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Downloaded by guest on September 28, 2021 eae erpr eetepeec fehnlmn nspace, in ethanolamine under of still presence are the NH here of report the We origin of debate. the nature the and yet present membranes phospholipids, first All the of together. keep made are they machinery membranes because 2021) metabolic cell 27, and January of review element material for key (received genetic 2021 a 9, are April approved membranes and Cell NJ, Princeton, University, Princeton Bahcall, A. Neta by Edited 21252 MD Towson, University, Towson Geosciences, and Astronomy Chile; 763-0355, Chile; Santiago 763-0355, Observatory, Santiago Array Observatory, Southern European Science, of Spain; Madrid, 28014 Nacional, Spain; a Requena-Torres A. Miguel and oeua oundniyo taoaiei neselrspace interstellar in ethanolamine of is density column The molecular membranes. in second-most-abundant and plest Rico-Villas Fernando V group simplest head the phospholipid ethanolamine, of space in Discovery PNAS early and assembling the membranes. to primitive of contributed evolution have onto could delivered Earth, if the and, early space in of efficiently (10 forms simi- proportion ethanolamine is the that in the medium found interstellar one decomposition that the the to in by find lar itself to we respect meteorite However, with the . in amino suggested synthesized they of is but material, it meteoritic that in presence its reported H to respect with dance ru a ensont esnhszdi raito exper- irradiation in synthesized alco- be acids, to phosphate fatty shown as The been 14). such has 13, , (10, group acids in phosphonic and present hols, be to passage known surface. both the on survive prebiotic impact the can the and atmosphere meteorites of planetary the and through fraction significant in 12) comets a (11, of that experiments bombardment impact demonstrated A the Laboratory pro- have 10). through space. been (9, Earth meteorites have from early and could the delivered molecules to prebiotic been vided of blocks have building repertoire early could the broad on Alternatively, molecules phospholipids 8). precursor (3, of the questioned of was conditions availability prebiotic Earth the possible but under phospho- synthesized (5–7), that be proposed could work Initial unknown. remains formed 1C. Fig. ) in or depicted as , acids), derived fatty chains [EtA], from (hydrocarbon ethanolamine tails with hydrophobic as nonpolar combined two such and group group bilayer phosphate head a a of (an made the head are within hydrophilic cells activities current 1 (Fig. metabolic all phospholipids of of the membranes enable 4). The as (3, cell. well life genetic of the as protect evolution material, and early encapsulate and membranes cellular emergence Indeed, the key of these process in Among the prerequisite fundamental 2). a is (1, compartmentalization mechanisms elements, replication with together L membranes cell etod Astrobiolog de Centro co .Rivilla M. ´ ıctor npriua,sm tutrlprso hshlpd are phospholipids of parts structural some particular, In were phospholipids first the which through process The N 2 f sbsdo he ai usses compartment, a subsystems: molecules basic information-bearing three and machinery, on metabolic based a is ife CH (1.51 = 01Vl 1 o 2e2101314118 22 No. 118 Vol. 2021 b sevtroAtosc iActi siuoNzoaed srfiia 02 lrne Italy; Florence, 50125 Astrofisica, de Nazionale Istituto Arcetri, di Astrofisico Osservatorio 2 CH 2 H hc om h yrpii edo h sim- the of head hydrophilic the forms which OH, | ± ethanolamine 0.07) a,b,1 a osj ueird netgcoe Cient Investigaciones de Superior Consejo ´ ıa, × a zsu Jim Izaskun , Bel , 2 10 A f(0.9 of 13 and | d tradPae omto aoaoy lse o ineigRsac,RKN ao3109,Japan; 351-0198, Wako RIKEN, Research, Pioneering for Cluster Laboratory, Formation Planet and Star nTercero en oeua clouds molecular ´ cm ,wihaecmoe fapolar a of composed are which B), −2 − g,h mligamlclrabun- molecular a implying , 1.4) enez-Serra ´ g × −6 eateto srnm,Uiest fMrln,CleePr,M 04;and 20742; MD Park, College Maryland, of University Astronomy, of Department c 10 .Teerslsindicate results These ). hohnZeng Shaoshan , | −10 rboi chemistry prebiotic rvosstudies Previous . a Jes , sMart us ´ fia–nttt ainld T de Nacional ´ ıficas–Instituto f d eateto cec prtos on tcm ag Millimeter/Submillimeter Large Atacama Joint Operations, Science of Department | ar Colzi Laura , ´ ın-Pintado ulse a 4 2021. 24, May Published 1 BY).y (CC distributed under is article access open This Submission.y Direct PNAS a is article This interest.y competing no declare discussion.y authors scientific publication; The the this to I.J.