MOLECULAR LEVEL STRUCTURAL ANALYSIS OF NATURAL ORGANIC MATTER AND OF HUMIC SUBSTANCES BY MULTINUCLEAR AND HIGHER DIMENSIONAL NMR SPECTROSCOPY

摘要

NMR spectroscopy offers uniquely versatile options to obtain molecular level structural characterization of natural organic matter (NOM) and humic substances (HS). By defining the relative amounts and some structural detail of fundamental building blocks, multinuclear quantitative one dimensional NMR spectroscopy provides the key margin of any structural model of NOM/HS. A large array of higher dimensional NMR spectra serves to enhance the reliability of NMR resonance assignments and allows to define rather extended substructures of NOM/HS. Owing to the nature of NOM/HS as a mixture of small and large molecules, related by a continuous range of weak and strong interactions, any exhaustive analysis of the NMR spectra of NOM/HS requires understanding of the physical processes initiated by the pulse sequences. The NMR spectral analysis has to be corroborated at all levels by comparison with NMR spectra of model compounds, data base search and adjusted schemes of calculations of NMR parameters.