Lipid lateral diffusion in multi-bilayers, and in monolayers at the air/water and heptane/water interfaces
Lipid lateral diffusion in multi-bilayers, and in monolayers at the air/water and heptane/water interfaces
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作者：
Adalsteinsson, T;Yu, H
本文研究了脂在空气/水（A/W）和油/水（O/W）界面上的多层叠层双层膜和单层膜中的侧向扩散。用于扩散测量的技术是光漂白后的荧光恢复，结合用于平衡表面压力的Wilhelmy板方法。使用的油是庚烷，脂质是L-α-二月桂酰磷脂酰胆碱（DLPC）。发现在多层膜系统中的扩散比单层膜中的扩散慢。在A/W接口处的2-3倍。另一方面，在O/W界面处的扩散被建立为在较低的脂质表面密度下是恒定的，而在A/W界面处的扩散在相同的脂质表面密度范围内是较快的。然而，在O/W和A/W界面处的差异随着表面密度的增加而减小，并且最终在相当于每个脂质分子40埃（2）的足够高的表面密度处完全消失。所观察到的不同的扩散系数分布相对于脂质表面密度被解释为烃分子在低脂质密度下到达表面，通过与脂质烃链交错的中间阶段，最终在高密度下挤出单层。一旦在界面处形成完全填充的单分子层，扩散主要由面内粘度控制，几乎不受上相和下相的影响。在多双层和单层的扩散系数的差异暂时归因于人工制品的多层堆叠的双层，而不是由并列的烃尾巴内的双层施加的额外的摩擦阻力。
Lipid lateral diffusion in multilamellar stacked bilayers and in monolayers at the interfaces of air/water (A/W) and oil/water (O/W) have been examined. The technique for the diffusion measurement is fluorescence recovery after photobleaching, in conjunction with the Wilhelmy plate method for equilibrium surface pressure. The oil used is heptane, and the lipid is L-alpha -dilauroylphosphatidylcholine (DLPC). The diffusion in the multi-bilayer system is found to be slower than that in monolayers. at the A/W interface by a factor of 2-3. On the other hand, the diffusion at the O/W interface is established to be constant at lower lipid surface density, while that at the A/W interface is faster in the same range of lipid surface density. The difference at the O/W and A/W interfaces, however, diminishes as the surface density increases and eventually disappears altogether at a high enough surface density that is equivalent to 40 Angstrom (2) per lipid molecule. The observed different diffusion coefficient profile with respect to the lipid surface density is interpreted as the hydrocarbon molecules coming to the surface at the low lipid density, through intermediate stages of interdigitation with lipid hydrocarbon chains, to eventual squeezing out of the monolayer at the high density. Once a fully packed monolayer is formed at the interface, the diffusion is primarily con trolled by the in-plane viscosity and scarcely affected by those of upper and lower phases. The difference in the diffusion coefficients in multi-bilayers and monolayers is tentatively attributed to an artifact of the multiple stacking of bilayers, not to an additional frictional resistance exerted by the apposing hydrocarbon tails within the bilayers.