The origin of maleimides in recent sediments - Sources, formation processes and palaeoenvironmental implications

叶绿素和细菌叶绿素是地球上最丰富和最重要的色素。这些化合物及其转化产物(绿素、卟啉、金属卟啉和马来酰亚胺)可以保存在现代湖泊和海洋沉积物、沉积岩和原油中，是有价值的古环境指标。其中，被认为是四吡咯氧化产物的马来酰亚胺(1H-吡咯-2，5-二酮)(即叶绿素、细菌叶绿素、相关衍生物、血红素、藻胆蛋白)迄今在现代沉积物中很少被研究，大多数研究集中在古代沉积物上。它们的形成过程仍不完全清楚，许多马来酰亚胺的前体也不清楚。在这个项目中，具有不同生物地球化学历史的水生系统中马来酰亚胺的特征将扩大对马来酰亚胺来源和在现代水环境中形成途径的有限了解，这是准确将其作为生物标志物应用的重要一步。例如，这些标志物可以用来描述生产力和碳循环、微生物群落结构、水柱性质(例如光带缺氧/真氧(持续性与周期性)、化学跃层深度)以及沉积和成岩过程中的沉积条件的变化。该项目旨在通过分析马来酰亚胺的分布并将其与在同一样品中获得的四吡咯进行比较来确定马来酰亚胺的来源。现有的确定具有非极性官能团的马来酰亚胺的分析方法将被修改，以包括极性马来酰亚胺。因此，这是分析最近沉积物中的极性马来酰亚胺的第一次尝试。此外，还将在环境样品中测量马来酰亚胺的稳定碳和氮同位素特征。这种方法将加强对有机碳和氮的新陈代谢和循环的理解，并重建生产力、养分循环和食物网关系的变化。

Chlorophylls and bacteriochlorophylls are the most abundant and most important pigments on Earth. These compounds and their transformation products (chlorins, porphyrins, metalloporphyrins and maleimides) can be preserved in recent limnic and marine sediments, sedimentary rocks and crude oils and serve as valuable palaeoenvironmental proxies. Among these, maleimides (1H-pyrrole-2,5-diones), the assumed oxidation products of tetrapyrroles (i.e. chlorophylls, bacteriochlorophylls, related derivatives, hemes, phycobilins) have so far hardly been studied in recent sediments, most studies being focused on ancient deposits. Their formation processes are still incompletely understood and precursors of many maleimides are not known. In this project, the characterisation of maleimides in aquatic systems with different biogeochemical history will expand the very limited knowledge of maleimide sources and formation pathways in recent aquatic environments, which represents an important step to accurately apply them as biomarkers. These markers might be used for instance to describe changes in productivity and carbon cycling, microbial community structure, water column properties (e.g. photic zone anoxia/euxinia (persistent versus periodic), chemocline depth) and depositional conditions during sedimentation and diagenesis. This project aims at identifying maleimide sources by analysis of their distributions and comparing these with tetrapyrroles obtained in the same samples. Existing analytical procedures to determine maleimides with apolar functional groups will be modified to include polar maleimides. It is, hence, the first attempt to analyse polar maleimides in recent sediments. Furthermore, stable carbon and nitrogen isotope signatures of maleimides will be measured in environmental samples. This approach will enhance the understanding of the metabolism and cycling of organic carbon and nitrogen and to reconstruct changes in productivity, nutrient cycling and food web relationships.