Rational Construction of an Artificial Binuclear Copper Monooxygenase in a Metal–Organic Framework

Abstract

Artificial enzymatic systems are extensively studied to mimic the structures and functions of their natural counterparts. However, there remains a significant gap between structural modeling and catalytic activity in these artificial systems. Herein we report a novel strategy for the construction of an artificial binuclear copper monooxygenase starting from a Ti metal−organic framework (MOF). The deprotonation of the hydroxide groups on the secondary building units (SBUs) of MIL-125(Ti) (MIL = Mateŕiaux de l'Institut Lavoisier) allows for the metalation of the SBUs with closely spaced Cu I pairs, which are oxidized by molecular O 2 to afford the Cu II 2 (μ 2 -OH) 2 cofactor in the MOF-based artificial binuclear monooxygenase Ti 8 -Cu 2 . An artificial mononuclear Cu monooxygenase Ti 8 -Cu 1 was also prepared for comparison. The MOF-based monooxygenases were characterized by a combination of thermogravimetric analysis, inductively coupled plasma−mass spectrometry, X-ray absorption spectroscopy, Fourier-transform infrared spectroscopy, and UV−vis spectroscopy. In the presence of coreductants, Ti 8 -Cu 2 exhibited outstanding catalytic activity toward a wide range of monooxygenation processes, including epoxidation, hydroxylation, Baeyer−Villiger oxidation, and sulfoxidation, with turnover numbers of up to 3450. Ti 8 -Cu 2 showed a turnover frequency at least 17 times higher than that of Ti 8 -Cu 1 . Density functional theory calculations revealed O 2 activation as the rate-limiting step in the monooxygenation processes. Computational studies further showed that the Cu 2 sites in Ti 8 -Cu 2 cooperatively stabilized the Cu−O 2 adduct for O−O bond cleavage with 6.6 kcal/mol smaller free energy increase than that of the mononuclear Cu sites in Ti 8 -Cu 1 , accounting for the significantly higher catalytic activity of Ti 8 -Cu 2 over Ti 8 -Cu 1 .

On the limit of proton-coupled electronic doping in a Ti(iv)-containing MOF

“…20 Combining the best of both approaches, metalorganic frameworks (MOFs) merge the benefits of heterogeneous catalysis and synthetic modularity. [21][22][23][24] Previous studies in MOF catalysis have primarily focused on thermally driven reactions at either the linker or node using intrinsic [25][26][27] and extrinsic [28][29][30] catalytically active metals. Conversely, MOF photoredox chemistry [31][32][33] typically focuses on electron transfer between the inorganic and organic MOF components 34 , shuttling electrons to interstitial molecular catalysts [35][36][37] or guests [38][39][40][41] .…”

Metal–Organic Frameworks as a Versatile Materials Platform for Unlocking New Potentials in Biocatalysis

“…Very recently, Lin and co‐workers fabricated a MOF‐based artificial binuclear copper monooxygenase, which possessed excellent catalytic activity in a series of monooxygenation reactions. Synthesized based on a Ti MOF, MIL125, [ 125 ] the hydroxide groups on the secondary building units (SBUs) of the MOF was deprotonated to trigger the metalation between closely spaced Cu I pairs and the SBUs, leading to the oxidization of Cu I to Cu II 2 (µ2‐OH) 2 by oxygen, which then worked as a cofactor in the artificial binuclear monooxygenase Ti8‐Cu 2 . It catalyzed various monooxygenation reactions including epoxidation hydroxylation and sulfoxidation with superior turnover number (up to 3450).…”

Controlled synthesis of Bi- and tri-nuclear Cu-oxo nanoclusters on metal–organic frameworks and the structure–reactivity correlations

“…The establishment of structure-reactivity correlations between the active centres and catalytic properties is regarded as an important platform for the rational design and engineering of more superior and selective systems. In recent years, various catalytic materials with atomic precision have been fabricated to achieve exciting performance in different applications, [9][10][11] such as [Cu 3 (μ-O) 3 ] 2+ supported on MOR zeolite for the selective oxidation of methane to methanol by Lercher et al 12 , and the engineering of MIL-101(Ti)-based Cu 2 species as artificial monooxygenase by Lin et al 13 The catalytic characteristics of NCs can generally be correlated to nuclearity (number of atoms), 15 electronic (HOMO-LUMO work functions and binding affinities) 16 and geometric properties (morphology and coordination environments) 17 of the active sites. Some reaction mechanisms are governed by the adsorption configurations of the substrates.…”