Grafting Poly(ethylene glycol) Epoxide to Amino-Derivatized Quartz:  Effect of Temperature and pH on Grafting Density

Abstract

Microparticle capillary electrophoresis was used to characterize the surface of quartz capillaries grafted with the glycidyl ether of poly(ethylene glycol) (E-PEG). Site dissociation modeling of capillary electrokinetic behavior provided estimates of surface group pK and density, plus the distance (d) from the surface to the hydrodynamic plane of shear. Native quartz appeared to possess silanol groups of pK 3.6 and 6.9 whose surface densities varied with quartz treatment. Aminopropylsilane derivatization of quartz silanol groups in toluene yielded a coating which was stable (>6 h) at pH 10.3 and 60 °C. Aqueous grafting of E-PEG to this surface was relatively independent of pH (7.3-10.3) and reaction time (6-24 h) but was significantly influenced by reaction temperature (25-95 °C) and salt composition. PEG-grafted capillaries exhibited greatly reduced electroosmosis from pH 2 to 11. Significant grafting could be obtained under mild conditions (6 h, 35 °C, 0.4 M K(2)SO(4), pH 6.9). These results suggest that PEG chains increasingly extend normal to a surface as their grafting density increases, and that PEG conformation influences grafting density. The methods described should aid the use of PEG-coated surfaces in a variety of applications.

PEG conjugation moderately protects adeno-associated viral vectors against antibody neutralization

“…The molecular basis of the protein repellant properties of PEG is reportedly attributed to a number of different interactions: steric repulsion due to the polymer chain, repulsion due to the presence of a hydration shell around the polymer chain, and/or electrostatic repulsion stemming from the polar monomeric units (Chapman et al, 2000;Harris and Zalipsky, 1997;Lee and Schaffer, 2003). For protein PEGylation, various types of crosslinking chemistry have been evaluated (Emoto et al, 1996;Kingshott et al, 2002;Roberts et al, 2002;Veronese, 2001;Veronese and Harris, 2002). In addition, PEGylation of therapeutic proteins such as interferon and tumor necrosis factor has been demonstrated to improve their pharmacokinetic profiles (Bailon et al, 2001;Kozlowski and Harris, 2001;Tsunoda et al, 1999;Yoshioka et al, 2004).…”

Characterization of Grafted Poly(ethylene glycol) on Si Wafers Using Scanning Probe Microscopy

“…The wafers were coated with 3-aminopropyltriethoxysilane (APTS) and heat cured at 190°C following hydrothermal treatment as described in detail elsewhere (8). A wafer cleaned and coated with APTS but not hydrothermally treated prior to heat curing was also prepared.…”

“…A wafer cleaned and coated with APTS but not hydrothermally treated prior to heat curing was also prepared. Monomethoxy-PEG-epoxide of M r 5000 (E-PEG 5000) (Shearwater Polymers) was grafted to the APTS-activated, hydrothermally treated, heat-cured surfaces by immersion of the samples for 6 h in a 10% (w/v) polymer solution in 0.45 M K 2 SO 4 at 30, 40, and 80°C so as to generate coatings of increasing PEG surface density (7,8). The coated surfaces were rinsed scrupulously after reaction and stored in doubly distilled and filtered water that had been purged of dissolved oxygen.…”

“…The density and uniformity of the coating are important for many applications. For these reasons, PEG coatings have been the focus of numerous studies, including theoretical modeling (2, 3) and experimental observations using techniques such as surface force analysis (4,5), X-ray photoelectron spectroscopy (6), electrophoresis (7,8), and ellipsometry (9). One technique which promises direct observation of microscale and molecular scale properties of PEG bound to surfaces is scanning probe microscopy (SPM) (10 -12) (also known as atomic force microscopy, AFM).…”

“…In the present note, we report what are believed to be the first in situ topographical images obtained with SPM in aqueous and organic solvents of PEG coatings prepared at different grafting densities. Studies are ongoing to evaluate these results and others against a background of measurements made on identical PEG coatings using a wider range of techniques (7)(8)(9).…”