INTRINSIC-VISCOSITY AND ROTATIONAL DIFFUSION OF BEAD MODELS FOR RIGIDMACROMOLECULES AND BIOPARTICLES

The conventional Kirkwood-Riseman (K-R) treatment of the intrinsic vis cosity of macromolecular bead models shows a deficiency when it is app lied to models with few beads, whose sizes are not much smaller than o f the modelled particle. We present a complete derivation of the intri nsic viscosity up to first order in interbead distances (Oseen-type hy drodynamic interaction), finding that a term that belongs to the zerot h-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 con formations.