Reversible dioxygen binding and phenol oxygenation in a tyrosinase model system.
The complex [Cu2(L-66)]2+ (L-66 = a,a'-bis¿bis[2-(1'-methyl-2'-benzimidazolyl)ethyl]amino¿-m-xylene) undergoes fully reversible oxygenation at low temperature in acetone. The optical [lambda(max) = 362 (epsilon 15000), 455 (epsilon 2000), and 550 nm (epsilon 900M(-1)cm(-1))] and resonance Raman features (760 cm(-1), shifted to 719cm(-1)(-1) with 18O2) of the dioxygen adduct [Cu2(L-66)(O2)]2+ indicate that it is a mu-eta2:eta2-peroxodicopper(II) complex. The kinetics of dioxygen binding, studied at - 78 degrees C, gave the rate constant k1 = 1.1M(-1) 5(-1) for adduct formation, and k(-1) =7.8 x 10(-5)s(-1), for dioxygen release from the Cu2O2 complex. From these values, the O2 binding constant K= 1.4 x 10(4)M(-1) at -78 degrees C could be determined. The [Cu2(L-66)(O2)]2+ complex performs the regiospecific ortho-hydroxylation of 4-carbomethoxyphenolate to the corresponding catecholate and the oxidation of 3,5-di-tert-butylcatechol to the quinone at -60 degrees C. Therefore, [Cu2(L-66)]2+ is the first synthetic complex to form a stable dioxygen adduct and exhibit true tyrosinase-like activity on exogenous phenolic compounds.
Santagostini
L
L
Dipartimento C.I.M.A., Università di Milano, Centro CNR, Italy.
Gullotti
M
M
Monzani
E
E
Casella
L
L
Dillinger
R
R
Tuczek
F
F
D008956:Models, Chemical; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism*; D013054:Spectrophotometry, Atomic
D010636:Phenols; D014442:Monophenol Monooxygenase; D010100:Oxygen