Active Site Models for the Cu_A Site of Peptidylglycine α-Hydroxylating Monooxygenase and Dopamine β-Monooxygenase

Abstract

A mononuclear copper(II) superoxo species has been invoked as the key reactive intermediate in aliphatic substrate hydroxylation by copper monooxygenases such as peptidylglycine α-hydroxylating monooxygenase (PHM), dopamine β-monooxygenase (DβM), and tyramine β-monooxygenase (TβM). We have recently developed a mononuclear copper(II) end-on superoxo complex using a N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane tridentate ligand, the structure of which is similar to the four-coordinate distorted tetrahedral geometry of the copper-dioxygen adduct found in the oxy-form of PHM (Prigge, S. T.; Eipper, B. A.; Mains, R. E.; Amzel, L. M. Science2004, 304, 864-867). In this study, structures and physicochemical properties as well as reactivity of the copper(I) and copper(II) complexes supported by a series of tridentate ligands having the same N-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane framework have been examined in detail to shed light on the chemistry dictated in the active sites of mononuclear copper monooxygenases. The ligand exhibits unique feature to stabilize the copper(I) complexes in a T-shape geometry and the copper(II) complexes in a distorted tetrahedral geometry. Low temperature oxygenation of the copper(I) complexes generated the mononuclear copper(II) end-on superoxo complexes, the structure and spin state of which have been further characterized by density functional theory (DFT) calculations. Detailed kinetic analysis on the O(2)-adduct formation reaction gave the kinetic and thermodynamic parameters providing mechanistic insights into the association and dissociation processes of O(2) to the copper complexes. The copper(II) end-on superoxo complex thus generated gradually decomposed to induce aliphatic ligand hydroxylation. Kinetic and DFT studies on the decomposition reaction have suggested that C-H bond abstraction occurs unimolecularly from the superoxo complex with subsequent rebound of the copper hydroperoxo species to generate the oxygenated product. The present results have indicated that a superoxo species having a four-coordinate distorted tetrahedral geometry could be reactive enough to induce the direct C-H bond activation of aliphatic substrates in the enzymatic systems.

Synthesis and characterisation of a mesocyclic tripodal triamine ligand

“…In the structures of both [1bH]PF 6 and [1b2H]OTf 2 the C--N--C fold angle is comparable to both previously reported protonated DACO moieties 61,68,70,71 as well as metal complexes containing the DACO moiety. 34 Furthermore, the bond lengths and angles were found to be in the region of those previously reported. This suggests that alkylation of the DACO ring at the C2, N1 and N2 positions should not hinder complex formation.…”

Transition Metal Complexes and the Activation of Dioxygen

“…In support of this capability, complex 82 (R ¼ phenethyl group) decays to yield 86 ( Figure 40) via a pathway shown by kinetic experiments and DFT calculations to proceed by ratelimiting intramolecular hydrogen atom abstraction by the coordinated superoxide from the benzylic C-H bond of the ligand phenethyl arm [286,287].…”

Quantum mechanical calculations suggest that lytic polysaccharide monooxygenases use a copper-oxyl, oxygen-rebound mechanism

“…[Cu(I)] complexes generate open shell singlet or triplet products due to the addition of triplet O 2 , and thus the standard KohnSham DFT is not directly applicable (44). We applied the Yamaguchi broken spin symmetry procedure (45) to compute the energy of the spin-purified low-spin (LS) state (46). We calculated two possible spin states if the complexes are open shell and found the energy of triplet products is always lower than the energy of the spin-purified LS state, unless otherwise stated.…”