Sum of electric and magnetic transition dipole moments – A new molecular descriptor for explaining enantiomeric enrichment of chiral amino acids by l- and r-circularly polarized light

Abstract

One of the big scientific questions is why all amino acids constituting biomolecules have the l-configuration in nature. Enantiomeric enrichment of chiral amino acids by left- and right-circularly polarized light (l- and r-CPL) could be part of the answer. Previous studies directly measured the enantiomeric excesses of amino acids initiated by l- and r-CPL. This study found well-known molecular properties for circular dichroism: electric transition dipole moment, magnetic transition dipole moment, rotational strength, and anisotropy factor could not explain those enantiomeric excess data. By means of DFT/TDDFT (B3LYP-D3BJ) with a basis set (def2-TZVPD), this study discovered that a new molecular descriptor: the sum of electric and magnetic transition dipole moments could provide an explanation of those enantiomeric excess data. In addition, this discovery may provide new theoretical insights into photochemical reactions initiated by l- and r-CPL and assist in establishing fundamental chemistry for the abiotic origin of life.