Dynamical Molecular Conformation and Structure of Cluster for Saturated and Unsaturated Fatty Acids in the Liquid State

通过密度、自扩散系数、^<13>C核磁共振自旋晶格弛豫时间和x射线衍射测量，研究了顺式不饱和脂肪酸（顺式-6-、顺式-9-和顺式-11-十八烯酸）、反式不饱和酸（反式-9-十八烯酸）和n-饱和酸（十八烯酸）的平移运动、动态分子构象和液相聚集结构。自扩散系数D的大小在350 K以下依次为顺式不饱和酸>反式不饱和酸>饱和酸。在350 K以上，反式酸的D值上升到顺式酸的D值。另一方面，各酸的ρ密度依次为顺式酸>反式酸>饱和酸；密度的顺序正好与自扩散系数和其他物理性质（如熔点和熔合热）的结果相反。这些酸的D值和ρ值之间的差异可以用它们的液体中的团簇模型很好地解释。

The translational movement, the dynamical molecular conformation, and the aggregate structure in the liquid state for three kinds of cis-type unsaturated fatty acids (cis-6-, cis-9-, and cis-11-octadecenoic acids), trans-type unsaturated acid (trans-9-octadecenoic acid), and n-saturated acid (octadecanoic acid) have been studied through the measurements of density, self-diffusion coefficient, ^<13>C NMR spin-lattice relaxation time, and X-ray diffraction. The magnitude of the self-diffusion coefficient, D, fell in sequence of cis-type unsaturated acids > trans-type acids > saturated acid below 350 K.Above 350 K the value of D for the trans-type acid rose to those for the cis-type acids. On the other hand, the density ρ for the acids also fell in the order of cis-type acids > trans-type acid > saturated acid ; the order of the density is just opposite to that expected from the results of the self-diffusion coefficient and other physical properties such as melting point and heat of fusion. This discrepancy between D and ρ values for the acids is well explained by the models of the clusters in their liquids.