-S., to actively led V.M.R., that contributed relevance projects authors data; scientific all biochemical the and and analyzed for V.M.R. support manuscript; the L.C. financial the the reviewed M.A.R.-T. investigated acquired and and I.J.-S. S.M. S.Z., C.B. paper; the I.J.-S., L.F.R.-A., wrote tools; C.B. I.J.-S., V.M.R., and J.M.-P., analysis V.M.R., research; ethanolamine; of designed of development contributed J.M.-P. the S.M. and J.M.-P., and to V.M.R., research; performed I.J.-S., P.d.V. and B.T., F.R.-V., V.M.R., L.F.R.-A., contributions: Author aatcCne,a hw nFg .Ti eini n fthe of one is region This 2. Fig. in the shown in complex G+0.693– as SgrB2 cloud Center, the molecular in Galactic located the G+0.693), toward (hereafter EtA 0.027 detected have We Results (20). (ISM) elusive medium far interstellar so the remained in has EtA precursors. of interstellar smaller detection from the formed However, is formation EtA the pos- that Another for is membranes. Earth sibility would cell early of This thereafter the and in asteroid. phospholipids EtA of parent of availability the the in under limit acids conditions amino unusual of was decomposition route specific thermal formation the chemical be possible to A proposed known. not is origin its (18). life of of origin of one the as for precursor environments considered direct likely (17), the vents a hydrothermal as alkaline (NH proposed archean , been amino has simplest the EtA 1C). Fig. addition, 2- (see In biolog- (PE) or in phospholipid glycinol membranes: second-most-abundant ical the as forms known it head and (also different the EtA the Regarding supports aminoethanol, phospholipids, space. which in of 16), form groups can (15, they analogs that idea interstellar of iments owo orsodnemyb drse.Eal [email protected] Email: addressed. be may correspondence whom To nteeouino h rtclua ebae eddfrthe for needed life. membranes of cellular roleemergence first relevant the of a evolution amphiphilic playing the thus in permeable phospholipids, trig- and as have efficient such could molecules of Earth prebiotic formation The early the planet. on gered our ethanolamine to of of thereafter availability bodies and minor System and Solar planetesimals the from to chem- transferred nebula interstellar been proto-Solar have the by could formed ethanolamine precursor Hence, efficiently a istry. is that confirms phospholipids medium interstellar of the in cloud lar h eeto fehnlmn (NH ethanolamine of detection The Significance t a enfudi h laaaStamtoie(9,yet (19), meteorite Sitta Almahata the in found been has EtA a a,b alsBriones Carlos , al eVicente de Pablo , ciaArepca EtbnTraa” 85 Madrid, 28850 Terradas”, “Esteban Aeroespacial ecnica ´ c NH bevtroAstron Observatorio 2 CH https://doi.org/10.1073/pnas.2101314118 2 a CH ua .Rodr F. Lucas , 2 stesmls one, simplest the is 1D) Fig. OH; c egoMart Sergio , raieCmosAtiuinLcne4.0 License Attribution Commons Creative mc ainl nttt Geogr Instituto Nacional, omico ´ 2 2 CH CH h 2 ´ ıguez-Almeida eateto Physics, of Department 2 CH OH,i simulated in COOH), 2 ´ ın H namolecu- a in OH) e,f e LADepartment ALMA , a | , f8 of 1 afico ´

ASTRONOMY C B D

A

Fig. 1. Structure of cellular membranes. (A) Schematic view of a cell. (B) Zoom-in view of the cell membrane, formed by a phospholipid bilayer. (C) Three- dimensional structure of the phospholipid PE, formed by a hydrophilic head composed of EtA, a phosphate group linked to glycerol, and two hydrophobic fatty-acid tails (black, red, blue, and white balls denote , , , and atoms, respectively). (D) EtA, the molecular species detected in space and reported in this work.

most chemically rich reservoirs of molecules in the galaxy, with a of the ice mantles of interstellar dust grains by large-scale low- plethora of organic species detected (21–25). The extremely rich velocity (<20 km·s−1) shocks (26) induced by a collision between gas-phase chemical composition of this region is due to erosion massive molecular clouds (27). For the typical (intermediate)

Fig. 2. Unblended or slightly blended transitions of EtA toward the G+0.693–0.027 . The quantum numbers involved in the transition are indicated in the upper left of each panel, and the energies of the upper level are indicated in the upper right. The red thick line depicts the best LTE fit to the EtA rotational transitions. The thin blue line shows the expected molecular emission from all of the molecular species identified in our spectral survey, overplotted to the observed spectra (gray histograms). The three-dimensional structure of EtA is shown in the center of the figure; black, red, blue, and white balls denote carbon, oxygen, nitrogen, and hydrogen atoms, respectively.

2 of 8 | PNAS Rivilla et al. https://doi.org/10.1073/pnas.2101314118 Discovery in space of ethanolamine, the simplest phospholipid head group Downloaded by guest on September 28, 2021 Downloaded by guest on September 28, 2021 icvr nsaeo taoaie h ipetpopoii edgroup head phospholipid simplest the ethanolamine, of space in Discovery al. et Rivilla LTE in predicted details the (see and model spectra best observed the used the finds We between which agreement EtA. MADCUBA−SLIM, to of of and emission tool fit the AUTOFIT LTE the of the parameters perform physical to molecules. the transitions other derive 14 these from sig- used not emission have or the We clean either by are 2, contaminated EtA Fig. toward nificantly in of line transitions reported solid 14 blue species a that with confirming other shown contribution is all species predicted molecular detected The and all from (21–25). species (29), works the previous ISM in of the G+0.693 all in includes far in which species so molecular survey, for spectral search extensive our molecule, other an any performed by produced have not we are EtA of transitions in the of listed and 3 Fig. in shown 2. are from Table transitions lines These cloud emission below). molecular this (see brighter in identified with already species observed molecular blended other the appear with Table consistent but in are spectra transitions provided 31 is in remaining with information The shown spectroscopic blended 1. are their slightly transitions and 2, or These Fig. molecules. unblended other either from appear emission which intensities of line (with 14 simulation LTE the by dicted them of tens low only the considering survey, (T excited the G+0.693 be by to covered expected fall range are that EtA spectral of the transitions condi- in (23,655) (LTE) numerous the equilibrium the Among under thermodynamic tions. EtA local of spectrum of synthetic assumption the pack- predicted MADCUBA We the (28). within age Line tool (Spectral Modeling) SLIM the and using Identification performed was EtA of transitions presented is in observations the about information Detailed scopes. Radioastronomie de Institut the Millim with out carried survey the spectral for ISM. target the in excellent species an molecular desorption new G+0.693 of shock-induced makes detection of con- , effect line interstellar the and of with blending along line hot This, of low-mass fusion. or problems hot- cores the in hot alleviating molecular than corinos, massive lower as substantially such is sources lines ter molecular excited, of are transitions density molecular the low-energy only Since 22). (21, low very yielding excited, 10(0,10)–9(0,9) thermally few a 9(4,5)–8(4,4) of G+0.693 of densities 9(3,7)–8(3,6) 9(2,8)–8(2,7) 8(2,6)–7(2,5) 94.7010488 8(1,7)–7(1,6) 91.8301065 8(2,7)–7(2,6) 91.6032870 8(0,8)–7(0,7) 89.7254251 7(1,6)–6(1,5) 84.2912932 5(0,5)–4(0,4) 82.8757878 4(1,3)–3(1,2) 80.0223886 4(2,2)–3(2,1) 76.6071016 logA 4(2,3)–3(2,2) 73.0048603 4(0,4)–3(0,3) 49.1932727 42.2557255 Transition 41.1366268 40.4083769 39.7379429 2) Fig. GHz in Frequency, (shown cloud molecular G+0.693 EtA the of toward transitions detected rotational blended slightly or unblended Einstein frequency, (rest [A information coefficients Spectroscopic 1. Table ocnr htteseta ie eetda h frequencies the at detected lines spectral the that confirm To pre- as EtA, of transitions brightest 45 the detected have We unbiased high-sensitivity a of data molecular the analyzed We h dnicto fterotational the of identification The Methods. and Materials ´ tiu IA)3- n h ee 0mradiotele- 40-m Yebes the and 30-m (IRAM) etrique ex ul o1 )(1 22). (21, K) 15 to ∼5 ,adeeg fteuprlvl [E levels upper the of energy and ], .T efr h fit the perform To Methods ). and Materials 10 4 cm T −3 ex nterneo o1 K 15 to 5 of range the in 2) h msini sub- is emission the (27), .89 25.5 29.2 26.0 23.5 −4.48695 19.8 −4.61854 18.6 −4.57780 19.2 −4.57750 16.9 −4.66443 14.6 −4.67140 7.2 −4.73500 5.5 −4.76916 6.7 −4.84093 6.7 −5.35979 4.8 −5.59088 −5.72208 −5.74549 −5.64603 ul s , T −1 ex up T esrdin measured )o h 14 the of ]) A ∗ > mK), 5 E up K , tla c nlg 3) nteeeprmns htlssof photolysis experiments, these inter- In of (32). irradiation analogs H ultraviolet ice of stellar experiments demonstrated been laboratory has EtA by of formation Grain-surface System. Solar known. the formed life that material of natal chemistry, subsystems the interstellar of three by part the synthesized being of been have blocks 31) therefore building (30, could The of acids ISM. that precursor amino the to and a in adds (23–25) EtA, detection ribonucleotides of This of (10 precursors hydrogen). ISM abundance molecular high the to relatively in respect a detection with phospholipids, clear of a report We Discussion the with and consistent fully from parameters transitions analysis: physical MADCUBA−AUTOFIT EtA derived 14 We the 2. Fig. using obtained (see diagram rotational MADCUBA in in description implemented further method diagram rotational 1.4) to (0.9 range the the in used value of a have observations from we EtA inferred hydrogen, of density molecular umn abundance the to derive respect To with (21–25). G+0.693 in analyzed (H (37). cloud + this CCH in abundant reaction been the through have phase might OH gas the G+0.693 in toward directly the detected produced Alternatively, HCCO desorption. of sputtering amount phase, low gas shock-induced the a in to in also result due consequently would and HCCO, This of grains. abundance dust ice on radical reactive highly of density column factor a in provided obtain detected are We tentatively detection Methods. this and have about reported G+0.693, details We detections in The (35). it. HCCO two L483 for and only Lupus-1A searched with be clouds also ISM, dark could cold the HNCCO the HCCO in toward (34). 