Ionic strength dependence of polyelectrolyte brush thickness

Zhulina, Ekaterina B.; Rubinstein, Michael

doi:10.1039/c2sm25863c

Cited by 65 publications

(75 citation statements)

References 38 publications

(156 reference statements)

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“…This includes theoretical work on polyelectrolyte brush behavior (27), as well as work on electrostatic modulation of DNA structural transitions: the double-stranded DNA overstretching transition (29) and the base unstacking transition of poly(dA) ssDNA (30). Here, we extend the approach by carefully analyzing the balance of electrostatic tension against entropic elasticity, a universal feature of polymer behavior.…”

Section: Resultsmentioning

confidence: 99%

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Single-stranded nucleic acid elasticity arises from internal electrostatic tension

Jacobson

McIntosh

Stevens

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Understanding of the conformational ensemble of flexible polyelectrolytes, such as single-stranded nucleic acids (ssNAs), is complicated by the interplay of chain backbone entropy and saltdependent electrostatic repulsions. Molecular elasticity measurements are sensitive probes of the statistical conformation of polymers and have elucidated ssNA conformation at low force, where electrostatic repulsion leads to a strong excluded volume effect, and at high force, where details of the backbone structure become important. Here, we report measurements of ssDNA and ssRNA elasticity in the intermediate-force regime, corresponding to 5-to 100-pN forces and 50-85% extension. These data are explained by a modified wormlike chain model incorporating an internal electrostatic tension. Fits to the elastic data show that the internal tension decreases with salt, from >5 pN under 5 mM ionic strength to near zero at 1 M. This decrease is quantitatively described by an analytical model of electrostatic screening that ascribes to the polymer an effective charge density that is independent of force and salt. Our results thus connect microscopic chain physics to elasticity and structure at intermediate scales and provide a framework for understanding flexible polyelectrolyte elasticity across a broad range of relative extensions.single-stranded nucleic acids | flexible polyelectrolytes | force spectroscopy | electrostatics S ingle-stranded nucleic acids (ssNAs) occur in many biological processes, such as RNA folding (1, 2) and DNA replication (3-5), generally in disordered conformations that fluctuate between various structures. These fluctuations create a significant entropic elasticity; thus, direct measurements of molecular elasticity (extension, X , as a function of applied force, fapp) constitute a powerful tool for studying the ssNA structural ensemble (6). In particular, measurements at a particular fapp are sensitive to the conformation within the corresponding tensile length, kB T /fapp (to within a scaling factor), where kB T is the thermal energy (7).ssNA structure-and that of flexible polyelectrolytes more generally-is complicated by the strong negative charge of the molecule. Multiple electrostatic and structural length scales share a similar magnitude (roughly 1 nm), disallowing models that consider only electrostatics or only backbone structure. In an uncharged flexible chain, the key structural scale is the persistence length, lp, defining the distance beyond which thermal fluctuations strongly bend the polymer. Electrostatic interactions introduce several competing length scales: the distance, b, between charged phosphates along the ssNA backbone; the distance over which electrostatic fields are screened in salty solution (the Debye length, κ −1 ); and the distance at which interactions between elementary charges in water have energy kB T (the Bjerrum length, lB ).Prior studies have elucidated ssNA elastic behavior in the lowand high-force limits. At low forces, corresponding to tensile lengths larger than κ −1 (i....

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Section: Resultsmentioning

confidence: 99%

“…Notwithstanding this limit, we expect the behavior modeled by Eq. 1 to extend from, at low force, the crossover to the excluded volume regime (fapp ∼ kB T /κ −1 ) (27) to, at high force, the transition from WLC to freely jointed chain (FJC) behavior (fapp ∼ kB Tlp/a 2 , where a is the chemical bond length) (14).…”

Section: Resultsmentioning

confidence: 99%

Single-stranded nucleic acid elasticity arises from internal electrostatic tension

Jacobson

McIntosh

Stevens

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Nonetheless, very recent work [59] does show that single-strand tethered DNA of ~1000 bases does follow brush scaling predictions for polyelectrolyte brush height [60] as a function of both chain density and ionic strength. So, to a certain extent, intermediate length polyelectrolyte brush behaviors in high ionic strength milieu can be predicted.…”

