Cationic Metalloporphyrins Research Articles

Interaction between DNA and cationic metalloporphyrins in ionic liquid solutions

We studied the interaction of water-soluble cationic metalloporphyrins, [Formula: see text]Py and TMPyP, with the DNA double helix in ionic liquid solutions using CD and absorption spectra. The dispersibility of their porphyrin complexes was improved by electrostatic interactions of the anions of the ionic liquid. In the case of Cu(II) and Zn(II) complexes, the [Formula: see text]Py complexes with pyridinium cations attached to the meso-phenyl groups via methylene groups intercalated into the DNA double helix, while the compact TMPyP complexes with pyridinium cations at the meso-position could not interact with DNA. Thus, it was suggested that the solvation behavior by ionic liquids depends on the structure of the porphyrin and also affects its interaction with DNA. Neither Mn(III) complexes with axial ligands could interact with DNA, regardless of the presence of the ionic liquids, due to their steric hindrance.

Benzimidazolium‐Decorated Metalloporphyrin Molecule and Polymer: a Reliable Preparation Method and Application in Catalyzing the Cycloaddition Reaction of CO2and Epoxides

AbstractDue to the synergistic effect of central metal and halide anion, cationic metalloporphyrins and derivatives exhibit outstanding catalytic activities for the cycloaddition reaction of epoxides and carbon dioxide. Herein, a generic strategy was developed to synthesize the benzimidazolium‐containing metalloporphyrin molecule and polymer. To demonstrate the method feasibility, we firstly synthesized the molecule1H, in which the benzimidazole groups were in‐site constructed by the cyclization of 5,10,15,20‐(4‐carboxyphenyl)‐porphyrin (H2TCPP) witho‐diaminobenzene (PEA). After post‐synthetic ionization and metallization, I−and Zn2+were introduced as the nucleophile and Lewis acid, respectively. The structure of1ZnILwas confirmed by single crystal X‐ray diffraction analysis. By using the similar conditions of model reaction,H2TCPPwas copolymerized with 1,2,4,5‐tetraaminobenzene (BTA) to prepare the polymerP‐1ZnIL. The prepared cationic molecule1ZnILand polymerP‐1ZnILshowed comparable activities in catalyzing the cycloaddition of carbon dioxide with epoxides to cyclic carbonates compared to the reported bifunctional catalysts based on metalloporphyrins.

Bio-Orthogonal Conjugation of a Cationic Metalloporphyrin to BSA and HSA via "Click" Chemistry.

In this study, we present a convenient method for the labelling of tyrosine residues on bovine serum albumin (BSA) and human serum albumin (HSA) and report for the first time their subsequent bio-orthogonal conjugation with porphyrins via "click" chemistry. We demonstrate that these serum proteins can be labelled with an alkyne-diazonium heterobifunctional linker and can then undergo chemo-selective bio-orthogonal conjugation with a water-soluble azido metalloporphyrin via "click" chemistry to yield protein-conjugates that retain their photodynamic properties. In our hands, this method was found to be highly reproducible, scalable, and tuneable which allows for the production of bioconjugates where the porphyrin-protein conjugate not only retains an ability to generate singlet oxygen but possess an enhanced relative singlet oxygen quantum yields relative to the porphyrin alone. Furthermore, we have investigated the photochemical properties of these conjugates through photospectrometric techniques and have determined that the porphyrin macrocycles remain appreciably photostable under light irradiation. Our phototoxic protein-photosensitizer-conjugates show excellent photodynamic activity against a human colorectal adenocarcinoma cancer cell line (HT-29) with cell viabilities of 7.7±0.5 % (IC50 8.76±2.14 μM) and 1.7±1.9 % (IC50 8.48±5.11 μM) for BSA and HAS, respectively, when irradiated with 20 J cm-2 of white-light. Importantly, neither of the conjugates was found to possess any significant "dark" toxicity even at concentrations of 100 μM. Furthermore, the natural fluorescent properties of the bioconjugates allowed for the determination of cellular uptake in vitro via fluorescence microscopy thus highlighting the potential theranostic applications of these unique protein-drug-conjugates.

