Oxomanganese Porphyrin Research Articles

Screening of different interactions in oxo-manganese porphyrin dimers containing axial N-donor ligands: a theoretical study.

A theoretical analysis for describing the dimeric assemblies of high-valent manganese(v)-oxo meso-tetraphenylporphyrin (TPP) ([(TPP)MnVO]22+) and meso-tetrakis(pentafluorophenyl)porphyrin (TPFPP) ([(TPFPP)MnVO]22+) in the presence of axial N-donor ligands is presented. Our theoretical results revealed two types interactions in dimers: a sandwich-like interaction between phenyl rings of porphyrin molecules, and a non-bonded T-shape interaction between nitrogen donors attached to Mn centers. The curvature in the geometry of porphyrin in the [(TPP)MnVO]22+/N-donor system is significantly smaller than that of [(TPFPP)MnVO]22+/N-donor system. Moreover, the Mn–N(ax) distances in [(TPFPP)MnVO]22+/N-donor system are shorter than those of [(TPP)MnVO]22+/N-donor system. Also, the donor–acceptor interaction between the imidazoles and the Mn centers are stronger than those of the other ligands in both porphyrins. These results are supported by atoms in molecules (AIM) and natural bond orbital (NBO) analysis.

The pKa value of the proximal water molecule trans to a high-valent MnV[double bond, length as m-dash]O porphyrin: towards the control of reactivity by pH.

The high-valent manganese-oxo species of Mn-TMPyP4 porphyrin interacts in the minor grooves of AT-rich regions of DNA and mediates hydroxylation of C-H bonds of deoxyribose leading to DNA break. The reaction was observed at different pHs. It is shown that the hydroxylation was not efficient at low pH (pH 6) while it worked well at higher pH (pH 8). Deprotonation of the coordinated water molecule, trans to the manganese-oxo entity, into a hydroxide anion drives high-valent manganese-oxo porphyrin toward hydroxylation at pH > 7.

Cumulant Approximated Second-Order Perturbation Theory Based on the Density Matrix Renormalization Group for Transition Metal Complexes: A Benchmark Study.

The complete active space second order perturbation theory (CASPT2) can be extended to larger active spaces by using the density matrix renormalization group (DMRG) as solver. Two variants are commonly used: the costly DMRG-CASPT2 with exact 4-particle reduced density matrix (4-RDM) and the cheaper DMRG-cu(4)-CASPT2 in which the 4-cumulant is discarded. To assess the accuracy and limitations of the latter variant DMRG-cu(4)-CASPT2 we study the spin state energetics of iron porphyrin Fe(P) and its model compound FeL2, a model for the active center of NiFe hydrogenase, and manganese-oxo porphyrin MnO(P)(+); a series of excited states of chromium hexacarbonyl Cr(CO)6; and the interconversion of two Cu2O2(2+) isomers. Our results clearly show that PT2 on top of DMRG is essential in order to obtain quantitative results for transition metal complexes. Good results were obtained with DMRG-cu(4)-CASPT2 as compared to full CASPT2 and DMRG-CASPT2 in calculations with small- and medium-sized active spaces. In calculations with large-sized active spaces (∼30 active orbitals), the performance of DMRG-cu(4)-CASPT2 is less impressive due to the errors originating from both the finite number of renormalized states m and the 4-RDM approximation.

(Invited) Oxidation Chemistry of Manganese Porphyrins in Interaction with DNA

Metalloporphyrins associated with oxygen atom donors are biomimetic models of heme, enzymes such as cytochrome P450 and peroxidases. Some cationic porphyrins recognize DNA (double-stranded DNA and G-quadruplex DNA) with high specificity and selectivity. In aqueous buffer manganese porphyrins are activated by oxone. Two examples of oxidation reactions mediated by cationic manganese porphyrins in complex with DNA will be presented. Oxidation can be directed toward DNA and results in highly selective DNA damage (i) or may be directed toward oxidation of small molecules in a heme DNAzyme context (ii). DNA damage mediated by manganese porphyrins allowed a better understanding of the reactivity of high-valent metal-oxo species. The reaction pathway (electron abstraction versus oxygen atom transfer) depends on the protonation state of the water molecule present as axial ligand trans to the metal-oxo. The analysis of the reaction products of a manganese porphyrin in complex with G-quadruplex DNA gives insights on the mode of interaction of the porphyrin with DNA. - Interaction of cationic manganese porphyrin with G-quadruplex nucleic acids probed by differential labeling of the two faces of the porphyrin V. Pradines, G. Pratviel Angew. Chem. Int. Ed. 52, 2185-2188 (2013) - Protonation state of trans axial water molecule switches the reactivity of high-valent manganese-oxo porphyrin J. Trzcionka, J. Irvoas, G. Pratviel New J. Chem. 37, 3581-3590 (2013) - Porphyrins in complex with DNA: modes of interaction and oxidation reactions G. Pratviel Coord. Chem. Rev. http://dx.doi.org/10.1016/j.ccr.2015.07.003

Stereoelectronic effects of porphyrin ligand on the oxygen transfer efficiency of high valent manganese-oxo porphyrin species: A DFT study

