DOI: 10.1002/chem.201303690
Meteorites as Catalysts for Prebiotic Chemistry Raffaele Saladino,*[a] Giorgia Botta,[a] Michela Delfino,[a] and Ernesto Di Mauro[b]
Meteorite late heavy bombardment[1] was a major event after the accretion of the earth. The relevance of organic syntheses driven by impact shocks was first proposed by Chyba and Sagan in 1992,[2] based on the scanty indications available at the time. How would the contribution by meteorites to an early earth organic pool compare with the syntheses these meteorites might have induced after their impact?[2] Here, we report the catalytic effect of several types of meteorites,[3a,b] iron, stony-iron,[3b] chondrites,[4] and achondrites (entreis 1–12 in Table 1[2, 5]) in the syntheses of organic molecules of prebiotic interest using the model reaction of the thermal condensation of formamide (NH2CHO).[6] NH2CHO is a ubiquitous molecule in the universe that has been observed in the comet Hale-Bopp,[7] in the stellar objects W33A,[8] NGC7538, and W3ACHTUNGRE(H2O),[9] in the interstellar Table 1. Meteorites used in NH2CHO condensation processes.
A
B C
D
1 2 3 4 5 6 7 8 9 10 11 12
Name[a]
Class
Type
Canyon-Diablo Campo-del-Cielo Sikhote-Alin Seymchan NWA4482 NWA2828 Gold basin Dhofar 959 Murchison NWA1465 NWA5357 Al-Haggounia 001
iron iron iron stony iron stony iron chondrite chondrite chondrite chondrite chondrite achondrites achondrites
IA hexaoctahedrite normal IAB hexaoctahedrite coarse IIB hexaoctahedrite coarsest pallasite main group pallasite anomalous enstatite ordinary L6 carbonaceoous LV3 anomalous diogenite aubrite
[a] References, composition, historical and terrestrial provenience, and cosmo-origin data are available as an appendix of this table in the Supporting Information (#1).
[a] Prof. R. Saladino, Dr. G. Botta, Dr. M. Delfino Dipartimento di Scienze Ecologiche e Biologiche Universit della Tuscia Via San Camillo De Lellis, 01100 Viterbo (Italy) Fax: (+ 39) 0761357242 E-mail: [email protected] [b] Prof. E. Di Mauro Istituto Pasteur—Fondazione Cenci Bolognetti c/o Dipartimento di Biologia e Biotecnologie “Charles Darwin” University la “Sapienza” Piazzale Aldo Moro, 5, Rome 00185 (Italy) E-mail: [email protected]
medium,[10] in Europa[11] and Orion-KL,[12] in the dense cloud SgrB2,[13] and in carbonaceous chondrites.[14] Recently, NH2CHO was identified as a common constituent of starforming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp and a potential influx of exogenous delivery to Earth as high as 0.1 mol km 2 yr 1 or 0.18 mmol m 12 per single impact.[15] From a synthetic point of view, NH2CHO could be either an alternative to hydrogen cyanide (HCN),[16] or a possible nonvolatile source of HCN.[17] Unlike HCN, NH2CHO has a boiling point of 210 8C without any azeotropic effect. Regardless of its initial concentration, physical phenomena were described that concentrate 1000-fold organic molecules in capillary spaces.[18] Additional concentration processes by eutectics, clays absorption and evaporation have been reviewed.[19, 6] Synthetic procedure: NH2CHO (2.5 mL) was treated with a catalytic amount of the appropriate meteorites powder (1.0 % in weight; similar grain size distribution of particles in the range of 0–125 mm) at 140 8C or 608 for 24 h. After removal of the catalyst and excess of NH2CHO, the products were analyzed by GC-MS. The condensation of NH2CHO in the absence of meteorite powder afforded purine as the only recovered product.[20] To avoid possible contamination problems due to the presence of terrestrial organics in the original sample (present in Murchison at the ppb range[21a, b]), the meteorite powders were extracted before their use with NaOH (0.1 n), CHCl3–CH3OH (2:1 v/v), and sulfuric acid. In the case of chondrites, achondrites, and stonyiron meteorites, the samples were also pyrolyzed at 600 8C. After the treatment, the powders did not release any trace of organic substances. The synthesis of large number of compounds was observed (Scheme 1): nucleobases and their analogues, carboxylic acids, amino acids, and low-molecularweight derivatives (miscellanea). We dub these reactions meteorite-catalyzed syntheses. Given the complexity of the mixtures, analysis was limited to products 1 ng mL 1. Because of the uncertainty of the stoichiometry of the reactions, the yield of products was calculated as mg (or mg) of product per mL of starting NH2CHO. Tables 2–6 show the 50 most abundant products (the m/z value and the abundance of peaks are in Supporting Information #2; selected chromatograms and the original m/z fragmentation spectra are in Supporting Information #3 and #4, respectively).
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201303690.
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Scheme 1. Syntheses of biogenic molecules from NH2COH catalyzed by meteorites. The compounds are numbered according to their mention in the text. Nucleobases and analogues: uracil (1), cytosine (2), isocytosine (3), dihydrouracil (4), purine (5), adenine (6), guanine (7), hypoxanthine (8), 2-aminopurine (9), 4ACHTUNGRE(3 H)-pyrimidinone (10), 2ACHTUNGRE(1 H)-pyrimidinone (11), 3-hydroxypyrimidine (12), and hydantoine (13). Acids: oxalic (14), glycolic (15), glyoxylic (16), acetic (17), pyruvic (18), propanoic (19), parabanic (20), lactic (21), malonic (22), malic (23), maleic (24), succinic (25), oxalacetic (26), ketoglutaric (27), hexanoic (28), pimelic (29), octanoic (30), and nonanoic (31). Amino acids: glycine (32), N-formylglycine (33), N-methylglycine (34), alanine (35), b-alanine (36), 2-methylalanine (37), valine (38), leucine (39), tert-leucine (40), b-amino isobutyric acid (b-AIBA) (41), 2-aminobutanoic acid (2ABA) (42), hydroxyproline (43), and phenylalanine (44). Miscellanea: diaminomalonitrile (DAMN) (45), carbodiimide (46), urea (47), guanidine (48), guanidine acetic acid (49), and glycocyanidine (50). Yields of the reactions are in Tables 2–6. GC-MS spectra of compounds (1–50) are in Supporting Information #4.
Nucleobases: The extraterrestrial origin of nucleobases detected in carbonaceous chondrites[21b, 22a,b] is not unequivoACHTUNGREcal.[22a] In the richest chondrites the highest purine yields were < 100 ppb, guanine reaching exceptionally 250 ppb, other compounds being lower by one to two orders of magnitude. In our syntheses we obtained: uracil (1), cytosine (2), isocytosine (iC) (3), 5,6-dihydrouracil (DHuracil, 4), purine (5), adenine (6), guanine (7), hypoxanthine (8), 2aminopurine [2ACHTUNGRE(NH2)purine, (9)], 4ACHTUNGRE(3 H)-pyrimidinone (10), 2ACHTUNGRE(1 H)-pyrimidinone (11), 3-hydroxypyrimidine (12), and hydantoine (13). Compounds (1–13) were synthesized in the range of 0.009 (NWA2828) and 2.33 mg mL 1 (Seymchan) (total amount of nucleobases disregarding the more abun-
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dant purine, pyrimidine and pyrimidinone derivatives), that is more than 100 times greater than those recovered in the original samples[21a, b] (Scheme 1, Table 2, Supporting Information #3 and #4). Irons, stony-irons, and achondrites showed a catalytic effect higher than chondrites. Mechanisms for the formation of nucleobases are well reviewed.[6] Adenine prevailed with chondrites and achondrites (with the exception of NWA1465, Murchison, and NWA2828), while comparable amounts of uracil, cytosine, and adenine were detected in the presence of iron and stony-iron meteorites. Guanine was synthesized only with achondrites, while large amounts of isocytosine (a well-known bioisoster of guanine[23]) were obtained. 2-Aminopurine (previously ob-
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Table 2. Synthesis of nucleobases and their analogues: products [mg] grouped by meteorite type. Product[a]
1 2 3 4 5 6 7 8 9 10 11 12 13
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
250.2 122.3 395.7 0.0 41.32[b] 250.5 0.0 380.6 0.0 1296.1 0.0 0.0 0.0
238.5ACHTUNGRE(245.1)[c] 51.4ACHTUNGRE(57.4) 790.6ACHTUNGRE(765.4) 0.0ACHTUNGRE(0.0) 19.06ACHTUNGRE(19.1) 211.3ACHTUNGRE(209.8) 0.0ACHTUNGRE(0.0) 489.2ACHTUNGRE(488.3) 0.0ACHTUNGRE(0.0) 4221.5ACHTUNGRE(4230) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
278.0 120.6 811.1 0.0 1.4 400.1 0.0 500.2 0.0 2470.8 0.0 0.0 0.0
345.2 30.6 1836.3 0.0 5.26 107.5 0.0 0.0 10.8 5545.4 20.1 15.4 0.0
300.6 32.3 689.2 0.0 1.86 103.5 0.0 0.0 128.6 2546.8 16.7 12.3 0.0
Chondrites
Achondrite
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
5.5ACHTUNGRE(5.1)[c] 2.3ACHTUNGRE(2.1) 1.1ACHTUNGRE(0.6) 0.0ACHTUNGRE(0.0) 0.03ACHTUNGRE(0.02) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 39.4ACHTUNGRE(40.1) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
34.2 23.2 270.3 0.0 2.37 499.5 0.0 0.0 0.0 344.5 50.6 23.9 0.0
61.2 32.5 323.5 0.0 1.38 510.3 0.0 0.0 0.0 350.9 41.8 25.6 0.0
33.4 13.4 337.9 0.0 0.7 50.3 0.0 0.0 0.0 6053.2 1687.6 31.6 264.6
50.6 29.8 249.6 0.0 2.66 41.4 0.0 0.0 0.0 362.8 1400.6 26.2 100.2
481.5 30.3 700.8 62.3 0.89 800.5 50.3 0.0 0.0 821.6 649.2 12.6 0.0
470.9 44.4 613.6 70.1 0.77 810.5 60.6 0.0 0.0 297.1 668.3 10.2 0.0
[a] The data are the mean values of three experiments. Products are given in mg mL 1. See Text. [b] Data expressed in mg mL 1. [c] Reaction performed with untreated meteorite.