Synergistically catalytic nanozymes based on heme-protein active site model for dual-signal and ultrasensitive detection of H2O2 in living cells

• A peroxidase-like nanozyme, two-dimensional nanonetwork, was developed by FeP and pSC 4 -AuNPs via the self-assembled method. • The catalytic mechanism was explained by the active site model, electron transfer promotion effect, and 2D morphology. • Colorimetric and electrochemical bioassays were performed on the in situ detection of H 2 O 2 in living cells. • The approach provides the catalytic and functional evolution for heme-proteins models via the combination with nanomaterials. Herein, a peroxidase-like nanozyme (FeP-pSC 4 -AuNPs), two-dimensional nanonetwork, was developed by a cationic metalloporphyrin (FeP) and supramolecular-modified gold nanoparticles (pSC 4 -AuNPs) via the self-assembled method in aqueous solution. It involved the synergistically catalytic effects of the nanomaterials and the structural mimic of a heme-protein active site. The host-guest recognition of the ordered assembly was studied by molecular docking, proving a favorable interaction between the supramolecular and FeP. The nanozyme showed a highly catalytic activity with the increase of 3.3 and 2.7 times compared to that of pSC 4 -AuNPs and FeP respectively. The mechanisms were explained by the heme-protein active site model, electron transfer promotion effect of AuNPs to FeP, and two-dimensional morphology. It was also robust to a wide range of pH, temperature, and storage conditions. Accordingly, the nanozyme was applied to the colorimetric and electrochemical bioassays for in situ detection of H 2 O 2 in living cells, demonstrating the satisfactory sensitivity. As a result, this study achieved the ordered fabrication of a nonozyme with the synthetic simplicity and superior catalytic performance, and will facilitate the researches on the development, rational design, and bioassay applications of nanozymes.

Kinetic Investigation on Tetrakis(4-Sulfonatophenyl)Porphyrin J-Aggregates Formation Catalyzed by Cationic Metallo-Porphyrins.

Under mild acidic conditions, various metal derivatives of tetrakis(4-N-methylpyridinium)porphyrin (gold(III), AuT4; cobalt(III), CoT4; manganese(III), MnT4 and zinc(II), ZnT4) catalytically promote the supramolecular assembling process of the diacid 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4) into J-aggregates. The aggregation kinetics have been treated according to a well-established model that involves the initial formation of a critical nucleus containing m porphyrin units, followed by autocatalytic growth, in which the rate evolves as a power of time. An analysis of the extinction time traces allows to obtain the rate constants for the auto-catalyzed pathway, kc, and the number of porphyrins involved in the initial seeding. The aggregation kinetics have been investigated at fixed H2TPPS4 concentration as a function of the added metal derivatives MT4. The derived rate constants, kc, obey a rate law that is first order in [MT4] and depend on the specific nature of the catalyst in the order AuT4 > CoT4 > MnT4 > ZnT4. Both resonance light scattering (RLS) intensity and extinction in the aggregated samples increase on increasing [MT4]. With the exception of AuT4, the final aggregated samples obtained at the highest catalyst concentration exhibit a negative Cotton effect in the J-band region, evidencing the occurrence of spontaneous symmetry breaking. The role of the nature of the metal derivative in terms of overall charge and presence of axial groups will be discussed.

Structure relationship of metalloporphyrins in inhibiting the aggregation of hIAPP

Metalloporphyrins (FeTBAP, MnTBAP, FeTMPyP and MnTMPyP) have been proposed as effective therapeutic agents in ONOO−-related disease including type 2 diabetes (T2D). As these metalloporphyrins share the structural similarities of the planar aromatic conjugation with a valuable class of inhibitors against amyloids fibrillation, they might be effective inhibitors via aromatic π-π stacking interactions with amyloid peptides. Here, we found that the anionic metalloporphyrins (FeTBAP and MnTBAP) are effective inhibitors against hIAPP fibrillation, while, the cationic metalloporphyrins (FeTMPyP and MnTMPyP) only have limited inhibitory effects. Besides, the porphyrin with iron center is more effective than the one with manganese center. Our results favor the electrostatic attraction contributes the main reason to the inhibitory effect between the anionic porphyrins and hIAPP, followed by the π-π stacking interactions between aromatic ring of porphyrins and hIAPP and the stronger coordination ability of iron center to hIAPP. Additionally, by comparison with FeTBAP, which can completely inhibit cytotoxicity induced by hIAPP via stabilizing hIAPP monomers, MnTBAP fails to reverse the cytotoxicity due to that it can only delay the transition of hIAPP from α-helix to β-sheet rich oligomers. Our results provide theoretical significance for further designing or screening of metalloporphyrins as bifunctional antidiabetic drugs.

