Infrared spectrum and structure of the homochiral serine octamer-dichloride complex

The amino acid serine is known to form a very stable octamer that has properties that set it apart from serine complexes of different sizes or from complexes composed of other amino acids. For example, both singly protonated serine octamers and anionic octamers complexed with two halogen ions strongly prefer homochirality, even when assembled from racemic D,L mixtures. Consequently, the structures of these complexes are of great interest, but no acceptable candidates have so far been identified. Here, we investigate anionic serine octamers coordinated with two chloride ions using a novel technique coupling ion mobility spectrometry-mass spectrometry with infrared spectroscopy, in combination with theoretical calculations. The results allow the identification of a unique structure for (Ser₈Cl₂)^2- that is highly symmetric, very stable and homochiral and whose calculated properties match those observed in experiments.