5). found (HCCO) Fig. ketenyl rarely dust-grain to in addition is on N area by HNCCO grains shaded of on formed chain gray (see the surfaces is 34) (33, in 5. Fig. EtA in of here summarized formation are discuss which the We ISM, for understood. the pathways not chemical still possible are several into EtA result of that glycine, formation routes acids detailed the amino the the However, as serine. such and species alanine, prebiotic other as well as and NH abundant be to the expected through surfaces. species on grain 5) CO, on (Fig. HNCCO and 38 HNC of ref. of by formation combination proposed the as proceed Alternatively, could EtA. grains of a that with (21) than G+0.693 is confirms of route toward density which This abundant column surfaces. is 37), grain on since 23, available plausible (22, are radicals imines abundances of imine variety that high a presents relatively G+0.693 5). with (Fig. NH radical imine km·s gives of EtA ity of for temperature model excitation LTE of an density best-fitting the column The also molecular 2). a but region Fig. the EtA in in identified of line species (blue emission the of the all from only emission predicted not considered have we 2 h omto otso t nteIMae oee,poorly however, are, ISM the in EtA of routes formation The the using analysis complementary a performed also have We NC ol lob omdo utgan rmketene from grains dust on formed be also could HNCCO literature the in proposed route only the knowledge, our To h usqethdoeaino NC a form can HNCCO of hydrogenation subsequent The 2 O:CH 2 C) fe w yrgnasrcin,adrato ihthe with reaction and abstractions, hydrogen two after CCO), T v HO(i.5.Ti pce ih lofr hog other through form also might species This 5). (Fig. CHCO → −1 LSR ex v oe hnta fEA COi xetdt ea be to expected is HCCO EtA. of that than lower ∼3 LSR e eal in details see ; CO+Hpooe yrf 6 ic C shighly is CCH since 36, ref. by proposed H + HCCO 12 = 3 r eysmlrt hs rmohrseispreviously species other from those to similar very are OH:NH 68.3 = ± K. 1 3 N HNie iha2::: itr ilsEtA yields mixture 20:2:1:1 a with ices :HCN ± 2.9 = . km·s 0.4 .Fg hw the shows 4 Fig. Methods). and Materials .Tederived The Methods). and Materials ×10 T −1 N × ex 14 https://doi.org/10.1073/pnas.2101314118 telnwdhwsfie o15 to fixed was linewidth (the 10 10.7 = (1.51± = cm N −10 (1.5 = −2 . atrof factor a , ± ∼ C 18 0.5 . ,adaveloc- a and K, 0.7 ± 0.07) 2) obtaining (26), O 0.3)×10 × × 10 aeil and Materials PNAS 10 13 0larger ∼20 13 13 −10 cm H | cm cm 2 −2 f8 of 3 with col- T −2 −2 a , ex , ,

ASTRONOMY Fig. 3. Transitions of EtA that appear blended in the observed spectra of G+0.693. All of them have line intensities >5 mK, according to the best LTE fit described in the text. The quantum numbers involved in the transition are indicated in the upper left of each panel, and the energies of the upper level are indicated in the upper right. The red thick line depicts the best LTE fit obtained fitting the EtA rotational transitions shown in Fig. 2. The thin blue line shows the predicted molecular emission from all of the molecular species identified in our spectral survey, overplotted to the observed spectra (gray histograms).

surface-chemistry routes. Ref. 39 proposed a barrierless reac- Since it has been observed that the abundance of C is indeed tion between NH3, CO, and atomic C (Fig. 5). Given that large in Galactic Center molecular clouds, around half of that three-body reactions are less efficient that two-body reactions, of CO (40), and considering that C is expected to be highly this route could contribute to the formation of NH2CHCO reactive, this route might be indeed viable in G+0.693. We only if a relatively high abundance of atomic C is available. note that the barrierless NH2CH + CO reaction proposed by