Preparation, characterization and catalytic oxidation properties of silica composites immobilized with cationic metalloporphyrins

Herein, the metalloporphyrins Co(II) (5, 10, 15, 20-tetra (4-(3-(N-ethyl-4-pyridyl)pyrazolyl)phenyl)porphyrin) (CoTEtPyP) and Mn(III) (5, 10, 15, 20-tetra(4-(3-(N-ethyl-4-pyridyl)pyrazolyl)phenyl)porphyrin) (MnTEtPyP(OAc)) were synthesized and characterized spectroscopically. The cationic metalloporphyrins were firstly immobilized on the surface of SiO2 by electrostatic attractions with hydrothermal method to get the gels. Then, the gels were extracted by supercritical CO2 to remove the redundant solvent molecules and the unreacted metal salt. The structures and properties of porphyrin–SiO2 porous composites (PSC1 and PSC2) were characterized by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, scanning electron microscopy, transmission electron microscope, powder X-ray diffraction, thermalgravimetric analysis and nitrogen sorption measurements. N2 absorptions have verified that the porous materials have large BET surface area and big N2 uptake capacity. The composites also have shown higher specific surface area and superior thermal stability. The catalytic activities of the new PSCs to the ethylbenzene oxidation carried out indicated that both of them exhibit highly selectivity of acetophenone (> 99%) with the conversion of 87.6% (PSC1) and 93.0% (PSC2), respectively.

Post-illumination cellular effects of photodynamic treatment.

Increased interest in clinical application of photodynamic therapy (PDT) in various medical fields poses a demand for better understanding of processes triggered by photo-treatment. Most of the work on PDT performed so far has focused on the immediate effects of photo-treatment. It is generally accepted that cellular damage occurs during light exposure and within a short period thereafter. If cells are not killed during the PDT, they might recover, depending on the extent of the photo-induced damage. Little is known, however, about the relationship between the properties of photosensitizers (PSs) and the delayed consequences of PDT. The aim of this work was to investigate cellular responses to sub-lethal photodynamic treatment and how toxicogenic potency may be affected by molecular features of the PS. Results demonstrated that for cationic porphyrin-based PSs, lipophilicity is the main factor determining the fate of the cells in the 24-hour post-illumination period. PSs with amphiphilic properties initiated oxidative reactions that continued in the dark, long after light exposure, and caused suppression of metabolism and loss of cell viability with concomitant changes in electrophoretic mobility of proteins, including caspases. Apoptotic activity was not stimulated in the post-illumination period. This study demonstrated that in PDT mediated by amphiphilic cationic metalloporphyrin PSs, even when immediate photo-damage is relatively mild, destructive oxidative processes initiated during PDT continue in the absence of light to substantially impair metabolism, and that post-illumination protein modification may modify utilization of cell death pathways.

Water-Soluble Cationic Metalloporphyrins: Specific G-Quadruplex-Stabilizing Ability and Reversible Chirality of Aggregates Induced by AT-Rich DNA.

Cu-TMPipPrOPP and Zn-TMPipPrOPP, two new cationic metallo derivatives of TMPipPrOPP (5,10,15,20-tetrakis{4-[3-(1-methyl-1-piperidinyl)propoxy]phenyl}porphyrin), a porphyrin with four bulky side chains, were synthesized and characterized. The interactions of the new metalloporphyrins with structurally different DNAs were then compared with those of TMPipPrOPP. The introduction of bulky side chains provides the porphyrin derivatives with excellent binding specificity for G-quadruplex DNA, which is reflected by (1) the significantly different optical responses of TMPipPrOPP toward G-quadruplexes in comparison with single-stranded and duplex DNAs and (2) the ability of the three porphyrin derivatives to effectively stabilize G-quadruplexes, with no or little effect on the stability of duplex DNA. TMPipPrOPP can achieve colorimetric and fluorescent discrimination of G-quadruplexes from single-stranded and duplex DNAs with extraordinary high specificity. Due the presence of metal ions, Cu-TMPipPrOPP and Zn-TMPipPrOPP are deprived of the ability for optical G-quadruplex recognition but show enhanced ability to stabilize G-quadruplexes. In addition, because of the presence of the four cationic side chain substituents, the three porphyrin derivatives can form chiral aggregates via electrostatic interactions along the surface of structurally diverse DNAs. The chirality of aggregates formed by TMPipPrOPP is not changed by the nature of the template DNAs, whereas aggregates formed by Cu-TMPipPrOPP and Zn-TMPipPrOPP in the presence of adenine-thymine (AT) rich duplex DNA show completely inverted chirality in comparison with those formed in the presence of other DNAs. Interestingly, the chirality of the aggregates can be reversibly switched many times by alternating the ratio of Cu-TMPipPrOPP (or Zn-TMPipPrOPP) to AT-rich duplex DNA.

