tion-desorption isotherm hysteresis (8). A study of the in-Thermally stimulated depolarization spectra of frozen aqueous teraction between proteins and highly disperse silicas is also suspensions of fumed silica show a dependence of relaxation proof interest because these oxides are used as sorbents and cesses on the concentration of silica (C SiO 2 ) due to a change in the supports for drugs immobilized for therapy purposes (9, 10).
particle-particle interaction (their electrical double layers) and
Proteins can also be considered as models of some toxins, the concentration of bulk water (ice) with increasing C SiO 2 . A which can be strongly adsorbed by fumed silica as an enterosignificant fraction of agglomerates of primary particle aggregates sorbent. Further, mineral particles containing such silicas as are not decomposed in aqueous suspensions of fumed silica. The asbestos aerosols can take part in the oxidation of proteins, thickness of an interfacial water layer perturbed by the silica sur-DNA, etc., and the active sites of the silica phase play an face or protein molecules was estimated from the dependence of 1 H NMR signal intensity of unfrozen water on temperature below important role in these reactions (9b).
273 K, separating the signals of water molecules weakly and
The primary particles of fumed silica synthesized at high strongly bound to the surface. Protein molecules adsorbed on temperature (diameter of ca. 10 nm) form aggregates (ca. fumed silica aggregates form hydrogen bonds with GSiOH or 200 nm) by siloxane bonds via coalescence of these hot GSiO 0 groups by amino groups, e.g., H / NR from the zwitterion particles; thereupon agglomerates (above 2 mm) of hydrofragments. Aqueous suspensions of mechanochemically activated gen-bonded aggregates cooled to ambient temperature are fumed silica do not lose protein adsorption ability during a long formed in air (11,12). In aqueous suspensions of fumed period in which the particles remain as microscaled agglomerates.
silica, these agglomerates can be partially or completely de-According to AM1-SM1 calculations, complexes such as composed due to interactions between water molecules and GSiO(H)rrrH / NRCOO 0 are stabilized in aqueous suspensions hydrophilic silica surfaces (11-15). Fumed silica in aqueof silica and the protein desorption rate decreases with increasing molecular weight of proteins. α§ 1997 Academic Press ous suspensions possesses a high adsorption ability for pro-Key Words: fumed silica; aqueous suspension; TSD; protein adteins (10) and their interaction can change both the structure sorption; 1 H NMR; AM1-SM1 calculations.
of the electrical double layer (EDL) of the silica particles or biopolymer molecules and the suspension stability (16, 17). The active sites on hydrophilic oxide surfaces form 166