Water-soluble Iron Porphyrin Research Articles

μ-Oxo Dimerization Effects on Ground- and Excited-State Properties of a Water-Soluble Iron Porphyrin CO2 Reduction Catalyst

Iron 5,10,15,20-tetra(para-N,N,N-trimethylanilinium)porphyrin (Fe-p-TMA) is a water-soluble catalyst capable of electrochemical and photochemical CO2 reduction. Although its catalytic ability has been thoroughly investigated, the mechanism and associated intermediates are largely unknown. Previous studies proposed that Fe-p-TMA enters catalytic cycles as a monomeric species. However, we demonstrate herein that, in aqueous solutions, Fe-p-TMA undergoes formation of a μ-oxo porphyrin dimer that exists in equilibrium with its monomeric form. The propensity for μ-oxo formation is highly dependent on the solution pH and ionic strength. Indeed, the μ-oxo form is stabilized in the presence of electrolytes that are key components of catalytically relevant conditions. By leveraging the ability to chemically control and spectrally address both species, we characterize their ground-state electronic structures and excited-state photodynamics. Global fitting of ultrafast transient absorption data reveals two distinct excited-state relaxation pathways: a three-component sequential model consistent with monomeric relaxation and a two-component sequential model for the μ-oxo species. Relaxation of the monomeric species is best described as a ligand-to-metal charge transfer (τ1 = ∼500 fs), an ionic strength-dependent metal-to-ligand charge transfer (τ2 = 2-4 ps), and finally relaxation of a ligand field excited state to the ground state (τ3 = 5 ps). Conversely, excited-state relaxation of the μ-oxo species proceeds via cleavage of an FeIII-O bond to generate transient FeIV═O and FeII porphyrin species (τ1 = 2 ps) that recombine to the ground-state μ-oxo species (τ2 = ∼1 ns). This latter lifetime extends to timescales relevant for chemical reactivity. It is therefore emphasized that further consideration of catalyst speciation and chemical microenvironments is necessary for elucidating the mechanisms of catalytic CO2 reduction reactions.

A water-soluble iron-porphyrin complex capable of rescuing CO-poisoned red blood cells.

We describe herein a small-molecule platform that exhibits key properties needed by an antidote for CO poisoning. The design features an iron-porphyrin complex with bulky substituents above and below the macrocyclic plane to provide a hydrophobic pocket for CO binding and to prevent the formation of inactive oxo-bridged dimers. Peripheral charged groups impart water solubility. We demonstrate that the Fe(II) complex of a porphyrin with 2,6-diphenyl-4-sulfophenyl meso substituents can bind CO, stoichiometrically sequester CO from carboxyhemoglobin, and rescue CO-poisoned red blood cells.

Association behavior and fluorescence quenching between cationic zinc porphyrin pendant groups on water-soluble polymers and anionic iron porphyrin guests

An amphiphilic cationic tripyridiniumylporphyrin monomer, i.e., ZnTrMPyP, was synthesized and copolymerized with acrylamide in water and dimethyl sulfoxide, respectively, to prepare the water-soluble random copolymer P-D and microblock copolymer P-W. The association behavior and fluorescence quenching between the copolymers and tetra(p-sulfonato phenyl)porphyrin (Fe(III)TSPP(Cl)) were studied via absorption and emission spectra. The results showed that relatively discrete pendant groups of ZnTrMPyP within P-D could form a ground state complex with FeTSPP by electrostatic interactions, and both static and dynamic mechanisms were active in this quenching process. In contrast, the microblock porphyrin pendant groups within P-W interacted with FeTSPP as an entity, and static quenching was dominant in this process. Salt effects on the formation of the copolymers and FeTSPP complex were also investigated through the addition of KNO3, and the results showed that this association can be weakened by the electrostatic shielding effect, and the fluorescence quenching constant could be reduced.

