We studied the formation of beta-haematin from haemin in the presence of different concentrations of chloroquine by using 300 K, 77 K and in-field (at 12 K) 57Fe Mössbauer spectrometry. We found that the 300 K and 77 K Mössbauer spectra of the samples changed from asymmetric to symmetric doublets as the chloroquine concentration increased. This change was ascribed to closer iron-iron distances. The Mössbauer spectra in presence of external field for the beta-haematins with the lowest chloroquine concentrations were adequately fitted with two sextets. The non-zero values for the intensities of the intermediate lines indicate that the magnetic moments of the irons were anti-parallel or quasi-parallel to the applied magnetic field. In contrast, the spectra for beta-haematins with the higher chloroquine concentrations showed an additional sextet, with an average hyperfine field value almost equal in intensity to the external applied field that pointed out to the presence of diamagnetic iron ions. These results suggested that there could not exist a stacking sequence of the type Fe3+-protoporphyrin(IX)–chloroquine-Fe3+-protoporphyrin(IX), but instead this interaction proceed via inhibition of crystal growing because, as it is generally accepted, b-haematin is covered with chloroquine.

Mossbauer studies of beta-Haematin formed in presence of chloroquine

ACS Fall 2021

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