Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
Phys Chem Chem Phys. 2021 Jan 21;23(2):1352-1362. doi: 10.1039/d0cp04486e.
Adsorption processes are central to ionic transport in industrial and biological membrane systems. Multivalent cations modulate the conductive properties of nanofluidic devices through interactions with charged surfaces that depend principally on the ion charge number. Considering that ion channels are specialized valves that demand a sharp specificity in ion discrimination, we investigate the adsorption dynamics of trace amounts of different salts of trivalent cations in biological nanopores. We consider here OmpF from Escherichia coli, an archetypical protein nanopore, to probe the specificity of biological nanopores to multivalent cations. We systematically compare the effect of three trivalent electrolytes on OmpF current-voltage relationships and characterize the degree of rectification induced by each ion. We also analyze the open channel current noise to determine the existence of equilibrium/non-equilibrium mechanisms of ion adsorption and evaluate the extent of charge inversion through selectivity measurements. We show that the interaction of trivalent electrolytes with biological nanopores occurs via ion-specific adsorption yielding differential modulation of ion conduction and selectivity inversion. We also demonstrate the existence of non-equilibrium fluctuations likely related to ion-dependent trapping-detrapping processes. Our study provides fundamental information relevant to different biological and electrochemical systems where transport phenomena involve ion adsorption in charged surfaces under nanoscale confinement.
吸附过程是工业和生物膜系统中离子传输的核心。多价阳离子通过与带电表面的相互作用来调节纳流道器件的导电性能，这种相互作用主要取决于离子电荷数。考虑到离子通道是专门的阀门，对离子的选择性要求非常高，我们研究了痕量的不同价态阳离子盐在生物纳米孔中的吸附动力学。在这里，我们选择大肠杆菌中的 OmpF 作为典型的蛋白质纳米孔，以探究生物纳米孔对多价阳离子的特异性。我们系统地比较了三种三价电解质对 OmpF 电流-电压关系的影响，并表征了每种离子诱导的整流程度。我们还分析了开放通道电流噪声，以确定离子吸附的平衡/非平衡机制的存在，并通过选择性测量评估电荷反转的程度。我们表明，三价电解质与生物纳米孔的相互作用是通过离子特异性吸附发生的，从而对离子传导和选择性反转进行了不同的调制。我们还证明了非平衡波动的存在，这可能与离子依赖的捕获-脱附过程有关。我们的研究为不同的生物和电化学系统提供了基本信息，这些系统中的输运现象涉及纳米尺度限制下带电表面的离子吸附。
