Meteoritics & Planetary Science 40, Nr 5, 779–787 (2005)
Abstract available online at http://meteoritics.org
Solid-state 13C NMR characterization of insoluble organic matter from Antarctic
CM2 chondrites: Evaluation of the meteoritic alteration level
Hikaru YABUTA1*†, Hiroshi NARAOKA1, 2, Kinya SAKANISHI3, and Hiroyuki KAWASHIMA3
1Department
of Earth Sciences, Okayama University, Tsushima-Naka 3-1-1, Okayama, 700-8530, Japan
of Space and Astronautical Science, Japan Aerospace Exploration Agency,
3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
3National Institute of Advanced Industrial Science and Technology, Onogawa 16-1, Tsukuba-West, Tsukuba 305-8569, Japan
†Present address: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW,
Washington D.C. 20015, USA
*Corresponding author. E-mail: [email protected]
2Institute
(Received 07 December 2004; revision accepted 30 March 2005)
Abstract–Chemical structures of the insoluble organic matter (IOM) from the Antarctic CM2
chondrites (Yamato [Y-] 791198, 793321; Belgica [B-] 7904; Asuka [A-] 881280, 881334) and the
Murchison meteorite were analyzed by solid-state 13C nuclear magnetic resonance (NMR)
spectroscopy. Different types of carbons were characterized, such as aliphatic carbon (Ali-C),
aliphatic carbon linked to hetero atom (Hetero-Ali-C), aromatic carbon (Aro-C), carboxyls (COOR),
and carbonyls (C=O). The spectra of the IOM from Murchison and Y-791198 showed two major
peaks: Ali-C and Aro-C, while the spectra from the other meteorites showed only one major peak of
Aro-C. Carbon distribution was determined both by manual integration and deconvolution. For most
IOM, the Aro-C was the most abundant (49.8–67.8%) of all carbon types. When the ratios of Ali-C
to Aro-C (Ali/Aro) were plotted with the atomic hydrogen to carbon ratio (H/C), a correlation was
observed. If we use the H/C as a parameter for the thermal alteration event on the meteorite parent
body, this result shows a different extent of thermal alteration. In addition, IOM with a lower Ali/Aro
showed a lower ratio of Ali-C to COOR plus C=O (Ali / (COOR + C=O)). This result suggests that
the ratio of CO moieties to aliphatic carbon in IOM might reflect chemical oxidation that was
involved in hydrothermal alteration.
INTRODUCTION
Carbonaceous chondrites retain volatile elements that
record the history of their chemical evolution in the universe.
The chondrites also contain a significant amount of organics,
most of which (70–99%) are complex macromolecular matter
that is insoluble in water, acids, or any organic solvent, and is
thus defined as insoluble organic matter (IOM). A number of
investigations have indicated that IOM is structurally
uncharacterized and isotopically heterogeneous (see Sephton
et al. 2002 for a recent review). The chemical structures of
IOM have been investigated by chemical degradation
(Hayatsu et al. 1977, 1980), various pyrolytic experiments
(Komiya et al. 1993; Sephton et al. 1998a, 1998b, 2000, 2003,
2004; Kitajima et al. 2002), solid-state 13C nuclear magnetic
resonance (NMR) spectroscopy (Cronin et al. 1987; Gardinier
et al. 2000; Cody et al. 2002; Cody and Alexander 2005), and
electron paramagnetic resonance (EPR) (Binet et al. 2002,
2004). Most of the investigations have revealed that IOM
includes mainly aliphatic and aromatic components. Recently,
solid-state 13C NMR has been shown to provide a quantitative
assessment of the carbon functional group distributions in
IOM. This technique enables non-destructive analysis,
revealing an intact picture of the organic macromolecule. It
has been performed so far on five carbonaceous chondrites:
Murchison (CM2) (Cronin et al. 1987; Gardinier et al. 2000;
Cody et al. 2002), Allende (CV) (Cronin et al. 1987), Orgueil
(CI) (Cronin et al. 1987; Gardinier et al. 2000; Cody and
Alexander 2005), Tagish Lake (C2) (Pizzarello et al. 2001;
Cody and Alexander 2005), and Elephant Moraine (EET)
92042 (CR2) (Cody and Alexander 2005).
The origin and history of IOM are still being discussed.
The similarity of chemical compositions between IOM and
interstellar organic matter (Ehrenfreund et al. 1991) and
significant excesses of D and 15N in IOM (e.g., Kerridge et al.
1987; Alexander et al. 1998) indicate that IOM was possibly
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© The Meteoritical Society, 2005. Printed in USA.
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H. Yabuta et al.
formed in the interstellar environment and afterward
experienced thermal metamorphism and/or aqueous alteration
on the meteorite parent body. The chemical constituents of
IOM could have been affected by those events. Komiya et al.
(1993) performed laboratory heating experiments with IOM
from several CM2 chondrites and revealed that IOM from
some chondrites possessed the thermally labile organic
fraction and that those from the other chondrites did not; this
may be related to meteoritic alteration events. Sephton et al.
