Hellberg Dirk, Scholz Fritz, Schubert Frank, Lovrić Milivoj, Omanović Dario, Hernández Víctor Agmo, Thede Richard
Institut für Chemie und Biochemie, Universität Greifswald, Greifswald, Germany.
J Phys Chem B. 2005 Aug 4;109(30):14715-26. doi: 10.1021/jp050816s.
The adhesion of liposomes on a mercury electrode leads to capacitive signals due to the formation of islands of lecithin monolayers. Integration of the current-time transients gives charge-time transients that can be fitted by the empirical equation Q(t) = Q(0) + Q(1)(1 - exp(-t/tau(1))) + Q(2)(1 - exp(-t/tau(2))), where the first term on the right side is caused by the docking of the liposome on the mercury surface, the second term is caused by the opening of the liposome, and the third term is caused by the spreading of the lecithin island on the mercury surface. The temperature dependence of the two time constants tau(1) and tau(2) and the temperature dependence of the overall adhesion rate allow determination of the activation energies of the opening, the spreading, and the overall adhesion process both for gel-phase 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and for liquid-crystalline-phase DMPC liposomes. In all cases, the spreading is the rate-determining process. Negative apparent activation energies for the spreading and overall adhesion process of liquid-crystalline-phase DMPC liposomes can be explained by taking into account the weak adsorption equilibria of the intact liposomes and the opened but not yet spread liposomes. A formal kinetic analysis of the reaction scheme supports the empirical equation used for fitting the charge-time transients. The developed kinetic model of liposome adhesion on mercury is similar to kinetic models published earlier to describe the fusion of liposomes. The new approach can be used to probe the stability of liposome membranes.
脂质体在汞电极上的粘附由于卵磷脂单层岛的形成而产生电容信号。对电流-时间瞬变进行积分可得到电荷-时间瞬变，其可用经验方程Q(t)=Q(0)+Q(1)(1 - exp(-t/τ(1)))+Q(2)(1 - exp(-t/τ(2)))拟合，其中右侧的第一项是由脂质体在汞表面的对接引起的，第二项是由脂质体的打开引起的，第三项是由卵磷脂岛在汞表面的铺展引起的。两个时间常数τ(1)和τ(2)的温度依赖性以及整体粘附速率的温度依赖性使得能够确定凝胶相1,2-二肉豆蔻酰-sn-甘油-3-磷酸胆碱（DMPC）和液晶相DMPC脂质体的打开、铺展以及整体粘附过程的活化能。在所有情况下，铺展都是速率决定过程。液晶相DMPC脂质体铺展和整体粘附过程的负表观活化能可以通过考虑完整脂质体以及已打开但尚未铺展的脂质体的弱吸附平衡来解释。对反应方案的形式动力学分析支持用于拟合电荷-时间瞬变的经验方程。所建立的脂质体在汞上的粘附动力学模型类似于早期发表的用于描述脂质体融合的动力学模型。这种新方法可用于探测脂质体膜的稳定性。
