Contribution Contributed Talk
Deuteration of interstellar glycine on low-temperature surfaces: A possible route to the formation of chiral molecules in dense molecular clouds
- Dr. Yasuhiro OBA
- Dr. Yasuhiro OBA (Institute of Low Temperature Science, Hokkaido University)
The simplest amino acid glycine (NH$_2$CH$_2$COOH: d$_0$-Gly) is an achiral amino acid. However, if one of the carbon-bound hydrogen is replaced with a deuterium atom, it becomes a chiral molecule (NH$_2$CHDCOOH: d$_1$-Gly). Although there have been no reports on the detection of chiral species in space, chiral glycine has a potential to be one of the primordial chiral molecules in space. We then performed laboratory experiments on the formation of chiral glycine by grain-surface reactions at low temperatures. Gaseous d$_0$-Gly was codeposited with deuterium (D) atoms or a mixture of hydrogen (H) and D atoms (H:D = 10:1) on an Al substrate (12 K) in an ultra-high vacuum reaction chamber. Reaction products were analyzed by using a high-resolution mass spectrometer. We confirmed the formation of d$1$-Gly and doubly deuterated glycine (NH$_2$CD$_2$COOH: d$_2$-Gly) in the reaction products, even under the H-dominant conditions. This result suggests that the formation of chiral glycine is possible in dense molecular clouds where H atoms dominate over D atoms. The following reactions are considered to play a role for the formation of chiral glycine: (1) NH$_2$CH$_2$COOH + D → NH$_2$CHCOOH + HD, and (2) NH$_2$CHCOOH + D → NH$_2$CHDCOOH. Since reaction (1) has a large barrier, this reaction would not proceed thermally at ~10 K. Quantum-tunneling is therefore necessary for the reaction to proceed at such low temperatures. At the presentation, we will show experimental results in more detail and another pathway to the formation of chiral glycine under the conditions of dense molecular clouds.