Determining the molecular weight, aggregation, structures and interactions of natural organic matter using diffusion ordered spectroscopy
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Notice bibliographique
Résumé
Abstract Diffusion ordered spectroscopy (DOSY) was applied to examine the chemical and physical properties of soil organic matter, a complex natural mixture. Soil organic matter extracts are often termed humic substances (HS), which traditionally have been thought to be high molecular weight, cross‐linked macromolecules with undetermined structures. Separation of the components in the studied humic acid (HA) clearly indicates that the HS studied here are pseudo‐high molecular weight materials only, and associations or aggregates of molecules of smaller molecular sizes, which can be disrupted with organic acids. At high concentration, these aggregates display diffusivities that are consistent with those observed in large proteins (>66 kDa). After disaggregation and at low concentration, DOSY NMR reveals components that have chemical shifts that are consistent with lignins, polysaccharides and peptides, and have diffusivities consistent with molecular weights of ∼2500, ∼1000 and 200–600 Da, respectively. Diffusion studies of fulvic acids (FA) indicate that little if any aggregation occurs in solution and that, on average, the components display diffusivities that are consistent with molecules that have relatively low molecular weights of ∼1000 Da. However, in addition to a range of small molecular components, DOSY NMR reveals for the first time direct evidence that larger molecular weight components also exist within the mixtures. In an FA isolated from the surface soil of an oak forest, large polysaccharides with average diffusivities similar to 6000 Da maltodextrins can be identified. In an FA from an agricultural soil, components consistent with peptides/proteins are identified that have aggregate/molecular sizes in the region of 12 000 Da. It is logical that an operationally defined extract of soils will result in a mixture of plant components at various stages of humification with a range of molecular sizes and structures rather than macromolecules with undetermined structures. In addition to advancing our structural understanding of natural organic matter (NOM), DOSY provides potential to study the interactions of these mixtures with contaminants. This paper explorers the interaction of a HA with two organic contaminants (MTBE and chlorsulfuron) and an FA with cadmium. Diffusion measurements show that MTBE has a weaker interaction with the organic materials than chlorsulfuron. Studies with cadmium suggest that the metal exhibits dynamic exchange which is fast on the NMR time‐scale. Such findings have strong implications for understanding the behavior and toxicity of cadmium in the environment. Although cadmium has an affinity for NOM, it is clear that it is not irreversibly bound and may be bioavailable under many conditions. Copyright © 2002 John Wiley & Sons, Ltd.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle