A cathodic voltammetric wave was observed in an aqueous suspension of mono-dispersed, spherical polyaniline-coated polystyrene particles, whereas no anodic wave was detected. This irreversibility was common to particles with eight different diameters ranging from 0.2 to 7.5 μm. Such irreversibility cannot be found at polyaniline-coated electrodes, and thus is a property of the dispersion of polyaniline latex. The reduction current was controlled by diffusion of dispersed particles. The reduction, being the conversion from the electrical conducting state to the resistive one, should begin at a point of contact between the conducting particle and the electrode in order to be propagated to the whole particle rapidly. In contrast, the oxidation proceeds slowly with the propagation of conducting zone, during which Brownian motion lets the particle detach from the electrode. The number of loaded aniline units per particle, determined by weight analysis, ranged from 6 × 106 (Ø 0.2 μm) to 3 × 1011 (Ø 7.5 μm) and was proportional to 2.9 powers of the particle diameter. The diffusion-controlled current of the cathodic wave was proportional to 2.4 powers of the diameter. The difference in these powers, 0.5, agreed with a theoretical estimation of the diffusion-controlled current, the diffusion coefficient for which was given by the Stokes-Einstein equation. 相似文献
A new type of unsaturated polyketone having cyclohexanone moiety in a π-conjugated main chain was prepared by polycondensation between 2,6-bis(4-bromobenzylidene)cyclohexanone and 2,5-dihexyloxy-p-phenylene diboric ester in the presence of Pd(PPh3)4. The polymer had good solubility in common organic solvents. Analysis by gel permeation chromatography (GPC; polystyrene standards) showed that the polymer had Mn and Mw values of 7800 and 18?200, respectively. The polymer exhibited a [η] value of 0.70 dl g−1 in benzene at 30 °C. The chloroform solution of the polymer showed an UV-Vis peak at 392 nm, and the PL spectrum gave a peak at 533 nm. DSC exhibited that the polymer had a Tg of 85 °C. The DSC data, observation with a polarizing microscope, X-ray diffraction data and UV-Vis data of the obtained polymer showed a phase transition above 200 °C. TGA showed that the polymer had good thermal stability with 5 wt% loss temperature of 407 °C under N2. Electrochemical oxidation (or p-doping) of the polymer started at about 0.7 V vs. Ag/AgNO3 and gave a peak at 1.06 V vs. Ag/AgNO3 with a color change of the film from yellow to deep red. The color change was followed by UV-Vis spectroscopy. The corresponding p-dedoping peak appeared at 0.58 V vs. Ag/AgNO3. 相似文献
In the preceding Letter Shelef [1] has proposed a mechanism for NO decomposition involving coordinatively unsaturated Cu2+ sites on which NO molecules are chemisorbed in the gem-dinitrosyl form. At reaction temperature this complex is supposed to decompose into N2 and O2 without involving a redox process. That such a process is feasible has been pointed out by Moser [2]. Shelef cited several reasons in support of this view and others that have led him to think that a cyclic redox mechanism is not operative. These arguments are countered herein and some new data are presented showing the infrared spectra of surface species recorded under in situ reaction conditions.On leave from Central Research Institute for Chemistry, Hungarian Academy of Sciences, H-1525 Budapest, Hungary. 相似文献
A mild, catalytic, atom economical synthesis of imidazo[1,2‐a]pyridines has been developed: catalytic dichloro(2‐pyridinecarboxylato)gold [PicAuCl2] in the presence of an acid produces a range of imidazo[1,2‐a]pyridines in good yields starting from alkynes and 2‐aminopyridine N‐oxides. This strategy is mild and foreseen to be of particular use for the installation of stereogenic centers adjacent to the imidazo[1,2‐a]pyridine ring without loss of enantiomeric excess.
The California mussel, Mytilus californianus, adheres in the highly oxidizing intertidal zone with a fibrous holdfast called the byssus using 3, 4-dihydroxyphenyl-l-alanine (DOPA)-containing adhesive proteins. DOPA is susceptible to oxidation in seawater and, upon oxidation, loses adhesion. Successful mussel adhesion thus depends critically on controlling oxidation and reduction. To explore how mussels regulate redox during their functional adhesive lifetime, we tracked extractable protein concentration, DOPA content and antioxidant activity in byssal plaques over time. In seawater, DOPA content and antioxidant activity in the byssus persisted much longer than expected—50% of extractable DOPA and 30% of extractable antioxidant activity remained after 20 days. Antioxidant activity was located at the plaque–substrate interface, demonstrating that antioxidant activity keeps DOPA reduced for durable and dynamic adhesion. We also correlated antioxidant activity to cysteine and DOPA side chains of mussel foot proteins (mfps), suggesting that mussels use both cysteine and DOPA redox reservoirs for controlling interfacial chemistry. These data are discussed in the context of the biomaterial structure and properties of the marine mussel byssus. 相似文献