title: Quantifying screening ion excesses in single-molecule force-extension experiments.
abstract: 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.
authors.affiliation: Materials Department, University of California, Santa Barbara, California 93106, USA. landy@mrl.ucsb.edu
authors.forename: Jonathan
authors.initials: J
authors.lastname: Landy
authors.forename: D B
authors.initials: DB
authors.lastname: McIntosh
authors.forename: O A
authors.initials: OA
authors.lastname: Saleh
mesh_terms: D000838:Anions / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry; D008956:Models, Chemical
chemical_list: D000838:Anions; D002412:Cations; D004277:DNA, Single-Stranded; D004573:Electrolytes; D004247:DNA