Oriented nucleation of β-hematin crystals induced at various interfaces: Relevance to hemozoin formation

The nucleation of malaria pigment (hemozoin) and β-hematin crystals (synthetic hemozoin) can be promoted by lipid molecules. To determine the orientation of β-hematin crystals nucleated by 1-myristoyl-glycerol (MMG) on the water surface, we undertook a grazing incidence synchrotron X-ray diffraction and X-ray reflectivity study. Our results indicate that premixed α-hematin with MMG yielded β-hematin nanocrystals oriented with the {100} face parallel to water surface, which we explain insofar that the spreading solution allows MMG molecular aggregation into clusters exposing OH groups and oxygen lone-pair electrons that interact with hematin molecules. Hematin molecules, which did not interact with MMG clusters, do not yield β-hematin, but rather an unknown crystalline phase. Independently, evidence is presented that self-assembled functionalized alkanethiol monolayers (SAMs) exposing OH groups induce β-hematin nucleation primarily via its {100} face, whereas those exposing CH₃ induce nucleation of either the {100} or {010} face, preferentially {010}. The results can be explained in terms of a difference in affinity of the SAMs to these two crystal faces. The two sets of β-hematin nucleation experiments, conducted under different conditions, strengthen the notion that MMG molecules, mimicking a digestive vacuole lipid surface, induce, via stereospecific interactions, oriented nucleation of β-hematin at the {100} face.