Dissecting current rectification through asymmetric nanopores.

Area of Science:

• Biophysics
• Nanotechnology
• Physical Chemistry

Background:

• Rectification, the directional preference of ion flow, is a known property of ion channels and synthetic nanopores.
• Existing explanations rely on phenomenological models like Eyring's rate theory, lacking a direct quantitative link to free energy profiles.
• A precise relationship between rectified current and voltage-dependent free energy landscapes remains unestablished.

Purpose of the Study:

• To establish a quantitative relationship between ion current rectification and the underlying free energy profile.
• To investigate how electrostatic pore polarity influences rectification in designed nanopores.
• To determine the factors governing cation and anion current rectification.

Main Methods:

• Design of synthetic nanopores with tunable electrostatic polarity.
• Molecular dynamics simulations to calculate free energy profiles.
• Quantification of voltage-dependent free energy barriers for ion permeation.

Main Results:

• Demonstrated that altering pore polarity effectively manipulates potassium and chloride current rectification.
• Quantified voltage-dependent free energy barriers, showing asymmetry in inward and outward ion flux barriers under an electromotive force.
• Established a direct correlation between the potential of mean force and the rectification rate.

Conclusions:

• Rectification arises from energy barrier asymmetry, which is dependent on the ion type and tunable via pore polarity.
• This mechanism does not necessitate ion binding sites, conformational changes, or specific pore geometries.
• The findings suggest that energy barrier asymmetry-driven rectification is a widespread phenomenon in ion channels.