Exploration of Neutral Versus Polyelectrolyte Behavior of Poly(ethylene glycol)s in Alkali Ion Solutions using Single-Nanopore Recording

International audienceWe examine the effect of alkali ions (Li+, Na+, K+, Rb+, Cs+) on the partitioning of neutral and flexible poly(ethylene glycol) into the alpha-hemolysin (α-HL) nanopore for a large range of applied voltages at high salt concentration. The neutral polymer behaves as if charged, that is, the event frequency increases with applied voltage, and the residence times decrease with the electric force for all cations except Li+. In contrast, in the presence of LiCl, we find the classical partitioning behavior of neutral polymers, that is, the event frequency and the residence times are independent of the applied voltage. Assuming that lithium does not associate with PEG enabled us to quantify the relative magnitude of the entropic and enthalpic contribution to the free- energy barrier and the number of complexed cations using two different arguments; the first estimate is based on the balance of forces, and the second is found comparing the blockade ratio in the presence of LiCl (no complexed ions) to the blockade ratio of chains in the presence of the other salts (with complexed ions). This estimate is in agreement with recent simulations. These findings demonstrate that the nanopore could prove useful for the rapid probing of the capabilities of different neutral molecules to form complexes with different ions

Electroosmosis through α-Hemolysin That Depends on Alkali Cation Type

International audienceWe demonstrate experimentally the existence of an electroosmotic flow (EOF) through the wild-type nanopore of α-hemolysin in a large range of applied voltages and salt concentrations for two different salts, LiCl and KCl. EOF controls the entry frequency and residence time of small neutral molecules (β-cyclodextrins, βCD) in the nanopore. The strength of EOF depends on the applied voltage, on the salt concentration, and, interestingly, on the nature of the cations in solution. In particular, EOF is stronger in the presence of LiCl than KCl. We interpret our results with a simple theoretical model that takes into account the pore selectivity and the solvation of ions. A stronger EOF in the presence of LiCl is found to originate essentially in a stronger anionic selectivity of the pore. Our work provides a new and easy way to control EOF in protein nanopores, without resorting to chemical modifications of the pore

Exploration of Neutral Versus Polyelectrolyte Behavior of Poly(ethylene glycol)s in Alkali Ion Solutions using Single-Nanopore Recording

We examine the effect of alkali ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) on the partitioning of neutral and flexible poly­(ethylene glycol) into the alpha-hemolysin (α-HL) nanopore for a large range of applied voltages at high salt concentration. The neutral polymer behaves as if charged, that is, the event frequency increases with applied voltage, and the residence times decrease with the electric force for all cations except Li⁺. In contrast, in the presence of LiCl, we find the classical partitioning behavior of neutral polymers, that is, the event frequency and the residence times are independent of the applied voltage. Assuming that lithium does not associate with PEG enabled us to quantify the relative magnitude of the entropic and enthalpic contribution to the free- energy barrier and the number of complexed cations using two different arguments; the first estimate is based on the balance of forces, and the second is found comparing the blockade ratio in the presence of LiCl (no complexed ions) to the blockade ratio of chains in the presence of the other salts (with complexed ions). This estimate is in agreement with recent simulations. These findings demonstrate that the nanopore could prove useful for the rapid probing of the capabilities of different neutral molecules to form complexes with different ions