Hindered Convection of Ficoll and Proteins in Agarose Gels

Abstract

The hindered convection of rigid macromolecules in hydrogels was studied by measuring the sieving coefficient (Θ, the ratio of filtrate concentration to retentate concentration) of various sizes of Ficoll for agarose membranes of varying concentrations. Samples of filtrate and retentate were fractionated by size-exclusion chromatography to obtain results for Ficolls with specific Stokes-Einstein radii (r S ) ranging from 3.0 to 7.0 nm, and the volume fraction of agarose (o) was varied from 0.04 to 0.08. Immunoglobulin G (IgG, r S = 5.2 nm) was also employed as a test solute. The values of Θ decreased with increasing r S or increasing o, as expected. That is, transport was increasingly hindered as steric solute-gel interactions became more prominent. The sieving coefficient for Ficoll was very similar to that for IgG of the same r S , as well as that for other globular proteins studied previously, indicating that molecular shape and charge were not important variables. The calculated values of the convective hindrance factor (K c , the ratio of solute velocity to fluid velocity) tended to increase above unity and then to decrease toward zero as r S was increased, a trend that is qualitatively consistent with predictions from a previously reported theory for the hindered convection of rigid spheres through regular arrays of parallel fibers.