QUANTITATIVE STUDY OF ETHER GROUP MOLECULES IN INSOLUBLE ORGANIC MATTER FROM CARBONACEOUS CHONDRITES BY CuO-NaOH SELECTIVE DEGRADATION

Introduction: It has long been known that insoluble organic matter (IOM) in carbonaceous chondrites is complex and macromolecular in nature, and that it constitutes the major portion of chondritic organics. Structural characterization of IOM is one of the most important approaches for determining the formation process of the IOM. Recent NMR analyses of the IOM [1, 2, 3, 4] from a variety of carbonaceous chondrites have determined the distributions of different types of carbon functional groups in bulk IOM. However, they were unable to distinguish between important functional groups, such as ethers (-C-O-C) from alcohols (C-O-H), due to broad NMR lines as well as similar resonant frequencies. Copper oxide-sodium hydroxide (CuO-NaOH) oxidation is a conventional technique that cleavages ether bonds selectively [5, 6]. This chemical degradation method is used extensively, especially for identifying components of terrestrial organic polymer (e.g., soil organics, lignin and coal, etc) [7, 8]. Hayatsu et al (1980) [9] is the only study that has applied CuONaOH degradation to IOM (albeit extracted in a different way from HCl/HF or CsF/HF treatments) from the Murchison meteorite. However, the relative concentrations of components produced by the degradation were not estimated. Also, their result may have been influenced by their IOM extraction procedure. In the present study, focusing on the ether group molecules in IOM, we have conducted CuO-NaOH degradation of the IOM from the Murchison meteorite. The conditions used were similar to those of [9], but advances in analytical techniques allows for precise identification of the degradation products and quantification of their relative abundances. Our future goal includes establishing the isotopic compositions of individual degradation products. Experimental: The IOM were purified by CsF/HF demineralization of Murchison meteorite powder [2]. For the CuO-NaOH degradation, a Teflon bomb (23ml) was loaded with 2.96 mg of IOM, 83mg CuO powder, 8.3mg of ammonium iron (II) sulfate hexahydrate [Fe(NH4)2(SO4)2 6H2O] and 2.5ml of 2M NaOH solution. The bomb was purged with N2 gas, sealed and heated at 170•‹C for 3hrs. After the bomb had cooled down, the liquid was transferred to a Teflon tube, acidified to pH < 1, and extracted with ethyl acetate. The extract was dried under N2 flow, derivatized with 100ul of N,O-bis-(trimethylsilyl) trifluoroacetamide (BSTFA) at 80•‹Cfor 3hrs, and analyzed by GC-MS on a Rtx-5Sil MS column (Restek, 30m x 0.25mm i.d.). Prior to the experiment, the CuO was baked at 500•‹C for 8hrs to eliminate terrestrial contaminants and the HCl and ethyl acetate were distilled twice. Result and discusion: Part of the total ion chromatogram (TIC) (retention time 10-30min) of carboxylic acids produced by CuO-NaOH degradation of Murchison IOM is shown in Fig. 1. All peaks were trimethylsilyl (TMS) derivatives an intense fragment ion (m/z 73) from TMS was present in the mass spectra of most peaks (Fig. 2). In summary, 14 dicarboxylic acids, 11 benzoic acids, 2 isomers of thiophenecarboxylic acids, 12 hydroxy acids, 2 hydroxydicarboxylic acids, 1 keto-acid, and 1 benzaldehyde were indentified (Table 1). Among these compounds, oxalic acid, malonic acid, fumaric acid, methylmaleic acid, dimethylsuccinic acids, methylenesuccinic acid, methylglutaric acid, benzeneacetic acids, pyruvic acid, hydroxybenzaldehyde, and all hydroxyand hydroxydicarboxylic acids were seen for the first time as products of CuO-NaOH degradation of Murchison IOM. Higher molecular weight compounds that were detected in [9], such as benzene triand tetra-carboxy-