Optimal transport and colossal ionic mechano-conductance in graphene crown ethers

Abstract

Biological ion channels balance electrostatic and dehydration effects to yield large ion selectivity alongside high transport rates. These macromolecular systems are often interrogated through point mutations of their pore domain, limiting the scope of mechanistic studies. In contrast, we demonstrate that graphene crown ether pores afford a simple platform to directly investigate optimal ion transport conditions, i.e., maximum current densities and selectivity. Crown ethers are known for selective ion adsorption. When embedded in graphene, however, transport rates lie below the drift-diffusion limit. We show that small pore strains (1%) give rise to a colossal (100%) change in conductance. This process is electromechanically tunable, with optimal transport in a primarily diffusive regime, tending toward barrierless transport, as opposed to a knock-on mechanism. These observations suggest a novel setup for nanofluidic devices while giving insight into the physical foundation of evolutionarily optimized ion transport in biological pores.

Colloquium : Ionic phenomena in nanoscale pores through 2D materials

“…These concepts culminate in functionalized, 2D pores. For instance, Sahu et al . (2019) recently report on the effect of strain on the ionic current.…”

“…Colossal mechano-conductance and optimal transport in a graphene crown ether pore (bottom inset) (Sahu et al ., 2019). Each oxygen and carbon at the pore rim has partial charge −0.24 e and 0.12 e , respectively.…”

Flat crown ethers with planar tetracoordinate carbon atoms

“…Embedding crown ethers in graphene 57 or carbon nanostructures 58 have been emerging to control their low structural rigidity. [59][60][61] Preorganizing the host molecule to suit the guest is a necessity for its potential applications. Here, instead of using a graphene environment, a novel approach has been followed by taking advantage of the concept of molecules with a ptC atom and consequentially making flat crown ethers to maximize its suitability.…”

Diffusion Limitations and Translocation Barriers in Atomically Thin Biomimetic Pores

“…The depletion of charge carriers in the pore, see Figure 3, is also consistent with the decrease in conductance and points to a diffusion-limited regime. At small voltages and minute strains, I K increases rapidly with strain due to the large electromechanical susceptibility of the pore [27]. A further increase of the strain causes I K to either decrease (for q O = −0.24 e) or saturate (for q O = −0.54 e), albeit the latter will also decrease when the electrostatic well disappears and dehydration begins to control the current.…”