Direct comparison of the chemical composition of alkylated CHN compounds and mineral composition in the Murchison meteorite

Soluble organic matter (SOM) in carbonaceous chondrites is an important aspect of understanding the origin and evolution of extraterrestrial organic matter. Interactions with minerals and water on planetesimals are essential for the formation and evolution of SOM, yet the detailed processes remain poorly understood. To elucidate these processes, it is necessary to establish relationships between SOM and minerals, particularly secondary minerals. In this study, nitrogen (N)-heterocyclic compounds (CHN compounds) in the methanol extracts of powdered Murchison meteorite fragments were characterized by high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC/HRMS). Their abundance patterns and chemical characteristics were examined in direct relation to mineral compositions determined by X-ray diffraction (XRD) from the same samples. Five homologous series of CHN compounds (alkylpyridines: CnH2n-4N+ or CnH2n-6N+, alkylpiperidines: CnH2n+2N+, and alkylimidazoles: CnH2n-1N2+ or CnH2n-3N2+, which were identified as positive ions) were identified from all of the samples. XRD analyses revealed inter-sample variability in the abundance of phyllosilicate, anhydrous silicates, sulfides, and carbonates. Several CHN homologous series exhibited systematic relationships with alteration minerals, particularly phyllosilicates and magnetite, whereas correlations with minor phases were generally weak. These relationships are consistent with water–mineral–organic interactions on the Murchison parent body, such as mineral-surface/interlayer interactions, fluid-driven chromatographic effects during aqueous alteration, redox-dependent alteration , and the potential heterogeneity of precursor organic molecules. Although this present approach is not universally applicable to all classes of SOM and requires careful evaluation of potential mineral alteration during extraction, it enables direct comparisons between soluble organics and minerals, thereby providing new insights into water–mineral–organic interactions on planetesimals.