Globular Polyampholytes: Structure and Translocation

NK Lee and Y Jung and A Johner and JF Joanny, MACROMOLECULES, 54, 2394-2411 (2021).

DOI: 10.1021/acs.macromol.0c02413

Polyampholytes (PAs) are polymers carrying electrical charges of both signs along their backbone. We consider synthetic PAs with a quenched random charge sequence. At low to moderate salt concentrations, PAs typically adopt pearl-necklace structures with collapsed globules linked by open strands. We study the structure of a PA as a function of its net charge by means of coarse-grained molecular dynamics simulations and analytical theory. It is shown theoretically and evidenced by simulations that the free energy drives quenched random PAs toward states with (very) polydisperse pearls. The translocation of a (partially) globular PA, driven by an electric field through a narrow pore, usually starts from a chain end in a tailed configuration. In our simulations, about half of all the observed PA configurations are tailed. The vast majority of the sequences visits tailed configurations long enough to initiate translocation like for open PAs. A detailed description of the tail size distribution and tail structure is obtained, and the survival statistics of tails is explored. The consequences of the pearl-necklace structures, observed in the simulations, for the translocation are discussed. Translocation itself is not simulated in this contribution.

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