Woodle M, Zhang J W, Mauzerall D
Rockefeller University, New York, New York 10021.
Biophys J. 1987 Oct;52(4):577-86. doi: 10.1016/S0006-3495(87)83247-2.
Advances in instrumentation allow electrical measurements across the planar lipid bilayer to be made with nanosecond time resolution. The electron transfer reaction between photoexcited magnesium octaethylporphyrin in the lipid to a variety of ionically charged acceptors in the water is found to be purely dynamic over a wide range of concentrations of acceptors and up to the time constant of the apparatus, 4 ns. The saturation of the amplitude of the photovoltage with increasing concentration of acceptor is caused by the finite lifetime of the excited state, not by formation of a static pigment-acceptor complex. The reactions are an excellent probe of the lipid-water interface over an extended time scale. No appreciable barrier to reaction exists at this interface beyond the 5-ns time. That is, any water or choline group structure may be evanescent on this time scale. Electrostatic interactions indicate that the acceptor molecules penetrate to the level of the phosphocholine groups with differing orientations. It will be possible to extend the time scale into the picosecond range by decreasing the response time and by deconvolutions.
仪器设备的进步使得能够以纳秒级的时间分辨率对平面脂质双层进行电学测量。研究发现，脂质中光激发的八乙基卟啉镁与水中各种带离子电荷的受体之间的电子转移反应，在受体浓度的广泛范围内以及直至仪器的时间常数（4纳秒）都是完全动态的。光电压幅度随受体浓度增加而饱和是由激发态的有限寿命引起的，而非形成静态色素 - 受体复合物。这些反应是在较长时间尺度上对脂质 - 水界面的极佳探针。在5纳秒之后，该界面不存在明显的反应障碍。也就是说，在这个时间尺度上，任何水或胆碱基团结构可能都是短暂的。静电相互作用表明，受体分子以不同取向渗透到磷酸胆碱基团的水平。通过缩短响应时间和进行去卷积，有可能将时间尺度扩展到皮秒范围。
