Nanocrystalline Aggregation of Serine Detected by Electrospray Ionization Mass Spectrometry:  Origin of the Stable Homochiral Gas-Phase Serine Octamer

Electrospray ionization sampling of 0.01 M solutions of serine reveals an unusually abundant protonated serine octamer, which demonstrates a strong preference for homochirality. Ion mobility spectra yield an experimental cross section that is consistent with a single “cubic” structure. Density functional theory calculations support experimental observations which suggest that the structure of the serine octamer is closely related to and formed from a small subsection of the crystal structure of anhydrous serine. The formation, bonding, and experimental constraints placed on the serine octamer are discussed in light of the proposed nanocrystalline structure. The mass spectra of the analogous molecules threonine and homoserine exhibit several similar features with that of serine and the likely structures for the octameric species are compared with that of the serine octamer. Finally, implications for the spontaneous symmetry breaking of a racemic mixture and the origin of life are addressed.