Enzymes fold into three-dimensional structures for spatial arrangement of amino acid residues and formation of specific motifs within their active sites, enabling their remarkable catalytic properties. Replicating such intricate folding and functional group distribution in synthetic systems could allow for efficient and mild catalysis with significant potential in green chemistry, but achieving this remains a major challenge. Inspired by structure and function of oxyanion hole-a fundamental structural feature in hydrolases, we designed a surfactant system comprising an aza-crown ether core and an alkyl tail, which self-assembles into tail-to-tail bilayer nanostructures capable of catalyzing hydrolytic reactions. The theoretical and experimental results reveal that the alkyl chain enhances the protonation and organization of the aza-crown ether, promoting ester substrate access and stabilizing the transition state, reminiscent of natural oxyanion hole mechanisms. It is observed that the alkylated aza-crown ether exhibits a 43.3-fold increase in catalytic efficiency (k_cat/K_m) compared to its non-alkylated counterpart. Additionally, the self-assembled alkylated aza-crown ether demonstrates efficient CO₂ hydration activity, resembling the function of carbonic anhydrase. This work offers a model for how simple molecules can evolve sophisticated catalysts through structural and functional optimization, offering new insights for the design of bioinspired catalyst in green chemistry.

Reconstructing enzymatic active sites presents a significant challenge due to the intricacies involved in achieving enzyme-like scaffold folding and spatial arrangement of essential functional groups. There is also a growing interest in building biocatalytic networks, wherein multiple enzymatic active sites are localized within a single artificial system, allowing for cascaded transformations. In this work, we report the self-assembly of imidazole or its derivatives with fluorenylmethyloxycarbonyl-modified histidine and Cu²⁺ to fabricate a supramolecular catalyst, which possesses catechol oxidase-like dicopper center with multiple imidazole as the coordination sphere. Transmission electron microscopy, low-temperature X-band continuous-wave electron paramagnetic resonance, K-edge X-ray absorption spectra/the extended X-ray absorption fine structure analysis, and density functional theory modeling were used for the structural characterization of the catalyst. The phenol derivatives and the dissolved oxygen were used as the substrates, with the addition of 4-aminoantipyrine to generate a red adduct with a maximum absorbance at 510 nm, for obtaining time-dependent absorbance change curves and estimating the activities. The results reveal that the addition of imidazole synergistically accelerates the oxidative activity about 10-fold and the hydrolysis activity about 14-fold than fluorenylmethyloxycarbonyl modified-histidine/Cu²⁺. The supramolecular nanoassembly also exhibits the ability to catalyze oxidation/hydrolysis cascade reactions, converting 2′,7′-dichlorofluorescin diacetate into 2′,7′-dichlorofluorescein. This process can be regulated through the methylation of the imidazole component at various positions. This work may contribute to the design of advanced biomimetic catalysts, and shed light on early structural models of the active sites of the primitive copper-dependent enzymes.

It is an important goal for supramolecular chemistry to develop synthetic enzyme mimics rivaling native enzymes, while de novo fabrication of such mimics remains a challenge. Alternatively, the catalytic groups from the supramolecular complex can be integrated with the active sites of natural enzymes. Herein, we present a supramolecular catalytic hybrid that is self-assembled from oligohistidine-based peptides and a heme-dependent peroxidase. The results indicate that the peptides altered the enzyme conformation, promoted the transitions between the resting and the intermediate states of the heme, and increased the turnover rate of the enzyme by up to three-fold. We propose that the histidine residues from the peptides may collaborate with the groups in the natural heme pocket to accelerate the catalytic cycles of the enzyme. Our observations underline the advantages of the supramolecular approach and suggest that molecular self-assembly may combine with enzymes to provide a simple strategy to engineer the enzymatic active sites.