Water-soluble Manganese Porphyrin Research Articles

Photocatalytic Oxygenation of Heterostilbenes—Batch versus Microflow Reactor

On the basis of earlier results with furan and thiophene derivatives of benzobicyclo[3.2.1]octadiene, photocatalytic oxygenation of novel furo- and thieno heterostilbenes with water-soluble manganese(III) porphyrins offered suitable possibilities to study their reactivities and reaction pathways depending on the heteroatom and the catalyst charge. The experiments were carried out in two reactors types (batch and microflow) to investigate the geometric effects. NMR spectroscopy, GC, and UPLC/MS analyses were applied for identification and quantification of the products. As our results indicated, the 2-thienyl and the common p-tolyl groups in the starting compounds remained intact due to their stronger aromaticity. Hence, the thieno derivative underwent oxygenation only at the open-chain part of the molecule, and the rates of its reactions were much lower than those of the furyl analogue. The less stable furan ring was easily oxygenated, its products with highest ratios were 2-furanon derivatives. Epoxide formation occurred at the open-chain parts of both substrates preferably by the anionic catalyst. Nevertheless, the conversion rates of the substrates were higher with the cationic porphyrin, according to electrophilic attacks by photogenerated Mn(V)=O species. Additionally, the reactions were significantly faster in microflow reactors due to the more favorable circumstances of mass transfer, diffusion, and light penetration.

Water-soluble manganese porphyrins as good catalysts for cipro- and levofloxacin degradation: Solvent effect, degradation products and DFT insights

Synthetic manganese porphyrins (MnPs), in the presence of oxidants, were employed for the degradation of fluoroquinolone antibiotics. Ciprofloxacin (CIP) and levofloxacin (LEV) degradation by iodosylbenzene, iodobenzene diacetate, H2O2 and meta-chloroperbenzoic acid using water-soluble MnP catalysts yielded thirteen and nine products, respectively, seven of which have been proposed for the first time. The MnP catalysts have demonstrated the ability to degrade these antibiotics to a high degree (up to 100% degradation). The structures of the degradation products were proposed based on mass spectrometry analysis, and density functional theory calculations could confirm how the substituent moieties attached to the basic chemical structure of the fluoroquinolones influence the degradation reactions. CIP has been shown to be a more reactive substrate towards the porphyrinic catalysts tested because of its three-membered ring. However, the catalysts could almost completely degrade LEV, highlighting the ability of these porphyrins to act as catalysts to degrade environmental pollutants.

Electrochemical properties and biomimetic activity of water-soluble meso-substituted Mn(III) porphyrin complexes in the electrocatalytic reduction of hydrogen peroxide

The aim of this study was to investigate biomimetic activity of water-soluble manganese porphyrin complexes with a series of meso-substituents of the porphyrin macrocycle in the electrocatalytic reduction of hydrogen peroxide in aqueous solutions and to obtain information on possible intermediates, processes, and mechanisms. Mn porphyrins were compared in the process of the electrocatalytic reduction of hydrogen peroxide at pH 4, 7.4, and 10 in the deoxygenated solutions and in the presence of oxygen. The highest sensitivity, defined as the reduction current increase in relation to the concentration of hydrogen peroxide, was found in the case of Mn(III) meso-tetra(N-methyl-4-pyridyl) porphyrin, MnTMPyP, in alkaline 2.9·10−2 A M−1 and acidic 1.6·10−2 A M−1 solutions in the presence of oxygen. The reduction currents at pH 7.4, 10, and 4 in the presence of H2O2 were about 4, 7, and 12 times higher, respectively, in the solutions with the MnTMPyP complex than those at a GCE without a porphyrin complex in the solution. The electrocatalytic reduction of hydrogen peroxide occurs in parallel with an oxidative degradation of the porphyrin catalyst depending on the conditions of the experiment and was most significant in the presence of oxygen. The effect of the functional substituents at the meso-positions of a porphyrin ligand on the electrocatalytic activity of the water-soluble Mn(III) porphyrins complexes is discussed and reaction mechanisms are proposed.