served in iron-sulfur/NH2COH syntheses),[24] and hypoxanthine, are prebiotically interesting.[25] The effect of the mineral on the selectivity of the reaction was previously reported for the condensation of NH2COH in the presence of cosmic dust analogues (CDAs), in which case the yield of pyrimidine nuocleobases increased by increasing the amount of iron in the catalyst[26] . Carboxylic acids: Carboxylic acids, including citric and pyruvic acids, were reported in carbonaceous chondrites in the ppb range.[21a] Meteorite-catalyzed syntheses afforded orders-of-magnitude higher yields (Scheme 1, Table 3). The 18 more abundant acids were: oxalic (14), glycolic (15), glyoxylic (16), acetic (17), pyruvic (18), propanoic (19), parabanic (20), lactic (21), malonic (22), malic (23), maleic
(24), succinic (25), oxalacetic (26), ketoglutaric (27), hexanoic (28), pimelic (29), octanoic (30), and nonanoic (31) acids. These compounds are part of numerous extant metabolic cycles: the components of direct and reversed citric acid, glycolysis, and gluconeogenesis cycles are immediately recognized.[27a, b] Iron and stony-iron meteorites performed as the best catalysts, followed by achondrites and chondrites. In terms of structural complexity (defined as the number of carbon atoms in the molecule, Cn), C3 and C4 acids prevailed with iron and stony-iron meteorites, while C2 and C5 acids (followed by C4) prevailed with chondrites. C2 and C3 acids were the major products of achondrites. The formation of acids 14–18 and 21 may be explained by the generation “in situ” of HCN followed by oligomerization to monoamino malonitrile (AMN) and diamino malonitrile (DAMN)
Table 3. Synthesis of carboxylic acids: products [mg] grouped by meteorite type. Product[a]
C2
C3
C4
C5 C6 C7 C8 C9
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
528.0 48.9 98.2 0.0 734.1 700.1 151.3 1792.2 32.5 360.3 132.2 146.5 2017.1 30.4 157.9 0.0 0.0 0.0
572.9ACHTUNGRE(541.0)[b] 103.0ACHTUNGRE(110.3) 145.6ACHTUNGRE(137.8) 0.0ACHTUNGRE(0.0) 700.0ACHTUNGRE(712.3) 514.6ACHTUNGRE(510.0) 218.2ACHTUNGRE(213.5) 1200.3ACHTUNGRE(1210.1) 33.4ACHTUNGRE(36.1) 900.9ACHTUNGRE(878.9) 62.4ACHTUNGRE(61.2) 125.9ACHTUNGRE(123.8) 3269.1ACHTUNGRE(3274) 31.1ACHTUNGRE(28.8) 153.4ACHTUNGRE(155.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
419.9 35.2 69.1 0.0 600.2 350.3 487.3 1665.2 40.1 354.7 45.3 267.3 1100.0 93.5 419.3 0.0 0.0 0.0
126.3 0.0 69.3 0.0 20.6 0.0 31.5 2048.3 0.0 0.0 377.1 0.0 260.2 894.4 0.0 27.5 0.0 2.4
112.3ACHTUNGRE(111.1)[b] 0.0ACHTUNGRE(0.0) 58.6ACHTUNGRE(59.3) 0.0ACHTUNGRE(0.0) 16.9ACHTUNGRE(21.4) 0.0ACHTUNGRE(0.0) 29.8ACHTUNGRE(28.7) 1407.4ACHTUNGRE(1410.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 46.2ACHTUNGRE(46.9) 0.0ACHTUNGRE(0.0) 278.5ACHTUNGRE(165.4) 870.4ACHTUNGRE(865.9) 0.0ACHTUNGRE(0.0) 3.1ACHTUNGRE(2.2) 0.0ACHTUNGRE(0.0) 19.0ACHTUNGRE(18.5)
Chondrites
Achondrite
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
5.7 0.0 4.5 0.0 0.0 0.0 0.0 16.3 0.0 0.0 0.0 0.0 0.0 4.9 0.0 0.0 0.0 3.58
105.4 0.0 1044.7 167.5 48.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 115.4 388.6 20.3 0.0 28.7 0.0
140.6 0.0 988.3 150.3 25.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 106.5 215.5 27.6 0.0 30.3 0.0
60.7 0.0 0.0 0.0 0.0 0.0 7.1 10.5 30.1 0.0 12.3 39.3 110.2 200.2 0.0 0.0 0.0 0.0
127.6 0.0 0.0 0.0 0.0 0.0 4.2 9.0 35.6 0.0 11.6 45.2 89.8 165.1 0.0 0.0 0.0 0.0
762.2 0.0 99.1 0.0 412.3 0.0 0.0 452.2 0.0 7.9 0.0 0.0 75.5 250.3 0.0 0.0 10.1 0.0
251.8 0.0 112.6 0.0 530.6 0.0 0.0 398.3 0.0 15.1 0.0 0.0 90.3 229.8 0.0 0.0 7.9 0.0
[a] The data are the mean values of three experiments. [b] Reaction performed with untreated meteorite.
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Table 4. Synthesis of amino acids: products [mg] grouped by meteorite type. Product[a]
32 33 34 35 36 37 38 39 40 41 42 43 44
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
321.5 767.5 11.3 42.6 47.3 72.6 0.0 47.7 0.0 218.6 0.0 0.0 110.3
300.6ACHTUNGRE(298.8)[b] 800.3ACHTUNGRE(805.1) 34.8ACHTUNGRE(34.0) 50.5ACHTUNGRE(49.6) 46.6ACHTUNGRE(47.0) 85.3ACHTUNGRE(88.3) 0.0ACHTUNGRE(0.0) 60.8ACHTUNGRE(61.4) 0.0ACHTUNGRE(0.0) 236.5ACHTUNGRE(235.8) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 127.6ACHTUNGRE(127.1)
486.7 700.5 9.8 78.5 84.3 123.3 0.0 112.2 0.0 300.4 0.0 0.0 108.2
90.1 56.2 0.0 15.3 18.5 0.0 0.0 72.3 0.0 3.2 0.0 24.4 0.0
88.4 79.5 0.0 45.5 7.9 0.0 0.0 19.7 0.0 4.1 0.0 30.3 0.0
Chondrites
Achondrites
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
73.05ACHTUNGRE(70.0)[b] 5.8ACHTUNGRE(6.6) 0.0ACHTUNGRE(0.0) 3.9ACHTUNGRE(4.1) 4.7ACHTUNGRE(4.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 6.1ACHTUNGRE(7.0) 5.4ACHTUNGRE(5.2) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
110.2 160.5 0.0 43.3 298.4 0.0 30.2 0.0 0.0 39.6 0.0 0.0 0.0
121.5 175.6 0.0 53.1 270.2 0.0 37.3 0.0 0.0 50.1 0.0 0.0 0.0
271.1 129.2 0.0 1.1 130.6 0.0 42.2 0.0 0.0 9.1 0.0 0.0 0.0
198.8 98.5 0.0 1.6 123.6 0.0 36.7 0.0 0.0 5.8 0.0 0.0 0.0
550.6 300.1 0.0 20.3 32.2 0.0 0.0 0.0 32.7 100.1 801.5 0.0 0.0
600.1 270.6 0.0 25.3 34.8 0.0 0.0 0.0 40.2 94.8 760.6 0.0 0.0
[a] The data are the mean values of three experiments. [b] Reaction performed with untreated meteorite.
