The electron spin as a chiral reagent

In contrast to the notion that enantiospecific chemical reactions require a chiral reagent molecule or catalyst, this work shows that enantioselective chemical transformations can be induced by the electron spin itself. As electrons are injected from a magnetized electrode into an adsorbed molecule, they have a distinct spin orientation relative to their velocity; i.e., they have a well-defined helicity. Thus, it is possible to replace a conventional enantiopure chemical reagent by spin-polarized electrons that provide the chiral bias for enantioselective reactions. Three examples of enantioselective chemistry, resulting from electron spin polarization, are presented. The first example demonstrates enantioselective association of a chiral molecule with an achiral self-assembled monolayer film that is spin-polarized. The other two studies show that the chiral bias provided by the electron helicity can drive both reduction and oxidation enantiospecific electrochemical reactions. In each case, the enantioselectivity does not result from enantiospecific interaction of the molecule with the ferromagnetic electrode, but rather it arises from the polarized spin that crosses the interface between the substrate and the molecule. In all three cases, the direction of the electron spin polarization defines the sense (left-handed versus right-handed) of the enantioselectivity. This work demonstrates a new mechanism for realizing enantioselective chemistry.