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Emergence of complexity in hierarchically organized chiral particles

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Science  08 May 2020:
Vol. 368, Issue 6491, pp. 642-648
DOI: 10.1126/science.aaz7949

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Complex chiral particles

Synthetic colloids are usually smooth, but nature can produce micrometer-scale particles with intricate structure and shape, such as the coccoliths produced by algae. Jiang et al. controlled the self-assembly of gold–cysteine nanoplatelets into a variety of chiral, hierarchically organized colloidal particles by changing the chiral fraction of cysteine and the nucleation temperature. Organic cations created electrostatic repulsions that favored edge assembly of the nanoplatelets, which in turn could create surfaces bearing twisted spikes.

Science, this issue p. 642

Abstract

The structural complexity of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. Although empirical observations of complex nanoassemblies are abundant, the physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for nonuniformly sized components. We report the self-assembly of hierarchically organized particles (HOPs) from polydisperse gold thiolate nanoplatelets with cysteine surface ligands. Graph theory methods indicate that these HOPs, which feature twisted spikes and other morphologies, display higher complexity than their biological counterparts. Their intricate organization emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOP phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties.

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