Water-soluble Manganese and Iron Mesotetrakis(carboxyl)porphyrin: DNA Binding, Oxidative Cleavage, and Cytotoxic Activities.

Two new water-soluble metal carboxyl porphyrins, manganese (III) meso-tetrakis (carboxyl) porphyrin and iron (III) meso-tetrakis (carboxyl) porphyrin, were synthesized and characterized. Their interactions with ct-DNA were investigated by UV-Vis titration, fluorescence spectra, viscosity measurement and CD spectra. The results showed they can strongly bind to ct-DNA via outside binding mode. Electrophoresis experiments revealed that both complexes can cleave pBR322 DNA efficiently in the presence of hydrogen peroxide, albeit 2-Mn exhibited a little higher efficiency. The inhibitor tests suggest the oxidative DNA cleavage by these two complexes may involve hydroxyl radical active intermediates. Notably, 2-Mn exhibited considerable photocytotoxicity against Hep G2 cell via triggering a significant generation of ROS and causing disruption of MMP after irradiation.

Mechanistic study of a manganese porphyrin catalyst for on-demand production of chlorine dioxide in water

A water-soluble manganese porphyrin complex was examined for the catalytic formation of chlorine dioxide from chlorite under ambient temperature at pH 5.00 and 6.90. Quantitative kinetic modeling allowed for the deduction of a mechanism that accounts for all experimental observations. Catalysis is initiated via an OAT (Oxygen Atom Transfer) reaction resulting in formation of a putative manganese(V) oxo species, which undergoes ET (Electron Transfer) with chlorite to form chlorine dioxide. As chlorine dioxide accumulates in solution, chlorite consumption slows down and ClO 2 reaches a maximum as the system reaches equilibrium. In phosphate buffer at pH 6.90, manganese(IV) oxo accumulates and its reaction with ClO 2 gives ClO 3-. However, at pH 5.00 acetate buffer proton coupled electron transfer (PCET) from chlorite to manganese(IV) oxo is fast and irreversible leading to chlorate formation only via the putative manganese(V) oxo species. These differences underscore how PCET rates affect reaction pathways and mechanism. The ClO 2 product can be collected from the aqueous reaction mixture via purging with an inert gas, allowing for the preparation of chlorine dioxide on-demand.

Water Proton Relaxivity, Superoxide Dismutase-like Activity, and Cytotoxicity of a Manganese(III) Porphyrin Having Four Poly(ethylene glycol) Tails

Abstract A high-molecular-weight water-soluble manganese(III) porphyrin having four poly(ethylene glycol) tails was prepared, which enhanced the T1 relaxation rate of water protons by ca. 7.5-fold compared with manganese(III)–tetra(4-sulfonatophenyl)porphyrin. The new compound also exhibited superoxide dismutase-like activity and significantly lower cytotoxicity.

Kinetic and mechanism of the aqueous selective oxidation of sulfides to sulfoxides: insight into the cytochrome P450-like oxidative metabolic process

The selective oxidation of sulfides with hydrogen peroxide to give sulfoxides was carried out in aqueous solution by water-soluble manganese porphyrin as mimics of cytochrome P450-like catalyst. Different factors that influencing the selective oxidation of sulfides, for example, catalyst, amount of catalyst, solvent and reaction temperature were investigated. MnTE4PyP (meso-tetrakis(N-ethylpyridinium-4-yl) manganese porphyrin) was efficient and selective catalyst for oxidation of various sulfides. The reaction showed first-order dependence in both [sulfide] and [ H 2 O 2], and a fractional order respect to catalyst. Oxygen atom transfer mechanism involves high-valence intermediate was proposed, which was supported by kinetic orders and spectrophotometric evidences.

