PORPHYRINS WITH FOUR COOH GROUPS 



65 



distinguished by their fluorescence pH curves in the pH range 2-6, but 

 this method is only applicable to pure preparations {773). Schwartz and 

 co-workers {2512) have recently observed that coproporphyrin I and III 



COPROPORPHYRIN TETRAMETHYL ESTER I, % 



140 



120 



20 

 -T" 



40 



60 



«o 



lOC 



Melting point 



Solidification point 



260 



220 



200 



-120 



100 



80 



60 



40 



20 



COPROPORPHYRIN TETRAMETHYL ESTER in,% 



Fig. 10. Melting point-composition curve for the tetramethyl esters of coproporphy- 

 rins I and III (after Jope and O'Brien, llt'26) : temperature at which softening and 



loss of double refractions begins on heating ( ); lower melting point characteristic 



of coproporphyrin III tetramethyl ester (...); melting point ( — ); solidification point 



(o-o). 



esters can be differentiated by the quenching of the fluorescence of type I 

 ester in 30% acetone in water, when the concentration of the porphyrins 

 was between 2.5 and 70 /zg. per 100 ml. 



