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Related Concept Videos

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Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
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Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
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The transport of solutes across the cell membrane is essential for metabolic processes, like maintaining cell size and volume, generating the action potential, exchanging nutrients and gases, etc. Membrane transport can be either passive or active. It can be simple diffusion, facilitated, or mediated transport aided by transport proteins such as transporters and channels.
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Diffusion Limitations and Translocation Barriers in Atomically Thin Biomimetic Pores.

Subin Sahu1,2,3, Michael Zwolak1

  • 1Biophysical and Biomedical Measurement Group, Microsystems and Nanotechnology Division, Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.

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Ionic transport through nano-pores is sensitive to pore size and ion interactions. Even with favorable energy landscapes, pore size and ion dynamics outside the pore can limit conductance, revealing kinetic bottlenecks.

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Area of Science:

  • Physical Chemistry
  • Materials Science
  • Nanotechnology

Background:

  • Ionic transport through nanoscale pores is governed by complex interactions, including ion dehydration and electrostatic forces within the free-energy landscape.
  • In atomically thin membranes like graphene, ion dynamics extend beyond the pore's geometric volume, influenced by factors such as membrane thickness and hydration layer radii.
  • Biomimetic pores, such as graphene crown ethers, exhibit unique transport behaviors sensitive to minute structural changes.

Purpose of the Study:

  • To investigate the intricate relationship between pore size, ion dehydration, electrostatic interactions, and ion dynamics in determining ionic transport through nanoscale pores.
  • To explore the regimes where ionic conductance is highly sensitive to pore size variations, particularly in biomimetic systems.
  • To understand how external ion dynamics and pore-free energy landscapes collectively influence ion translocation and conductance.

Main Methods:

  • Theoretical analysis of ionic transport considering translocation barriers and potential wells within the free-energy landscape.
  • Examination of ion dynamics both inside and outside the pore, accounting for multiple length scales like membrane thickness, hydration layer radii, and Debye length.
  • Focus on graphene crown ether as a biomimetic pore model to study pore size sensitivity and conductance characteristics.

Main Results:

  • Ionic transport is highly sensitive to pore size in specific regimes due to the interplay of ion dehydration and pore charge interactions, where picometer-scale changes can significantly alter conductance.
  • In other regimes, despite a near-barrierless free energy landscape, the intrinsic small pore size imposes large resistance.
  • The overall conductance can plateau and become independent of pore-free energy characteristics when diffusion and drift effects dominate, indicating rapid translocation after ion arrival within the pore's capture radius.

Conclusions:

  • The study reveals distinct regimes governing ionic transport in nanoscale pores, highlighting the critical role of pore size and external ion dynamics.
  • Measurement of conductance plateaus can provide estimates of kinetically limiting features and constrain local electromechanical conditions.
  • Understanding these complex transport mechanisms is crucial for designing advanced nanoporous materials and devices.