title: Electrochemical behavior of pyrroloquinoline quinone immobilized on silica gel modified with zirconium oxide.
abstract: Pyrroloquinoline quinone (PQQ) was immobilized on the silica gel surface modified with zirconium oxide, designated as Si:Zr, by the carboxylic groups of the PQQ molecule and the zirconium oxide on the silica surface. The electrochemistry of PQQ immobilized on the Si:Zr matrix, incorporated in a carbon paste electrode, was evaluated using the cyclic voltammetry technique. The Si:Zr:PQQ-modified electrode showed a redox couple at E(m)=(E(pa1)+E(pc))/2=-0.150 V vs SCE at pH 7, close to that observed in aqueous solution, and another oxidation peak, E(pa2)=-0.100 V vs SCE. Studies in different pH solutions in the range of 3-7 showed that the first oxidation peak, E(pa1), is highly dependent on the solution pH shifting from to -0.175 to 0.100 V vs SCE, while E(pa2) remains practically constant at 0.100 V as the pH decreases from 7 to 3. The immobilized PQQ electrode presented the property to electrocatalyze the NADH at 150 mV vs SCE. The effect of addition of Ca(2+) ions on the electrode electroactivity for the NADH oxidation was also verified. Different from that observed for the PQQ immobilized on other electrode materials, the Ca(2+) ions did not influence the electrocatalytical response; however, the electrode stability was considerably improved in the presence of Ca(2+) ions, indicating that the matrix surface has a great influence on the electrochemical behavior of PQQ.
authors.affiliation: Instituto de Química, UNICAMP, Universidade Estadual de Campinas, P.O. Box 6154, 13083-970, Campinas, SP, Brazil.
authors.forename: Miyuki
authors.initials: M
authors.lastname: Yamashita
authors.forename: Christiana A
authors.initials: CA
authors.lastname: Pessôa
authors.forename: Lauro T
authors.initials: LT
authors.lastname: Kubota
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002244:Carbon / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008956:Models, Chemical; D009243:NAD / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry*; D011804:Quinolines / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013053:Spectrophotometry; D014466:Ultraviolet Rays; D015040:Zirconium / Q000737:chemistry*
chemical_list: D016227:Benzoquinones; D007477:Ions; D011758:Pyrroles; D011804:Quinolines; C410406:pyrroloquinoline; D009243:NAD; C004532:quinone; D002244:Carbon; D012822:Silicon Dioxide; D015040:Zirconium; C028541:zirconium oxide; D002118:Calcium