Pharmaceutical Effect of Manganese Porphyrins on Manganese Superoxide Dismutase Deficient Mice

Mice lacking manganese-superoxide dismutase (Mn-SOD) activity exhibit typical pathology of dilated cardiomyopathy (DCM). In the present study, the structure-activity relationship between the water-soluble manganese (Mn) porphyrin with SOD activity and the in vivo pharmaceutical effect on DCM is reported. The Mn-SOD-deficient mice were treated with Mn-porphyrins for 3 weeks. The treatment of a Mn-porphyrin, MnM2Py(2)P, suppressed the progression of cardiac dilation. These results suggest that the Mn-porphyrin MnM2Py(2)P treatment is proposed as a potential therapy for DCM.

Enantioselective Manganese-Porphyrin-Catalyzed Epoxidation and C–H Hydroxylation with Hydrogen Peroxide in Water/Methanol Solutions

The asymmetric epoxidation of alkene and hydroxylation of arylalkane derivatives by H(2)O(2) to give optically active epoxides (enantiomeric excess (ee) up to 68%) and alcohols (ee up to 57%), respectively, were carried out in water/methanol solutions using chiral water-soluble manganese porphyrins as catalysts.

Biomimetic models of nitric oxide synthase for the oxidation of oximes to carbonyl compounds catalyzed by water-soluble manganese porphyrins in aqueous solution

A mild green and efficient approach for hydrogen peroxide oxidative converting oximes to the corresponding carbonyl compounds with a water-soluble manganese porphyrin as catalyst in water/acetone mixture has been developed. The water-soluble manganese porphyrin showed an excellent activity for the oxidative deoximation reactions of various oximes under ambient conditions in the absence of any additive. The oxidative deoximation was through the formation of high valent oxo-manganese species, which was confirmed by in situ UV-vis spectroscopy.

In Vivo Participation of Artificial Porphyrins in Electron-Transport Chains: Electrochemical and Spectroscopic Analyses of Microbial Metabolism

The effects of artificial porphyrins on the electron-transport chains of living microbes were investigated. The participation of porphyrins in the microbial electron-transport chains was demonstrated by spectroscopic and current-generation measurements. Large enhancement of the microbial current generation was accomplished by adding a cationic water-soluble manganese porphyrin as an electron mediator.

Chlorite Dismutation to Chlorine Dioxide Catalyzed by a Water‐Soluble Manganese Porphyrin

Chloride oxyanions are of interest because of their use as disinfectants and concerns over their accumulation in the environment. A water-soluble manganese porphyrin catalyzes the dismutation of chlorite (ClO2−) to chlorine dioxide (ClO2) through a series of electron- and atom-transfer reactions. A high-valent manganese(IV) oxo species is observed and the ClO2 product inhibits the reaction.

A “Push−Pull” Mechanism for Heterolytic O−O Bond Cleavage in Hydroperoxo Manganese Porphyrins

A water-soluble manganese porphyrin, 5,10,15,20-tetrakis-(1,3-dimethylimidazolium-2-yl)porphyrinatomanganese(III) (Mn(III)TDMImP) is shown to react with H(2)O(2) to generate a relatively stable dioxomanganese(V) porphyrin complex (a compound I analog). Stopped-flow kinetic studies revealed Michaelis Menton-type saturation kinetics for H(2)O(2). The visible spectrum of a compound 0 type intermediate, assigned as Mn(III)(OH)(OOH)TDMImP, can be directly observed under saturating H(2)O(2) conditions (Soret band at 428 nm and Q bands at 545 and 578 nm). The rate-determining O-O heterolysis step was found to have a very small activation enthalpy (ΔH(≠) = 4.2 ± 0.2 kcal mol(-1)) and a large, negative activation entropy (ΔS(≠) = -36 ± 1 cal mol(-1) K(-1)). The O-O bond cleavage reaction was pH independent at 8.8 < pH < 10.4 with a first-order rate constant of 66 ± 12 s(-1). These observations indicate that the O-O bond in Mn(III)(OH)(OOH)TDMImP is cleaved via a concerted "push-pull" mechanism. In the transition state, the axial (proximal) (-)OH is partially deprotonated ("push"), while the terminal oxygen in (-)OOH is partially protonated ("pull") as a water molecule is released to the medium. This mechanism is reminiscent of O-O bond cleavage in heme enzymes, such as peroxidases and cytochrome P450, and similar to the fast, reversible O-Br bond breaking and forming reaction mediated by similar manganese porphyrins. The small enthalpy of activation suggests that this O-O bond cleavage could also be made reversible.

