Gel formation by an N-fluorenyl-9-methoxycarbonyl (Fmoc)-based molecule was investigated and the chirality amplification observed during the self-assembly process could be switched on and off by controlling the solvent environment. The molecules could form gel in mixed solvents of water and dimethyl sulfoxide (DMSO) at either a high water fraction to afford flat nanofibers or a low water fraction to generate nanofibers with supramolecular chirality. At a moderate fraction of water, the molecules self-assemble into a precipitate composed of nanosheets. Furthermore, the gels showed different mechanical properties and thermal stabilities. Mechanism studies showed that π–π stacking interactions between the aromatic Fmoc groups and hydrogen bondings between the amide groups played important roles in the self-assembly process of the different gels. This study strives to shed light on the tuning of chiral gels with various nanostructures via controlled self-assembly, which might have potential use in smart materials.
Recreating the intricate enzymatic sites within in artificial materials poses a significant challenge due to the complex folding characteristics of enzymes. In this study, we designed a supramolecular catalyst by assembling intramolecularly folding G-quadruplex DNA with Fmoc-amino acid aggregates and Cu2+. This supramolecular material possesses active sites and catalytic functions that rely on copper clusters, mirroring the functionality of catechol oxidase. Experimental and theoretical simulations showed that Fmoc-amino acids interact with G-quadruplex DNA through groove binding, facilitating Cu2+ coordination to both components, thereby enhancing the oxidative catalysis of Cu2+ upon assembly. Our catalyst exhibited excellent tolerance to high temperature, varying ionic strength, and extended room-temperature storage in aqueous solutions. Moreover, our supramolecular complex effectively catalyzed the degradation of doxorubicin, a drug with a high affinity for the DNA component, demonstrating its potential for removing pharmacological pollutants. Additionally, by integrating a photoisomerizable azobenzene derivative as a ligand to the G-quadruplex DNA, we can switch the activity of the enzyme-mimetic catalyst between on and off states by adjusting the irradiation wavelength. This multicomponent approach offers a promising avenue for the design and engineering of active, adaptable supramolecular catalysts.
Shan Li,Haifeng Wu,Yuanxi Liu,Baoli Zhang,Shichao Xu,Zhen-Gang Wang
Enzymes rely on protein folding to create functional sites essential for their catalytic activity. Reproducing enzymatic active sites in artificial systems has been difficult due to the intricate folding patterns that enzymes demonstrate. Inspired by natural systems, we developed a supramolecular copper-cluster-dependent catechol oxidase. This system is constructed through the self-assembly of flavin adenine dinucleotide (FAD) with fluorenylmethyloxycarbonyl-modified amino acids (e.g., Fmoc-lysine) and Cu2+ ions. Fmoc-amino acids self-associate through fluorenyl stacking, facilitating the formation of oxidase-mimetic copper clusters. FAD self-assembles with Fmoc-amino acids via aromatic stacking, enabling the incorporation of adenine and amino acid groups to form a coordination sphere around Cu2+. The self-assembly of FAD with Fmoc-amino acids enhances the oxidase-like activity of Cu2+ by over 100-fold. It is estimated that each copper can catalyze the transformation of ca. 80 substrate molecules within 15 min. The catalyst demonstrated thermophilic properties and excellent storage stability. When exposed to 460 nm light, the activity of the FAD/Fmoc-K/Cu2+ complex is further enhanced, potentially due to cooperative interaction between FAD and lumichrome generated from FAD photodegradation. These findings have implications for the design of advanced enzyme-mimetic catalysts.
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