page_title: Cholestane
section_title: Preservation
hierarchical_section_title: Cholestane / Preservation
caption_attribution_description: English: Cholesterol degrades to cholestane by loss of OH functional group and saturation of double bond (indicated in pink). Stereochemistry of the molecule is maintained in this degradation.
context_page_description: Cholestane is a saturated tetracyclictriterpene. This carbon-27 biomarker is produced by diagenesis of cholesterol and is one of the most abundant biomarkers in the rock record. Presence of cholestane in environmental samples are commonly interpreted as an indicator of animal life and/or traces of O₂, as animals are known for exclusively producing cholesterol, and thus has been used to draw evolutionary relationships between ancient organisms of unknown phylogenetic origin and modern metazoan taxa. Cholestane is made in low abundance by other organisms, but because these other organisms produce a variety of sterols it cannot be used as a conclusive indicator of any one taxa. It is often found in analysis of organic compounds in petroleum.
context_section_description: Cholesterol has 256 stereoisomers, but only one of them is formed naturally in production of cholesterol (3β-ol, 5α (H), 14α (H), 17α (H), 20R) and is therefore the primary stereoisomer of interest for cholestane measurements. Deviations from this stereochemistry often reflects diagenesis, thermal maturation and preservation bias.
  Diagenesis typically leads to the loss of functional groups and double bonds in organic molecules. For cholestane specifically, diagenesis of cholesterol to cholestane produces a molecule that is fully saturated compared to its steroid counterpart. This process occurs without the loss or gain of carbon atoms and therefore can serve as an indicator of the original steroid produced by the organism in the environment.
  Thermal alteration can also cause loss of the alkane side-chain at C₁₇. An  experiment demonstrated that over 4 weeks at 300 °C, cholestane underwent 17% decomposition of its alkane side chain. In contrast, the polycyclic structure (C₁₋₁₇) is very thermally stable. Diagenetic processes can also cause methyl shifts and aromatization.
caption: Cholesterol degrades to cholestane by loss of OH functional group and saturation of double bond (indicated in pink). Stereochemistry of the molecule is maintained in this degradation.
exif: {}