Increased Protein Sorption in Poly(acrylic acid)-Containing Films through Incorporation of Comb-Like Polymers and Film Adsorption at Low pH and High Ionic Strength

Abstract

In principle, incorporation of comb-like block copolymers in multilayer polyelectrolyte films can both increase film thickness relative to coatings containing linear polymers and provide more swollen films for increased sorption of proteins. In the absence of added salt, alternating adsorption of 5 bilayers of protonated poly(allylamine) (PAH) and comb-like poly(2-hydroxyethyl methacrylate)-graft-poly(acrylic acid) (PHEMA-g-PAA) leads to ∼2-fold thicker coatings than adsorption of PAH and linear PAA, and the difference in the thicknesses of the two coatings increases with the number of bilayers. Moreover, the (PAH/PHEMA-g-PAA)n films sorb 2- to 4-fold more protein than corresponding films prepared with linear PAA, and coatings deposited at pH 3.0 sorb more protein than coatings adsorbed at pH 5.0, 7.0, or 9.0. In fact changes in deposition pH and addition of 0.5 M NaCl to polyelectrolyte adsorption solutions alter protein sorption more dramatically than variations in the constituent polymer architecture. When deposited from 0.5 M NaCl at pH 3, both (PAH/PHEMA-g-PAA)5 and (PAH/PAA)5 films increase in thickness more than 400% upon adsorption of lysozyme. These films contain a high concentration of free –COOH groups, and subsequent deprotonation of these groups at neutral pH likely contributes to increased protein binding. Lysozyme sorption stabilizes these films, as without lysozyme films deposited at pH 3 from 0.5 M NaCl desorb at neutral pH. Films deposited at pH 9 from 0.5 M NaCl are more stable and also bind large amounts of lysozyme. The high binding capacities of these films make them attractive for potential applications in protein isolation or immobilization of enzymes.

The architecture of responsive polymeric ligands on protein binding and recovery

“…13,19 Comb-like polymer architecture has been shown to increase the number of binding sites leading to an improved capacity for protein binding. 20,21 Recently, dendritic butyl HIC ligands immobilized on resins were shown to improve graing density and capacity. 22 However, only two branching degrees of the dendritic ligands were investigated in their study.…”

Formation of High-Capacity Protein-Adsorbing Membranes through Simple Adsorption of Poly(acrylic acid)-Containing Films at Low pH

“…27–34 Additionally, our recent work shows that deposition of (PAH/PAA) n films at pH 3 rather than pH 5 leads to a ~6-fold increase in lysozyme adsorption. 35 Thus we thought that in membranes, PAH/PAA adsorption at low pH would give a high density of free –COOH groups that bind cationic proteins through ion-exchange interactions. (By free, we mean that the –COOH groups are not deprotonated and ion-paired with neighboring ammonium groups of PAH during deposition.)…”

Functionalizing Microporous Membranes for Protein Purification and Protein Digestion

“…Fortunately, film thickness and swelling, and consequently the extent of protein capture, vary greatly with polyelectrolyte composition and deposition conditions (35)(36)(37)(38)(39)(40)(41). Ma and coworkers (42) increased lysozyme adsorption approximately sixfold in poly(allylamine)/poly(acrylic acid) (PAA) multilayer films by lowering the pH of deposition solutions from 5 to 3. Addition of acid to deposition solutions protonates most of the -COOH groups of PAA, but during binding at neutral pH, deprotonation of these -COOH groups yields highly ionized films that swell and capture positively charged lysozyme.…”