10:45 AM - 11:00 AM
[MTT42-06] High resolution mass spectrometry analysis of alkaline copper oxide degradation products from insoluble organic matter in carbonaceous chondrite
Keywords:Carbonaceous chondrite, Insoluble organic matter(IOM), Alkaline copper oxide degradation, High resolution mass spectrometry analysis, Asteroid
Introduction
It has been thought that asteroids, comets, and cosmic dusts delivered prebiotic organic molecules to the early Earth (Ehrenfreund et al. 2000). Carbonaceous chondrite, which are probably derived from carbonaceous asteroids, contains acid-insoluble organic matter (IOM) that accounts for a major part of the total organic carbon of the meteorite (Pizzarello et al. 2006). According to the previous studies, IOM is composed of aromatic molecular network crosslinking with short-branched aliphatic chains and various oxygen functional groups (Cody et al. 2002). However, because of its complex structure, the intact structure of IOM is still unknown. For better understanding of the chemical structure of IOM at a molecular level, we chemically degraded IOM by an alkaline CuO oxidation, which selectively cleaves ether bonds of macromolecules, and analyzed the decomposition products by using a high resolution mass spectrometry.
Sample and Methods
Insoluble organic matter was purified from the powdered sample (676 mg) of Murchison carbonaceous CM2 chondrite by an acid treatment with HCl/HF. The obtained IOM was heated with CuO (10 mg), 2N NaOH aq (2.5 ml), and ammonium iron (II) sulfate hexahydrate (1.2mg) at 170℃, 3 hours. After heating, the sample were extracted with ethyl acetate. The extracts were concentrated into 100μl and were analyzed by a high-resolution mass spectrometry (LTQ Orbitrap XL, Thermo Fisher Scientific) negative ion mode.
Results and Discussion
In this study, 222 ion peaks were identified as the alkaline CuO oxidation products of IOM from Murchison meteorite. Based on the exact masses of the ion peaks, possible composition formula were individually estimated. The main ion peaks, such as m/z 165.01946 (C8H6O4), m/z 121.02982 (C7H6O2), m/z 181.01428 (C8H6O5), m/z 137.02463 (C7H6O3), m/z 209.00905 (C9H6O6), are probably corresponded to benzendicarboxylic acid, benzoic acid, hydroxybenzendicarboxylic acid, hydroxybenzoic acid, and benzenetricarboxylic acid, respectively, which were previously identified by a gas chromatography coupled with mass spectrometry (GCMS) measurement of the alkaline CuO oxidation products of Murchison IOM (Hayatsu et al. 1980). In addition, the ion peaks corresponded to the other twenty-two compounds identified by Hayatsu et al. (1980), were also detected in this study. As a result, 195 ion peaks were newly identified in this study. According to an unsaturation degree of the possible composition formula, the peaks can be classified into 95 kinds of aliphatic carboxylic acids, 98 kinds of 1-3 ring-aromatic carboxylic acids and/or phenols, 9 kinds of nitrogen-containing compounds, 15 kinds of sulfur-containing compounds. Furthermore, the composition formula corresponded to dicarboxylic acids ranging from C2 to C15 were identified in this study, implying that longer aliphatic chains are ether-linked between aromatic moieties in IOM than reported by the previous studies. There results demonstrate that a structure of IOM in carbonaceous chondrite is more complex than previously thought, and they constrain the origin and evolution of organic compounds in the early Solar System.
It has been thought that asteroids, comets, and cosmic dusts delivered prebiotic organic molecules to the early Earth (Ehrenfreund et al. 2000). Carbonaceous chondrite, which are probably derived from carbonaceous asteroids, contains acid-insoluble organic matter (IOM) that accounts for a major part of the total organic carbon of the meteorite (Pizzarello et al. 2006). According to the previous studies, IOM is composed of aromatic molecular network crosslinking with short-branched aliphatic chains and various oxygen functional groups (Cody et al. 2002). However, because of its complex structure, the intact structure of IOM is still unknown. For better understanding of the chemical structure of IOM at a molecular level, we chemically degraded IOM by an alkaline CuO oxidation, which selectively cleaves ether bonds of macromolecules, and analyzed the decomposition products by using a high resolution mass spectrometry.
Sample and Methods
Insoluble organic matter was purified from the powdered sample (676 mg) of Murchison carbonaceous CM2 chondrite by an acid treatment with HCl/HF. The obtained IOM was heated with CuO (10 mg), 2N NaOH aq (2.5 ml), and ammonium iron (II) sulfate hexahydrate (1.2mg) at 170℃, 3 hours. After heating, the sample were extracted with ethyl acetate. The extracts were concentrated into 100μl and were analyzed by a high-resolution mass spectrometry (LTQ Orbitrap XL, Thermo Fisher Scientific) negative ion mode.
Results and Discussion
In this study, 222 ion peaks were identified as the alkaline CuO oxidation products of IOM from Murchison meteorite. Based on the exact masses of the ion peaks, possible composition formula were individually estimated. The main ion peaks, such as m/z 165.01946 (C8H6O4), m/z 121.02982 (C7H6O2), m/z 181.01428 (C8H6O5), m/z 137.02463 (C7H6O3), m/z 209.00905 (C9H6O6), are probably corresponded to benzendicarboxylic acid, benzoic acid, hydroxybenzendicarboxylic acid, hydroxybenzoic acid, and benzenetricarboxylic acid, respectively, which were previously identified by a gas chromatography coupled with mass spectrometry (GCMS) measurement of the alkaline CuO oxidation products of Murchison IOM (Hayatsu et al. 1980). In addition, the ion peaks corresponded to the other twenty-two compounds identified by Hayatsu et al. (1980), were also detected in this study. As a result, 195 ion peaks were newly identified in this study. According to an unsaturation degree of the possible composition formula, the peaks can be classified into 95 kinds of aliphatic carboxylic acids, 98 kinds of 1-3 ring-aromatic carboxylic acids and/or phenols, 9 kinds of nitrogen-containing compounds, 15 kinds of sulfur-containing compounds. Furthermore, the composition formula corresponded to dicarboxylic acids ranging from C2 to C15 were identified in this study, implying that longer aliphatic chains are ether-linked between aromatic moieties in IOM than reported by the previous studies. There results demonstrate that a structure of IOM in carbonaceous chondrite is more complex than previously thought, and they constrain the origin and evolution of organic compounds in the early Solar System.