pH-Dependent Immobilization of Proteins on Surfaces Functionalized by Plasma-Enhanced Chemical Vapor Deposition of Poly(acrylic acid)- and Poly(ethylene oxide)-like Films

Abstract

The interaction of the proteins bovine serum albumin (BSA), lysozyme (Lys), lactoferrin (Lf), and fibronectin (Fn) with surfaces of protein-resistant poly(ethylene oxide) (PEO) and protein-adsorbing poly(acrylic acid) (PAA) fabricated by plasma-enhanced chemical vapor deposition has been studied with quartz crystal microbalance with dissipation monitoring (QCM-D). We focus on several parameters which are crucial for protein adsorption, i.e., the isoelectric point (pI) of the proteins, the pH of the solution, and the charge density of the sorbent surfaces, with the zeta-potential as a measure for the latter. The measurements reveal adsorption stages characterized by different segments in the plots of the dissipation vs frequency change. PEO remains protein-repellent for BSA, Lys, and Lf at pH 4-8.5, while weak adsorption of Fn was observed. On PAA, different stages of protein adsorption processes could be distinguished under most experimental conditions. BSA, Lys, Lf, and Fn generally exhibit a rapid initial adsorption phase on PAA, often followed by slower processes. The evaluation of the adsorption kinetics also reveals different adsorption stages, whereas the number of these stages does not always correspond to the structurally different phases as revealed by the D- f plots. The results presented here, together with information obtained in previous studies by other groups on the properties of these proteins and their interaction with surfaces, allow us to develop an adsorption scenario for each of these proteins, which takes into account electrostatic protein-surface and protein-protein interaction, but also the pH-dependent properties of the proteins, such as shape and exposure of specific domains.

Molecular evidence of stereo-specific lactoferrin dimers in solution

“…At these pH values the LF net charge is +23e, +14e and +4e. Titration simulations estimate pI to 9.4, slightly above the experimental range, 8-9 [17,18,19]. At pH 5 the interaction is purely repulsive due to a large net charge of the proteins.…”

Ultralow Friction of a Tetrahedral Amorphous Carbon Film Lubricated with an Environmentally Friendly Ester-Based Oil

“…To take into account the effects of the viscoelastic properties of the adsorbed layer, ∆D is plotted against ∆f in Fig. 9 to eliminate time as an explicit parameter and to obtain additional information on the adsorption processes through an analysis of the slope, ∂D/∂f, which indicates that an increase in the viscosity or thickness of the adsorbed layers [15]. In the initial phase, the ∆D-∆f plots for all based oils show the same linear slope.…”

Filmes ultrafinos de ésteres de celulose: preparo, caracterização e imobilização de proteínas

“…Os valores de G LIS determinados para o poliânion poli(ácido acrílico), PAA, são da mesma ordem de grandeza daqueles encontrados para CMCAB. 31 Além disso, ocorrem interações hidrofóbicas entre resíduos hidrofóbicos de LIS e os radicais butila. Por outro lado, o pI da BSA 32 é geralmente dado como uma faixa de 4,7 a 4,9.…”

“…Porém, a presença do grupo carboximetil (CM) no CM-CAB provavelmente intensifica as interações do tipo dipolo-dipolo ou ligações de hidrogênio com a proteína. A adsorção de BSA sobre filmes de PAA é uma ordem de grandeza menor que aquela observada sobre CAB ou CMCAB, 31 indicando que a adsorção sobre os ésteres de celulose é provavelmente dirigida por interações hidrofóbicas.…”