PHILIP GEORGE 



entropy data a little more closely because configurational changes 

 within the protein fabric might accompany complex formation 

 and contribute substantially to the observed entropy change. 



This effect can best be looked for by comparing the dif- 

 ferences between the entropy of the parent compound and that 

 of its complex. Standard entropies of substances in solution 

 are denoted by S^, referred to as a partial molal entropy, and 

 values are available for most inorganic ions and simple neutral 

 molecules (31). Hence, since entropy is an additive property, 

 in the formation of the complex ML from the parent compound 

 M and the ligand L, 



M + L . ML 



the entropy change AS° is given by 



AS° = 6ml ■" Sm — Si, 



The difference between the partial molal entropies of the com- 

 plex ML and the parent compound M is thus : 



Since the charge does not change in the formation of complexes 

 with neutral ligands, (-S^l ~ S^) may be compared directly 

 with 5l, for it is a measure of the gain or loss in entropy when 

 the ligand is bound to the metal and the water molecule liberated. 

 For example, when the inorganic cations, Cu^^, Zn2+, Co 2+, 

 Ni^+, etc., combine with ammonia for which 5° = 26.3 e.u., 

 (-^L - Sli) is 23 e.u. (19). In the formation of FeN02+ 

 (-^ML - -^m) is 9.8 e.u., 5° for NO being 28.9 e.u. (31). Now 

 the partial molal entropies of O2 and CO are 25.7 and 25.5 e.u., 

 respectively, very similar to the values for NH3 and NO ; hence 

 for the ferromyoglobin complexes values of (^^l ~ -^m) 

 ranging between +10 and +25 e.u. might have been expected. 

 The actual values are —4.3 and —10.7 e.u., shown diagram- 

 matically with those for the inorganic complexes in Figure 2. 

 This is evidence that an additional change in configuration or 

 solvation does occur in the formation of the ferrohemoprotein 



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