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UV-Vis, NMR, and Mössbauer studies have revealed that [Fe(TMP)(N(3))(2)], showing the Mössbauer parameters quite similar to those of the ferryl species of MauG, CytP450(BM3), Cyt P450(CAM), and CPO, exists as equilibrium mixtures of Fe(iv) porphyrin and Fe(iii) porphyrin radical cation.
Citations
... Oxidation of am etalloporphyrin occurs either at the coordinated metal center or at the porphyrin macrocycle. [3,7,8] However,inmost of the cases,oxidation produces porphyrin p-cation radicals at the lower potentials.I nt he disilver(II) porphyrin dimer reported herein, the Ag II center is oxidized to Ag III upon stepwise oxidations and displays Ag III ···Ag III interactions in the 2e À -oxidized complex, leading to interesting photophysical properties. ...
... Ag···Ag separation has also decreased to 4.692 from adistance of 5.824 observed in the unoxidized complex syn-1.AMPS of 3.39 is observed for the complex syn-1·I 3 along with al ateral shift of 3.24 ,w hich suggests stronger intermacrocyclic interactions. However,both the Ag II centers are oxidized to Ag III in the 2e À -oxidized complexes syn-1·(PF 6 ) 2 and syn-1·(SbF 6 ) 2 ,which is clearly reflected in their reduced Ag À N por distances of 2.031(5) and 2.032 (8) ,r espectively,a sc ompared to the unoxidized complex syn-1.A lthough no Ag III porphyrin structure has been reported so far, such reduction of AgÀ N por distance from Ag II to Ag III is clearly visible in the complex with N-confused porphyrin. [13] Unlike in other 2e Àoxidized complexes of the ethane-bridged porphyrin dimer reported earlier that stabilize only the anti form of the complex, two porphyrin cores in syn-1·(X) 2 are not only in syn conformation but the rings are even more cofacial. ...
The interaction between two Ag(II)porphyrins, connected covalently through a highly flexible ethane bridge, in the metalloporphyrin dimer has been investigated upon stepwise oxidations. X-ray structure determination of one and two-electron oxidized complexes has clearly revealed only metal-centered oxidation that results in short Ag-N (porphyrin) distance with large distortion in the porphyrin macrocycle. The 2e-oxidized complex exhibits significant metallophilic interaction in the form of a close Ag(III)***Ag(III) contact that brings two porphyrin ring more cofacial with syn-conformation which would otherwise stabilize in an anti-form. The interaction also leads to an intense emission peak at 546 nm at 77 K in the photoluminescence study.
The pressure to environmental concern from toxic precursors of metalloporphyrin synthesis and the inadequate understanding of metalloporphyrin with β-site substituents on activation of peroxides have impeded the full potential of metalloporphyrin for the oxidation of recalcitrant organic compounds. Here, we report a “green” iron(III) chlorophyll derived from naturally abundant chlorophyll. It shows remarkable degradation efficiency of bisphenol A in the presence of hydrogen peroxide, with a second-order rate constant of 87.3 ± 1.1 L·mmol⁻¹·min⁻¹, which is 7-fold faster than the degradation rate of the Fenton oxidation system. It also demonstrates a wide pH tolerance range of 4-12 and is barely affected by concomitant inorganic anions or natural organic matter. Different from the generation of oxygen-centered radicals, including •OH and •O2⁻, in the Fenton system, a high-valent iron (Ⅳ) -oxo chlorin π-cation radical is formed with an atypical pathway of homolytic O−O bond cleavage via a proton-coupled electron transfer process and is responsible for the degradation of bisphenol A, which is confirmed with spectroscopic studies and theoretical analysis. This abundant “green” catalyst could be beneficial for wastewater treatment by addressing the limitation of a narrow acidic pH range and the susceptibility to scavenging of nonselective radicals in conventional Fenton reactions.
Studies on the electronic and magnetic structures of iron(II), iron(III), and iron(IV) porphyrin complexes and their radical cations are important for understanding aspects of the biological processes of heme proteins, including hemoglobin, myoglobin, cytochrome P450, catalase, and peroxidase. This chapter describes the main factors that stabilize the oxidation states, spin states, and electron configurations of these complexes. Special emphasis has been placed on 1 H NMR spectroscopy as a method of revealing the spin–spin interactions in iron porphyrin radical cations.