(1998a, 1998b, 2000) carried out hydrous (H2O-) pyrolysis of
IOM considering hydrous activity on the meteorite parent
body and identified a variety of polycyclic aromatic
hydrocarbons (PAHs) with their carbon isotopic
compositions. Recently, they applied a new advanced
technique, hydro- (H2-) pyrolysis, for the further
characterization of IOM (Sephton et al. 2004). Kitajima et al.
(2002) used pyrolysis-gas chromatography coupled with mass
spectrometry (pyr-GC/MS) to analyze the pyrolyzates of IOM
from CM chondrites and determined their degrees of
graphitization during thermal metamorphism. Naraoka et al.
(2004) proposed an organic parameter of thermal alteration
using carbon, hydrogen, and nitrogen concentrations of IOM.
In conjunction with those studies, the structural classification
of IOM within the same meteorite classes is required for
better understanding of its history. It is also important to
clarify relationships between IOM constituents and soluble
organic compounds such as amino acids and carboxylic acids,
because it has been suggested that the presence of soluble
organic compounds in meteorites is probably related to an
alteration event on the meteorite parent body (Bunch and
Chang 1980; Shimoyama and Harada 1984; Cronin and
Chang 1993).
In the present study, carbon functional group
distributions in IOM from several Antarctic CM2 chondrites
were revealed using solid-state 13C-NMR spectroscopy. The
IOM from Murchison was used as a reference. We focused on
determining the ratio of aliphatic to aromatic carbons of the
IOM in order to investigate whether the chemical structures of
IOM could be related to alteration event.
MATERIAL AND METHODS
Samples
Five Antarctic CM2 chondrites (Yamato [Y-] 791198 and
793321, Belgica Mountains [B-] 7904, and Asuka [A-]
881280 and 881334) and the Murchison meteorite were
analyzed. The Antarctic meteorites were collected by the
Japanese Antarctic Research Expeditions and were classified
mineralogically by Yanai and Kojima (1995).
Preparation of IOM
Each powdered meteorite sample (1.0–2.6 g) that had
previously been extracted with boiling water and organic
solvent was rinsed with 6 M HCl at room temperature for
12 hr. The extracted residue was shaken with 8 M HF/3 M
HCl in a Teflon container at room temperature to 70 °C for
more than 48 hr, followed by washing with 6 M HCl. This
process was repeated several times. The demineralized
residue was washed with water, methanol, dichloromethane,
hexane, and CS2, in that order, and was dried under vacuum.
Elemental Analyses
Carbon, H, and N contents in the IOM were determined
using a CHN analyzer (Pelkin Elmer 240 or Carlo Erba EA1180). The results of the elemental analysis are summarized
in Table 1, including information on C and H2O (+) contents
and extractable organic compounds in bulk samples.
Solid-State 13C NMR
Solid-state 13C-NMR spectra were obtained on a
Chemagnetics CMX-300 spectrometer at a field strength
corresponding to 75.6 MHz for 13C and 300.5 MHz for 1H.
Each sample was packed into a zirconium rotor 5 mm in
diameter and spun at the magic angle (54°44′). The cross
polarization (CP) and magic angle spinning (MAS) method
was applied in order to obtain spectra with a higher signal to
noise ratio in a short period. To accomplish effective CP
transfer and reduce the exhibition of spinning side bands
(SSB) that could interfere other peaks, the variable amplitude
cross polarization (VACP) experiment with MAS was applied
with a contact time of 1 msec, a spinning speed of 10 kHz, a
pulse delay of 4 sec, and a 90° 1H pulse width of 4 µsec. The
contact time was determined by our previous study, which has
conducted variable contact time experiments in a range of
0.1–5 msec for coals and several organic standards such as
hexamethylbenzene, glycine, polystyrene, poly-(methyl
methacrylate), and poly-2-vinylnaphthalene. It has been
confirmed that the signal intensities were maximum and the
relative proportions of functional groups were correctly
obtained for each sample around at 1 msec. The acquisitions
on each sample were performed in the range of 21726–84107
(Table 1), depending on the strength of the signal. The
spectral peaks were identified and integrated in two methods:
manual integration and deconvolution. Manual integration
was applied for the following ranges (Kidena et al. 1996): 0–
60 ppm (aliphatic carbon; Ali-C), 60–80 ppm (aliphatic
carbon linked to hetero atom (O and/or N); Hetero-Ali-C),
80–150 ppm (aromatic carbon; Aro-C), 150–180 ppm
(carboxyls; COOR, R=H and/or alkyl group), and 180–
200 ppm (carbonyls; C=O). Deconvolution was performed on
the basis of Gardinier et al. (2000) and Cody et al. (2002). The
Gaussian peak heights and widths were carefully adjusted so
that the spectrum combining those peaks could fit the original
spectrum for all the samples.
Insoluble organic matter from Antarctic CM2 chondrites
781
Table 1. Sample weights, C, H, and N contents, and NMR acquisition numbers for the IOM, C, and H2O (+) contents in
bulk samples, and characteristics on soluble organic compounds from the Antarctic CM2 chondrites and Murchison
meteorite.
IOM
Bulk
Ca
(wt%)
H2O (+)b
(wt%)
Soluble
organic
compoundsc
2.29
1.68
1.13
2.46
1.49
1.6–2.5
12.8
6.5
2.1
17.6
n.d.
n.d.
