AZAPORPIIYRINS 89 



since stronger acid would also extract weakly basic chlorophyll derivatives 

 {366 JOH). 



It is open to doubt wliether the easy splitting of reduced heraatin 

 compounds by acids has not sometimes falsified the results of por- 

 phyrin estimations in blood and organs. The protoporphyrin content 

 of blood, e.g., is so small that a very slight degree of hemoglobin 

 decomposition during the isolation would suffice to lead to entirely 

 wrong results. This may explain the greatly divergent results for 

 the protoporphyrin content of erythrocytes found by various authors. 

 Thomas {2797) reports that 10% alcoholic hydrochloric acid forms 

 protoporphyrin from hemoglobin on irradiation with light. 



8. TETRAPYRROLIC RING COMPOUNDS 

 RELATED TO PORPHYRINS 



8.1. Azaporphyrins 



The azaporphyrins form an interesting link between the porphyrins 

 in which the four pyrrolic rings are linked by -^ CH groups and the 

 phthalocyanins in which four isoindole (benzopyrrole) nuclei are linked 

 by tertiary nitrogen. In the azaporphyrins one, two, or four of the 

 \ CH groups* linking i)yrrolic rings are replaced by tertiary nitrogen. 



Fig. 21. Monoazaporphyrins. 

 They were first obtained by Fischer and collaborators and named 

 iminoporphyrins, later imidoporphyrins. The nomenclature used 

 here was suggested by Helberger {1231). It is comprehensive and 

 needs no specific explanation. 



* These <rroup.s have heen ternu'd "nis" (ineso) groups by Fischer (rf. S61, p. 173) 

 and labeled a, /^, y, 8. The term '"nieso" is, however, unsuitable for obvious reasons 

 and the lettering has not always l)een applied consistently icf. also Chapter IV), 

 and a, ^ in this connection must not l)e confused with the oc- and /^-positions on the 

 pyrrole nucleus. 



