Amazing stuff!
"... In a new study ... the researchers found that an electron experiences a magnetic field of different strength when traveling through each mirror-image form. This asymmetric behavior not only challenges conventional assumptions but also lends support to a theory about how life began on Earth. ...
Although chiral molecules can exist in two forms, scientists realized more than 150 years ago that living organisms “choose” only one: a left-handed form for proteins and a right-handed form for sugars, DNA and RNA. ...
A first step toward solving the puzzle came in 1999, when ... passed an electric current – a stream of electrons – through chiral molecules and discovered that each mirror-image form behaves differently. Electrons act like tiny magnets, with north and south poles, and possess a property called spin, which determines their magnetic orientation. As these tiny magnets move through a chiral molecule, they follow a spiral path, which causes them to experience a magnetic force that can either accelerate or hinder their motion. The researchers found that the two mirror-image forms exert opposite effects: One mainly speeds up electrons whose north pole aligns with their direction of motion, while the other speeds up electrons whose north pole points in the opposite direction. ...
that the two mirror-image forms not only favor electrons with opposite spins but also transmit them with different efficiencies. ...
The experiments revealed substantial differences in the strength of the magnetic field experienced by electrons in the two forms ...
“Our breakthrough was realizing that the difference between these two seemingly identical forms only emerges in motion,” ..."
From the 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."
Dynamic breaking of mirror symmetry in spin-dependent electron transport through chiral media causes enantiomeric excesses (open access)
Adsorption of crystals of a biological chiral molecule onto a gold-coated cobalt surface. Larger crystals of one specific form of the molecule (left) tend to accumulate on this surface to a greater degree than those of its mirror-image form (right). ...
Fig. 1. The alignment of the total spin and the magnetic vectors.
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