Suezaki Y, Tamura K, Takasaki M, Kamaya H, Ueda I
Physics Laboratory, Saga Medical School, Japan.
Biochim Biophys Acta. 1991 Jul 22;1066(2):225-8. doi: 10.1016/0005-2736(91)90190-j.
Long-chain n-alcohols decrease the main phase-transition temperature of lipid vesicle membranes at low concentrations but increase it at high concentrations. The nonlinear phenomenon is unrelated to the interdigitation and is analyzed by assuming that alcohols form solid solutions with solid as well as liquid phases. The biphasic response originates from the balance of the free energy difference of alcohols in the liquid and solid membranes (delta gA) and the alcohol-lipid interaction free energy difference (delta u) between the two phases. When delta gA less than 0 and delta u greater than 0, or delta gA less than delta u less than 0, the transition temperature decreases monotonously according to the increase in the alcohol concentration. When delta gA greater than 0 and delta u less than 0, or delta gA greater than delta u greater than 0, it increases monotonously. Biphasic response occurs with a minimum temperature when delta u greater than delta gA greater than 0, and with a maximum temperature when delta u less than delta gA less than 0. When the alcohol carbon-chain length becomes closer to the lipid carbon-chain length, delta u is equalized by delta gA, and the temperature minimum of the main transition is shifted to extremely low alcohol concentrations. Hence, long-chain alcohols predominantly elevate the main transition temperature and lose their anesthetic potency. High pressure decreased both delta gA and delta u. Presumably, high pressure improves the packing efficiency of liquid membranes and decreases the difference between the solid and liquid membrane properties.
长链正构醇在低浓度时会降低脂质囊泡膜的主相变温度，但在高浓度时会升高该温度。这种非线性现象与相互交叉无关，通过假设醇类与固相和液相形成固溶体来进行分析。双相响应源于醇类在液态和固态膜中的自由能差（δgA）以及两相之间醇 - 脂质相互作用自由能差（δu）的平衡。当δgA小于0且δu大于0，或者δgA小于δu小于0时，相变温度会随着醇浓度的增加而单调降低。当δgA大于0且δu小于0，或者δgA大于δu大于0时，相变温度会单调升高。当δu大于δgA大于0时，双相响应会出现最低温度；当δu小于δgA小于0时，会出现最高温度。当醇的碳链长度变得更接近脂质的碳链长度时，δu会被δgA抵消，主相变的最低温度会转移到极低的醇浓度处。因此，长链醇主要升高主相变温度并失去其麻醉效力。高压会降低δgA和δu。据推测，高压提高了液态膜的堆积效率，并减小了固态和液态膜性质之间的差异。
