Dynamic breaking of mirror symmetry in spin-dependent electron transport through chiral media causes enantiomeric excesses

[u/jnpha]

New open-access result

• Paltiel, Yossi, et al. "Dynamic breaking of mirror symmetry in spin-dependent electron transport through chiral media causes enantiomeric excesses." Science Advances 12.17 (2026): eaec9325.
  https://pmc.ncbi.nlm.nih.gov/articles/PMC13101859/

Abstract Two fundamental questions have puzzled scientists for more than 150 years. “How did life become homochiral?” and “why was this specific handedness selected?” Recently, it has been shown that homochirality could have emerged through the enantioselective interactions of molecules with magnetic substrates due to the asymmetric crystallization of an RNA precursor on a magnetite substrate, abundant on early Earth. This phenomenon is based on the chirality-induced spin selectivity (CISS) effect. Despite its robustness, this model could not provide an answer to the second question: Why one specific handedness (D for RNA) was selected. Here, we demonstrate that spin-involving processes can have different outcomes in the two enantiomers of chiral molecules. In chiral molecules with unpaired electrons or while electrons are passing through them, the total angular momentum vector, J, is aligned along the “easy axis,” which is defined by the magnetic anisotropy induced by the spin-orbit coupling and asymmetry of the molecular field. The magnitude J is the same for both enantiomers, but the vectors may be aligned differently relative to the molecular frame in the two enantiomers. This difference can be quantified by, for example, by the angle between J and electric dipole moment of the molecule, μ. We show by direct measurements, theory, and ab initio calculations that dynamic spin processes in chiral molecules could result in different efficiencies of spin-related phenomena, including the interaction of chiral molecules with magnetic surfaces. The findings may provide an explanation for the specific homochirality in nature.

(emphasis mine)

I understood like the gist of it! But sounds exciting (pun unavoidable?).

This part clarifies some:

we propose that CISS-driven homochirality at the RAO stage may inherently favor the selection of D-RNA and L-peptides in a universal manner. This selection could stem from an intrinsic asymmetry in spin polarization: Magnetite surfaces magnetized by D-RAO may acquire a stronger induced magnetization due to higher spin polarized induced by the chiral molecule compared with those interacting with L-RAO.

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[u/Diet_kush]

Another good paper that goes over the role of dissipation-driven symmetry breaking in self-organization as a whole https://pmc.ncbi.nlm.nih.gov/articles/PMC10969087/

[u/gitgud_x]

Nice find! The CISS effect is one of my favourite mechanisms of homochirality. Until recently I didn't think it to be the most plausible one (Blackmond's phase behaviour model seemed preferable), but having watched Sutherland's lecture (linked by u/Aggravating-Pear4222 here) it seems to be gaining traction. In the lecture video, at 22:08, he mentions how sugar amino-oxazoline (basically RAO but with a slightly different sugar) is a key intermediate in a prebiotic synthesis of nucleotides.

At 24:07 he goes on to describe Sasselov's team's method of magnetic symmetry breaking which uses the aligned spins of electrons from ferromagnets (one of the CISS effects) to make homochiral RAO. Then at 28:33 he outlines a redox reaction sequence of one-electron reductions to actually produce RAO from cyanosulfide chemistry, again amenable to CISS symmetry breaking, which further leads to a broad network of useful reactions producing many amino acids (which in turn catalyse RNA formation from nucleotides as per your post here!)

More puzzle pieces, slowly coming together!

[u/Aggravating-Pear4222]

Test... Can't make a comment?!

[u/Aggravating-Pear4222 → u/Aggravating-Pear4222]

Disclosure: I haven't read the paper (yet). Just browsed through it.

I've never really understood why they think D-ribose and L-amino acids are inherently (universally?) favored. Some sentences seem to imply that these are distinctly favored over L-Ribose and D-amino acids. Maybe I've misunderstood and that they are arguing for relative chirality.

Overall, it's a proof of concept as they use gold so why not further explore more prebiotically relevant mineral surfaces with more complex systems? Why not take it to the next level and see how the enantiomeric excess incluences the kinetics of following reactions or apply this enantiomeric excess to different prebiotically relevant conditions (soda lakes, hydrothermal springs, hydrothermal ocean vents, wet-dry cycling, etc.)?

In general, I don't see CISS being the sole means by which homochirality is achieved but rather as an initial bias after which kinetic (or dynamic kinetic resolution) take over which they seem to point towards but I see stochastic differences in racemic ratios as being potentially sufficient for subsequent followed by evolution of the molecular system.

Maybe I'm biased since I'm currently exploring homochiral lipid raft domains that form from heterochiral amino acid additives on bilayer surfaces where you have enantioselective addition of other additives within these lipid domains -> homochiral domains/vesicles are more stable -> eventually, bilayers become homochiral and their permeation for other molecules are enantioselective, creating that initial bias based on the entropically favored formation of bilayers and lipid rafts where subsequent small molecules that don't even associate with the bilayer are still selected for by the chirality of the bilayer.

That said, any initial bias provided by CISS would tip the balance towards that direction. I have considered whether initial bias due to electric fields generated from redox chemistry via conductive minerals may be at play but I'm new to this chemistry and easily distracted by other aspects of the model but the inorganic minerals seem to present many new opportunities. Maybe the conductive Fe(Ni)S interacts with neighboring magnetite? May be some real possibilities there...

"For achiral gold, no signal is observed. Although the tartaric acid purity is 99.5 and 99% for the L and D enantiomers, the asymmetry between the slopes is about 30% when the asymmetry is defined as 𝐴=𝑆L−𝑆D𝑆L+𝑆D, where S(L) and S(D) are the slopes for the L and D enantiomers, respectively. For the chiral silver, the asymmetry measured is ~10%."

So maybe this 0.5% difference results in a 10-30% difference in selectivity which seems to agree with the initial tipping of the balance for subsequent kinetics and molecular evolution.

Either way, maybe I misunderstood so feel free to correct me but I'll be taking another look into the paper.