Grafted block complex coacervate core micelles and their effect on protein adsorption on silica and polystyrene

We have studied the formation and the stability of grafted block complex coacervate core micelles (C3Ms) in solution and the influence of grafted block C3M coatings on the adsorption of the proteins β-lactoglobulin, bovine serum albumin, and lysozyme. The C3Ms consist of a grafted block copolymer PAA21-b-PAPEO14 (poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylene oxide)), with a negatively charged PAA block and a neutral PAPEO block and a positively charged homopolymer P2MVPI (poly(N-methyl 2-vinyl pyridinium iodide). In solution, these C3Ms partly disintegrate at salt concentrations between 50 and 100 mM NaCl. Adsorption of C3Ms and proteins has been studied with fixed-angle optical reflectometry, at salt concentrations ranging from 1 to 100 mM NaCl. In comparison with the adsorption of PAA21-b-PAPEO14 alone adsorption of C3Ms significantly increases the amount of PAA21-b-PAPEO14 on the surface. This results in a higher surface density of PEO chains. The stability of the C3M coatings and their influence on protein adsorption are determined by the composition and the stability of the C3Ms in solution. A C3M-PAPEO14/P2MVPI43 coating strongly suppresses the adsorption of all proteins on silica and polystyrene. The reduction of protein adsorption is the highest at 100 mM NaCl (>90%). The adsorbed C3M-PAPEO14/P2MVPI43 layer is partly removed from the surface upon exposure to an excess of β-lactoglobulin solution, due to formation of soluble aggregates consisting of β-lactoglobulin and P2MVPI43. In contrast, C3M-PAPEO14/P2MVPI228 which has a fivefold longer cationic block enhances adsorption of the negatively charged proteins on both surfaces at salt concentrations above 1 mM NaCl. A single PAA21-b-PAPEO14 layer causes only a moderate reduction of protein adsorption

Effect of pore size on adsorption of a polyelectrolyte to porous glass

The adsorption of quaternized poly(vinylpyridine) (QPVP) on controlled pore glass (CPG) size, over the ionic strength range 0.001-0.5 M was found to display nonmonotonic behavior as a function of pore size. Both adsorption kinetics and ionic strength effects deviated dramatically from behavior typical of adsorption on flat surfaces when the ratio of the pore radius Rp to the polymer hydrodynamic radius Rh became smaller than ca. 2. Ionic strength enhancement of adsorption for small pore sizes was observed at much higher salt concentrations than is typical for polycation adsorption on flat surfaces. The amount of polymer adsorbed per unit surface area of glass GA, in 0.5 M NaCl, exhibited a shallow maximum at Rp/Rh ˜ 5. Since the value of GA for small pore size CPG is strongly depressed by the large surface area, an alternative and more interesting observation is that the amount of polymer adsorbed per gram of CPG, Gw, displays a strong maximum when Rp is equal to or slightly smaller than Rh. The efficiency with which QPVP binds anionic micelles to (negatively charged) CPG (grams of surfactant/grams of QPVP) increases strongly with diminishing pore size, indicating that the configuration of polycation bound to small pores favors micelle binding. Since the micelles are larger than small pores, the results indicate that when Rp <Rh, adsorbed polycation molecules reside only partially within the pore. The results of this study are supported by simulations of polyelectrolytes within cylindrical cavitie

Heterogeneity of polyelectrolyte diffusion in polyelectrolyte-protein coacervates: A H-1 pulsed field gradient NMR study

Proton pulsed field gradient (PFG) NMR was used to study the diffusion of poly(diallyldimethylammonium chloride) (PDADMAC) in coacervates formed from this polycation and the protein bovine serum albumin (BSA). Application of high (up to 30 T/m) magnetic field gradients in PFG NMR measurements allowed probing the diffusion of PDADMAC on a length scale of displacements as small as 100 nm in coacervates formed at different pH's and ionic strengths, i.e., conditions of varying protein-polycation interaction energy. Studies were carried out for a broad range of diffusion times and corresponding values of the mean square displacements. Several ensembles of PDADMAC polycations with different diffusivities were observed in the measured range of diffusion times. The existence of these ensembles and the pattern of their changes with increasing diffusion time support the hypothesis about the microscopic heterogeneity of PDADMAC-BSA coacervates and also provide evidence for the dynamic disintegration and reformation of dense domains