Precursors of fatty alcohols in the ISM: Discovery of n-propanol
  Theories on the origins of life propose that early cell membranes were
synthesized from amphiphilic molecules simpler than phospholipids such as fatty
alcohols. The discovery in the interstellar medium (ISM) of ethanolamine, the
simplest phospholipid head group, raises the question whether simple
amphiphilic molecules are also synthesized in space. We investigate whether
precursors of fatty alcohols are present in the ISM. For this, we have carried
out a spectral survey at 7, 3, 2 and 1 mm toward the Giant Molecular Cloud
G+0.693-0.027 located in the Galactic Center using the IRAM 30m and Yebes 40m
telescopes. Here, we report the detection in the ISM of the primary alcohol
n-propanol (in both conformers Ga-n-C3H7OH and Aa-n-C3H7OH), a precursor of
fatty alcohols. The derived column densities of n-propanol are (5.5+-0.4)x10^13
cm^-2 for the Ga conformer and (3.4+-0.3)x10^13 cm^-2 for the Aa conformer,
which imply molecular abundances of (4.1+-0.3)x10^-10 for Ga-n-C3H7OH and of
(2.5+-0.2)x10^-10 for Aa-n-C3H7OH. We also searched for the AGa conformer of
n-butanol (AGa-n-C4H9OH) without success yielding an upper limit to its
abundance of <4.1x10^-11. The inferred CH3OH:C2H5OH:C3H7OH:C4H9OH abundance
ratios go as 1:0.04:0.006:<0.0004 toward G+0.693-0.027, i.e. they decrease
roughly by one order of magnitude for increasing complexity. We also report the
detection of both syn and anti conformers of vinyl alcohol, with column
densities of (1.11+-0.08)x10^14 cm^-2 and (1.3+-0.4)x10^13 cm^-2, and
abundances of (8.2+-0.6)x10^-10 and (9.6+-3.0)x10^-11, respectively. The
detection of n-propanol, together with the recent discovery of ethanolamine in
the ISM, opens the possibility that precursors of lipids according to theories
of the origin of life, could have been brought to Earth from outer space.
