Supramolecular Organization in Calf-Thymus DNA Solutions under Flow in Dependence with DNA Concentration

Abstract

DNA dynamics and flow properties are of great importance for understanding its functions. DNA is a semiflexible polymer chain characterized by having a large persistence length of around 50 nm and high charge density; DNA chains are interacting efficiently at high concentrations, in dependence of the ionic concentration. In relation with DNA molecular characteristics, it is also known that DNA solutions are able to form liquid crystalline phases over a critical polymer concentration. In this work, the supramolecular organization in calf-thymus DNA solution, with low degree of entanglement, appearing under flow was studied in a wide DNA concentration range from 2 to 10 mg/mL, at a pH of 7.3 and 20 °C. The rheological behavior of the system was studied using steady state flow and oscillatory measurements. Transient regimes were also tested by imposing controlled shear rates on a short time up to steady state. Furthermore, a combination of visual observations and flow birefringence measurements was proposed to reach a better understanding of the obtained rheological behavior. The presence of a shear-induced texture is revealed under flow for the calf-thymus DNA solutions at C DNA> 5 mg/mL and attributed to organized domains of DNA molecules, named in the text as crystalline parts, which are progressively oriented under shear. Finally, at high shear rates (over 100 s–1), it is shown that for the DNA solutions the orientation of these organized DNA domains and connecting chains under flow goes to an anisotropic monodomain.

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

“…Due to condensed counterions in 1-1 electrolytes, there exists a range of distances less than the Debye length where polyions attract each other [6,7,8,9,10]. Birefringence has previously shown that textures corresponding to orientated, ordered domains are induced under shear flow for DNA concentrations higher than 5 mg/mL at low ionic concentration [11]. A schematic representation of the evolution of these solutions at rest and under flow was proposed [11].…”

“…Birefringence has previously shown that textures corresponding to orientated, ordered domains are induced under shear flow for DNA concentrations higher than 5 mg/mL at low ionic concentration [11]. A schematic representation of the evolution of these solutions at rest and under flow was proposed [11]. Understanding the nonlinear behavior of entangled DNA solutions using rheology has been the subject of previous work.…”

“…From a mechanical point of view, in the steady-state flow curve, the onset of a stress plateau above a critical shear has been associated with the existence of nonhomogeneous flow [11]. In that work, the supramolecular organization in entangled calf-thymus DNA solutions under flow was studied in a large DNA concentration range between 2 and 10 mg/mL in TE buffer (ionic concentration equivalent to 0.01 M) at pH = 7.3 and at 20 °C.…”

Shear Induced Interactions Cause Polymer Compression

“…Calf thymus DNA shows decreasing viscosity with shear rate and increasing viscosity with temperature 23 . A recent study by Bravo-Anaya et al interprets the observed rheological behaviour as resulting from interacting aggregates of the DNA molecules in flow 22 . The interaction between the DNA molecules is suggested to be driven by H-bonding.…”

“…It should be noted that DNA does not show the same rheological behaviour as that observed for typical random coil polymers. Typical random coil polymers have conformation that is determined by their entropy and show decreasing viscosity with increasing shear rate and increasing temperature 22,23 . Calf thymus DNA shows decreasing viscosity with shear rate and increasing viscosity with temperature 23 .…”