Solvent-induced conformation gating of single-molecule charge transport in valinomycin and valinomycin-K+ junctions

Abstract

Gaining insights into charge transport related to conformational changes and ion transport in valinomycin (VM) is crucial for understanding the underlying physiological processes and advancing ion carrier applications. Observing these processes in single molecules provides deeper insights and precision than those obtained through conventional ensemble measurements. Herein, we employed a single-molecule conductance measurement method based on the scanning tunneling microscopy break-junction (STM-BJ) to measure the charge transport of individual VM molecules in both non-polar and polar solvents, as well as when mediated by K⁺ ions. Single-molecule conductance measurements revealed that the bracelet and propeller-type conformations of VM in both non-polar and polar solvents significantly affect its conductance. In polar solvents, the propeller-type conformation of VM demonstrated a well-defined conductance signature, single-molecule rectification feature, and through-space transmission mechanism. Specifically, the introduction of K⁺ ions in polar solvents induced a conformational transition from the propeller-type to the bracelet-type form, facilitating K⁺ binding recognition. These observations were further supported by density functional theory combined with non-equilibrium Green’s function calculations. This study enhanced the fundamental understanding of the electronic transport mechanisms in VM and valinomycin-K⁺ molecular junctions, offering insights into VM ionophores and promoting supramolecular sensing applications.

Graphical abstract