ON THE NATURE OF HEMOPROTEIN REACTIONS 



complexes resulting in a considerable entropy decrease of about 

 14 to 36 e.u. 



The same effect is apparent with the ferrihemoprotein 

 complexes, although, since the charge changes in the formation 

 of complexes with anionic ligands, the basis of comparison is a 

 little more complicated. For the ion-pair complexes of mon- 

 atomic cations a simple rule holds. ("S^il — -^^i) is constant for 

 the same metal ion and a series of anions, as shown in Table I 

 for the ferric ion. It is as if the dominant feature is the diminu- 

 tion in charge accompanying complex formation, and the 



20 

 o- 

 20- 



40 

 60 



e.u. 



1 



20 



♦ 



FeX 



2+ 



NH, 



NO^ 



IONIC IRON 

 FeY^ 

 .2+ ^OH 



:=^;cNS 



\Br 



r.3+ 



CO' 



Pz 



Mb 



3Fe 



Mb 



N3 



,CN 



■QH 



Fe Y 



Mb 



^'^Mb^ MYOGLOBIN 



Fig. 2. Values of S" in aqueous solution for ferrous and ferric ions and 

 the relative values for myoglobin in the ferrous and ferric oxidation states, 

 together with the values for some of their complexes. Fea,^ and FcaqT, ferrous 

 and ferric ions; FeX^^, ferrous ion complexes with neutral ligands X; FeY^"^, 

 ferric ion complexes with anionic ligands Y~; FcMb, Fe^^,, FcMbX, and 

 FejvibY, the corresponding myoglobin derivatives. 



composition of the ion-pair complex is of little consequence. 

 The rule also holds reasonably well for ion-pair complexes 

 formed by complex cations (7). (5ml — -^m) values for the 

 complexes of Co(NH3)6+ with CI", Br", and I" are 34.2, 34.3, 

 and 37.1 e.u., respectively, and for the complexes of Co(en)3 

 with Br- and I", 32.3 and 34.1 e.u., where en stands for ethylene- 

 diamine. There are just enough data now to infer that the same 

 rule also holds approximately for ferrihemoprotein complexes. 

 (5^L - ^m) has the values -5.1, -0.5, and +4.2 e.u. for 

 the OH", F-, and CN" complexes of ferrimyoglobin, and — 10.4, 



355 