Abundant
Depleted
Depleted
Depleted
Depleted
Abundant
13C
Samples
Weight
(mg)
C
(wt%)
H
(wt%)
N
(wt%)
H/C
N/C
NMR
acquisition
number
Y-791198
Y-793321
B-7904
A-881280
A-881334
Murchison
28.9
34.7
17.8
34.0
17.6
33.0
57.6
64.2
64.3
63.7
47.6
56.9
3.20
1.90
0.79
1.53
1.37
3.30
3.20
1.90
0.79
2.75
2.17
2.60
0.67
0.36
0.15
0.29
0.34
0.70
0.037
0.039
0.029
0.037
0.039
0.039
28200
24880
63400
21726
84107
25265
a Naraoka
et al (1997); Kerridge (1985).
and Kojima (1996).
c Shimoyama and Harada (1984); Shimoyama et al. (1979a, 1979b, 1985, 1986, 1989, 1990, 1994); Cronin et al. (1988); Naraoka et al. (1988, 1999, 2000).
b Yanai
RESULTS AND DISCUSSION
Structural Characterization
The CP/MAS 13C-NMR spectra of the IOM of five
Antarctic chondrites and Murchison meteorite are shown in
Fig. 1. The spectra of Murchison showed two major signals of
Aro-C at 130 ppm and Ali-C at 30 ppm. The peak of Aro-C
includes protonated (∼100 to ∼130 ppm), non-protonated
(∼130 to ∼150 ppm), phenolic, and methoxyl substituted
aromatic carbons (~145 to ~160 ppm). The peak of Ali-C is
due to methylene (CH2), methyne (CH) (33 ppm), and methyl
(CH3) (15 ppm) groups. The width at the range of 60–80 ppm
corresponds to Hetero-Ali-C. The shoulders at the ranges of
150–180 ppm and 180–200 ppm indicate the presence of
COOR and C=O, respectively. The ranges of −20–0 and 200–
250 ppm are SSBs derived from the signal of Aro-C. This
identification result is very similar to those of Cronin et al.
(1987), Gardinier et al. (2000), and Cody et al. (2002). The
spectrum of Y-791198 is very similar to that of Murchison and
each type of carbon was identified as well. The signals of CH2
and CH3 are separated a little more clearly than those of
Murchison. On the other hand, the spectra of Y-793321 and
A-881280 show one sharp signal of Aro-C and are very
similar to each other. The total signal of Ali-C, including
shoulders and their widths, are depleted in these spectra
compared to those of Murchison and Y-791198. A-881334
shows an intermediate spectrum between Murchison type and
Y-793321 type. The intensity of the spectra of B-7904 is very
weak. The weak spectra of B-7904 occurs possibly because
the sample amounts were low (17.8 mg) and/or because these
samples
contained
predominant
aromatic
carbon
nondetectable by CP/MAS, such as quaternary carbon atoms
distant from 1H in the condensed aromatic structure.
Nevertheless, the broad peaks of Aro-C for the samples arose
at 130 ppm by taking longer acquisition time. Considering the
low signal to noise ratio of this spectrum, their baselines were
adjusted manually for precise quantification.
Carbon Functional Group Distribution
Figures 2a and 2b show the relative abundances of
different types of carbons in the IOM of Antarctic chondrites
and the Murchison meteorite, which were estimated by
manual integration (Fig. 2a) and deconvolution with
Gaussian peaks (Fig. 2b) for the 13C-NMR spectra of the
IOM. In Fig. 2a, variations of percentages of Ali-C, HeteroAli-C, Aro-C, COOR, and C=O for those samples were in a
range of 8.2–27.6, 2.8–7.9, 49.8–67.8, 11.2–22.2, and 2.4–
6.6%, respectively. For all the IOM samples, the relative
abundance of Aro-C was higher than any other carbon type,
supporting prior investigations that have indicated a highly
aromatic nature of meteoritic IOM (e.g., Hayatsu et al. 1977;
Sephton et al. 2000). The relative abundance of Aro-C is also
referred to the aromaticity factor (fa, when the relative
abundance of Aro-C is 100%, fa is equal to 1). In this study,
the fa of Murchison IOM was 0.50, a value that is similar to
those reported by Cronin et al. (1987) and Gardinier et al.
(2000) (∼0.40 and 0.52, respectively). It has been suggested
that the aromaticity factor may depend on the contact time for
the CP/MAS method. Cronin et al. (1987) applied a contact
time of 1 msec. Gardinier et al. (2000) indicated the fa value
via variable contact time experiments and fitting of the
variation of intensity with contact time for each type of
carbon. Cody et al. (2002) revealed that a contact time of
4.5 msec is needed for a complete magnetization transfer to
the aromatic carbon by variable contact time experiments.
They reported an fa between 0.61 and 0.66 for Murchison.
Using the longer contact time, the intensity of spectra of B7904 in this study (Fig. 1) might be increased. On the other
hand, Derenne et al. (2003) showed that even much longer
contact time (9.6 msec) could not hold for Orgueil IOM and
suggested that only single pulse (SP) spectra could lead to
quantitative data on polyaromatic macromolecules like IOM.
