SPECIFICITY IN SURFACE REACTIONS 35 



which may arise at a surface. This is given by Boltz- 

 mann's theorem, 



C. 



E 

 RT 



e is) 



where C^ = concentration at the adsorbing surface; Cj 

 = bulk concentration; E = energy of adsorption; R = 

 = gas constant; T = absolute temperature. 



The energy E may be regarded as made up of three 

 components, one associated with the ionic groups, one 

 with the polar groups and one with the non-polar groups. 

 Minimal values for adrenaline are 



Adrenaline ionic polar non-polar total E Cs/Cb 



HO OH ^°° ^°°° ^^°° ^^°° 2x10^ 



H0()— CH-CH2-NH-CH3 



The values taken for the energies are minimal. Yet when 

 these energies are summed, the concentration of adrena- 

 line which may arise at a surface is seen to be of the 

 order of 10^ times that which is found in the bulk phase. 

 Under favourable conditions the energies may well be 

 larger and could easily give rise to a relative concentra- 

 tion of the order of lo^^. 



But before it is permissible to sum the energies in the 

 way in which we have just done, it is necessary to pro- 

 vide an interface at which all three mechanisms for ad- 

 sorption may become effective to an optimal degree. 

 This means that the surface at which the drug is ad- 

 Cell Physiology 3 . -::» r- 1 i-i 



\2 



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