Viscosity measurements of DNA solutions with and without condensing agents.

Aqueous solutions calf thymus DNA at three concentrations were studied by viscosity measurements at ambient pressure. A gravitational capillary viscometer and a rotating cylinder viscometer were employed. Three polycations were tested as viscosity-reducing agents with measurements from 25°C to 50°C. The most significant viscosity reduction was achieved with spermine in a solution of DNA at 2 mg/ml concentration. Measurements of DNA solutions without agents from 10°C to 90°C revealed concentration-dependent viscosity maxima in the range from 50°C to 65°C. The associated increases in viscosity were as high as 400%. A two-liquids model for solutions of double- and single-stranded DNA was developed that closely represented the experimental data.