Cody and Alexander (2005) also presented the quantitative
data from both of VACP-MAS and SP-MAS NMR spectra of
IOM from Murchison, Orgueil, Tagish Lake, and EET 92042,
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H. Yabuta et al.
Fig. 1. Solid-state CP/MAS 13C NMR spectra of the insoluble organic matter of the Antarctic CM2 chondrites and the Murchison meteorite.
The spectra were identified for the following ranges: 0–60 ppm (aliphatic carbon; Ali-C), 60–80 ppm (aliphatic carbon linked to hetero atom
[O and/or N]; Hetero-Ali-C), 80–150 ppm (aromatic carbon; Aro-C), 150–180 ppm (carboxyls; COOR, R=H and/or alkyl group), and 180–
200 ppm (carbonyls; C=O). The ranges of −20–0 and 200–250 ppm were spinning side bands (∗) derived from the signal of Aro-C.
Insoluble organic matter from Antarctic CM2 chondrites
783
Fig. 2. Relative abundances of different functional groups of carbons in the insoluble organic matter of the Antarctic CM2 chondrites and the
Murchison meteorite derived in (a) manual integration and (b) deconvolution with Gaussian peaks for solid-state 13C-NMR spectra of IOM.
The percentage of aliphatic carbon (Ali-C) is shown as white, aliphatic carbon linked to hetero atom (Hetero-Ali-C) is shown as shaded,
aromatic carbon (Aro-C) is shown as black, carboxyls (COOR) are shown as cross-hatching, and carbonyl (C=O) is shown as light gray.
and described that the differences observed between the two
methods derived aromaticities likely reflected preferential
signal enhancement of protonated organic compounds in
VACP, rather than due to SP detecting additional
nonprotonated aromatic moieties. They concluded that the
two methods cannot be compared to indicate significant
quantities of large polyaromatic moieties in IOM. In this
study, we did not use SP consciously, since our sample
amounts (Table 1) could be unsuitable for the method
involving low signal to noise caused from signal limitation
by the 13C spin lattice relaxation. In addition, an enormously
long time would be needed for the 13C spin lattice relaxation
in the SP experiment and an even longer time for low
amounts of the sample. Here, the most important thing is that
a consistent contact time is chosen as described in methods.
Even if an artificially low estimate of fa occurred at the
contact time of 1 msec, the fa values and ratios of aliphatic to
aromatic carbons determined for each IOM still enable a
relative comparison among meteorites and they do not
change the conclusions in this study. The fa value of the IOM
of Y-791198 (0.50) showed similar levels to that of
Murchison. Those of Y-793321 (0.68), A-881280 (0.65), A881334 (0.57), and B-7904 (0.62) were ∼10–20% higher than
those of Murchison and Y-791198. Of the relative
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H. Yabuta et al.
abundances of Ali-C, the second highest were for Murchison
(27.6%) and Y-791198 (21.9%). Those of Y-793321, A881280, and A-881334 were ∼10 ± 2%. The relative
abundances of Hetero-Aro-C, COOR, and C=O showed
nearly the same values respectively for all the samples. In
Fig. 2b, percentage variations of Ali-C, Hetero-Ali-C, Aro-C,
COOR, and C=O for the same samples were 3.5–25.1, 2.1–
27.1, 47.4–61.2, 8.1–23.2, and 0–8.6%, respectively. The
results were roughly similar to those in Fig. 2a. However,
deconvolution might have brought some errors, particularly
to weak spectra of IOM of B-7904 and a minor signal of
Hetero-Ali-C. The relative abundances of some carbons in
such spectra and signal were likely overestimated compared
to those by manual integration. For example, the relative
abundances of Hetero-Ali-C were estimated very high in B7904 (27.1%), which brought very low abundances of Ali-C
(3.7%). In such cases, manual integration could be more
reliable.
Carbon Functional Group Distributions of IOM and
Alteration Event on the Meteorite Parent Body
Naraoka et al. (2004) showed a changing sequence of the
hydrogen to carbon (H/C) and nitrogen to carbon (N/C) ratios
by heating the IOM of several CM2 chondrites. In particular,
the H/C decreased significantly, from ∼0.7 to ∼0.3, after
heating the IOM up to 800 °C. They suggested that hydrogen
could have been lost from the IOM during thermal events on
meteorite parent bodies and proposed the chemical sequence
as a new parameter for the thermal alteration extent of
carbonaceous chondrites. According to this hypothesis, the H/
C could reflect the IOM chemical structures consisting of
different carbon types. In this study, the ratio of aliphatic
carbon to aromatic carbon in each IOM, Ali/Aro, was
obtained from the NMR spectra and is shown in Fig. 3 to
investigate the relationships with H/C for each IOM. The Ali/
Aro ratios which are derived both in manual integration and
deconvolution (as reflected by error bars) showed similar
values in most of IOM. As expected, a correlation was
observed between Ali/Aro ratios and H/C values. This
relationship indicates that the H/C variation reflects the
distributions of aliphatic and aromatic carbons in IOM.
