Reactions of nitric oxide and nitrogen dioxide with coenzyme Q: involvement of the isoprenic chain

Abstract

The formation of a di-tert-alkyl nitroxide has been observed by Electron Spin Resonance during the exposure of coenzyme CoQ₁₀, in both the oxidized and reduced forms, to nitrogen dioxide (˙NO₂) or to nitric oxide (˙NO) in the presence of oxygen. The same kind of nitroxide has been observed also with CoQ₁, CoQ₃ or with 1-phenyl-3-methyl-2-butene, chosen as model compounds. In all cases, the formation of the nitroxide may be justified only by admitting the involvement of the isoprenic chain of the coenzymes and in particular the addition of ˙NO₂ to the double bond. A mechanism which accounts for the formation of the nitroxide as well as the other compounds observed in the reactions is proposed and confirmed by a spectroscopic investigation (FT-IR, ¹H NMR, X-ray analysis) and by ESI-MS.