Propionamide (C2H5CONH2): The largest peptide-like molecule in space
  Peptide bonds, as the molecular bridges that connect amino acids, are crucial
to the formation of proteins. Searches and studies of molecules with embedded
peptide-like bonds are thus important for the understanding of protein
formation in space. Here we report the first tentative detection of
propionamide (C2H5CONH2), the largest peptide-like molecule detected in space
toward Sagittarius B2(N1) at a position called N1E that is slightly offset from
the continuum peak. A new laboratory measurements of the propionamide spectrum
were carried out in the 9-461 GHz, which provide good opportunity to check
directly for the transition frequencies of detected interstellar lines of
propionamide. Our observing result indicates that propionamide emission comes
from the warm, compact cores in Sagittarius B2, in which massive protostellars
are forming. The column density of propionamide toward Sgr B2(N1E) was derived
to be 1.5\times 10^{16} cm^-2, which is three fifths of that of acetamide, and
one nineteenth of that of formamide. This detection suggests that large
peptide-like molecules can form and survive during star-forming process and may
form more complex molecules in the interstellar medium. The detection of
propionamide bodes well for the presence of polypeptides, as well as other
complex prebiotic molecules in the interstellar medium.
