Assemblies of concanavalin A onto carboxymethylcellulose

The immobilization of Concanavalin A, (Con A), onto flat surfaces formed by ultrathin films of carboxymethylcellulose, CMC, silicon wafers or spin-coated poly(methyl methacrylate), (PMMA), was studied by ellipsometry, contact angle measurements and atomic force microscopy (AFM). The formation of Con A monolayer was only observed onto CMC films. The adsorption constant of Con A onto CMC films was determined as being (2.1 +/- 0.2) x 10(6) L mol(-1). After assembling Con A onto CMC surfaces, these became more hydrophobic, indicating a molecular orientation of Con A hydrophilic residues to the polysaccharide and Con A hydrophobic residues to the air. The affinity of Con A for hydroxyl rich silicon surfaces or for more hydrophobic PMMA films was very weak, evidencing that nonspecific interactions play a marginal role. For comparison, the immobilization of Con A onto hybrid particles of PMMA/CMC was investigated by means of UV-spectrophotometry. Such particles carry CMC chains attached to the surface, as evidenced by mean zeta potential value of -40 mV. The adsorption constant determined for Con A onto PMMA/CMC particles was one order of magnitude smaller than that found for Con A onto CMC films. This finding indicates that the substrate geometry might influence the molecular arrangement of sugar residues on the surface, consequently affecting the sugar-Con A interaction (cluster effect).