Boggs J M, Mason J T
Biochim Biophys Acta. 1986 Dec 16;863(2):231-42. doi: 10.1016/0005-2736(86)90263-4.
Several saturated asymmetric and symmetric phosphatidylcholines were studied by ESR spectroscopy and differential scanning calorimetry in order to determine the behavior of a fatty acid spin labeled near its terminal methyl, 16-doxylstearate, in the mixed interdigitated gel phase and the Lc subgel phase and other properties of these lipids. This spin label was motionally restricted in the mixed interdigitated gel phases of 18:10PC and 18:12PC. The motional restriction was similar to that reported earlier for fully interdigitated phases. This spin label was motionally restricted almost to the same degree in 10:18PC suggesting that this asymmetric lipid may also form a mixed interdigitated bilayer. In contrast the spin label had more motion in the gel phase of 18:14PC than in symmetric forms of PC, consistent with conclusions from X-ray diffraction studies that this less asymmetric lipid does not form a mixed interdigitated phase. The spin label was partially frozen out of the Lc subgel phases of symmetric forms of PC and 18:14PC formed by storage at low temperature. The phase behavior of the other asymmetric lipids also depended on the sample history. Storage at low temperature caused 10:18PC and 18:12PC to go into ordered phases. The enthalpy of the transition of these ordered phases to the liquid-crystalline phase was 2-2.4-times greater than that of the transition of the gel phase formed on cooling back from the liquid-crystalline phase. The temperature of this high enthalpy transition was 0.8 K below that of the lower enthalpy gel to liquid-crystalline phase transition for 18:12PC, but 4.6 K higher for 10:18PC. The spin label was frozen out of these ordered phases, as it was out of the Lc subgel phases, suggesting that 18:12PC and 10:18PC may also form an Lc phase. 18:10PC was not observed to form an ordered phase although storage of the sample at low temperatures did affect the temperature of its transition from the liquid-crystalline phase back to the gel phase upon cycling through its phase transition.
通过电子自旋共振光谱（ESR）和差示扫描量热法研究了几种饱和的不对称和对称磷脂酰胆碱，以确定脂肪酸自旋标记物（16-脱氧硬脂酸）在其末端甲基附近在混合交叉指状凝胶相和Lc亚凝胶相中的行为以及这些脂质的其他性质。该自旋标记物在18:10PC和18:12PC的混合交叉指状凝胶相中运动受限。这种运动受限与先前报道的完全交叉指状相的情况相似。该自旋标记物在10:18PC中运动受限程度几乎相同，这表明这种不对称脂质也可能形成混合交叉指状双层。相比之下，自旋标记物在18:14PC的凝胶相中的运动比在对称形式的PC中更多，这与X射线衍射研究的结论一致，即这种不对称性较小的脂质不会形成混合交叉指状相。自旋标记物在低温储存形成的对称形式的PC和18:14PC的Lc亚凝胶相中部分冻结。其他不对称脂质的相行为也取决于样品历史。低温储存导致10:18PC和18:12PC进入有序相。这些有序相向液晶相转变的焓比从液晶相冷却回来形成的凝胶相转变的焓大2至2.4倍。对于18:12PC，这种高焓转变的温度比低焓凝胶向液晶相转变的温度低0.8K，但对于10:18PC则高4.6K。自旋标记物从这些有序相中冻结出来，就像它从Lc亚凝胶相中冻结出来一样，这表明18:12PC和10:18PC也可能形成Lc相。尽管在低温下储存样品确实会影响其在经历相变循环时从液晶相回到凝胶相的转变温度，但未观察到18:10PC形成有序相。
