Potential Shift and its Proportionality to the Concentration of Adsorbed Catalyst

Cause of the Potential Shift and its Proportionality to the Concentration of Adsorbed Catalyst 

A similar effect of the appearance of a negative potential shift is also observed when FeEP is replaced by Co EP or by metalless porphyrins. This means that a redox reaction at the interface is catalyzed only by porphyrins having as a central atom a transition metal which is capable of accepting electrons. The influence of the nature of the central atom in the porphyrin on the Volta potential value and the reaction rate was also observed for other redox reactions at water/octane, water/decane, water/chlo-roform and water/dichloroethane interfaces [57-59]. 

If in the presence of CP and 2N-methylamino-l,4-naphthaquinone (MANQ) in octane, a reducing agent such as NADH or ascorbate is added to the aqueous phase then a negative potential shift is observed caused by the catalytic electron-exchange reaction (Fig. 10) [51]. 

M 2N-methylamino-1,4-naphthoquinone, 7xlO MCP, 10-2 M tris-HCl pH 7.1 Potential referred to solution without NADH [52] 

The dependence of surface potential and reaction rate on the NADH concentration are similar (Fig. 11), and the potential shift in the given system is proportional to the oxidation rate of NADH. The obtained result agrees well with the theoretical model of a heterogeneous catalytic reaction proposed earlier [23-25], according to which the potential shift at the interface between immiscible liquids relative to the supporting electrolyte is directly proportional to the rate of the heterogeneous electron-exchange reaction. 

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