Institute for Polymer Research, Department of Chemistry, University of Waterloo, Waterloo ON N2L 3G1, Canada.
Langmuir. 2010 Jul 6;26(13):10985-94. doi: 10.1021/la9045429.
Time-resolved fluorescence measurements on liposomes prepared with 1 mol % pyrene-labeled lipids (PLLs) with a headgroup bearing either an alcohol (PSOH) or an imido diacetic acid (PSIDA) and 99 mol % 1-palmitoyl-2-oleyl-3-sn-phosphatidylcholines (POPC) or 99 mol % distearylphosphatidylcholine (DSPC) were performed to investigate how lipids phase separate within the membrane bilayer. Global analysis of the fluorescence decays with the fluorescence blob model (FBM) led to the conclusion that the PLLs were homogeneously distributed on the surface of POPC vesicles while the PLLs phase-separated in the DSPC vesicles. The analysis yielded the fraction of aggregated pyrenes, f(agg). The large f(agg) values found for PSIDA suggest that the imido diacetic acid headgroup of PSIDA induces self-aggregation and phase separation in both membranes. The addition of external cations such as Cu(2+) and La(3+) was shown to hinder diffusional encounters between PSIDAs. The cations seem to target preferentially unassociated PSIDAs rather than aggregated PSIDA clusters. Accounting for the quenching of pyrene by Cu(2+) enables one to use PSIDA to probe the microviscosity of the lipid membrane. Using this effect, the environment of PSIDA in the DSPC membrane was found to be about 6 times more viscous than that in the POPC membrane. This difference is attributed to the difference in viscosity of the fluid POPC membrane and the gel-like DSPC membranes.
用 1 摩尔%芘标记的脂质（PLLs）制备的脂质体进行时间分辨荧光测量，其头部基团带有醇（PSOH）或亚氨基二乙酸（PSIDA），并带有 99 摩尔% 1-棕榈酰基-2-油酰基-3-sn-磷脂酰胆碱（POPC）或 99 摩尔%二硬脂酰基磷脂酰胆碱（DSPC），以研究脂质如何在膜双层内相分离。用荧光团团块模型（FBM）对荧光衰减进行全局分析，得出结论，PLLs在 POPC 囊泡表面均匀分布，而 PLLs 在 DSPC 囊泡中相分离。该分析得出了聚集芘的分数，f(agg)。对于 PSIDA，大的 f(agg) 值表明 PSIDA 的亚氨基二乙酸头基在两种膜中诱导自聚集和相分离。添加外部阳离子，如 Cu(2+)和 La(3+)，被证明可以阻止 PSIDAs 之间的扩散相遇。这些阳离子似乎优先靶向未结合的 PSIDAs，而不是聚集的 PSIDA 簇。考虑到 Cu(2+)对芘的猝灭，可以使用 PSIDA 来探测脂质膜的微粘度。利用这种效应，发现 PSIDA 在 DSPC 膜中的环境比在 POPC 膜中的环境粘度大约大 6 倍。这种差异归因于流体 POPC 膜和凝胶状 DSPC 膜的粘度差异。
