Investigations of B- and β-hematin

Abstract The preparation from ferriprotoporphyrin IX (FP) in aqueous acid medium of the related pigments β- and B-hematin [see G. Blauer and M. Akkawi, Biochem. Mol. Biol. Int. 35, 231 (1995)] is presented under different conditions. Both pigments are characterized by infrared spectra which differ in the range of 1600–1700 cm −1 in their strong bands with absorption peaks measured at 1648 ± 2 cm −1 for B-hematin and at 1663 ± 1 cm −1 for β-hematin. The pH dependence of B-hematin formation at 37°C and at different concentrations of acetic acid and FP exhibits a maximum yield near pH 4. The formation of β-hematin at 70°C shows high yield in 6 M acetic acid or in the presence of 0.028 M trichloroacetate at pH 4.6. The dependence of the yield of the pigments on the time and temperature of incubation, concentration of FP, and the presence of different electrolytes was investigated. Both B- and β-hematin are either insoluble or very slightly soluble in different solvents at room temperature, and appear to dissociate into regular FP in strongly alkaline aqueous medium. In the presence of different quinoline-based drugs, the formation of both B- and β-hematin at pH 4–5 is inhibited. Under certain conditions, the effect of added carboxylic acids on pigment formation is suggested to be due, at least in part, to the prevention of initial hydrogen bonding among FP carboxyl groups. For both B- and β-hematin, branched and cyclic macromolecular structures are proposed involving linkages between an FP iron and a side-chain carboxylate group of another FP, in addition to hydrogen bonds between FP carboxyl groups. B- and β-hematin are assumed to differ in molecular weight and the extent of bond formation. Possible mechanisms for β-hematin production from B-hematin and certain relations between the synthetic pigments and the malaria pigment are suggested.