Electrophoresis in Polymer Solutions: Mechanisms of Molecular Sieving

Passsage of rigid, “spherical” proteins in the range of 2−5 nm radius, R (40−500 kDa molecular weight), through semidilute solutions of a representative polymer, polyethylene glycol in the molecular weight range of (0.6−8) × 10 6, gives rise to a size dependent retardation (“molecular sieving”) analogous to that in a porous network composed of random planes. The average distance between those planes being equal to the screening length, ξ, the retardation can be described by log(μ/μ 0 ) = −( ARc 0.75 ) where A is a constant dependent on solvent and type of monomer and c is the polymer concentration.