title: Catecholase activity of a series of dicopper(II) complexes with variable Cu-OH(phenol) moieties.
abstract: The catecholase activity of a series of dicopper(II) complexes containing different numbers of phenol groups coordinated to the metal centers was studied to identify functional as well as structural models for the type III copper enzymes tyrosinase and catechol oxidase. The syntheses and characterization of complexes [Cu(2)(H(2)bbppnol)(mu-OAc)(H(2)O)(2)]Cl(2).2H(2)O (1) and [Cu(2)(Hbtppnol)(mu-OAc)](ClO(4))(2) (2) were previously reported by us (Inorg. Chim. Acta 1998, 281, 111-115; Inorg. Chem. Commun. 1999, 2, 334-337), and complex [Cu(2)(P1-O(-))(OAc(-))](ClO(4))(2) (3) was previously reported by Karlin et al. (J. Am. Chem. Soc. 1997, 119, 2156-2162). The catalytic activity of the complexes 1-3 on the oxidation of 3,5-di-tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di-tert-butyl-o-benzoquinone characteristic absorption band at about 400 nm over time in methanol saturated with O(2)/aqueous buffer pH 8 solutions at 25 degrees C. The complexes were able to oxidize 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity. A kinetic treatment of the data based on the Michaelis-Mentèn approach was applied. The [Cu(2)(H(2)bbppnol)(mu-OAc)(H(2)O)(2)]Cl(2) small middle dot2H(2)O complex showed the highest catalytic activity of the three complexes as a result of a high turnover rate (k(cat) = 28 h(-1)) combined with a moderate substrate-catalyst binding constant (K(ass) = 1.3 x 10(3) M(-1)). A mechanism for the oxidation reaction is proposed, and reactivity differences, k(cat)/K(M) of the complexes, were found to be dependent on (DeltaE)(1,2), the difference in the driving force for the reduction reactions Cu(II)(2)/Cu(II)Cu(I) and Cu(II)Cu(I)/Cu(I)(2).
authors.affiliation: Institut für Physikalische Chemie, Technische Universität Darmstadt, D-64287 Darmstadt, Germany. ademir@qmc.ufsc.br
authors.forename: Ademir
authors.initials: A
authors.lastname: Neves
authors.forename: Liane M
authors.initials: LM
authors.lastname: Rossi
authors.forename: Adailton J
authors.initials: AJ
authors.lastname: Bortoluzzi
authors.forename: Bruno
authors.initials: B
authors.lastname: Szpoganicz
authors.forename: Clayton
authors.initials: C
authors.lastname: Wiezbicki
authors.forename: Erineu
authors.initials: E
authors.lastname: Schwingel
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Haase
authors.forename: Sergei
authors.initials: S
authors.lastname: Ostrovsky
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D004156:Catechol Oxidase / Q000737:chemistry* / Q000378:metabolism; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008956:Models, Chemical; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000737:chemistry / Q000378:metabolism; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D014867:Water; D003300:Copper; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase