Significance
The detection of ethanolamine (
N
H
2
C
H
2
C
H
2
OH) in a molecular cloud in the interstellar medium confirms that a precursor of phospholipids is efficiently formed by interstellar ...chemistry. Hence, ethanolamine could have been transferred from the proto-Solar nebula to planetesimals and minor bodies of the Solar System and thereafter to our planet. The prebiotic availability of ethanolamine on early Earth could have triggered the formation of efficient and permeable amphiphilic molecules such as phospholipids, thus playing a relevant role in the evolution of the first cellular membranes needed for the emergence of life.
Cell membranes are a key element of life because they keep the genetic material and metabolic machinery together. All present cell membranes are made of phospholipids, yet the nature of the first membranes and the origin of phospholipids are still under debate. We report here the presence of ethanolamine in space,
N
H
2
C
H
2
C
H
2
OH, which forms the hydrophilic head of the simplest and second-most-abundant phospholipid in membranes. The molecular column density of ethanolamine in interstellar space is
N
= (1.51
±
0.07)
×
10
13
c
m
−
2
, implying a molecular abundance with respect to
H
2
of
(
0.9
−
1.4
)
×
10
−
10
. Previous studies reported its presence in meteoritic material, but they suggested that it is synthesized in the meteorite itself by decomposition of amino acids. However, we find that the proportion of the molecule with respect to water in the interstellar medium is similar to the one found in the meteorite (
10
−
6
). These results indicate that ethanolamine forms efficiently in space and, if delivered onto early Earth, could have contributed to the assembling and early evolution of primitive membranes.
The chemical compounds carrying the thiol group (-SH) have been considered essential in recent prebiotic studies regarding the polymerization of amino acids. We have searched for this kind of ...compound toward the Galactic Center quiescent cloud G+0.693–0.027. We report the first detection in the interstellar space of the trans-isomer of monothioformic acid (t-HC(O)SH) with an abundance of ∼1 נ10−10. Additionally, we provide a solid confirmation of the gauche isomer of ethyl mercaptan (g-C2H5SH) with an abundance of ∼3 נ10−10, and we also detect methyl mercaptan (CH3SH) with an abundance of ∼5 נ10−9. Abundance ratios were calculated for the three SH-bearing species and their OH analogs, revealing similar trends between alcohols and thiols with increasing complexity. Possible chemical routes for the interstellar synthesis of t-HC(O)SH, CH3SH, and C2H5SH are discussed, as well as the relevance of these compounds in the synthesis of prebiotic proteins in the primitive Earth.
Abstract
Radio-loud quasars at high redshift (
z
≥ 4) are rare objects in the universe and rarely observed with Very Long Baseline Interferometry (VLBI). But some of them have flux density ...sufficiently high for monitoring of their apparent position. The instability of the astrometric positions could be linked to the astrophysical process in the jetted active galactic nuclei in the early universe. Regular observations of the high-redshift quasars are used for estimating their apparent proper motion over several years. We have undertaken regular VLBI observations of several high-redshift quasars at 2.3 GHz (
S
band) and 8.4 GHz (
X
band) with a network of five radio telescopes: 40 m Yebes (Spain), 25 m Sheshan (China), and three 32 m telescopes of the Quasar VLBI Network (Russia)—Svetloe, Zelenchukskaya, and Badary. Additional facilities joined this network occasionally. The sources have also been observed in three sessions with the European VLBI Network in 2018–2019 and one Long Baseline Array experiment in 2018. In addition, several experiments conducted with the Very Long Baseline Array in 2017–2018 were used to improve the time sampling and the statistics. Based on these 37 astrometric VLBI experiments between 2017 and 2021, we estimated the apparent proper motions of four quasars: 0901+697, 1428+422, 1508+572, and 2101+600.
Abstract
A quarter century after the detection of the last interstellar carboxylic acid, acetic acid (CH
3
COOH), we report the discovery of a new one, the
cis-trans
form of carbonic acid (HOCOOH), ...toward the Galactic center molecular cloud G+0.693–0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also directly identified several pairs of unblended lines in the astronomical data (between 75 and 120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for
cis-trans
HOCOOH of
N
= (6.4 ± 0.4) × 10
12
cm
−2
, which yields an abundance with respect to molecular H
2
of 4.7 × 10
−11
. Meanwhile, the extremely low dipole moment (about 15 times lower) of the lower-energy conformer,
cis-cis
HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H
2
of ≤1.2 × 10
−9
, which suggests that
cis-cis
HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a
cis-cis
/
cis-trans
ratio of ≤25, consistent with the smaller energy difference between both conformers compared with the relative stability of
trans-
and
cis
-formic acid. Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the solar system, which could be inherited during the star formation process.
We report the first detection in the interstellar medium (ISM) of a C2H5O2N isomer: syn-glycolamide (NH2C(O)CH2OH). The exquisite sensitivity at sub-mK levels of an ultradeep spectral survey carried ...out with the Yebes 40 m and IRAM 30 m telescopes toward the G+0.693–0.027 molecular cloud has allowed us to unambiguously identify multiple transitions of this species. We derived a column density of (7.4 ± 0.7) × 1012 cm−2, which implies a molecular abundance with respect to H2 of 5.5 × 10−11. The other C2H5O2N isomers, including the higher-energy anti conformer of glycolamide and two conformers of glycine, were not detected. The upper limit derived for the abundance of glycine indicates that this amino acid is surely less abundant than its isomer glycolamide in the ISM. The abundances of the C2H5O2N isomers cannot be explained in terms of thermodynamic equilibrium; thus, chemical kinetics need to be invoked. While the low abundance of glycine might not be surprising, based on the relative low abundances of acids in the ISM compared to other compounds (e.g., alcohols, aldehydes, or amines), several chemical pathways can favor the formation of its isomer glycolamide. It can be formed through radical–radical reactions on the surface of dust grains. The abundances of these radicals can be significantly boosted in an environment affected by a strong ultraviolet field induced by cosmic rays, such as that expected in G+0.693–0.027. Therefore, as shown by several recent molecular detections toward this molecular cloud, it stands out as the best target to discover new species with carbon, oxygen, and nitrogen with increasing chemical complexity.
