Immobilization of xyloglucans extracted from Hymenaea coubaril (HXG) and Tamarindus indica seeds (TXG) on Si/SiO2 wafers or amino-terminated wafers from aqueous solution at concentration of 0.5 g L-1 and pH 3.5 has been investigated by means of ellipsometry and atomic force microscopy (AFM) measurements. Experiments were carried out under equilibrium conditions (adsorption) and non-equilibrium conditions (casting). Under equilibrium conditions neither TXG nor HXG chains adsorbed from solution onto Si/SiO2 surfaces, indicating that negatively charged SiO- groups on the surface do not attract XG chains. Casting TXG and HXG solutions onto Si/SiO2 surfaces led to layers (2.4 ± 0.4) nm and (3.8 ± 0.9) nm thick, respectively. TXG and HXG adsorbed onto amino-terminated surfaces forming layers (1.0 ± 0.1) nm and (1.3 ± 0.1) nm thick, respectively. Upon casting solutions of TXG and HXG onto amino-terminated surfaces, aggregates and fibrils appeared more frequently on the surface, increasing the mean thickness and roughness values. Regardless the substrate, HXG chains tended to form thicker layers than TXG chains did. This trend can be explained with basis on the molecular characteristics of HXG, namely, higher molecular weight and persistence length. The adsorption isotherms of concanavalin A (Con A) onto HXG- and TXG-covered amino-terminated wafers presented maximum adsorbed amount of (3.3 ± 0.3) mg m-2. AFM images shown Con A molecules as small entities densely packed on the surface. The presence of fibrils and aggregates was observed only when the TXG and HXG surfaces were prepared by casting. There ConA molecules adsorbed predominantly on regions free of fibrils and aggregates.
xyloglucans; concanavalin A; thin films; atomic force microscopy; ellipsometry
