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Title: Advanced solid-state NMR spectroscopy of natural organic matter

item MAO, JINGDONG - Old Dominion University
item CAO, XIAOYAN - Brandeis University
item Olk, Daniel - Dan
item CHU, WENYING - Old Dominion University
item SCHMIDT-ROHR, KLAUS - Brandeis University

Submitted to: Progress in Nuclear Magnetic Resonance Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2016
Publication Date: 5/1/2017
Citation: Mao, J., Cao, X., Olk, D.C., Chu, W., Schmidt-Rohr, K. 2017. Advanced solid-state NMR spectroscopy of natural organic matter. Progress in Nuclear Magnetic Resonance Spectroscopy. 100:17-51. doi: 10.1016/j.pnmrs.2016.11.003.

Interpretive Summary: Natural organic matter plays important roles in soil performance and water quality. One property of natural organic matter that might help explain its contributions is its composition. An important method for studing the composition of natural organic matter is nuclear magnetic resonance spectroscopy. Here we review the technical concepts of nuclear magnetic resonance spectroscopy, summarize the knowledge gained regarding the composition of natural organic matter, and describe its applications to understanding the behavior of natural organic matter in aquatic and soil settings. This summary identifies the most important accomplishments that have been achieved through nuclear magnetic resonance spectroscopy, and it suggests promising areas of future research. This work will benefit scientists who use this method to study natural organic matter and also researchers who study the contributions of natural organic matter in water bodies and soils.

Technical Abstract: Solid-state NMR is essential for the characterization of natural organic matter (NOM) and is gaining importance in geosciences and environmental sciences. This review is intended to highlight advanced solid-state NMR techniques, especially the systematic approach to NOM characterization, and their applications to the study of NOM. We discuss some basics of how to acquire high-quality and quantitative solid-state 13C NMR spectra, and list some common technical mistakes that lead to unreliable spectra of NOM. The identifications of specific functional groups in NOM, primarily based on 13C spectral-editing techniques, are detailed and the theoretical backgrounds of some recently-developed spectral-editing techniques are provided. The applications of solid-state NMR to investigate nitrogen in NOM are described, focusing on the limitations of widely-used 15N CP/MAS and the potential of improved advanced NMR techniques for characterizing N forms in NOM. Then connectivites and proximites based on advanced 2D NMR are reviewed, and the techniques used for identifying proximites, heterogeneities and domains dealt with and some examples of proximites, heterogeneities and domains are provided. In addition, the NMR techniques for studying segment dynamics and examples of segment dynamics in NOM are reviewed. We also briefly summarize the applications of solid-state NMR to NOM of various sources, soil organic matter, aquatic organic matter, organic matter in atmospheric particulate matter, carbonaceous meteoritic organic matter, and fossil fuels. Finally, structural models derived based on NMR structural information and outlook are provided.