Structure effect of water-soluble iron porphyrins on catalyzing protein tyrosine nitration in the presence of nitrite and hydrogen peroxide

Water-soluble iron porphyrins, such as FeTPPS (5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrinato iron (III)), FeTMPyP (5,10,15,20-tetrakis (N-methyl-4′-pyridyl) porphyrinato iron (III) chloride) and FeTBAP (5,10,15,20-tetrakis (4-benzoic acid) porphyrinato iron (III)), are highly active catalysts for peroxynitrite decomposition and thereby have been suggested as therapeutic agent for inflammatory diseases that implicate the involvement of nitrotyrosine formation. Here, we systemically investigated catalytic properties of FeTPPS, FeTMPyP and FeTBAP on protein nitration in the presence of hydrogen peroxide and nitrite. We showed that FeTPPS, FeTBAP and FeTMPyP all exhibited higher peroxidase activity in compared with hemin. As to protein nitration, the catalytic effect of FeTPPS and FeTBAP are effective in the presence of hydrogen peroxide and nitrite, while negligible BSA nitration was observed in the case of FeTMPyP. Moreover, the underlying mechanism of the oxidation of FeTPPS, FeTBAP and FeTMPyP was further studied. Collectively, our results suggest that, compound I and II species are involved in as the key intermediates in FeTMPyP/H2O2 system as similar as those in FeTPPS/H2O2 and FeTBAP/H2O2 system. As compared to weak antioxidants, TPPS and TBAP, however, TMPyP scavenges oxo-Fe (IV) intermediates of FeTMPyP at a faster rate by significant self-degradation; results in the shortest lifetimes of OFeIV-TMPyP and the lowest catalytic activity on oxidizing tyrosine and nitrite; and therefore, attributes to inactivation of FeTMPyP in protein nitration. In addition, association of FeTMPyP to BSA was found weak, while strong binding of FeTPPS and FeTBAP were observed. The weak binding keeps away of target residue of BSA from the center of FeTMPyP where the RNS is generated, which might be attributed as additional factors to the inactivation of FeTMPyP in protein nitration.

Enhanced Mimetic Enzyme Activity of Phosphorylated Porphyrin Nanocomposite Induced by Localized Surface Plasmon Resonance for Colorimetric Assay.

Plasmon-enhanced light harvesting has been of great interest to enhance the catalytic efficiency of some composites or hybrids. The enhanced peroxidase-like activity of phosphorylated iron(III) porphyrin (TPPFe(III))-based nanocomposite, induced by localized surface plasmon resonance for a colorimetric assay, was developed in this study. Firstly, a phosphate group modification strategy was adopted to synthesize water-soluble iron(III) porphyrin materials. Then, the as-synthesized TPPFe(III) was covalently attached to core-shell gold nanorods (GNRs), GNR@Au2S/AuAgS, to form TPPFe(III)-GNR@Au2S/AuAgS nanocomposite, which shows greatly enhanced peroxidase-like activity compared to TPPFe(III). A mechanism for the enhanced peroxidase-like activity of TPPFe(III)-GNR@Au2S/AuAgS was proposed, which results from a synergic effect of hot electrons excited by localized surface plasmon resonance and photogenerated electrons of the TPPFe(III), verified by experiments. Furthermore, a fast colorimetric assay for the detection of H2O2 and glucose was established based on the unique property of TPPFe(III)-GNR@Au2S/AuAgS. This colorimetric assay was applied to determine practical human serum samples; satisfactory results demonstrate this method has high accuracy. The present study would not only provide some insights into the mechanism of plasmon-activated enzyme-like reactions, but also offer new strategies for improving the catalytic activity of a mimetic enzyme.

Oxidation of 2,6-di-tert-butylphenol with tert-butyl hydroperoxide catalyzed by iron porphyrin tetrasulfonate, iron porphyrin tetracarboxylate and their supported analogues in a water-methanol mixture.

