HEMES, HEMINS 167 



From the fact that heme iron is not removed by o-phenanthroline 

 or a,a'-dipyridyl (bipyridine), we can conclude that the iron in heme 

 is far less dissociated than the iron in ferrocyanide, at least in neutral 

 solvents. While for the removal of iron from ferric hematin com- 

 pounds concentrated sulfuric acid is required, dilute hydrochloric 

 acid or even glacial acetic acid is able to remove iron from heme or 

 hemochromes {886,2823,2872). Conversely, iron is readily introduced 

 into porphyrin by heating with ferrous acetate in acetic acid, the 

 autoxidation of the heme to hemin shifting the equilibrium toward 

 complete formation of hemin. 



Figure 1 shows the absorption curve of heme in phosphate buffer 

 at pH 7. The asymmetric nature of the broad band in the green 

 indicates that it is the resultant of two separate bands, the maxima 

 of which lie approximately at 550 xnp. and 575 m/i, the latter being 

 the more intense. Under certain circumstances these two bands may 

 be distinguished in the visual spectroscope. 



According to this curve, c'^^m = 5.5. Varying values (5.0 to 6.7) 

 have been found for the absorption in different buffers (Drabkin, 

 629; Heilmeyer, 1213; and Zeile and Gnant, 3165). 



Drabkin {629) and Warburg and co-workers have found the position 

 of the Soret band at 415 m^, while Callaghan's study indicates that 

 the maximum lies at a somewhat shorter wavelength. 



3.2. Hemins 



Chlorohemin, generally called hemin, C34H3204N4FeCl, is the form 

 in which the prosthetic group of hemoglobin has been longest known 

 and is most stable. Typical rhomb-shaped crystals of "a-hemin" 

 (Teichmann, 275J^) are obtained if a hemoglobin solution is heated 

 with acetic acid containing some sodium chloride to a temperature 

 just below the boiling point. This method, which is of interest for 

 the detection of blood stains in forensic medicine, is also the best 

 method of preparation of hemin (Schalfejeff, 2035,2436; Fischer, 797). 

 Hemin is recrystallized from pyridine-cliloroform {1601) or quinine- 

 chloroform {1307) mixtures. 



Hemins probably contain the positively charged complex: 



-1 + 



Fe 

 N ^N 



