PHILIP GEORGE 



Since the formation of both oxymyoglobin and oxyhemoglobin 

 are highly exothermic, about 16 and 14 kcal./mole, respectively, 

 this has the effect of enhancing the resistance toward oxidation 

 through an increase in the endothermicity of the over-all 

 electron transfer by these large amounts. 



The coexistence of the two reaction paths — combination to 

 form the stable oxygen complex and electron transfer giving 

 irreversible oxidation — is an uncommon feature in chemical 



40 



o 

 E 

 t)b30 



O 



m20 



c 



V 



■^ 10 



o 



Q. 



D Fe;^+Or 



20 



AFe„^*+0, 



16 



BFe.O, 



Iron— oxygen distance 



Fig. 4. Schematic potential energy diagram for the reaction of oxygen with 

 ferromyoglobin, giving Oi" and ferrimyoglobin (25). 



kinetics, and the detailed mechanism can be envisaged with the 

 help of the schematic potential energy diagram given in Figure 

 4. The positions of state A (FCp"^ + O2 infinitely separated) 

 and state B (Fep"^02, the oxygen complex) are defined by the 

 heat of formation of the oxygen complex, and that of state D 

 (Fcp"^ + O2", infinitely separated) by the calculation employing 

 the ionization potential and other thermochemical data referred 

 to above. State C, in which an electron has been transferred 

 within the complex, Fep"*"02~, but separation of the products 

 has not yet occurred, has been placed 20 kcal./mole above state 



368 