Therefore, it can be suggested that Ali/Aro of IOM shows
different extents of thermal alteration on the meteorite parent
body as well as H/C; lower Ali/Aro (lower H/C) implies
higher alteration levels. Based on these results, the order of
alteration level is shown as follows (weak < intense);
Murchison (Ali/Aro = 0.46–0.55) ∼ Y-791198 (0.37–0.44) <
Y-793321 (0.17–0.19) ∼ A-881334 (0.16–0.19) ∼ A-881280
(0.15–0.16) < B-7904 (0.06–0.13) (the ranges count the
values derived both in manual integration and
deconvolution). This order was similar to those estimated by
the other methods such as Si-Mg-Fe ratios of chondrules and
matrixes (Kojima et al. 1984), phyllosilicate analyses (Akai
1990, 1992; Akai and Tari 1997; Lipschutz et al. 1999), and
pyrolysis of IOM (Shimoyama et al. 1991; Kitajima et al.
2002).
Figure 3 shows that the aliphatic structures of the IOM
could be modified in some way during thermal alteration, by
being aromatized, graphitized, or lost. Wdowiak et al. (1988)
heated Orgueil IOM under vacuum at different temperatures
and found that new weak aromatic features appeared along
with the decrease of the aliphatic content by infrared
spectroscopy. They argued that the aliphatic components
were removed by C-C bond cracking and that aromatic ones
were formed by heating. A study by Kitajima et al. (2002) on
pyrGC/MS used a model in which labile portions in IOM
were released and primary large polyaromatic moieties
remained as graphite sheet during thermal alteration.
Recently, Cody and Alexander (2005) compared 13C NMR
spectra of IOM belonging to different meteorite classes (CR,
CI1, CM2, and C2) and clearly showed that the progressive
loss of intensity in aliphatic moieties was compensated for by
increases in aromatic carbon and carboxyl carbon. They
pointed out that the conversion of aliphatic moieties to
aromatic ones would be unlikely during the low temperature
hydrothermal alteration, and suggested that the final
modifications from low to moderate temperatures involving
chemical oxidation during aqueous alteration on the parent
body resulted in partial conversion of aliphatic carbons
(including carbons bound with hetero atoms) to CO moieties
(COOR and C=O).
In order to examine their hypothesis, the ratio of Ali-C to
the sum of COOR and C=O, Ali/(COOR + C=O), was
obtained from the NMR spectra and is shown in Fig. 4 to
investigate the relationship with Ali/Aro for each IOM. Both
ratios are derived both in manual integration and
deconvolution (as reflected by error bars). A rough
correlation was seen between the two ratios, indicating that
the ratio of CO moieties to aliphatic carbon was abundant in
highly altered IOM. According to the values of Ali/(COOR +
C=O), the order of alteration level is shown as follows (weak
< intense); Murchison (1.37–1.67) < Y-791198 (0.56–0.92) ∼
Y-793321 (0.52–0.93) < A-881280 (0.50–0.55) ~ A-881334
(0.31) ∼ B-7904 (0.37–0.43) (the ranges count the values
derived both in manual integration and deconvolution). This
order was similar to those estimated by Fig. 3. Based on the
discussion by Cody and Alexander (2005) and on Fig. 4,
thermal alteration might result in chemical oxidation in
addition to hydrothermal alteration. Remusat et al. (2005)
suggested that the oxygen contents in IOM reflected
oxidation levels of the meteoritic organic matter upon the
hydrothermal event, which also supports the interpretation in
this study. Note that the plot of Y-793321 was located
between Murchison (and Y-791198) and A-881334 (A881280 and B-7904) in Fig. 4. It is known that Y-793321 is
classified to the weakly (moderate) altered CM2 chondrites
by several investigations described above. Figure 4 appears to
Insoluble organic matter from Antarctic CM2 chondrites
785
Fig. 3. Correlation plots between the ratio of aliphatic carbon to
aromatic carbon (Ali/Aro) and the atomic hydrogen to carbon (H/C)
ratio of IOM of the Antarctic CM2 chondrites and the Murchison
meteorite. The Ali/Aro ratios were derived both in manual integration
and deconvolution with Gaussian peaks for solid-state 13C-NMR
spectra of IOM, as reflected by the error bars.
Fig. 4. Correlation plots between Ali/Aro and the ratio of aliphatic
carbon to the sum of carboxyls and carbonyls (Ali/(COOR + C=O))
of IOM of the Antarctic CM2 chondrites and the Murchison
meteorite. The plots were derived both in manual integration and
deconvolution with Gaussian peaks for solid-state 13C-NMR spectra
of IOM, as reflected by the error bars.
show that Y-793321 experienced relatively intense thermal
alteration, but also slight degrees of chemical oxidation
during hydrous activity in its parent body. Also, Y-793321 has
been known to have heterogeneity due to its solar–noble gas
enrichment and impact features (Nakamura et al. 2000) and a
variety of clasts exhibiting different degrees of aqueous
alteration (Tonui et al. 2002).
