Role of Electrostatic Interactions on Supramolecular Organization in Calf-Thymus DNA Solutions under Flow

Abstract

Previous investigations were conducted on two concentrations of DNA solution: 4 mg/mL, for which it has been shown that no supramolecular organization is induced under flow at low shear rates; and 10 mg/mL, in which a liquid crystalline-type texture is formed under flow at low shear rates, attesting to an orientation of pre-organized chains. Rheological experiments are discussed and their results supported by small-angle X-ray scattering (SAXS) and flow birefringence visualization experiments. Scattering from polyelectrolytes has a characteristic signal, which is here observed in SAXS, showing a strong correlation peak between charged chains in water, for both concentrations. This peak is weaker in the presence of 0.01 M NaCl and suppressed in salt excess at 0.1 M NaCl. No plateau in the σ( γ ˙ ) plot was observed in analysis of rheological experiments on low DNA concentration (4 mg/mL). As typically observed in polyelectrolyte systems both the dynamic moduli and shear viscosity were higher in water as electrostatic forces dominate, than in the presence of salt, especially at low shear rates. The rheological results for concentrations of 0.01 M NaCl are lower than in water as expected due to partial screening of electrostatic repulsions. Rheological data for concentrations of 0.1 M NaCl are unexpected. Electrostatic forces are partially screened in the low salt concentration, leading to a drop in the rheological values. For high salt concentration there are no longer interchain repulsions and so steric interactions dominate within the entangled network leading to the subsequent increase in rheological parameters. Regardless of the solvent, at high shear rates the solutions are birefringent. In the 10 mg/mL case, under flow, textures are formed at relatively low shear rate before all the chains align going to a pseudonematic liquid crystalline phase at high shear rate. The electrostatic repulsion between semi-rigid chains induces a correlation between the chains leading to an electrostatic pseudo-gel in water and loosely in 0.01 M NaCl at low stress applied. To the best of our knowledge, this is the first time that such behavior is observed. In 0.1 M NaCl, DNA behavior resembles the corresponding neutral polymer as expected for polyelectrolyte in salt excess, exhibiting a yield stress. When texture appears in water and in 0.01 M NaCl, a critical transition is observed in rheological curves, where the viscosity decreases sharply at a given critical shear stress corresponding to a plateau in the σ( γ ˙ ) plot also observed in creep transient experiment.

Nanoscopic Structure of Complexes Formed between DNA and the Cell-Penetrating Peptide Penetratin

“…The radius of the cylinder core was fitted at R c = 0.8 ± 0.4 nm, whereas the thickness of the shell was found to be Δ S = 0.5 ± 0.4 nm. These values are in close agreement with reported values for DNA strands, with bases and phosphate groups forming the core of duplexes surrounded by a shell of hydration and counterion layers. , The cross-sectional radius ( R CS ) due to electrostatic repulsion between DNA chains was found to be R CS = 8.4 ± 1.1 nm, revealing average separation of about 16.8 nm between chains, in close agreement with previous data on calf-thymus DNA solutions …”

“…32,43 The cross-sectional radius (R CS ) due to electrostatic repulsion between DNA chains was found to be R CS = 8.4 ± 1.1 nm, revealing average separation of about 16.8 nm between chains, in close agreement with previous data on calf-thymus DNA solutions. 44 In the case of PNT/DNA complexes, the shape of the SAXS profiles is quite different, and data exhibit multiple structural levels across the q range investigated. By inspecting upper curves in Figure 1, we find out that the low q range is characterized by a power law decay scaling with exponents close to −4.…”

Intermolecular Interactions in Polyelectrolyte and Surfactant Complexes in Solution

“…The viscosity is polyelectrolyte concentration dependent. At high polyelectrolyte concentrations, the viscosity is high due to the interconnectivity between chains from physical crosslinks between PESC aggregates (Figure 14) [128,132,134,135]. The solutions go from a viscoelastic fluid to more elastic as the phase becomes more gel-like [132,135].…”

Azolylpyrimidinediols as Novel Structural Scaffolds of DNA-Groove Binders against Intractable Acinetobacter baumannii

“…The sodium ion quenching experiment was used to further verify the interaction mode of compound 7a with DNA. Assuming that triazolyl PD 7a was mainly binding DNA with highly negatively charged through electrostatic interaction, increasing the concentration of the Na + ion could promote the interaction between Na + ion and DNA phosphate groups, change the charge distribution of DNA structure, and destroy the electrostatic interaction between DNA and the tested molecule, , thus causing a significant variation in the absorption of the DNA–compound system. As shown in Figure S4, the absorbance of the DNA– 7a complex exposed teeny change or just kept stable with increasing in contents of sodium chloride, which revealed that the electrostatic effect was not the main interaction.…”