Polymorphism and Phase Transition Behaviors of Lipids and Related Long-chain Compounds Containing Unsaturated Acyl Chains

磷脂和甘油酯是构成细胞膜的重要物质，具有生物学功能活性。天然存在的脂质化合物由长的酰基链连接到一个极性基团上组成，其中近一半的酰基链被不饱和酰基链占据，这些不饱和酰基链赋予膜流动性并促进生物活性，本研究的目的是阐明不饱和酰基链特征性功能的分子机制。用红外光谱、拉曼光谱、X射线衍射、差示扫描量热等方法研究了一系列顺式单不饱和脂肪酸和顺式不饱和甘油三酯的多晶型结构，并与其热力学稳定性和固态相变行为进行了关系。确定了芥酸的γ相和γ_1相以及岩芹酸的低熔点相和高熔点相的晶体结构。本文还研究了芥酸α相和α_1相的分子结构和晶体结构。烯烃基团的构象、聚亚甲基链段的亚胞结构、双分子层的多型结构和链的流动性已被阐明为理解不饱和脂质化合物的物理化学性质和相变行为的基调。顺式单不饱和脂肪酸中发生的有序-无序型热可逆γ-<double arrow>α和γ_1 <double arrow>α_1转变被认为是构成层状界面的甲基侧烷基链的部分熔融过程。研究了2-位被油酰基链占据的三甘油酯的多晶型现象。它已被揭示，一个大的分子位移发生在一个连贯的方式在饱和脂肪酸的固态转变。

Phospholipids and glycerides are important materials as main constituents of the cell membranes, bearing the biological functional activities. Naturally occurring lipid compounds consist of long acyl chains joined to a polar group and nearly half of the acyl chains are occupied by unsaturated ones which give the membranes fluidity and promote the biological activity.The aim of this research project is to elucidate the molecular mechanism of the characteristic function of the unsaturated acyl chains. Polymorphic structures in relation to the thermodynamic stability and the behavior of solid-state phase transition for a series of cis-monounsaturated fatty acids as well as cis-unsaturated triglycerides were investigated by means of IR and Raman spectroscopy, X-ray analysis, DSC, etc.Unsaturated fatty acids exhibit very complicated polymorphism. The crystal structures of the gamma and gamma_1 phases of erucic acid and the low-melting and high-melting phases of petroselinic acid were fully determined. The molecular and crystal structures of the alpha and alpha_1 phases of erucic acid were also studied. Conformation of the olefine group, subcell structure of the polymethylene chain segments, polytypic structure of the bimolecular layers, and chain mobility have been clarified as the keynote for understanding the physicochemical properties and the phase transition behaviors of the unsaturated lipid compounds. The order-disorder type thermoreversible gamma <double arrow>alpha and gamma_1<double arrow>alpha_1 transitions occurring in cis-monounsaturated fatty acids were recognized as a partial melting process of the methylsided alkyl chains constituting the lamellar interface. The polymorphism of triblycerides whose 2-position is occupied by an oleoyl chain have been investigated. It has been revealed that a large molecular displacement takes place in a coherent fashion during solid-state transitions in saturated fatty acids.