Side-Chain and Ring-Size Effects on Permeability in Artificial Water Channels

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Computational Chemistry

Background:

• Artificial water channels (AWCs) offer stable water permeation with rates comparable to aquaporins.
• Ligand-appended pillar[n]arenes (LAPs) are a class of AWCs with tunable ring-size (m) and side-chain length (n).

Purpose of the Study:

• To investigate how ring-size and side-chain length in LAPs influence water permeability.
• To elucidate the mechanisms governing water transport in these AWCs.

Main Methods:

• All-atom molecular dynamics simulations were employed to calculate channel permeabilities.
• The collective diffusion model was used to analyze water transport.
• Analysis focused on the internal water-wire characteristics and surrounding channel structure.

Main Results:

• Water permeability decreases with increasing pillar[n]arene ring-size due to enhanced hydrophilic interactions.
• Water permeability increases with increasing side-chain length, driven by terminal group partitioning into hydrophilic blocks.
• For LAP6, longer side chains increase pore size and water permeability.
• For LAP5, flexible side chains enhance water-wire length and hydrophilic block access, overcoming nonmonotonic pore size trends.

Conclusions:

• Ring-size and side-chain length are critical parameters for tuning AWC water permeability.
• Side-chain length significantly impacts water transport through effects on pore size, water-wire structure, and bilayer interactions.
• LAPs offer a promising platform for designing efficient artificial water channels.