Optico-hydrodynamic properties of high molecular weight DNA. II. Effect of aqueous glycerol solvents.

Abstract

AbstractThe optical and hydrodynamic properties of T2 bacteriophage DNA have been determined by steady‐state flow birefringence and viscosity in glycerol–aqueous buffer solvents at 25°C. Flow birefringence and extinction angle data were obtained over a velocity gradient range of 0.1 to 5 sec−1 and at concentrations from 3 to 55 μg/ml in solvents containing approximately 30, 42, and 48 vol‐% glycerol. Large optical backgrounds were observed in the mixed solvent flow birefringence studies which presented special experimental difficulties; these are described and their effect upon the flow birefringence data are discussed. The data on extinction angle provide no evidence for an internal viscosity effect on the stationary‐state hydrodynamic properties of high molecular weight DNA over a range of solvent viscosity from 0.9 to 4.6 cP. Both the optical and hydrodynamic properties under present conditions of measurement appear to be self‐consistent in terms of the values for these quantities in neutral aqueous buffer solution. Interpretation of the birefringence is complicated by uncertainties inherent in calculating the form anisotropy of DNA in non‐aqueous solvents, but the data imply no large changes in helical structure with increasing glycerol concentration. Both intact and slightly degraded DNA samples were investigated, and no significant polydispersity effects were observed under the experimental conditions described.