Ni TPP Research Articles

Molecular anchoring stabilizes low valence Ni(i)TPP on copper against thermally induced chemical changes

The strong molecule-surface interaction, followed by charge transfer at the interface, plays a fundamental role in the thermal stability of the layer by rigidly anchoring the porphyrin molecules to the copper substrate.

Effect of Ultraviolet Irradiation on Proton Transfer Facilitated by 5,10,15,20-Tetraphenyl-21H,23H-porphine and Its Metal Complexes at a Water/1,2-Dichloroethane Interface.

We examined photochemical effects by ultraviolet irradiation on facilitated proton transfer at a water/1,2-dichloroethane (W/DCE) interface by ion-transfer voltammetry using a Xe flash lamp. 5,10,15,20-Tetraphenyl-21H,23H-porphine (H2TPP) or its metal complex, such as cobalt (Co(II)TPP), zinc (Zn(II)TPP), and nickel (Ni(II)TPP) complexes, was added into the DCE phase as an ionophore for the facilitated proton transfer. After we irradiated the W/DCE interface through the W phase, the voltammetric waves for proton transfer facilitated by H2TPP and Co(II)TPP were remarkably enhanced and shifted to the lower potential region, compared to those before irradiation. We confirmed from the pH and argentometric titrations that such enhancements and shifts of the waves were caused by hydrogen chloride (HCl) produced by photodecomposition of DCE. On the other hand, the waves for proton transfer facilitated by Zn(II)TPP and Ni(II)TPP were very small from the beginning, and showed neither enhancement nor any shift upon irradiation.

Novel Nickel Superoxide Dismutase Treatment Delays FeCl3‐induced Arterial Thrombosis in Rats

Nickel complexes, [Ni(H2BA(R)TPP)](ClO4)2 (R = Ph for 1 or iPr for 2), supported by a pentadentate ligand H2BA(R)TPP were synthesized to mimic the nickel superoxide dismutase (NiSOD). Diabetes may exacerbate oxidative stress‐induced thrombosis. We explored the antioxidant activity and its biomedical effects of the synthetic NiSOD in the FeCl3‐induced carotid arterial thrombosis in the type I diabetic rats.We determined the scavenging reactive oxygen species responses in vitro by a chemiluminescent amplification method. Female Wistar rats in vivo were used and divided into four groups: control rats, streptozotocin (STZ, 60 mg/kg) treated rats, control rats with NiSOD (10 μg/ml), and STZ rats with NiSOD treatment. We investigated the underlying mechanisms of NiSOD on arterial thrombosis by immunohistochemistry and western blotting.Our data showed that NiSOD dose‐dependently decreased O2‐. and H2O2. The FeCl3‐induced time to occlusion of the carotid artery was 21±5 min in control rats, 21±2 min in STZ rats, 24±4 min in control rats with NiSOD treatment and 28±6 min in STZ rats with NiSOD (10 μg/ml), respectively. By western blot and immunohistochemistry, FeCl3 increased reactive oxygen species production, chemokine (C‐X3‐C motif) ligand 1 (CX3CL1), intercellular adhesion molecule 1 (ICAM‐1), vascular cell adhesion molecule‐1 (VCAM‐1), 4‐hydroxynonenal (4‐HNE) and 3‐nitrotyrosine (3‐NT) expression in the damaged arterial endothelium. NiSOD treatment significantly depressed the level of reactive oxygen species, CX3CLl, ICAM‐1, VCAM‐1, 4‐HNE and 3‐NT in the endothelial areas of control and STZ rats.These data suggest that a synthesized NiSOD can protect oxidative stress‐induced arterial thrombosis through the actions of antioxidant, anti‐adhesion, anti‐inflammation.

Synthesis and characterization of Ni(III)N3S2 complexes as active site models for the oxidized form of nickel superoxide dismutase.

Nickel complexes, [Ni(H2BA(R)TPP)](ClO4)2 (R = Ph for 1 or iPr for 2), supported by a pentadentate ligand H2BA(R)TPP were synthesized and oxidized to form Ni(III) species having a N3S2 coordination environment to mimic the active site of the oxidized form of nickel superoxide dismutase (NiSODox). The Ni(III) species 2(+) exhibited a rhombic signal with g values at 2.15, 2.12 and 2.02 similar to that of NiSODox. DFT calculations revealed that 2(+) has an unpaired electron primarily located in the dz2 orbital of the Ni(III) center, which strongly overlaps with the pz orbital of the axial pyridine nitrogen of H2BA(Pr)TPP.

Styrene polymerization catalyzed by metal porphyrin complex/MAO for in situ synthesizing polystyrene containing air stable π cation radicals

A novel catalyst system based on nickel(II) tetraphenylporphyrin (Ni(II)TPP) and methylaluminoxane for styrene polymerization was developed. This catalyst system has a high thermal stability and show fairly good activity. The obtained polystyrene (PS) was isotactic-rich atactic polymer by C-13 NMR analysis, and its molecular weight distribution was rather narrow (M-w/M-n approximate to 1.6, by GPC analysis). ESR revealed that Ni(II)TPP pi cation radicals were formed in the polymerization and could remain in the resulting PS stably. The mechanism of the polymerization was discussed and a special coordination mechanism was proposed. The PS product containing Ni(II)TPP pi cation radicals can be used as a potential functional material.

