青海湖沉积物中的无环类异戊二烯化合物

Acyclic Isoprenoids in Sediments of Qinghai Lake

本文用GC-MS分析了青海湖沉积物中无环类异戊二烯化合物的特征。青海湖沉积物中姥鲛烷/植烷比值(Pr/Ph)都小于1,表明沉积物沉积时的环境是还原(缺氧)条件。沉积物中的C_(18)类异戊二烯酮相对正烷基-2-酮随深度增加有减少趋势,这可能是C_(18)类异戊二烯酮向其烷烃对应物转化的结果。作者还首次报道了青海湖沉积物中的植烯醛和姥鲛烯醛,它们是植醇降解过程中重要的中间产物。它们的检出对植醇成岩过程中各步骤解释具有一定意义。

Acyclic isoprenoid compounds with 20 or fewer carbon atoms are relatively abundant and widespread components of modern sediments. These compounds mainly originaic from the phytyl side -chain of chlorophyll- a. This is a subject that has long interested geochemists partly because functionalized acyclic iso-prenoids have proved to be useful biological markers in themselves and because the hydrocarbon counterparts such as phytane are widespread in shales and petroleums. This paper discusses the characteristics of acyclic isoprenoids in sediments of Qinghai lake by GC -MS. Pristane/phytane ratios (Pr/Ph) in sediments of Qinghai lake are much less than 1, which is suggestive of an auoxic depositional environment. C18 isoprenoid ketone with respect to n - alkan-2- ones in the sediments shows a decreasing trend with depth, this may be the result of transformation of C18 isoprenoid ketone to its corresponding hydrocarbon. Besides . GC- MS analyses demonstrated the presence of E and Z pristenals, and E and Z phytenals in sediments of Qinghai Lake. This appears to be the first report of E / 7 pristenals and E/ Z phytenais in salt lake sediment. Although phytenal has long been proposed as an important intermediate in the degradation of phytol to phytanic acid , it is perhaps surprising that only two papers have reported phytenais in sediments so far. They firstly reported phytenals in marine and freshwater sediments. But there has been no report of pristenal in sediment. The recent finding that phytenal is formed by the abiotic photodecomposition of phytol has been proposed as a new pathway for the decomposition of the phytyl side -chain of chlorophyll -a in the water column. Due to the presence of numorous photosensitizers in water, free phytol can be photooxidized in the eu-photie layer and lead to the formation of Cu iscprenoid ketone. E/Z pristenals and E/Z phytenais. These photoproducts can be transfereed rapidly from the surface to the sediment. Detection of phytenais and pristenals in sediments of Qinghai lake is of some importance to the elucidation of the steps in the phytol diagenetic pathway.