Some factors influencing power and energy capabilities of RuO2 supercapacitors.

Ruthenium oxide electrodes prepared by different routes were studied and the results discussed in terms of the possibility of using these electrodes in high power/high energy supercapacitors. The supercapacitor electrodes were prepared by mixing RuO(2) particles with a binder (Nafion(®) or polyvinilydenfluoride) in various ratios. The results show that charging/discharging reaction of RuO(2) consists of at least two redox reactions taking place simultaneously at different rates. The contribution of each reaction in the overall process depends on the hydration of RuO(2) as well as on the type of binder and binder/RuO(2) ratio. From both energy and power capability of supercapacitors the best electrode composition would be hydrous RuO(2) with ~20% Nafion(®) as a binder. Asymmetric supercapacitors assembled with RuO(2) and activated carbon as a counter electrode gave 26 and 12 W h kg(-1) at average specific power of 5 W g(-1) for RuO(2)/Nafion(®) and RuO(2)/polyvinylidene fluoride, respectively.

Ionization, lipophilicity and solubility properties of repaglinide.

Potentiometric and spectrophotometric titrations were used for the determination of ionization behaviour, lipophilicity and solubility profile of repaglinide. Acid-base equilibria were characterized by means of protonation macro- and microconstants using Target Factor Analysis of spectrophotometric data. Lipophilicity profiles were evaluated by determination of partition coefficients of neutral and ionized forms of repaglinide in biphasic octanol/water system. The intrinsic solubilities of repaglinide were determined from the solubility data and temperature dependence of intrinsic solubilities were evaluated using van't Hoff equation. Repaglinide possesses two protonation sites and in aqueous solutions exhibits ampholitic properties. At isoelectric pH the zwitterionic form of the molecule predominates over the uncharged form with the tautomeric ratio, logKz=1.9. The difference between calculated and measured logP values, as well as the difference between logP values of uncharged form of repaglinide, HR0, and either one of mono-charged forms indicated the significant partition of zwitterion into octanol. Temperature dependence of solubility data revealed exothermic dissolution process with DeltasolH=-36 kJmol-1 and negative entropy of solution of DeltasolS=-0.19 kJK-1mol-1.

Electrochemical reduction of desmycosin, structure investigation and antibacterial evaluation of the resulting products.

Electrochemical reduction of desmycosin at the mercury electrode in aqueous medium was investigated by cyclic voltammetry and preparative scale electrolysis was carried out for the isolation and identification of products. Structure analyses of the resulting products were accomplished by MS, 1D and 2D NMR spectroscopy. The results obtained show that dimerization and two electron reduction of desmycosin occur in parallel yielding a symmetric dimer at position C13 and 10,11-dihydrodesmycosin as the end products. 10,11-dihydrodesmycosin shows decreased antibacterial activity in vitro in comparison with desmycosin, while the dimer is inactive.

Electrochemical oxidation of azithromycin and its derivatives.

The electrochemical oxidation of azithromycin was investigated in order to elucidate the mechanism for possible oxidative metabolic pathways in humans. Electrochemical studies were carried out by cyclic voltammetry and preparative scale electrolysis at glassy carbon electrodes. It was found that azithromycin undergoes anodic oxidation at one or both amine groups with the rapid follow-up chemistry of intermediate radical cation. Main products of the oxidation were determined by HPLC analysis and were identified as a protonated azithromycin and products obtained by demethylation of the 3'-dimethylamino or macrolactone amino group.

Acid-base and electrochemical properties of manganese meso(ortho- and meta-N-ethylpyridyl)porphyrins: voltammetric and chronocoulometric study of protolytic and redox equilibria.

Growing interest in redox-active compounds as therapeutics for oxidative stress-related diseases led to the design of metalloporphyrins as some of the most potent functional SOD-mimics. Herein we report a detailed electrochemical study of the protolytic and redox equilibria of manganese ortho and meta substituted N-ethylpyridyl porphyrins (MnPs), MnTE-2-PyP(5+) and MnTE-3-PyP(5+), in aqueous solutions. The electrochemical parameters of redox processes for all experimentally available species have been determined, as well as their diffusion coefficients and estimated sizes of aqueous cavities. The results indicate that possible changes of the intracellular acidity cannot affect the antioxidant activity of MnPs in vivo, since no change in the E(Mn(III)P/Mn(II)P) values was observed below pH 10. Furthermore, the results confirm that both of these MnPs can be efficient redox scavengers of peroxynitrite (ONOO(-)), another major damaging species in vivo. This can occur by either single-electron reduction or two-electron reduction of ONOO(-), involving either the Mn(IV)P/Mn(III)P redox couple or Mn(IV)P/Mn(II)P redox couple. In addition to kred(ONOO(-)) reported previously, the thermodynamic parameters calculated herein imply a strong and identical driving force for the reaction of both ortho and meta isomeric MnPs with ONOO(-). An enlargement of both Mn(III)P complexes upon an increase of the solution pH was also observed and attributed to the reduction of positive charge on the central ion caused by deprotonation of the axial water molecules. This expansion of aqueous cavities suggests the formation of a solvent cage and the increased lipophilicity of Mn(III)P complexes caused by increased electron density on the Mn ion.