Effect of modification of alumina surfaces by ozone on adsorption behavior of bovine serum albumin at alumina-water interfaces

Abstract

The relationship between the surface properties of aluminum oxide (Al 2O 3) after ozone exposure and the adsorption behavior of bovine serum albumin (BSA) at Al 2O 3-water interfaces was studied at the isoelectric point (IEP) of BSA. Al 2O 3 particles were exposed to ozone generated from oxygen or dry air at various concentrations of 50 to 1,000 ppm. Isotherms for BSA adsorption onto ozonized oxygen- and ozonized air-exposed Al 2O 3, which showed good fits to the Langmuir equation, had gentler initial slopes and lower saturation values ( Γ s) than the isotherm for adsorption onto native Al 2O 3. The desorption rate of preadsorbed BSA during alkali cleaning was highest for ozonized air-exposed Al 2O 3 followed by ozonized oxygen-exposed and native Al 2O 3. X-ray photoelectron spectroscopic analysis showed no significant differences in the states of aluminum-oxygen chemical bonds at the outermost surfaces of Al 2O 3 before and after ozone exposure. The adsorption affinity of water vapor for Al 2O 3 surfaces decreased slightly as a result of their exposure to ozonized oxygen, but increased when the surfaces were exposed to ozonized air. The IEP of Al 2O 3 was shifted to the acidic side by exposure to both the ozonized gases. The extent of the decrease in the affinity of BSA adsorption and of the shift in the IEP increased with increasing ozone concentration, and were much greater for ozonized air-exposed Al 2O 3. The difference in the effects of ozone exposure was interpreted as arising from the formation of nitrate groups on the ozonized air-exposed Al 2O 3 surfaces, derived from nitrogen oxides in ozonized air. The value of Γ s was found to be correlated with the surface charge densities of Al 2O 3 after ozone exposure. It was concluded that the lower adsorption affinity of BSA for Al 2O 3 surfaces was attributed to the decrease in the density of hydroxyl groups by the oxidative action of ozone, and to the formation of nitrate groups on Al 2O 3 surfaces induced by the synergistic actions of ozone and nitrogen oxides.