THE EFFECT OF THE CRYOPROTECTIVE SUGAR, TREHALOSE ON THE PHASE-BEHAVIOR OF MIXED DISPERSIONS OF DIOLEOYL DERIVATIVES OF PHOSPHATIDYLETHANOLAMINE AND PHOSPHATIDYLCHOLINE
Li. Tsonev et al., THE EFFECT OF THE CRYOPROTECTIVE SUGAR, TREHALOSE ON THE PHASE-BEHAVIOR OF MIXED DISPERSIONS OF DIOLEOYL DERIVATIVES OF PHOSPHATIDYLETHANOLAMINE AND PHOSPHATIDYLCHOLINE, Liquid crystals, 17(5), 1994, pp. 717-728
The phase behaviour of a mixed dispersion of dioleoyl derivatives of p
hosphatidylethanolamine and phosphatidylcholine (3:1, by weight) in an
excess of water was compared with that in 1.8 M trehalose using dynam
ic X-ray diffraction, differential scanning calorimetry and freeze-fra
cture electron microscopy. The phase transitions of the fully-hydrated
dispersion observed upon heating, proceeded with lamellar-gel --> lam
ellar liquid crystalline --> inverse cubic --> inverse hexagonal phase
at temperatures of -10-degrees-C, 49-degrees-C, and 67-degrees-C, res
pectively. Our results confirm the existence of an inverse cubic phase
of this system and support the model mechanism for the lamellar/non-l
amellar phase transition previously suggested by Siegel (1986, Biophys
. J. 49, 1155, 1171). Dispersion of the binary lipid mixture in a 1.8
M solution of the naturally occurring cryoprotective disaccharide, tre
halose, inhibited the formation of both lamellar liquid crystalline an
d inverse cubic phases and resulted in a direct transition from lamell
ar-gel to inverse hexagonal phase at about -6-degrees-C. The effect of
trehalose is discussed in terms of a 'water replacement' model and Ho
fmeister effects on water structure. Trehalose is regarded as a kosmot
ropic agent that may also interact directly with the lipid polar group
s. Comparison of the relationship between temperature and the dimensio
ns of the inverse hexagonal phase formed in the presence and absence o
f trehalose suggests that the osmotic effect of the impermeant trehalo
se prevents water molecules from being taken up by the hexagonal mesop
hase which is normally more hydrated that the lamellar phase.