In this study, two water-soluble iron porphyrins bearing sulfonate and carboxylate functionalities (FePTS and FePTC, respectively) and their supported analogues were used as catalysts for the oxidation of 2,6-di-tert-butylphenol (DTBP) in a water-methanol mixture. tert-Butyl hydroperoxide (TBHP) was the oxidant and the volume ratio of water to methanol in the mixture was 1-8. The major products of the DTBP oxidation were 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone (DPQ) and 4,4'-dihydroxy-3,3',5,5'-tetra-tert- butylbiphenyl (H2DPQ). Also 2,6-di-tert-butyl-1,4-benzoquinone (BQ) was the minor product of the oxidation. The results showed that FePTC was more catalytically active than FePTS in the oxidation and gave the highest TON and TOF values in comparison to those for metalloporphyrin and metallophthalocyanine based catalysts in the DTBP oxidation given in the literature. In addition, the ecotoxicity tests of the DTBP oxidation mixtures before and after oxidative catalytic treatment toward Artemia salina were performed. It was found that the toxicity of the catalytically treated DTBP mixture containing residual DTBP and products was lower than the catalytically untreated DTBP mixture.

Spectroscopic studies of water-soluble superstructured iron(III) porphyrin. Interaction with the bovine serum albumin protein

Acid-base equilibrium of the “one-face”-hindered sulfonated porphyrin, α5,15-[2,2′(dodecamethyleneoxy),(5-sulfonato)diphenyl]-10,20-bis(2-hydroxy,5-sulfonatophenyl)porphyrinato iron(III), has been studied by paramagnetic 1H NMR. The isotropically shifted signals change in a fast exchange regime on the NMR time-scale. 1H longitudinal relaxation times and temperature dependence of the chemical shifts were measured and analyzed. The electronic structure of hydroxo specie is characteristic of a six- or five-coordinate high-spin iron(III) porphyrin with an S = 5/2 ground state. The 1H NMR titration allowed determination of the acidity constant, pKa 6.2 (0.1 M KNO3, 25 °C). In addition, we also report the interaction between the monohydroxo iron(III) porphyrin and the bovine serum albumin protein. From a 1H NMR titration, we have determined the affinity apparent constant, log Kap 3.2 (pH 7, KNO3 0.1 M, 25 °C). The formation of superstructured iron porphyrin-albumin protein adduct was confirmed by electronic absorption spectroscopy and electron paramagnetic resonance.

In situ polymerization of soil organic matter by oxidative biomimetic catalysis

BackgroundAgricultural practices that enhance organic matter content in soil can play a central role in sequestering soil organic carbon (SOC) and reducing greenhouse gases emissions.MethodsWe used a water-soluble iron-porphyrin to catalyze directly in situ oxidative polymerization of soil organic matter in the presence of H2O2 oxidant, with the aim to enhance OC stabilization, and, consequently, reduce CO2 emissions from soil. The occurred SOC stabilization was assessed by monitoring soil aggregate stability, OC distribution in water-soluble aggregates, soil respiration, and extraction yields of humic and fulvic acids.ResultsSoil treatment with H2O2 and iron-porphyrin increased the physical stability of water-stable soil aggregates and the total OC content in small aggregates, thereby suggesting that the catalyzed oxidative polymerization increased OC in soil and induced a soil physical improvement. The significant reduction of CO2 respired by the catalyst- and H2O2-treated soil indicated an enhanced resistance of polymerized SOC to microbial mineralization. The catalyzed oxidative polymerization of SOC also significantly decreased the extraction yields of humic and fulvic acids from soil.ConclusionsThe oxidative catalytic technology described here may become an efficient agricultural practice for OC sequestration in soils and contribute to mitigate global changes.Graphical abstractCatalyzed polymerization of soil organic matter.

Diazo ester insertion in N[sbnd]H bonds of amino acid derivatives and insulin catalyzed by water-soluble iron and ruthenium porphyrin complexes (FeTSPPCl) as application of carbenoid transfer in aqueous media

The metal complex FeTSPPCl (5,10,15,20-tetrakis)-(4-sulfonato-phenyl)-porphyrin-iron(III) chloride is an active catalyst for carbenoid insertion in NH bonds of aminoacid derivatives in aqueous media. A variety of diazoacetates and methyl diazophosphonate were used as carbenoid precursors. The commercially available iron porphyrin complex can also selectively catalyze alkylation of the N-terminus of insulin (chain B).

ChemInform Abstract: Efficient Iron(III) Porphyrins‐Catalyzed Oxidation of Guanidoximes to Cyanamides in Ionic Liquids.

