Symmetry breaking in the formation of chiral nanocrystals

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Symmetry breaking in the formation of chiral nanocrystals

Gil Markovich

School of Chemistry, Tel Aviv University

Chirality (lack of mirror symmetry) is a fundamental property of biomolecules (amino acids, proteins, nucleic acids, DNA, sugars), and an essential part of their complex structures. Remarkably, almost all such biomolecules are of a single handedness (homochirality), and the reason for this symmetry breaking is one of the key questions in understanding the origin of life.

We are interested in symmetry breaking in inorganic compounds. Many inorganic compounds crystallize in chiral space group, such as quartz, for example. Our group has been studying the breaking of left-right symmetry in the formation of nanocrystals of such compounds. We have shown, that using small chiral bio-molecules which interact with the crystals’ building blocks, it is possible to achieve such symmetry break. In particular, we have been working with the chiral TbPO₄×H₂O nanocrystals, and have shown that their handedness can be controlled by preparing the nanocrystals in the presence of certain natural chiral molecules, such as tartaric acid. We use circularly polarized luminescence measurements of Eu³⁺ dopant ions in the nanocrystals to follow the handedness and enantiomeric purity of the produced nanocrystals.[1] Using single particle circularly polarized luminescence microscopy we were able to determine the handedness of individual nanocrystals and confirmed that we obtain a single mirror image (enantiomer) of the terbium phosphate nanocrystals when prepared with tartaric acid molecules.[2] We also discovered that at low enough synthesis temperatures the nanocrystals (almost-) spontaneously, randomly break symmetry (in the presence of minute amounts of chiral material) and propose a model for the symmetry breaking effects in the nanocrystal formation. This kind of super-sensitive symmetry-breaking effects could serve as models for the riddle of homochirality of biomolecules at the origin of life.

References

1. U. Hananel, A. Ben-Moshe, H. Diamant, G. Markovich, Proc. Natl. Acad. Sci. USA 116, 11159-11164 (2019)
2. E. Vinegrad, U. Hananel, G. Markovich, O. Cheshnovsky, ACS Nano 13, 601–608 (2019).