Aqueous Suspensions of Fumed Silica and Adsorption of Proteins

Thermally stimulated depolarization spectra of frozen aqueous suspensions of fumed silica show a dependence of relaxation processes on the concentration of silica (CSiO2) due to a change in the particle–particle interaction (their electrical double layers) and the concentration of bulk water (ice) with increasingCSiO2. A significant fraction of agglomerates of primary particle aggregates are not decomposed in aqueous suspensions of fumed silica. The thickness of an interfacial water layer perturbed by the silica surface or protein molecules was estimated from the dependence of1H NMR signal intensity of unfrozen water on temperature below 273 K, separating the signals of water molecules weakly and strongly bound to the surface. Protein molecules adsorbed on fumed silica aggregates form hydrogen bonds with ≡SiOH or ≡SiO−groups by amino groups, e.g., H+NR from the zwitterion fragments. Aqueous suspensions of mechanochemically activated fumed silica do not lose protein adsorption ability during a long period in which the particles remain as microscaled agglomerates. According to AM1–SM1 calculations, complexes such as ≡SiO(H)···H+NRCOO−are stabilized in aqueous suspensions of silica and the protein desorption rate decreases with increasing molecular weight of proteins.