EQUILIBRIUM STUDIES OF LECITHIN-CHOLESTEROL INTERACTIONS .1. STOICHIOMETRY OF LECITHIN-CHOLESTEROL COMPLEXES IN BULK SYSTEMS
EQUILIBRIUM STUDIES OF LECITHIN-CHOLESTEROL INTERACTIONS .1. STOICHIOMETRY OF LECITHIN-CHOLESTEROL COMPLEXES IN BULK SYSTEMS
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DOI：
10.1016/s0006-3495(78)85500-3
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发表时间：
1978-01-01
影响因子：
3.4
通讯作者：
GERSHFELD, NL
中科院分区：
文献类型：
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作者：
GERSHFELD, NL
据报道，卵磷脂和胆固醇在水分散体中的最大摩尔比为2：1、1：1或1：2。本研究通过分析(A)无水混合物(制备大多数分散体)中的相关系和(B)制备水分散体的各种方法来检查分离结果的来源，目的是避免可能导致卵磷脂-胆固醇化学计量比变化的亚稳态的形成。用差示扫描量热法(DSC)测定了胆固醇(CHOL)与双肉豆蔻酰基(DML)和双棕榈酰基卵磷脂(DPL)无水混合物的温度-组成相图。当卵磷脂与胆固醇的摩尔比为2：1和1：2时，可稳定到70℃；当x(Chol)和lt；0.33时，两相共存：络合物(2：1)+纯卵磷脂；当0.33<；x(Chol)<；0.67时，络合物(2：1)和(1：2)作为单独的相共存。用差示扫描量热法和D2O-H2O梯度等密度离心法测定了这些混合物在水中的相图。通过各种方法(涡流、透析法、超声法)制备水分散体，结果相同，但如下所述。所提供的数据支持以下相关系。当x(Chol)<；0.33时，两种脂相共存：纯卵磷脂和络合物(2：1)，其中卵磷脂相的性质取决于温度是否低于或高于凝胶-液晶转变温度T_c。因此，配合物(2：1)在Tc值以下与凝胶态共存，在Tc值以上与液晶共存。密度顺序为凝胶->>络合物(2：1)>液晶。与密度变化较大的DML和DPL相比，在5°-45°C范围内，络合物(2：1)的密度对温度的敏感度较低。当Chenx(Chol)>；0.33时，Chol相与络合物(2：1)共存，无水络合物(1：2)在H2O中明显不稳定。所得结果与制备脂质分散体的方法和温度无关。然而，当分散体是通过超声或用溶剂ATT>；TC制备时，形成明显的1：1络合物。有证据表明，1：1复合体是亚稳定的。
The maximum molar ratio of lecithin:cholesterol in aqueous dispersions has been reported to be 2:1, 1:1, or 1:2. The source of the desparate results has been examined in this study by analyzing (a) the phase relations in anhydrous mixtures (from which most dispersions are prepared) and (b) various methods of preparing aqueous dispersions, with the purpose of avoiding the formation of metastable states that may be responsible for the variability of the lecithin-cholesterol stoichiometry. Temperature-composition phase diagrams for anhydrous mixtures of cholesterol (CHOL) with dimyristoyl (DML) and with dipalmitoyl (DPL) lecithin were obtained by differential scanning calorimetry (DSC). Complexes form with molar ratios for lecithin:CHOL of 2:1 and 1:2; they are stable up to 70°C. Whenx(CHOL) < 0.33, two phases coexist: complex (2:1) plus pure lecithin; when 0.33<x(CHOL) < 0.67 complexes (2:1) and (1:2) coexist as separate phases. The corresponding phase diagram in water for these mixtures was determined by DSC and isopycnic centrifugation in D2O-H2O gradients. Aqueous dispersions were prepared by various methods (vortexing, dialysis, sonication) yielding identical results except as noted below. The data presented supports the following phase relations. Whenx(CHOL) < 0.33, two lipid phases coexist: pure lecithin plus complex (2:1) where the properties of the lecithin phase are determined by whether the temperature is below or aboveTc, the gel-liquid crystal transition temperature. Therefore, complex (2:1) will coexist with gel state belowTcand with liquid crystal aboveTc. The densities follow in the order gel > complex (2:1) > liquid crystal. The density of complex (2:1) is less sensitive to temperature in the range 5°-45°C compared to the temperature dependence for DML and DPL where large changes in density occur atTc. Whenx(CHOL) > 0.33, CHOL phase coexists with complex (2:1); anhydrous complex (1:2) is apparently not stable in H2O. The results are independent of the method and temperature used for preparing the lipid dispersions. However, when dispersions are prepared by sonication or with solvents atT>Tc, an apparent 1:1 complex is formed. Evidence suggests the 1:1 complex is metastable.