Synthesis of Organic Matter in Aqueous Environments Simulating Small Bodies in the Solar System and the Effects of Minerals on Amino Acid Formation

Abstract

The extraterrestrial delivery of organics to primitive Earth has been supported by many laboratory and space experiments. Minerals played an important role in the evolution of meteoritic organic matter. In this study, we simulated aqueous alteration in small bodies by using a solution mixture of H₂CO and NH₃ in the presence of water at 150 °C under different heating durations, which produced amino acids after acid hydrolysis. Moreover, minerals were added to the previous mixture to examine their catalyzing/inhibiting impact on amino acid formation. Without minerals, glycine was the dominant amino acid obtained at 1 d of the heating experiment, while alanine and β-alanine increased significantly and became dominant after 3 to 7 d. Minerals enhanced the yield of amino acids at short heating duration (1 d); however, they induced their decomposition at longer heating duration (7 d). Additionally, montmorillonite enhanced amino acid production at 1 d, while olivine and serpentine enhanced production at 3 d. Molecular weight distribution in the whole of the products obtained by gel chromatography showed that minerals enhanced both decomposition and combination of molecules. Our results indicate that minerals affected the formation of amino acids in aqueous environments in small Solar System bodies and that the amino acids could have different response behaviors according to different minerals.

Keywords: amino acids; ammonia; aqueous alteration; formaldehyde; olivine; phyllosilicates; small Solar System bodies.

Figure 1

Chromatograms of the acid-hydrolyzed (a) unheated formaldehyde-ammonia-water (FAW) treated at RT (0 d), and FAW heated at 150 °C for (b) 1 d, (c) 3 d, and (d) 7 d under the following conditions: without minerals “FAW”, with added olivine “FAWO”, with added montmorillonite “FAWM”, and with added serpentine “FAWS”. Asp: aspartic acid, Glu: glutamic acid, Ser: serine, Gly: glycine, Ala: alanine, β-Ala: β-alanine, γ-ABA: γ-aminobutyric acid.

Figure 2

Total amino acid concentrations (control-corrected values) of the unheated FAW samples treated at RT (0 d) and the heated FAW at 150 °C for 1 d, 3 d, and 7 d after acid hydrolysis. Note that the error is the standard deviation (1 σ) of three or more separate experimental runs. The total amino acids include six amino acids: Gly, Ala, β-Ala, Ser, Asp, and Glu.

Figure 3

Amino acid concentrations (control-corrected values) in the FAW samples (with and without minerals) heated at 150 °C after acid hydrolysis for (a) 1 d, (b) 3 d, and (c) 7 d. The error is the standard deviation (1 σ) of three or more separate experimental runs.

Figure 4

The concentrations (control-corrected values) of (a) Gly, (b) Ala, (c) β-Ala, (d) Ser, (e) Asp, and (f) Glu of the unheated FAW treated at RT (0 d) and the FAW samples heated at 150 °C for 1 d, 3 d, and 7 d after acid hydrolysis. The error is the standard deviation (1 σ) of three or more separate experimental runs.

Figure 5

Micro-Fourier transform infrared (FTIR) spectra for the region of 700–4000 cm⁻¹ of FAW heated at 150 °C for 1 d.

Figure 6

Micro-FTIR spectra for the region of 700–4000 cm⁻¹ of FAW heated at 150 °C for 3 d.

Figure 7

Micro-FTIR spectra for the region of 700–4000 cm⁻¹ of FAW heated at 150 °C for 7 d.

Figure 8

Trends in relative organic functional group concentrations with time for the soluble organics of FAW (with and without minerals) as determined by FTIR for the peak intensity ratios of (a) C=O (ester)/C=C, (b) C=O (carboxyl, aldehyde, amide)/C=C, (c) C=O (carboxyl, aldehyde, amide)/C=O (ester), (d) CH₂/CH₃, and (e) (CH₂ + CH₃)/C=C. The C=O (ester), C=O (carboxyl, aldehyde, amide), and C=C peak intensities are obtained by the peak top height of the band around 1765, 1700, and 1600 cm⁻¹, respectively, with the linear baseline between 1840 and 1520 cm⁻¹. The CH₂ and CH₃ peak intensities are obtained by the peak top height of the band at 2935 cm⁻¹ (CH₂) and the band at 2960 cm⁻¹ (CH₃), respectively, with the linear baseline between 3010 and 2790 cm⁻¹.

Figure 9

Gel filtration chromatograms of the FAW heated at 150 °C for (a) 1 d, (b) 3 d, and (c) 7 d.

Figure 10

(a) Chromatogram of the protein standard: (1) Lactalbumin (Mwt: 14,073 Da, RT: 12.5 min), (2) insulin (Mwt: 5807 Da, RT: 14.9 min), and (3) vitamin B12 (Mwt: 1355 Da, RT: 31.8 min). (b) Logarithm of the molecular weight of the protein standard as a function of retention time. Note; Mwt: molecular weight, RT: retention time.

Figure 11

The ratios (%) of each peak area among the total areas of the three major peaks (Peak 1: 12.6–15.2 min, Peak 2: 15.4–17.5 min, and Peak 3: 17.7–20.1 min) of the FAW heated at 150 °C for (a) 1 d, (b) 3 d, and (c) 7 d.