2-Pyridyl disulfide immobilized

When the silver electrode covered by a cyt. c layer is transferred into 4-PySSPy solution, the SERRS signals of cyt. c disappear because cyt. c is completely displaced by 4-PySSPy. However, cyt. c is subsequently immobilized on top of the 4-PySSPy modified electrode and a rapid electrode reaction takes place at the formal potential of the native one. The adsorption of bis-(2-pyridyl) disulfide (2-PySSPy) and cyt. c is competitive. Bis-(2-pyridyl) disulfide coadsorbs with cyt. c on the silver electrode and the electrochemical function of this adsorbed layer is similar to that of the film formed by 4,4 -bipy coadsorbed with cyt. c. 

Modified electrodes for biocatalysis use either electron mediators or promoters immobilized on the electrode surface -. In both cases, redox enzyme molecules are in solution and in contact with the common electron mediators for redox enzymes such as cytochrome c and ferredoxin. An electron promoter is not a mediator since it does not take part in electron transfer in the potential region of interest. An electrode modified with promoter molecules has enables some redox enzymes to directly transfer electrons. It has been shown that 4,4 -bipyridyl, bis(4-pyridyl)sulfide, and bis 4-pyridyl)disulfide are excellent promoters of electron transfer of cytochrome c. Cytochrome c gives a reversible cyclic voltammogram at gold electrodes modified with these promoters. 

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