John Charkoudian

Transport of proteins through gel-filled porous membranes

Abstract Membranes with a mean pore diameter of 0.5 μm were filled with neutral polyacrylamide (PA) gels at fixed crosslink density. The gel was synthesized in the membranes by impregnating the pores with a solution of monomer and crosslinker and then initiating polymerization by ultraviolet radiation. The rate of diffusion and convection (ultrafiltration) of two proteins, ribonuclease A (RNAse) and bovine serum albumin (BSA), was measured as a function of the amount of gel in the pores expressed as the volume fraction (φ) occupied by the polymer forming the gel network. The diffusion rate of potassium chloride (KCl) and glucose was also measured to determine the effects of the gel on small molecules. The effective diffusion coefficient (Deff), normalized by the diffusion coefficient in bulk solution (Do), and the reflection coefficient (σ) were correlated with the parameter ( a s a f )φ where as is the Stokes-Einstein radius of the solute molecule and af is the radius of the PA chains (6 A) forming the gel network inside the pores. Both D eff D o and 1-σ decreased sharply as ( a s a f )φ approached the value 0.6. The gel had only a small effect on the diffusion of KCl and glucose. From the experimental results we conclude that gel-filled porous membranes can be fabricated with no significant defects and excellent selectivity based on molecular size.

Membrane surface for carbohydrate analysis

Abstract A poly(methyldiallylamine-chlorohydrin) polymer was used to surface modify microporous PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and UPE (ultra high molecular weight polyethylene) membranes. These membranes were used to covalently bond hydrophilic charged carbohydrate molecules. The surfaces were characterized in terms of the structural variations of the monomer units. Immobilization occurs by a two-step process whereby strong imagewise electrostatic forces bring nucleophile (charged carbohydrate conjugate) and electrophile (membrane surface desorptive media groups) into close proximity for a pH triggered reaction to covalently bond the carbohydrate. The immobilization potential of the surfaces is described by the chlorohydrin and epoxy groups available for reaction, and is inversely proportional to the amount of alkali employed during membrane surface modification. Conjugation of complex carbohydrate mixtures to a charged fluorophore, followed by electrophoresis, transfer t...