means of transducing optical signals recorded by the monolayers as amperometric responses. An SP-modified monolayer on a Au electrode photostimulated the redox communication of pyrroloquinorinoquinone (PQQ) with the electrode interface. The electrical communication of PQQ with the SP monolayer state generated by visible light irradiation (lambda > 475 nm) is inefficient. However, effective electrical communication is attained between PQQ and the protonated merocyanine monolayer electrode ((MRH)(+) electrode) generated by illumination (360 nm < lambda < 400 nm). Reversible photoisomerization of the monolayer between the SP and (MRH)(+) states is transduced by cyclic amperometric responses. A mixed PQQ + SP monolayer on a Au electrode provides an active electrode for the photostimulated oxidation of NAD(P)H cofactors in the presence of Ca2(+) ions. While the PQQ + SP monolayer electrode exhibits effective electrocatalytic properties towards the oxidation of NAD(P)H, the PQQ + (MRH)(+) monolayer electrode state reveals poor electrocatalytic properties towards oxidation of the cofactors. Reversible photoisomerization of the monolayer across the PQQ + SP and PQQ + (MRH)(+) states provides a means of transducing the recorded optical signals by means of the electrocatalyzed oxidation of the cofactors as light-controlled amperometric responses.

关键词： 农村电气化   低压电网   农村用电   用电量   上海市   小电厂   乡村工业   变电站   伤亡事故   上海农村  

摘要： 上海市是我国最早使用电力的地区,自1882年7月英商在上海南京路外滩开始办电以来,已有100多年历史。上海农村郊县的用电,从1911年开始,在人员比较集中的乡镇,随着照明、碾米、榨油等需要,纷纷办起了小电厂,至今也有80多年历史。

关键词： CONVECTIVE DIFFUSION   MICROGRAVITATION   ELECTROCHEMICAL CELL   NUMERICAL EXPERIMENT   ANALYTICAL APPROXIMATION  

摘要： A newly developed algorithm and a computer program are applied to processes in an electrochemical cell with a liquid working medium in a steady state nearly equal to the limiting current for low Grashof and Prandtl-Schmidt number ranges, with sub-critical values of the Rayleigh number, when the vortex structure has the simplest possible form. Analytical approximations of the basic functional characteristics obtained by numerical experimentation are found for small values of the generalized parameters. It is shown that in this case these characteristics cannot be approximated by Newman's and other conventional formulae.

关键词： PHOSPHORIC ACID DERIVATIVES   WHITE PHOSPHORUS   ELECTROSYNTHESIS   ALCOHOL WATER SOLUTION  

摘要： It has been established that the process of splitting of the P - P bonds of the white phosphorus molecules is initiated by cathode-generated nucleophiles (HO-, RO-), while functionalization of the P-H bond formed in phosphoric oligomers occurs under the action only of alcohol. The primary product after splitting of all the P-P bonds in phosphoric oligomers is dialkylphosphite (in alcohol-water media), or trialkylphosphite (in absolute alcohol), in the course of electrolysis being transformed into trialkylphosphate. Formation of esters of pyrophosphoric acid with reduced protogenic character of the medium was examined. It is proposed that under these conditions nucleophilic reagents of the type (]P)c-O- form and participate in splitting of the P-P bonds.

摘要： The cathodic reduction of [(η3-C3H5)Pd(Ph2P-C2H4-PPh2)]+, A, in acetonitrile solution affords Pd(Ph2P-C2H4-PPh2)2, B, and Pd(η3-C3H5)2, C. Its cyclic voltammetric behaviour is studied as a function of scan rate and concentration of A. These results and relevant coulometric experiments indicate a primary reversible charge transfer reaction followed by a fast second order process producing P1 and P2. This picture is complicated by a subsequent reaction of B with A leading to a dimeric electroactive species which is reduced at a slightly more negative potential value than A. The rate constants of individual chemical reactions were evaluated by digital simulation and best fit with experimental results.