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

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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.