We have analyzed the interactions of a series of nitroxide radicals with ligands containing a phenol moiety coupled with different polyarnine fragments, and their CuII and ZnII complexes, by EPR experiments. Nitroxide radicals are good mimics of the properties of pollutant molecules, e.g., organic compounds having different polarities and charges, surfactants, and polyaromatics. Charged, polar, and low-polarity sites in the ligands and complexes are all available for interactions; in particular, the ability to entrap the radicals in a vice-like structure, by the formation of phenyl sandwich complexes, determines the type of selective interaction that occurs when a chain or planar aromatic structure is present. For closely packed complexes, ZnII has a cooperative effect in the interaction with the radical; it allows both the entrance of low-polarity radicals at the low-polarity sites of the complex and the interactions of polar or charged radicals at the polar sites of the complexes. Conversely, CuII coordinates to the amino groups of the ligands and blocks the entry of radicals, which, thus, impedes their insertion into the structure of the complexes. The opposite behavior, with respect to that of CuII and ZnII, was found for the complexes that have more open structures. The complexes that have cyclic ligands exhibit a poor ability to interact with radicals, but, for the ligands in the absence of the coordinating metals, the interactions are significantly enhanced as a result of the entrance of the radicals into the cyclic structures. In all cases, stronger interactions occur when both hydrophilic and hydrophobic sites are involved. The neutral-surfactant probe forms aggregates mainly with the cooperative effect of the copper complexes. UV/Vis measurements confirmed the results obtained by EPR and indicate that weak interactions occur between the radicals and the complexes or ligands; they also confirmed the formation of 1:1 adducts.

Nitroxide Radicals Interacting with Polyamine-Phenolic Ligands and Their Metal Complexes

Cangiotti M.;Formica M.;Fusi V.
;
Giorgi L.;Micheloni M.
;
Ottaviani M. F.
;
2004-01-01

Abstract

We have analyzed the interactions of a series of nitroxide radicals with ligands containing a phenol moiety coupled with different polyarnine fragments, and their CuII and ZnII complexes, by EPR experiments. Nitroxide radicals are good mimics of the properties of pollutant molecules, e.g., organic compounds having different polarities and charges, surfactants, and polyaromatics. Charged, polar, and low-polarity sites in the ligands and complexes are all available for interactions; in particular, the ability to entrap the radicals in a vice-like structure, by the formation of phenyl sandwich complexes, determines the type of selective interaction that occurs when a chain or planar aromatic structure is present. For closely packed complexes, ZnII has a cooperative effect in the interaction with the radical; it allows both the entrance of low-polarity radicals at the low-polarity sites of the complex and the interactions of polar or charged radicals at the polar sites of the complexes. Conversely, CuII coordinates to the amino groups of the ligands and blocks the entry of radicals, which, thus, impedes their insertion into the structure of the complexes. The opposite behavior, with respect to that of CuII and ZnII, was found for the complexes that have more open structures. The complexes that have cyclic ligands exhibit a poor ability to interact with radicals, but, for the ligands in the absence of the coordinating metals, the interactions are significantly enhanced as a result of the entrance of the radicals into the cyclic structures. In all cases, stronger interactions occur when both hydrophilic and hydrophobic sites are involved. The neutral-surfactant probe forms aggregates mainly with the cooperative effect of the copper complexes. UV/Vis measurements confirmed the results obtained by EPR and indicate that weak interactions occur between the radicals and the complexes or ligands; they also confirmed the formation of 1:1 adducts.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11576/2663656
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