Mössbauer studies of different types of hematin

Three types of hematin, β-(synthetic malaria pigment), B- and R-(regular) hematin, which differ in part of their infrared spectra and in their solubility in different solvents, have been investigated by Mössbauer spectroscopy at both 4.1 and 90 K. At the latter temperature, all hematins show an asymmetric shape which indicates slow spin-spin relaxation. The R-hematin shows, in addition, a second component which is considered to be due to antiferromagnetic coupling between dimeric units of ferriprotoporphyrin IX. The quadrupole splitting is smaller in β-hematin compared with B- and R-hematin, indicating a more symmetrical charge distribution around the iron in β-hematin. The larger relaxation times observed for β-hematin indicate larger iron-iron distances than in B- or R-hematin.