Sorption of Proteins by Slightly Cross-Linked Polyelectrolyte Hydrogels:  Kinetics and Mechanism

Abstract

Sorption of proteins such as cytochrome c, lysozyme or protamine by slightly cross-linked poly(acrylic acid) and bovine serum albumin by slightly cross-linked poly(N,N-dimethyl-N-ethylaminoethyl methacrylate bromide) hydrogels in salt-free and saline aqueous solutions was studied. The polyanionic hydrogel uptakes the proteins at pH below their isoelectric points while polycationic one at pH above them. As a result highly swollen original hydrogel transforms into relatively compact cross-linked polyelectrolyte-protein complex. Sorption of proteins by slightly cross-linked polyelectrolyte hydrogels is a chemically drawn diffusion process. The driving force of the process comes from the gain in the free energy of the interpolyelectrolyte coupling reaction between the protein and oppositely charged segments of the polyelectrolyte network. Apparently the mechanism of protein uptake is similar to that earlier proposed for linear polyelectrolytes. It involves a "relay-race" transfer of protein molecules from one fragment of polyelectrolyte network to the other without radial mixing via interpolyelectrolyte exchange reaction. As a result "core-shell" constructs consisting of an outer weakly swollen complex shell and a highly swollen hydrogel core are formed at intermediate stages of the process. The rate of sorption is determined by the rate of the interpolyelectrolyte exchange reaction, that is the rate of the formation of free fragments of polyelectrolyte network (vacancies) on the inner complex-hydrogel boundary. The amount of vacancies depends on the area of this boundary. Kinetic curves of protein sorption by hydrogels in neutral salt-free solutions could not be fitted under the terms of Fickian diffusion but can be expressed in terms of the kinetic equation derived for a frontal heterogeneous reaction. At the same time kinetics of protein sorption obeys to Fick's diffusion law when the salt concentration increased.

Characterization of Insulin Adsorption Behavior on Amphoteric Charged Membranes

“…One possible reason for the non-Fickian behavior is the reaction between insulin and the charge groups of the grafted polyelectrolyte chains when insulin and the membrane carried opposite charge. Such reaction changed the structure of the interface between the membrane and solution 31 or the charge properties of the membranes, which makes the interfacial diffusion of insulin from the solution to the membrane become important in the insulin adsorption. As a consequence, insulin adsorption behavior changed with the adsorbed amount.…”

A Macrophage−Nanozyme Delivery System for Parkinson's Disease

“…Therefore, it is crucial to protect the activity of the enzyme inside of the cell-carrier. Incorporation into polymeric nanocarries (nanospheres, liposomes, micelles, nanoparticles) can provide such protection (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60) (61)(62)(63). The enzyme polyelectrolyte complexes can be prepared at the nanoscale by self-assembly of enzymes with oppositely charged block polyelectrolytes containing ionic and nonionic water soluble blocks (64,65).…”

Nanogele als pharmazeutische Trägersysteme: winzige Netzwerke mit großen Möglichkeiten

“…Können die Biomakromoleküle das Nanogel durchdringen, wandert die zunächst oberflächlich gebildete Front von ionischen Komplexen zwischen den Polymerketten in den Kern des Gels. [84] Durch diesen Effekt können auch deutlich größere Polyelektrolytnetzwerke effizient mit Biomakromolekülen beladen werden (Abbildung 6). [85] Dieses Prinzip wurde genutzt, um Polynucleotide in kationischen Nanogelen zu immobilisieren.…”