Molecule of the Month Cholesterol

By Paul Farrimond

 

Cholesterol is a common natural product, produced by many plants and animals, including humans, although it is not found in bacteria or archaea. Being widely distributed in the biosphere it is common in environmental samples such as soils and sediments, and consequently could be encountered in surface sediment or environmental surveys and forensic geochemistry (oil spill) studies. However, the alcohol group makes cholesterol more difficult to analyse by gas chromatography methods; derivatisation of the functional group is needed.

 

Although cholesterol is not found in oils and mature source rocks, its diagenetic products are. These include the steranes and diasteranes with 27 carbon atoms which form during sediment burial and maturation, and are routinely analysed in petroleum geochemistry. Because cholesterol is so widespread in the environment, these C₂₇ steranes are not themselves specific indicators of certain types of organic matter or depositional conditions, but they are useful when used in parameters with other compounds. For example, the relative proportion of C₂₇ to C₂₉ steranes comprises a well-known parameter that is sensitive to the types of organic matter present (algal vs. land plant) and hence the broad depositional environment. Interestingly, this parameter, and an associated ternary plot, was originally devised using sterols in modern sediments (Huang & Meinschein, 1979) and was only later adapted to steranes and used in petroleum geochemistry.

 

Reference:

Huang W.-Y. & Meinschein W.G. (1979). Sterols as ecological indicators. Geochimica et Cosmochimica Acta 43, 739-745.