(236c) Hindered Transport Of Macromolecules

It is well known that the diffusivities of solutes in liquid-filled pores of molecular dimensions decrease rapidly with increases in molecular size. Likewise, sieving in filtration processes is based largely on the size-selectivity of the membrane. For solute molecules that are large enough to act as hydrodynamic particles (such as proteins), the hindrances to diffusive or convective transport can be explained by a combination of particle-wall hydrodynamic interactions and steric restrictions. Although less well studied, there are many instances in which diffusion or sieving in biological or synthetic membranes is affected also by molecular charge. For solutes and pores of like charge, diffusional permeabilities and sieving coefficients are typically reduced and reflection coefficients are increased, sometimes markedly. The strengths and limitations of existing theories for hindered transport will be discussed, including their application to biological and biomimetic materials.