KINETICS AND MECHANISM OF TRANSITIONS INVOLVING THE LAMELLAR, CUBIC, INVERTED HEXAGONAL, AND FLUID ISOTROPIC PHASES OF HYDRATED MONOACYLGLYCERIDES MONITORED BY TIME-RESOLVED X-RAY-DIFFRACTION
KINETICS AND MECHANISM OF TRANSITIONS INVOLVING THE LAMELLAR, CUBIC, INVERTED HEXAGONAL, AND FLUID ISOTROPIC PHASES OF HYDRATED MONOACYLGLYCERIDES MONITORED BY TIME-RESOLVED X-RAY-DIFFRACTION
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DOI：
10.1021/bi00394a008
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发表时间：
1987-10-06
期刊：
影响因子：
2.9
通讯作者：
CAFFREY, M
中科院分区：
文献类型：
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作者：
CAFFREY, M
在20 - 120 ℃的温度范围内，水合单酰基甘油酯单油酸甘油酯和单反油酸甘油酯经历的各种热致相变的动力学和机理的研究。C和0 - 5 M NaCl。测量是通过使用时间分辨X射线衍射在康奈尔高能同步辐射源。层状链有序/无序，层状/立方（体心，空间群No.8），立方（体心，8号）/立方（原始，第4号），立方（体心，12号）/立方（原始，第4号），立方（原始，N.4）/流体各向同性，立方（体心，No.12）/倒六边形，立方体（原始，第4号）/倒置六边形，在主动加热和被动冷却下，通过使用温度跃变来实现相变，检查了六方/流体各向同性转变。发现除了立方（体心，No.8）/立方（基元，No.4）和立方（体心，No.12）/立方（基元，No.4）冷却转变之外的所有转变（1）是可重复的，（2）是可逆的，和（3）具有≤ 1的渡越时间（完成转变所需的时间）上限。3秒。对于加热方向上的各种相变记录的最短过渡时间为≤ 0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 1.9（层状链熔融），≤1.7[层状液晶/立方（体心，No.8）]，≤0.5[立方（体心，No.8）/立方（基元，No.4）]，≤0.9[cubic（primitive. No. 4）/六边形]，1.3[立方（体心，No.12）/立方（基元，No.4）和立方（体心，No.12）/六边形]，以及0.6 s（六边形/流体各向同性）。对于上述例外情况，转变缓慢，过渡时间范围为0.5至30分钟，并显示出明显的滞后和/或过冷。无论转变的方向如何，除了一个之外，所有的都似乎是在时间分辨方法的灵敏度限制内的两个状态。在层状液晶/立方（体心，第8号）过渡的情况下，一个稳定的中间体的未知身份是显而易见的。除了时间分辨测量之外，还获得了在20 - 120 ℃温度范围内各相稳定性的数据。C和0至5M NaCl。在完全水合的单油酸甘油酯的情况下，高盐强烈地倾向于六方相而不是立方相（体心，8号），并且稍微提高六方/流体各向同性转变温度。在完全水合的单反油酸甘油酯的情况下，在不存在盐的情况下未观察到的六方相在高盐浓度下变成主导相。在这种情况下，立方（体心，No.8）/立方（原始，No.4）和层状液晶/立方（体心，No.8）转变温度降低，而层状链有序/无序转变的温度随着NaCl浓度增加。的结构参数和热膨胀系数的长间距为各相作为盐浓度的函数。
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.degree. 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, N.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 .ltoreq. 3 s. The shortest transit times recorded for the various phase changes in the heating direction were .ltoreq. 1.9 (lamellar chain melting), .ltoreq. 1.7 [lamellar liquid crystal/cubic (body centered, No. 8)], .ltoreq. 0.5 [cubic (body centered, No. 8)/cubic (primitive, No. 4)], .ltoreq. 0.9 [cubic (primitive. No. 4)/hexagonal], .ltoreq. 1.3 [cubic (body centered, No. 12)/cubic (primitive, No. 4) and cubic (body centered, No. 12)/hexagonal], and .ltoreq. 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 senstivity 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.degree. 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. With fully hydrated monoelaidin, the hexagonal phase which is not observed in the absence of salt becomes the dominant phase at high salt concentration. In this case, the cubic (body centered, No. 8)/cubic (primitive, No. 4) and lamellar liquid crystal/cubic (body centered, No. 8) transition temperatures decrease while that of the lamellar chain order/disorder transition increases with NaCl concentration. Structural parameters and thermal expansivity of the long spacings for the various phases as a function of salt concentration are presented.