Nitric Oxide Oxygenation Reactions of Cobalt-Peroxo and Cobalt-Nitrosyl Complexes

Abstract

Here, we report a comparative study of nitric oxide oxidation (NOO) reactions of Co III -peroxo (Co III −O 2 2− ) and Co-nitrosyl ({CoNO} 8 ) complexes bearing the same N 4 -donor ligand (HMTETA) framework. In this regard, we prepared and characterized two new [(HMTETA)Co III (O 2 2− )] + (2, S = 2) and [(HMTETA)Co(NO)] 2+ (3, S = 1) complexes from [(HMTETA)Co II (CH 3 CN) 2 ] 2+ (1). Both complexes (2 and 3) are characterized by different spectroscopic measurements, including their DFT-optimized structures. Complex 2 produces Co II -nitrato [(HMTETA)Co II (NO 3 − )] + (Co II −NO 3 − , 4) complex in the presence of NO. In contrast, when 3 reacted with a superoxide (O 2 •− ) anion, it generated Co II -nitrito [(HMTETA)-Co II (NO 2 − )] + (Co II −NO 2 − , 5) with O 2 evolution. Experiments performed using 18/16 O-labeled superoxide ( 18 O 2 •− / 16 O 2 •− ) showed that O 2 originated from the O 2 •− anion. Both the NOO reactions are believed to proceed via a presumed peroxynitrite (PN) intermediate. Although we did not get direct spectral evidence for the proposed PN species, the mechanistic investigation using 2,4di-tert-butylphenol indirectly suggests the formation of a PN intermediate. Furthermore, tracking the source of the N-atom in the above NOO reactions using 15 N-labeled nitrogen ( 15 NO) revealed N-atoms in 4 (Co II − 15 NO 3 − ) and 5 (Co II − 15 NO 2 − ) derived from the 15 NO moiety.

Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide–Dioxygen Interconversion

“…Besides the biological metabolism of O 2 – into O 2 and H 2 O 2 catalyzed by superoxide dismutase (SOD), , heme proteins (i.e., oxyhemoglobin and oxymyoglobin) were reported to promote the dioxygenation of NO into biologically benign NO 3 – . − In lipopolysaccharide (LPS)-activated macrophages, a dinitrosyl iron unit (DNIU) [Fe­(NO) 2 ] was discovered as a metallocofactor assembled under inflammatory conditions based on the formation of a distinctive electron paramagnetic resonance (EPR) signal at g = 2.03. − Inspired by natural utilization of (non)­heme centers for maintaining biological NO/O 2 – homeostasis, biomimetic studies on reactions between (a) [M­(O 2 n – )] complexes ( n = 1 or 2) and NO, − (b) [M­(NO) x ] complexes ( x = 1 or 2) and O 2 , ,− and (c) [M­(NO)] complexes and O 2 – were performed to identify the formation of metal-bound peroxynitrite intermediates, − of which rearrangement into NO 2 – and NO 3 – occurred via formation of transient • NO 2 species. In particular, Nam, Karlin, Kumar, and co-workers pioneered investigations of reactivity of {Co­(NO)} 8 complexes toward O 2 – . , During reaction of O 2 – with complexes [(L)­Co­(NO)] 2+ (L = 12-TMC, 13-TMC, or HMTETA), transient formation of the intermediate [(L)­Co 2+ (OONO)] + followed by O–O bond cleavage was reported to yield complex [(L)­Co­(NO 2 )] + with O 2(g) evolution. Similar to other metal-bound peroxynitrite intermediates, the proposed [(L)­Co 2+ (OONO)] + intermediate features phenol nitration reactivity for conversion of 2,4-di- tert -butyl phenol (DTBP) into 2,4-di- tert -butyl-6-nitrophenol (NO 2 -DTBP).…”

Mechanistic insights into nitric oxide oxygenation (NOO) reactions of {CrNO}5and {CoNO}8

“…Therefore, [(BPMEN)Co(NO)] 2+ ({CoNO} 8 , 1 ) and [(BPMEN)Cr(NO)(Cl − )] + ({CrNO} 5 , 2 ) complexes 43 (BPMEN = N , N ′-bis(2-pyridylmethyl)-1,2-diaminoethane) were explored for their reactivity towards O 2 ˙ − (KO 2 /18-crown-6), to understand the effect of the metal center and the spin state/magnetic properties (Scheme 1). Following our previous reports, 43,44 we synthesized new {CoNO} 8 and {CrNO} 5 complexes and calculated various physical parameters for 1 and 2 to determine their thermal stability, the NO oxidation reactions and the intermediates involved (Scheme 1, reactions a and b). Complex 1 generates a Co II –nitrito complex [(BPMEN)Co II (NO 2 − ) 2 ] (Co II –NO 2 − , 3 ) + O 2 in the presence of O 2 ˙ − via a proposed thermally unstable [Co–PN] + species (Scheme 1, reaction c).…”

Exploring the carbonic anhydrase-mimetic [(PMDTA)2ZnII2(OH−)2]2+ for nitric oxide monooxygenation

“…The FT-IR spectra of 3 showed a characteristic peak for NO 2 − stretching at 1271 cm −1 (Zn II – 14 NO 2 − ) (SI, Fig. S4a†) 29 which shifted to 1245 cm −1 (Zn II – 15 NO 2 − ) (ESI, Fig. S4b†) when 3 was prepared by reacting 1 with 15 NO, indicating that the N atom in the NO 2 − ligand is derived from NO.…”