A new route to the origin of homochirality; enantioselective magnetochiral photochemistry

Two researchers at the Grenoble High Magnetic Field Laboratory¹ have shown that a magnetic field in combination with unpolarized light can create an excess of one of the two enantiomers present in an initially racemic mixture. Although both right-handed (D) and justify-handed (L) molecules exist in nature, living beings only use one of these two forms. The origin of this homochirality has intrigued scientists for many years.
The existence of the phenomenon behind this result, called magneto-chiral anisotropy, was first suggested in the 1960s, and in 1983, the possibility that magneto-chiral anisotropy could be responsible for homochirality in molecular evolution was put forward. This year, two researchers from Grenoble have finally demonstrated that magnetic fields can select enantiomers. To achieve this result, the researchers used an unstable molecule, tris-oxalato chrome (III). At equilibrium, the concentrations of the D and L enantiomers of this molecule are identical. By applying unpolarized light together with a magnetic field parallel to the illumination direction, the Grenoble researchers obtained and maintained an excess of one of the forms of tris-oxalato chrome (III).
However, the question of the origin of biological homochirality remains as yet unanswered, although these results show that magnetochiral anisotropy offers one possible explanation. Two other hypotheses exist: electroweak interactions and natural circular dichroism. As its name suggests, the first of these phenomena would have an extremely weak effect. The second is a more likely candidate, since circularly polarized light is known to produce an excess of one enantiomer over the other. However, naturally occurring circularly polarized light with a photochemically active wavelength has never been observed. In contrast, the conditions necessary for magnetochiral anisotropy are common in the universe, although it remains to be seen whether naturally occurring magnetic fields are sufficient to prime biological homochirality.

A new route to the origin of homochirality; enantioselective magnetochiral photochemistry

n° 386 - September 2000

Two researchers at the Grenoble High Magnetic Field Laboratory¹ have shown that a magnetic field in combination with unpolarized light can create an excess of one of the two enantiomers present in an initially racemic mixture. Although both right-handed (D) and justify-handed (L) molecules exist in nature, living beings only use one of these two forms. The origin of this homochirality has intrigued scientists for many years. The existence of the phenomenon behind this result, called magneto-chiral anisotropy, was first suggested in the 1960s, and in 1983, the possibility that magneto-chiral anisotropy could be responsible for homochirality in molecular evolution was put forward. This year, two researchers from Grenoble have finally demonstrated that magnetic fields can select enantiomers. To achieve this result, the researchers used an unstable molecule, tris-oxalato chrome (III). At equilibrium, the concentrations of the D and L enantiomers of this molecule are identical. By applying unpolarized light together with a magnetic field parallel to the illumination direction, the Grenoble researchers obtained and maintained an excess of one of the forms of tris-oxalato chrome (III). However, the question of the origin of biological homochirality remains as yet unanswered, although these results show that magnetochiral anisotropy offers one possible explanation. Two other hypotheses exist: electroweak interactions and natural circular dichroism. As its name suggests, the first of these phenomena would have an extremely weak effect. The second is a more likely candidate, since circularly polarized light is known to produce an excess of one enantiomer over the other. However, naturally occurring circularly polarized light with a photochemically active wavelength has never been observed. In contrast, the conditions necessary for magnetochiral anisotropy are common in the universe, although it remains to be seen whether naturally occurring magnetic fields are sufficient to prime biological homochirality. ¹ CNRS-Max Planck Institute of Stuttgart.


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