THE magnetic properties of haemoglobin are well established1. The prosthetic group of haemoglobin has a protoporphyrin structure (ferrohaem) in which the iron atom is ionically bound. Consequently there are in deoxyhaemoglobin four unpaired electrons per iron atom leading to a paramagnetic moment of 5.35 Bohr magnetons per haem group. Oxyhaemoglobin on the other hand is diamagnetic. Other iron-containing haemoproteins such as ferrihaemoglobin have been shown by magnetic susceptibility measurements2 to possess magnetic moments per haem group which correspond reasonably closely to those predicted from the number of unpaired electrons per iron atom. Consequently red blood cells containing deoxyhaemoglobin when placed in a magnetic field B0 (Tesla) with field gradient dB0/dz may be expected to experience a magnetic force FM (Newtons) in the z direction given by FM = (χV/μ0)B0(dB0/dZ) (1) where χ is the (SI) susceptibility of the red blood cell, V (m3) its volume and μ0 the permeability of free space.
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MELVILLE, D., PAUL, F. & ROATH, S. Direct magnetic separation of red cells from whole blood. Nature 255, 706 (1975). https://doi.org/10.1038/255706a0
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