30 



B. Dempsey, M. B. Lowe and J. N. Phillips 



where the subscripts d and vi' refer to the micellar and water phases respec- 

 tively, and 



Tij. is the number of molecules of species x\ 



Na is the number of detergent molecules in the micellar phase ; and 



A'^ is the number of water molecules in the system. 



When an ion, e.g. a hydrogen ion H+ or a metal ion M++, is introduced 

 into such a system it will presumably prefer the aqueous environment exclu- 

 sively to that of the lipid micelle. Accordingly, any reaction involving such 

 an ion and the porphyrin molecule must take place within the aqueous phase, 

 the detergent micelles acting as a readily available reservoir for the porphyrin 

 molecules. 



Typical reactions which may be studied in this way are : 



PH2 + 2H+ 



PH, + M++ 



PH3+ + H+ 

 MP -f- 2H+ 



PH. 



ionization 

 chelation 



(1) 

 (2) 



The products of such reactions may or may not be solubilized depending on 

 their nature. For example, one might expect the nonionic metal complex 



// 



y—NH 





=N 



HC 



H 



NH 



N-< 



to) (b) (c) 



Fig. 1 



(a) Dimethyl protoporphyrin ester (DMPP) 



(b) Dimethyl mesoporphyrin ester (DMMP) 



(c) Tetramethyl coproporphyria III ester (TMCP) 

 M = — CH3 V = — CH=CH2 



E = — CH2— CH3 P = — CH2— CH2— COOCH3 



(MP) but not the ionic porphyrin species (PH3+ and PH4++) to be readily 

 solubilized. 



The purpose of this paper is to indicate the type of data that may be 

 obtained using the solubilization technique and to suggest how such data may 

 be interpreted. The following discussion is primarily concerned with the 

 ionization (as in equation (1)), co-ordination (as in equation (2)) and spectro- 

 scopic behaviour of porphyrins. 



In particular, the discussion will refer to the behaviour of the fully esterified 

 derivatives of mesoporphyrin IX (DMMP), protoporphyrin IX (DMPP) 

 and coproporphyrin III (TMCP) (see Fig. 1). The detergent solutions used 



