Intramolecular disorder and its relation to mesophase structure in lipid/water mixtures

NMR spin-half pair dipolar echo measurements are reported for the lamellar (dispersions and multibilayer stacks) and hexagonal phases of potassium palmitate/²H₂O mixtures. In the lamellar L_β and L_γ (gel) phases the alkyl chains are rigid and perfectly ordered, while in the lamellar L_α and hexagonal phases they are flexible and disordered. In particular, the measurements show that in the fluid lamellar L_α phase the chain is “bent” at the C₉–C₁₀ segment; but is “straight” in the hexagonal phase.