Enantiomer-selective photolysis of cold gas-phase tryptophan in L-serine clusters with linearly polarized light.

Photostability of cold gas-phase tryptophan (Trp) enantiomers in L-serine (L-Ser) clusters at 8 K as a model for interstellar molecular clouds was examined using a tandem mass spectrometer containing a cold ion trap to investigate the hypothesis that homochirality in gas-phase Ser clusters promotes the enantiomeric enrichment of other amino acids via enantiomer-selective photolysis with linearly polarized light. In the UV excitation of heterochiral H(+) (L-Ser) 3(D-Trp), the CO2-eliminated product in the cluster was observed. In contrast, the photodissociation mass spectrum of homochiral H(+)(L-Ser)3(L-Trp) showed that photolysis of amino acids in the cluster did not occur due to the evaporation of L-Ser molecules. In the spectra of the homochiral H(+)(L-Ser) (L-Trp) and heterochiral H(+)(L-Ser) (D-Trp), the evaporation of L-Ser was the primary reaction pathway, and no difference between the L- and D-enantiomers was observed. The findings confirm that when 3 L-Ser units are present in the cluster, the photolytic decomposition of Trp is enantiomerically selective.