Nature of the Iron–Oxygen Bond in Oxyhæmoglobin

HÆMOGLOBIN (Hb) can combine with molecular oxygen to give oxyhæmoglobin (HbO2) in which one molecule of oxygen is associated with one hæmin group1. In hæmoglobin the iron is in the ferrous state, and it is generally assumed that the combination with molecular oxygen does not change its valency so that HbO2 is likewise supposed to be a ferrous compound. However, it would appear that many of the physical properties of oxyhæmoglobin are at variance with such a view. Principally these are1 : (1) magnetic properties ; (2) absorption spectrum ; (3) acid dissociation constant. These facts suggest that the conversion of hæmoglobin into oxyhæmoglobin is associated with a more profound electronic rearrangement.