Phase behavior and rheological properties of DNA-cationic polysaccharide mixtures

Associative aqueous mixtures over a range of concentrations of double- (ds) or single- (ss) stranded DNA with dilute or semidilute solutions of two cationic derivatives of hydroxyethyl cellulose (cat-HEC and cat-HMHEC,(1) the latter carrying grafted hydrophobic groups), were studied. The phase behavior showed an interesting asymmetry: Phase separation occurred immediately when small (sub-stoichiometric) amounts of cationic polyelectrolyte were added to the DNA solution, but redissolution into a single cat-(HM)HEC/DNA/H(2)O phase occurred already with a modest charge excess of the cationic polyelectrolyte, at a charge ratio approximately independent of the overall polyelectrolyte concentration. Cat-HEC/dsDNA/H(2)O and cat-HEC/ssDNA/H(2)O systems presented a considerable difference in the extension of the phase separation region. The one-phase samples with excess cationic polyelectrolyte were studied by rheology. The presence of DNA strengthened the viscoelastic behavior of the solutions of the cationic polyelectrolytes, reflected in an increase in storage modulus and viscosity. Differences in phase behavior and rheology were observed, particularly between systems containing cat-HEC or cat-HMHEC, but also between dsDNA and ssDNA. Thus, these systems allow for the preparation of DNA formulations with widely variable rheology and water uptake.