Naraoka et al. (2004) have shown that the chondrites
with higher H/C (Murchison and Y-791198) contain a variety
of soluble organic molecules, but that those with lower H/C
(Y-793321, A-881281, A-881334, and B-7904) do not (Table
1). They assumed that the thermally altered chondrites lost
their soluble organic compounds. Many have considered that
some of the soluble organic compounds may have been
produced by aqueous alteration of IOM (Bunch and Chang
1980; Cronin and Chang 1993; Sephton et al. 1998).
Moreover, Cody and Alexander (2005) suggested that the
progressive oxidation of IOM preferentially targeted the
aliphatic carbon and led hydroxylation to yield water-soluble
organic compounds such as carboxylic acids. As we can see
from Figs. 3 and 4 in this study, the modification of aliphatic
carbon of IOM is likely related to the presence or formation
of soluble organic compounds in the CM2 chondrites.
However, the chondrites with lower Ali/Aro and Ali/(COOR
+ C=O) values (Y-793321, A-881281, A-881334, and B7904) do not contain soluble organic compounds. Possible
explanations are that thermal alteration after the aqueous
alteration could have lost such compounds, or that long
duration with hydrous activity may lose them (Naraoka et al.
1997).
CONCLUSIONS
For structural classification of IOM belonging to the
same meteorite classes, solid-state 13C-NMR analyses were
performed for IOM from five Antarctic CM2 chondrites and
the Murchison meteorite. Five carbon types, Ali-C, HeteroAli-C, Aro-C, COOR, and C=O, were identified for each
IOM. Their relative abundances varied among the IOM: 8.2–
27.6% (Ali-C), 2.8–7.9% (Hetero-Ali-C), 49.8–67.8% (AroC), 11.2–22.2% (COOR), and 2.4–6.6% (C=O). Ali/Aro
showed a correlation with H/C that is related to the thermal
alteration event on the meteorite parent body. Also, lower Ali/
Aro (highly altered IOM) included lower Ali/(COOR + C=O),
which could support the hypothesis of the partial conversion
of aliphatic carbons to CO moieties during hydrothermal
alteration. This study showed that the chemical structures of
the IOM could be related to the alteration level of the
meteorites. In particular, modification of aliphatic carbon of
IOM during the alteration events was likely related to
formation of soluble organic compounds in the carbonaceous
chondrites. Further studies are necessary to elucidate
relationships between IOM constituents and soluble organic
compounds.
Acknowledgments–We acknowledge the National Institute of
Polar Research (NIPR) of Japan for providing Antarctic
meteorites. We thank Dr. Masatoshi Komiya for practical
advice on purifying the IOM. We also thank Dr. Kazushige
Tomeoka and Dr. Tomoki Nakamura for giving mineralogical
perspectives to improve this study. We are grateful to Dr.
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H. Yabuta et al.
Sylvie Derenne and Dr. George D. Cody for enlightening and
favorable reviews. We also thank Professor Sandra Pizzarello
for helpful comments on an early version of this manuscript.
All NMR analyses were performed at the Energy Technology
Research Institute, National Institute of Advanced Industrial
Science and Technology (AIST). This work was supported by
the Research Grant for Fellowship No. 00008846 from
Japanese Society for the Promotion of Science (JSPS) to H. Y.
and a Grant-in-Aid for Scientific Research from the Japanese
Ministry of Education, Culture, Sports, Science and
Technology (MEXT) to H. N.
Editorial Handling—Dr. Scott Sandford
REFERENCES
Akai J. 1990. Mineralogical evidence of heating events in Antarctic
carbonaceous chondrites Y-86720 and Y-82162. Proceedings of
the NIPR Symposium on Antarctic Meteorites 3:55–68.
Akai J. 1992. T-T-T diagram of serpentine and saponite, and
estimation of metamorphic heating degree of Antarctic
carbonaceous chondrites. Proceedings of the NIPR Symposium
on Antarctic Meteorites 5:120–135.
Akai J. and Tari S. 1997. Thermally metamorphosed Antarctic CM
and CI carbonaceous chondrites in Japanese collections, and
transformation processes of phyllosilicates (abstract).
Proceedings, Workshop on Parent Body and Nebular
Modification of Chondritic Materials. p. 4015.
Alexander C. M. O’D., Russell S. S., Arden J. W., Ash R. D., Grady
M. M., and Pillinger C. T. 1998. The origin of chondritic
macromolecular organic matter: A carbon and nitrogen isotope
study. Meteoritics & Planetary Science 33:603–622.
Binet L., Gourier D., Derenne S., and Robert F. 2002. Heterogeneous
distribution of paramagnetic radicals in insoluble organic matter
from the Orgueil and Murchison meteorites. Geochimica et
Cosmochimica Acta 66:4177–4186.
Binet L., Gourier D., Derenne S., Robert F., and Ciofini I. 2004.
Occurrence of abundant diradicaloid moieties in the insoluble
organic matter from the Orgueil and Murchison meteorites: A
fingerprint of its extraterrestrial origin? Geochimica et
Cosmochimica Acta 68:881–891.
Bunch T. E. and Chang S. 1980. Carbonaceous chondrites-II.
Carbonaceous chondrite phyllosilicates and light element
geochemistry as indicators of parent body processes and surface
conditions. Geochimica et Cosmochimica Acta 44:1543–1577.
