Physiochemical Characterization and Stability of Lipidic Cubic Phases by Solution NMR

Lipidic inverse bicontinuous cubic phases (LCPs), formed via the spontaneous self-assembly of lipids such as monoolein, have found increasing applications in the stabilization and crystallization of integral membrane proteins for structural characterization using X-ray crystallography. Their use as effective drug release matrices has also been demonstrated. Nuclear magnetic resonance (NMR) spectroscopy, both solution and solid state, has previously been employed for the characterization of LCPs and related systems. Herein, we report a number of novel features of solution NMR for probing the fundamental composition and structural properties of monoolein-based LCPs. These include (1) more complete assignments of both H-1 and C-13 chemical shifts, (2) direct quantification of hydration level in LCPs using one-dimensional (1D) H-1 NMR, and (3) monitoring longer-term stability of LCPs and evaluating alterations introduced into standard LCPs at the submolecular level.