The effect of alpha-tocopherol on the structure and phase behavior of dilau
royl-, dimyristoyl-, dipalmitoyl-, and distearoyl-phosphatidylcholines was
examined using X-ray diffraction and freeze-fracture electron microscopic m
ethods. A ripple phase was observed in all of the mixtures at temperatures
well below the pretransition temperature of the corresponding pure phosphol
ipid, Freeze-fracture studies indicated that with proportion of alpha-tocop
herol less than 5 mol% a ripple phase with large periodicity (50-150 nm) pr
edominated and with about 10 mol% alpha-tocopherol a ripple phase of period
icity about 16 nm was formed. With more than 10 mol% alpha-tocopherol plana
r bilayers tended to be formed. Partial phase diagrams of mixed aqueous dis
persions of saturated phosphatidylcholines and alpha-tocopherol over temper
ature ranges about the gel to liquid-crystal phase boundary have been const
ructed. alpha-Tocopherol-enriched domains form ripple phases that coexist w
ith regions of lamellar gel phase of the pure phospholipid in mixtures cont
aining less than 10 mol% alpha-tocopherol. The presence of increasing amoun
ts of alpha-tocopherol in the phospholipid causes an increase in the propor
tion of ripple phase at the expense of pure phospholipid bilayer indicating
that the alpha-tocopherol-enriched domains might possess a defined stoichi
ometry of the two constituents. (C) 2000 Academic Press.