Photodynamic inactivation of methicillin-resistant Staphylococcus aureus and Escherichia coli: A metalloporphyrin comparison

Increasing rates of antibiotic resistance coupled with the lack of novel antibiotics threatens proper clinical treatment and jeopardizes their use in prevention. A photodynamic approach appears to be an innovative treatment option, even for multi-drug resistant strains of bacteria. Three components are utilized in photodynamic inactivation: a photosensitizer, light source, and oxygen. Variations in photosensitizers strongly influence microbial binding and bactericidal activity. In this study, four different cationic metalloporphyrins (Cu2+, Fe2+, Pd2+, Zn2+) were compared to the free-base ligand 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin regarding their electronic properties and generation of reactive oxygen species upon subsequent 405nm violet-blue irradiation. Staphylococcus aureus and Escherichia coli were used as representatives of Gram-positive and -negative, respectively, to assess bactericidal effects by the photodynamic process. Bacterial cultures were pre-incubated with porphyrins and exposed to varying doses of 405nm irradiation (0–30J/cm2). Metalloporphyrins containing Cu2+ and Fe2+ demonstrated minimal effects on viability. Pronounced bactericidal activity was evident with free-base ligand, Zn2+, and Pd2+; though significantly stronger effects were apparent with Pd2+. Photodynamic killing was directly proportional to reactive oxygen species production post-illumination. These data provide new insight into the influence of metal chelation on photosensitizer activity on bactericidal singlet oxygen production. The strong anti-microbial photodynamic action through the use of a portable light-emitting diode over short time intervals (seconds) provides support for its potential use in self-treatment.

Photophysical and photochemical properties of manganese complexes with cationic porphyrin ligands: Effects of alkyl substituents and micellar environment

Abstract Although Mn(III) porphyrins were considered earlier to be very weakly emissive, the fluorescence displayed by Mn(III) complexes with the cationic TMPyP 2+ ligand (H 2 TMPyP 4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin) as well as with its other alkyl (such as hexyl and dodecyl) derivatives proved to be strong enough for a comparative study. Elongation of the alkyl substituent increased both the quantum yield and the lifetime of the emission for the Mn(III) porphyrins, while resulted in an opposite effect for the corresponding free bases in homogeneous solutions. The presence of cationic micelles, however, reversed this tendency regarding the emission lifetime of the complexes. These cationic metalloporphyrins were applied in a photocatalytic system involving triethanolamine (TEOA) as a sacrificial electron donor and methylviologen (MV 2+ ) as an acceptor. In the first step of the catalytic process outer-sphere photoinduced reduction of the metal center took place via quenching of the triplet excited state of these metalloporphyrins by TEOA. The corresponding manganese(II) porphyrins formed in this way were also photoactive; they forwarded an electron to MV 2+ upon irradiation, regenerating the starting complex. Elongation of the alkyl substituents increased the quantum yield of the formation of methylviologen radical (MV ●+ ) in this system, but considerably decreased the durability of the photocatalyst. Anionic micelles totally hindered the photoinduced generation of Mn(II) porphyrins, while cationic micellar environment appreciably increased the efficiency of the accumulation of MV ●+ .

Thermodynamics Binding of Tetrakis (2,3,5,6-Tetrafluoro-N,N',Nʺ-Trimethyl Ammonium Phenyl) Porphyrin Nickel(II) With Calf Thymus DNA

