The effect of biodegradation on steranes and terpanes in crude oils
The effect of biodegradation on steranes and terpanes in crude oils
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DOI：
10.1016/0016-7037(79)90051-6
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发表时间：
1979
影响因子：
5
通讯作者：
W. K. Seifert;J. Moldowan
中科院分区：
文献类型：
--
作者：
W. K. Seifert;J. Moldowan
甾烷和萜烷的生物降解速度比类异戊二烯慢，并在中度生物降解中存活。严重的生物降解导致常规甾烷的破坏，二甾烷（20 R优于20 S）和三环萜烷的存活，并将藿烷转化为A/B环脱甲基藿烷。这些残留物可作为生物降解原油的源指纹。分子光谱分析表明，未降解和中度降解化石燃料中甾烷的结构主要为14β，17β（H）（20 R + S）。这些化合物加上常规5α-甾烷（20 R）的20 S差向异构体被鉴定为胆甾烷异构化物（300°C，Pt/C）中的主要组分，其5β-对应物为次要组分，从而可以评估相对热力学稳定性。从三个不同的盆地严重降解的原油中观察到的光学活性的增加被解释为细菌转化的萜烷和甾烷的新的光学活性物种加上富集后者的n+异构烷烃消耗，而不是总细菌合成的结果。GC-MS-C诊断离子剖面是一种方便的工具，用于测量复杂化石燃料混合物中单个diasterane和常规甾烷的相对丰度，以及区分差向异构体和环状骨架异构体系列。本文介绍了一种用5β-胆烷加标质谱积分法测定甾烷绝对含量的新方法。
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 14β, 17β(H) (20R + S) by molecular spectroscopy. These compounds plus the 20S epimers of regular 5α-steranes (20R) were identified as major constituents and their 5β-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 byn+ 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 5β-cholane and integration of mass chromatograms is described.