An electrochemically controllable nanomechanical molecular system utilizing edge-to-face and face-to-face aromatic interactions

[formula: see text] A new molecular system, 2,11-dithio[4,4]metametaquinocyclophane containing a quinone moiety, was designed and synthesized. As the quinone moiety can readily be converted into an aromatic pi-system (hydroquinone) upon reduction, the nanomechanical molecular cyclophane system exhibits a large flapping motion like a molecular flipper from the electrochemical redox process. The conformational changes upon reduction and oxidation are caused by changes of nonbonding interaction forces (devoid of bond formation/breaking) from the edge-to-face to face-to-face aromatic interactions and vice versa, respectively.     

Electrochemistry of conductive polymers 38. Electrodeposited poly(3,4-ethylenedioxy-thiophene) studied by current sensing atomic force microscopy

Electrical and morphological properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films electrodeposited on gold-on-silicon electrodes by galvanostatic, potentiostatic, and potentiodynamic methods have been determined using current sensing atomic force microscopic experiments. Surface morphologies and vertical conductivities of PEDOT films were affected by the experimental parameters including the preparation method, the current density, the potential, and the potentiodynamic cyclic number. Band gaps obtained from current-voltage curves of dedoped PEDOT were in excellent agreement with those obtained from absorption spectra. When the film thickness was increased on the gold-on-silicon electrode, the topographic images were not very well defined due to the high roughness but conductivities increased significantly in all the galvanostatically, potetiostatically, and potentiodynamically grown PEDOT films.     

From Modified Electrodes to Digital Instrumentation in Electroanalytical Chemistry

Work done on applications of modified electrodes to electroanalytical chemistry and digital instrumentation for electrochemical measurements in our laboratory in recent years will be presented. First, applications of modified electrodes with conducting polymer films and selfassembled monolayers (SAMs) of thiolated cyclodextrins will be demonstrated.     

Rational design of biologically important chemosensors: a novel receptor for selective recognition of acetylcholine over ammonium cations

[structure: see text] In consideration of competition between cation-pi and hydrogen bond interaction forces, we designed a novel receptor, 1,3,5-tris(pyrrolyl)benzene, which shows high selectivity for acetylcholine (ACh). The selectivity of the receptor for ACh over other ammonium cations is demonstrated by the ion-selective electrode (ISE) method in buffer solution. The binding free energy of the receptor with ACh in chloroform solution is measured to be 3.65 kcal/mol in the presence of chloride anion by nuclear magnetic resonance spectroscopy, and that in water is estimated to be much greater ( approximately 6 kcal/mol).     

Determination of electron transfer kinetic parameters by fourier transform electrochemical impedance spectroscopic analysis

A new attempt to obtain electron transfer kinetic parameters at an electrified electrode/electrolyte interface using Fourier transform electrochemical impedance spectroscopic (FTEIS) analyses of small potential step chronoamperometric currents is presented. The kinetic parameters thus obtained allowed mass transport free voltammograms to be constructed in an overpotential region, where the diffusion limits the electron transfer reaction, using the Butler-Volmer (B-V) relation. The B-V voltammograms clearly distinguish electrode reactions that are not much different in their electron transfer kinetic parameters, thus showing very similar normal linear sweep voltammetric (SCV) behaviors. Electrochemical reduction of p-benzoquinone, which displays nearly the same SCV responses at a gold electrode regardless whether the electrode is covered by a thiolated beta-cyclodextrin self-assembled monolayer, was taken as an example for the demonstration. The results show that the two voltametrically similar systems display very different electron transfer characteristics.     

Electrochemistry of conductive polymers 36. pH dependence of polyaniline conductivities studied by current-sensing atomic force microscopy

We demonstrate from our current-sensing atomic force microscopic studies that both electrical and topographical properties of electrochemically prepared polyaniline (PAn) films are affected by their preparation conditions. The electrical properties of the fully doped PAn films prepared in 0.30 M nitric acid with its pH and ionic strength adjusted to 0.50 can be described as a conductor with an average conductivity of 49 (+/-13) S/cm with primarily a compact structure resulting from a relatively small growth rate. The doped PAn films prepared at pH 5.0, for example, have compact structures with large grains and lightly doped semiconducting properties with an average conductivity of about 1.54 (+/-0.09) x 10(-4) S/cm. From these data, we conclude that the degree of protonation of the monomers and the main reactions taking place during an early stage of the polymerization reaction are important factors determining the chemical structures as well as their conductivities and morphologies of the PAn films.     

Electrochemical generation of ferrate in acidic media at boron-doped diamond electrodes

An extremely strong oxidant, ferrate (Fe(VI) or FeO4(2-), has been produced electrochemically in an acidic aqueous medium for the first time.     

Effects of organic additives on zinc electrodeposition at iron electrodes studied by EQCM and in situ STM

Effects of organic additives, such as benzoic acid (BA) and poly(ethylene glycol)s (PEGs), on the initial stage of the zinc electrodeposition have been investigated at iron electrodes using cyclic voltammetry, electrochemical quartz crystal microbalance measurements and in situ electrochemical scanning tunneling microscopy in an acidic zinc chloride solution in efforts to gain a molecular-level understanding of their roles. BA is adsorbed strongly at the sites of more negative potentials on the electrode, although it is randomly adsorbed on the iron surface at around an open circuit potential. Its role seems to control the deposition rate at the dendritic sites by blocking the active surface via adsorption. On the contrary, PEGs are adsorbed more or less evenly with a well-ordered structure on the iron surface and appear to desorb in the underpotential deposition region of zinc ions, which helps inhibit proton reduction by effectively blocking the electrode surface.     

FLUORESCENCE AND ELECTROGENERATED CHEMILUMINESCENCE STUDIES OF SEVERAL DIMETHYL-SUBSTITUTED BENZO[a]PYRENES

Abstract— Absorption spectra, molar absorptivities, fluorescence spectra and fluorescence quantum yields of five dimethylbenzo[a]pyrenes (DMBP) in benzene solutions at room temperature are reported. Electrogenerated chemiluminescence (ecl) spectra and the relative eel intensities of these compounds to that of 9,10-diphenylanthracene in the 1:1 acetonitrile-benzene mixed solvent with tetra- n -butyl-ammonium perchlorate as a supporting electrolyte are also reported. Both fluorescence quantum yield and ecl intensity studies show that the vicinal dimethyl substitution lowers the fluorescence and eel efficiency, and this effect is more pronounced in a compound whose K-region is blocked. The compounds in which the L-region is blocked showed much higher fluorescence and eel efficiency. The fluorescence of DMBP molecules is quenched by the donor molecule, tri- p -tolylamine with a diffusion controlled rate to form an emitting exciplex. The cation radical of TPTA and the radical anion of the DMBPs are shown to form an exciplex efficiently by the eel experiments. Both quenching and eel results indicate that all DMBPs studied here are good acceptors.     

Modification of indium-tin oxide (ITO) glass with aziridine provides a surface of high amine density

The surface of indium-tin oxide (ITO) substrates was successfully modified with aziridine. Modification of the surface was achieved through facile ring-opening, and hyperbranching polymerization of the ring-strained heterocycle initiated from the reactive group on the surface. Amine density of the aziridine-modified ITO measured with UV-vis spectrophotometry is 10 amines/nm2. Cyclic voltammetric analysis showed that the aziridine-modified electrode was less active for Ru(NH3)6(3+) in comparison with the pristine electrode, while no difference was observed for Fe(CN)6(4-). Electrochemical impedance spectroscopic experiments unveiled that the modified electrode was more efficient for electron transfer to the latter species than to the former.