4 of 8 | PNAS Rivilla et al. https://doi.org/10.1073/pnas.2101314118 Discovery in space of ethanolamine, the simplest phospholipid head group Downloaded by guest on September 28, 2021 Downloaded by guest on September 28, 2021 nt fEAad ec,ti pce ol epoue ythe by produced be could species this between hence, reaction nondiffusive and, EtA of units (CH (CH toward and reactions hydrogenation the in icvr nsaeo taoaie h ipetpopoii edgroup head phospholipid solid simplest The the ethanolamine, work. of this space in in proposed Discovery routes formation al. the et show Rivilla we in black, proposed In chemistry. been 47). gas-phase have denote (41, arrows arrows green colored dashed and with and (39), indicated reactions, cyan reactions chemistry (41), chemical surface orange The indicate (38), chain. arrows hydrogenation blue a (36), to magenta corresponds work: area previous shaded gray The cloud. molecular 5. Fig. intermedi- simple conditions, of as prestellar such under formation radicals ate sugars nonenergetic and laboratory the recent acids In of amino EtA. 43) of precursor (42, key experiments a be might which of cal, formation the to contribute 5). also (Fig. might 41 ref. 12(0,12)–11(0,11) text. the in 12(1,12)–11(1,11) described 11(3,9)–10(3,8) 11(1,10)–10(1,9) 112.8698247 11(2,10)–10(2,9) 10(2,8)–9(2,7) 112.7422238 10(3,7)–9(3,6) 111.7757005 111.0166375 11(0,11)–10(0,10) 108.8642389 11(1,11)–10(1,10) 10(4,6)–9(4,5) 105.5481523 10(4,7)–9(4,6) 103.9759166 10(1,9)–9(1,8) 103.7762062 10(3,8)–9(3,7) 103.5718907 10(2,9)–9(2,8) 102.2528632 9(2,7)–8(2,6) 102.0183898 10(1,10)–9(1,9) 101.8639901 9(3,6)–8(3,5) 101.7229298 9(1,8)–8(1,7) 99.3388437 9(4,6)–8(4,5) 95.0023981 9(0,9)–8(0,8) 94.3821793 9(1,9)–8(1,8) 93.0416052 8(3,5)–7(3,4) 92.4964225 8(4,4)–7(4,3) 91.7192567 8(4,5)–7(4,4) 85.6467486 8(3,6)–7(3,5) 85.1653931 8(1,8)–7(1,7) 82.2698610 7(2,5)–6(2,4) 81.4863522 5(2,4)–4(2,3) 81.4392902 5(1,5)–4(1,4) log 81.4338930 4(1,4)–3(1,3) 75.9126193 3(1,2)–2(1,1) 73.4680803 50.4153833 Transition 47.8493375 38.3746402 31.7653500 GHz Frequency, of spectra observed 3) the Fig. in (see blended G+0.693 appear that EtA of transitions Einstein frequency, (rest [A information coefficients Spectroscopic 2. Table h yrgnto of hydrogenation The intensities line have transitions All umr fteceia otspooe o h omto fEAi h S.Temlclrseisi e aebe eetdtwr h G+0.693 the toward detected been have red in species molecular The ISM. the in EtA of formation the for proposed routes chemical the of Summary ul ,adeeg fteuprlvl [E levels upper the of energy and ], 3 NH H.Teerdcl ersn h structural the represent radicals These OH). 2 CH NH 2 2 and Hcudyedthe yield could CH NH K codn otebs T fit LTE best the to according mK, >5 CH 2 CH 2 Haeefiinl formed efficiently are OH 2 and .59 35.9 35.9 36.3 −4.25393 33.2 −4.25550 33.5 −4.29721 29.4 −4.28448 31.2 −4.31491 30.5 −4.35654 30.5 −4.39964 34.1 −4.36532 34.1 −4.36815 27.9 −4.45637 30.9 −4.45929 28.3 −4.39813 24.3 −4.42905 25.6 −4.43880 26.2 −4.49975 23.0 −4.49166 29.2 −4.55708 21.0 −4.52562 21.0 −4.62007 21.7 −4.62059 24.8 −4.62876 24.8 −4.73500 21.6 −4.80646 17.0 −4.80721 15.7 9.1 −4.74841 7.4 −4.78270 5.1 −4.85633 3.5 −5.39849 −5.40899 −5.71626 −6.00114 CH A ul 2 s , Ho h sur- the on OH NH up −1 )o the of ]) NH 2 CH 2 CHCO 3 2 NH E radi- up K , 2 ) 1 oform to 41, (22). G+0.693 in abundant are between that product species intermediate two 47), an is (CH it methanimine since G+0.693 of in species grains complex other (44–46). form ISM to the routes have viable reactions as radical–radical proposed Similar been 5). (Fig. grains dust of face corner. ihtecnetaino hsseismaue nmeteoritic in measured species this of concentration the with of dance its obtain accuracy. to higher with work G+0.693 spectrum laboratory rotational toward new microwave motivate EtA should frequen- of and searches detection predicted Our the ISM. makes of the accuracy in tification the although (∼ cies 48, theoretically studied ref. been (NH have by species aminoacetaldehyde this of is spectra the rotational EtA in into EtA results of precursors possible these of survey. spectral any G+0.693 for search not rotational no HNCCO, is for there available Unfortunately, 5). (Fig. EtA data (N the density to fit column linear molecular best the the is for line transitions values T black EtA The derived 14 1. The Table the points. and to 2 correspond Fig. dots in red shown The Methods. and Materials 4. Fig. ex h eeto fEArpre nti okwt nabun- an with work this in reported EtA of detection The Moreover, h eutmt tpo h yrgnto hi that chain hydrogenation the of step penultimate The ln ihterucranis r niae nbu nteuprright upper the in blue in indicated are uncertainties, their with along , NH oainldarmo t.Teaayi rcdr sdsrbdin described is procedure analysis The EtA. of diagram Rotational ssilnthg nuhfrayrlal iden- reliable any for enough high not still is 0.2%) ∼ 2 10 CH NH NH −10 2 2 H rmsn pce o uueinterstellar future for species promising a CHO 2 CH NH ihrsetto respect with CH 2 H n ehlmn (CH methylamine and NH) 2 2 2 O hc a ehdoeae oform to hydrogenated be can which CO, CH NH ol ec ihC,a rpsdb ref. by proposed as CO, with react could 2 2 sepce ob rsn ntedust the on present be to expected is HO or CHCO, https://doi.org/10.1073/pnas.2101314118 H 2 nbe og comparison rough a enables NH 2 CH 2 CH 2 3 O ow can- we so CO, NH 2 PNAS H) The CHO). 2 4,42, (41, ) n the and ) | f8 of 5

ASTRONOMY Fig. 6. Transitions of HCCO tentatively identified in the spectra of G+0.693. The rotational quantum numbers involved in the transition are indicated in the upper left of each panel, and the energies of the upper level are indicated in the upper right. The thick red line depicts the LTE synthetic spectrum of HCCO. The thin blue line shows the predicted molecular emission from all of the molecular species identified in our spectral survey, overplotted to the observed spectra (gray histograms).