Amino acids: Amino acids are present in carbonaceous chondrites.[29a,b, 30] As abundant products, we observed glycine (32), N-formylglycine (33), N-methylglycine (34), alanine (35), b-alanine (36), 2-methylalanine (37), valine (38), leucine (39), tert-leucine (40), b-amino isobutyric acid (bAIBA) (41), 2-amino butanoic acid (2-ABA) (42), hydroxyproline (43), and phenylalanine (44) (Table 4). With the only exception of b-AIBA and 2-ABA, glycine and alanine (and their derivatives) prevailed. Achondrites and iron meteorites were the most reactive, followed by chondrites and stony-iron meteorites. Amino acids were probably produced by a thermal induced Strecker-like condensation.[6]
acids derivatives.[32] In fact, carbodiimide, urea, guanidine and guanidine acetic acid are all involved in the catalytic cycle for the formation of N-formyl glycine 33 (the detailed description of formation of 33 is in Supporting Information #5). This hypothesis is partly demonstrated through the synthesis of 33 in high yield by treatment of commercially available 49 with NH2CHO. Note that this process is a well-recognized synthetic and theoretical probe for the formation of the peptide bond.[33] Since the chemical (alkaline and acidic) and thermal treatment (600 8C) of the meteorite samples may have significantly affected their catalytic properties, the reactions with Canyon-Diablo and NWA2828 were repeated with untreated samples. As reported in Tables 2–5, we observed a reactivity similar to that previously obtained.
Miscellanea: Low-molecular-weight reactive intermediates were also detected (Table 5) including: diamino malonitrile (DAMN) (45), carbodiimide (46), urea (47), guanidine (48), guanidine acetic acid (49), and glycocyanidine (50) (that is the cyclic form of 49). DAMN (HCN tetramer) is a key intermediate in the synthesis of purines and pyrimidines from HCN.[31] Carbodiimide is a well-known condensing agent. Excess of NH2CHO and the presence of carbodiimide were probably responsible for the formation of N-formyl amino
Syntheses at different temperatures: As representative examples, the reactivity of Canyon Diablo, Campo-del-Cielo, Sikhote-Alin, and Al-Haggounia was evaluated also at 60 8C. All the meteorites proved to be efficient in the synthesis of prebiotically relevant molecules even at this relatively low temperature, the carboxylic acids generally prevailing on nucleobases and amino acids, respectively. In accordance with data at 140 8C, the C3 and C4 acids were the most abundant products in the presence of iron meteorites,
(actually detected in the reaction mixture), hydrolysis, and successive redox processes[28] .
Table 5. Synthesis of low-molecular-weight compounds (miscellanea): products [mg] grouped by meteorite type. Product[a]
45 46 47 48 49 50
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
230.4 260.3 2000.1 0.0 225.4 0.0
165.3 ACHTUNGRE(157.9)[b] 205.1ACHTUNGRE(203.4) 14003.8ACHTUNGRE(13987.0) 0.0ACHTUNGRE(0.0) 289.7ACHTUNGRE(288.4) 0.0ACHTUNGRE(0.0)
530.1 1046.6 6869.4 0.0 250.3 0.0
110.8 253.7 4191.3 0.0 104.6 0.0
98.3 121.3 3800.1 0.0 112.5 0.0
Chondrites
Achondrites
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
0.0ACHTUNGRE(0.0)[b] 0.0ACHTUNGRE(0.0) 4.1ACHTUNGRE(3.9) 0.0ACHTUNGRE(0.0) 87.3ACHTUNGRE(88.8) 0.0ACHTUNGRE(0.0)
0.0 53.3 0.0 0.6 5.3 25.1
0.0 80.3 0.0 0.5 42.5 23.6
17.4 6.3 0.0 15.5 20.6 0.0
12.4 23.5 0.0 18.3 18.4 0.0
181.7 0.0 9.1 0.0 549.9 32.3
170.3 0.0 11.1 0.0 498.5 29.2
[a] The data are the mean values of three experiments. [b] Reaction performed with untreated meteorite.
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while C2 and C3 prevailed with Al-Haggounia (achondrite). With the only exception of b-AIBA and 2-ABA, the simplest amino acids, glycine and alanine, prevailed. As a general trend, the yields and structural complexity of products were higher at 140 8C than at 60 8C (especially for amino acids) (Table 6).
Table 6. Synthesis of carboxylic acids, nucleobases, amino acids, and lowmolecular-weight compounds (miscellanea) in reactions of NH2COH at 60 8C and/or diluted NH2COH at 140 8C. Product[a]
Canyon Campo Campo Sikhote Al Diablo del Cielo del Cielo[b] Alin Haggounia
carboxylic acids [mg] C2 oxalic 528.0 glycolic 48.9 glyoxylic 98.6 C3 pyruvic 734.3 propanoic 700.4 parabanic 151.0 lactic 1792.6 malonic 32.5 C4 malic 360.4 maleic 132.4 succinic 146.3 oxaloacetic 2017.1 C5 ketoglutaric 30.2 C6 hexanoic 157.9
54.6 25.1 100.5
13.0 5.2 17.9
37.0 7.0 4.2
36.0 0.0 23.3
35.9 75.3 40.0 153.9 15.1
4.0 0.0 0.0 27.1 9.3
462.2 112.5 146.8 150.3 11.0
19.7 0.0 0.0 105.3 0.0
795.5 41.3 20.1 562.1
7.5 3.1 1.8 10.5
14.3 12.0 36.9 15.4
4.1 0.0 0.0 21.3
23.5
0.5
25.5
17.2
37.3
10.0
135.2
0.0
nucleobases [mg] uracil 250.6 cytosine 122.3 isocytosine 395.7 DHuracil 0.0 41.3 purine[c] adenine 250.3 guanine 0.0 hypoxanthine 380.3 4ACHTUNGRE(3 H)-pyr 1296.1
95.1 30.1 87.3 0.0 13.8 179.9 0.0 34.5 368.5
12.5 11.6 26.4 0.0 1.2 5.9 0.0 8.5 11.6
130.4 60.2 122.6 0.0 0.3 185.2 0.0 50.5 117.5
175.3 11.5 238.7 14.3 0.2 77.3 23.6 0.0 112.2
miscellanea [mg] carbodiimide urea guanidine ac. DAMN
260.3 2000.4 225.4 230.2
27.8 230.5 46.3 88.4
0.3 14.1 1.9 3.4
850.0 154.6 143.9 234.2
0.0 5.7 234.8 59.9
amio acids [mg] glycine formyl glycine methyl glycine alanine b-alanine methyl alanine leucine tert-leucine b-AIBA 2-ABA phenylalanine
321.2 767.5 11.2 42.6 47.5 72.2 47.7 0.0 218.4 0.0 110.6
20.1 70.2 34.5 33.0 23.3 39.8 43.6 0.0 104.3 0.0 42.5
2.9 4.5 0.0 9.2 0.3 1.2 5.4 0.0 3.1 0.0 0.0
41.6 29.6 3.2 31.3 27.2 36.6 22.0.0 0.0 89.1 0.0 39.1
77.9 66.8 0.0 7.6 27.4 0.0 0.0 21.5 14.6 138.0 0.0
Synthesis in NH2COH/H2O mixture: A novel experiment was performed to better modeling the prebiotic scenario using Campo del Cielo in diluted NH2COH (NH2COH/ H2O = 1.0:10 v/v) at 140 8C. We observed the formation of several products largely similar to those formed from neat NH2COH. The yields were lower compared to the reaction carried out in the absence of H2O, probably due to hydrolytic processes (Table 6). These data are in accordance with results previously obtained in the condensation of dilute NH2COH (NH2COH/H2O = 7.0:30 v/v) with iron sulfur minerals.[24] Campo del Cielo performed as an efficient catalyst, the general trend of reactivity being largely comparable to that of neat NH2COH. Simple versus complex catalytic systems: The data in Tables 2–6 were compared with those obtained with untreated minerals and metal oxides (usually present as components in meteorites) studied singly[6]: for example, iron/ sulfur minerals (troilite, pyrrothite, pyrite), basalt, and olivine (Table 7). Iron/sulfur minerals were the most efficient catalysts for the synthesis of carboxylic acids and amino acids (pyrrothite and troilite being more reactive than pyrite), in agreement with the general order of reactivity observed with meteorites: iron and stony-iron meteorites > achondrites and chondrites. On the other hand, meteorites were more efficient catalysts than their individual mineralogical components, highlighting the presence of a synergistic effect. A similar behavior was observed for nucleobases. In this case pyrite was more reactive than pyrrothite and troilite. Pyrite and pyrrothite are reciprocally transformed by redox processes leading to the formation of acetic and thioacetic acids (Wachtershausers model).[34] In this transformation, carboxylic acids, amino acids and nucleobases may be synthesized with different efficiencies depending on the redox-state of the mineral (e.g., pyrite versus pyrrothite). Irrespective to catalytic system, carbodiimide was produced in high yield potentially favoring polymerization processes. In conclusions, meteorite-catalyzed syntheses afford panels of organic compounds candidates that could fit several of the early earth environments and scenarios proposed in the literature, such as: hydrothermal alkaline vents,[35] anoxic geothermal fields[36] or “warm little ponds” (for specific references and discussion on the source of organics in early earth see Supporting Information #6). It is plausible that the complex molecular interactions leading to life became possible when the relevant components were brought into proximity. In this perspective the catalytic properties of meteorites appears to be an important element in making available the suitable precursors for life at the time of their highest occurrence during the late heavy bombardment. In origin-of-life perspectives, meteorites thus become not only carriers of organic compounds formed or gathered during their permanence in space, but acquire the role of potential chemical reactors upon arrival on earth.
