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Multicomponent protein adsorption in supported cationic polyacrylamide hydrogels



Partitioning and transport of proteins in charged polyacrylamide gels were studied for single and two-component protein mixtures. The gels were synthesized within fused-silica capillaries allowing a direct microscopic determination of concentration profiles in the gel during adsorption and desorption of fluorescently labeled proteins. α-lactalbumin, ovalbumin, and BSA were used as model proteins spanning molecular masses between 15 and 65 kDa. The proteins were conjugated to green and red rhodamine fluorescent labels, allowing simultaneous and independent determinations of two proteins during binary adsorption. The proteins were found to be favorably but reversibly partitioned into the gel and could be eluted at high salt concentrations. The transient concentration profiles were found to be consistent with a Fickian diffusion model with a driving force based on the adsorbed phase concentration gradient. The diffusivity and adsorption capacity of the proteins determined from the microscopic data compared favorably to results previously obtained from macroscopic studies of Q-HyperD, a gel-filled particle chemically similar to the gels synthesized in this work. Coadsorption and sequential adsorption experiments also resulted in diffuse concentration profiles indicating that the underlying transport mechanism is the same as for single component transport. The diffusion model was extended to predict the two-component cases. Predictions were reasonably accurate for co-adsorption, but gave rates higher than seen experimentally for sequential adsorption, probably as a result of diffusion flux coupling or other nonidealities. © 2005 American Institute of Chemical Engineers AIChE J, 2005