Water soluble iron(III) porphyrins immobilized in imidazolium ionic liquids serve as an effective catalyst for the H2O2 mediated oxidation of guanidoximes to selectively give corresponding cyanamides in good yields. The use of ionic liquid with non-coordinating counter anion PF6 affords the product in high yield by facilitating the formation of anionic iron peroxo intermediate.

Asymmetric Oxidation and Carbene Transfer Reactions Catalyzed By Metalloporphyrins in Water

The development of environmentally benign reactions is an important goal in synthetic organic chemistry and chemical engineering. However, catalytic enantioselective reactions using transition-metal complexes in protic or aqueous solvents are within limited ranges. The current applications of asymmetric catalysis using metalloporphyrins will be reported (1). Distinct methodologies have been developed for carbene transfer and oxidation reactions such as the use of water-soluble catalysts (2). Comparison between hydrophobic and hydrophilic solvents will be discussed from an asymmetric point of view. Catalytic enantioselective oxidations using transition-metal complexes are limited when the oxidant is hydrogen peroxide. The two main difficulties of using hydrogen peroxide in the presence of transition metal complexes are the homolytic cleavage generating OH radicals and the catalase reaction with formation of dioxygen. Asymmetric sulfoxidation, epoxidation of alkenes and hydroxylation catalyzed by iron and manganese porphyrins will be described (3). Thus the asymmetric epoxidation of styrene derivatives by H2O2 (or UHP) to give optically active epoxides (ee up to 81%) and hydroxylation of alkanes to give optically active secondary alcohols (ee up to 78%) were carried out in methanol and water using chiral water-soluble iron porphyrins as catalysts. (1) Recent Advances in Catalysis by Water-Soluble Metalloporphyrins G. Simonneaux, P. Le Maux, S. Chevance and H. Srour. Handbook of Porphyrin Science, 2012, Vol. 21, 377-410 (2) Enantioselective Manganese-Porphyrin-Catalyzed Epoxidation and C-H hydroxylation with Hydrogen Peroxide in Water/Methanol Solutions H. Srour, P. Le Maux and G. Simonneaux. Inorg. Chem. 2012, 51, 5850-5856. (3) Metal-catalyzed asymmetric sulfoxidation, epoxidation and hydroxylation by hydrogen peroxide Hassan Srour, Paul Le Maux, Soizic Chevance, Gérard Simonneaux. Coord. Chem. Rev., 257 (2013) 3030– 3050

Efficient iron(III) porphyrins-catalyzed oxidation of guanidoximes to cyanamides in ionic liquids

Water soluble iron(III) porphyrins immobilized in imidazolium ionic liquids serve as an effective catalyst for the H2O2 mediated oxidation of guanidoximes to selectively give corresponding cyanamides in good yields. The use of ionic liquid with non-coordinating counter anion PF6 affords the product in high yield by facilitating the formation of anionic iron peroxo intermediate.

Copolymerization of 2,4-dichlorophenol with humic substances by oxidative and photo-oxidative biomimetic catalysis

We evaluated the catalytic activity of a water-soluble iron-porphyrin in an oxidative coupling reaction to form covalent bonds between 2,4-dichlorophenol (2,4-DCP) and humic molecules. The biomimetic catalysis in the presence of H₂O₂ was tested in the dark and in daylight, and changes in reaction products were revealed by high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy. In all conditions, iron-porphyrin was effective in promoting complete disappearance of 2,4-DCP, although catalyst activity was enhanced in daylight (with a maximum turnover number of 85.13). Further evidence of the occurred covalent coupling between 2,4-DCP and humic molecules was revealed by diffusion-ordered nuclear magnetic resonance (DOSY-NMR) spectroscopy that showed a reduced diffusivity of 2,4-DCP after the catalytic reaction. These findings indicate that iron-porphyrin is an efficient catalyst for the covalent binding of polyhalogenated phenols to humic molecules, thereby suggesting that the copolymerization reactions may become a useful technology to remediate soils and waters contaminated by halogenated phenols and their analogues.

