Ultracentrifugation Studies of Polyelectrolytes in Polyglucose Density Gradient

An ideal solute for density gradient ultracentrifugation of polymers in aqueous solution should be inert and readily soluble in water to form an extended range of solution densities of low viscosity. High molecular weight is an added attraction because osmotic effects are minimized. Highly branched spherical synthetic polysaccharides fulfill these requirements. High degree of branching is a consequence of the condensation of polyfunctional monomers. Density and relative viscosity of solutions of polyglucose, sucrose, and of a natural sucrose polymer, Ficoll, are compared. The behavior of various polyelectrolytes was studied in low viscosity polyglucose density gradients in equilibrium buoyant density measurement in the ultra-centrifuge. Macromolecules or macromolecular complexes attain low apparent equilibrium buoyant density, probably because of an excluded volume effect of the solute. This allows sedimentation to isopycnic position of complex biopolymers in inert polyglucose solutions, which otherwise can be attempted only in concentrated solutions of heavy salts (such as CsCI or Cs₂SO₄). Such salts, however, may salt out, or through osmotic effects degrade or alter the properties of certain biologic macromolecular complexes.