Doktora Tez Savunması - A New Spin on the Origin of Homochirality

A New Spin on the Origin of Biological Homochirality

Abstract: Essential molecules of life—amino acids, nucleic acids, and sugars—are chiral; they exist in mirror-symmetrical pairs. However, biological systems exclusively use only one form of these pairs: right-handed sugars and nucleic acids, along with left-handed amino acids. This phenomenon characterizes life as homochiral. However, the origins of this asymmetry remain elusive, and it is this long-standing mystery that we address in this thesis. The chiral-induced spin selectivity (CISS) effect has established a strong coupling between electron spin and molecular chirality, and this coupling paves the way for breaking the chiral molecular symmetry by spin-selective processes. Achiral magnetic surfaces, when spin-polarized, can function as chiral agents due to the CISS effect, serving as templates for the asymmetric crystallization of chiral molecules. In this thesis, we studied the spin-selective crystallization of racemic ribo-aminooxazoline (RAO), a central precursor of RNA, on magnetite surfaces—achieving homochirality in two crystallization steps. Moreover, we have shown the chirality-induced avalanche magnetization of magnetite by RAO molecules, which verifies the reciprocal nature of the effect and allows for a cooperative feedback between chiral molecules and magnetic surfaces. Finally, based on empirical evidence, we propose a pathway through which the achieved homochirality in a single chiral compound, RAO, can efficiently propagate throughout the entire prebiotic network, starting from D-nucleic acids, to L-peptides, and then to homochiral metabolites. Our results demonstrate a prebiotically plausible way of achieving systems-level homochirality from completely racemic starting materials.

References:
[1] S. F. Ozturk, D. D. Sasselov, Proceedings of the National Academy of Sciences 2022, 119, e2204765119.
[2] S. F. Ozturk, Z. Liu, J. D. Sutherland, D. D. Sasselov, Science Advances 2023, 9, eadg8274.
[3] S. F. Ozturk, D. K. Bhowmick, Y. Kapon, Y. Sang, A. Kumar, Y. Paltiel, R. Naaman, D. D. Sasselov, Nature Communications 2023, 14, 6351.
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[6] Saplakoglu, Yasemin. (2023). Magnetism May Have Given Life Its Molecular Asymmetry. Quanta Magazine.

Dissertation Chair: Mikhail Lukin
Research Advisor/Co-Chair: Dimitar Sasselov
Dissertation Committee: Markus Greiner, Jack Szostak