Preparation and characterization of a dye–ligand adsorbent for lysozyme adsorption

Dye–ligand macroreticular poly(styrene-co-divinylbenzene) microparticles with different pore properties have been obtained and used as adsorbents of proteins. To do so, plain microparticles were first coated with poly(vinyl alcohol) to shield the hydrophobic polymer surface from non-specifically adsorbing protein. The poly(vinyl alcohol) coating was then chemically cross-linked with glutaraldehyde to obtain a stable layer. Following this, Cibacron Blue F3GA, which was chosen as the dye affinity ligand, was immobilized on these microparticles to obtain specific protein adsorption. After each modification step, the pore size distributions of the microparticles were determined, observing that the adsorption of poly(vinyl alcohol) clogged micropores and low-interval mesopores, and that only microparticles with a high pore volume, basically due to high-interval mesopores and macropores, largely continued to exhibit these pores. The batch adsorption properties of the functionalized microparticles were studied using lysozyme as a model protein, observing that the existence of high-interval mesopores and macropores was essential in the adsorption of the protein. In fact, it was only possible to evaluate the adsorption characteristics in the case of microparticles that largely continued to display this kind of pores after their functionalization. Adsorption equilibrium was found to be described well by the Sips model, with a maximum adsorption capacity of 100.8 mg g−1 dry adsorbent. With regard to adsorption kinetics, both pore-diffusion and solid-diffusion models were used to estimate the diffusion coefficients, with the observation that the simplified solid-diffusion model was reliable for describing the experimental kinetic data, with a diffusion coefficient of 1.4 × 10−9 cm2 s−1. The non-specific adsorption of lysozyme on the functionalized microparticles was found to be 2.6 mg g−1 dry adsorbent. Finally, regarding desorption of the protein, it was observed that more than 73% of the lysozyme adsorbed was readily desorbed in a desorption medium containing 1.0 mol L−1 NaCl at pH 7.3.