Makino K, Yamada T, Kimura M, Oka T, Ohshima H, Kondo T
Faculty of Pharmaceutical Sciences, Science University of Tokyo, Japan.
Biophys Chem. 1991 Nov;41(2):175-83. doi: 10.1016/0301-4622(91)80017-l.
Neutral liposomes composed of DMPC (dimyristoylphosphatidylcholine), DPPC (dipalmitoylphosphatidylcholine) or DSPC (distearoylphosphatidylcholine) are found to exhibit non-zero zeta potentials in an electric field even when they are dispersed in solution at pH 7.4. A model for the orientation of lipid head groups is proposed to explain the observed non-zero zeta potentials. The dependence of the zeta potential on temperature and ionic strength is analyzed via this model to obtain the information on the direction of the lipid head group in the liposome surface region. The direction of the lipid head group is found to be sensitive to the temperature and the ionic strength of the medium. At low ionic strengths, the phosphatidyl groups are located at the outer portion of the head group region. At constant temperature, as the ionic strength increases, the choline group approaches the outer region of the bilayer surface while the phosphatidyl group hides behind the surface. At the phase transition temperature of the lipid, the phosphatidyl group lies in the outer-most region of the surface and the choline group is in the inner-most region.
由二肉豆蔻酰磷脂酰胆碱（DMPC）、二棕榈酰磷脂酰胆碱（DPPC）或二硬脂酰磷脂酰胆碱（DSPC）组成的中性脂质体，即使在pH值为7.4的溶液中分散时，在电场中也表现出非零的ζ电位。提出了一个脂质头部基团取向模型来解释观察到的非零ζ电位。通过该模型分析ζ电位对温度和离子强度的依赖性，以获得脂质体表面区域脂质头部基团方向的信息。发现脂质头部基团的方向对介质的温度和离子强度敏感。在低离子强度下，磷脂酰基团位于头部基团区域的外部。在恒定温度下，随着离子强度的增加，胆碱基团接近双层表面的外部区域，而磷脂酰基团则隐藏在表面后面。在脂质的相变温度下，磷脂酰基团位于表面的最外层区域，胆碱基团位于最内层区域。
