Shipley G G, Avecilla L S, Small D M
J Lipid Res. 1974 Mar;15(2):124-31.
The phase behavior of bovine brain sphingomyelin in water has been determined by polarizing light microscopy, differential scanning calorimetry, and X-ray diffraction. Lamellar phases, in which water is intercalated between sheets of lipid molecules arranged in the classical bilayer fashion, are present over much of the phase diagram. An order-disorder transition separates the high temperature, liquid crystalline, lamellar phase from a more ordered lamellar phase at low temperatures. The hydration characteristics of sphingomyelin are similar to the structurally related lecithin in that only limited amounts of water are incorporated above and below the transition. Above the transition at 47 degrees C, a maximum of 35% by weight of water can be incorporated between the lipid bilayers, the total thickness at maximum hydration being 60.2 A, the lipid thickness 38 A, and the surface area per lipid molecule at the interface 60 A(2). Water in excess of 35% by weight is present as a separate phase. Below the phase transition, at 25 degrees C a maximum of 42% by weight of water may be incorporated between the lipid bilayers. On increasing the hydration, the lamellar repeat distance increases from 63.5 A to a limiting value of 76 A. Within this hydration range the calculated lipid thickness decreases from 63.5 to 42.5 A, and the surface area per lipid molecule increases from 36.1 to 53.6 A(2). Although these changes may be accounted for by a structure in which the hexagonally packed ordered hydrocarbon chains tilt progressively with respect to the normal to the bilayer plane on increasing hydration, it is possible that changes in other more complex lamellar structures may be responsible for these variations in lipid thickness and surface area.
通过偏光显微镜、差示扫描量热法和X射线衍射法测定了牛脑鞘磷脂在水中的相行为。在相图的大部分区域都存在层状相，其中水插层在以经典双层方式排列的脂质分子片层之间。有序-无序转变将高温液晶层状相与低温下更有序的层状相分隔开来。鞘磷脂的水合特性与结构相关的卵磷脂相似，即在转变温度以上和以下仅结合有限量的水。在47℃的转变温度以上，脂质双层之间最多可结合35%（重量）的水，最大水合时的总厚度为60.2 Å，脂质厚度为38 Å，界面处每个脂质分子的表面积为60 Ų。超过35%（重量）的水以单独的相存在。在相变温度以下，在25℃时，脂质双层之间最多可结合42%（重量）的水。随着水合作用的增加，层状重复距离从63.5 Å增加到极限值76 Å。在这个水合范围内，计算出的脂质厚度从63.5 Å减小到42.5 Å，每个脂质分子的表面积从36.1 Ų增加到53.6 Ų。尽管这些变化可能由一种结构来解释，即随着水合作用的增加，六方堆积的有序烃链相对于双层平面的法线逐渐倾斜，但也有可能是其他更复杂的层状结构变化导致了脂质厚度和表面积的这些变化。
