Springer International Publishing
Cham
Springer
40538
2196-5641
Chemical and Biological Technologies in Agriculture
Chem. Biol. Technol. Agric.
Life Sciences
Agriculture
Organic Chemistry
Plant Biochemistry
Soil Science & Conservation
Plant Physiology
Biomedical and Life Sciences
1
1
1
1
1
3
2014
12
2014
The Author(s)
2014
24
10.1186/s40538-014-0024-y
24
24
Reduced complexity of multidimensional and diffusion NMR spectra of soil humic fractions as simplified by Humeomics
Research
1
9
2014
11
4
2014
7
17
2014
11
4
2014
12
3
Nebbioso et al.; licensee Springer.
2014
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (
http://creativecommons.org/licenses/by/4.0
), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.
Antonio
Nebbioso
antonio.nebbioso@unina.it
Pierluigi
Mazzei
pierluigi.mazzei@unina.it
Davide
Savy
davide.savy@unina.it
Centro Interdipartimentale di Ricerca per la Spettroscopia di Risonanza Magnetica, Nucleare per l’Ambiente
l’Agro-alimentare e i Nuovi Materiali (CERMANU), Università di Napoli Federico II
80055
Portici
Italy
Abstract
Background
Humeomics is a sequential step-wise chemical fractionation that simplifies the complex matrix of a humic acid (HA) and weakens its supramolecular interactions, thereby allowing a detailed characterization of the involved molecules. A recalcitrant residual end product of Humeomics, namely RES4, was successfully solubilized here in alkaline conditions and subjected to a semi-preparative high-performance size exclusion chromatography (HPSEC).
Results
The resulting six size fractions separated by HPSEC were analyzed by different NMR techniques. 1D 1H-NMR spectra did not reveal significant molecular differences among size fractions, although all of them differed from the spectrum of the bulk RES4 especially in signal intensity for aliphatic materials, which were assigned by 2D NMR to lipidic structures. Diffusion-ordered spectroscopy (DOSY)-NMR spectra showed that the homogeneity of RES4 was significantly changed by the HPSEC separation. In fact, nominally large size fractions, rich in lipidic signals, had significantly lower and almost constant diffusivity, due to stable supramolecular associations promoted by hydrophobic interactions among alkyl chains. Conversely, diffusivity is gradually increased with the content of aromatic and hydroxyaliphatic signals, which accompanied the reduction of fractions sizes and was related to smaller superstructures.
Conclusions
This study not only confirmed the occurrence of supramolecular structures in the recalcitrant humic residue of Humeomics, but also highlighted that more homogeneous size fractions were more easily characterized by NMR spectroscopy.
Keywords
Humeomics
HPSEC
Liquid-state NMR
DOSY-NMR
Supramolecular associations
Humic acids
Recalcitrant organic matter
Diffusivity
Nuclear magnetic resonance
Molecular fractionation