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Comparative Analysis of Partial Structures of a Peat Humic and Fulvic Acid Using One- and Two-Dimensional Nuclear Magnetic Resonance Spectroscopy

^a GSF-Research Center for Environment and Health, Institute of Ecological Chemistry, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany
^b Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, 119899 Moscow, Russia

* Corresponding author (hertkorn{at}gsf.de)

Received for publication June 2, 2000. Nuclear magnetic resonance (NMR) resonance integrals obtained from one-dimensional NMR spectra provide semiquantitative contents of humic constituents with limited resolution in structural detail. When supplemented by connectivity information available from homo- and heteronuclear two-dimensional NMR spectra a more reliable assignment of humic substructures becomes available. This is demonstrated with a comparative one- and two-dimensional NMR analysis of a fulvic and a humic acid obtained from Eriophorum peat. An example of a detailed analysis of the proton chemical shift region normally attributed to carbohydrates shows substantial contributions from amino acids, amino and desoxy sugars, and highly oxidized aliphatic chains of intermediate length. The very good resolution of structural detail by a combined analysis of all NMR spectra shows that the effect of the fractionation procedure on the composition and chemical structure of humic materials is very significant. The comparison of the partial structures comprising humic acid (HA) and fulvic acid (FA) of the peat humic materials studied indicates that FA is diagenetically downstream of HA, favoring the biopolymer degradation (BD) model of humification.

Abbreviations: A, B, C,...Y, standard one-letter abbreviations for proteinaceous amino acids • AC, abiotic condensation • BD, biopolymer degradation • COSY, correlated spectroscopy • F1, vertical frequency axis in two-dimensional nuclear magnetic resonance spectra (X nucleus–calculated data) • F2, horizontal frequency axis in two-dimensional nuclear magnetic resonance spectra (proton-detected data) • FA, fulvic acids • HA, humic acids • HMQC, heteronuclear multiple quantum correlation • HS, humic substances • HSQC, heteronuclear single quantum coherence • NMR, nuclear magnetic resonance • TOCSY, total correlation spectroscopy