Catalytic activity of lipase immobilized onto ultrathin films of cellulose esters.

Ultrathin (approximately 2.0 nm) films of cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) supported on Si wafers have been prepared by adsorption and characterized by means of ellipsometry, atomic force microscopy (AFM), and contact angle measurements. CA, CAP, and CAB ultrathin films were characterized in air just after their formation and after annealing under reduced pressure at temperature higher than the corresponding melt temperature. Upon annealing, CA, CAP, and CAB ultrathin films became smoother and more hydrophobic, evidencing molecular reorientation at the solid-air interface. CA, CAP, and CAB films were used as supports for the immobilization of lipase. The adsorption of lipase onto annealed films was more pronounced than that onto untreated films, showing the strong affinity of lipase for the more hydrophobic substrates. Enzymatic activity was evaluated by a standard procedure, namely, (spectrophotometric) measurement of p-nitrophenol, the product formed from the hydrolysis of p-nitrophenyl dodecanoate (p-NPD). Lipase immobilized onto hydrophobic films exhibited higher activity than that of free lipase and could be recycled three times while retaining relatively high activity (loss of ca. 30% of original enzymatic activity). The effect of storing time on the activity of immobilized lipase was studied. Compared with free lipase, that immobilized onto more hydrophobic films retained 70% activity after 1 month. More importantly, the latter level of activity is similar to that of free lipase. However, lipase immobilized onto more hydrophilic films retained 50% and 30% activity after 20 and 30 days, respectively. These results are explained in terms of surface wettability and the contribution of the interactions between the polar residues of lipase and the glucopyranosyl moieties of cellulose ester to maintain the natural conformation of immobilized enzyme.

Sugar-based anionic surfactants: synthesis and micelle formation of sodium methyl 2-acylamido-2-deoxy-6-O-sulfo-D-glucopyranosides.

The following sequence of reactions has been employed to synthesize the title anionic surfactants: [chemical reaction: see text] where R=C7H15; C11H23; and C15H31, respectively, and Py refers to pyridine. Aggregation of the surfactants synthesized (predominantly alpha anomers) in water was studied at 40 degrees C by conductivity measurements. Increasing the chain length of R decreases the critical micelle concentration (CMC) and the degree of counter-ion dissociation. The dependence of the Gibbs free energy of micellization and CMC on the length of R is similar to other ionic surfactants, but the head-group, i.e., the sulfated sugar moiety is less hydrophilic than the structurally related group -(OCH2-CH2)2-OSO3-Na+, most probably because of intermolecular H-bonding in the micellar pseudo-phase