Non-equilibrium formation of the cubic phase in a monoolein/water system

¹ Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences Schmiedlstraße 6, 8042 Graz, Austria
² Dipartimento di Scienze Applicate ai Sistemi Complessi, Università Politecnica delle Marche - Via Ranieri 65, 60131 Ancona, Italy
³ Department of Physical Chemistry, Uppsala University PO Box 579, 75123 Uppsala, Sweden

Corresponding author: michael.rappolt@elettra.trieste.it

Received: 31 March 2006
Accepted: 29 May 2006

Abstract

Time-resolved small-angle X-ray diffraction experiments have been carried out to investigate the transformation from the cubic gyroid to the cubic diamond phase. The transition was induced by rapid addition of water to a monoolein/water system changing the initial water concentration of 26% w/w to excess of water conditions. The transformation proceeds in two steps: at the beginning, the two cubic mesophases have a strongly differing lipid/water composition and are accompanied by an intermediate phase. This phase vanishes as the ratio of cell parameters exceeds 1.50. Thereafter, the transition continues by a direct nearly isoareal transformation of the cubic minimal surfaces. Lateral area per lipid molecule, molecular shape and principle curvatures are about the same in this regime.