In this study, aggregation behavior of a water soluble cationic metalloporphyrin, meso-tetrakis (2,3,5,6-tetrafluoro-N,N´,N´´-trimethyl ammonium phenyl) porphyrin nickel(II) [Ni(II)(TF4TMAPP)]4+ is investigated in 5 mM aqueous phosphate buffer of pH 7.0 at 25.0 °C and various ionic strengths using optical absorption and resonance light scattering spectroscopic methods. The results suggest that [Ni(II)(TF4TMAPP)]4+ do not aggregate in the experimental concentration range. Also, the interaction of cationic metalloporphyrin, [Ni(II)(TF4TMAPP)]4+ with calf thymus DNA (ct-DNA) is studied in 5 mM aqueous phosphate buffer of pH 7.0 by optical absorption, resonance light scattering (RLS), fluorescence spectroscopy and thermal denaturation measurements. The binding constants are determined by analysis of the optical absorption spectra of the [Ni(II)(TF4TMAPP)]4+ at various temperatures using SQUAD software. The thermodynamic parameters are also calculated by van't Hoff equation. The results indicate that the process is entropy-driven and suggest that the main driving forces are the outside binding mode.

Heterogeneous oxidation of the dye Brilliant Green with H2O2 catalyzed by supported manganese porphyrins

Synthetic metalloporphyrins can oxidize organic substrates efficiently and selectively in the presence of different oxygen donors. In an attempt to propose new catalytic systems to treat industrial effluents, researchers have recently turned their attention to the performance of metalloporphyrin-based catalysts in bleaching reactions of organic dyes used in the textile industry. The present work has investigated the cationic metalloporphyrins [Mn(T4MPyP)]Ac5 (MnP1) and [Mn(Br8T3MPyP)]Cl5 (MnP2) immobilized on two inorganic supports, namely magnetite coated with silica obtained by the hydrolytic sol-gel process (S-Mag) and nanotubes of raw halloysite clay mineral (Hallo), as catalysts in the bleaching reaction of the dye Brilliant Green by hydrogen peroxide (30%). The catalysts elicited up to 22.9 times higher reaction rates as compared with the rates of the control reactions. It was possible to use the immobilized complexes in successive oxidation reactions without significant decrease in the catalytic activity. The catalysts MnP-S-Mag displayed magnetic properties, which allowed their fast separation from the reaction medium with the aid of a simple magnet. A 2k full factorial design (4 factors and k levels) study of catalyst use under different experimental conditions, showed that time and molar ratio affected the dye bleaching reaction.

Gadolinium Meso-Tetrakis(4-Pyridyl)Porphyrin as a MRI Contrast Agent: Comparison with Anionic and Cationic Metallo-Porphyrins

Gadolinium Meso-Tetrakis(4-Pyridyl)Porphyrin as a MRI Contrast Agent: Comparison with Anionic and Cationic Metallo-Porphyrins

Preparation and electrochemical behaviour study of layered Bi2SrTa2O9with a cationic manganese porphyrin

Layered Bi2SrTa2O9 was achieved by solid-phase synthesis and then cationic metalloporphyrin 5,10,15,20-tetrakis(N-methylpyridinium-4-yl) porphyrinato manganese (MnTMPyP), was intercalated into layered material Bi2SrTa2O9 by a guest-exchange method using n-PrNH3 +-SrTa2O7 as a precursor. The new intercalation multicomposite MnTMPyP-SrTa2O7 was characterised using X-ray diffraction, infrared and scanning electron micrograph images. Moreover, the MnTMPyP-SrTa2O7 nanocomposite exhibited fine electrocatalytic activity towards oxygen reduction.

Preparation of heterogeneous cationic metalloporphyrin/heteropolyanion composite catalysts and their high catalytic activity in hydroxylation of cyclohexane with molecular oxygen

A new route to improve the metalloporphyrin catalysts is developed, and it is to constitute heterogeneous composite catalysts with immobilized cationic metalloporphyrins and heteropolyanions. By using the method of synchronously synthesizing and immobilizing porphyrins on cross-linked polystyrene microspheres (CPS microspheres), the immobilized porphyrin TAPP-CPS microspheres, on which ternary amine (TA) group-containing phenyl porphyrin (PP) was immobilized, were first prepared, and then the immobilized cationic porphyrin TMPP-CPS microspheres, in whose structure trimethylammoniophenyl porphyrin (TMPP) was contained, were obtained via quaternization reaction. Finally, three immobilized metalloporphyrins, CoTMPP-CPS (shorten as CoP-CPS), MnTMPP-CPS (MnP-CPS) and FeTMPP-CPS (FeP-CPS), were gained through coordination reactions. These immobilized metalloporphyrins were composited with heteropolyanions by right of the mutual electrostatic interaction with phosphotungstic (PW) acid and phosphomolybdic (PMo) acid as reagents, respectively, resulting in several heterogeneous metalloporphyrin/heteropolyanion composite catalysts such as CoPPW-CPS, CoPPMo-CPS and MnPPW-CPS. The composite catalysts were used in the catalytic hydroxylation reaction of cyclohexane with molecular oxygen as oxidant, and their catalytic performances were investigated. The experimental results show that the heterogeneous composite catalysts have extraordinarily high catalytic activity in the hydroxylation reaction of cyclohexane by molecular oxygen, and the cyclohexanol yield in 8 h can get up to 45.5 %. More importantly, the catalytic activity of the heterogeneous composite catalysts is obviously higher than that of the immobilized cationic metalloporphyrins, and the enhanced catalytic activity is originated from a protection of heteropolyanions against the deactivation of metalloporphyrins.

