10:45 AM - 12:15 PM
[PPS08-P05] Organic synthesis experiments to constrain the heliocentric distances of chondrite parent body accretion
Keywords:carbonaceous chondrites, small bodies, insoluble organic matter, ammonia, hexamethylenetetramine, aqueous alteration
The locations where small bodies were formed are important for clarifying the process of the formation of planets. There is a possibility that the current locations of small bodies are different from the locations where small bodies were formed[1]. Isotope ratio of the material contained in meteorites is an example of an index of where small bodies were formed. However, isotope ratio has a problem of variation after alteration in small bodies. Therefore, in this study, we aimed to constrain the heliocentric distances of the formation of small bodies using the molecular structure of insoluble organic matter in extraterrestrial materials. There is a possibility that insoluble organic matter in carbonaceous chondrites was formed from simple molecules during aqueous alteration in their parent bodies[2]. In this case, starting materials before alteration vary according to the region of the formation of parent bodies. In this study, we synthesized organic matter simulating insoluble organic matter in extraterrestrial material from the various starting materials, and examined whether differences in the molecular structures of the products arose.
In this study, we focused on nitrogen sources in the starting materials which insoluble organic matter in meteorites were formed from inside or outside the ammonia snow line. The outside of the ammonia snow line shall contain ammonia as a nitrogen source, and the inside shall contain hexamethylenetetramine (C6H12N4, HMT). Thus we prepared the starting solutions with compositions of H2O : HCHO : CH3OH : NH3 : hexamethylenetetramine (HMT) : glycolaldehyde (GA) = (1)100 : 4 : 2 : 1.5 : 0 : 0.5, (2)100 : 4 : 2 : 0 : 0 : 0.5, (3)100 : 4 : 2 : 0 : 0.375 : 0.5, (4)100 : 0 : 2 : 0 : 0.375 : 0.5. This composition was decided by considering the composition of the molecules observed in comets. Ca(OH)2 was added to the solution of the samples as a catalyst. The 500 µL solution of each sample was put into glass tubes. After solution was frozen, the glass tubes were sealed. The samples in the glass tubes were heated at 150℃ for 72 hours. After being heated, solid products were separated from liquid products by centrifuging. The solid products were washed with HCl, H2O, CH3OH and CH2Cl2, and were dried. The dried products were analyzed by using micro FT-IR. The same experiments were performed on condition that Ca(OH)2 is not added or GA is not included in starting materials.
The heights of the peaks of aliphatic CH2, aliphatic CH3, C=O and C=C were measured from the infrared spectra of the solid products synthesized in the experiments, and the (CH3+CH2)/C=C, C=O/C=C and CH2/CH3 ratios were calculated. On all conditions, the C=O/C=C ratios of the samples which did not include any nitrogen sources (2) were clearly different from these of the samples which included nitrogen sources (1), (3), (4). This difference indicates that the characteristics of the products vary according to whether a nitrogen source is included in the starting materials. Meanwhile, the (CH3+CH2)/C=C, C=O/C=C and CH2/CH3 ratios of the samples which included NH3 as a nitrogen source in the starting materials (1) are relatively close to these of the samples which included HCHO and HMT as a nitrogen source (3). There was not a clear difference between the sample (1) and (3), so by infrared spectroscopic analysis, it was not confirmed that the characteristics of the products vary according to the difference between NH3 and HMT in the starting materials.
In this experiment, the difference in the products which arose from the difference between NH3 and HMT was not confirmed. However, it was revealed that the products vary according to whether a nitrogen source are included in the starting materials. Based on these results, we are planning to analyze the experimental products by other methods, and to conduct experiments using compounds other than NH3 and HMT as nitrogen sources, in the future.
References
[1] H. F. Levison et al., Nature 2009, 460, 7253.
[2] G. D. Cody et al., PNAS 2011, 108, 48.
In this study, we focused on nitrogen sources in the starting materials which insoluble organic matter in meteorites were formed from inside or outside the ammonia snow line. The outside of the ammonia snow line shall contain ammonia as a nitrogen source, and the inside shall contain hexamethylenetetramine (C6H12N4, HMT). Thus we prepared the starting solutions with compositions of H2O : HCHO : CH3OH : NH3 : hexamethylenetetramine (HMT) : glycolaldehyde (GA) = (1)100 : 4 : 2 : 1.5 : 0 : 0.5, (2)100 : 4 : 2 : 0 : 0 : 0.5, (3)100 : 4 : 2 : 0 : 0.375 : 0.5, (4)100 : 0 : 2 : 0 : 0.375 : 0.5. This composition was decided by considering the composition of the molecules observed in comets. Ca(OH)2 was added to the solution of the samples as a catalyst. The 500 µL solution of each sample was put into glass tubes. After solution was frozen, the glass tubes were sealed. The samples in the glass tubes were heated at 150℃ for 72 hours. After being heated, solid products were separated from liquid products by centrifuging. The solid products were washed with HCl, H2O, CH3OH and CH2Cl2, and were dried. The dried products were analyzed by using micro FT-IR. The same experiments were performed on condition that Ca(OH)2 is not added or GA is not included in starting materials.
The heights of the peaks of aliphatic CH2, aliphatic CH3, C=O and C=C were measured from the infrared spectra of the solid products synthesized in the experiments, and the (CH3+CH2)/C=C, C=O/C=C and CH2/CH3 ratios were calculated. On all conditions, the C=O/C=C ratios of the samples which did not include any nitrogen sources (2) were clearly different from these of the samples which included nitrogen sources (1), (3), (4). This difference indicates that the characteristics of the products vary according to whether a nitrogen source is included in the starting materials. Meanwhile, the (CH3+CH2)/C=C, C=O/C=C and CH2/CH3 ratios of the samples which included NH3 as a nitrogen source in the starting materials (1) are relatively close to these of the samples which included HCHO and HMT as a nitrogen source (3). There was not a clear difference between the sample (1) and (3), so by infrared spectroscopic analysis, it was not confirmed that the characteristics of the products vary according to the difference between NH3 and HMT in the starting materials.
In this experiment, the difference in the products which arose from the difference between NH3 and HMT was not confirmed. However, it was revealed that the products vary according to whether a nitrogen source are included in the starting materials. Based on these results, we are planning to analyze the experimental products by other methods, and to conduct experiments using compounds other than NH3 and HMT as nitrogen sources, in the future.
References
[1] H. F. Levison et al., Nature 2009, 460, 7253.
[2] G. D. Cody et al., PNAS 2011, 108, 48.