272 L. A. NIKOLAEV 



sitional complex with either a greater or a lesser entropy than the complex of 

 reaction without a catalyst. 



Thus, for the catalytic oxidation of pyrogallol we obtained the following 

 values for this difference, depending on the nature of the addendum (Table 4). 



Table 4 



Difference in entropy between the catalysed and uncatalysed reaction 



at 20°C 



In those cases in which acceleration of the reaction is associated with an 

 increase in the entropy of activation we must take it that the reaction is brought 

 about by the formation of a 'loose' transitional complex. The existence of such 

 'loosening' of the structure at the moment of transformation is evident from the 

 association, upon which I have already remarked, between instability and activity 

 of the complex catalyst. Under favourable conditions (when there is a sufficient 

 concentration of the addendum in the solution) the structure of the complex ion 

 is re-established. 



In biological systems there is probably a more precise method for the rapid 

 restoration of that part of the active group in which loosening of the structure 

 was reqtoired in order to attain a high degree of catalytic activity. 



The formation of a complex compound often brings about a sudden increase 

 in the pre-exponential multiplier. This is clearly the simplest way of increasing 

 the activity of the ion. If one wishes to lower the energy of activation one must 

 alter the nature of the addendum, i.e. follow the course which Langenbeck took. 



Attempts to activate complex compounds by adsorption have been com- 

 paratively ineffective. We have tried to adsorb haemin and the iron ion on 

 activated charcoals derived from various sources and found that the degree of 

 dispersion of the particles of the carbon corresponded with the increase in 

 activity both for simple and complex ions, but the degree of activation was 

 greater for the simple iron ion than for the porphyrin complex. Thus, in general, 

 complex formation hinders any increase in activity which may be brought about 

 by adsorption. This result, of course, must be considered alongside the great 

 specificity of the activizing effect of the protein components of biocatalysts. In 

 this connection great interest attaches to those cases in which model structures 

 can also be activated by adsorption on organic substances of high molecular 

 weight [16]. 



