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Chiral Inorganic Nanoparticles

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One of the rapidly expanding fields of inorganic materials is chiral inorganic nanostructures (CNI). This talk will cover both experiment and theory of CNI starting with the origin and multiple components of mirror asymmetry of individual NPs and their assemblies. Differences and similarities with chiral strctures known from other fields of chemistry will be discussed as well. Developement of the field of CNI started from the observation of strong circular dichroism for single nanoparticles (NPs) and their assemblies. It is currently being expanded to sophisticated constructs involving nanostructures from metals, semiconductors, ceramics, and nanocarbons. Besides the well-established chirality transfer from bioorganic molecules extensively used in organic chemistry, other methods to impart handedness to nanoscale matter specific to inorganic materials were discovered. They include 3D lithography, multiphoton chirality transfer, polarization effects in nanoscale assemblies, and others. Multiple chiral geometries were observed with characteristic scales from ångströms to microns. For many of them uniquely strong polarization rotation and high values of chiral anisotropy factors was observed. It will be shown that, the high values of chiroptical activity found in CNI are due to strong resonances of incident electromagnetic radiation with plasmonic and excitonic states typical for metals and semiconductors typical for inorganic matter. At the same time, distinct similarities of CNI with chiral supramolecular and biological systems also emerged. They can be seen in the synthesis and separation methods, chemical properties of individual NPs, geometries of the NP assemblies, and interactions with biological counterparts. For instance, semiconductor NPs modified by L- and D-aminoacids spontaneously assemble into biosimilar helices with near unity enantiomeric excess, e.g. 98%. The analysis of these similarities with known biological, supramolecular, and liquid crystalline materials help us understand in greater depth the role of chiral asymmetry in Nature and accelerate the development of technologies based on chiroplasmonic and chiroexcitonic effects. Technological prospects of chiral inorganic materials with current front runners being biosensing, chiral catalysis, and chiral photonics will be presented.

Relevant References:
  1. Chen, W. et al. Nanoparticle Superstructures Made by Polymerase Chain Reaction: Collective Interactions of Nanoparticles and a New Principle for Chiral Materials. Nano Lett. 2009, 9(5), 2153.
  2. Kotov, N.A. Inorganic Nanoparticles as Protein Mimics Science, 2010, 330, 188.
  3. Ma, M.; et al. Attomolar DNA Detection with Chiral Nanorod Assemblies. Nature Comm. 2013, 4, 2689.
  4. Yan, W.; et al. Self-Assembly of Chiral Nanoparticle Pyramids with Strong R/S Optical Activity. J. Am. Chem. Soc. 2012, 134(36), 15114.
  5. Srivastava, S.; et al Light-Controlled Self-Assembly of Semiconductor Nanoparticles into Twisted Ribbons. Science 2010, 327, 1355–1359.
  6. J.Yeom, et al Chiral Templating of Self-Assembling Nanostructures by Circularly Polarized Light, Nature Mater. 2015, 14, 66.
  7. W. Feng, et al Assembly of Mesoscale Helices with Near Unity Enantiomeric Excess and Light-Matter Interactions for Chiral Semiconductors, Science Advances, 2017, 3(3) e1601159.

About the speaker: Prof. Kotov is a pioneer in the synthesis of nanoparticles and their self-assembly. He is a Fellow of the Royal Society of Chemistry, Thompson Reuters Highly Cited Researcher, MRS Fellow, and the MRS Medal winner, amongst numerous other awards.

This talk is part of the Bottom-Up Synthesis series.

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