Effect of chain unsaturation on the structure and thermotropic properties of galactocerebrosides.
Effect of chain unsaturation on the structure and thermotropic properties of galactocerebrosides.
复制标题
链不饱和度对半乳脑苷脂结构和热致性质的影响。
DOI：
10.1016/s0006-3495(89)82803-6
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发表时间：
1989
影响因子：
3.4
通讯作者：
Shipley,GG
中科院分区：
文献类型：
--
作者：
Reed,RA;Shipley,GG
差示扫描量热法 (DSC) 和 X 射线衍射已用于研究增加链不饱和度对水合脑苷脂 N-硬脂酰、-油酰和 -亚油酰半乳糖基鞘氨醇（分别为 NSGS、NOGS 和 NLnGS）的结构和性质的影响。水合（70 wt% 水）NSGS 的 DSC 显示在 85 摄氏度时发生吸热转变（δ H=18.0 kcal/mol NSGS），并在 40–60 摄氏度时发生广泛的放热转变，后者取决于之前的冷却速率。在 21、61 和 86 摄氏度下记录的 X 射线衍射图为亚稳态和稳定结晶 NSGS 双层相之间的相互转化提供了证据。不饱和链脑苷脂的性质更为复杂。水合 NOGS 在 44.8 摄氏度时显示出单一吸热转变（δ H=11.5 kcal/mol NOGS）。然而，NOGS 在 49 摄氏度下孵育 24 小时会导致在 55.5 摄氏度下发生第二次转变。通过在 0 到 49 摄氏度之间循环 NOGS，可以实现完全转化为这种较高熔点相（δ H = 12.1 kcal/mol NOGS）。 X 射线衍射证实了所有温度下的双层相，并描绘了 21 摄氏度下的结晶相（双层周期 d = 56.5A）、47 摄氏度下的第二结晶相（d = 69.9A）和 59 摄氏度下的液晶相（d = 52.0A）之间的转化。不饱和度较高的 NLnGS 显示出两个转变，即 28 摄氏度时的急剧转变（δ H=8.0 kcal/mol NLGS）和 42 摄氏度时的宽阔、低焓转变（δ H=0.4 kcal/mol NLGS）。同样，两个转变之间的孵育导致 44 摄氏度下的单一转变（δ H=9.3 kcal/mol NLGS）。 X射线衍射证明了两种结晶双层相（d=55.2A和d=68.4A）与液晶双层相（d=51.8A）之间的转化。因此，脑苷脂酰胺连接的脂肪酰基链中不饱和度的增加导致链熔化温度降低（NSGS 大于 NOGS 大于 NLnGS），并对其结构特性产生显着影响。
Differential scanning calorimetry (DSC) and x-ray diffraction have been used to study the effect of increasing chain-unsaturation on the structure and properties of the hydrated cerebrosides N-stearoyl, -oleoyl, and -linoleoyl galactosylsphingosine (NSGS, NOGS, and NLnGS, respectively). DSC of hydrated (70 wt% water) NSGS shows an endothermic transition at 85 degrees C (delta H=18.0 kcal/mol NSGS) and a broad exothermic transition at 40–60 degrees C, the latter being dependent upon the previous cooling rate. X-Ray diffraction patterns recorded at 21, 61, and 86 degrees C provide evidence for interconversions between metastable and stable crystalline NSGS bilayer phases. The properties of the unsaturated-chain cerebrosides are more complex. Hydrated NOGS shows a single endothermic transition at 44.8 degrees C (delta H=11.5 kcal/mol NOGS). However, incubation of NOGS at 49 degrees C for 24 h results in a second transition at 55.5 degrees C. By cycling NOGS between 0 and 49 degrees C complete conversion into this higher melting phase (delta H=12.1 kcal/mol NOGS) is achieved. X-ray diffraction confirms a bilayer phase at all temperatures and delineates the conversions between a crystalline phase at 21 degrees C (bilayer period d=56.5A), a second crystalline phase at 47 degrees C (d = 69.9A), and a liquid crystalline phase at 59 degrees C (d = 52.0A). The more unsaturated NLnGS shows two transitions, a sharp transition at 28 degrees C (delta H=8.0 kcal/mol NLGS) and a broad, low-enthalpy transition at 42 degrees C (delta H=0.4 kcal/mol NLGS). Again, incubation between the two transitions leads to a single transition at 44 degrees C (delta H=9.3 kcal/mol NLGS). X-ray diffraction demonstrates conversions between two crystalline bilayer phases (d = 55.2A and d=68.4A), and a liquid crystalline bilayer phase (d = 51.8A). Thus, increased unsaturation in the amide-linked fatty acyl chain of cerebrosides results in decreased chain-melting temperatures (NSGS greater than NOGS greater than NLnGS) and has marked effects on their structural properties.