Construction of Supramolecular Chiral Polyaniline-Gold Nanocomposite as Nanozyme for Enantioselective Catalysis

Abstract: Enantioselective catalysis is ubiquitous in biological organisms and closely related to biological production and metabolism. The design and development of nanozymes with high enantioselectivities are essential for various bio-related applications. Currently, investigations of nanozymes are primarily focused on their catalytic activity. However, the enantioselectivity of nanozymes, a significant feature, has been rarely studied. In view of the few reports related to enantioselective catalysis, nanozymes have mainly been constructed with chiral molecule-modified nanoparticles. Because the selectivity of natural enzymes not only depends on the molecular chirality of chiral species, such as amino acids, but is also closely related to the chiral supramolecular microenvironment generated by the spatial arrangement and folding of proteins, the construction of active chiral substances with chiral supramolecular microenvironment for nanozymes is also an effective way to design nanozymes with excellent enantioselectivities. Additionally, to improve the enantioselectivity, an understanding of the influencing parameters for select factor of chiral nanozymes is essential. Herein, we report the successful construction of nanocomposites composed of supramolecular M-polyaniline (M-PANI) twisted nanoribbons assembled without any chiral molecules, and Au nanoparticles (NPs) of three different sizes (3, 10, and 16 nm). The characterization results from scanning electron microscopy, transmission electron microscopy, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy confirmed the successful fabrication of M-PANI-Au nanocomposites. The evident signals in the circular dichroism spectra of the M-PANI-Au nanocomposites indicated their potential as chiral nanozymes. Considering the catalytic oxidation of chiral R-/S-3,4-dihydroxyphenylalanine (R-/S-DOPA) enantiomers as a model reaction, the three M-PANI supported Au NPs demonstrated higher catalytic selectivity for R-DOPA than for S-DOPA, as confirmed by the kinetic absorption curves, revealing the high potential of M-PANI-Au nanocomposites as enantioselective nanozymes. Interestingly, according to the kinetic assay study, the M-PANI nanocomposite with 3 nm Au NPs had a higher selection factor (2.59) than those of 10 nm Au NPs (1.46) and 16 nm Au NPs (1.58), which could be attributed to the strongest chirality transfer effect from the supramolecular chiral PANI to 3 nm Au NPs. Therefore, chirality transfer from chiral supramolecular scaffolds to nanozymes is a key factor influencing the enantioselective catalysis and can provide direct guidance for the future design and construction of chiral supramolecular nanozymes with high enantioselectivities.