Calf thymus a i d salmon sperm deoxyribonncleic acid were degradcd by high-shear stirring to molecular weights M in the range of 1.3-3.2 X lo6 and purified by chromatography on methylated bovine serum albumin. Dynamic viscoelastic properties of the fragmented products, in aqueous glycerol solutions in the concentration range of c = 0.003-0.01 g./ml., were investigated with the apparatus of Birnboim and Ferry.
At values of the product cM higher than 4 X 103, the frequency dependence of the components of the complex shear modulus, G' and G", displayed a plateau region in which G' > G" -ovlqS, similar to that observed in concentrated solutions of coiling polymers where it is attributed to an entanglement network (W is radian frequency, v1 volume fraction of solvent, and qs solvent viscosity). The width of this plateau region on the logarithmic frequency scale is given by A = 3.8 (log c M -3.56). At lower values of cM, the freqnency dependence is intermediate between those predicted by the theory of Zimm for flexible coiled macromolecules and by the theory of Kirkwood and Auer for rods. Fitting to the Zimm theory gives highly discrepant values for molecnlar weights, while fitting the low-frequency end of the dispersion to the Kirkwood-Auer theory gives reasonable agreement for both molecnlar weight and rotary diffusion coefficient. I t is concluded that the helical fragments appear as nearly rigid rods in their behavior at very low frequencies, but at higher frequencies reveal substantial bending flexihility.