Thermotropic mesomorphism of a model system for the plant epicuticular wax layer
Thermotropic mesomorphism of a model system for the plant epicuticular wax layer
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DOI：
10.1016/s0006-3495(02)75418-0
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发表时间：
2002-01-01
影响因子：
3.4
通讯作者：
Vaz, WLC
中科院分区：
文献类型：
--
作者：
Carreto, L;Almeida, AR;Vaz, WLC
作为植物表皮蜡层的模型，我们用差示扫描量热法和傅里叶变换红外光谱法（FTIR）研究了1-十四醇和1-十八烷醇及其二元混合物在5 ~ 70 ℃之间的相行为。这两种纯化合物显示出两个放热相变，对应于从液相到六方堆积固相（S-HEX）的转变，其在较低温度下转变为正交堆积固相（S-ORT）。在加热S-ORT固体时，获得具有对应于放热转变焓的总和的转变焓的单一吸热转变。这些转换也遵循使用FTIR光谱在CH 2-伸缩（对称和不对称）和CH 2-摇摆振动模式。在液体，S-HEX，和S-ORT相的纯化合物的FTIR光谱被用来模拟在相变区的实验光谱。模拟使我们能够估计纯化合物的过渡区中每个相的摩尔分数。采用差示扫描量热法和傅立叶变换红外光谱法，得到了1-十四醇和1-十八醇二元混合物的相图。FTIR研究的二元混合物制备的一个全氘代成分和其他nondeuterated允许研究的热致行为的每一个组成部分的混合物独立。该混合物表现出低共熔行为，其低共熔点在十八醇（X-18）的摩尔分数为0.12和0.18之间，温度接近32 ℃。在32 ℃以下，固相的二元混合物，一个是S-ORT相，另一个是S-HEX相，共存到接近25 ℃，低于25 ℃，两个固相都是S-ORT相。我们讨论了这种复杂的相行为在一个简单的二元混合物中的两个长链烷醇的背景下，更复杂的相行为预期的植物表皮蜡层的可能相关性。
As a model for the epicuticular wax layer of plant cuticular membranes, we have studied the phase behavior of 1-tetradecanol and 1-octaclecanol and their binary mixtures between 5 and 70degreesC, using differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). Both pure compounds show two exothermic phase transitions corresponding to a transformation from a liquid phase to a hexagonally packed solid phase (S-HEX), which at lower temperatures transforms to an orthorhombically-packed solid phase (S-ORT). On heating the S-ORT solid a single endothermic transition with a transition enthalpy corresponding to the sum of the exothermic transition enthalpies is obtained. These transitions were also followed using FTIR spectroscopy in the CH2-stretching (symmetric and asymmetric) and CH2-rocking vibration modes. The FTIR spectra of the pure compounds in the liquid, S-HEX, and S-ORT phases were used to simulate experimental spectra in the phase transition regions. The simulations allowed us to estimate the molar fractions of each phase in the transition regions of the pure compounds. A phase diagram for the binary mixture of 1-tetradecanol and 1-octadecanol was obtained using differential scanning calorimetry and FTIR. FTIR studies on binary mixtures prepared from one perdeuterated component and the other nondeuterated permitted studying the thermotropic behavior of each component in the mixture independently. The mixture shows an eutectic behavior with an eutectic point between a molar fraction of octadecanol (X-18) of 0.12 and 0.18 and a temperature of similar to32degreesC. Below 32degreesC, a binary mixture of solid phases, one an S-ORT phase and the other an S-HEX phase, coexist up to similar to25degreesC, below which both solid phases are S-ORT phases. We discuss the possible relevance of this complex phase behavior in a simple binary mixture of two long-chain alkanols in the context of the far more complex phase behavior expected for the plant epicuticular wax layer.