Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms.
We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.
Koval
Iryna A
IA
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
Selmeczi
Katalin
K
Belle
Catherine
C
Philouze
Christian
C
Saint-Aman
Eric
E
Gautier-Luneau
Isabelle
I
Schuitema
Anna Maria
AM
van Vliet
Marcel
M
Gamez
Patrick
P
Roubeau
Olivier
O
Lüken
Matthias
M
Krebs
Bernt
B
Lutz
Martin
M
Spek
Anthony L
AL
Pierre
Jean-Louis
JL
Reedijk
Jan
J
D002384:Catalysis; D004156:Catechol Oxidase / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004789:Enzyme Activation; D008024:Ligands; D047028:Macrocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013696:Temperature
D008024:Ligands; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D003300:Copper; D004156:Catechol Oxidase