174 V. HEMATIN COMPOUNDS 



between the hydroxyl group of one hematin molecule and the iron 

 atom of a second. Sucrose and other alcohols may be able to break 

 this linkage, and thus produce monomeric hematin with ionic linkages. 



4. HEMOCHROMES AND HEM/CHROMES 

 4.1. Hemochromes 



Hemochromes had been prepared in crystalline form from hematin 

 long before.their relationship to hemoglobin was correctly understood 

 (c/. Chapter VI). v. Zeynek {317 Jf) obtained solid ammonia hemo- 

 chrome by reduction of hematin in ammoniacal alcohol with hydrazine 

 hydrate; he and his collaborators later prepared crystalline pyridine 

 hemochrome (1459,3175), which contained two molecules of pyridine 

 bound to heme {cf. also 886,1276,1277). Heme can combine to form 

 hemochromes with a great variety of nitrogenous substances including 

 ammonia, primary amines, carbylamines, hydrazine, pyridine, and 

 pyridine compounds such as nicotine, imidazole compounds, and 

 piperidine. Hence it also combines with denatured proteins, in 

 which hemochrome-forming groups are accessible and sterically in 

 a favorable position {cf. Chapters VI and VIII). Cyanide also forms 

 compounds with heme, but their nature is different from that of 

 hemochromes {cf. Section 5.3.). 



The possibility exists that one molecule of heme may combine 

 with one molecule of each of two different nitrogenous compounds. 

 Compounds of this type containing one molecule of cyanide with 

 one of base have been described by Hill {1277), Krebs {1579), Anson 

 and Mirsky (7^), and Drabkin {620). The evidence for the formation 

 of mixed hemochromes with pyridine and globin will be discussed 

 in Chapter VI, Section 2.4.4. 



Magnetochemical investigations have shown that in hemochromes 

 the iron is bound to the four porphyrin nitrogens and to two additional 

 nitrogen atoms of the combining nitrogenous substances by six d-sp^ 

 covalent bonds, with no unpaired electrons. The paramagnetism of 

 heme thus disappears in hemochrome formation and hemochromes 

 are diamagnetic {2126). 



4.1.1. Affinity of Heme for Bases. The affinity of heme for 

 various nitrogenous bases varies considerably. It is very high for 

 denatured globin {621,1322) and cyanide, intermediate for pyridine * 

 and 4-methylimidazole, low for ammonia, methylamine, phenylhy- 