Section: Idealized Tethered Polymer Chain Modelsmentioning

confidence: 99%

Biophysical properties of nucleic acids at surfaces relevant to microarray performance

2014

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Both clinical and analytical metrics produced by microarray-based assay technology have recognized problems in reproducibility, reliability and analytical sensitivity. These issues are often attributed to poor understanding and control of nucleic acid behaviors and properties at solid-liquid interfaces. Nucleic acid hybridization, central to DNA and RNA microarray formats, depends on the properties and behaviors of single strand (ss) nucleic acids (e.g., probe oligomeric DNA) bound to surfaces. ssDNA’s persistence length, radius of gyration, electrostatics, conformations on different surfaces and under various assay conditions, its chain flexibility and curvature, charging effects in ionic solutions, and fluorescent labeling all influence its physical chemistry and hybridization under assay conditions. Nucleic acid (e.g., both RNA and DNA) target interactions with immobilized ssDNA strands are highly impacted by these biophysical states. Furthermore, the kinetics, thermodynamics, and enthalpic and entropic contributions to DNA hybridization reflect global probe/target structures and interaction dynamics. Here we review several biophysical issues relevant to oligomeric nucleic acid molecular behaviors at surfaces and their influences on duplex formation that influence microarray assay performance. Correlation of biophysical aspects of single and double-stranded nucleic acids with their complexes in bulk solution is common. Such analysis at surfaces is not commonly reported, despite its importance to microarray assays. We seek to provide further insight into nucleic acid-surface challenges facing microarray diagnostic formats that have hindered their clinical adoption and compromise their research quality and value as genomics tools.

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“…Furthermore, the swollen thickness of polyelectrolyte brushes on a flat surface in solution is determined by many factors, such as graft density, excluded volume interactions, osmotic pressure (the concentration of mobile ions inside and outside the brush), electrostatic interactions (Debye length and electrostatic persistence length), restoring force of the stretched chains, and chain elasticity (Kuhn segment length). Recent theoretical studies based on scaling models predict the swollen brush thickness and structures depending on ionic strength [6,7]; however, the experimental characterization at the brush/solution interface is also important to understand the actual brush structure in solution.…”

Section: Introductionmentioning

confidence: 99%

Neutron reflectivity study of the swollen structure of polyzwitterion and polyeletrolyte brushes in aqueous solution

Kobayashi

Ishihara

Takahara

2014

Journal of Biomaterials Science, Polymer Edition

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The swollen brush structures of polycation and zwitterionic polymer brushes, such as poly(2-methacryloyloxyethyltrimethylammonium chloride) (PMTAC), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate] (PMAPS), in aqueous solutions of various ionic strengths were characterized by neutron reflectivity (NR) measurements. A series of the polyelectrolyte brushes were prepared by surface-initiated controlled radical polymerization on silicon substrates. A high-graft-density PMTAC brush in salt-free water (D2O) adopted a two-region step-like structure consisting of a shrunk region near the Si substrate surface and a diffuse brush region with a relatively stretched chain structure at the solution interface. The diffuse region of PMTAC was reduced with increase in salt (NaCl) concentration. The PMAPS brush in D2O formed a collapsed structure due to the strong molecular interaction between betaine groups, while significant increase in the swollen thickness was observed in salt aqueous solution. In contrast, no change was observed in the depth profile of the swollen PMPC brush in D2O with various salt concentrations. The unique solution behaviors of zwitterionic polymer brushes were described.

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Ionic strength dependence of polyelectrolyte brush thickness

Cited by 65 publications

References 38 publications

Single-stranded nucleic acid elasticity arises from internal electrostatic tension

Single-stranded nucleic acid elasticity arises from internal electrostatic tension

Biophysical properties of nucleic acids at surfaces relevant to microarray performance

Neutron reflectivity study of the swollen structure of polyzwitterion and polyeletrolyte brushes in aqueous solution

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