The present work focuses on the hydrothermal synthesis and properties of porous coordination polymers of metal–porphyrin framework (MPF) type, namely, {[Pr4(H2TPPS)3]·11H2O}n (UPJS-10), {[Eu/Sm(H2TPPS)]·H3O⁺·16H2O}n (UPJS-11), and {[Ce4(H2TPPS)3]·11H2O}n (UPJS-12) (H2TPPS = 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrakisbenzenesulfonate(4-)). The compounds were characterized using several analytical techniques: infrared spectroscopy, thermogravimetric measurements, elemental analysis, gas adsorption measurements, and single-crystal structure analysis (SXRD). The results of SXRD revealed a three-dimensional open porous framework containing crossing cavities propagating along all crystallographic axes. Coordination of H2TPPS4– ligands with Ln(III) ions leads to the formation of 1D polymeric chains propagating along the c crystallographic axis. Argon sorption measurements at −186 °C show that the activated MPFs have apparent BET surface areas of 260 m² g–1 (UPJS-10) and 230 m² g–1 (UPJS-12). Carbon dioxide adsorption isotherms at 0 °C show adsorption capacities up to 1 bar of 9.8 wt % for UPJS-10 and 8.6 wt % for UPJS-12. At a temperature of 20 °C, the respective CO2 adsorption capacities decreased to 6.95 and 5.99 wt %, respectively. The magnetic properties of UPJS-10 are characterized by the presence of a close-lying nonmagnetic ground singlet and excited doublet states in the electronic spectrum of Pr(III) ions. A much larger energy difference was suggested between the two lowest Kramers doublets of Ce(III) ions in UPJS-12. Finally, the analysis of X-band EPR spectra revealed the presence of radical spins, which were tentatively assigned to be originating from the porphyrin ligands.
By exploiting an established on-surface metallation strategy, we address the ability of the corrolic macrocycle to stabilise transition metal ions in high-valent (III) oxidation states in metal-supported molecular layers. This...
The effect of intermacrocyclic interactions was studied by controlled and stepwise oxidations of a monometallic silver(II) porphyrin dimer that contains a highly flexible ethane bridge. Monometallic dimers are unique systems and behave differently from their dimetallic analogues on the basis of their available sites for storing oxidizing equivalents. UV‐visible spectrometry, ¹H NMR spectroscopy, XPS and single crystal X‐ray diffraction studies clearly suggest the removal of the first electron from the metal center. The removal of the second electron occurred from the ring center to form a π‐cation radical and, thereby, form a very unique mixed‐valent species. However, unlike in all other ethane‐bridged metalloporphyrin dimers reported earlier, the 2e‐oxidized species showed quite unusual structures depending on the nature of counter ions. Ions, such as SbF6, SbCl6 and PF6, are engaged in strong interactions with the porphyrin π‐cation radical and causes substantial structural changes, including large deformation of the ring. The solid‐state structure remains intact in solution as well. The observations are further supported by DFT calculations.
Metalloporphyrin tapes form in a solvent‐free oxidative chemical vapor deposition process on glass substrates. The metal center (M = NiII, CuII, ZnII, CoII, PdII, FeIIICl, 2H) in the 5,15‐disubstituted porphyrin monomer affects the initial C–C coupling step and consequently the formation of triply or doubly linked porphyrin tapes as well as the interchain interaction in the tape as shown by optical spectroscopy, high resolution mass spectrometry and X‐ray photoelectron spectroscopy. Optical spectroscopy and conductive atomic force microscopy reveal that these factors influence the near‐infrared absorbance and the electrical conductivity of the films. Consequently, the metal ion of the metalloporphyrin allows tuning of the macroscopic properties of the thin films composed of metalloporphyrin tapes.
Composite of porphyrins and piezoelectric materials is a promising method to overcome the limitation of photocatalytic response of composite catalysts, inhibit photogenerated electron-hole recombination and enhance photocatalytic degradation performance. Here, the Fe-S electronic channel is formed by the combination of MoS2 and iron porphyrin, which enhances the electron transfer performance of iron porphyrin to MoS2 semiconductor. At the same time, two-dimensional MoS2 surface with piezoelectric properties forms an electric field, which further enhances charge separation and piezoelectric catalytic performance. The photoexcitation of porphyrin and the piezoelectric excitation of molybdenum sulfide cooperate with each other under the simultaneous action of light and ultrasound. Oxygen radicals and hydroxyl radicals are enhanced, and the catalytic degradation performance is further enhanced. By strengthening the interaction between porphyrins and piezoelectric materials, especially bonding, a good and stable catalyst for pollutant degradation and purification was prepared.
The reaction of a cobalt porphyrin complex, [(F8TPP)Co], 1 {F8TPP = 5,10,15,20-tetrakis(2,6-difluorophenyl)porphyrinate dianion} in dichloromethane with nitric oxide (NO) led to the nitrosyl complex, [(F8TPP)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 H2O2 in acetonitrile (or THF) solution at -40 °C (or -80 °C) to result in the corresponding Co(III)-nitrate complex, [(F8TPP)Co(NO3)], 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.
The interaction between two AgII porphyrins, connected covalently through a highly flexible ethane bridge, in a metalloporphyrin dimer has been investigated upon stepwise oxidation. X-ray structure determination of one and two-electron oxidized complexes has clearly revealed only metal-centered oxidation that results in short Ag−N (porphyrin) distance with large distortion in the porphyrin macrocycle. The 2e-oxidized complex exhibits significant metallophilic interaction in the form of a close AgIII⋅⋅⋅AgIII contact that brings two porphyrin rings more cofacial with syn-conformation, which would otherwise stabilize in an anti-form. The interaction also leads to an intense emission peak at 546 nm at 77 K in the photoluminescence study.
