Jiří Klíma

Measured and Calculated Oxidation Potentials of 1-X-12-Y-CB11Me10– Anions

Cyclic voltammetry of 31 icosahedral carborane anions 1-X-12-Y-CB(11)Me(10)(-) at a Pt electrode in liquid SO(2) revealed a completely reversible one-electron oxidation even at low scan rates, except for the anions with Y = I, which are oxidized irreversibly up to a scan rate of 5.0 V/s, and the anion with X = COOH and Y = H, whose oxidation is irreversible at scan rates below 1.0 V/s. Relative reversible oxidation potentials agree well with RI-B3LYP/TZVPP,COSMO and significantly less well with RI-BP86/TZVPP,COSMO or RI-HF/TZVPP,COSMO calculated adiabatic electron detachment energies. Correlations with HOMO energies of the anions are nearly as good, even though the oxidized forms are subject to considerable Jahn-Teller distortion. Except for the anion with X = F and Y = Me, the oxidation potentials vary linearly with substituent σ(p) Hammett constants. The slopes (reaction constants) are ~0.31 and ~0.55 V for positions 1 and 12, respectively.

Ultrasound-assisted anodic oxidation of diuron

Abstract Bulk electrolysis of diuron (3-(3,4-dichlorophenyl)-1,1-dimethyl urea) was carried out at a glassy carbon anode with ultrasound in order to avoid a total blockage of the electrode surface by a passivating film. The major oxidation product P1 isolated in 23% yield resulted from the loss of one electron and one proton with formation of a nitrogen radical and of the corresponding NN dimer. Two more compounds P2 and P3 were isolated in 12 and 10% yields. They are suggested to originate from an intramolecular Fries rearrangement in dimer P1, i.e. the migration of an amide group from a monomeric unit of the dimer to the aromatic ring of the second one, with formation of a dichloro– N , N –dimethyl benzamide derivative. This rearrangement would be related to a strong adsorption of the intermediate nitrogen radical. It would occur at the positively charged electrode surface concomitantly with the N–N bonding formation. Several non-identified minor compounds were generated, which could involve multi-electron oxidation processes, since the overall oxidation process of diuron required more than one electron.

A spectroelectrochemical study of chemisorption, anodic polymerization and degradation of salicylic acid on conductor and TiO2 surfaces

Abstract In situ uv -vis and SNIFTIR spectroscopy and their combination with electrochemical techniques have been used for investigation of interaction of salicylic acid (SA) with various forms of TiO 2 (pyrolyzed layers of TiO 2 and a collodial solution of TiO 2 Q-particles). For comparison, conductor electrodes (Pt, Au, Glassy carbon and F-doped SnO 2 ) have been used. SA (0.01–0.1 M aqueous or acetonitrile solutions) is chemisorbed on TiO 2 surfaces through its carboxylic group forming C-T complexes with TiO 2 . Electrochemical oxidation of SA on conductor electrodes leads to a formation of an insulating layer due to anodic polymerization. A similar polymerization process has been observed on illuminated TiO 2 . Besides that, SA undergoes a photoanodic degradation on TiO 2 where formic acid as one of intermediates has been identified.

Electrolysis at a disc electrode in a thin electrolyte layer

Abstract Equations describing current and concentration of electroactive species at constant potential in a thin electrolyte layer at a disc electrode were derived on the assumption that the current is controlled either by the rate of the electrode process or by the rate of diffusion. Measurements of the anodic diffusion current in a solution of 0.005 M K 4 Fe(CN) 6 in 1 M KCl in a cell with a controllable thickness of the electrolyte layer showed the possibilities and limitations of the method.

A frame-supported ultrathin electrospun polymer membrane for transplantation of retinal pigment epithelial cells

We report on the design and fabrication of a frame-supported nanofibrous membrane for the transplantation of retinal pigment epithelial (RPE) cells, which is a promising therapeutic option for the treatment of degenerative retinal disorders. The membranous cell carrier prepared from 640 nm-thick poly(DL-lactide) fibres uniquely combines high porosity, large pore size and low thickness, to maximize the nutrient supply to the transplanted cells in the subretinal space and thus to enhance the therapeutic effect of the transplantation. The carrier was prepared by electrospinning, which made it easy to embed a 95 μm-thick circular supporting frame 2 mm in diameter. Implantations into enucleated porcine eyes showed that the frame enabled the ultrathin membrane to be handled without irreversible folding, and allowed the membrane to regain its flat shape when inserted into the subretinal space. We further demonstrated that the minimum membrane thickness compatible with the surgical procedure and instrumentation employed here was as low as 4 μm. Primary porcine RPE cells cultivated on the membranes formed a confluent monolayer, expressed RPE-specific differentiation markers and showed transepithelial resistance close to that of the native RPE. Most importantly, the majority of the RPE cells transplanted into the subretinal space remained viable. The ultrathin, highly porous, and surgically convenient cell carrier presented here has the potential to improve the integration and the functionality of transplanted RPE cells.

Anodic Oxidation of 18 Halogenated and/or Methylated Derivatives of CB11H12–

Anodic oxidation of [CB11H12]- and 18 of its halogenated and/or methylated derivatives was examined. Reversible oxidation was found for four of the anions in liquid SO2 and for four more in 1,1,1,3,3,3-hexafluoroisopropyl alcohol. The oxidation occurred at ∼1 V (for [CB11Me12]-) up to more than 4 V (for [1-H-(2-6)-F5-(7-12)-(CF3)6-CB11]-) relative to ferrocene/ferricinium. The anodic peak potentials are reproduced by a set of additive position-sensitive substituent increments.

FTIR spectro-photoelectrochemical cell with adjustable solution layer thickness. Photocurrent transients at photoexcited TiO2 polycrystalline electrodes

Abstract Chronoamperometric curves under photoexcitation were measured at a polycrystalline TiO 2 electrode in iodide-containing solutions using an FTIR spectro-photoelectrochemical cell with a solution layer thickness adjustable from zero up to about 10 mm with an accuracy of ±10 μ m. The shape of the curves is controlled by changes in the effective exciting light intensity due to light absorption in solution by generated intermediates and products. The influence of initial electrolyte concentration and solution layer thickness on the shape of the I − t curves is explained.

(Spectro) Electrochemical investigation of reduction mechanism of a new energetic molecule 2,2-dinitroethene-1,1-diamine (FOX-7) in aprotic solvents

The electrochemical reduction behaviour of a new promising energetic material 2,2-dinitroethene-1,1-diamine (FOX-7) was investigated in acetonitrile, dimethylformamide and dimethylsulfoxide at mercury, platinum, gold and glassy carbon electrodes. Instead of expected consumption of four to eight electrons necessary for reduction of nitro groups, only two electrons are consumed. In acetonitrile, the starting form of FOX-7 is the olefinic, nearly planar structure polarized by the push-pull effect, the first electron attacks one of the nitro groups. The electrochemical as well as in situ UV-vis-NIR and EPR spectroelectrochemical results are in agreement with autoprotonation reduction mechanism. The radical intermediate was intercepted and identified by EPR spectrometry where an alternation line-width (AL) effect was observed.