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Improvements in the Two-Dimensional Nuclear Magnetic Resonance Spectroscopy of Humic Substances

^a Dep. of Chemistry, The Ohio State Univ., 100W. 18th Avenue, Columbus, OH 43210
^b Dep. of Plant and Soil Sciences, Box 9555, Mississippi State University, MS 39762

View larger version (29K): [in a new window]   Fig. 1. Correlation spectroscopy (COSY) spectra of the fulvic acid acquired at 600 MHz. Standard COSY experiment (A), double quantum filtered correlation spectroscopy (DQF-COSY) (B), and expanded central region of the DQF-COSY highlighting couplings from sugars (C). Boxes 1 and 2 highlight regions where couplings from sugars and aromatic compounds in humic substances fall. The couplings in these structures tend to be close to the central diagonal. Note how the coupling information from these moieties is difficult to decipher in spectrum (A) but are clearly visible in spectrum (B).

View larger version (20K): [in a new window]   Fig. 2. Full spectrum (A) and expanded central region (B) of the heteronuclear multiple quantum coherence (HMQC) spectrum acquired at 600 MHz using 128 scans. Region 1 is consistent with C–H bonds from various aliphatic structures including fatty acids and amino acids side chains. Region 2 is consistent with units in amino acids, sugars, methoxy, and methylene groups next to ester and ether groups. Region 3 is consistent with aromatic fragments (Simpson et al., 2001).

View larger version (17K): [in a new window]   Fig. 3. Echo/anti-echo heteronuclear single quantum coherence (HSQC) of the fulvic acid acquired at 600 MHz using 32 scans. Full spectrum (A) and expanded central region (B).

View larger version (23K): [in a new window]   Fig. 4. Echo/anti-echo heteronuclear single quantum coherence (HSQC) of the fulvic acid acquired at 800 MHz using 32 scans. Full spectrum (A) and expanded central region (B).