Photophysics and halide quenching of a cationic metalloporphyrin in water

In this work, the steady state S0-S1 and S0-S2 absorption and emission behaviour of the water-soluble tetrakis(N-methyl-4-pyridyl)porphyrin zinc(ii) tetrachloride (ZnTMPyP) in media of constant and high ionic strength, both with and without iodide ions as a fluorescence quencher, was measured. The quenching of the ZnTMPyP S1 state by iodide ions proceeds primarily through diffusion-limited interaction in an encounter pair but the formation of a loose association between the ZnTMPyP S1 state and iodide ions also provides a minor quenching pathway. The ZnTMPyP S2 state was quenched minimally by iodide, likely through an electron transfer mechanism at an average donor-acceptor distance of ~0.7 nm. The results presented here highlight the notion that significant iodide quenching of the ZnTMPyP S1 state can be a source of inefficiencies in porphyrin-based dye-sensitized solar cells. The minimal quenching of the S2 state indicates that no significant loss of efficiency will be introduced by using iodide as component of the electrolyte system in upconversion by triplet-triplet annihilation (UC-TTA) enhanced solar cells.

Differential Coordination Demands in Fe versus Mn Water-Soluble Cationic Metalloporphyrins Translate into Remarkably Different Aqueous Redox Chemistry and Biology

The different biological behavior of cationic Fe and Mn pyridylporphyrins in Escherichia coli and mouse studies prompted us to revisit and compare their chemistry. For that purpose, the series of ortho and meta isomers of Fe(III) meso-tetrakis-N-alkylpyridylporphyrins, alkyl being methyl to n-octyl, were synthesized and characterized by elemental analysis, UV/vis spectroscopy, mass spectrometry, lipophilicity, protonation equilibria of axial waters, metal-centered reduction potential, E(1/2) for M(III)P/M(II)P redox couple (M = Fe, Mn, P = porphyrin), kcat for the catalysis of O2(•-) dismutation, stability toward peroxide-driven porphyrin oxidative degradation (produced in the catalysis of ascorbate oxidation by MP), ability to affect growth of SOD-deficient E. coli, and toxicity to mice. Electron-deficiency of the metal site is modulated by the porphyrin ligand, which renders Fe(III) porphyrins ≥5 orders of magnitude more acidic than the analogous Mn(III) porphyrins, as revealed by the pKa1 of axially coordinated waters. The 5 log units difference in the acidity between the Mn and Fe sites in porphyrin translates into the predominance of tetracationic (OH)(H2O)FeP complexes relative to pentacationic (H2O)2MnP species at pH ∼7.8. This is additionally evidenced in large differences in the E(1/2) values of M(III)P/M(II)P redox couples. The presence of hydroxo ligand labilizes trans-axial water which results in higher reactivity of Fe relative to Mn center. The differences in the catalysis of O2(•-) dismutation (log kcat) between Fe and Mn porphyrins is modest, 2.5-5-fold, due to predominantly outer-sphere, with partial inner-sphere character of two reaction steps. However, the rate constant for the inner-sphere H2O2-based porphyrin oxidative degradation is 18-fold larger for (OH)(H2O)FeP than for (H2O)2MnP. The in vivo consequences of the differences between the Fe and Mn porphyrins were best demonstrated in SOD-deficient E. coli growth. On the basis of fairly similar log kcat(O2(•-)) values, a very similar effect on the growth of SOD-deficient E. coli was anticipated by both metalloporphyrins. Yet, while (H2O)2MnTE-2-PyP(5+) was fully efficacious at ≥20 μM, the Fe analogue (OH)(H2O)FeTE-2-PyP(4+) supported SOD-deficient E. coli growth at as much as 200-fold lower doses in the range of 0.1-1 μM. Moreover the pattern of SOD-deficient E. coli growth was different with Mn and Fe porphyrins. Such results suggested a different mode of action of these metalloporphyrins. Further exploration demonstrated that (1) 0.1 μM (OH)(H2O)FeTE-2-PyP(4+) provided similar growth stimulation as the 0.1 μM Fe salt, while the 20 μM Mn salt provides no protection to E. coli; and (2) 1 μM Fe porphyrin is fully degraded by 12 h in E. coli cytosol and growth medium, while Mn porphyrin is not. Stimulation of the aerobic growth of SOD-deficient E. coli by the Fe porphyrin is therefore due to iron acquisition. Our data suggest that in vivo, redox-driven degradation of Fe porphyrins resulting in Fe release plays a major role in their biological action. Possibly, iron reconstitutes enzymes bearing [4Fe-4S] clusters as active sites. Under the same experimental conditions, (OH)(H2O)FePs do not cause mouse arterial hypotension, whereas (H2O)2MnPs do, which greatly limits the application of Mn porphyrins in vivo.

Cationic Metalloporphyrins Imobilized in Faujasite Zeolites as a Cytochrome P-450 Mimic

Metalloporphyrins immobilized into NaY zeolite are described as catalysts for hydrocarbon oxyfuntionalization. Manganese(III) and iron(III)tetrakis(4-N-methylpyridyl)-porphyrin (MnP1 and FeP1), and manganese(III) and iron(III) tetrakis(4-N-benzylpiridil)-porphyrin (MnP2 and FeP2) were impregnated (MnP1-NaYimp, FeP1-NaYimp, MnP2-NaYimp, FeP2-NaYimp, respectively) and encapsulated (MnP1-NaY, FeP1-NaY, MnP2-NaY and FeP2-NaY) into the NaY zeolite. These catalysts were used in the oxidation of (Z)-cyclooctene, cyclohexane, and adamantane by iodosylbezene (PhIO). These systems were able to epoxidize (Z)-cyclooctene with cis-epoxycyclooctane yields as high as 100%. By using cyclohexane and adamantane as substrate, the susceptibility of the benzyl groups on the porphyrin ring of the MnP materials, led to a different distribution of the oxidized products. With FePs, this susceptibility was not detected because the species responsible for the oxidations, FeIV(O)P·+, is more active than MnV(O)P. In conclusion, cationic metalloporphyrins immobilized into NaX zeolites, are good cytochrome P-450 models is less polar solvents since the selectivity of the system indicates the “in cage” solvent oxygen rebound oxidative process.

Characterization of Immobilized Composite Catalysts of Cationic Metalloporphyrin and Heteropoly Anion in Oxidation of Ethyl Benzene by Molecular Oxygen

An immobilized cationic phenyl porphyrin was prepared with crosslinked polystyrene (CPS) microspheres as carriers via synthesis and immobilization.A kind of immobilized cationic cobalt porphyrin was obtained through a coordination reaction between the immobilized cationic phenyl porphyrin and the cobalt salt.In the composite reactions,phosphotungstic acid (HPW) and phosphomolybdic acid (HPMo) with Keggin structures were used as reagents,respectively,and the combination of the cationic cobalt porphyrin (CoP) with the heteropoly anions by electrostatic interaction led to the formation of the immobilized composite catalysts of CoPPW-CPS and CoPPMo-CPS.We then characterized these immobilized composite catalysts.The immobilized composite catalysts were used in the oxidation of ethylbenzene by molecular oxygen,and their catalytic characters were investigated.The results show that the immobilized composite catalysts possess high catalyst activity.They can transform ethyl benzene into acetophenone with high selectivity,and the yield of acetophenone after 12 h reaches 30.1%.The catalytic activity of the immobilized composite catalysts is 75% higher than that of the immobilized cobalt porphyrin.The catalytic activity of CoPPW-CPS is higher than that of CoPPMo-CPS.The cobalt porphyrin in the composite is the catalyst component as the heteropoly has no catalytic activity.However,the heteropoly anion has a protective effect on the metalloporphyrin against its deactivation during the catalytic reaction.In the oxidation reaction,there is an optimum addition for catalyst,and adding excessive catalyst inhibits its activity.The composite catalysts show good recycle properties.