LEONOR MICHAELIS 



case of oxidation in organic chcinisliy. However, according to our 

 present usage of the term, this reaction is so dissimilar from what is 

 now considered to be a typical oxidation that it is no longer classified 

 among the oxidations — it has, in fact, been termed "oxygenation" by 

 Conant. The real oxidation of hemoglobin, according to modern 

 definition, is its conversion to methemoglobin, because, according to 

 the present stage of knowledge and on the basis of our present model 

 of atomic and molecular structures, the oxygen of oxyhemoglobin is 

 attached to hemoglobin without aflfecting the electronic structure of 

 the iron atom,* whereas in methemoglobin no oxygen is attached to 

 hemoglobin at all — rather, the iron atom of hemoglobin contains one 

 electron more than the iron atom of methemoglobin. The removal of 

 that electron from hemoglobin is now considered as typical for its 

 oxidation. When ferrous chloride reacts with chlorine, ferric chloride 

 is formed. Since ferrous compounds can be converted to ferric com- 

 pounds by oxygen also, ferric iron has always been considered an oxi- 

 dation product of ferrous iron. Yet, if this conversion is brovight 

 about by chlorine, oxygen plays no part in the "oxidation." 



What is common in most processes formerly designated as oxi- 

 dation, disregarding such an exceptional case as the formation of oxy- 

 hemoglobin, can only be stated in terms that would have been quite 

 incomprehensible to the originators of the concept of oxidation. This 

 common property can be defined, in terms of the present state of the 

 atom model, by saying that, after its oxidation, a molecule has been 

 deprived of one electron, or of two electrons; these two cases of oxida- 

 tion are distinguished by the terms "univalent" and "bivalent." The 

 oxidation of ferrous ion to ferric ion, or of ferrocyanide ion, [Fe(CN)6]^~ 

 to ferricyanide ion, [Fe(CN)6]^~, are examples of univalent oxidation. 

 The oxidation of stannous ion, Sn"'""'', to stannic ion, Sn^+, is a bivalent 

 oxidation. In those cases in which the oxidation, or, in other words, 

 the withdrawal of the electron, is brought about by oxygen, the oxygen 

 is the acceptor of the electron. The fate of oxygen after acceptance 

 of the electron will be discussed on page 220. Other reagents, such as 



* This statement involves another difficulty based on facts unknown until 

 recently. Since hemoglobin is paramagnetic, but oxyhemoglobin diamagnetic, 

 as Pauling and Coryell have shown, some change in electronic structure due to 

 the attachment of oxygen must be postulated here too. But it is not of the type 

 one would now call oxidation. 



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