Radical Stabilization in Dissolved Humates

článek v časopise - ostatní, Jost

angličtina

Quinoid entities, in which quinone and hydroquinone groups equilibrate via a semiquinone radical intermediate, are a common structural feature in humic materials. The electron paramagnetic resonance (EPR) signals of these radicals are significantly enhanced in the presence of diamagnetic divalent metal ions such as Mg2+, while mono-valent ions do not show the effect. The addition of trivalent ions leads to rapid precipita-tion, leaving little room for observation. It was noted that the metal ions producing EPR signal enhancement were also underwent effective bridging interactions with humic sub-units, forming pseudomicellar structures. Particle growth determined through dynamic light scattering measurements coincided with the onset of EPR signal enhancement, and surface tension measurements further corroborated the coincidence of aggregation. The addition of a chaotrope (urea), which broke up the humic structures, eliminated the EPR signal increases. These observations strongly suggested that bridging interactions by di-valent metal ions, and the intramolecular aggregation that accompanied it, led to signifi-cant stabilization of semiquinone radicals within the humic structure.

Humic acid , semiquinone, EPR enhancement, bridging interactions, aggregation , radical stabilization

BAKAJOVÁ, B.; von WANDRUSZKA, R.

2011

25. 11. 2011

2162-1969

Open Journal of Physical Chemistry

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Spojené státy americké

55

60

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