Transformation between Inverse Bicontinuous Cubic Phases of a Lipid from Diamond to Gyroid.

The transformation between inverse bicontinuous cubic phases of a lipid from diamond (QII(D)) to gyroid (QII(G)) in the single crystal region of monoolein was studied. X-ray diffraction data indicate that the single orientation of the QII(D) phase was converted into an almost single orientation of the QII(G) phase. The [111] and [11̅0] directions of a single crystal of the QII(D) phase corresponded to the [202] and [04̅0] directions of the QII(G) phase, respectively. This orientation relationship indicated that one direction in the four-branched water channels of the QII(D) phase was preserved in the three-branched water channels of the QII(G) phase. Using this relationship, a transformation model was constructed in which one direction of the water channels was preserved while another direction appeared.