Li X, Schick M
Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA.
Biophys J. 2000 Jan;78(1):34-46. doi: 10.1016/s0006-3495(00)76570-2.
We introduce a microscopic model of a lipid with a charged headgroup and flexible hydrophobic tails, a neutral solvent, and counter ions. Short-ranged interactions between hydrophilic and hydrophobic moieties are included as are the Coulomb interactions between charges. Further, we include a short-ranged interaction between charges and neutral solvent, which mimics the short-ranged, thermally averaged interaction between charges and water dipoles. We show that the model of the uncharged lipid displays the usual lyotropic phases as a function of the relative volume fraction of the headgroup. Choosing model parameters appropriate to dioleoylphosphatidylethanolamine in water, we obtain phase behavior that agrees well with experiment. Finally we choose a solvent concentration and temperature at which the uncharged lipid exhibits an inverted hexagonal phase and turn on the headgroup charge. The lipid system makes a transition from the inverted hexagonal to the lamellar phase, which is related to the increased waters of hydration correlated with the increased headgroup charge via the charge-solvent interaction. The polymorphism displayed upon variation of pH mimics that of the behavior of phosphatidylserine.
我们引入了一个微观模型，该模型包含一个带有带电头部基团和柔性疏水尾部的脂质、一种中性溶剂以及抗衡离子。亲水性和疏水性部分之间的短程相互作用以及电荷之间的库仑相互作用都被纳入其中。此外，我们还纳入了电荷与中性溶剂之间的短程相互作用，它模拟了电荷与水偶极子之间的短程热平均相互作用。我们表明，不带电脂质的模型根据头部基团的相对体积分数呈现出常见的溶致相。选择适合水中二油酰磷脂酰乙醇胺的模型参数，我们得到了与实验结果吻合良好的相行为。最后，我们选择一个溶剂浓度和温度，在此条件下不带电脂质呈现反相六角相，然后开启头部基团电荷。脂质体系从反相六角相转变为层状相，这与通过电荷 - 溶剂相互作用与增加的头部基团电荷相关的水合水增加有关。pH变化时所呈现的多晶型现象模拟了磷脂酰丝氨酸的行为。
