Morphology Control of Hairy Nanopores

Abstract

The properties of polymer layers end-grafted to the inner surface of nanopores connected to solvent reservoirs are studied theoretically as a function of solvent quality and pore geometry. Our systematic study reveals that nanoconfinement is affected by both pore radius and length and that the conformations of the polymer chains strongly depend on their grafting position along the nanopore and on the quality of the solvent. In poor solvent, polymer chains can collapse to the walls, form a compact plug in the pore, or self-assemble into domains of different shape due to microphase separation. The morphology of these domains (aggregates on pore walls or stacked micelles along the pore axis) is mainly determined by the relationship between chain length and pore radius. In other cases the number of aggregates depends on pore length. The presence of reservoirs decreases confinement at pore edges due to the changes in available volume and introduces new organization strategies not available for infinite nanochannels. In good solvent conditions, chains grafted at the pore entrances stretch out of the pore, relieving the internal osmotic pressure and increasing the entropy of the polymers. Our study also addresses the experimentally relevant case of end-grafted chains on the outer walls of the membrane surrounding the nanopore. The effect of these polymer chains on the organization within the nanopore depends on solvent quality. For good solvents the outer chains increase the confinement of the chains at the entrance of the pore; however, the effect does not result in new structures. For poor solvents the presence of the outer polymer layer may lead to changes in the morphology of the microphase-separated domains. Our results show the complex interplay between the different interactions in a confined environment and the need to develop theoretical and experimental tools for their study.

Effect of charge, hydrophobicity, and sequence of nucleoporins on the translocation of model particles through the nuclear pore complex

“…We attribute this discrepancy to the following: i) Difference in the modeled systems: The MD simulations are for a planar surface grafted with 100-aa-long FG-Nups, whereas we model the sequences of the FG-Nups determined for yeast grafted inside a pore that mimics the experimental size and shape of the yeast NPC. We have shown in previous work (27) that increasing chain length and decreasing the radius of curvature of the pore may disfavor the formation of chain aggregates in comparison to the homogeneous system. ii) MD simulations in the study by Miao and Schulten (22) are initialized in a fully stretched configuration of the 100-aa model FG-Nups and run for a few microseconds.…”

“…We study the translocation of different model particles to elucidate the role of the different interactions in the system and understand their interplay. Our predictions are based on a molecular theory developed to study the structure, thermodynamics, and transport behavior of responsive polymers end-grafted to surfaces of arbitrary geometry (26,27) that is extended here to study the translocation of large particles through a nanopore, the NPC. The theory (Methods) is based on a free energy formulation that explicitly treats the size, shape, conformations, and charge state of all the molecular species and accounts for the nontrivial coupling between molecular organization, physical interactions, and chemical equilibrium.…”

Transport mechanisms in nanopores and nanochannels: can we mimic nature?

“…At pH 2, the 4PVP chains are charged and therefore adopt rod-like conformations, reaching the center of the channel. At pH 10, the chains are uncharged and they collapse on the channel walls due to the hydrophobic interactions among pyridine segments [43]. Therefore, the polymer is homogeneously distributed inside the nanochannel in the open conductivity state, whereas the axis of the channel is free of polymer segments in the close state.…”

Challenges in Multiscale Modeling of Polymer Dynamics

“…Still, a number of important applications were newly added in the recent past, including block copolymers and nanocomposites [53]; screening effects in polyelectrolyte brushes [54]; mixed polymer brushes [55]; harvesting cells cultured on thermoresponsive polymer brushes [56,57]; morphology control of hairy nanopores [58]; and the effect of charge, hydrophobicity and sequence of nucleoporins on the translocation of model particles through the nuclear pore complex [59]; to mention a few.…”