Cody G. D., Alexander C. M. O’D., and Tera F. 2002. Solid-state (1H
and 13C) nuclear magnetic resonance spectroscopy of insoluble
organic residue in the Murchison meteorite: A self-consistent
quantitative analysis. Geochimica et Cosmochimica Acta 66:
1851–1865.
Cody G. D. and Alexander C. M. O’D. 2005. NMR studies of
chemical structural variation of insoluble organic matter from
different carbonaceous chondrite groups. Geochimica et
Cosmochimica Acta 69:1085–1097.
Cronin J. R. and Chang S. 1993. Organic matter in meteorites:
Molecular and isotopic analyses of the Murchison meteorite. In
The chemistry of life’s origins, edited by Greenberg J. M.,
Mendoza-Gomez C. X., and Pirronello V. Dordrecht, The
Netherlands: Kluwer Academic. pp. 209–258.
Cronin J. R., Pizzarello S., and Frye J. S. 1987. 13C NMR
spectroscopy of the insoluble carbon of carbonaceous chondrites.
Geochimica et Cosmochimica Acta 51:299–303.
Cronin J. R., Pizzarello S., and Cruikshank D. P. 1988. Organic
matter in carbonaceous chondrites, planetary satellites, asteroids,
and comets. In Meteorites and the early solar system, edited by
Kerridge J. F. and Matthews M. S. Tucson, Arizona: The
University of Arizona Press. pp. 819–857.
Derenne S., Rouzaud J.-N., Maquet J., Bonhomme C., Florian P., and
Robert F. 2003. Abundance, size and organization of aromatic
moieties in insoluble organic matter of Orgueil and Murchison
meteorites (abstract #1316). 34th Lunar and Planetary Science
Conference. CD-ROM.
Ehrenfreund P., Robert F., D’Hendencourt L., and Behar F. 1991.
Comparison of interstellar and meteoritic organic matter at 3.4
microns. Astronomy and Astrophysics 252:712–717.
Gardinier A., Derenne S., Robert F., Behar F., Largeau C., and
Maquet J. 2000. Solid state CP/MAS 13C NMR of the insoluble
organic matter of the Orgueil and Murchison meteorites:
Quantitative study. Earth and Planetary Science Letters 184:9–
21.
Hayatsu R., Matsuoka S., Scott R. G., Studier M. H., and Anders E.
1977. Origin of organic matter in the early solar system—VII.
The organic polymer in carbonaceous chondrites. Geochimica et
Cosmochimica Acta 41:1325–1339.
Hayatsu R., Winans R. E., Scott R. G., McBeth R. L., Moore L. P., and
Studier M. H. 1980. Phenolic ethers in the organic polymer of the
Murchison meteorite. Science 207:1202–1204.
Kerridge J. F. 1985. Carbon, hydrogen, and nitrogen in carbonaceous
chondrites: Abundances and isotopic compositions in bulk
samples. Geochimica et Cosmochimica Acta 49:1707–1714.
Kerridge J. F., Chang S., and Ship R. 1987. Isotopic characterization
of kerogen-like material in the Murchison carbonaceous
chondrite. Geochimica et Cosmochimica Acta 51:2527–2540.
Kidena K., Murata S., and Nomura M. 1996. Studies on the chemical
structural change during carbonization process. Energy & Fuels
10:672–678.
Kitajima F., Nakamura T., Takaoka N., and Murae T. 2002.
Evaluating the thermal metamorphism of CM chondrites by
using the pyrolytic behavior of carbonaceous macromolecular
matter. Geochimica et Cosmochimica Acta 66:163–172.
Kojima H., Ikeda Y., and Yanai K. 1984. The alteration of chondrules
and matrices in new Antarctic carbonaceous chondrites.
Proceedings of the Ninth Symposium on Antarctic Meteorites. pp.
184–199.
Komiya M., Shimoyama A., and Harada K. 1993. Examination of
organic compounds from insoluble organic matter isolated from
some Antarctic carbonaceous chondrites by heating experiments.
Geochimica et Cosmochimica Acta 57:907–914.
Lipschutz M. E., Zolensky M. E., and Bell M. S. 1999. New
petrographic and trace element data on thermally
metamorphosed carbonaceous chondrites. Antarctic Meteorite
Research 12:57–80.
Nakamura T., Kitajima F., and Tanaka N. 2000. Thermal effects on
mineralogy, noble gas composition, and carbonaceous material
in CM chondrites (abstract). Proceedings, Workshop on
Extraterrestrial Materials from Cold and Hot Deserts. p. 61.
Naraoka H., Shimoyama A., Komiya M., Yamamoto H., and
Harada K. 1988. Hydrocarbons in the Yamato-791198
carbonaceous chondrites from Antarctica. Chemical Letters 17:
831–834.
Naraoka H., Shimoyama A., Matsubaya O., and Harada K. 1997.
Carbon isotopic compositions of Antarctic carbonaceous
chondrites with relevance to the alteration and existence of
organic matter. Geochemical Journal 31:155–168.
