Enhanced Water Permeation in Positively Charged Water Channels: Insights into the Molecular Mechanism

The high selectivity and permeability of aquaporin proteins in water transport inspired the design of artificial water channels (AWCs). The water transport efficiency of both AQPs and AWCs is influenced by charged groups at the pore entrance. Here, we explored the mechanism of charge effects in pillar[5]arene AWCs using molecular dynamics (MD) simulations. The simulations demonstrate that the positively charged AWCs (Ch⁺) exhibit higher water permeability compared to the negatively charged AWCs (Ch^-). The higher permeability of Ch⁺ channels stems from the shorter hydrogen bond lifetimes between water molecules at the entrance region. In line with this, the rotational dynamics of water is faster in the entrance region of Ch⁺. Further analyses revealed two factors contributing to the distinct water dynamics in Ch⁺ and Ch^- channels: the direct interactions of the NH₃ ⁺/COO^- groups with water and the counter ions (Cl^-/K⁺) around these charged groups. NH₃ ⁺ groups in Ch⁺ channels exert less stable H-bond interaction with water than the COO^- group in Ch^- channels. K⁺ ions concentrated around the COO^- groups retard the water rotation more effectively than the Cl^- ions around the NH₃ ⁺ groups. These findings provide insights into the design principles of high-performance AWCs at the molecular level.