ABSTRACT
The adsorption of gossypol, a toxic pigment and the major colorant in cottonseed oil, has been studied, using silicas and aluminas of different surface areas and pore size distributions. Gossypol has a high affinity for alumina surface, the adsorption isotherm follows the Langmuir equation, and the maximum amount adsorbed is compatible with a monolayer of molecules on the surface; this is indicative of chemisorption. The affinity for a silica surface is much lower and the adsorption isotherm follows the Freundlich equation. The amount adsorbed is also influenced by the pore size distribution, the useful surface area being that developed by pores larger than 3 nm, i.e., 2 to 3 times the size of the adsorbate. Copyright 2000 Academic Press.
ABSTRACT
The surface properties of patterned surfaces made by a combination of photolithography and oxygen plasma treatment of polystyrene (PS) were investigated. PS and plasma-treated PS (PSox) were first characterized using X-ray photoelectron spectroscopy and the study of wetting dynamics (Wilhelmy plate method) in water and in solutions of different pH. The results indicated that the PSox surface may be viewed as covered with a polyelectrolyte-like gel, which swells depending on pH. It was then shown, using atomic force microscopy (AFM), that the adhesion force measured on PS with a silicon tip in water was higher compared with that measured on PSox. This feature allowed imaging of the oxidation patterns using the adhesion mapping mode. The origin of the pulloff force contrast, which could not be explained by combining Johnson-Kendall-Roberts theory and thermodynamic considerations, was attributed to repulsion between the tip and hydrated polymer chains present on the oxidized surface. Imaging was also performed in the lateral force mode, a higher friction being recorded on PS than on PSox. Copyright 1999 Academic Press.
ABSTRACT
The adsorption of catalase on calcium hydroxyapatite is reported in this study. In all the solutions investigated, catalase adsorption takes place under conditions where the adsorbent and the adorbate are both negatively charged and is accompanied by the release of phosphate ions. This suggests that electrostatic attraction does not play a leading role in the adsorption process. However, electrostatic repulsion does play a role as evidenced by the influence of the solution composition on the maximum amount adsorbed. In fact, the amount adsorbed increases when the surface charge tends to be less negative (decrease of pH and phosphate concentration, presence of calcium) or when the electrical charges are screened as a result of the ionic strength increase. This was confirmed by the electrophoretic mobility which becomes more negative after protein adsorption. The rate of catalase adsorption is extremely low; the time required to reach a stationary concentration is 60 and 125 h in potassium nitrate and phosphate solution, respectively. The reversibility of catalase was examined with respect to changes in the bulk solution concentration. No significant desorption was obtained after several days of observation. The adsorption, desorption, and kinetic aspects have been discussed in relation to changes in the the protein structure upon interaction and to the microstructural characteristics of the mineral. Copyright 1998 Academic Press.
ABSTRACT
The influence of Pluronic F68 [a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer surfactant], serum albumin (HSA), and fetal calf serum (FCS) on the adsorption of type I collagen by polymer substrates was investigated using radiolabeling and XPS analysis. Three different kinds of polystyrene substrates with increasing level of hydrophobicity were used. Change in the state of hydration of the sorbent and protein surfaces appears to be the main driving force for collagen adsorption. Pluronic F68 strongly reduces collagen adsorption, the reduction being more pronounced with higher substrate hydrophobicity. This explains why epithelial cell adhesion on substrates preconditioned with a solution of Pluronic F68 and collagen is strongly influenced by substrate hydrophobicity. Collagen adsorption is also reduced in the presence of HSA and FCS, but the reduction and its sensitivity to substrate hydrophobicity are lower than with Pluronic F68.
