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Kerogen‐bound and free hopanoic acids in the messel oil shale kerogen
Author(s) -
Abbott Geoffrey D.,
Bashir F. Zahra,
Sugden Mark A.
Publication year - 2001
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.1069
Subject(s) - kerogen , chemistry , oil shale , tetramethylammonium hydroxide , galactan , pyrolysis , hopanoids , fraction (chemistry) , organic chemistry , alkylbenzenes , organic matter , stereochemistry , geology , polysaccharide , source rock , paleontology , benzene , structural basin
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.