Highly efficient controllable oxidation of alcohols to aldehydes and acids with sodium periodate catalyzed by water-soluble metalloporphyrins as biomimetic catalyst

Highly efficient controllable oxidation of alcohols to aldehydes or acids by sodium periodate in the presence of water-soluble manganese porphyrins (meso-tetrakis(N-ethylpyridinium-4-yl)manganese porphyrin, MnTEPyP) with different reaction media has been reported. The manganese porphyrin showed excellent activity for the controllable oxidation of various alcohols under mild conditions. Moreover, different factors influencing alcohol oxidation, for example, oxidant, catalyst amount, temperature, and solvent, have been investigated. A plausible mechanism for the controllable oxidation of alcohol has been proposed.

Water exchange rates of water-soluble manganese(iii) porphyrins of therapeutical potential

The activation parameters and the rate constants of the water-exchange reactions of Mn(III)TE-2-PyP(5+) (meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin) as cationic, Mn(III)TnHex-2-PyP(5+) (meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin) as sterically shielded cationic, and Mn(III)TSPP(3-) (meso-tetrakis(4-sulfonatophenyl)porphyrin) as anionic manganese(iii) porphyrins were determined from the temperature dependence of (17)O NMR relaxation rates. The rate constants at 298 K were obtained as 4.12 x 10(6) s(-1), 5.73 x 10(6) s(-1), and 2.74 x 10(7) s(-1), respectively. On the basis of the determined entropies of activation, an interchange-dissociative mechanism (I(d)) was proposed for the cationic complexes (DeltaS(double dagger) = approximately 0 J mol(-1) K(-1)) whereas a limiting dissociative mechanism (D) was proposed for Mn(III)TSPP(3-) complex (DeltaS(double dagger) = +79 J mol(-1) K(-1)). The obtained water exchange rate of Mn(III)TSPP(3-) corresponded well to the previously assumed value used by Koenig et al. (S. H. Koenig, R. D. Brown and M. Spiller, Magn. Reson. Med., 1987, 4, 52-260) to simulate the (1)H NMRD curves, therefore the measured value supports the theory developed for explaining the anomalous relaxivity of Mn(III)TSPP(3-) complex. A magnitude of the obtained water-exchange rate constants further confirms the suggested inner sphere electron transfer mechanism for the reactions of the two positively charged Mn(iii) porphyrins with the various biologically important oxygen and nitrogen reactive species. Due to the high biological and clinical relevance of the reactions that occur at the metal site of the studied Mn(iii) porphyrins, the determination of water exchange rates advanced our insight into their efficacy and mechanism of action, and in turn should impact their further development for both diagnostic (imaging) and therapeutic purposes.

Cyclic voltammetry of water-soluble manganese porphyrins in the presence of cyclodextrins

The addition of cyclodextrins (α-CD, β-CD, 2-hydroxopropyl-β-CD and γ-CD) to aqueous solutions of representative cationic ( MnTMPyP ) and anionic ( MnTPPS 4) water-soluble Mn porphyrins only substantially affect the behavior of the Mn (III)/ Mn (II) couple when inclusion complexes (i.e. for MnTPPS 4) are formed. The voltammetric responses were interpreted under the assumption that the inclusion complexes are electroactive, which occurs after their adsorption on the electrode surface. In addition, the results point to a higher affinity of the cyclodextrins for Mn II TPPS 4 than for Mn III TPPS 4.

Decoloration of Azo Dyes by Hydrogen Peroxide Catalyzed by Water-Soluble Manganese Porphyrins

Water-soluble manganese porphyrins are catalysts for the decoloration of azo dyes by hydrogen peroxide under mild conditions (pH 8.0 and 25°C). The decoloration rate depends on the structure of the manganese porphyrin and the added ligands.

