Enantiomeric Control of Intrinsically Chiral Nanocrystals

Abstract

The chiral aspect of inorganic crystals that crystallize in chiral space groups has been largely ignored until recently, partly due to difficulties in characterizing the chiroptical properties of bulk crystals, and also due to the difficulty in separating (sub)micrometer‐scale chiral crystal enantiomers. In recent years, the colloidal synthesis of intrinsically chiral nanocrystals (NCs) of several chiral inorganic compounds with significant enantiomeric excess has been demonstrated. This is achieved through the use of chiral molecular ligands, which bind to the atomic/ionic components of the crystals, preferentially forming one crystal enantiomorph. Here, recent progress on several aspects of these NCs is described, including the connection between ligand structure and its ability to direct NC handedness, chiral amplification in the synthesis leading to enantiopure NC samples, spontaneous symmetry breaking, the formation of NCs with chiral shapes, the connection between lattice and shape chirality and mixed contributions of atomic‐scale and shape chirality to the chiroptical properties.

Shining light on chiral inorganic nanomaterials for biological issues

“…Bürgi 24 and coworkers, for example, fabricated chiral Au 38 (SR) 24 nanoclusters (Figure 2 A) using thiolate ligands (SR) which showed intrinsically chiral features. Similar intrinsic chirality has also been observed in semiconducting nanomaterials such as HgS nanocrystals 25 (Figure 2 B), Eu 3+ doped TbPO 4 NPs 26 (Figure 2 C) and CdSe/ZnS quantum dots (QDs) 27 (Figure 2 D). However, since the synthesis of these nanostructures produces very often racemic mixtures, it is necessary to separate the enantiomers for further applications.…”

Chirality communications between inorganic and organic compounds

“…Such “indirect transfer” process has also been observed in other material systems, 86,87 such as zeolites and MOFs, 88 silica, 83 CuO, 84 ZnO, 89 TiO 2, 90,91 CaCO 3, 85 and so forth. The common feature of these materials is that almost all of them contain spiral structures.…”

“…The structural evolution process could mimic the biogeneration of chiral objects, in which the structure varied along time and spiral structures gradually expanded. 9 Such "indirect transfer" process has also been observed in other material systems, 86,87 such as zeolites and MOFs, 88 silica, 83 CuO, 84 ZnO, 89 TiO 2, 90,91 CaCO 3, 85 and so forth. The common feature of these materials is that almost all of them contain spiral structures.…”

Chiral Transition Metal Oxides: Synthesis, Chiral Origins, and Perspectives

“…The introduction of chirality to TMOs has revolutionized the motif of TMOs with respect to their applications in area of chiroptical sensing and detection, enantioselective catalysis, biological‐tissue‐based therapy, and chirality‐based devices. Since a body of related reviews has well summarized the details about the possible applications of chiral inorganic NCs, [ 6,47–55 ] we would prefer only to highlight some representative examples of chiral TMOs here: 1)Chiroptical sensing and detection: Xu and co‐workers [ 56 ] reported recently that chiral CuxOS@ZIF‐8 nanostructures can be used as ultrasensitive probe for detection of H 2 S in vivo with the limit of detection of 0.3 × 10 −9 and 2.2 × 10 −9 m for CD and fluorescence methods because H 2 S can reduce the chiroptical intensity and increase the fluorescent signal of the nanostructures ( Figure A). Jiang's group [ 57 ] also demonstrated that cysteine‐capped Au/Fe 3 O 4 NPs can enantioselectively detect the percentage of d ‐tyrosine in a mixture of enantiomers via cysteine as the chiral selector. 2)Enantioselective catalysis: Qu and co‐workers [ 58 ] developed phenylalanine‐modified cerium oxide nanoparticles (CeNPs) as chiral nanozyme for stereoselective oxidation of 3,4‐dihydroxyphenylalanine (DOPA) enantiomers where l ‐CeNP showed higher catalytic ability for oxidation of d ‐DOPA while d ‐CeNP were more effective to l ‐DOPA (Figure 4B).…”