Mercury electrode, adsorption cytochrome

It is important to note that proteins tend to denature during such an adsorption process on noble metals or carbon electrodes. In addition, the stability of the adsorbed sensing layer is highly dependent on the pH value and ionic strength of the solution as well as the temperature, the electrode material, and other additional factors. For instance, as early as 1972 direct ET was observed on mercury electrodes employing cytochrome c as redox protein [108]. Reversible electrochemical behavior of cytochrome c was not observed because the protein denatured on the surface. 

Cytochrome c3 has a positive charge (pi = 10.5) and displays problems of adsorption at a mercury electrode. However, these problems are avoided using a glassy carbon electrode, Figure 13,26 in that, as said above, such a material behaves as a negatively charged surface. 

A striking feature of the cytochromes c3 is their ability to modify an electrode surface in such a way as to facilitate subsequent electron transfer (21). Among the different cytochromes studied to date, only cytochrome c3 can be oxidized and reduced with high electrochemical reversibility at an electrode-solution interface without any mediator or promoter (16, 21). This reversibility contrasts with the more usual situation in which the protein absorbs on the electrode surface, thus preventing further electron transfer. Alternatively, rather slow (k° < 10 3 cm/s) heterogeneous electron transfer rates are observed. Using Miyazaki cytochrome c3 and a mercury electrode on which specific adsorption of cytochrome c3 is known to occur, the ad-... 

It is apparent that the cytochrome c electron transfer reaction at mercury electrodes is complex and dependent on a number of parameters. The adsorption of cytochrome c at mercury is in and of itself a complicated process. The formation of the first monolayer is rapid and chemically irreversible. 

Although rapid adsorption of cytochrome c at mercury electrodes is widely accepted based on diverse experimental results, " the structure of this primary adsorption layer remains a point of controversy. If the cytochrome c... 

Evidence for the adsorption of metmyoglobin and methemoglobin on mercury electrodes is consistent with irreversible, diffusion-controlled adsorption during the formation of the primary monolayer. The same general experimental strategy has been used to characterize these processes as was used in the study of cytochrome c. Scheller et have used... 

The consequence of this behavior is a favorable adsorptive stripping response, as saturation effects are minimized. The "complexes of cytochrome c or ferritin with the mercury electrode are useful analogs of protein/protein complexes, which are the basis of many biological redox processes. 

Figure 12. Adsorption study of cytochrome c at the hanging mercury drop electrode by cyclic voltammetry. Solution contained 0.01 M Tris-HCl buffer, pH 7.6, electrode...

There is considerable evidence that cytochrome C3 strongly adsorbs on mercury. Mercury drops from a DME formed in solutions containing cytochrome C3 do not coalesce for 30 minutes and electrocapillary curves are lowered. At the hanging mercury drop electrode cyclic voltammetry of cytochrome C3 from Desulfovibrio vulgaris, strain Hildenborough, and also from Desulfovibrio desulfuricans, strain Norway, gave further evidence of adsorption. Each sample exhibited a peak at ca. OV characteristic of adsorption, i.e., current was directly proportional to scan rate. Film transfer... 

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