Hw. Meyer et al., Hydration of DMPC and DPPC at 4 degrees C produces a novel subgel phase with convex-concave bilayer curvatures, CHEM PHYS L, 105(2), 2000, pp. 149-166
Hydration of dimyristoyl- and dipalmitoylphosphatidylcholines at 4 degrees
C results in the formation of a characteristic subgel phase designated P-cc
. Examination of the phase by freeze-fracture electron microscopy shows con
vex-concave deformations of the planar bilayer which are of two types. A sm
aller type with a radius of curvature of about 20 nm predominates in DMPC,
and a larger type with about 70 nm radii of curvatures dominates in DPPC. T
he P-cc phase can also be formed in samples hydrated at temperatures above
the main phase transition if the dispersion is frozen slowly and subsequent
ly incubated at 4 degrees C for several days. The subgel P-cc phase was dis
tinguished from the subgel L-c phase by the temperature of transition, pack
ing of the acyl chains on the basis of wide-angle X-ray diffraction, and H-
2-NMR spectra characteristic of a 'solid-ordered' phase. Vibrational spectr
a of the carbonyl and phosphate regions are consistent with a partially red
uced hydration state. The origin of the convex-concave bilayer deformation
is believed to result from constraints imposed by limiting hydration of the
headgroup and a frustration arising from the spontaneous curvature of both
monolayers. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.