Binding of Dual-Function Hybridized Metal - Organic Capsules to Enzymes for Cascade Catalysis

Abstract

The combination of chemo- and biocatalysis for multistep syntheses provides attractive advantages in terms of evolvability, promiscuity, and sustainability striving for desirable catalytic performance. Through the encapsulation of flavin analogues by both NADH and heme mimics codecorated heteroleptic metal-organic capsules, herein, we report a progressive host-guest strategy to imitate cytochrome P450s catalysis for cascade oxidative coupling catalysis. Besides the construction of stable dual-function metal-organic capsules and the modification of cofactor-decorated capsules at the domain of enzymes, this supramolecular strategy involves multistage directional electron flow, affording reactive ferric peroxide species for inducing oxygenation. Under light irradiation, the metal-organic capsule selectively converts stilbene to oxidative coupling products (including 2-oxo-1,2-diphenylethyl formate, 2-alkoxy-1,2-diphenylethanone) in tandem with enzymatic reactions respectively, at the domain of natural enzymes. The ingenious combination of capsules and enzymes with the in situ-regenerated capsule-loaded NADH cofactor promises non-native coupling reactions by forming regional cooperation and division. This abiotic-biotic conjugated host-guest strategy is conducive to the de novo creation of multifunctional components approaching active enzymatic sites for reinforced matter and energy transporting, demonstrating a key role of multicomponent supramolecular catalysts for one-pot integrated catalytic conversions.

Figure 1

Comparation of natural and artificial tandem catalysis. (a) Multi-enzyme cascades comprising flavin-mediated cytochrome P450 oxygenase and dehydrogenase connected by the diffusion of nicotinamide cofactor couple (NADH/NAD⁺). (b) Construction of the heteroleptic metal–organic capsule Pd–ZPP(Fe) with both NADH and heme model comodified ligands through self-assembly for mimicking cytochrome P450s via encapsulating flavin analogue RFT, combining artificial and natural catalysis within enzymatic pockets by virtue of cofactor channels for a host–guest semibiological system applying to in situ biomimetic oxidation.

Figure 2

Characterization of macrocycle hosts and host–guest species. (a) Partial ¹H NMR spectra of the metallacycle Pd–ZPP(H) (1.0 mM), RFT (1.0 mM), Pd–ZPP(H) (1.0 mM), and RFT (1.0 mM) mixture in equal concentrations, and ¹H DOSY spectra of Pd–ZPP(H) with log D = −9.40 in d₆-DMSO. (b) ESI-MS of Pd–ZPP(Fe) (1.0 mM) and the mixture of Pd–ZPP(Fe) (1.0 mM) and RFT (1.0 mM) in DMF; the insets show the measured and simulated isotopic patterns at m/z = 898.6375 and 1034.6769, respectively. (c) Structure of the macrocycle Pd–ZPP(Fe) optimized using the PM6 semiempirical method, showing the distribution of the NADH-mimicking sites and porphyrin groups and the square coordination geometry of palladium ions. (d) Resulting beleaguered confined space of Pd–ZPP(Fe). Pd dark green, Fe orange, P wine, O red, N blue, C gray, and H white. (e) and (f) Docking study optimized model of Pd–ZPP(Fe) ⊃ RFT, representing the location of RFT in Pd–ZPP(Fe)’s cavity to meet the close proximity between NADH, flavin, and porphyrin models.

Figure 3

Characterization of the interactions between Pd–ZPP(Fe) and RFT. (a) Luminescence spectra of RFT (10.0 μM) upon the addition of Pd–ZPP(Fe) (7.5 μM) in CH₃CN/H₂O (1:1). (b) Luminescence decay of RFT (10.0 μM) in CH₃CN and of the aforementioned solution upon the addition of Pd–ZPP(Fe) (10.0 μM). (c) UV–vis spectra of Pd–ZPP(Fe) (10.0 μM) and RFT (10.0 μM) in CH₃CN under 455 nm. Inset shows the differential spectra as a function of irradiation time. (d) Differential UV–vis absorption spectra of Pd–ZPP(Fe) (10.0 μM) in CH₃CN/H₂O (1:1) upon the addition of RFT (total 10.0 μM). (e) Luminescence spectra of RFT (10.0 μM) in CH₃CN/H₂O (1:1) upon the addition of Pd–ZPP(Fe) (10.0 μM) of both Pd–ZPP(Fe) (10.0 μM) and ATP (50.0 μM). (f) ITC experiments of Pd–ZPP(Fe) upon the addition of RFT and of FDH in the CH₃CN/H₂O (1:1) solution.

Figure 4

Characterization of the interactions between Pd–ZPP(Fe) and RFT or enzymes. (a) EPR spectra collected at 150 K for the system containing Pd–ZPP(Fe) (1.0 mM) treating with H₂O₂ (10.0 mM) or RFT (1.0 mM) upon the irradiation of xenon lamp in DMF/H₂O (1:1). (b) UV–vis absorption spectra of Pd–ZPP(Fe) (10.0 μM) upon the addition of FDH (total 0.5 μM) in CH₃CN/H₂O (1:1). (c) Family of luminescence spectra of Pd–ZPP(Fe) (10.0 μM) upon the addition of FDH (total 0.5 μM) in CH₃CN/H₂O (1:1). (d) Theoretical docking study optimized model of Pd–ZPP(Fe) ⊃ RFT with enzyme FDH. (e) Differential UV–vis absorption spectra of Pd–ZPP(Fe) (10.0 μM) upon the addition of enzyme ADH (total 0.1 μM) in CH₃CN/H₂O (1:1). (f) Family of luminescence spectra of Pd–ZPP(Fe) (10.0 μM) in CH₃CN/H₂O (1:1) upon the addition of ADH (total 1.0 μM).

Figure 5

Schematic of the supramolecular catalytic oxidation of cis-stilbene, showing the synergistic catalytic behavior of artificial and natural enzymes within the confined environment and in situ regeneration of the NADH model under enzymatic catalysis.