Synthetic Hemozoin (β-Hematin) Crystals Nucleate at the Surface of Neutral Lipid Droplets that Control Their Sizes

• Published in: Crystal growth & design Vol. 13; no. 10; pp. 4442 - 4452
• Main Authors: Ambele, Melvin A, Sewell, B. Trevor, Cummings, Franscious R, Smith, Peter J, Egan, Timothy J
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 02.10.2013
• Subjects: Condensed matter: structure, mechanical and thermal properties; Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction; Electron diffraction and scattering; Exact sciences and technology; Physics; Structure of solids and liquids; crystallography; Emulsions; Crystal form; Electron diffraction; Ultrasonic waves; Lipids; Interfaces; Transmission electron microscopy; EEL spectroscopy; Imaging; Droplets; Size control; Microcrystal; Acetone; Methanol
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg4009416

Emulsions of monopalmitoylglycerol (MPG) and of a neutral lipid blend (NLB), consisting of MPG, monostearoylglycerol, dipalmitoylglycerol, dioleoylglycerol, and dilineoylglycerol (4:2:1:1:1), the composition associated with hemozoin from the malaria parasite Plasmodium falciparum, have been used to mediate the formation of β-hematin microcrystals. Transmission electron microscopy (TEM), electron diffraction, and electron spectroscopic imaging/electron energy loss spectroscopy (ESI/EELS) have been used to characterize both the lipid emulsion and β-hematin crystals. The latter have been compared with β-hematin formed at a pentanol/aqueous interface and with hemozoin both within P. falciparum parasites and extracted from the parasites. When lipid and ferriprotoporphyrin IX solutions in 1:9 v/v acetone/methanol were thoroughly premixed either using an extruder or an ultrasound bath, β-hematin crystals were found formed in intimate association with the lipid droplets. These crystals resembled hemozoin crystals, with prominent {100} faces. Lattice fringes in TEM indicated that these faces made contact with the lipid surface. The average length of these crystals was 0.62 times the average diameter of NLB droplets, and their size distributions were statistically equivalent after 10 min incubation, suggesting that the lipid droplets also controlled the sizes of the crystals. This most closely resembles hemozoin formation in the helminth worm Schistosoma mansoni, while in P. falciparum, crystal formation appears to be associated with the much more gently curved digestive vacuole membrane, which apparently leads to formation of much larger hemozoin crystals, similar to those formed at the flat pentanol–water interface.