A Small‐molecule Model System of Galactose Oxidase: Geometry, Reactivity, and Electronic Structure

Abstract

The active site of galactose oxidase (GOase) contains a copper atom coordinated by a tyrosyl radical. This enzyme catalyzes the two‐electron oxidation of alcohols to aldehydes. We present a GOase model system, which catalytically mediates the conversion of ethanol to acetaldehyde with a TON of 74. The crystal structure of the mononuclear copper complex [CuII(L6‐H)(CH3CN)](ClO4)2 coordinated by acetonitrile reveals an apical position for the phenol group. Furthermore we prepared the dimeric complex [(CuII)2(L6)2](PF6)2, which was structurally characterized as well. Cleavage of the dimer along with formation of the phenoxyl radical was effected by cerium(IV) ammonium nitrate. The dimer could also be cleaved by treatment with pyridine. In order to obtain information about the interaction between the unpaired electron in the d‐orbital of CuII to the electron in the half‐occupied orbital of the tyrosyl radical DFT is employed. In the ground state a ferromagnetic coupling (S = 1) is obtained.

Copper Complexes of the Tetradentate N,N′‐Bis(2‐amino‐3,5‐di‐tert‐butylphenyl)‐2,2′‐diaminobiphenyl Ligand

“…For the unactivated 2-phenylethanol the TON was more modest, as it caps at 80 � 6 at 24 h (same value at 6 h). This TON is comparable to that reported for the oxidation of ethanol by a tripodal model complex of galactose oxidase (NEt 3 as base, 74 TON in 23 h) [20] but remains inferior to that reported by Wieghardt for iminosemiquinone copper systems towards unactivated alcohols. [10a,21] We did not detect any appreciable amount of product for the more challenging 2-phenylpropan-1-ol and 1-phenylpropan-2-ol.…”

Magnetostructural Properties of Some Doubly-Bridged Phenoxido Copper(II) Complexes

“…The latter intense band can be assigned to the bridged phenoxido charge transfer transition (L-O → Cu II LMCT) [ 12 , 20 , 63 , 64 ], whereas the former low intense broad band is attributed to d-d transition in five-coordinate Cu(II) complexes, which was occasionally accompanied with a weaker intense broad band around 850–890 nm. The d-d transition feature in solution is consistent with a distorted square pyramidal geometry (SP) around the central Cu(II) ion [ 32 , 48 , 49 ]. Thus, the distorted SP geometrical assignments observed in DMSO, CH 3 CN, or acetone solution, were retained in the solid state (see X-ray section).…”

“…The first approach was achieved though the interaction Cu(II) salts with tridentate ligand-based phenolates in their skeletons [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ], and the second approach was via the design of bicompartmental phenolates bearing two pendent arms of N-donor groups [ 1 , 2 , 3 , 4 , 5 , 6 , 42 , 43 ]. A third approach was also used through the design of tripodal pyridyl tetradentate ligands containing one or two phenolate arms [ 12 , 14 , 15 , 20 , 29 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ].…”