Open reduction potential

The special properties of lipoic acid arise from the ring strain experienced by oxidized lipoic acid. The closed ring form is approximately 20 kj higher in energy than the open-chain form, and this results in a strong negative reduction potential of about —0.30 V. The oxidized form readily oxidizes cyanides to isothiocyanates and sulfhydryl groups to mixed disulfides. 

Legault, Mori and Leckie have used open-circuit potential vs. time measurements and cathodic reduction of rust patinas for the rapid laboratory evaluation of the performance of low-alloy weathering steels. The steel specimens are first exposed for 48 h to the vapour of an 0-(X)l mol dm sodium bisulphite solution maintained at 54°C (humid SOj-containing atmosphere) to stimulate corrosion under atmospheric conditions. They are then subjected to two types of test (tt) open-circuit potential-time tests for periods up to 3 000 s in either distilled water or 0 -1 mol dm Na2S04 and... 

Figure 15-15. Relative luminescence intensity (open markers) compared with pristine MEH-PPV of composite films of MEH-PPV with CM and a series of TCNQ-like acceptors 1-6 (see Fig. 15-2 lor abbreviations) as a function of their reduction potentials at 80 K. Riglil-liand axis shows the ratio of the photoinduced absorption intensity of the bands at 1.34 and 1.22 eV (solid markers) (reproduced by permission of the American Institute of Physics from Ref. 1871).

Fig. 42. Single positively and negatively going scans through the vanadia redox region. The electrolyte is K2S207 with 4.0% K2S04,1.0% V2Os, 370 °C, lOOmV/s. The open circuit potentials are denoted by X, symbols are as follows (A) positive, (C) negaitve, (1) air environment, (2) 1.0% S02 in N2, (3) 1.0% S02, 10.0% 02 in N2, and IV and V represent the vanadia complex oxidation and reduction as before.

Fig. 2. Current-potential curves in Evans diagram [29] format for reduction of Cu2+ ions and oxidation of H2CO. and are the equilibrium, or open circuit, potentials for the Cu2+ reduction and H2CO oxidation reactions, respectively. Assuming negligible interfering reactions, the vertical dashed lines indicate the exchange current densities for the two half reactions, and the deposition current for the complete electroless solution. Adapted from ref. 23.

The O2 reduction reaction affects not only the steady-state deposition kinetics, but also the initiation of deposition, the so-called induction time [126, 127], At the beginning of the deposition process, the open circuit potential (Eoc) of either a uniformly catalytically active substrate, or a catalyst particle on an insulator, will be higher than that required for electroless deposition to occur. This is a consequence of the surface of the catalyst being covered with O or OH species which mask the catalytic activity of the surface the value of would be expected to be in the range of... 

Homocitrate acting as a leaving group modulating the reduction potential of Mo and opening up coordination sites for hydrides... 

The dissolution of PS during PS formation may occur in the dark or under illumination. Both are essentially corrosion processes, by which the silicon in the PS is oxidized and dissolved with simultaneous reduction of the oxidizing species in the solution. The material in the PS, which is distant from the growing front is little affected by the external bias due to the high resistivity of PS and is essentially at the open circuit potential (OCP). Such corrosion process is responsible for the formation of micro PS of certain thickness (stain film) in HF solutions containing oxidants under an unbiased condition. 

FIG. 70. Voltammograms on an argon ion-bombarded, annealed CdTe( 100) surface in 50 mM K2SO4 pH = 5.6 (A) reduction from the open circuit potential to —2.0 V (B) oxidation from the open circuit potential to -1-0.30 V and reversing to —0.55 V, under illuminated conditions (C) reduction following (B) from open circuit potential to —1.8 V and reversing to —0.50 V. 

In terms of nobility, the open circuit potentials for the B210/NVP system at all temperatures are more positive than the B40 panels. The open circuit potentials for the B210/GBL system at all temperatures are generally more negative than the B40 panels. The open circuit potential trends for the B210/GBL system mimic the B210/NVP system. However, the effects are not as pronounced. We propose that in the GBL system there is a reduction in the cathode/anode area ratio as suggested by Leidheiser (16). 

Fig. 14. pH dependence of the heme reduction potential vs NHE in the heme protein maquette, [H10A24J2, demonstrating the 210 mV range of observed between pH 4 and 11. Data for Fe(protoporph3rrin IX, filled squares) and Fe(protoporph3rrin IX dimethyl ester, open circles) are shown. Reprinted with permission from Ref. (160) copyright 1998 American Chemical Society. 

Paunovic (31) studied the induction period for the overall process, dividing it into dependence of the open-circuit potential (OCP) on the oxidation and reduction... 

Figure 1, Polarization curve for the electrochemical reduction of oxygen coupled with the electrochemical oxidation of an unspecified organic impurity O.C, designates the open circuit potentials...

Promotion and deactivation of unsupported and alumina-supported platinum catalysts were studied in the selective oxidation of 1-phenyl-ethanol to acetophenone, as a model reaction. The oxidation was performed with atmospheric air in an aqueous alkaline solution. The oxidation state of the catalyst was followed by measuring the open circuit potential of the slurry during reaction. It is proposed that the primary reason for deactivation is the destructive adsorption of alcohol substrate on the platinum surface at the very beginning of the reaction, leading to irreversibly adsorbed species. Over-oxidation of Pt active sites occurs after a substantial reduction in the number of free sites. Deactivation could be efficiently suppressed by partial blocking of surface platinum atoms with a submonolayer of bismuth promoter. At optimum Bi/Ptj ratio the yield increased from 18 to 99 %. 

Other Substrates Deposition of cadmium was also studied on Bi, Sn and Pb [303], Ni [304], reticulated vitreous carbon [305], Ti [306], and indium tin oxide [307]. UPD of Cd on tellurium results in CdTe formation [270, 308]. Electrodes coated with conducting polymers were also used to deposit cadmium electrochemi-cally. In the case of polyaniline, the metal reduction potential corresponds to the neutral (nonconducting) state of the polymer, therefore cadmium was found to deposit on the substrate-glassy carbon electrode surface, in the open pores of the polymer film [309, 310]. 

To facilitate sequencing analysis and enzymatic cleavage, reduction and alkylation of the peptides to open their potential disulfide bridges is recommended. Several alkyl groups can be used acrylamide, iodoacetamide, and 4-vinylpyridine (4-VP). S-pyridylethylation is preferred over the other alkyl groups when Edman degradation (PTH-4-pyridylethylated-Cys is commercially available) and MS (addition of 57 Da per alkylated cysteine residue) have to be performed. 

---