Computer Science
Scientific paper
Jan 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979gecoa..43..111s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 43, Issue 1, pp.111-126
Computer Science
17
Scientific paper
Steranes and terpanes biodegrade at a slower rate than isoprenoids and survive moderate biodegradation. Heavy biodegradation results in destruction of regular steranes, survival of diasteranes (20R better than 20S) and tricyclic terpanes and transformation of hopanes to Ring A/B demethylated hopanes. These survivors can be used as source fingerprints in biodegraded crudes. The structure of predominant steranes in undegraded to moderately degraded fossil fuels was proven to be 14 , 17 (H) (20R + S) by molecular spectroscopy. These compounds plus the 20S epimers of regular 5 -steranes (20R) were identified as major constituents and their 5 -counterparts as minor components in a cholestane isomerizate (300°C, Pt on C), allowing assessment of relative thermodynamic stabilities. An observed increase of optical activity in heavily degraded crudes from three different basins is interpreted to be the result of bacterial transformation of terpanes and steranes to new optically active species plus enrichment of the latter by n + isoparaffin depletion rather than total bacterial synthesis. Diagnostic ion profiling by GC-MS-C is a convenient tool for surveying the relative abundance of individual diasteranes and regular steranes plus distinguishing epimeric and ring skeletal isomeric series in complex fossil fuel mixtures. A new practical method of determining the absolute quantities of individual steranes by spiking with 5 -cholane and integration of mass chromatograms is described.
Moldowan Michael J.
Seifert Wolfgang K.
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