title: Immobilization of myoglobin on phosphate and phosphonate grafted-zirconia nanoparticles.
abstract: We investigated the adsorption and catalytic activity of myoglobin (Mb) immobilized on colloidal particles of zirconia covalently grafted with phosphoric (ZrO2-P) and benzenephosphonic acid (ZrO2-BP). The maximum adsorption was reached after 1 h of contact and was greater on a hydrophilic support, ZrO2-P, compared to a hydrophobic support, ZrO2-BP. The equilibrium isotherms fitted the Langmuir equation, suggesting the presence of a monolayer of protein molecules on the surface of the nanoparticles. The nanostructured biocomposites are active in the oxidation of 2-methoxyphenol (guaiacol) by hydrogen peroxide. The oxidation catalyzed by immobilized Mb followed a Michaelis-Menten kinetics, similar to that observed in the oxidation by free Mb. Furthermore, the catalytic efficiency is similar to that of free Mb and higher than that of "large-size" biocatalysts (with sizes larger than 1 mum). In the latter case, the kinetic parameters, k(cat) and K(M), indicate that this is mostly due to an increased affinity of the nano-biocomposite for the substrate. The activity of the nano-biocomposites decreases slightly as the amount of adsorbed protein increases. This is mainly due to the formation of a nonordered monolayer, which reduces the accessibility of the substrate to the active center.
authors.affiliation: Dipartimento di Chimica, Università di Perugia, via Elce di Sotto, 8, 06123 Perugia, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Bellezza
authors.forename: Antonio
authors.initials: A
authors.lastname: Cipiciani
authors.forename: Maria Anna
authors.initials: MA
authors.lastname: Quotadamo
mesh_terms: D000327:Adsorption; D006861:Hydrogen Peroxide / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D009211:Myoglobin / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D063065:Organophosphonates / Q000737:chemistry*; D010084:Oxidation-Reduction; D011506:Proteins; D015040:Zirconium / Q000737:chemistry*
chemical_list: D009211:Myoglobin; D063065:Organophosphonates; D011506:Proteins; D006861:Hydrogen Peroxide; D015040:Zirconium; C028541:zirconium oxide