Discovery of the interstellar chiral molecule propylene oxide (CH3CHCH2O)

Chiral molecule discovered in space A chiral molecule is one that has two forms that are mirror images of each other: enantiomers. Biological systems overwhelmingly use one enantiomer over another, and some meteorites show an excess of one type. The two forms are almost identical chemically, so how this excess first arose is unknown. McGuire et al. used radio astronomy to detect the first known chiral molecule in space: propylene oxide. The work raises the prospect of measuring the enantiomer excess in various astronomical objects, including regions where planets are being formed, to discover how and why the excess first appeared. Science, this issue p. 1449 The first chiral molecule detected in space may offer clues to the origin of enantiomer excess. Life on Earth relies on chiral molecules—that is, species not superimposable on their mirror images. This manifests itself in the selection of a single molecular handedness, or homochirality, across the biosphere. We present the astronomical detection of a chiral molecule, propylene oxide (CH3CHCH2O), in absorption toward the Galactic center. Propylene oxide is detected in the gas phase in a cold, extended molecular shell around the embedded, massive protostellar clusters in the Sagittarius B2 star-forming region. This material is representative of the earliest stage of solar system evolution in which a chiral molecule has been found.

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