Standard-state potential, determining voltammetry

Application of these curves may have as other objective to uncover the kinetic characteristics of the electrode electron transfer. This cannot be done in the absence of catalysis since the RDEV response is nil insofar as the steady-state response of an attached species is nil. Cyclic voltammetry could be used instead. The response is not nil, but the signal is in general small, often hardly emerging from the baseline current. Determining the standard potential under these conditions is generally feasible, but an accurate... 

The current-potential relationship of the totally - irreversible electrode reaction Ox + ne - Red in the techniques mentioned above is I = IiKexp(-af)/ (1+ Kexp(-asteady-state voltammetry, a. is a - transfer coefficient, ks is -> standard rate constant, t is a drop life-time, S is a -> diffusion layer thickness, and

logarithmic analysis of this wave is also a straight line E = Eff + 2.303 x (RT/anF) logzc + 2.303 x (RT/anF) log [(fi, - I) /I -The slope of this line is 0.059/a V. It can be used for the determination of transfer coefficients, if the number of electrons is known. The half-wave potential depends on the drop life-time, or the rotation rate, or the microelectrode radius, and this relationship can be used for the determination of the standard rate constant, if the formal potential is known. 

Numerous electrochemical measurements have been carried out with the ruthenium diimin complexes [15], mainly with the aim of comparing electron-transfer processes in the ground and in the excited state, and for the determination of the character of the frontier orbitals. Much less data are known for the cyclometallated analogs. By far the most popular method for the electrochemical measurements is cyclic voltammetry (CV). The measurements are mostly done in nonaqueous solutions (acetonitrile, dimethylfor-mamide, etc.). A general difficulty in such measurements is the reference potential, and the use of an internal standard like, for example, Ru(bpy)2 + is therefore highly recommended. Table 1 contains a compilation of electrode potentials of cyclometallated complexes of the type considered in this review. For comparison, the values of Ru(bpy) + are included in the table. 

The indole singlet excited state can also be quenched by electron transfer if suitable acceptors are present [13]. The oxidation potentials of N-acetyltryptophan methyl ester, 4, and iV-methoxycarbonyltryptamine, 5, in acetonitrile solvent have been determined by cyclic voltammetry versus the standard calomel electrode to be 0.82 and 0.75, respectively [14a]. In methanol solution, the oxidation potential of iV-methylindole has been... 

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