[a] The data are the mean values of three experiments with standard deviation less than 0.1 %. [b] Reaction performed with diluted NH2COH (NH2COH/H2O = 1.0:10 v/v) at 140 8C. [c] Data expressed in mg mL 1.
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Table 7. Synthesis of carboxylic acids, nucleobases, amino acids, and low-molecular-weight compounds (miscellanea) in reactions of NH2COH with selected minerals and metal oxides at 140 8C. Product[a] carboxylic acids [mg] oxalic glycolic glyoxylic acetic pyruvic propanoic parabanic lactic. malonic succinic oxaloacetic ketoglutaric pentanoic eptanoic
Troilite
Pyrrothite
Pyrite
20.6 28.6 46.4 0.0 12.2 5.4 12.4 23.9 15.0 43.2 6.9 45.9 0.0 0.0
30.4 20.3 80.8 0.0 49.9 9.9 39.9 120.5 39.8 79.7 10.5 180.9 49.8 0.0
0.3 0.0 1.2 0.0 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.3 0.0 12.3
0.0 0.0 9.3 122.2 4.8 0.0 0.0 39.2 0.0
0.0 0.0 10.1 250.2 10.8 0.1 0.0 0.7 0.2
0.0 0.0 480.2 > 1000.0 180.3 0.0 0.0 250.2 0.0
miscellanea [mg] carbodiimide urea guanidine
0.0 44.9 0.0
29.8 10.8 0.3
amino acids [mg] glycine formyl glycine methylglycine b-alanine methyl alanine formyl alanine b-AIBA
22.2 12.5 0.0 7.3 0.0 11.3 23.3
87.6 63.1 0.0 10.6 0.0 20.5 50.2
nucleobases [mg] uracil cytosine isocytosine purine adenine hypoxanthine 2-NH2 purine 4ACHTUNGRE(3 H)pyrimidone 3(OH)pyrimidine
Chalcopyrite 1.3 0.0 138.6 7.9 0.0 0.0 0.0 0.0 0.0 17.3 0.0 2.2 0.0 0.0
Volcanic basalt
Olivine
Hydrotalcite
0.7 5.7 0.0 0.0 5.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
11.8 9.5 0.0 0.0 1.8 0.0 0.0 2.6 4.9 5.9 140.4 0.0 0.0 0.0
81.9 0.0 0.0 7.2 0.0 0.0 2.2 7.0 3.1 0.0 0.0 0.0 0.0 0.0
6.93 909.1 560.3 > 1000.0 200.3 0.0 0.0 91.2 1.2
0.0 0.0 5.7 437.5 2.1 1.0 0.0 8.3 0.0
0.8 4.7 27.6 0.0 0.0 0.0 0.0 5.2 20.5
0.0 0.0 83.7 3289.7 0.0 0.0 0.0 184.1 0.0
110.5 99.9 0.0
> 1000.0 6.7 524.4
0.0 0.0 10.2
0.0 0.2 0.0
0.0 0.0 43.9
0.0 1.3 0.0 0.0 0.0 0.0 0.0
29.1 0.0 1.8 0.0 0.6 0.0 0.0
2.9 33.9 0.0 0.0 0.0 0.9 0.0
26.8 11.3 0.0 0.0 98.8 33.9 0.0
55.4 2.6 0.0 1.2 0.0 1.4 0.0
[a] The data are the mean values of three experiments. Minerals are not treated.
Experimental Section The reactions were performed by heating NH2COH (2.5 mL) at 140 8C or 60 8C for 24 h in the presence of meteorite powder (1.0 % by weight relative to NH2COH, grain size distribution of particles in the range of 0– 125 mm). At the end of the reaction the mineral was recovered by centrifugation (6000 rpm, 10 min, Haereus Biofuge), and the excess NH2COH removed by distillation (40 8C, 4 10 4 barr). The crude product was analyzed by GC-MS after treatment with N,N-bistrimethylsilyl trifluoroACHTUNGREacetACHTUNGREamide in pyridine (620 mL) at 60 8C for 4 h in the presence of betulinic acid as internal standard (3.0 mg). Mass spectrometry was performed by the following program: injection temperature 280 8C, detector temperature 280 8C, gradient 100 8C 2 min, 10 8C min 1 for 60 min. To identify the structure of the products, two strategies were followed. First, the spectra were compared with commercially available electron mass spectrum libraries such as NIST (Fison, Manchester, UK). Secondly, GC-MS analysis was repeated with standard compounds. All products have been recognized with a similarity index (S.I.) greater than 98 % compared to the reference standards. In order to evaluate the possible role of inorganic constituents of the meteorite powder in the condensation of NH2COH, the reaction was repeated under similar experimental conditions with
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a panel of selected minerals and metal oxides (detailed materials and methods and the procedure for preparation of meteorite powder are in Supporting Information #7).
Acknowledgements This work is supported by the Italian Space Agency “MoMa project” and by ASI-INAF n. I/015/07/0 “Esplorazione del Sistema Solare”. Thanks to Silvia Lopizzo for helpful contributions.
Keywords: amino acids · carboxylic acids · molecular evolution · nucleobases · prebiotic chemistry
[1] B. A. Cohen, T. D. Swindle, D. A. Kring, Science 2000, 290, 1754 – 1756. [2] C. Chyba, C. Sagan, Nature 1992, 355, 125 – 132.
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[3] a) V. F. B. Buchwald, Handbook of Iron Meteorites, Vol. 3, University of California Press, Berkeley, California, 1975; b) D. W. Mittlefehldt, T. J. McCoy, C. A. Goodrich, A. Kracher, Rev. Mineral. 1988, 36, 4-001 – 4-496. [4] H. C. Connolly Jr., C. Smith, G. K. Benedix, L. Folco, K. Righter, J. Zipfel, A. Yamaguchi, H. C. Aoudjehane, J. N. Grossmann, Meteorit. Planet. Sci. 2007, 42, 1647 – 1694. [5] “Classification of Meteorites”: A. N. Krot, K. Keil, C. A. Goodrich, E. R. D. Scott, M. K. Weisberg, in Treatise on Geochemistry, Meteorites, Comets, and Planets, Vol. 1 (Ed.: A. M. Davis), Elsevier, Oxford, 2004, pp. 83 – 128. [6] R. Saladino, G. Botta, S. Pino, G. Costanzo, E. Di Mauro, Chem. Soc. Rev. 2012, 41, 5526 – 5565. [7] D. Bockele-Morvan„ D. C. Lis, J. E. Wink, D. Despois, J. Crovisier, R. Bachiller, D. J. Benford, N. Biver, P. Colom, J. K. Davies, E. Grard, B. Germain, M. Houde, D. Mehringer, R. Moreno, G. Paubert, T. G. Phillips, H. Rauer, Astron. Astrophys. 2000, 353, 1101 – 1114. [8] W. A. Schutte, A. C. A. Boogert, A. G. G. M. Tielens, D. C. B. Whittet, P. A. Gerakines, J. E. Chiar, T. de Graauw, Astron. Astrophys. 1999, 343, 966 – 976. [9] S. E. Bisschop, J. K. Jorgensen, E. F. van Dishoeck, E. B. M. Wachter, Astron. Astrophys. 2007, 465, 913 – 929. [10] P. M. Solomon, Phys. Today 1973, 26, 32 – 40. [11] For representative examples see: M. Levy, S. L. Miller, K. Brinton, J. L. Bada, Icarus 2000, 145, 609 – 613. [12] G. A. Blake, E. C. Sutton, C. R. Masson, T. G. Phillips, Astrophys. J. Suppl. Ser. 1986, 60, 357 – 374. [13] a) S. E. Cummins, R. A. Linke, P. Thaddeus, Astrophys. J. Suppl. Ser. 1986, 60, 819 – 878; b) B. E. Turner, Astrophys. J. Suppl. Ser. 1991, 76, 617 – 686; c) A. Nummelin, P. Bergman, A. Hjalmarson, P. Friberg, W. M. Irvine, T. J. Millar, M. Ohishi, S. Saito, Astrophys. J. Suppl. Ser. 2000, 128, 213 – 243. [14] G. W. Cooper, J. R. Cronin, Geochim. Cosmochim. Acta 1995, 59, 1003 – 1015. [15] G. R. Adande, N. J. Woolf, L. M. Ziurys, Astrobiology 2013, 13, 439 – 453. [16] E. Di Mauro, R. Saladino, E. N. Trifonov, J. Biomol. Struct. Dyn. 2013, DOI: 10.1080/07391102.2013.783509. [17] H. L. Barks, R. Buckley, G. A. Grieves, E. Di Mauro, N. V. Hud, T. M. Orlando, ChemBioChem 2010, 11, 1240 – 1243. [18] P. Baaske, F. Weinert, S. Duhr, K. Lemke, M. J. Russell, D. Braun, Proc. Natl. Acad. Sci. USA 2007, 104, 9346 – 51. [19] R. Saladino, C. Crestini, S. Pino, G. Costanzo, E. Di Mauro, Phys. Life Rev. 2012, 9, 84 – 104.
