In Situ13C and23Na Magic Angle Spinning NMR Investigation of Supercritical CO2Incorporation in Smectite–Natural Organic Matter Composites

We hypothesised that, during occlusion inside granular aggregates of oxide-rich soils, the light fraction organic matter would undergo a strong process of decomposition, either due to the slow process of aggregate formation and stabilisation or due to digestion in the macro- and meso-fauna guts. This process would favour the accumulation of recalcitrant materials inside aggregates. The aim of this study was to compare the dynamics and the chemical composition of free and occluded light fraction organic matter in a natural cerrado vegetation (woodland savannah) and a nearby pasture (Brachiaria spp.) to elucidate the transformations during occlusion of light fraction in aggregates of a clayey Oxisol. Nuclear Magnetic Resonance of the 13C, with Cross Polarisation and Magic Angle Spinning (13C-CPMAS-NMR), and 13C/12C isotopic ratio were combined to study organic matter composition and changes in carbon dynamics, respectively. The occluded light fraction had a slower turnover than the free light fraction and the heavy fraction. Organic matter in the occluded fraction also showed a higher degree of decomposition. The results confirm that processes of soil organic matter occlusion in the typical "very fine strong granular" structure of the studied oxide-rich soil led to an intense transformation, selectively preserving stable organic matter. The small amount of organic material stored as occluded light faction, as well as its stability, suggests that this is not an important or manageable sink for sequestration of atmospheric CO2.

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Cross-polarization 13C-NMR spectroscopy with ‘magic angle’ spinning characterizes organic matter in whole soils

Nature ◽

10.1038/294648a0 ◽

1981 ◽

Vol 294 (5842) ◽

pp. 648-650 ◽

Cited By ~ 39

Author(s):

Michael A. Wilson ◽

Ronald J. Pugmire ◽

Kurt W. Zilm ◽

Kuan M. Goh ◽

Sammy Heng ◽

...

Keyword(s):

Organic Matter ◽

Nmr Spectroscopy ◽

13C Nmr ◽

13C Nmr Spectroscopy ◽

Magic Angle Spinning ◽

Magic Angle ◽

Cross Polarization ◽

Angle Spinning

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Fast magic angle spinning solid-state 51V NMR characterization of vanadium oxide catalysts supported on TiO2

Journal de Chimie Physique ◽

10.1051/jcp/1994910909 ◽

1994 ◽

Vol 91 ◽

pp. 909-915 ◽

Cited By ~ 2

Author(s):

D Courcot ◽

P Bodart ◽

C Fernandez ◽

M Rigole ◽

M Guelton

Keyword(s):

Solid State ◽

Vanadium Oxide ◽

Magic Angle Spinning ◽

Oxide Catalysts ◽

Magic Angle ◽

51V Nmr ◽

Nmr Characterization ◽

Angle Spinning ◽

Fast Magic Angle Spinning

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Pulse Shaped Dynamic Nuclear Polarization Under Magic Angle Spinning

10.26434/chemrxiv.9788471.v1 ◽

2019 ◽

Cited By ~ 1

Author(s):

ASIF EQUBAL ◽

Kan Tagami ◽

Songi Han

Keyword(s):

Electron Spin ◽

Lattice Relaxation ◽

Magic Angle Spinning ◽

Spin Lattice Relaxation ◽

Magic Angle ◽

Total Electron ◽

Spin Lattice ◽

Maximum Benefit ◽

Selective Saturation ◽

Angle Spinning

In this paper, we report on an entirely novel way of improving the MAS-DNP efficiency by shaped μw pulse train irradiation for fast and broad-banded (FAB) saturation of the electron spin resonance. FAB-DNP achieved with Arbitrary Wave Generated shaped μw pulse trains facilitates effective and selective saturation of a defined fraction of the total electron spins, and provides superior control over the DNP efficiency under MAS. Experimental and quantum-mechanics based numerically simulated results together demonstrate that FAB-DNP significantly outperforms CW-DNP when the EPR-line of PAs is broadened by conformational distribution and exchange coupling. We demonstrate that the maximum benefit of FAB DNP is achieved when the electron spin-lattice relaxation is fast relative to the MAS frequency, i.e. at higher temperatures and/or when employing metals as PAs. Calculations predict that under short T<sub>1e </sub>conditions AWG-DNP can achieve as much as ~4-fold greater enhancement compared to CW-DNP.

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