OTHER COMPOUNDS OF HEME AND HEMATIN 191 



cyanide fcrroporpliyrin. the mixed cyanide-base compounds are known only 

 in the ferric state. Reduction of pyridine cyanide ferriporphyrin for example, 

 results in the production of pyridine hemochrome (Drabkin, 620). 



5.3.4. Absorption Spectra of Cyanide Compounds. Dicyanide 



ferriporphyrin has a single broad absorption band in the green region 

 of the spectrum, differing in this regard from the normal hemtchromes. 

 Monocyanide ferroporphyrin has a hemochrome type of spectrum, 

 but is anomalous in having only one nitrogenous group coordinated 

 with the iron atom. Dicyanide ferroporphyrin, with two nitrogenous 

 groups, has, as we have seen, a two-banded spectrum, but the order of 

 strength of the bands is reversed from that of hemochromes (Table VII) . 



5.3.5. Linkage of Cyanide. The cyanide compounds have in com- 

 mon with the hem /chromes and hemochromes covalent linkage of the 

 nitrogenous substance with the iron atom. It is, however, difficult 

 to correlate the form of the absorption spectrum with the constitution 

 of the various complexes. Pauling assumes that in these substances 

 the cyanide is linked through the carbon, not the nitrogen, atom; if 

 this is so, we may perhaps assume that it is this mode of linkage which 

 influences the spectrum, and that the charge on the complex has 

 little or no effect. In this way, the similarity of spectrum of dicyanide 

 ferriporphyrin, cyanide base ferriporphyrin, and cyanide hemiglobin 

 may be explained, but not, on the other hand, the similarity of 

 hemochromes and monocyanide ferroporphyrin. 



5.4. Other Compounds of Heme and Hematin 



Combination of heme or hematin with a number of different substances 

 has been reported. Methylcarbylamine and its homologs (R • N = C) com- 

 bine only with heme, not with hematin compounds (cf. Warburg and collab- 

 orators, 29 1 8, 29 5 Jf, 29 56). Methylcarbylamine hemoglobin is discussed in 

 Chapter VI, Section 2. '2. 6. Similarly Holden has recently reported that 

 acetonitrile (CH3'C= N) combines with heme giving spectra similar to 

 those with two and four bands obtained at low and intermediate concen- 

 trations of cyanide. Whetlier the substances obtained are fully analogous to 

 the cyanide compounds, the failure to obtain the dicyanide type of spectrum 

 being due to a very high dissociation constant of the corresponding diacetoni- 

 trile ferroporphyrin, or whether the four-banded spectrum l)eIongs to a 

 different type of compound, remains to be determined. 



Compounds with azide have received imduly little attention. Ball {12It) 

 assumes that azide behaves similarly to cyanide in combining witli both 

 ferrous and ferric liematin compounds. 



Sulfhydryl compounds of simple hematins are unknown. 



