Identification of novel sulfur-containing petroporphyrins in a natural bitumen: Potential biomarkers for aerobic organisms

Abstract

In this study, a serial of novel sulfur-containing petroporphyrins were identified in a natural bitumen by chemical derivatization and solvent extraction. In contrast to previously reported sulfur-containing petroporphyrins, the new petroporphyrins exhibit reduced unsaturation and are characterized by a reduced number of double-bond equivalences (number of rings plus double bonds). Molecular structures of these sulfur-containing petroporphyrins were further elucidated by multiple collision-induced dissociation in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results indicate that sulfur atoms are present as cyclic thioether on the side chain of porphyrin, suggesting that these compounds may have evolved from heme a or heme o in aerobic organisms. We thereby propose a potentially diagenetic pathway of these compounds. Due to the relative stability of cyclic thioethers in the porphyrin structure, potential geochemical information could be carried by these compounds, which warrants further investigation.