Document Detail

Absence of mobile carbohydrate domains in dry humic substances proven by NMR, and implications for organic-contaminant sorption models.
MedLine Citation:
PMID:  16570593     Owner:  NLM     Status:  MEDLINE    
The mobility and domain structure of various standard humic substances have been investigated by 1H and 1H-13C solid-state nuclear magnetic resonance (NMR) experiments. In four dry humic acids, a fulvic acid, a natural organic matter sample, and a whole peat sample, segments that undergo fast, large-amplitude motions account for <9% of the sample. This disproves a previous suggestion, based on 1H NMR data, that flexible domains, presumably carbohydrates, make up >40% of various humic acids; these putative mobile domains were also linked to dual-mode sorption. In particular, neither the polar alkyl (carbohydrate) nor the aromatic components show any fast, large-amplitude mobility. A small fraction of mobile nonpolar alkyl segments identified by us before is the only component undergoing large-amplitude motions, apart from absorbed water that we observe in humic acids exposed to ambient air. 1H-13C wide-line separation NMR shows that, contrary to previous suggestions, the dipolar couplings in the aromatic regions are smaller than in the polar alkyl segments, most likely due to differences in local 1H densities. Series of 1H-13C heteronuclear correlation experiments with 1H spin diffusion reveal close proximity of aromatic and polar alkyl segments in several humic acids, precluding carbohydrate domains on a scale of > 1-nm diameter. In the standard peat humic acid, nonpolar aromatic segments also do not form sorption domains of significant size, while nonpolar aliphatic domains, which we had previously shown to correlate with sorption capacity, have been confirmed.
J D Mao; K Schmidt-Rohr
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Environmental science & technology     Volume:  40     ISSN:  0013-936X     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2006 Mar 
Date Detail:
Created Date:  2006-03-30     Completed Date:  2006-11-08     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0213155     Medline TA:  Environ Sci Technol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1751-6     Citation Subset:  IM    
Department of Chemistry, Gilman Hall, Iowa State University, Iowa 50011, USA.
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MeSH Terms
Carbohydrates / analysis*,  chemistry
Environmental Monitoring*
Humic Substances / analysis*
Hydrocarbons, Aromatic / analysis
Magnetic Resonance Spectroscopy / methods
Organic Chemicals / analysis*
Water Pollutants, Chemical / analysis*
Reg. No./Substance:
0/Carbohydrates; 0/Humic Substances; 0/Hydrocarbons, Aromatic; 0/Organic Chemicals; 0/Water Pollutants, Chemical

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