It's the spin that makes the difference
Biomolecules such as amino acids and sugars occur in two mirror-image forms – in all living organisms, however, only one is ever found. Why this is the case is still unclear. Researchers at Empa and Forschungszentrum Jülich in Germany have now found evidence that the interplay between electric and magnetic fields could be at the origin of this phenomenon.
The so-called homochirality of life – the fact that all biomolecules in living organisms only ever occur in one of two mirror-image forms – has puzzled a number of scientific luminaries, from the discoverer of molecular chirality, Louis Pasteur, to William Thomson (Lord Kelvin) and Nobel Prize winner Pierre Curie. A conclusive explanation is still lacking, as both forms have, for instance, the same chemical stability and do not differ from each other in their physico-chemical properties. The hypothesis, however, that the interplay between electric and magnetic fields could explain the preference for one or the other mirror-image form of a molecule – so-called enantiomers – emerged early on.
It was only a few years ago, though, that the first indirect evidence emerged that the various combinations of these force fields can indeed "distinguish" between the two mirror images of a molecule. This was achieved by studying the interaction of chiral molecules with metallic surfaces that exhibit a strong electric field over short distances. The surfaces of magnetic metals such as iron, cobalt or nickel thus allow electric and magnetic fields to be combined in various ways – the direction of magnetization is simply reversed, from "North up – South down" to "South up – North down". If the interplay between magnetism and electric fields actually triggers "enantioselective" effects, then the strength of the interaction between chiral molecules and magnetic surfaces should also differ, for example – depending on whether a right-handed or left-handed molecule "settles" on the surface.