Among the Various methods for characterizing macromolecules in solution, hydrodynamic techniques play a major role. Since the advent of the ultracentrifuge and the development of viscometric apparatus, sedimentation coefficients and intrinsic viscosities have been extensively used to learn about the size and shape of synthetic and biological polymers. More recently, refined techniques such as quasielastic light scattering, transient electric birefringence and fluorescence anisotropy decay have made it possible to obtain in a simple and rapid way quantitative information of high precision on the translational and rotational brownian dynamics of dissolved macromolecules.

Two theories relating the translational and rotational diffusion coefficients D_t and D_r of a rod‐like macromolecule to its length and diameter, proposed by Broersma [J. Chem. Phys. 74, 6989 (1981)], and Tirado and García de la Torre [J. Chem. Phys. 7 1, 2581 (1979); 7 3, 1986 (1980)] are shown to predict different values of the coefficients for a particle of given dimensions. Next, we use the two theories to analyze existing experimental data of sedimentation coefficients s and translational and rotational diffusion coefficients of short DNA fragments, and obtain values of the hydrated diameter of DNA d which is treated as an adjustable parameter. The results are compared with the expected value, d≂26Å. This comparison favors clearly the Tirado–Garcia de la Torre theory in the case of D_t and s. For D_r, and using a rise per base pair r=3.4 Å, this theory gives best agreement for all the data examined, while when r=3.3 Å, the agreement depends on the source of data.

The hydrodynamic interaction equations and the interaction tensor that appear in the theoretical formalism for calculating translational friction coefficients of rigid particles modeled as assemblies of beads, are formulated in cylindrical coordinates. For symmetric top particles, the cylindrical shielding tensors of symmetry‐equivalent beads are the same, and have only five nonzero components. This effects a great simplification with respect to the Cartesian formalism. Application is made to the end‐effect correction, for translational motion of right circular cylinders modeled as stacks of rings, extrapolated to zero bead size. No appreciable changes in the translational friction coefficients are found when the hollow cylindrical models are capped at the ends with disc‐shaped plates. For finite cylinders with axial ratio p≳2, our results, as well as those from other theoretical and experimental studies, are in remarkable disagreement with the previous calculations by Broersma.