PROPERTIES OF FERROUS COMPOUNDS 215 



2.2.2. Hemoglobin (Reduced Hemoglobin, Ferrohemoglobin, 



Hb). This is prepared from oxyhemoglobin by evacuation, equili- 

 bration with inert gases, or by the addition of chemical reducing 

 agents such as Stokes' solution, titanous tartrate, ammonium hydro- 

 sulfide, or sodium dithionite (Na2S204). With the first one of these 

 methods care must be taken that some denaturation does not occur 

 from frothing, while with the chemical reducing agents, the pH must 

 be controlled. A large excess of the reagent and reoxygenation are 

 particularly dangerous if dithionite is the reducer, since hydrogen 

 peroxide is formed during its autoxidation. These considerations are 

 of the greatest importance if alterations of the molecule are to be 

 avoided. 



Hemoglobin has a broad band, maximum 560 m^t- While oxyhemo- 

 globin or denatured globin hemochrome are fairly readily detectable 

 with the hand spectroscope in the presence of excess hemoglobin, 

 small amounts of hemoglobin in the presence of the other compounds 

 are not. The spectrum is not sensitive to changes of pH between 

 5.5 and 9.5, while outside these limits denaturation may commence, 

 the actual pH limits of stability' varying somewhat with different 

 hemoglobins. 



The magnetic susceptibility of hemoglobin shows that it has four 

 unpaired electrons per iron atom, the bond being, therefore of an 

 ionic type (2127,27^8). 



2.2.3. Carboxyhemoglobin (Carbon Monoxide Hemoglobin, 



HbCO). Carboxyhemoglobin was discovered by Claude Bernard in 

 1858 (24-3) and independently by Hoppe-Seyler a little later. Since 

 the affinity of hemoglobin for carbon monoxide is much greater than 

 that for oxygen, the former gas readily replaces the latter. The 

 spectrum of carboxyhemoglobin in the visible region is difficult to 

 distinguish from that of oxyhemoglobin with the hand spectro- 

 scope although the a band of the latter is sharper. The maximum 

 of the a-band shifts from 577 mju in oxyhemoglobin to 570 m/x in 

 carboxyhemoglobin; this may readily be distinguished with a rever- 

 sion spectroscope. The spectrum of carboxyhemoglobin like that of 

 oxyhemoglobin, is not sensitive to pH changes. The molecule con- 

 tains no unpaired electrons, the bonds being covalent. Pauling and 



Coryell {2127) assign to carboxyhemoglobin a structure resonating _^ 



between A and B: >^6ilC>J/"^ 



^ILISRARY 



