Intrinsic viscosity and rotational diffusion of bead models for rigid macromolecules and bioparticles

Abstract

The conventional Kirkwood-Riseman (K-R) treatment of the intrinsic viscosity of macromolecular bead models shows a deficiency when it is applied to models with few beads, whose sizes are not much smaller than of the modelled particle. We present a complete derivation of the intrinsic viscosity up to first order in interbead distances (Oseen-type hydrodynamic interaction), finding that a term that belongs to the zeroth-order contribution is missing in the usual description. This term is simply proportional to the total volume of the bead model. The nature of this correction for viscosity is similar to a previously described correction for rotational coefficients. We discuss the performance of these corrections for various simple models, including ellipsoids as well as oligomeric structures in rodlike, chainlike and polyhedral conformations.