961
个编辑
更改
无编辑摘要
共晶转变Eutectic transformation指的是一类互溶液体（由两种不同成分组成的单相液体）经过冷却后，转变成为两个不同的固相。同样的过程，由一类固态开始转变成为两个不同的固相，则称为共析转变。
共晶转变Eutectic transformation指的是一类互溶液体（由两种不同成分组成的单相液体）经过冷却后，转变成为两个不同的固相。同样的过程，由一类固态开始转变成为两个不同的固相，则称为共析转变。
共晶转变Eutectic transformation
* A [[metastable]] to equilibrium phase transformation. A metastable polymorph which forms rapidly due to lower surface energy will transform to an equilibrium phase given sufficient thermal input to overcome an energetic barrier.
* A [[metastable]] to equilibrium phase transformation. A metastable polymorph which forms rapidly due to lower surface energy will transform to an equilibrium phase given sufficient thermal input to overcome an energetic barrier.
Phase transitions play many important roles in biological systems. Examples include the lipid bilayer formation, the coil-globule transition in the process of protein folding and DNA melting, liquid crystal-like transitions in the process of DNA condensation, and cooperative ligand binding to DNA and proteins with the character of phase transition.
Phase transitions play many important roles in biological systems. Examples include the lipid bilayer formation, the coil-globule transition in the process of protein folding and DNA melting, liquid crystal-like transitions in the process of DNA condensation, and cooperative ligand binding to DNA and proteins with the character of phase transition.
相变在生物系统中也起到许多重要的作用。比如包括脂质双层Lipid bilayer的形成，蛋白质折叠Protein folding和DNA解链DNA melting过程中的坍塌转变Coil–globule transition，DNA缩合DNA condensation过程中的液晶转变，以及具有相变特征的配体与DNA和蛋白质的结合配体。
In biological membranes, gel to liquid crystalline phase transitions play a critical role in physiological functioning of biomembranes. In gel phase, due to low fluidity of membrane lipid fatty-acyl chains, membrane proteins have restricted movement and thus are restrained in exercise of their physiological role. Plants depend critically on photosynthesis by chloroplast thylakoid membranes which are exposed cold environmental temperatures. Thylakoid membranes retain innate fluidity even at relatively low temperatures because of high degree of fatty-acyl disorder allowed by their high content of linolenic acid, 18-carbon chain with 3-double bonds. Gel-to-liquid crystalline phase transition temperature of biological membranes can be determined by many techniques including calorimetry, fluorescence, spin label electron paramagnetic resonance and NMR by recording measurements of the concerned parameter by at series of sample temperatures. A simple method for its determination from 13-C NMR line intensities has also been proposed.
In biological membranes, gel to liquid crystalline phase transitions play a critical role in physiological functioning of biomembranes. In gel phase, due to low fluidity of membrane lipid fatty-acyl chains, membrane proteins have restricted movement and thus are restrained in exercise of their physiological role. Plants depend critically on photosynthesis by chloroplast thylakoid membranes which are exposed cold environmental temperatures. Thylakoid membranes retain innate fluidity even at relatively low temperatures because of high degree of fatty-acyl disorder allowed by their high content of linolenic acid, 18-carbon chain with 3-double bonds. Gel-to-liquid crystalline phase transition temperature of biological membranes can be determined by many techniques including calorimetry, fluorescence, spin label electron paramagnetic resonance and NMR by recording measurements of the concerned parameter by at series of sample temperatures. A simple method for its determination from 13-C NMR line intensities has also been proposed.
在生物膜Biological membranes中，凝胶到液晶的相变在生物膜的生理机能中起关键作用。在凝胶相中，由于膜脂质脂肪酰基链的流动性低，膜蛋白的运动受到限制，因此在行使其生理作用方面受到限制。植物非常依赖于暴露于寒冷环境温度下叶绿体类囊体膜的光合作用。类囊体膜即使在相对较低的温度下也能保持固有的流动性，这是由于其高含量的亚麻酸，带有3个双键的18碳链允许高度的脂肪酰基紊乱。基于众多技术，包括量热法，荧光法，自旋标记电子顺磁共振和NMR，通过记录一系列样品温度下有关参数的测量值，来确定生物膜的凝胶到液晶的相变温度。同时还提出了一种由13-C NMR谱线强度测定的简单方法。