Quantifying screening ion excesses in single-molecule force-extension experiments

We derive a thermodynamic identity that allows one to infer the change in the number of screening ions that are associated with a charged macromolecule as the macromolecule is continuously stretched. Applying this identity to force-extension data on both single-stranded and double-stranded DNA, we f...

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Bibliographic Details
Published inPhysical review letters Vol. 109; no. 4; p. 048301
Main Authors Landy, Jonathan, McIntosh, D B, Saleh, O A
Format Journal Article
LanguageEnglish
Published United States 27.07.2012
Subjects
Anions - chemistry
Cations - chemistry
DNA - chemistry
DNA, Single-Stranded - chemistry
Electrolytes - chemistry
Models, Chemical
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Summary:We derive a thermodynamic identity that allows one to infer the change in the number of screening ions that are associated with a charged macromolecule as the macromolecule is continuously stretched. Applying this identity to force-extension data on both single-stranded and double-stranded DNA, we find that the number of polymer-associated ions depends nontrivially on both the bulk salt concentration and the bare rigidity of the polymer, with single-stranded DNA exhibiting a relatively large decrease in ion excess upon stretching. We rationalize these observations using simple models for polyelectrolyte extension.
ISSN:1079-7114
DOI:10.1103/PhysRevLett.109.048301