Abstract
We present the first detection in space of O-protonated carbonyl sulfide (HOCS
+
), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the ...observation of all
K
a
= 0 transitions ranging from
J
lo
= 2 to
J
lo
= 13 of HOCS
+
covered by our survey, we derive a column density of
N
= (9 ± 2) × 10
12
cm
−2
, translating into a fractional abundance relative to H
2
of ∼7 × 10
−11
. Conversely, the S-protonated HSCO
+
isomer remains undetected, and we derive an upper limit to its abundance with respect to H
2
of ≤3 × 10
−11
, a factor of ≥2.3 less abundant than HOCS
+
. We obtain an HOCS
+
/OCS ratio of ∼2.5 × 10
−3
, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of HOCS
+
is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionization rates (10
−15
–10
−14
s
−1
) are needed to reproduce the observed abundance of HOCS
+
. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find an HOCO
+
/HOCS
+
ratio of ∼31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value (∼37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.
Abstract
Amines, particularly primary amines (R-NH
2
), are closely related to the primordial synthesis of amino acids since they share the same structural backbone. However, only a limited number of ...amines has been identified in the interstellar medium, which prevents us from studying their chemistry as well as their relation to prebiotic species that could lead to the emergence of life. In this Letter, we report the first interstellar detection of vinylamine (C
2
H
3
NH
2
) and tentative detection of ethylamine (C
2
H
5
NH
2
) toward the Galactic center cloud G+0.693-0.027. The derived abundance with respect to H
2
is (3.3 ± 0.4) × 10
−10
and (1.9 ± 0.5) × 10
−10
, respectively. The inferred abundance ratios of C
2
H
3
NH
2
and C
2
H
5
NH
2
with respect to methylamine (CH
3
NH
2
) are ∼0.02 and ∼0.008, respectively. The derived abundance of C
2
H
3
NH
2
, C
2
H
5
NH
2
, and several other NH
2
-bearing species are compared to those obtained toward high-mass and low-mass star-forming regions. Based on recent chemical and laboratory studies, possible chemical routes for the interstellar synthesis of C
2
H
3
NH
2
and C
2
H
5
NH
2
are discussed.
We report the first detection in the interstellar medium of N-cyanomethanimine (H2CNCN), the stable dimer of HCN of highest energy and the most complex organic molecule identified in space containing ...the prebiotically relevant NCN backbone. We have identified a plethora of a-type rotational transitions with 3 ≤ Jup ≤ 11 and Ka ≤ 2 that belong to this species toward the Galactic center G+0.693-0.027 molecular cloud, the only interstellar source showing the three cyanomethanimine isomers (including the Z- and E-isomers of C-cyanomethanimine, HNCHCN). We have derived a total column density for H2CNCN of (2.9 ± 0.1) × 1012 cm−2, which translates into a total molecular abundance with respect to H2 of (2.1 ± 0.3) × 10−11. We have also revisited the previous detection of E- and Z-HNCHCN and found a total C/N-cyanomethanimine abundance ratio of 31.8 ± 1.8 and a Z/E-HNCHCN ratio of 4.5 ± 0.2. While the latter can be explained on the basis of thermodynamic equilibrium, chemical kinetics are more likely responsible for the observed C/N-cyanomethanimine abundance ratio, where the gas-phase reaction between methanimine (CH2NH) and the cyanogen radical (CN) arises as the primary formation route.
Context.
Theories of the origins of life propose that early cell membranes were synthesised 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 synthesised in space.
Aims.
We investigate whether precursors of fatty alcohols are present in the ISM.
Methods.
To do this, we have carried out a spectral survey at 7, 3, 2 and 1 mm towards the Giant Molecular Cloud G+0.693-0.027 located in the Galactic centre using the IRAM 30 m and Yebes 40 m telescopes.
Results.
Here, we report the detection in the ISM of the primary alcohol
n
-propanol (in both conformers
Ga
-
n
-C
3
H
7
OH and
Aa
-
n
-C
3
H
7
OH), a precursor of fatty alcohols. The derived column densities of
n
-propanol are (5.5 ± 0.4) × 10
13
cm
−2
for the
Ga
conformer and (3.4 ± 0.3) × 10
13
cm
−2
for the
Aa
conformer, which imply molecular abundances of (4.1 ± 0.3) × 10
−10
for
Ga
-
n
-C
3
H
7
OH and of (2.5 ± 0.2) × 10
−10
for
Aa
-
n
-C
3
H
7
OH. We also searched for the
AGa
conformer of
n
-butanol
AGa
-
n
-C
4
H
9
OH without success, yielding an upper limit to its abundance of ≤4.1 × 10
−11
. The inferred CH
3
OH:C
2
H
5
OH:C
3
H
7
OH:C
4
H
9
OH abundance ratios are 1:0.04:0.006:≤0.0004 towards G+0.693-0.027, that is, 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) × 10
14
cm
−2
and (1.3 ± 0.4) × 10
13
cm
−2
, and abundances of (8.2 ± 0.6) × 10
−10
and (9.6 ± 3.0) × 10
−11
, respectively.
Conclusions.
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.
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