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