Chiral recognition ability of alanine dipeptides studied by ultraviolet photodissociation spectroscopy and water adsorption of cold gas-phase hydrogen-bonded clusters

Abstract

Enantiomer-selective reactions in cold gas-phase hydrogen-bonded clusters of l-alanine dipeptide (l-Ala2) and tryptophan (Trp) enantiomers were investigated as a model for chemical evolution in interstellar molecular clouds using a tandem mass spectrometer equipped with an electrospray ionization source and cold ion trap. The ultraviolet-photoinduced NH2CHCOOH elimination and l-Ala2 detachment from the clusters showed the same wavelength dependence at 265–290 nm for heterochiral H+(d-Trp) (l-Ala2) and homochiral H+(l-Trp) (l-Ala2). The elimination of CO2 from the heterochiral clusters was the main reaction at 265–282 nm, while the elimination of CO2 from the homochiral hydrogen-bonded clusters was suppressed by intermolecular interactions. Water molecules preferentially adsorbed on the surface of the heterochiral hydrogen-bonded clusters, indicating a larger number of free X–H groups (X = O and N) on the surface of the heterochiral clusters compared to the surface of the homochiral clusters.