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[20] R. Saladino, U. Ciambecchini, C. Crestini, G. Costanzo, R. Negri, E. Di Mauro, ChemBioChem 2003, 4, 514 – 521. [21] a) G. Cooper, C. Reed, D. Nguyen, M. Carter, Y. Wang, Proc. Natl. Acad. Sci. USA 2011, 108, 14015 – 14020; b) M. P. Callahan, E. Karen, H. Smith, J. Cleaves, J. Ruzicka, J. C. Sterna, D. P. Glavin, C. H. House, J. P. Dworkin, Proc. Natl. Acad. Sci. USA 2011, 108, 13995 – 13998. [22] a) P. G. Stoks, A. W. Schwartz, Geochim. Cosmochim. Acta 1981, 45, 563 – 569; b) Z. Martins, O. Botta, M. L. Fogel, Earth Planet. Sci. Lett. 2008, 270, 130 – 136. [23] A. K. Oyelere, J. R. Pardon, S. A. Strobel, Biochemistry 2002, 41, 3667 – 3675. [24] R. Saladino, V. Neri, C. Crestini, G. Costanzo, M. Graciotti, E. Di Mauro, J. Am. Chem. Soc. 2008, 130, 15512 – 15518. [25] X. Sun, J. K. Lee, J. Org. Chem. 2010, 75, 1848 – 1854. [26] R. Saladino, C. Crestini, V. Neri, J. R. Brucato, L. Colangeli, F. Ciciriello, E. Di Mauro, G. Costanzo, ChemBioChem 2005, 6, 1368 – 1374. [27] a) D. L. Nelson, M. M. Cox in Lehninger Principles of Biochemistry, 3rd ed. Worth, New York, 2000, pp. 567 – 597; b) E. Smith, H. J. Morowitz, Proc. Natl. Acad. Sci. USA 2004, 101, 13168 – 13173. [28] A. Eschenmoser, Chem. Biodiversity 2007, 4, 554 – 573. [29] a) A. S. Burton, J. C. Stern, J. E. Elsila, D. P. Glavin, J. P. Dworkin, Chem. Soc. Rev. 2012, 41, 5459 – 72; b) S. Pizzarello, G. W. Cooper, G. J. Flynn, in Meteorites and the Early Solar System II (Eds.: D. S. Lauretta, H. Y. McSween), University of Arizona Press, Tuscon, 2006, p. 625. [30] D. P. Glavin, J. P. Dworkin, Proc. Natl. Acad. Sci. USA 2009, 106, 5487 – 5492. [31] See for example: R. Glaser, B. Hodgen, D. Farrelly, E. Mckee, Astrobiology 2007, 7, 455–470, and referenced cited therein. [32] G. H. Hegazy, H. I. Ali, Bioorg. Med. Chem. 2012, 20, 1259 – 1270. [33] See for example: a) T. Oie, G. H. Loew, S. K. Burt, R. D. MacElroy, J. Am. Chem. Soc. 1983, 105, 2221 – 2227; b) Y. J. Pu, R. K. Vaid, S. K. Boini, R. W. Towsley, C. W. Doecke, D. Mitchell, Org. Process Res. Dev. 2009, 13, 310 – 314; c) D. T. Halfen, V. Ilyushin, L. M. Ziurys, Astrophys. J. 2011, 743, 60. [34] G. Wachtershauser, Proc. Natl. Acad. Sci. USA 1990, 87, 200 – 204. [35] N. Lane, W. Martin, Cell 2012, 151, 1406 – 1416. [36] A. Y. Mulkidjanian, A. Y. Bychkov, D. V. Dibrova, M. Y. Galperin, E. V. Koonin, Proc. Natl. Acad. Sci. USA 2012, 109, E821.
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Received: September 20, 2013 Published online: November 7, 2013
Chem. Eur. J. 2013, 19, 16916 – 16922
Meteorites as Catalysts for Prebiotic Chemistry Raffaele Saladino,*[a] Giorgia Botta,[a] Michela Delfino,[a] and Ernesto Di Mauro[b]
Meteorite late heavy bombardment[1] was a major event after the accretion of the earth. The relevance of organic syntheses driven by impact shocks was first proposed by Chyba and Sagan in 1992,[2] based on the scanty indications available at the time. How would the contribution by meteorites to an early earth organic pool compare with the syntheses these meteorites might have induced after their impact?[2] Here, we report the catalytic effect of several types of meteorites,[3a,b] iron, stony-iron,[3b] chondrites,[4] and achondrites (entreis 1–12 in Table 1[2, 5]) in the syntheses of organic molecules of prebiotic interest using the model reaction of the thermal condensation of formamide (NH2CHO).[6] NH2CHO is a ubiquitous molecule in the universe that has been observed in the comet Hale-Bopp,[7] in the stellar objects W33A,[8] NGC7538, and W3ACHTUNGRE(H2O),[9] in the interstellar Table 1. Meteorites used in NH2CHO condensation processes.
A
B C
D
1 2 3 4 5 6 7 8 9 10 11 12
Name[a]
Class
Type
Canyon-Diablo Campo-del-Cielo Sikhote-Alin Seymchan NWA4482 NWA2828 Gold basin Dhofar 959 Murchison NWA1465 NWA5357 Al-Haggounia 001
iron iron iron stony iron stony iron chondrite chondrite chondrite chondrite chondrite achondrites achondrites
IA hexaoctahedrite normal IAB hexaoctahedrite coarse IIB hexaoctahedrite coarsest pallasite main group pallasite anomalous enstatite ordinary L6 carbonaceoous LV3 anomalous diogenite aubrite
[a] References, composition, historical and terrestrial provenience, and cosmo-origin data are available as an appendix of this table in the Supporting Information (#1).
[a] Prof. R. Saladino, Dr. G. Botta, Dr. M. Delfino Dipartimento di Scienze Ecologiche e Biologiche Universit della Tuscia Via San Camillo De Lellis, 01100 Viterbo (Italy) Fax: (+ 39) 0761357242 E-mail: [email protected] [b] Prof. E. Di Mauro Istituto Pasteur—Fondazione Cenci Bolognetti c/o Dipartimento di Biologia e Biotecnologie “Charles Darwin” University la “Sapienza” Piazzale Aldo Moro, 5, Rome 00185 (Italy) E-mail: [email protected]
medium,[10] in Europa[11] and Orion-KL,[12] in the dense cloud SgrB2,[13] and in carbonaceous chondrites.[14] Recently, NH2CHO was identified as a common constituent of starforming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp and a potential influx of exogenous delivery to Earth as high as 0.1 mol km 2 yr 1 or 0.18 mmol m 12 per single impact.[15] From a synthetic point of view, NH2CHO could be either an alternative to hydrogen cyanide (HCN),[16] or a possible nonvolatile source of HCN.[17] Unlike HCN, NH2CHO has a boiling point of 210 8C without any azeotropic effect. Regardless of its initial concentration, physical phenomena were described that concentrate 1000-fold organic molecules in capillary spaces.[18] Additional concentration processes by eutectics, clays absorption and evaporation have been reviewed.[19, 6] Synthetic procedure: NH2CHO (2.5 mL) was treated with a catalytic amount of the appropriate meteorites powder (1.0 % in weight; similar grain size distribution of particles in the range of 0–125 mm) at 140 8C or 608 for 24 h. After removal of the catalyst and excess of NH2CHO, the products were analyzed by GC-MS. The condensation of NH2CHO in the absence of meteorite powder afforded purine as the only recovered product.[20] To avoid possible contamination problems due to the presence of terrestrial organics in the original sample (present in Murchison at the ppb range[21a, b]), the meteorite powders were extracted before their use with NaOH (0.1 n), CHCl3–CH3OH (2:1 v/v), and sulfuric acid. In the case of chondrites, achondrites, and stonyiron meteorites, the samples were also pyrolyzed at 600 8C. After the treatment, the powders did not release any trace of organic substances. The synthesis of large number of compounds was observed (Scheme 1): nucleobases and their analogues, carboxylic acids, amino acids, and low-molecularweight derivatives (miscellanea). We dub these reactions meteorite-catalyzed syntheses. Given the complexity of the mixtures, analysis was limited to products 1 ng mL 1. Because of the uncertainty of the stoichiometry of the reactions, the yield of products was calculated as mg (or mg) of product per mL of starting NH2CHO. Tables 2–6 show the 50 most abundant products (the m/z value and the abundance of peaks are in Supporting Information #2; selected chromatograms and the original m/z fragmentation spectra are in Supporting Information #3 and #4, respectively).
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201303690.
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Scheme 1. Syntheses of biogenic molecules from NH2COH catalyzed by meteorites. The compounds are numbered according to their mention in the text. Nucleobases and analogues: uracil (1), cytosine (2), isocytosine (3), dihydrouracil (4), purine (5), adenine (6), guanine (7), hypoxanthine (8), 2-aminopurine (9), 4ACHTUNGRE(3 H)-pyrimidinone (10), 2ACHTUNGRE(1 H)-pyrimidinone (11), 3-hydroxypyrimidine (12), and hydantoine (13). Acids: oxalic (14), glycolic (15), glyoxylic (16), acetic (17), pyruvic (18), propanoic (19), parabanic (20), lactic (21), malonic (22), malic (23), maleic (24), succinic (25), oxalacetic (26), ketoglutaric (27), hexanoic (28), pimelic (29), octanoic (30), and nonanoic (31). Amino acids: glycine (32), N-formylglycine (33), N-methylglycine (34), alanine (35), b-alanine (36), 2-methylalanine (37), valine (38), leucine (39), tert-leucine (40), b-amino isobutyric acid (b-AIBA) (41), 2-aminobutanoic acid (2ABA) (42), hydroxyproline (43), and phenylalanine (44). Miscellanea: diaminomalonitrile (DAMN) (45), carbodiimide (46), urea (47), guanidine (48), guanidine acetic acid (49), and glycocyanidine (50). Yields of the reactions are in Tables 2–6. GC-MS spectra of compounds (1–50) are in Supporting Information #4.
