The transport of an organic cation across a 4-5 nm liposome bilayer is observed in real time using second harmonic generation.It is proposed that an electrostatic barrier between the inside and outside of the liposome develops as the cation crosses the bilayer.This would explain why the SHG signal does not approach zero at long times.To test this mechanism,the antibiotic valinomycin,which can transport alkali ions across a phospholipid bilayer,is introduced into the system.It is found that the transport time is reduced by a factor of three from 90 +-2 s to 30 +- 1 s with 1.25 x 10~(-8) M valinomycin concentration,and a factor of fifteen to 6.2 +-0.2 s with 1.25 x 10~(-8) M valinomycin concentration.In addition,the SHG signal approaches zero,which further supports the presence of an electrostatic barrier that can be eliminated by the alkali ion transporter valinomycin.
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机译：使用二次谐波可以实时观察到有机阳离子在4-5 nm脂质体双层上的传输，这表明当阳离子穿过双层时，脂质体内部和外部之间会形成静电屏障。为什么要检测SHG信号长时间不趋于零。为了测试这种机理，将能够将碱离子跨过磷脂双层转运的抗生素缬氨霉素引入了系统。发现转运时间减少了一个因素。浓度为1.25 x 10〜（-8）M的金霉素为90 + -2 s至30 +-1 s，浓度为1.25 x 10〜（-8）M的金霉素为15〜6.2 + -0.2 s。此外，SHG信号接近于零，这进一步支持了静电屏障的存在，该屏障可以被碱金属离子转运缬氨霉素消除。
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