Matti V, Säily J, Ryhänen S J, Holopainen J M, Borocci S, Mancini G, Kinnunen P K
Helsinki Biophysics and Biomembrane Group, Institute of Biomedicine, University of Helsinki, Helsinki FIN-00014, Finland.
Biophys J. 2001 Oct;81(4):2135-43. doi: 10.1016/S0006-3495(01)75861-4.
Monolayers of a cationic gemini surfactant, 2,3-dimethoxy-1,4-bis(N-hexadecyl-N;N-dimethyl-ammonium)butane dibromide (abbreviated as SS-1) and its mixtures with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were studied using a Langmuir balance. More specifically, we measured the force-area (pi-A) curves and determined the elastic area compressibility modulus (C) as a function of lateral packing pressure and the mole fraction of the cationic lipid (X(SS-1)), with and without DNA in the subphase. Both SS-1 and POPC exhibited smooth compression isotherms, indicating their monolayers to be in the liquid expanded state. Even low contents (X(SS-1) < 0.05) of SS-1 in a POPC monolayer condensed the film dramatically, up to 20% at 30 mN/m. This effect is suggested to reflect reorientation of the P(-)-N(+) dipole of the POPC headgroup. Accordingly, the magnitude of the condensing effect diminishes with X(SS-1) and is not observed for mixed films of dioleoylglycerol and SS-1. Reorientation of the P(-)-N(+) dipole is further supported by the pronounced increase in monolayer dipole potential psi due to SS-1. The presence of DNA in the subphase affected the mixed POPC/SS-1 monolayers differently depending on the constituent lipid stoichiometry as well as on the DNA/SS-1 charge ratio. At a DNA concentration of 0.63 microM (in base pairs) condensation of neat POPC monolayers was evident, and this effect remained up to X(SS-1) < 0.5, corresponding to DNA/SS-1 charge ratio of 1.25. An expansion due to DNA, evident as an increase in DeltaA/molecule, was observed at X(SS-1) > 0.5. At a higher concentration of DNA (1.88 microM base pairs) in the subphase corresponding to DNA/SS-1 charge ratio of 3.75 at X(SS-1) = 0.5, condensation was observed at all values of X(SS-1).
使用朗缪尔天平研究了阳离子双子表面活性剂2,3 - 二甲氧基 - 1,4 - 双（N - 十六烷基 - N，N - 二甲基铵）丁烷二溴化物（简称为SS - 1）及其与1 - 棕榈酰 - 2 - 油酰 - sn - 甘油 - 3 - 磷酸胆碱（POPC）混合物的单层膜。更具体地说，我们测量了力 - 面积（π - A）曲线，并确定了弹性面积压缩模量（C）作为横向堆积压力和阳离子脂质摩尔分数（X(SS - 1)）的函数，同时研究了亚相中有无DNA的情况。SS - 1和POPC均表现出平滑的压缩等温线，表明它们的单层膜处于液体扩张状态。即使在POPC单层膜中SS - 1含量较低（X(SS - 1) < 0.05）时，也会使膜显著凝聚，在30 mN/m时凝聚高达20%。这种效应被认为反映了POPC头部基团P(-)-N(+)偶极子的重新定向。因此，凝聚效应的大小随X(SS - 1)减小，并且在二油酰甘油与SS - 1的混合膜中未观察到。由于SS - 1导致的单层膜偶极电势ψ的显著增加进一步支持了P(-)-N(+)偶极子的重新定向。亚相中DNA的存在对混合的POPC/SS - 1单层膜的影响因脂质组成化学计量以及DNA/SS - 1电荷比而异。在DNA浓度为0.63 μM（碱基对）时，纯POPC单层膜明显凝聚，并且这种效应一直持续到X(SS - 1) < 0.5，对应于DNA/SS - 1电荷比为1.25。在X(SS - 1) > 0.5时，观察到由于DNA导致的膜扩张，表现为每分子ΔA增加。在亚相中DNA浓度较高（1.88 μM碱基对）时，对应于X(SS - 1) = 0.5时DNA/SS - 1电荷比为3.75，在所有X(SS - 1)值下均观察到凝聚现象。
