Development of structural mass-spectrometric methods for the comprehensive comparison of natural organic matter on an individual molecular composition level

拟议项目的主要目的是开发一种新的方法，在结构层面上检查天然有机物质(NOM)的个别成分。NOM在全球碳循环中发挥着重要作用，但其分子复杂性阻碍了对其环境作用的深入研究，以及分子组成与起源之间的联系。通过超高分辨率质谱仪(如FTICR MS)对NOM进行的最新生物地球化学研究受到其仅将NOM视为分子式的集合的观点的限制，而且关于反应性的结论往往基于相当非特定的元素比率。此外，关于NOM的结构多样性程度以及来自不同环境的NOM是否总是会聚到相同的共同结构基序上，存在相互矛盾的证据。这一基本讨论是生物地球化学研究的核心，但为了更深入地了解NOM在环境中的形成、反应和命运，NOM的分子水平分析需要从单个分子式到化学结构的发展。为了这个项目，我们将使用官能团和碳骨架特定同位素标记的强大组合，结构指示碎片的超高分辨率质谱学和应用化学信息学方法来在单个分子水平上提出NOM的结构归属，通过FTICR MS和氢甲基化、还原和乙酰化的结合，将分别列举各个NOM组分中的羰基和酚基。在二维核磁共振分析的基础上，还提出了碳骨架的附加标记。同时，确定预选离子胞内碎裂的碎裂树和中性损失矩阵，然后进行样本聚类，以评估来自不同环境的DOM的结构相似程度。数据处理管道将适用于同位素标记和串联FTICR MS实验。化学信息学方法和FTICR MS数据挖掘在化学数据库中的应用将使我们能够创建一个工具来生成与所研究的NOM样品中的特定化合物接近的结构。我们将进一步检验NOM分子组分的结构是由其来源和生物地球化学边界条件驱动的假设。因此，NOM分子结构因环境不同而不同，可用于重建生物地球化学历史和预测其未来的反应。所提出的项目和工作流程将克服目前NOM生物地球化学的局限性，为建立单个NOM分子组分的定量结构-活性关系铺平道路。该项目开发的工作流程有望成为NOM生物地球化学研究和未来碳循环研究的新标准。

The primary aim of the proposed project is to develop a new approach for examination of individual components of natural organic matter (NOM) on a structural level. NOM plays a major role in the global carbon cycle but its molecular complexity hampers thorough investigation of its environmental role and connection between molecular composition and origin. State-of-the art biogeochemical studies of NOM by ultra-high resolution mass spectrometry, e.g. FTICR MS, are limited by their view of NOM as collection of molecular formulas only and often conclusions on reactivity are based on rather nonspecific elemental ratios. Also, there is contradicting evidence on the degree of structural diversity within NOM and whether NOM from different environments will always converge to the same common structural motifs.This fundamental discussion is at the core of biogeochemical research but in order to obtain a deeper understanding of the formation, reactivity and fate of NOM in the environment, molecular level analysis of NOM needs to advance from individual molecular formulas to chemical structures.For this project we will use a powerful combination of functional group and carbon skeleton specific isotope tagging, ultra-high resolution mass spectrometry with structure-indicative fragmentation and application of chemoinformatics approaches to propose NOM structural assignments on an individual molecular level.To this end carboxylic, carbonyl and phenolic groups in the individual NOM components will be enumerated by combination of FTICR MS and deuteromethylation, reduction and acetylation, respectively. Additional tagging of carbon skeleton will be also proposed on the basis of two-dimensional NMR analysis. At the same time, fragmentation trees and neutral loss matrix of in-cell fragmentation of pre-selected ions will be determined followed by sample clustering to assess the degree of structural similarity between DOM from different environments. Data processing pipelines will be adapted to both isotope tagging and tandem FTICR MS experiments. Application of chemoinformatics approaches and FTICR MS data-mining in chemical databases will enable to create a tool for the generation of structures which are close to particular compounds in NOM samples under investigation.We will further test the hypothesis that structures of NOM molecular components are driven by its sources and biogeochemical boundary conditions. As a consequence, NOM molecular structures differ between environments and could be used to reconstruct the biogeochemical history and to predict its future reactivity.The proposed project and workflows will overcome current limitations in NOM biogeochemistry paving the way for quantitative structure-activity relationships of individual NOM molecular components. The developed workflows in this project are expected to become a new standard in biogeochemical research of NOM and future carbon cycle studies.