Inclusion complexes of PBN-type nitrone spin traps and their superoxide spin adducts with cyclodextrin derivatives: parallel determination of the association constants by NMR titrations and 2D-EPR simulations.
(1)H NMR and electron paramagnetic resonance (EPR) titrations were used to determine the association constants of the complexes of alpha-phenyl-N-tert-butylnitrone (PBN) analogues and their superoxide spin adducts, respectively, with methylated beta-cyclodextrins. A 1:1 stoichiometry for the nitrones with randomly methylated beta-cyclodextrin and 2,6-di-O-methyl-beta-cyclodextrin and 1:1 and 1:2 stoichiometries for the corresponding cyclodextrin-nitroxide complexes were observed. After the superoxide radical spin trapping reaction, EPR titrations afforded the association constants of the corresponding cyclodextrin-nitroxide complexes. Two-dimensional EPR simulations indicated a bimodal inclusion of the nitroxide free radical spin adducts into the cyclodextrins. For all the nitrone-cyclodextrin and nitroxide-cyclodextrin complexes, the association constants were always higher for the nitroxide complexes than for the nitrone complexes. A cooperative system concerning the complexation of the nitroxide spin adduct with a cyclodextrin was evidenced by EPR titrations. The efficiency of the cyclodextrin inclusion technique to trap superoxide and to resist bioreduction by sodium l-ascorbate was also investigated.
Bardelang
David
D
Laboratoire SREP, UMR 6517 CNRS et Universités d'Aix-Marseille 1, 2 et 3, Avenue Escadrille Normandie Niemen, Marseille 13397, France.
Rockenbauer
Antal
A
Karoui
Hakim
H
Finet
Jean-Pierre
JP
Tordo
Paul
P
D003505:Cyclodextrins / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009589:Nitrogen Oxides / Q000737:chemistry*; D013113:Spin Labels; D013481:Superoxides / Q000737:chemistry*
D003505:Cyclodextrins; D009589:Nitrogen Oxides; D013113:Spin Labels; C015388:nitrones; D013481:Superoxides