Nucleobases: The extraterrestrial origin of nucleobases detected in carbonaceous chondrites[21b, 22a,b] is not unequivoACHTUNGREcal.[22a] In the richest chondrites the highest purine yields were < 100 ppb, guanine reaching exceptionally 250 ppb, other compounds being lower by one to two orders of magnitude. In our syntheses we obtained: uracil (1), cytosine (2), isocytosine (iC) (3), 5,6-dihydrouracil (DHuracil, 4), purine (5), adenine (6), guanine (7), hypoxanthine (8), 2aminopurine [2ACHTUNGRE(NH2)purine, (9)], 4ACHTUNGRE(3 H)-pyrimidinone (10), 2ACHTUNGRE(1 H)-pyrimidinone (11), 3-hydroxypyrimidine (12), and hydantoine (13). Compounds (1–13) were synthesized in the range of 0.009 (NWA2828) and 2.33 mg mL 1 (Seymchan) (total amount of nucleobases disregarding the more abun-
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dant purine, pyrimidine and pyrimidinone derivatives), that is more than 100 times greater than those recovered in the original samples[21a, b] (Scheme 1, Table 2, Supporting Information #3 and #4). Irons, stony-irons, and achondrites showed a catalytic effect higher than chondrites. Mechanisms for the formation of nucleobases are well reviewed.[6] Adenine prevailed with chondrites and achondrites (with the exception of NWA1465, Murchison, and NWA2828), while comparable amounts of uracil, cytosine, and adenine were detected in the presence of iron and stony-iron meteorites. Guanine was synthesized only with achondrites, while large amounts of isocytosine (a well-known bioisoster of guanine[23]) were obtained. 2-Aminopurine (previously ob-
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Table 2. Synthesis of nucleobases and their analogues: products [mg] grouped by meteorite type. Product[a]
1 2 3 4 5 6 7 8 9 10 11 12 13
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
250.2 122.3 395.7 0.0 41.32[b] 250.5 0.0 380.6 0.0 1296.1 0.0 0.0 0.0
238.5ACHTUNGRE(245.1)[c] 51.4ACHTUNGRE(57.4) 790.6ACHTUNGRE(765.4) 0.0ACHTUNGRE(0.0) 19.06ACHTUNGRE(19.1) 211.3ACHTUNGRE(209.8) 0.0ACHTUNGRE(0.0) 489.2ACHTUNGRE(488.3) 0.0ACHTUNGRE(0.0) 4221.5ACHTUNGRE(4230) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
278.0 120.6 811.1 0.0 1.4 400.1 0.0 500.2 0.0 2470.8 0.0 0.0 0.0
345.2 30.6 1836.3 0.0 5.26 107.5 0.0 0.0 10.8 5545.4 20.1 15.4 0.0
300.6 32.3 689.2 0.0 1.86 103.5 0.0 0.0 128.6 2546.8 16.7 12.3 0.0
Chondrites
Achondrite
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
5.5ACHTUNGRE(5.1)[c] 2.3ACHTUNGRE(2.1) 1.1ACHTUNGRE(0.6) 0.0ACHTUNGRE(0.0) 0.03ACHTUNGRE(0.02) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 39.4ACHTUNGRE(40.1) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
34.2 23.2 270.3 0.0 2.37 499.5 0.0 0.0 0.0 344.5 50.6 23.9 0.0
61.2 32.5 323.5 0.0 1.38 510.3 0.0 0.0 0.0 350.9 41.8 25.6 0.0
33.4 13.4 337.9 0.0 0.7 50.3 0.0 0.0 0.0 6053.2 1687.6 31.6 264.6
50.6 29.8 249.6 0.0 2.66 41.4 0.0 0.0 0.0 362.8 1400.6 26.2 100.2
481.5 30.3 700.8 62.3 0.89 800.5 50.3 0.0 0.0 821.6 649.2 12.6 0.0
470.9 44.4 613.6 70.1 0.77 810.5 60.6 0.0 0.0 297.1 668.3 10.2 0.0
[a] The data are the mean values of three experiments. Products are given in mg mL 1. See Text. [b] Data expressed in mg mL 1. [c] Reaction performed with untreated meteorite.
served in iron-sulfur/NH2COH syntheses),[24] and hypoxanthine, are prebiotically interesting.[25] The effect of the mineral on the selectivity of the reaction was previously reported for the condensation of NH2COH in the presence of cosmic dust analogues (CDAs), in which case the yield of pyrimidine nuocleobases increased by increasing the amount of iron in the catalyst[26] . Carboxylic acids: Carboxylic acids, including citric and pyruvic acids, were reported in carbonaceous chondrites in the ppb range.[21a] Meteorite-catalyzed syntheses afforded orders-of-magnitude higher yields (Scheme 1, Table 3). The 18 more abundant acids were: oxalic (14), glycolic (15), glyoxylic (16), acetic (17), pyruvic (18), propanoic (19), parabanic (20), lactic (21), malonic (22), malic (23), maleic
(24), succinic (25), oxalacetic (26), ketoglutaric (27), hexanoic (28), pimelic (29), octanoic (30), and nonanoic (31) acids. These compounds are part of numerous extant metabolic cycles: the components of direct and reversed citric acid, glycolysis, and gluconeogenesis cycles are immediately recognized.[27a, b] Iron and stony-iron meteorites performed as the best catalysts, followed by achondrites and chondrites. In terms of structural complexity (defined as the number of carbon atoms in the molecule, Cn), C3 and C4 acids prevailed with iron and stony-iron meteorites, while C2 and C5 acids (followed by C4) prevailed with chondrites. C2 and C3 acids were the major products of achondrites. The formation of acids 14–18 and 21 may be explained by the generation “in situ” of HCN followed by oligomerization to monoamino malonitrile (AMN) and diamino malonitrile (DAMN)
Table 3. Synthesis of carboxylic acids: products [mg] grouped by meteorite type. Product[a]
C2
C3
C4
C5 C6 C7 C8 C9
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
528.0 48.9 98.2 0.0 734.1 700.1 151.3 1792.2 32.5 360.3 132.2 146.5 2017.1 30.4 157.9 0.0 0.0 0.0
572.9ACHTUNGRE(541.0)[b] 103.0ACHTUNGRE(110.3) 145.6ACHTUNGRE(137.8) 0.0ACHTUNGRE(0.0) 700.0ACHTUNGRE(712.3) 514.6ACHTUNGRE(510.0) 218.2ACHTUNGRE(213.5) 1200.3ACHTUNGRE(1210.1) 33.4ACHTUNGRE(36.1) 900.9ACHTUNGRE(878.9) 62.4ACHTUNGRE(61.2) 125.9ACHTUNGRE(123.8) 3269.1ACHTUNGRE(3274) 31.1ACHTUNGRE(28.8) 153.4ACHTUNGRE(155.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
419.9 35.2 69.1 0.0 600.2 350.3 487.3 1665.2 40.1 354.7 45.3 267.3 1100.0 93.5 419.3 0.0 0.0 0.0
126.3 0.0 69.3 0.0 20.6 0.0 31.5 2048.3 0.0 0.0 377.1 0.0 260.2 894.4 0.0 27.5 0.0 2.4
112.3ACHTUNGRE(111.1)[b] 0.0ACHTUNGRE(0.0) 58.6ACHTUNGRE(59.3) 0.0ACHTUNGRE(0.0) 16.9ACHTUNGRE(21.4) 0.0ACHTUNGRE(0.0) 29.8ACHTUNGRE(28.7) 1407.4ACHTUNGRE(1410.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 46.2ACHTUNGRE(46.9) 0.0ACHTUNGRE(0.0) 278.5ACHTUNGRE(165.4) 870.4ACHTUNGRE(865.9) 0.0ACHTUNGRE(0.0) 3.1ACHTUNGRE(2.2) 0.0ACHTUNGRE(0.0) 19.0ACHTUNGRE(18.5)
Chondrites
Achondrite
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
5.7 0.0 4.5 0.0 0.0 0.0 0.0 16.3 0.0 0.0 0.0 0.0 0.0 4.9 0.0 0.0 0.0 3.58
105.4 0.0 1044.7 167.5 48.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 115.4 388.6 20.3 0.0 28.7 0.0
140.6 0.0 988.3 150.3 25.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 106.5 215.5 27.6 0.0 30.3 0.0
60.7 0.0 0.0 0.0 0.0 0.0 7.1 10.5 30.1 0.0 12.3 39.3 110.2 200.2 0.0 0.0 0.0 0.0
127.6 0.0 0.0 0.0 0.0 0.0 4.2 9.0 35.6 0.0 11.6 45.2 89.8 165.1 0.0 0.0 0.0 0.0
762.2 0.0 99.1 0.0 412.3 0.0 0.0 452.2 0.0 7.9 0.0 0.0 75.5 250.3 0.0 0.0 10.1 0.0
251.8 0.0 112.6 0.0 530.6 0.0 0.0 398.3 0.0 15.1 0.0 0.0 90.3 229.8 0.0 0.0 7.9 0.0
[a] The data are the mean values of three experiments. [b] Reaction performed with untreated meteorite.