Comparative study of structure-properties relationship for novel beta-halogenated lanthanide porphyrins and their nickel and free bases precursors, as a function of number and nature of halogens atoms.

The synthetic route of partially beta-halogenated via a "metal-assisted" reaction and perhalogenated terbium complexes is described. This protocol allows the facile insertion of the halogens (bromines or chlorides) to the porphyrin peripheral positions. The electronic absorption spectra and the redox potentials of the free porphyrins as well as the terbium complexes are dramatically affected as the number of halogen atoms increase. In fact, two antagonistic effects are responsible for that, the inductive and the distortion effects on the porphyrin ring. They result in a red shift for the Soret band and a stabilization/destabilization of the HOMOs/LUMOs which in turn is manifested by variations on the redox potentials. The novel crystal structure of the Ni(Cl(8)TPP) is discussed in great detail and compared with the previously reported structures of Tb(Cl(8)TPP) (OAc)(DMSO)(2) x 3PhCH(3) x MeOH and H(2)(Br(8)TPP), as well as with other perhalogenated nickel porphyrins available in the literature.

Ultrafast Vibrational Relaxation and Ligand Photodissociation/Photoassociation Processes of Nickel(II) Porphyrins in the Condensed Phase

We have carried out a femtosecond transient absorption spectroscopic study on nickel(II) porphyrins in various solvents in order to obtain detailed information on vibrational relaxation processes occurring in the initial stage after photoexcitation to the highly excited states. We found the decay process of time constant of approximately 1 ps corresponding to the intramolecular vibrational relaxation process for Ni(II)TPP and Ni(II)OEP in toluene. In addition to this process, the intermolecular vibrational relaxation process with 10−20 ps lifetime was also observed for Ni(II)OEP in toluene, although its contribution to the overall decay process is relatively weak probably due to the weak solute/solvent interaction. In coordinating solvents such as pyridine and piperidine, we observed the intramolecular vibrational relaxation processes before complete population of the bottleneck excited metal 1|0,dz2〉 or 3|0,3(d,d)〉 state. In this case, it is likely that the intermolecular vibrational relaxation process a...

Electrochemical oxidation of nickel(II) tetraphenylporphyrin in benzonitrile

Earlier, nickel(II)tetraphenylporphyrin [Ni(II)TPP] was reported to undergo stepwise one-electron oxidation to Ni(III)TPP + and Ni(III)TPP 2⨥ in benzonitrile and to Ni(II)TPP ⨥ and Ni(II)TPP 2+, and Ni(II)TPP ⨥ and Ni(III)TPP 2⨥ in dichloromethane. We report here the results of our study which indicates that Ni(II)TPP ⨥ and Ni(II)TPP 2+ are the oxidation products in both solvents.

Electrochemical oxidation of nickel(II) tetraphenylporphyrin in benzonitrile

Abstract Earlier, nickel(II)tetraphenylporphyrin [Ni(II)TPP] was reported to undergo stepwise one-electron oxidation to Ni(III)TPP + and Ni(III)TPP 2⨥ in benzonitrile and to Ni(II)TPP ⨥ and Ni(II)TPP 2+ , and Ni(II)TPP ⨥ and Ni(III)TPP 2⨥ in dichloromethane. We report here the results of our study which indicates that Ni(II)TPP ⨥ and Ni(II)TPP 2+ are the oxidation products in both solvents.

Effets de β-substitutions sur la complexation axiale de Ni IITPP par des bases de Lewis

The electrochemical reduction of β-substituted Ni II tetraphenylporphyrin was studied in DMF at a mercury electrode in order to determine the effect of axial ligand complexation in the presence of water or pyridine. The Ni II complex which is electroreduced is either the mono or bis liganded species. In contrast no axial ligand coordination is observed for the unsubstituted Ni TPP and this is the species which is electroreduced in DMF alone. This complexation of the β-substituted species is a consequence of the enhanced metal-ring interaction and especially of the d π-π * backbonding.

Catalytic reduction of nitric oxide over tetraphenylporphyrin complexes

Catalytic reduction of nitric oxide with molecular hydrogen proceeded over metallo-tetraphenylporphyrins in the temperature range 200 – 350 °C in a circulating reactor. The activity order of the complexes was FeClTPP ≪ CoTPP ⩽ NiTPP ≫ CuTPP > ZnTPP, indicating the strong influence of central metal ions. CoTPP which adsorbed nitric oxide produced molecular nitrogen and nitrous oxide as well as ammonia, whereas Ni, Cu, and ZnTPP which do not stationarily adsorb nitric oxide, produced ammonia selectively. The reducing reactivities of carbon monoxide, ammonia, and methane were examined over CoTPP. The reactivities of these reducing agents were H 2 > CO > NH 3 > CH 4. Ammonia was found to enhance the adsorption of nitric oxide over CoTPP. The catalytic reaction is discussed in terms of the correlation between the electronic structure of the metalporphyrins and their activity for the adsorption and reduction of nitric oxide.

Electron transport via metalloporphyrins

The controlled potential electrolysis of Ni(II) meso-tetraphenylporphyrin (Ni(II)TPP) gives at room temperature the corresponding metalloporphyrin π-cation radical [Ni(II)TPP]+ •. Upon freezing a solution of the π-cation radical to 77 K an internal electron transfer occurs to give [Ni(III)TPP]+. A discussion of the routes of electron transport in heme proteins is given, and the roles of metalloporphyrin π-cation radicals in electron transport is evaluated.