Issue 5, 2010

Crystallization of synthetic haemozoin (β-haematin) nucleated at the surface of lipid particles

Abstract

The mechanism of formation of haemozoin, a detoxification by-product of several blood-feeding organisms including malaria parasites, has been a subject of debate; however, recent studies suggest that neutral lipids may serve as a catalyst. In this study, a model system consisting of an emulsion of neutral lipid particles was employed to investigate the formation of β-haematin, the synthetic counterpart of haemozoin, at the lipidwater interface. A solution of monoglyceride, either monostearoylglycerol (MSG) or monopalmitoylglycerol (MPG), dissolved in acetone and methanol was introduced to an aqueous surface. Fluorescence, confocal and transmission electron microscopic (TEM) imaging and dynamic light scattering analysis of samples obtained from beneath the surface confirmed the presence of homogeneous lipid particles existing in two major populations: one in the low micrometre size range and the other in the hundred nanometre range. The introduction of haem (Fe(III)PPIX) to this lipid particle system under biomimetic conditions (37 °C, pH 4.8) produced β-haematin with apparent first-order kinetics and an average half life of 0.5 min. TEM of monoglycerides (MSG or MPG) extruded through a 200 nm filter with haem produced β-haematin crystals aligned and parallel to the lipidwater interface. These TEM data, together with a model system replacing the lipid with an aqueous organic solvent interface using either methyl laurate or docosane demonstrated that the OH and C[double bond, length as m-dash]O groups are apparently necessary for efficient nucleation. This suggests that β-haematin crystallizes via epitaxial nucleation at the lipidwater interface through interaction of Fe(III)PPIX with the polar head group. Once nucleated, the crystal grows parallel to the interface until growth is terminated by the curvature of the lipid particle. The hydrophobic nature of the mature crystal favours an interior transport resulting in crystals aligned parallel to the lipidwater interface and each other, strikingly similar to that seen in malaria parasites.

Graphical abstract: Crystallization of synthetic haemozoin (β-haematin) nucleated at the surface of lipid particles

Article information

Article type
Paper
Submitted
16 Jul 2009
Accepted
23 Oct 2009
First published
20 Nov 2009

Dalton Trans., 2010,39, 1235-1244

Crystallization of synthetic haemozoin (β-haematin) nucleated at the surface of lipid particles

A. N. Hoang, K. K. Ncokazi, K. A. de Villiers, D. W. Wright and T. J. Egan, Dalton Trans., 2010, 39, 1235 DOI: 10.1039/B914359A

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