Yoshino A, Yoshida T, Okabayashi H, Kamaya H, Ueda I
Department of Applied Chemistry, Nagoya Institute of Technology, Japan.
Biochim Biophys Acta. 1992 Jun 11;1107(1):55-60. doi: 10.1016/0005-2736(92)90328-j.
The effects of dilute salts and anesthetics were studied on the impedance dispersion in the dipalmitoylphosphatidylcholine (DPPC) liposomes. Below the pre-transition temperature, the apparent activation energy for conductance in DPPC-H2O without salts was equivalent to pure water, 18.2 kJ mol-1. This suggests that the mobile ions (H3O+ and OH-) interact negligibly with the lipid surface below the pre-transition temperature. At pre-transition temperature, the apparent activation energy of the conductance decreased by the increase in the DPPC concentrations. The effects of various salts (LiCl, NaCl, KCl, KBr, and KI) on the apparent activation energy of the conductance were studied. Changes in anions, but not in cations, affected the activation energy. The order of the effect was Cl- less than Br- less than I-. Cations appear to be highly immobilized by hydrogen bonding to the phosphate moiety of DPPC. The smaller the ionic radius, the more ions are fixed on the surface at the expense of the free-moving species. The apparent activation energy of the transfer of ions at the vesicle surface was estimated from the temperature-dependence of the dielectric constant, and was 61.0 kJ mol-1 in the absence of electrolytes. In the presence of electrolytes, the order of the activation energy was F- greater than Cl- greater than Br- greater than I-. When the ionic radius is smaller, these anions interact with the hydration layer at the vesicle surface and the ionic transfer may become sluggish. In the absence of electrolytes, the apparent activation energy of the dielectric constant decreased by the increase in halothane concentrations. In the presence of electrolytes, however, the addition of halothane increased the apparent activation energy. We propose that the adsorption of halothane on the vesicle surface produces two effects: (1) destruction of the hydration shell, and (2) increase in the binding of electrolytes to the vesicle surface. In the absence of electrolytes, the first effect predominates and the apparent activation energy is decreased. In the presence of electrolytes, the latter effect predominates and the apparent activation energy is increased.
研究了稀盐和麻醉剂对二棕榈酰磷脂酰胆碱（DPPC）脂质体中阻抗分散的影响。在转变前温度以下，无盐的DPPC-H2O中电导的表观活化能与纯水相当，为18.2 kJ·mol-1。这表明在转变前温度以下，移动离子（H3O+和OH-）与脂质表面的相互作用可忽略不计。在转变前温度时，电导的表观活化能随DPPC浓度的增加而降低。研究了各种盐（LiCl、NaCl、KCl、KBr和KI）对电导表观活化能的影响。阴离子而非阳离子的变化影响活化能。影响顺序为Cl-小于Br-小于I-。阳离子似乎通过与DPPC的磷酸基团形成氢键而高度固定。离子半径越小，固定在表面的离子越多，自由移动的离子则越少。根据介电常数的温度依赖性估算了囊泡表面离子转移的表观活化能，在无电解质时为61.0 kJ·mol-1。在有电解质存在时，活化能顺序为F-大于Cl-大于Br-大于I-。当离子半径较小时，这些阴离子与囊泡表面的水化层相互作用，离子转移可能会变得缓慢。在无电解质时，介电常数的表观活化能随氟烷浓度的增加而降低。然而，在有电解质存在时，添加氟烷会增加表观活化能。我们认为氟烷在囊泡表面的吸附产生两种效应：（1）破坏水化壳，（2）增加电解质与囊泡表面的结合。在无电解质时，第一种效应占主导，表观活化能降低。在有电解质存在时，后一种效应占主导，表观活化能增加。
