Effect of DNA's Molecular Weight on their Solution Viscosity, Critical Concentrations, and Liquid Crystals Formation

The study of the dynamics of nucleic acids in solution, their flow properties, and viscoelasticity is of great importance for understanding their biological functions. Many important properties of nucleic acids, such as DNA, depend on polymer concentration, C DNA , molecular weight ( M W ), rigidity, and external salt content, the latter parameter affecting electrostatic interactions. Furthermore, DNA molecular chains can organize, in vitro, into liquid crystalline phases at high C DNA . In this work, three DNA samples with different M W were studied in solution in a broad concentration range (C DNA from 0.025 to 200 mg mL −1 , depending on DNA M W ). Firstly, the intrinsic viscosities and M W for all DNA samples were determined through capillary and rheological measurements. Then, the overlap concentrations, C *, were estimated from the relation C * ≈ [ η ] −1 . DNA chain characteristics were then analyzed in terms of the influence of DNA M W on the solution viscosities and on the overlap parameter, C DNA [ η ]. Flow birefringence appearance was identified by screening a wide C DNA range through visual observations with crossed polarizers. Finally, crossed‐light polarized microscopy was used to identify the appearance of liquid crystals at rest, confirming that higher C DNA are needed to obtain liquid crystals for low M W DNA samples.