Temperature and Pressure Effects on C–H Abstraction Reactions Involving Compound I and II Mimics in Aqueous Solution

The presented results cover a comparative mechanistic study on the reactivity of compound (Cpd) I and II mimics of a water-soluble iron(III) porphyrin, [meso-tetrakis(2,4,6-trimethyl-3-sulfonatophenyl)porphinato]iron(III), Fe(III)(TMPS). The acidity of the aqueous medium strongly controls the chemical nature and stability of the high-valent iron(IV) oxo species. Reactivity studies were performed at pH 5 and 10, where the Cpd I and II mimics are stabilized as the sole oxidizing species, respectively. The contributions of ΔH(‡) and ΔS(‡) to the free energy of activation (ΔG(‡)) for the oxidation of 4-methoxybenzaldehyde (4-MB-ald), 4-methoxybenzyl alcohol (4-MB-alc), and 1-phenylethanol (1-PhEtOH) by the Cpd I and II mimics were determined. The relatively large contribution of the ΔH(‡) term in comparison to the -TΔS(‡) term to ΔG(‡) for reactions involving the Cpd II mimic indicates that the oxidation of selected substrates by this oxidizing species is clearly an enthalpy-controlled process. In contrast, different results were found for reactions with application of the Cpd I mimic. Depending on the nature of the substrate, the reaction at room temperature can be entropy-controlled, as found for the oxidation of 4-MB-alc, or enthalpy-controlled, as found for 1-PhEtOH. Importantly, for the first time, activation volumes (ΔV(‡)) for the oxidation of selected substrates by both reactive intermediates could be determined. Positive values of ΔV(‡) were found for reactions with the Cpd II mimic and slightly negative ones for reactions with the Cpd II mimic. The results are discussed in the context of the oxidation mechanism conducted by the Cpd I and II mimics.

A Water-Soluble Iron Porphyrin as a Highly Efficient and Recyclable Catalyst for Peroxynitrite Decomposition

Peroxynitrite can be highly efficient catalyzed to harmless products with a turnover frequency 34.5 s-1by micromolar concentration of water-soluble iron porphyrin, 5, 10, 15, 20-tetrakis-(4-carboxyphenyl)-porphyrin-Fe(III)-chloride (T(p-COOH)PPFe(III)Cl). Then we used spectroscopic and kinetic to study its decomposition mechanism and rate in bionic environment (25 mM sodium bicarbonate). The data reveal that this catalytic reaction is a recyclable reaction. Peroxynitrite is decomposed to nitrate (NO3-) and nitrite (NO2-) through forming [oxoFe(IV)]+intermediate. Moreover, the [oxoFe(IV)]+intermediate is reduced back to the starting porphyrin. It is noted that the oxidized iron porphyrin can be reduced by the reducing agent in the solution. In addition, we also find the catalytic rate constant is higher in the presence of sodium bicarbonate than the absence of sodium bicarbonate. They are 1.26×106M-1s-1and 1.17×106M-1s-1, respectively.

Remediation of highly contaminated soils from an industrial site by employing a combined treatment with exogeneous humic substances and oxidative biomimetic catalysis

Remediation of two polluted soils from a northern Italian industrial site heavily contaminated with organic contaminants was attempted here by subjecting soils first to addition with an exogenous humic acid (HA), and, then, to an oxidation reaction catalyzed by a water-soluble iron-porphyrin (FeP). An expected decrease of detectable organic pollutants (>50%) was already observed when soils were treated only with the H2O2 oxidant. This reduction was substantially enhanced when oxidation was catalyzed by iron-porphyrin (FeP+H2O2) and the largest effect was observed for the most highly polluted soil. Even more significant was the decrease in detectable pollutants (70–90%) when soils were first amended with HA and then subjected to the FeP+H2O2 treatment. This reduction in extractable pollutants after the combined HA+FeP+H2O2 treatment was due to formation of covalent CC and COC bonds between soil contaminants and amended humic molecules. Moreover, the concomitant detection of condensation products in soil extracts following FeP addition confirmed the occurrence of free-radical coupling reactions catalyzed by FeP. These findings indicate that a combined technique based on the action of both humic matter and a metal-porhyrin catalyst, may become useful to quantitatively reduce the toxicity of heavily contaminated soils and prevent the environmental transport of pollutants.

