Chiral Recognition in Cold Gas-Phase Cluster Ions of Carbohydrates and Tryptophan Probed by Photodissociation
Chiral recognition between tryptophan (Trp) and carbohydrates such as d-glucose (d-Glc), methyl-α-d-glucoside (d-glucoside), d-maltose, and d-cellobiose in cold gas-phase cluster ions was investigated as a model for chemical evolution in interstellar molecular clouds using a tandem mass spectrometer containing a cold ion trap. The photodissociation mass spectra of cold gas-phase clusters that contained Na+, Trp enantiomers, and d-maltose showed that Na+(d-Glc) was formed via the glycosidic bond cleavage of d-maltose from photoexcited homochiral Na+(d-Trp)(d-maltose), while the dissociation did not occur in heterochiral Na+(l-Trp)(d-maltose). The enantiomer-selective dissociation was also observed in the case of d-cellobiose. The enantiomer-selective glycosidic bond cleavage of disaccharides suggested that photoexcited d-Trp could prevent chemical evolution of sugar chains from d-enantiomer of carbohydrates in molecular clouds. The spectra of gas-phase clusters that contained Na+, Trp enantiomers, and d-Glc indicated that enantiomer-selective protonation of l-Trp from d-Glc could induce enantiomeric excess via collision-activated dissociation of the protonated l-Trp. In the case of protonated clusters, photoexcited H+(l-Trp) dissociated via Cα–Cβ bond cleavage in the presence of d-Glc or d-glucoside, where the excited states of H+(l-Trp) contributed to the enantiomer-selective reaction in the clusters. These enantiomer selectivities in cold gas-phase clusters indicated that chirality of a molecule induced enantiomeric excess of other molecules via enantiomer-selective reactions in molecular clouds.
KeywordsChemical evolution Molecular cloud Enantiomer Chirality Mass spectrometry
This work was supported by JSPS KAKENHI Grant Number 17 K14441.
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