Experiments show that beams of left- or right-handed electrons are not equal-opportunity destroyers of molecules having two mirror-image forms, which supports the idea that primordial cosmic rays generated the asymmetry in biological molecules.
An asymmetric reaction billions of years ago between electrons and the ancestors of biomolecules might explain why today’s DNA always appears as a right-handed helix. Now researchers have shown that a beam of right-handed electrons—whose spin and direction of motion align according to the right hand—breaks apart more right-handed molecules at low energies than left-handed ones. Unlike previous experiments showing such a difference, the reactions occurred in the gas phase and with low-energy electrons, which allowed for a more precise description of the electron-molecule interactions. The researchers say their results are an important step toward more direct tests of the hypothesis that nuclear asymmetries led to asymmetries in present-day biomolecules.
Many molecules come in both left- and right-handed (chiral) forms, but natural DNA is always right-handed. The asymmetry “is one of the few unsolved fundamental questions in [the] natural sciences,” says Uwe Meierhenrich, a physical chemist at the University of Nice Sophia Antipolis in France.
One possible explanation comes from nuclear physics. The radioactive decay of a nucleus is more likely to produce a left-handed electron than a right-handed one—meaning that it’s more likely to spin in the direction of your left hand’s curled fingers when you point your left thumb in the direction of its motion. When this asymmetry was discovered in 1957, “it showed us that God is not ambidextrous,” says Timothy Gay of the University of Nebraska in Lincoln. Continue reading Electron Handedness Affects Gas Molecule Breakup