Caffrey M
Department of Chemistry, Ohio State University, Columbus 43210-1173.
Biochemistry. 1987 Oct 6;26(20):6349-63. doi: 10.1021/bi00394a008.
A study of the dynamics and mechanism of the various thermotropic phase transitions undergone by the hydrated monoacylglycerides monoolein and monoelaidin, in the temperature range of 20-120 degrees C and from 0 to 5 M NaCl, has been undertaken. Measurements were made by using time-resolved X-ray diffraction at the Cornell High-Energy Synchrotron Source. The lamellar chain order/disorder, lamellar/cubic (body centered, space group No. 8), cubic (body centered, No. 8)/cubic (primitive, No. 4), cubic (body centered, No. 12)/cubic (primitive, No. 4), cubic (primitive, No. 4)/fluid isotropic, cubic (body centered, No. 12)/inverted hexagonal, cubic (primitive, No. 4)/inverted hexagonal, and hexagonal/fluid isotropic transitions were examined under active heating and passive cooling by using a jump in temperature to effect phase transformation. All of the transitions with the exception of the cubic (body centered, No. 8)/cubic (primitive, No. 4) and the cubic (body centered, No. 12)/cubic (primitive, No. 4) cooling transitions were found (1) to be repeatable, (2) to be reversible, and (3) to have an upper bound on the transit time (time required to complete the transition) of less than or equal to 3 s. The shortest transit times recorded for the various phase changes in the heating direction were less than or equal to 1.9 (lamellar chain melting), less than or equal to 1.7 [lamellar liquid crystal/cubic (body (body centered, No. 8)], less than or equal to 0.5 [cubic (body centered, No. 8)/cubic (primitive, No. 4)], less than or equal to 0.9 [cubic (primitive, No. 4)/hexagonal], less than or equal to 1.3 [cubic (body centered, No. 12)/cubic (primitive, No. 4) and cubic (body centered, No. 12)/hexagonal], and less than or equal to 0.6 s (hexagonal/fluid isotropic). For the exceptions noted above, the transitions were slow with transit times ranging from 0.5 to 30 min and displayed pronounced hysteresis and/or undercooling. Regardless of the direction of the transitions, all but one appear to be two state to within the sensitivity limits of the time-resolved method. In the case of the lamellar liquid crystal/cubic (body centered, No. 8) transition a stable intermediate of unknown identity was apparent. In addition to the time-resolved measurements, data were obtained on the stability of the various phases in the temperature range of 20-120 degrees C and from 0 to 5 M NaCl. In the case of fully hydrated monoolein, high salt strongly favors the hexagonal over the cubic (body centered, No. 8) phase and slightly elevates the hexagonal/fluid isotropic transition temperature.(ABSTRACT TRUNCATED AT 400 WORDS)
已对水合单酰甘油单油酸甘油酯和单反油酸甘油酯在20至120摄氏度以及0至5M氯化钠范围内经历的各种热致相变的动力学和机制进行了研究。测量是在康奈尔高能同步加速器源使用时间分辨X射线衍射进行的。通过温度跃升来实现相变，在主动加热和被动冷却条件下研究了层状链有序/无序、层状/立方（体心，空间群编号8）、立方（体心，编号8）/立方（简单立方，编号4）、立方（体心，编号12）/立方（简单立方，编号4）、立方（简单立方，编号4）/流体各向同性、立方（体心，编号12）/反相六角形、立方（简单立方，编号4）/反相六角形以及六角形/流体各向同性转变。除了立方（体心，编号8）/立方（简单立方，编号4）和立方（体心，编号12）/立方（简单立方，编号4）冷却转变外，所有转变均被发现：（1）是可重复的；（2）是可逆的；（3）转变时间（完成转变所需的时间）上限小于或等于3秒。在加热方向上记录的各种相变的最短转变时间小于或等于1.9（层状链熔化）、小于或等于1.7 [层状液晶/立方（体心，编号8）]、小于或等于0.5 [立方（体心，编号8）/立方（简单立方，编号4）]、小于或等于0.9 [立方（简单立方，编号4）/六角形]、小于或等于1.3 [立方（体心，编号12）/立方（简单立方，编号4）和立方（体心，编号12）/六角形]以及小于或等于0.6秒（六角形/流体各向同性）。对于上述例外情况，转变缓慢，转变时间范围为0.5至30分钟，并表现出明显的滞后和/或过冷现象。无论转变方向如何，除了一种情况外，在时间分辨方法的灵敏度极限内似乎都是双态的。在层状液晶/立方（体心，编号8）转变的情况下，出现了一个身份不明的稳定中间体。除了时间分辨测量外，还获得了在20至120摄氏度以及0至5M氯化钠范围内各种相稳定性的数据。对于完全水合的单油酸甘油酯，高盐强烈有利于六角形相而非立方（体心，编号8）相，并略微提高了六角形/流体各向同性转变温度。（摘要截断于400字）
