Gold Nanocluster Isomerization Drives Supramolecular Transition from Heterochiral to Homochiral Helices

The transformation of metal nanocluster (MNC)-based heterochiral assemblies into their homochiral analogues is a compelling goal inspired by the ubiquitous homochirality observed in living systems. Owing to the intricate factors governing nanomaterial chirality, the precise control of supramolecular chirality in MNCs remains rarely demonstrated. Herein, we demonstrated the coassembly behavior of AuNCs protected by 6-propyl-2-thiouracil (Au₃PRT₃) with chiral mandelic acid (MA), which revealed the formation of hybrid chiral superstructures of P- and M-helices in a single system. Combined experimental and theoretical studies comprehensively reveal that the enol-keto isomerization of the Au₃PRT₃ staple motif is primarily responsible for the emergence of P- and M-helices during coassembly. The negatively charged enol-type Au₃PRT₃ (Au₃PRT₃^enol) interacts directly with S-MA molecules and forms parallel malposed dimers, resulting in the formation of P-helices. In contrast, the dissociation of H⁺ ions triggers enol-keto isomerization within the PRT ligand. The resulting keto-type isomer (Au₃PRT₃^keto) then interacts with S-MA molecules, promoting vertical stacking of dimers that lead to the formation of M-helices. Based on this observation, the addition of S-MA molecules with the preformed Au₃PRT₃^keto exclusively induces the formation of homochiral M-helices. In this way, the toggling of multiple chiral superstructures was achieved by leveraging facile Au₃PRT₃^enol-Au₃PRT₃^keto isomerization. This work elucidates the precise control of chiral structures by isomerization of surface motifs of AuNCs and presents a paradigm for investigating the structure-property relationship of AuNC materials. This approach offers a strategic pathway for constructing artificial supramolecular composite systems with diverse chiral architectures, potentially advancing our understanding of chirality evolution in natural systems and aiding its biomimetic replication.