Ruthenium porphyrin and oxidant convert N-nitrosodialkylamines into direct-acting mutagen in the Ames assay

The Ames assay is used for short-term screening of mutagens/carcinogens that induce DNA damage. Most mutagens/carcinogens require enzymatic activation through oxidation by cytochrome P450 in an S-9 mix to exert their mutagenicity. Chemical models for cytochrome P450, consisting of water-soluble or water-insoluble iron porphyrin plus an oxidant, have been used to produce frameshift mutagens from aromatic amines, heterocyclic amines and polyaromatic hydrocarbons. In this study, the mutagenicity of N-nitrosodialkylamines was assayed in the presence of a chemical model, which consists of 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrinatoruthenium(IV) dichloride (RuMe3) and 2,6-dichloropyridine N-oxide (Cl2pyNO). The chemical model activated symmetrical N-nitrosodialkylamines (alkyl = methyl, ethyl, propyl, butyl), and unsymmetrical N-nitroso-N-methylalkylamine (alkyl = propyl, butyl) in Salmonella typhimurium YG7108. Furthermore, the mutagenicity of N-nitrosodipropylamine (NDP) in S. typhimurium YG7108 was higher than that in S. typhimurium TA1535, suggesting that the mutagenicity derived from NDP using the chemical model was due to DNA alkylation. The results showed that the chemical model can activate N-nitrosodialkylamines to induce base substitution mutations.

Degradation of 2,4-dichlorophenol and coupling into humic matter by oxidative biomimetic catalysis with iron-porphyrin

We evaluated the activity of a water-soluble iron-porphyrin as catalyst of an oxidative reaction of 2,4-dichlorophenol (2,4-DCP) in the presence of humic molecules, whereby the phenol disappearance should proceed through self-olygomerization and co-polymerization within humic matter. The catalyzed coupling reaction was conducted with H2O2 as oxidizing agent with and without humic matter (HA) and followed by High Performance Liquid Chromatography (HPLC), upon incubation in either dark or daylight conditions. UV- and Fluorescence-detected signals of reaction products separated by HPLC were collected and structurally characterized by GC–MS. The 2,4-DCP degradation by the catalyzed oxidative reaction without addition of HA was complete in both incubation conditions and showed reaction products such as dehalogenated and hydroxylated phenols, and dimers/trimers of the dechlorinated phenol. With the presence of HA, 2,4-DCP was degraded in the dark by only 75% of initial content, whereas degradation was again complete in daylight, which showed similar reaction products as in the dark. These results reveal that the catalyzed oxidative reaction in the presence of HA was less efficient in the dark, possibly because 2,4-DCP was protected from oxidation by absorption into humic hydrophobic domains. Conversely, photo-oxidation combined to chemical oxidation to enhance the coupling reactivity in daylight conditions, most likely through co-polymerization of 2,4-DCP in humic molecules. This work confirms the potentiality of an oxidative coupling reaction catalyzed by iron-porphyrin in co-polymerizing halogenated pollutants into humic matter and detoxifying the environment.

Enantioselective water-soluble iron–porphyrin-catalyzed epoxidation with aqueous hydrogen peroxide and hydroxylation with iodobenzene diacetate

The asymmetric epoxidation of styrene derivatives by H2O2 (or UHP) to give optically active epoxides (ee up to 81%) and hydroxylation of alkanes to give optically active secondary alcohols (ee up to 78%) were carried out in methanol and water using chiral water-soluble iron porphyrins as catalysts.

Distant protonated pyridine groups in water-soluble iron porphyrin electrocatalysts promote selective oxygen reduction to water

Fe(III)-meso-tetra(pyridyl)porphyrins are electrocatalysts for the reduction of dioxygen in aqueous acidic solution. The 2-pyridyl derivatives, both the triflate and chloride salts, are more selective for the desired 4e(-) reduction than the isomeric 4-pyridyl complexes. The inward-pointing pyridinium groups influence proton delivery despite their distance from the iron centre.