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April 2006, Langmuir, 22 (10), 4498–4503, 2006
The Application of 1H High-Resolution Magic-Angle Spinning NMR for the Study of Clay-Organic Associations in Natural and Synthetic Complexes
André J. Simpson1, Myrna J. Simpson1, William L. Kingery2, Brent A. Lefebvre3, Arvin Moser3, Antony J. Williams3, Mikhail Kvasha3, Brian P. Kelleher1
1Department of Chemistry, University of Toronto, Scarborough College, 1265 Military Trail, Toronto, Ontario, Canada, M1C 1A4;
2Department of Plant and Soil Sciences, Mississippi State University, Mississippi State, Mississippi 39762;
3Advanced Chemistry Development, Inc., 110 Yonge Street, 14th Floor, Toronto, Ontario, Canada, M5C 1T4
Abstract
The preferential sorption of model compounds to calcium-exchanged montmorillonite surfaces was investigated using 1H high-resolution magic-angle spinning (HR-MAS) and liquid-state NMR. Synthetic mixtures, representing the major structural categories abundant in natural organic matter (NOM), and two soil extracts were sorbed to montmorillonite. The NMR spectra indicate that, of the organic components observable by 1H HR-MAS NMR, aliphatic components preferentially sorb to the clay surface, while carbohydrates and amino acids mainly remain in the supernatant. These results may help explain the highly aliphatic nature of organic matter associated with clay fractions in natural soils and sediments. Investigations using the synthetic mixtures demonstrate a specific interaction between the clay surface and the polar region in 1-palmitoyl-3-stearoyl-rac-glycerol. Similar observations were obtained with natural soil extracts. The results presented have important implications for understanding the role of organoclay complexes in natural processes, and provides preliminary evidence that HR-MAS NMR is a powerful analytical technique for the investigation of organoclay complex structure and conformation.
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