material (19). Considering that the abundance of water in the transform spectrometers with a spectral coverage of 2.5 GHz and a spectral −4 ISM is of the order of 10 (49), the EtA/H2O abundance ratio resolution of 38 kHz. The final spectra were smoothed to a resolution of measured in G+0.693 is of the order of 10−6. The Almahata 251 kHz, corresponding to a velocity resolution of 1.7 km·s−1 at 45 GHz. Sitta meteorite, where EtA was detected (19), has been clas- We covered a total spectral range from 31.075 GHz to 50.424 GHz. The sified as a ureilite with an anomalously high fraction of other position switching mode was used, with the reference position located at (−88500, +29000) with respect to G+0.693 (24, 27). The telescope pointing and materials, the enstatite chondrites (EC) being the most abundant focus were checked every 1 or 2 h through pseudo-continuum observations (50). Interestingly, EC meteorites have recently been proposed toward VX Sgr, a red hypergiant star near the target source. The spectra as the origin source of most of Earth’s water (51). Therefore, ∗ were measured in units of antenna temperature, TA , since the molecular meteorites such as Almahata Sitta could have simultaneously emission toward G+0.693 is extended over the beams (55). The noise of the delivered to Earth not only water but also prebiotic chemicals spectra depends on the frequency range, reaching values as low as 1.0 mK, such as EtA. From the concentration of EtA measured in the while in some intervals it increases up to 4.0 mK. The half-power beam width Almahata Sitta meteorite of 20 ppb (19), and the average con- (HPBW) of the telescope is 4800 at 36 GHz. centration of water in EC meteorites (∼7,500 ppm) (51), we IRAM 30-m telescope. We have carried out a spectral survey at 3 mm using −6 the IRAM 30-m telescope. The observations were performed in two observ- derive a meteoritic EtA/H2O abundance ratio of 3 ×10 . This ing runs during 2019: 10 to 16 April and 13 to 19 August, from project value is consistent with that derived in the ISM. Although iso- numbers 172-18 (Principal Investigator J.M.-P.) and 018-19 (Principal Inves- topic analysis of EtA would be needed to confirm its interstellar tigator V.M.R.). We used the broad-band Eight MIxer Receiver (EMIR) and origin in meteorites, our results suggest that phospholipid pre- the fast Fourier transform spectrometers in FTS200 mode, which provided cursors such as EtA formed in the ISM could have been stored a channel width of ∼200 kHz. The final spectra were smoothed to a 609 in planetesimals and minor bodies of the , to be KHz, i.e., a velocity resolution of 1.8 km·s−1 at 100 GHz. The full spectral subsequently transferred to early Earth. coverage is 71.770 to 116.720 GHz. The telescope pointing and focus were Once EtA was available on Earth’s surface, it could form phos- checked every 1.5 h toward bright sources. The spectra were also measured in units of antenna temperature, ∗. The noise of the spectra (in ∗) is 1.3 pholipids (in particular PE; see Fig. 1C) under plausible early TA TA Earth conditions, as proposed by ref. 6 and confirmed by pre- to 2.8 mK in the range 71 to 90 GHz, 1.5 to 5.8 mK in the range 90 to biotic experiments (7). It is commonly assumed that the first cell membranes could have been composed of amphiphilic molecules Table 3. Spectroscopic information (rest frequency, Einstein such as fatty acids/, which are chemically simpler than coefficients [A ], and energy of the upper levels [E ]) of the phospholipids (3, 8). However, the availability of EtA in an ul up rotational transitions of ketenyl (HCCO) tentatively detected early Earth could have enabled the progressive replacement of toward the G+0.693 molecular cloud (shown in Fig. 6) fatty acids/alcohols by more efficient and permeable amphiphilic −1 molecules such as phospholipids. In this scenario, the protocells Frequency, GHz Transition logAul, s Eup,K could have been able to incorporate from the environment the 43.3176674 2(3,3)–1(2,2) −6.0192 3.1 precursor molecules required to start the synthesis of RNA and 43.3211451 2(3,2)–1(2,1) −6.1404 3.1 eventually other polymeric molecules (52, 53) needed for the first 43.3295421 2(2,2)–1(1,1) −6.0343 3.1 replicative and metabolic processes of life. This has important 43.3354627 2(2,1)–1(1,0) −6.2739 3.1 implications not only for theories of the origin of life on Earth 43.3368615 2(3,2)–1(2,2) −6.6741 3.1 but also on other habitable planets and satellites anywhere in the 43.3373040 2(2,1)–1(2,1) −6.4207 3.1 universe. 