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Table 4. Synthesis of amino acids: products [mg] grouped by meteorite type. Product[a]
32 33 34 35 36 37 38 39 40 41 42 43 44
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
321.5 767.5 11.3 42.6 47.3 72.6 0.0 47.7 0.0 218.6 0.0 0.0 110.3
300.6ACHTUNGRE(298.8)[b] 800.3ACHTUNGRE(805.1) 34.8ACHTUNGRE(34.0) 50.5ACHTUNGRE(49.6) 46.6ACHTUNGRE(47.0) 85.3ACHTUNGRE(88.3) 0.0ACHTUNGRE(0.0) 60.8ACHTUNGRE(61.4) 0.0ACHTUNGRE(0.0) 236.5ACHTUNGRE(235.8) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 127.6ACHTUNGRE(127.1)
486.7 700.5 9.8 78.5 84.3 123.3 0.0 112.2 0.0 300.4 0.0 0.0 108.2
90.1 56.2 0.0 15.3 18.5 0.0 0.0 72.3 0.0 3.2 0.0 24.4 0.0
88.4 79.5 0.0 45.5 7.9 0.0 0.0 19.7 0.0 4.1 0.0 30.3 0.0
Chondrites
Achondrites
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
73.05ACHTUNGRE(70.0)[b] 5.8ACHTUNGRE(6.6) 0.0ACHTUNGRE(0.0) 3.9ACHTUNGRE(4.1) 4.7ACHTUNGRE(4.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0) 6.1ACHTUNGRE(7.0) 5.4ACHTUNGRE(5.2) 0.0ACHTUNGRE(0.0) 0.0ACHTUNGRE(0.0)
110.2 160.5 0.0 43.3 298.4 0.0 30.2 0.0 0.0 39.6 0.0 0.0 0.0
121.5 175.6 0.0 53.1 270.2 0.0 37.3 0.0 0.0 50.1 0.0 0.0 0.0
271.1 129.2 0.0 1.1 130.6 0.0 42.2 0.0 0.0 9.1 0.0 0.0 0.0
198.8 98.5 0.0 1.6 123.6 0.0 36.7 0.0 0.0 5.8 0.0 0.0 0.0
550.6 300.1 0.0 20.3 32.2 0.0 0.0 0.0 32.7 100.1 801.5 0.0 0.0
600.1 270.6 0.0 25.3 34.8 0.0 0.0 0.0 40.2 94.8 760.6 0.0 0.0
[a] The data are the mean values of three experiments. [b] Reaction performed with untreated meteorite.
Amino acids: Amino acids are present in carbonaceous chondrites.[29a,b, 30] As abundant products, we observed glycine (32), N-formylglycine (33), N-methylglycine (34), alanine (35), b-alanine (36), 2-methylalanine (37), valine (38), leucine (39), tert-leucine (40), b-amino isobutyric acid (bAIBA) (41), 2-amino butanoic acid (2-ABA) (42), hydroxyproline (43), and phenylalanine (44) (Table 4). With the only exception of b-AIBA and 2-ABA, glycine and alanine (and their derivatives) prevailed. Achondrites and iron meteorites were the most reactive, followed by chondrites and stony-iron meteorites. Amino acids were probably produced by a thermal induced Strecker-like condensation.[6]
acids derivatives.[32] In fact, carbodiimide, urea, guanidine and guanidine acetic acid are all involved in the catalytic cycle for the formation of N-formyl glycine 33 (the detailed description of formation of 33 is in Supporting Information #5). This hypothesis is partly demonstrated through the synthesis of 33 in high yield by treatment of commercially available 49 with NH2CHO. Note that this process is a well-recognized synthetic and theoretical probe for the formation of the peptide bond.[33] Since the chemical (alkaline and acidic) and thermal treatment (600 8C) of the meteorite samples may have significantly affected their catalytic properties, the reactions with Canyon-Diablo and NWA2828 were repeated with untreated samples. As reported in Tables 2–5, we observed a reactivity similar to that previously obtained.
Miscellanea: Low-molecular-weight reactive intermediates were also detected (Table 5) including: diamino malonitrile (DAMN) (45), carbodiimide (46), urea (47), guanidine (48), guanidine acetic acid (49), and glycocyanidine (50) (that is the cyclic form of 49). DAMN (HCN tetramer) is a key intermediate in the synthesis of purines and pyrimidines from HCN.[31] Carbodiimide is a well-known condensing agent. Excess of NH2CHO and the presence of carbodiimide were probably responsible for the formation of N-formyl amino
Syntheses at different temperatures: As representative examples, the reactivity of Canyon Diablo, Campo-del-Cielo, Sikhote-Alin, and Al-Haggounia was evaluated also at 60 8C. All the meteorites proved to be efficient in the synthesis of prebiotically relevant molecules even at this relatively low temperature, the carboxylic acids generally prevailing on nucleobases and amino acids, respectively. In accordance with data at 140 8C, the C3 and C4 acids were the most abundant products in the presence of iron meteorites,
(actually detected in the reaction mixture), hydrolysis, and successive redox processes[28] .
Table 5. Synthesis of low-molecular-weight compounds (miscellanea): products [mg] grouped by meteorite type. Product[a]
45 46 47 48 49 50
Iron meteorites Canyon Diablo
Campo del Cielo
Sikhote Alin
Stony iron meteorites Seymchan NWA 4482
230.4 260.3 2000.1 0.0 225.4 0.0
165.3 ACHTUNGRE(157.9)[b] 205.1ACHTUNGRE(203.4) 14003.8ACHTUNGRE(13987.0) 0.0ACHTUNGRE(0.0) 289.7ACHTUNGRE(288.4) 0.0ACHTUNGRE(0.0)
530.1 1046.6 6869.4 0.0 250.3 0.0
110.8 253.7 4191.3 0.0 104.6 0.0
98.3 121.3 3800.1 0.0 112.5 0.0
Chondrites
Achondrites
NWA 2828
Gold Basin
Dhofar 959
NWA 1465
Murchison
NWA 5357
Al Haggounia
0.0ACHTUNGRE(0.0)[b] 0.0ACHTUNGRE(0.0) 4.1ACHTUNGRE(3.9) 0.0ACHTUNGRE(0.0) 87.3ACHTUNGRE(88.8) 0.0ACHTUNGRE(0.0)
0.0 53.3 0.0 0.6 5.3 25.1
0.0 80.3 0.0 0.5 42.5 23.6
17.4 6.3 0.0 15.5 20.6 0.0
12.4 23.5 0.0 18.3 18.4 0.0
181.7 0.0 9.1 0.0 549.9 32.3
170.3 0.0 11.1 0.0 498.5 29.2
[a] The data are the mean values of three experiments. [b] Reaction performed with untreated meteorite.
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while C2 and C3 prevailed with Al-Haggounia (achondrite). With the only exception of b-AIBA and 2-ABA, the simplest amino acids, glycine and alanine, prevailed. As a general trend, the yields and structural complexity of products were higher at 140 8C than at 60 8C (especially for amino acids) (Table 6).
