Interactions between a humic acid and a paramagnetic cation as assessed by CPMAS 13C NMR spectroscopy

Risultato della ricerca: Other

Abstract

Humic substances (HSs) are natural organic materials playing a very important role in environment due to theirability in interacting with organic and inorganic compounds. From the one side, HSs can reduce the toxic effectsof organic and inorganic contaminants, while, from the other side, they can enhance availability of nutrients, suchas cations, to living organisms including plants. For this reason it is very crucial to understand the mechanisms ofthe interactions between humic substances and the environmentally relevant chemical components. In the presentwork, we have investigated the mechanisms of interaction between a HS and iron (III) by using cross polarizationmagic angle spinning (CPMAS) 13C NMR spectroscopy. For that, complexes between HS and different amountsof Fe(III) were prepared. All the HS-Fe(III) complexes were analysed by variable contact time (VCT) NMR experimentsin order to obtain estimations of the values of the cross-polarization time (TCH) and the proton longitudinalrelaxation time in the rotating frame (T1rho(H)). Results confirmed literature findings by which carboxyl groupsare the most important humic fraction endowing with the ability to chelate Fe(III). However, our results alsodemonstrated that direct bondages between HS and Fe(III) involve the remaining polar systems such as carbohydratesand peptides. Conversely, alkyls and aromatics appeared not to be directly bound to the paramagnetic iron(III). We also evaluated the distances between Fe(III) and the different functional groups in the HS through theanalysis of the proton spin diffusion into the HS-Fe(III) complexes.
Lingua originaleEnglish
Numero di pagine0
Stato di pubblicazionePublished - 2009

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