A nitrosyl complex
of MnII-porphyrinate, [(F20TPP)MnII(NO)], 1 (F20TPPH2 = 5,10,15,20 tetrakis(pentafluorophenyl)porphyrin), was synthesized and
characterized. Spectroscopic and structural characterization revealed
complex 1 as a penta-coordinated MnII-nitrosyl
with a linear Mn–N–O (180.0°) moiety. Complex 1 does not react with O2. However, it reacts with
superoxide (O2
–) in THF at −80
°C to result in the corresponding nitrate (NO3
–) complex, 2, via the formation of a presumed
MnIII-peroxynitrite intermediate. ESI-mass spectrometry
and UV–visible and X-band EPR spectroscopic studies suggest
the generation of MnIV-oxo species in the reaction through
homolytic cleavage of the O–O bond of the peroxynitrite ligand
as proposed in NOD activity. The intermediate formation of the MnIII-peroxynitrite was further supported by the well accepted
phenol ring nitration which resembles the biologically well-established
tyrosine nitration.
The reaction of a cobalt porphyrin complex, [(F 8 TPP)Co], 1 {F 8 TPP = 5,10,15,porphyrinate dianion} in dichloromethane with nitric oxide (NO) led to the nitrosyl complex, [(F 8 TPP)Co(NO)], 2. Spectroscopic studies and structural characterization revealed it as a bent nitrosyl of {CoNO} 8 description. It was stable in the presence of dioxygen. However, it reacts with H 2 O 2 in acetonitrile (or THF) solution at −40 °C (or −80 °C) to result in the corresponding Co(III)-nitrate complex, [(F 8 TPP)Co(NO 3 )], 3. The reaction presumably proceeds via the formation of a Co-peroxynitrite intermediate. X-Band electron paramagnetic resonance and electrospray ionization−mass spectroscopic studies suggest the intermediate formation of the [(porphyrin)Co(III)−O • ] radical, which in turn supports the generation of the corresponding Co(IV)-oxo species during the reaction. This is in accord with the homolytic cleavage of the O−O bond in heme-peroxynitrite proposed in the nitric oxide dioxygenases activity. In addition, the characteristic peroxynitrite-induced phenol ring reaction was also observed.
In general, the nitrosyl complexes of Mn(II)−porphyrinate having the {Mn(NO)} 6 configuration are not considered as HNO or nitroxyl (NO − ) donors because of [Mn I −NO + ] nature. A nitrosyl complex of Mn(II)− porphyrin, [Mn(TMPP 2− )(NO)], 1 [TMPPH 2 = 5,10,15,20-tetrakis-4-methoxyphenylporphyrin], is shown to release HNO in the presence of HBF 4 . It is evidenced from the characteristic reaction of HNO with triphenylphosphine and isolation of the [(TMPP 2− )Mn III (H 2 O) 2 ](BF 4 ), 2. This is attributed to the fact that H + from HBF 4 polarizes the NO group whereas the BF 4 − interacts with metal ion to stabilize the Mn(III) form. These two effects cooperatively result in the release of HNO from complex 1. In addition, complex 1 behaves as a nitroxyl (NO − ) donor in the presence of [Fe(dtc) 3 ] (dtc = diethyldithiocarbamate anion) and [Fe(TPP)(Cl)] (TPP = 5,10,15,20-tetraphenylporphyrinate) to result in [Fe(dtc) 2 (NO)] and [Fe(TPP)(NO)], respectively.
A series of copper(II) and cobalt(II) coordination compounds with 2-substituted benzimidazole derived monodentate and bidentate ligands have been prepared and characterized by microanalysis, IR and UV-Vis spectroscopy. Synthesized metal complexes have been screened for their in vitro antioxidant and antitumor activity. The complex 4a showed significant nitric oxide free radical scavenging activity (IC 50 65µg/ml), while 3i and 3g showed potent superoxide dismutase activity with IC 50 of 0.26 and 0.28 µM respectively. In vitro cytotoxicity study with human breast MCF-7 and CNS SF 268 cancer cell lines showed that the most active 2-benzyl-1H-benzimidazole Cu(II) complex 3a inhibited the growth of cancer cells at 20 µM concentration.
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