Advanced solid-state NMR spectroscopy of natural organic matter

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 a 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 C NMR spectra, and address some common technical mistakes that lead to unreliable spectra of NOM. The identification of specific functional groups in NOM, primarily based onC spectral-editing techniques, is described and the theoretical background of some recently-developed spectral-editing techniques is provided. Applications of solid-state NMR to investigating nitrogen (N) in NOM are described, focusing on limitations of the widely used N CP/MAS experiment and the potential of improved advanced NMR techniques for characterizing N forms in NOM. Then techniques used for identifying proximities, heterogeneities and domains are reviewed, and some examples provided. In addition, NMR techniques for studying segmental dynamics in NOM are reviewed. We also briefly discuss applications of solid-state NMR to NOM from various sources, including soil organic matter, aquatic organic matter, organic matter in atmospheric particulate matter, carbonaceous meteoritic organic matter, and fossil fuels. Finally, examples of NMR-based structural models and an outlook are provided.

Concepts and Misconceptions of Humic Substances as the Stable Part of Soil Organic Matter: A Review

“…Modifications of the CP MAS procedure, as proposed by Peerson et al [15] and Cook et al [16], cannot correct the problems of CP MAS spectroscopy [10]. Today, CP MAS 13 C NMR spectroscopy is at best a semi-quantitative method [17].…”

A molecular fluorophore in citric acid/ethylenediamine carbon dots identified and quantified by multinuclear solid‐state nuclear magnetic resonance

“…[11] Nuclear magnetic resonance (NMR) is ideally suited to comprehensively characterize the chemical composition of carbon dots, based on predictable chemical shifts of resonances due to the chemical bonding environment. Beyond just taking "the" 13 C NMR spectrum, spectral editing can be applied to selectively observe the signals of certain types of carbons, for example, C not bonded to H, [24] CH (methines), [25] sp 3 -hybridized C, [26] and C bonded to N. [27,28] It is a great advantage of NMR over the other aforementioned characterization techniques that it is intrinsically quantitative, meaning that the area fraction of a resolved peak is equal to the fraction of the nuclei in the corresponding specific chemical environment, if the experiment is performed properly. Multiple cross polarization (multiCP) 13 C NMR has been shown to provide the needed efficient, [29,30] nearly distortionless excitation of all carbon sites in organic materials with a sufficiently high H:C ratio.…”

Adsorption of Herbicide Diuron in Pineapple-Growing Soils of Eastern Thailand

“…The dominant signal of this region was found at 72 ppm and 104 ppm, which was assigned as polysaccharide [24]. The signal at 104, which was between 95 ppm and 112 ppm, was also the signal region of sugar (alkyl O-C-O) [25]. Moreover, at signal 56 ppm, it represented the carbon from methoxyl group derived from lignin and α-protein [26].…”

“…This was because high content of aromatic carbon in soils arose from fire or burning of plant biomass, which accelerated oxidation processes [22,[30][31]. For the carbonyl carbon (at 160-190 ppm), it was very low in all soil samples (7.22-9.26%) and was found in carboxylic acid (-COOH) dominant peak at 173 ppm [25].…”