Biomimetic degradation of lignin and lignin model compounds by synthetic anionic and cationic water soluble manganese and iron porphyrins

The biomimetic oxidation of 5-5′ condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is reported. The oxidative efficiency of manganese and iron meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin chloride (TDCSPPMnCl and TDCSPPFeCl, respectively), meso-tetra-3-sulphonatophenyl porphyrin chloride (TSPPMnCl) and manganese meso-tetra(N-methylpyridinio)porphyrin pentaacetate (TPyMePMn(CH3COO)5) was compared on the basis of the oxidation extent of the models tested. Manganese porphyrins were found more effective in degrading lignin substructures than iron ones. Among them the cationic TPyMePMn(CH3COO)5, never used before in lignin oxidation, showed to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. The use of quantitative 31P NMR allowed the focusing on the occurrence of different degradative pathways depending on the catalyst used. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and carboxylic acids. Noteworthy, no significant condensation reactions occurred during manganese porphyrins catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins a substantial increase of condensed substructures was detected.

New non-ionic water-soluble porphyrins: evaluation of manganese(III) polyhydroxylamide porphyrins as MRI contrast agents

A new series of metalloporphyrins (M = zinc(II) and manganese(III)), utilizing polyhydroxylamide substituents to achieve water solubility, has been synthesized and spectroscopically characterized. Two of these compounds, [Mn III(TPPAS)Cl] and (Mn III (TPPIS)Cl], have been evaluated as potential MRI contrast enhancement agents. The water proton magnetic relaxation rate, (1/ T 1), of aqueous [Mn III(TPPAS)Cl] solutions has been measured as a function of field strength over the range of Larmor frequencies from 0.01 to 30 MHz. Results show a typical relaxation rate pattern, similar to other water-soluble manganese (III) porphyrin compounds, over this frequency range. Conductivity and osmolality measurements for [Mn III(TPPAS)Cl] in water demonstrate complete dissociation of the chloride ion to yield [Mn III(TPPAS)(H 2O) 2) +. The two axial water ligands provide a reasonable explanation as to the source of the greater than expected proton relaxation rate of manganese(III) porphyrin compounds, in general. Variable-temperature NMR studies of the H 2TPPAS and H 2TPPIS free ligands reveal the occurrence of proton tautomerism, as indicated by two temperature dependent H β pyrrole proton signals. Actual magnetic resonance images of Sprague-Dawley rats, to which [Mn III(TPPAS))Cl] had been administered, showed significant image enhancement in the heat, liver, lungs and gastrointestinal tract. However, with an acute toxicity of 0.1 mmol kg −1, the cationic [Mn III(TPPAS)(H 2O) 2] + compound is too toxic for clinical use.

Electrocatalytic oxidation of alkenes by water-soluble manganese porphyrins in aqueous media: a comparison of the reaction products at different oxidation states

Manganese(III) tetrakis(N-methyl-4-pyridyl)porphine (MnTMPyP) is water-soluble and exhibits a reversible MnIII/II redox couple in acidic solutions. However, the MnIV/III couple cannot be seen by cyclic voltammetry in aqueous solutions of pH < 8. Spectroelectrochemical methods have shown that (H2O)MnIIITMPyP undergoes a one-electron oxidation with slow heterogeneous electron transfer rate to form OMnIITMPyP, which then oxidizes cyclopent-2-ene-1-acetic acid (1) catalytically to give cyclopent-2-ene-4-one-1-acetic acid (2). Further electrochemical oxidation of OMnIVTMPyP causes the deactivation of the catalyst, presumably due to porphine ring degradation. A sterically hindered porphyrin, manganese(III) tetrakis(sulfonatomesityl)porphine (MnTSMP), is first oxidized at the morphine ring and is stable as a radical cation (H2O)MnIIITSMP+. in pH < 2 solutions. In pH 8.5 buffer solutions, MnIIITSMP is oxidized totally by two electrons at Eappl = + 1.05 V. The electrogenerated OMnIVTSMP+. reacts rapidly with 1 to give 2 and cyclopent-2,3-diol-1-acetic acid (3). The reaction mechanisms are proposed.