Multinuclear NMR investigation of phosphatidylcholine organogels
Multinuclear NMR investigation of phosphatidylcholine organogels
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DOI：
10.1021/jp960811i
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发表时间：
1996-09-12
影响因子：
--
通讯作者：
Luisi, PL
中科院分区：
文献类型：
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作者：
Capitani, D;Segre, AL;Luisi, PL
用多核核磁共振研究了大豆卵磷脂和一系列合成磷脂酰胆碱在环己烷中少量水存在下形成的有机凝胶。NMR测量基于H-1、C-13和P-31动力学参数和谱线宽度。为了研究凝胶化过程，在不同量的添加水下用样品进行测量。对于质子和磷共振，凝胶形成的开始清楚地证明了线宽的加宽。在第一组测量中，研究大豆卵磷脂。结果表明，随着水的加入，卵磷脂的不同质子的线宽变得更宽，每个都达到不同的程度。特别重要的是在甘油主链的sn-1位的孪位质子的硬化。P-31 NMR T-2测量允许凝胶形成和非凝胶形成溶剂之间的区别。NMR谱线宽度增宽也存在于流变学数据显示没有高粘度的区域，例如，在高水含量和/或低卵磷脂浓度下。这被认为表明，即使在不存在高粘度宏观凝胶结构的情况下，甘油部分和磷酸盐也存在相当大的分子硬化。为了研究分子结构对凝胶形成动力学的影响，研究已经扩展到在281和300 K之间合成的形成凝胶的磷脂酰胆碱，例如1，2-二油酰-sn-甘油-3-磷酸胆碱（DOPC）; 1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱（POPC）在300 K，1，2-二棕榈酰-sn-甘油-3-磷酸胆碱（DPPC）在313 ~ 333 K; 1，2-二亚油酰基-sn-甘油基-3-磷酸胆碱（DLPC）在281 K.在所有凝胶上，P-31 NMR T-2值的差异非常小，而质子和磷的线宽似乎对分子结构的差异更加敏感。因此，这项研究使人们能够绘制出卵磷脂凝胶的相当一般的图像，其中分子结构与凝胶形成过程中的动态参数相关，而动态参数又与粘度和相变温度等宏观物理性质相关。通过比较所有这些数据，DOPC似乎是最接近天然卵磷脂的模型。然而，即使在这种情况下，也需要谨慎，因为DOPC中甘油部分的局部运动比大豆卵磷脂中受到更多阻碍。
A multinuclear NMR investigation of organogels formed by soybean lecithin and by a series of synthetic phosphatidylcholines in cyclohexane in the presence of a small amount of water is presented. The NMR measurements are based on H-1, C-13, and P-31 dynamic parameters and the line width. To study the gelation process, measurements are carried out with samples at different amounts of added water. Both for proton and phosphorus resonances, the onset of the gel formation is clearly evidenced by a broadening of the line width. In the first set of measurements soybean lecithin is studied. It is shown that as water is being added, the line widths of the different protons of lecithin become broader, each to a different extent. Particularly significant is the stiffening of the geminal protons at the sn-1 position of the glycerol backbone. P-31 NMR T-2 measurements allow the distinction between gel-forming and nongel-forming solvents. The NMR line width broadening is also present in regions in which rheology data show no high viscosity, e.g., at high water content and/or at low lecithin concentration. This is thought to indicate that a considerable molecular stiffening of the glycerol moiety and of the phosphate is present even in the absence of a high viscosity macroscopic gel structure. To study the influence of the molecular structure on the dynamics of gel formation, studies have been extended to synthetic gel-forming phosphatidylcholines, such as 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) between 281 and 300 K; 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at 300 K, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) between 313 and 333 K; 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) at 281 K. On all gels, differences in P-31 NMR T-2 values are quite small, while the line widths, both on protons as well as on phosphorus, appear to be much more sensitive to differences in the molecular architecture. Accordingly, this study allows one to draw a quite general picture of lecithin gels in which the molecular structure is linked to the dynamic parameters during gel formation, which are in turn linked to the macroscopic physical properties such as viscosity and phase transition temperature. By comparison of all these data, it appears DOPC is the closest model to natural lecithin. Even in this case, however, caution is required, since local motions in the glycerol moiety are more hindered in DOPC than in soybean lecithin.