固醇在生物膜的組成與功能中扮演了重要的角色。在含有膽固醇的人造細胞膜研究中發現，當脂質膜中加入膽固醇後會形成sterol-rich以及sterol-poor的區塊。一般認為這些處於liquid-ordered態的sterol-rich區塊即為細胞膜上的脂筏。另一方面，在某些含其他種類固醇的人造細胞膜研究中並未觀察到liquid-ordered這種相態。而在本論文中，我們研究豆固醇對於POPE-d31膜在物理性質方面的影響。 本研究使用氘核磁共振（2H NMR）來量測由POPE-d31和豆固醇所組成之model membranes。將不同濃度（最高50 mol %）的豆固醇樣品在不同溫度下量測以取得核磁共振光譜。結果顯示豆固醇會降低膠態POPE-d31脂雙層膜的有序程度，而這個影響十分有限。不過另一方面，在液晶態的POPE-d31膜中，豆固醇反而增加了膜上脂質分子碳鏈的有序程度。我們從實驗結果得出了溫度對豆固醇濃度的POPE-d31脂質膜相圖。豆固醇對於膠態相變到液晶態的相變溫度影響不大，不過明顯降低了液晶態相變到inverted hexagonal態的相變溫度。此外，在POPE-d31與豆固醇組成的膜中並未觀察到liquid-ordered相態。比較豆固醇以及其他固醇對於POPE-d31之影響的結果顯示，存在於固醇疏水端碳鏈上的雙鍵或支鏈會減少固醇增加POPE-d31碳鏈之有序程度的能力。 ;Sterols play important roles in membrane organization and functions. Model membranes containing cholesterol reveal that the addition of cholesterol in lipid membranes results in sterol-poor and sterol-rich domains. The sterol-rich domain, in the liquid-ordered phase, is thought to be the lipid raft found in cell membranes. On the other hand, in some model membranes liquid-ordered phase is not observed. In this work, we investigate the effect of stigmasterol on the physical properties 1-palmitoyl-d31-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE-d31) membranes. Model membranes composed of POPE-d31 and stigmasterol were studied using deuterium nuclear magnetic resonance. NMR spectra were taken as a function of temperature and stigmasterol concentration up to 50 mol %. Stigmasterol decreases membrane order of the gel-phase POPE-d31 bilayers and this effect is very limited. In contrast, stigmasterol increases the chain order of the liquid-crystalline (lc) phase POPE-d31 bilayers slightly. The temperature-composition phase diagram is presented. The addition of stigmasterol does not affect the gel-to-lc phase transition significantly, however it decreases the temperature of lc-to-HII phase transition strongly. In addition, there is no liquid-ordered phase observed in POPE-d31/stigmasterol membranes. A comparison between stigmasterol and other sterols suggest that the extra double bond and the extra methyl group in the acyl chain of sterol hinder the ability of sterol to increase POPE-d31 chain order.