86.6191857 4(4,3)–3(3,3) −6.9202 10.4 Materials and Methods 86.6423419 4(5,5)–3(4,4) −5.0703 10.4 86.6438483 4(5,4)–3(4,3) 5.0942 10.4 Astronomical Observations. We have analyzed a high-sensitivity spectral sur- − vey of the molecular cloud G+0.693–0.027 conducted with the Yebes 40-m 86.6558306 4(4,4)–3(3,3) −5.0772 10.4 telescope (Guadalajara, Spain) and the IRAM 30-m telescope (Granada, 86.6574849 4(4,3)–3(3,2) −5.1070 10.4 Spain). The observations were centered at the equatorial coordinates of 86.6652791 4(5,4)–3(4,4) −6.3845 10.4 ◦ 0 G+0.693: RA(J2000) = 17 h 47 m 22s, DEC(J2000) = −28 21 27”. 108.2823800 5(5,4)–4(4,4) −6.7293 15.6 Yebes 40-m telescope. The observations were carried out with the Yebes 108.3040553 5(6,6)–4(5,5) −4.7698 15.6 40-m telescope located in Yebes (Guadalajara, Spain), during six observing 108.3051187 5(6,5)–4(5,4) −4.7840 15.6 sessions in February 2020, as part of the project 20A008 (Principal Investi- 108.3178903 5(5,5)–4(4,4) −4.7747 15.6 gator I.J.-S.). We used the new Nanocosmos Q-band (7-mm) high-electron- 108.3190248 5(5,4)–4(4,3) −4.7916 15.6 mobility transistor receiver that enables ultrabroad-band observations in 108.3280559 5(6,5)–4(5,5) 6.2997 15.6 two linear polarizations (54). The receiver is connected to 16 fast Fourier −

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J. 1. srbooy(A)i Madrid: in (CAB) ardDt ueAayi nIae sasfwr eeoe tteCne of Center the at developed software a is ImageJ on Analysis Cube Data Madrid odrv h hsclprmtr rmtemlclreiso,w have we emission, molecular the from parameters physical the derive To (version 61004 entry spectroscopic the used have we EtA, of case the For ocmueterltv oeua bnac ihrsett molecular to respect with abundance molecular relative the compute To max- half at width (full linewidth the fixed we EtA, of analysis the For tv at odtosadrlso ebae npeilgcleouin in evolution” prebiological in membranes of roles and conditions earth itive conditions. prebiotic in membranes (2009). 274–284 Chem. Curr. (2015). h rsrasbtenceityadbiology. and chemistry between crossroads the B Soc. R. Trans. life?Philos. of origin T ex ex k ,E hrod .Ecbr,D ps Fraino hshlpd ne prim- under phospholipids of “Formation Epps, D. Eichberg, J. Sherwood, E. o, × FWHM ∼ ´ i evn hog h equation the through kelvin) (in up steBlzancntn,tefeunyo h transition, the of frequency the constant, Boltzmann the is 10 1K a enitroae rmtevle eotdi h JPL the in reported values the from interpolated been has K) 11 ,Eouinadsl-sebyo protocells. of self-assembly and Evolution e, ftetastosue nteaayi pnarnebten4.8 between range a span analysis the in used transitions the of ) ´ v −2 LSR −10 log(N –7(2005). 1–27 259, 0m nterne15t 1 H.The GHz. 116 to 115 range the in mK ∼10 o1 km·s 15 to ) sn h expression the using ) 68.3 = . 18 up ), 5km·s 15 = c ,1.35 O, /g T stesedo ih,and light, of speed the is ex ± up n h eoiy(v velocity the and , . km·s 0.4 ) Q = N −1 ln,uigtetoajcn temperatures: adjacent two the using plane, ×10 up 00 https://cab.inta-csic.es/madcuba/. 1.5K 716.8160. = K) (18.75 log(N −1 hc erdcswl h bevdspectral observed the well reproduces which , n 43.Tepsto wthn oewas mode switching position The 34.3”. and = h oainldarmi acltdfollow- calculated is diagram rotational The ), h dnicto ftemlclrlines molecular the of identification The 23 8π −1 W N /Q(T Nature cm 8420 (2011). 2894–2901 366, k (1.51 = . i evnklmtr e eod,i con- is second), per kilometers kelvin (in ν −2 2 W ex )) 2) ehv sue 20 a assumed have We (26). 88 (1977). 78–80 266, /(hc T − 2 ± ex LSR oundniyadpropagated and density column 2 log(e) 3 0.07)×10 fteeiso.Temolecular The emission. the of eelf sfe parameters. free as left were ) oundniyifre from inferred density column A A ul u ul ), N olwrlevel lower to n.J ice.Cl Biol. Cell Biochem. J. Int. .Ter Biol. Theor. J. steEnti coefficient Einstein the is × i centimeters (in E up 13 HPBW /(kT cm −2 ex ), , fteobser- the of T l ex hn the Then, . 11–22 381, 00 − 10.7 = +290 , % h ∗ 2 N ,and ), up sthe is error SLIM Light Top. [2] (in [1] 41, χ 00 ± Q 2 ) 0 .Pzael,E hc,Teognccmoiino abncosmtoie:Teevo- The meteorites: carbonaceous of composition organic The Shock, E. Pizzarello, S. 10. fehnlmn aebe eoie nteCnr eAstrobiologia de Centro the in deposited been at repository have ethanolamine of Availability. Data hydrogen. molecular of to abundance molecular a into translates density where y,GA 126(AOOMS,adteSaihMnsei eCecae ERC-2013- Ciencia Grant de Ministerio Synergy Spanish the through and Innovaci (ERC) (NANOCOSMOS), from 610256 Council support G.A. acknowledge SyG, B.T. Research and P.d.V. European studentship. ICU the Intro from JAE Technol- support CSIC funding Aerospace a acknowledges State of L.F.R.-A. MDM-2017-0737. Institute Spanish project [CSIC]–National ogy) the Council Research from National support “Mar through Excelencia and partial de PID2019-105552RB-C41 Unidad project 2019-T1/TIC-15379). received through Life; (AEI) L.C. Agency of Research and Origins J.M.