Abstract
Compact macromolecular dendrons have previously been shown to induce the formation of discontinuous inverse micellar assemblies with Fd3m symmetry in monoolein/water systems. Here, we demonstrate that a large PAMAM dendron (G5: fifth generation) induces the formation of a very unusual mesophase with P4(3)32 symmetry. This mesophase had previously been observed in monoolein/ water systems only on addition of cytochrome c. The P4(3)32 mesophase can be considered an intermediate phase between the bicontinuous Ia3d and discontinuous micellar mesophases. We present a detailed investigation of the phase behavior of monoolein/water as a function of GS concentration and temperature. Addition of 1% G5 in 85/15 monoolein/water system induces a transition from the L-alpha to Ia3d phase. Further increase in G5 concentration to above 2% induces the formation of the P4(3)32 phase. In contrast to this, incorporation of lower generation PAMAM dendrons (G2 G4) in monoolein/water yields a qualitatively different phase diagram with the formation of the reverse micellar Fd3m phase. PAMAM dendrons of all generations, G2 G5, bear terminal amine groups that interact with the monoolein headgroup. The compact molecular architecture dendrons and these attractive interactions induce bending of the monoolein bilayer structure. For smaller dendrons, G2 G4, this results in the formation of the Fd3m phase. However, the large size of the G5 dendron precludes this and a rare intermediate phase between the Ia3d and discontinuous micellar phase, and the P4(3)32 mesophase forms instead.