THE EFFECTS OF TEMPERATURE AND ELECTROLYTE ON THE REDOX POTENTIAL OF CYTOCHROME-C AT A CHEMICALLY-MODIFIED MICROBAND GOLD ELECTRODE

The dependence of formal potential (E(0)') on temperature for cytochro me c in phosphate buffer solution at various pH was investigated by th e microband gold electrode modified with a new promoter 4,6-dimethyl-2 -mercaptopyrimidine (DMMP). The temperature dependence of the E(0)' sh owed a biphasic character in slightly alkaline solution with a turning point at ca. 45 degrees. However, the E(0)' values decreased monotoni cally with the increasing temperature in acidic and neutral media. The thermodynamic parameters of the electron transfer reaction for cytoch rome c at the chemically modified microband electrode were estimated. The E(0)' and the changes of standard Gibb's free energy (Delta G(0)), entropy (Delta S-0) and enthalpy (Delta H-0) for the reduction of fer ricytochrome c at 25 degrees C and pH 7.0 were 0.272V (vs. NHE) -26.2 kJ mol(-1), -123.7 J mol(-1) K-1 and -63.1 kJ mol(-1), respectively. T he effect of buffer component on the E(0)' was also studied in binding (phosphate) and nonbinding (Tris/cacodylic acid) neutral buffer media . The results showed that the E(0)' in Tris/cacodylic acid buffer solu tion shifted positively by about 10 mV in comparison with that in phos phate buffer solution.