24-n-Propylcholestane is a steranebiomarker molecule often found in marine source rocks.[1][2] It is a C30 molecule, meaning that it is composed of thirty carbon atoms, and is one of the leading ways to distinguish a marine source rock from a terrigenous sample. It is composed of three six-carbon rings and one five-carbon ring, with two methyl groups and one eleven carbon side chain. 24-n-Propylcholestane has a molar mass of 414.76 g/mol.
24-n-Propylcholestane is a sterane, which are derived from sterols after being buried in the sediment. Sterols turn into steranes by saturating the sterol's double bond and removing the alcohol group.[3] Steranes are fairly stable, and are often found in source rocks and crude oils.[3]
24-n-Propylcholestane is derived from 24-n-propylcholesterol, which is made in the modern ocean by Chrysophytealgae.[4] Because of its known modern creator, it is thought that traces of 24-n-propylcholestane in ancient sediments were likely produced by older algaes of the same order Chrysophyte.[1] The marine algae is consumed by marine invertebrates, and so 24-n-propylcholesterols are also found in invertebrates, despite not being produced by them.[1] Regardless of which organism is observed containing 24-n-propylcholesterols, the molecule originated from Chrysophyte algae.
The ratio of 24-n-propylcholestanes to 24-iso-propylcholestanes is used as an indicator for the presence of sponges.
Detection
In sediments, steranebiomarkers are found as a mixture of stereoisomers. It can be difficult to separate out a specific stereoisomer, as is necessary for the detection of solely 24-n-propylcholestane. Because of this, 24-n-propylcholestane can be fairly difficult to detect using gas chromatography-mass spectrum (GC-MS). It has a m/z of 414 and a secondary peak at 217, and can be easily confused for a different group of C30 molecules, 4ɑ-methylsteranes.[1]
