Reaction of a Co(III)-Peroxo Complex and NO: Formation of a Putative Peroxynitrite Intermediate

Abstract

A Co(II) complex, [Co(L)]Cl, 1 of the ligand L (L = bis(2-ethyl-4-methylimidazol-5-yl)methane) upon reaction with HO in methanol solution at -40 °C resulted in the formation of the corresponding Co(III)-peroxo complex [Co(L)(O)] (2). The addition of NO gas to the freshly generated solution of the complex 2 led to the formation of the Co(II)-nitrato complex 3 through the putative formation of a Co(II)-peroxynitrite intermediate, 2a. The intermediate 2a was found to mediate the nitration of the externally added phenol resembling the nitration of tyrosine in biological systems.

Exploring the nitric oxide dioxygenation (NOD) reactions of manganese–peroxo complexes

“…18 Saha et al followed the generation of Co II –NO 3 − in the NOD reaction of a Co III –O 2 2− (d 6 ) species. 19 Similarly, Nam and co-workers explored the NOD reaction of Cr IV –O 2 2− (d 2 ), Fe III –O 2 2− (d 5 ), and Fe III –O 2 ˙ − (d 5 ) producing NO 3 − upon reaction with NO (NO + ) via a proposed PN intermediate. 15 d , e ,20 In addition to NO 3 − generation, the NOM product (NO 2 − ) was also observed in various Nitric Oxide Oxygenation (NOO) reactions of metal–oxygen adducts with NO and also in metal–nitrosyl reactions with ROS.…”

Nitric Oxide Dioxygenase Activity of a Nitrosyl Complex of Mn(II)-Porphyrinate in the Presence of Superoxide: Formation of a Mn(IV)-oxo Species through a Putative Peroxynitrite Intermediate

“…In both the reactions, the involvement of a Cr­(III)-peroxynitrite intermediate, [Cr III (14-TMC)­(OONO)­(Cl)] + was presumed. ,,, The reaction of an Fe­(III)-peroxo complex of the same ligand, [Fe III (14-TMC)­(O 2 )] + , with NO + was also reported to proceed through the peroxynitrite intermediate . An example of the formation of a presumed peroxynitrite intermediate in the reaction of the cobalt-peroxo complex of a nonporphyrinate ligand with NO was reported recently from our laboratory …”

Dioxygenation Reaction of a Cobalt-Nitrosyl: Putative Formation of a Cobalt–Peroxynitrite via a {CoIII(NO)(O2–)} Intermediate

“…The biological relevance of NO inspires a wide range of studies of its coordination and interaction with transition metal centers and subsequently, their dioxygenation reaction. An extensive study has been done in this direction with the Fe-proteins and their models. , Recently, the examples involving other transition metal ions in the generation and reactivity of ONOO – are reported . The Karlin’s group reported the example of a peroxynitrite complex from the reaction of a mixed-valent nitrosyl complex of Cu­(I)­Cu­(II), [Cu I,II 2 (UN-O – )­(NO)] 2+ with O 2 .…”

“…On the other hand, cobalamins (Cbls) are known to react with NO to form nitrosocobalamins (NOCbls) in a diffusion-controlled rate and are believed to scavenge NO efficiently in vivo . NOCbl is reported to react with O 2 to result in nitrocobalamin through the formation of peroxynitrito Co­(III) intermediate. , In addition, the Co-containing systems are found to be more promising with respect to the observation of peroxynitrite complexes . We have demonstrated recently that a nitrosyl complex of Co-porphyrinate reacts with H 2 O 2 to result in Co­(III)-nitrite .…”