202 V. HEMATIN COMPOUNDS 



case still remain porphyrin hemins) and in the nucleus. Similarly 

 "green hemins" of very different structure exist. The "green hemin" 

 of Warburg and Negelein {2952) (verdohemin, cf. Chapter X) has a 

 structure widely different from that of green pheophorbid or chlorin 

 hematin compounds or froin that of green polyazahematins. 



8.2. Monoazahematin Compounds 



Monoazahemin, C33H3i04N5FeCl, and monoazamesohemin, C33H35- 

 04N5FeCl are crystalline compounds, greatly resembling hemin and 

 mesohemin. Their structure is discussed in Chapter III, Section 8.1, 

 They were obtained by Lemberg {1687) by the action of ammonia 

 on verdohemochrome, followed by treatment with hydrochloric acid. 

 The iron is held even more firmly than in hemin, little being removed 

 even by concentrated sulfuric acid. The greater stability of the 

 azaheme nucleus (and also of complex salts of phthalocyanin) is 



perhaps related to the fact that replacement of "^CH by ^ N narrows 



the ring and thus makes the iron atom an even better fit between the 

 four nitrogen atoms of the pyrrolic rings. 



Like heme, azaheme combines with nitrogenous bases giving liemochromes 

 which are oxidizable to hem/chromes. As in the porphyrin series the affinity 

 of monoazaheme to ammonia is smaller than that to pyridine or denatured 

 globin. The azahemochromes have a typical liemochrome spectrum, although 

 the two bands are somewhat closer together than in normal porphyrin- 

 heraochromes and visible as separate bands only at low concentration. The 

 a-bands of pyridine azahemochromes lie 8 m^c further toward the red than 

 those of the corresponding pyridine hemochromes, and the usual lO-m/i 

 difference is found between proto and meso compounds. Spectroscopically 

 the distinction of ammonia azahemochromes from ammonia hemochromes is 

 easier than that of the corresponding pyridine compounds. The difference 

 in the position of the a-bands is in this case 11 m/U, the bands of ammonia 

 monoazahemochrome lying at 51'i and .550 mju (weak). The Soret band of 

 azahematin compounds has the same position and height as that of hematin 

 compounds. Azahemochromes are red in neutral, green in alkaline, solution. 

 While the spectral difference is similar to that between hem/chromes and 

 hem/chrome hydroxides, it is much more apparent to the naked eye. 



Holden has made the remarkable observation that at pM 6.4 a blue-green 

 ferrous azaheme cyanide compound is formed with an absorption band at 

 60,S mjx, while in alkaline solution a dicyanide ferroazaporphyrin of the 

 usual type occurs. 



The close similarity between azahematin and hematin compounds disap- - 

 pears, however, when they are combined with native globin since the globin 

 compound of the azaheme does not combine reversibly with oxygen, but is 