-P., Cosmic (COOL: I.J.-S., V.M.R. grant by Urbana. experiencia) operated Agenda con the is through y Madrid Observatory de Movilidad Atracci Comunidad Yebes the Transportes, (IGN) from support at de Institute funding acknowledges telescope Ministerio Geographic IGN, National radio the the 40-m Astronomy/National and The Advance- and the (Germany), (Spain). for Science Sciences Society Planck of Universe Max ment (France), supported for Research is Scientific Institute IRAM for runs. Center National observing tele- different the 40-m the of Yebes during by and context suggestions help 30-m prepa- for IRAM the for the staff the in to Bermejo scope grateful ethanolamine during Ruiz are of We advice Marta chemistry. references prebiotic useful thank bibliographic We his several manuscript. for about this manuscript. Ciudad the of of David quality ration the thank improve warmly to us We helped which reviewers, the by ACKNOWLEDGMENTS. a for transitions unblended of density two column the well reproduce MADCUBA-SLIM using tra spectra LTE produced assuming have and from We emission 6). by (Fig. contaminated species not only other are since 5(6,5) respectively) tentative, GHz, and considered 108.3051187 is 5(6,6)−4(5,5) and be transitions the should the detection transitions, of spectra This information two The spectroscopic 3. cor- Table the 5 −4. lines and in and 6, listed HCCO 4−3, Fig. of 2−1, in transitions shown groups are rotational three works the spectroscopic identified to several tentatively responding on have based 2019), We (June (65–67). 041506 entry G+0.693–0.027. CDMS toward the (HCCO) Ketenyl of Detection Tentative 2. molecular Table in other shown is from spectroscopic transitions The emission these cloud. of molecular with G+0.693 information the blended in appear identified already that species text, main the intensities line EtA. of Transitions Blended log(N for values data the above. derives the provide fits MADCUBA 4) that which Fig. line from straight in the line of (black coefficients points The units. velocity in data where indicate (∆W bars intensity error expression integrated the The velocity using 1). the Table of and 2 uncertainty Fig. the (see transitions blended slightly and transitions the of levels upper the of kelvin) pns II o udn upr rmgat Y21-56-21Pand AYA2016-75066-C2-1-P grants from support PID2019-106235GB-I00. funding for MICIU Spanish .C hb,C aa,Edgnu rdcin xgnu eieyadipc shock impact and delivery exogenous production, Endogenous Sagan, C. Chyba, C. evolution: biological 9. of roots Chemical Escosura, la de A. Briones, C. Ruiz-Mirazo, K. 8. .M a,J iheg .Or J. Eichberg, J. Rao, M. 7. i.4sostepo flog(N of plot the shows 4 Fig. uinr tr ha fbiochemistry. (2010). of ahead story lutionary life. of origins the for (1992). inventory 132 An molecules: organic systems. of functional synthesis autonomous of development of process a Biol. as Open life of origins The .W emr d Aaei rs,Lno,17) pp. conditions. earth 1978), primitive London, Press, (Academic Ed. Deamer, 1–21. W. D. Membranes, Transducing rms nd aet netgdrMdldd1(contrataci 1 Modalidad Investigador Talento de on ´ g n(II)truhpoetPD09171G-2.BT hnsthe thanks B.T. PID2019-107115GB-C21. project through (MICIU) on up ´ stenieo h pcr and spectra the of noise the is and 700(2017). 170050 7, https://cab.inta-csic.es/astrochem/data.html v LSR T E A ∗ up oeua pcr n t fteubeddtransitions unblended the of fits and spectra Molecular ∆W N 5km·s 65 = K speitdb h T iuaindsrbdin described simulation LTE the by predicted as mK, >5 ∼ r epcieytesaitclwih n nry(in energy and weight statistical the respectively are 0.5 = eakoldetecntutv omnsraised comments constructive the acknowledge We ,Snhsso hshtdltaoaieudrpossible under phosphatidylethanolamine of Synthesis o, rms ´ .Ml Evol. Mol. J. × ad azu-etod Astrobiolog de Maeztu”-Centro de ´ ıa epeeti i.3tetastoso t with EtA of transitions the 3 Fig. in present We −1 10 × 13 and up (∆v N cm /g and FWHM up /FWHM −2 – (1987). 1–6 25, odSrn ab eset Biol. Perspect. Harb. Spring Cold versus ) https://doi.org/10.1073/pnas.2101314118 T tikrdln nFg ) hscolumn This 6). Fig. in line red (thick ex ∆v calculating , 0km·s 20 = ) 0.5 steseta eouino the of resolution spectral the is E (,)(t183453GHz 108.3040553 (at −4(5,4) up × ∼ Q o l fteubeddor unblended the of all for FWHM 0.4 stepriinfunction. partition the is −1 × h rdce spec- predicted The . Q , 10 (68). n log(e)/T and /Q) ,wihi derived is which ), T (T ex −10 ex nd doctores de on ´ Nature PNAS f1 n a and K 10 of ehv used have We sexplained as ) ihrespect with a(Spanish ´ ıa a002105 2, 125– 355, | f8 of 7 [3] ex ,

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