Naraoka H., Shimoyama A., and Harada K. 1999. Molecular
distribution of monocarboxylic acids in the Asuka carbonaceous
chondrites from Antarctica. Origins of Life and Evolution of the
Biosphere 29:187–201.
Naraoka H., Shimoyama A., and Harada K. 2000. Isotopic evidence
Insoluble organic matter from Antarctic CM2 chondrites
from an Antarctic carbonaceous chondrite for two reaction
pathways of extraterrestrial PAH formation. Earth and Planetary
Science Letters 184:1–7.
Naraoka H., Mita H., Komiya M., Yoneda S., Kojima H., and
Shimoyama A. 2004. A chemical sequence of macromolecular
organic matter in the CM chondrites. Meteoritics & Planetary
Science 39:401–406.
Pizzarello S., Huang Y., Becker L., Preda R. J., Nieman R. A.,
Cooper G., and Williams M. 2001. The organic content of the
Tagish Lake meteorite. Science 293:2236–2239.
Remusat L., Derenne S., Robert F., and Knicker H. Forthcoming.
New pyrolytic and spectroscopic data on Orgueil and Murchison
insoluble organic matter: A different origin than soluble?
Geochimica et Cosmochimica Acta.
Sephton M. A. 2002. Organic compounds in carbonaceous
meteorites. Natural Products Reports 19:292–311.
Sephton M. A., Pillinger C. T., and Gilmour I. 1998a. δ13C of free and
macromolecular aromatic structures in the Murchison meteorite.
Geochimica et Cosmochimica Acta 62:1821–1828.
Sephton M. A., Pillinger C. T., and Gilmour I. 1998b. Small-scale
hydrous pyrolysis of macromolecular material in meteorites.
Planetary and Space Science 47:181–187.
Sephton M. A., Pillinger C. T., and Gilmour I. 2000 Aromatic
moieties in meteoritic macromolecular materials: Analyses by
hydrous pyrolysis and 13C of individual compounds. Geochimica
et Cosmochimica Acta 64:321–328.
Sephton M. A., Verchovsky A. B., Bland P. A., Gilmour I.,
Grady M. M., and Wright I. P. 2003. Investigating the variations
in carbon and nitrogen isotopes in carbonaceous chondrites.
Geochimica et Cosmochimica Acta 67:2093–2108.
Sephton M. A., Love G. D., Watson J. S., Verchovsky A. B., Wright
I. P., Snape C. E., and Gilmour I. 2004. Hydropyrolysis of
insoluble carbonaceous matter in the Murchison meteorite: New
insights into its macromolecular structure. Geochimica et
Cosmochimica Acta 68:1385–1393.
Shimoyama A., Ponnamperuma C., and Yanai K. 1979a. Amino acids
in the Yamato-74662 meteorite, an Antarctic carbonaceous
chondrite. Proceedings of the Fourth Symposium on Antarctic
Meteorites. pp. 196–205.
787
Shimoyama A., Ponnamperuma C., and Yanai K. 1979b. Amino
acids in the Yamato carbonaceous chondrite from Antarctica.
Nature 282:394–396.
Shimoyama A. and Harada K. 1984. Amino acid depleted
carbonaceous chondrites (C2) from Antarctica. Geochemical
Journal 18:281–186.
Shimoyama A., Harada K., and Yanai K. 1985. Amino acids from the
Yamato-791198 carbonaceous chondrite from Antarctica.
Chemistry Letters 14:1183–1186.
Shimoyama A., Naraoka H., Yamamoto H., and Harada K. 1986.
Carboxylic acids in the Yamato-791198 carbonaceous chondrite
from Antarctica. Chemistry Letters 15:1561–1564.
Shimoyama A., Naraoka H., Komiya M., and Harada K. 1989.
Analyses of carboxylic acids and hydrocarbons in Antarctic
carbonaceous chondrites, Yamato-74662, and Yamato-793321.
Geochemical Journal 23:181–193.
Shimoyama A., Hagishita S., and Harada K. 1990. Search for nucleic
acid bases in carbonaceous chondrites from Antarctica.
Geochemical Journal 24:343–348.
Shimoyama A., Komiya M., and Harada K. 1991. Release of organic
compounds from some Antarctic CI and CM chondrites by
laboratory heating. Proceedings of the NIPR Symposium on
Antarctic Meteorites 4:247–260.
Shimoyama A. and Shigematsu R. 1994. Dicarboxylic acids in the
Murchison and Yamato-791198 carbonaceous chondrites.
Chemical Letters 23:523–526.
Tonui E., Zolensky M., and Lipschutz M. 2002. Petrography,
mineralogy and trace element chemistry of Yamato-86029,
Yamato-793321, and Lewis Cliff 85332: Aqueous alteration and
heating events. Antarctic Meteorite Research 15:38–58.
Wdowiak T. J., Flickinger G. C., and Cronin J. R. 1988. IR
spectroscopy of acid insoluble residues of carbonaceous
chondrites. Astrophysics and Space Science Library 149:145–
152.
Yanai K. and Kojima H. 1995. Catalog of the Antarctic meteorites
collected from December 1969 to December 1994 with special
reference to those represented in the collections of the National
Institute of Polar Research. Tokyo: National Institute of Polar
Research. 230 pp.