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Since the isolation of soil organic matter in 1786, tens of thousands of publications have searched for its structure. Nuclear magnetic resonance (NMR) spectroscopy has played a critical role in defining soil organic matter but traditional approaches remove key information such as the distribution of components at the soil-water interface and conformational information. Here a novel form of NMR with capabilities to study all physical phases termed Comprehensive Multiphase NMR, is applied to analyze soil in its natural swollen-state. The key structural components in soil organic matter are identified to be largely composed of macromolecular inputs from degrading biomass. Polar lipid heads and carbohydrates dominate the soil-water interface while lignin and microbes are arranged in a more hydrophobic interior. Lignin domains cannot be penetrated by aqueous solvents even at extreme pH indicating they are the most hydrophobic environment in soil and are ideal for sequestering hydrophobic contaminants. Here, for the first time, a complete range of physical states of a whole soil can be studied. This provides a more detailed understanding of soil organic matter at the molecular level itself key to develop the most efficient soil remediation and agricultural techniques, and better predict carbon sequestration and climate change.

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Metabolic mixtures are often analyzed via NMR spectroscopy as it provides a metabolic profile without sample alteration in a noninvasive manner. These mixtures however tend to be very complex and demonstrate considerable spectral overlap resulting in assignments that are sometimes ambiguous given the range of current NMR methods available. De novo molecular identification in these mixtures is generally accomplished using chemical shift information and J-coupling based experiments to determine spin connectivity information, but these techniques fall short when a molecule of interest contains nonrelaying centers. A method is presented here that enhances intramolecular spatial interactions via supercooled water and uses the resulting spatial correlations to edit mixtures. This is accomplished by utilizing nuclear Overhauser effect spectroscopy (NOESY) at subzero temperatures in capillaries to enhance NOE and provide more complete spin systems. This technique is applied to a standard mixture of three known molecules in D 2 O with overlapping resonances and is further demonstrated to assign molecules in a worm tissue extract. The current method proves to be a powerful complement to existing methods such as total correlation spectroscopy (TOCSY) to expand the range of molecules that can be assigned in situ without physical separation of mixtures.

Environmental context Novel technology is used to examine oil contaminated soil to better understand this longstanding problem. The data indicate that oil forms a non-discriminant layer over all the soil components, which in their natural state would be exposed to water, and that it retains certain polar compounds while contributing other oil contaminants to the surrounding porewater and groundwater. Such molecular level information helps to better understand the reoccurrence of hydrophobicity in remediated soil, and could lead to novel clean-up methods. Abstract Comprehensive multiphase (CMP) NMR spectroscopy is a novel NMR technology introduced in 2012. CMP NMR spectroscopy permits the analysis of solid, gel and liquid phases in unaltered natural samples. Here the technology is applied to control and oil contaminated soils to understand the molecular processes that give rise to non-wettable soils. 13C solid-state NMR spectroscopy is found to be excellent for studying the bulk rigid components of the soils whereas 1H solution and gel-state NMR provide a complimentary overview to subtleties occurring at the soil–water interface. Considered holistically the NMR data support the finding that the oil forms a non-discriminant layer over all the soil components, which in the natural state, would be exposed to water. Specifically, the oil was found to preferentially coat aliphatics and carbohydrates that normally stick out at the soil–water interface. In addition, it was shown that the oil forms a barrier that keeps small polar molecules such as formic acid inside the soil. At the soil–water interface selective oil components, such as asphaltenes, were found to exhibit unrestricted diffusion, suggesting that these components could leach into surrounding groundwater.

1 Sediment cores (ca. 6 m) from an estuarine environment gave insights into the composition 2 and preservation of recalcitrant organic carbon (OC) in the environment. The coring locations 3 provided organic matter (OM) of terrestrial and of marine origins. Our study specifically 4 focused on the humin (HU); the OM fraction that is most difficult to isolate and to 5 characterise. HU fractions were compared with the total OM recovered after removal of the 6 associated mineral colloids. 7Solid state and multiphase (nuclear magnetic resonance) NMR experiments were 8 carried out on dried and swollen samples to obtain comparative information about the whole 9 and the fractionated samples. The total OM associated with the clay-sized fraction provided a 10 standard that allowed differences between the fractions to be observed. 11The NMR data have provided new insights into the molecular structures that become 12 part of the long term C sink in sediments. The recalcitrant OC in the sediments is composed 13 mainly of aliphatic hydrocarbon material that may be protected from, or otherwise 14 unavailable for degradation. Microbial peptides and carbohydrates were also shown to be 15 important contributors to the C sink and these biomolecules may be from living or preserved 16 necromass. Lignin residues formed only a small part of the OM in the surface sediments but 17 made a larger contribution at depth. Highly ordered components in HU (that resists swelling 18 by dimethylsulphoxide, DMSO) play a major role in C sequestration. 19

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