Tyrosinase Reactivity in a Model Complex: An Alternative Hydroxylation Mechanism
Liviu M. Mirica,1
Michael Vance,1
Deanne Jackson Rudd,1
Britt Hedman,2*
Keith O. Hodgson,1,2*
Edward I. Solomon,1*
T. Daniel P. Stack1*
The binuclear copper enzyme tyrosinase activates O
2 to form
a µ-
2:
2-peroxodicopper(II) complex, which oxidizes phenols
to catechols. Here, a synthetic µ-
2:
2-peroxodicopper(II)
complex, with an absorption spectrum similar to that of the
enzymatic active oxidant, is reported to rapidly hydroxylate
phenolates at –80°C. Upon phenolate addition at extreme
temperature in solution (–120°C), a reactive intermediate
consistent with a bis-µ-oxodicopper(III)-phenolate complex,
with the O–O bond fully cleaved, is observed experimentally.
The subsequent hydroxylation step has the hallmarks of an electrophilic
aromatic substitution mechanism, similar to tyrosinase. Overall,
the evidence for sequential O–O bond cleavage and C–O
bond formation in this synthetic complex suggests an alternative
intimate mechanism to the concerted or late stage O–O
bond scission generally accepted for the phenol hydroxylation
reaction performed by tyrosinase.
2 Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford University, CA 94309, USA.
* To whom correspondence should be addressed. E-mail: stack{at}stanford.edu (T.D.P.S.); edward.solomon{at}stanford.edu (E.I.S.); hodgson{at}ssrl.slac.stanford.edu (K.O.H.); hedman{at}ssrl.slac.stanford.edu (B.H.)
