Gleeson J T, Erramilli S, Gruner S M
Department of Physics, Joseph Henry Laboratories, Princeton University, New Jersey 08544.
Biophys J. 1994 Aug;67(2):706-12. doi: 10.1016/S0006-3495(94)80531-4.
The manner in which ice forms in lamellar suspensions of dielaidoylphosphatidylethanolamine, dielaidoylphosphatidylcholine, and dioleoylphosphatidylcholine in water depends strongly on the water fraction. For weight fractions between 15 and 9%, the freezing and melting temperatures are significantly depressed below 0 degree C. The ice exhibits a continuous melting transition spanning as much as 20 degrees C. When the water weight fraction is below 9%, ice never forms at temperatures as low as -40 degrees C. We show that when water contained in a lamellar lipid suspension freezes, the ice is not found between the bilayers; it exists as pools of crystalline ice in equilibrium with the bound water associated with the polar lipid headgroups. We have used this effect, together with the known chemical potential of ice, to measure hydration forces between lipid bilayers. We find exponentially decaying hydration repulsion when the bilayers are less than about 7 A apart. For larger separations, we find significant deviations from single exponential decay.
在水中，二反油酰磷脂酰乙醇胺、二反油酰磷脂酰胆碱和二油酰磷脂酰胆碱的层状悬浮液中冰的形成方式在很大程度上取决于水的比例。对于15%至9%的重量分数，凝固温度和熔化温度显著低于0摄氏度。冰呈现出跨度高达20摄氏度的连续熔化转变。当水的重量分数低于9%时，在低至-40摄氏度的温度下冰从未形成。我们表明，当层状脂质悬浮液中所含的水结冰时，在双层之间未发现冰；它以结晶冰池的形式存在，与极性脂质头基团相关的结合水处于平衡状态。我们利用这种效应，结合已知的冰的化学势，来测量脂质双层之间的水化力。当双层间距小于约7埃时，我们发现水化斥力呈指数衰减。对于更大的间距，我们发现与单指数衰减有显著偏差。
