Hydrophobic resins, protein adsorption

Initial solid phase synthesis25 was carried out on Merrifield s resin (1 % crosslinked chloromethylated styrene/divinylbenzene copolymer, 200-400 mesh) because of its track record in solid-phase peptide synthesis.26 Unfortunately, the Merrifield resin has limitations as a carbohydrate carrier to study interactions between the carbohydrates and relevant binding proteins. The hydrophobic nature of the resin leads to nonspecific, irreversible protein adsorption.27 Later work utilized Rapp s TentaGel, an amphiphilic, polyethylene glycol resin.28... 

More recently, Fernandez et al. carried out a series of studies on the conformation and dynamics of proteins adsorbed onto hydrophobic resins used in hydrophobic interaction chromatography (HIC), with the objective of understanding whether protein adsorption would compromise protein recovery. 

Polymeric reversed phase resins are synthesized from divinylbenzene with styrene, methylstyrene or other styrenic monomers. Divinylbenzene is the major component and provides crosslinking. These resins are macroporous, and the surface area is usually in excess of 300 m2 / g. This surface area provides the adsorptive surface for retention of hydrophobic species. These resins can be used for matrix elimination of surfactants, weak carboxylic acids, fats, proteins, etc. 

Adsorption of enzymes to various polymeric resins is a straightforward means for immobilization. Zwitterionic molecules such as proteins can bind to both anionic and cationic ion exchange resins. Hydrophobic macroporous resins are also useful for immobilizing many enzymes, particularly lipases. For example, an immobilized form of Candida antarctica lipase B (CAL-B) on acrylic resin has been sold for many years under the name, Novozym 435 (N435). The enzyme is produced in a modified Aspergillus organism by submerged fermentation and is subsequently adsorbed onto a macroporous... 

One of the characteristics of affinity chromatography is that the rate of adsorption of a protein to a ligand on a resin tends to be a rate-limiting step. This is in sharp contrast to ion exchange or hydrophobic interaction chromatography, where the adsorption step can be considered to be essentially at equilibrium, and interparticle and intraparticle diffusion dominate the overall rate of adsorption. 

There are two major reasons for modification of pore surfaces in some polymeric resins (1) hydrophiiization of hydrophobic surfaces and (2) an increase in loading capacity and kinetics of ion-exchange resins. The former is typical of styrene-divinylbenzene copolymers that are too hydrophobic to be used directly for the separation of biopolymers in some modes. In this case, hydrophilic polymers such as dextran, poly(oxyethylene), poly(ethylene imine), and poly-(vinyl alcohol) are adsorbed and cross-linked on [35,43] or covalently linked to the pore surface to form a thin biopolymer friendly barrier on the hydrophobic surface. Regnier [44] was one of the first to develop a covalently attached hydrophilic coating that substantially decreased the nonspecific irreversible adsorption of proteins. 

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