REDOX SYSTEMS; ELECTRON TRANSFER PROCESSES 



181 



TABLE 7-4. Redox Potentials f m7 of Some Important Biochemical Reactions. 



Note: At pH 7, and at 50 percent oxidation, measured against the normal hydrogen electrode. 

 Values given are approximate. Complete data on these and many other biological redox systems are given 

 by Clark. 2 



E° is the value when the ratio of activities of oxidized and reduced species 

 is unity (In 1 = 0), and the second term is the correction for any ratio not 

 equal to unity. 



Usually T is 37° C (310°K); R is always 8.3 jou/deg mole, F is always 

 96,500 cou/equiv; and In x = 2.303 log x. Insertion of these numbers gives 

 the common form of the Nernst Equation 



„ „ (1060 , 



E = £° log (a ox /a red ) 



For the simplest case, 



H 2 = 2H + + 2e 



the a red = 1, being an element; n = 2; and since pH = -log (a H .), and 

 E° = by definition, the emf of the hydrogen electrode, referred to the 

 NHE, as a function of pH is: 



E = -0.06 x pH volts 



