Kerogen-bound and free hopanoic acids in the messel oil shale kerogen

✍ Scribed by Geoffrey D. Abbott; F. Zahra Bashir; Mark A. Sugden

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 165 KB
• Volume: 13
• Category: Article
• ISSN: 0899-0042
• DOI: 10.1002/chir.1069

✦ Synopsis

Abstract

The distribution of the free and bound hopanoic acids in both unheated and heated (350°C for 50 h) kerogens, isolated from the Messel oil shale, were analyzed by GC‐MS. The bound acids were released by subjecting the kerogen to three different treatments, namely, thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH), as well as basic and acidic hydrolyses. All of these methods gave a series of hopanoic acids ranging from C~30~ to C~34~, in which the biological 17β, 21β(H) configuration is prominent. Both 22__R__ and 22__S__ epimers are present for the C~30~ acid, whereas the others are dominated by the sidechain 22__R__‐configuration. Thermochemolysis in the presence of TMAH was the most efficient in releasing kerogen‐bound hopanoids. Following pyrolysis, the acids are generated and released into the free fraction with apparent epimerization occurring at C‐17, C‐21, and C‐22. The bound hopanoic acids may be both chemically bonded as well as possibly being physically encapsulated within the macromolecular fraction of sedimentary organic matter. They are therefore either generated by breaking the bonds which bind them to the kerogen or they are released as a result of the macromolecular cage being broken apart. Chirality 13:510–516, 2001. © 2001 Wiley‐Liss, Inc.