Researchers from the Hebrew University of Jerusalem and Weizmann Institute of Science recently demonstrated that the direction of a magnetic field can influence the isotopic fractionation of a chiral biomolecule, establishing a clear experimental link between electron spin, molecular chirality, and isotope-dependent behavior on magnetized surfaces.
The study focuses on L-methionine, a chiral amino acid, and examines how molecules containing different carbon isotopes - 12C and 13C - interact with magnetized surfaces. While isotopic fractionation is widely used to trace biochemical pathways, the mechanisms governing isotope selectivity in chiral systems have remained poorly understood.
Using a magnetic filtration setup, the researchers passed solutions of L-methionine through surfaces embedded with microscopic magnetic particles. These surfaces could be magnetized in opposite directions, enabling controlled investigation of spin-dependent interactions. Mass spectrometry analysis revealed that the isotopic composition of methionine was altered after interaction with the magnetic filter. Specifically, the fractionation between 13C- and 12C-containing molecules depended on the magnetization direction, with molecules differing only in carbon isotope composition exhibiting measurably different interaction dynamics with oppositely magnetized surfaces.
This behavior suggests that isotope selectivity is not governed solely by mass differences, but also by spin-dependent effects arising from the coupling between electron spin polarization and nuclear properties.
The observed effect is consistent with chiral-induced spin selectivity (CISS), in which chiral molecules preferentially interact with electrons of a specific spin orientation. In this framework, L-methionine acts as a spin filter, and its interaction with a magnetic surface becomes sensitive to both molecular handedness and spin polarization.
The key advance in this work is the demonstration that CISS-driven processes extend to isotopic discrimination. Because isotopes differ in nuclear spin and mass, their coupling to electron spin leads to distinct transport and interaction behavior under magnetic conditions. As a result, reversing the magnetization alters which isotope is preferentially retained or transmitted through the filter, with the system exhibiting dynamic behavior including transient capture and release.
The experiment shows that 13C- and 12C-methionine exhibit different retention profiles on magnetized filters, that the sign and magnitude of isotopic fractionation depend on magnetic orientation, and that both natural-abundance and 13C-enriched samples display spin-dependent fractionation effects. These results provide direct evidence that electron spin polarization contributes to isotopic behavior in chiral molecular systems.
“This work introduces spin as a new player in isotope chemistry,” the researchers explain.
By linking magnetic interactions, chirality, and isotope effects, the study establishes a new framework for understanding isotopic fractionation in biological and chemical systems. Spin- and chirality-dependent interactions could eventually enable selective enrichment or separation of isotopes using magnetic surfaces, while also impacting how isotopic signatures in biomolecules are interpreted. The findings further suggest that magnetic environments could have influenced isotopic distributions and symmetry breaking in early chemical systems, potentially contributing to the emergence of homochirality.
More broadly, the results indicate that isotopic fractionation in biomolecules - often used as a fingerprint of biosynthetic origin - may partly arise from spin-dependent interactions rather than purely thermodynamic or kinetic effects. Even subtle quantum properties such as electron spin can measurably influence chemical outcomes when coupled with molecular chirality and magnetic fields, adding a new physical dimension to isotope chemistry.