This title appears in the Scientific Report :
2008
Please use the identifier:
http://dx.doi.org/10.2116/analsci.24.1183 in citations.
Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances
Dynamics of Cross Polarization in Solid State Nuclear Magnetic Resonance Experiments of Amorphous and Heterogeneous Natural Organic Substances
Nuclear magnetic resonance (NMR) experiments on carbon-13 in the solid state were done with cross polarization (CP) and magic angle spinning (MAS) in order to overcome the low NMR sensitivity of C-13 and the chemical shift anisotropy, respectively. In the present research, CPMAS C-13-NMR spectra wer...
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Personal Name(s): | Conte, P. |
---|---|
Berns, A. E. | |
Contributing Institute: |
Agrosphäre; ICG-4 |
Published in: | Analytical sciences, 24 (2008) S. 1183 - 1188 |
Imprint: |
Tokyo
Japan Society for Analytical Chemistry
2008
|
Physical Description: |
1183 - 1188 |
DOI: |
10.2116/analsci.24.1183 |
Document Type: |
Journal Article |
Research Program: |
Terrestrische Umwelt |
Series Title: |
Analytical Sciences
24 |
Subject (ZB): | |
Publikationsportal JuSER |
Nuclear magnetic resonance (NMR) experiments on carbon-13 in the solid state were done with cross polarization (CP) and magic angle spinning (MAS) in order to overcome the low NMR sensitivity of C-13 and the chemical shift anisotropy, respectively. In the present research, CPMAS C-13-NMR spectra were collected by modulating the contact time needed for cross polarization (variable contact times experiments, VCT) on two different humic acids (a soil-HA and a coal-HA). VCT data were fitted by a model containing either a monotonic or a non-monotonic cross polarization term. The non-monotonic model, which fitted the experimental results better than the monotonic one, provided two cross-polarization rates, thereby suggesting that two different mechanisms for the energy transfer from protons to carbons arise in amorphous and heterogeneous humic substances. The first mechanism was a fast proton-to-carbon energy transfer due to protons directly bound to carbons. The second mechanism was related to a slow transfer mediated by local segmental motions. Different domains in the humic acids were identified. Soil-HA was made of rigid domains, containing mainly aromatic and carboxylic moieties, and fast moving domains, containing alkyl, C-O and C-N groups. Coal-HA showed a rigid aromatic domain that was differentiated from a very mobile domain made of alkyl and COOH groups. |