Table 6. Synthesis of carboxylic acids, nucleobases, amino acids, and lowmolecular-weight compounds (miscellanea) in reactions of NH2COH at 60 8C and/or diluted NH2COH at 140 8C. Product[a]
Canyon Campo Campo Sikhote Al Diablo del Cielo del Cielo[b] Alin Haggounia
carboxylic acids [mg] C2 oxalic 528.0 glycolic 48.9 glyoxylic 98.6 C3 pyruvic 734.3 propanoic 700.4 parabanic 151.0 lactic 1792.6 malonic 32.5 C4 malic 360.4 maleic 132.4 succinic 146.3 oxaloacetic 2017.1 C5 ketoglutaric 30.2 C6 hexanoic 157.9
54.6 25.1 100.5
13.0 5.2 17.9
37.0 7.0 4.2
36.0 0.0 23.3
35.9 75.3 40.0 153.9 15.1
4.0 0.0 0.0 27.1 9.3
462.2 112.5 146.8 150.3 11.0
19.7 0.0 0.0 105.3 0.0
795.5 41.3 20.1 562.1
7.5 3.1 1.8 10.5
14.3 12.0 36.9 15.4
4.1 0.0 0.0 21.3
23.5
0.5
25.5
17.2
37.3
10.0
135.2
0.0
nucleobases [mg] uracil 250.6 cytosine 122.3 isocytosine 395.7 DHuracil 0.0 41.3 purine[c] adenine 250.3 guanine 0.0 hypoxanthine 380.3 4ACHTUNGRE(3 H)-pyr 1296.1
95.1 30.1 87.3 0.0 13.8 179.9 0.0 34.5 368.5
12.5 11.6 26.4 0.0 1.2 5.9 0.0 8.5 11.6
130.4 60.2 122.6 0.0 0.3 185.2 0.0 50.5 117.5
175.3 11.5 238.7 14.3 0.2 77.3 23.6 0.0 112.2
miscellanea [mg] carbodiimide urea guanidine ac. DAMN
260.3 2000.4 225.4 230.2
27.8 230.5 46.3 88.4
0.3 14.1 1.9 3.4
850.0 154.6 143.9 234.2
0.0 5.7 234.8 59.9
amio acids [mg] glycine formyl glycine methyl glycine alanine b-alanine methyl alanine leucine tert-leucine b-AIBA 2-ABA phenylalanine
321.2 767.5 11.2 42.6 47.5 72.2 47.7 0.0 218.4 0.0 110.6
20.1 70.2 34.5 33.0 23.3 39.8 43.6 0.0 104.3 0.0 42.5
2.9 4.5 0.0 9.2 0.3 1.2 5.4 0.0 3.1 0.0 0.0
41.6 29.6 3.2 31.3 27.2 36.6 22.0.0 0.0 89.1 0.0 39.1
77.9 66.8 0.0 7.6 27.4 0.0 0.0 21.5 14.6 138.0 0.0
Synthesis in NH2COH/H2O mixture: A novel experiment was performed to better modeling the prebiotic scenario using Campo del Cielo in diluted NH2COH (NH2COH/ H2O = 1.0:10 v/v) at 140 8C. We observed the formation of several products largely similar to those formed from neat NH2COH. The yields were lower compared to the reaction carried out in the absence of H2O, probably due to hydrolytic processes (Table 6). These data are in accordance with results previously obtained in the condensation of dilute NH2COH (NH2COH/H2O = 7.0:30 v/v) with iron sulfur minerals.[24] Campo del Cielo performed as an efficient catalyst, the general trend of reactivity being largely comparable to that of neat NH2COH. Simple versus complex catalytic systems: The data in Tables 2–6 were compared with those obtained with untreated minerals and metal oxides (usually present as components in meteorites) studied singly[6]: for example, iron/ sulfur minerals (troilite, pyrrothite, pyrite), basalt, and olivine (Table 7). Iron/sulfur minerals were the most efficient catalysts for the synthesis of carboxylic acids and amino acids (pyrrothite and troilite being more reactive than pyrite), in agreement with the general order of reactivity observed with meteorites: iron and stony-iron meteorites > achondrites and chondrites. On the other hand, meteorites were more efficient catalysts than their individual mineralogical components, highlighting the presence of a synergistic effect. A similar behavior was observed for nucleobases. In this case pyrite was more reactive than pyrrothite and troilite. Pyrite and pyrrothite are reciprocally transformed by redox processes leading to the formation of acetic and thioacetic acids (Wachtershausers model).[34] In this transformation, carboxylic acids, amino acids and nucleobases may be synthesized with different efficiencies depending on the redox-state of the mineral (e.g., pyrite versus pyrrothite). Irrespective to catalytic system, carbodiimide was produced in high yield potentially favoring polymerization processes. In conclusions, meteorite-catalyzed syntheses afford panels of organic compounds candidates that could fit several of the early earth environments and scenarios proposed in the literature, such as: hydrothermal alkaline vents,[35] anoxic geothermal fields[36] or “warm little ponds” (for specific references and discussion on the source of organics in early earth see Supporting Information #6). It is plausible that the complex molecular interactions leading to life became possible when the relevant components were brought into proximity. In this perspective the catalytic properties of meteorites appears to be an important element in making available the suitable precursors for life at the time of their highest occurrence during the late heavy bombardment. In origin-of-life perspectives, meteorites thus become not only carriers of organic compounds formed or gathered during their permanence in space, but acquire the role of potential chemical reactors upon arrival on earth.
[a] The data are the mean values of three experiments with standard deviation less than 0.1 %. [b] Reaction performed with diluted NH2COH (NH2COH/H2O = 1.0:10 v/v) at 140 8C. [c] Data expressed in mg mL 1.
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Table 7. Synthesis of carboxylic acids, nucleobases, amino acids, and low-molecular-weight compounds (miscellanea) in reactions of NH2COH with selected minerals and metal oxides at 140 8C. Product[a] carboxylic acids [mg] oxalic glycolic glyoxylic acetic pyruvic propanoic parabanic lactic. malonic succinic oxaloacetic ketoglutaric pentanoic eptanoic
Troilite
Pyrrothite
Pyrite
20.6 28.6 46.4 0.0 12.2 5.4 12.4 23.9 15.0 43.2 6.9 45.9 0.0 0.0
30.4 20.3 80.8 0.0 49.9 9.9 39.9 120.5 39.8 79.7 10.5 180.9 49.8 0.0
0.3 0.0 1.2 0.0 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.3 0.0 12.3
0.0 0.0 9.3 122.2 4.8 0.0 0.0 39.2 0.0
0.0 0.0 10.1 250.2 10.8 0.1 0.0 0.7 0.2
0.0 0.0 480.2 > 1000.0 180.3 0.0 0.0 250.2 0.0
miscellanea [mg] carbodiimide urea guanidine
0.0 44.9 0.0
29.8 10.8 0.3
amino acids [mg] glycine formyl glycine methylglycine b-alanine methyl alanine formyl alanine b-AIBA
22.2 12.5 0.0 7.3 0.0 11.3 23.3
87.6 63.1 0.0 10.6 0.0 20.5 50.2
nucleobases [mg] uracil cytosine isocytosine purine adenine hypoxanthine 2-NH2 purine 4ACHTUNGRE(3 H)pyrimidone 3(OH)pyrimidine
Chalcopyrite 1.3 0.0 138.6 7.9 0.0 0.0 0.0 0.0 0.0 17.3 0.0 2.2 0.0 0.0
Volcanic basalt
Olivine
Hydrotalcite
0.7 5.7 0.0 0.0 5.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
11.8 9.5 0.0 0.0 1.8 0.0 0.0 2.6 4.9 5.9 140.4 0.0 0.0 0.0
81.9 0.0 0.0 7.2 0.0 0.0 2.2 7.0 3.1 0.0 0.0 0.0 0.0 0.0
6.93 909.1 560.3 > 1000.0 200.3 0.0 0.0 91.2 1.2
0.0 0.0 5.7 437.5 2.1 1.0 0.0 8.3 0.0
0.8 4.7 27.6 0.0 0.0 0.0 0.0 5.2 20.5
0.0 0.0 83.7 3289.7 0.0 0.0 0.0 184.1 0.0
110.5 99.9 0.0
> 1000.0 6.7 524.4
0.0 0.0 10.2
0.0 0.2 0.0
0.0 0.0 43.9
0.0 1.3 0.0 0.0 0.0 0.0 0.0
29.1 0.0 1.8 0.0 0.6 0.0 0.0
2.9 33.9 0.0 0.0 0.0 0.9 0.0
26.8 11.3 0.0 0.0 98.8 33.9 0.0
55.4 2.6 0.0 1.2 0.0 1.4 0.0
[a] The data are the mean values of three experiments. Minerals are not treated.
Experimental Section The reactions were performed by heating NH2COH (2.5 mL) at 140 8C or 60 8C for 24 h in the presence of meteorite powder (1.0 % by weight relative to NH2COH, grain size distribution of particles in the range of 0– 125 mm). At the end of the reaction the mineral was recovered by centrifugation (6000 rpm, 10 min, Haereus Biofuge), and the excess NH2COH removed by distillation (40 8C, 4 10 4 barr). The crude product was analyzed by GC-MS after treatment with N,N-bistrimethylsilyl trifluoroACHTUNGREacetACHTUNGREamide in pyridine (620 mL) at 60 8C for 4 h in the presence of betulinic acid as internal standard (3.0 mg). Mass spectrometry was performed by the following program: injection temperature 280 8C, detector temperature 280 8C, gradient 100 8C 2 min, 10 8C min 1 for 60 min. To identify the structure of the products, two strategies were followed. First, the spectra were compared with commercially available electron mass spectrum libraries such as NIST (Fison, Manchester, UK). Secondly, GC-MS analysis was repeated with standard compounds. All products have been recognized with a similarity index (S.I.) greater than 98 % compared to the reference standards. In order to evaluate the possible role of inorganic constituents of the meteorite powder in the condensation of NH2COH, the reaction was repeated under similar experimental conditions with
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a panel of selected minerals and metal oxides (detailed materials and methods and the procedure for preparation of meteorite powder are in Supporting Information #7).
Acknowledgements This work is supported by the Italian Space Agency “MoMa project” and by ASI-INAF n. I/015/07/0 “Esplorazione del Sistema Solare”. Thanks to Silvia Lopizzo for helpful contributions.
Keywords: amino acids · carboxylic acids · molecular evolution · nucleobases · prebiotic chemistry
[1] B. A. Cohen, T. D. Swindle, D. A. Kring, Science 2000, 290, 1754 – 1756. [2] C. Chyba, C. Sagan, Nature 1992, 355, 125 – 132.
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Received: September 20, 2013 Published online: November 7, 2013
Chem. Eur. J. 2013, 19, 16916 – 16922
