Evidence for the Formation of a Two-Electron Oxidation Product of Deferoxamine That's Likely to be an Oxoammonium Cation

These authors [Sabourault et al., 1989: (http://www.ncbi.nlm.nih.gov/pubmed/2574220)] found evidence that a species can be formed through the two-electron oxidation of deferoxamine (two successive one-electron oxidations of deferoxamine, with the one-electron oxidation product, formed through the one-electron oxidation of deferoxamine by any of a number of different oxidants, being the deferoxamine nitroxide species (see below). In my view, this is the oxoammonium cation (a.k.a. nitrosonium) species of deferoxamine, and, although it's a short-lived species, in comparison to the nitroxide species that can be stable for 10-20 minutes or so, this species (the authors refer to it as R, in comparison to RH(rad) and RH2 for deferoxamine nitroxide and deferoxamine) can undergo a one-electron reduction by ferrous heme ("cyt c-Fe2+") to deferoxamine nitroxide and ferric heme. In addition, the authors found evidence that deferoxamine nitroxide can undergo a one-electron oxidation by ferric heme to form this species, R, and ferrous heme as products. I don't see what else it could be except the oxoammonium species. The authors also found evidence that two molecules of deferoxamine nitroxide can participate in a reaction that forms one molecule of R and one molecule of deferoxamine as products. So it basically has to be the oxoammonium cation species, in my view, and I've shown quick sketches of the reactions that the authors listed, in shorthand, in the article. Anyway, it's interesting to see it.

One-electron oxidation of deferoxamine to deferoxamine nitroxide by a hydroperoxyl radical (protonated form of the superoxide radical anion):

One-electron oxidation of deferoxamine nitroxide, by a hydroperoxyl radical, to the oxoammonium cation species and hydrogen peroxide (HOOH):



One-electron reduction of the oxoammonium cation species, by superoxide, to deferoxamine nitroxide and the one-electron oxidation product of superoxide--molecular oxygen. This, along with the other reactions, is essentially the same mechanism whereby cyclic nitroxide radicals can, via an oxoammonium intermediate, mediate their superoxide-dismutase-mimetic activity [Samuni et al., 2002: (http://pet.radiology.uiowa.edu/downloads/Xiang%20Wu%20Papers/Application/2002/NCI/Kinetics%20and%20mechanism%20%2321B.pdf)]:



Reaction of two molecules of deferoxamine nitroxide to form deferoxamine and the oxoammonium species. Other researchers have, incidentally, found experimental results that his reaction


One-electron reduction, by ferrous heme, of the oxoammonium cation species to the nitroxide and ferric heme:



One-electron oxidation of the nitroxide to the oxoammonium species by ferric heme, forming ferrous heme, also, as a product: