Orientation and motion of amphiphilic spin labels in hexagonal lipid phases.

The acyl chain of spin-labeled fatty acids intercalates between the lipid hydrocarbon chains in hexagonal and micellar phases with the carboxyl group anchored at the lipid water interface. The spectra are characteristic of anisotropic motion and cannot be distinguished from the spectra of these probes in lamellar dispersions. In the hexagonal and micellar phases the molecular motion of the spin label increases as it is moved further away from the carboxyl group, similar to the behavior in the lamellar phase (Jost et al. (1971) J. Mol. Biol. 59, 77-98). The similarity in packing of the acyl chains in the hexagonal and lamellar phases suggests that localized regions of hexagonal phase are compatible with a bilayer matrix.