The structure and properties of the N[Formula: see text]–Mn–O bonds of high valent manganese-oxo of the second and third generation porphyrins in the presence of imidazole have been studied by means of density functional (DFT) method with 6-31G* basis set in the gas phase as well as water solution. The geometric structures, frontier molecular orbitals, thermodynamic parameters, aromaticity indices and physical properties such as chemical potential and chemical hardness of [(TPP)(ImH)MnO][Formula: see text] and its derivatives were calculated. The obtained results showed that [(TPP)(ImH)MnO][Formula: see text] bearing halogen atoms at the [Formula: see text]-pyrrole positions had a saddle conformation with low Mn–O strength. The electron density ([Formula: see text] and Laplacian ([Formula: see text] properties at critical points of the N[Formula: see text]–Mn–O bonds, estimated by AIM calculations, indicate that Mn–O bonds in third generation porphyrins have lower [Formula: see text] and Mn–N[Formula: see text] distances have higher [Formula: see text] than the second generation ones. The calculations of aromaticity indices for chelated rings at the porphyrin center show that HOMA and NICS in third generation porphyrins are generally lower than that of second ones which is in agreement with their saddle conformation. These results are supported by natural bond orbital (NBO) analysis.

The protonation state of trans axial water molecule switches: the reactivity of high-valent manganese-oxo porphyrin

The cationic manganese porphyrin (Mn-TMPyP) was activated by an oxygen atom donor KHSO5 (oxone) to form a high-valent manganese-oxo species (MnVO) in aqueous buffer. The high-valent MnVO mediated oxidative damage of short double-stranded DNA models. The nature of the oxidation products (guanine oxidation DGh, 2Ih, imidazolone, and 2-deoxyribose oxidation, 2-deoxyribonolactone) and the mechanism of their formation varied with the pH of the reaction. Oxidation proceeded mainly through the electron transfer mechanism at pH 6 while oxygen atom transfer proved to be favored at pH 8. This was evidenced by different ratios of products arising from different mechanisms of oxidation as a function of pH but also by different mechanisms leading to the same oxidation product (DGh) as a function of pH. The reactivity shift of the active manganese-oxo species was attributed to the protonation state of the proximal water molecule as an axial ligand (trans to the oxo). A high-valent manganese-oxo in the oxo-hydroxo form (HO–MnVO) at higher pH undergoes oxygen atom transfer reactions while in the oxo-aqua form (H2O–MnVO) at lower pH it performs oxidation reactions by electron transfer. These data are an illustration of the influence of the “push” effect of the proximal ligand on the changing reactivity of high-valent metal-oxo species. They also give access to the pKa of the axially bound water molecule of manganese-oxo porphyrin.

Highly efficient photocatalytic oxygenation reactions using water as an oxygen source

The effective utilization of solar energy requires photocatalytic reactions with high quantum efficiency. Water is the most abundant reactant that can be used as an oxygen source in efficient photocatalytic reactions, just as nature uses water in an oxygenic photosynthesis. We report that photocatalytic oxygenation of organic substrates such as sodium p-styrene sulfonate occurs with nearly 100% quantum efficiency using manganese(III) porphyrins as an oxygenation catalyst, [Ru(II)(bpy)(3)](2+) (bpy = 2,2'-bipyridine) as a photosensitized electron-transfer catalyst, [Co(III)(NH(3))(5)Cl](2+) as a low-cost and weak one-electron oxidant, and water as an oxygen source in a phosphate buffer solution (pH 7.4). A high-valent manganese-oxo porphyrin is proposed as an active oxidant that effects the oxygenation reactions.

Allylic oxidation of cyclohexene catalyzed by manganese porphyrins: DFT studies

The present paper summarizes density functional theory studies on hydroxylation of cyclohexene catalyzed by manganese oxo porphyrin. The reaction is preceded by the physisorption of the substrate over the catalyst molecule at the distance of 2.18 Å. Next, a hydrogen atom form the C–H bond is abstracted by the catalyst oxo group and the cyclohexene radical is readily bound to the OH group formed at a catalyst active site. Formation of alcohol requires spin crossing on the reaction pathway. Present studies show that alcohol is formed on the catalyst active site via oxygen rebound mechanism without the cyclohexene radical dissociation. Results are compared with the data obtained earlier for epoxidation. The intermediate structures, found for both pathways, clearly indicate that each may lead to only one reaction product.

Use of Short Duplexes for the Analysis of the Sequence‐Dependent Cleavage of DNA by a Chemical Nuclease, a Manganese Porphyrin

A manganese porphyrin, manganese(III)-bis(aqua)-meso-tetrakis(4-N-methylpyridiniumyl)porphyrin, in the presence of KHSO5 is able to perform deoxyribose or guanine oxidation depending on its mode of interaction with DNA. These two reactions involve an oxygen-atom transfer or an electron transfer, respectively. The oxidative reactivity of the manganese-oxo porphyrin was compared on short oligonucleotide duplexes of different sequences. The major mechanism of DNA damage is due to deoxyribose hydroxylation at a site of strong interaction, an (A.T)3 sequence. Guanine oxidation by electron transfer was found not to be competitive with this major mechanism. It was found that a single intrastrand guanine was three orders of magnitude less reactive than an (A.T)3 sequence. The reactivity of a 5'-GG sequence was found to be intermediate and was estimated to be two orders of magnitude less than that of an (A.T)3 site. Short oligonucleotide duplexes, as double-stranded-DNA models, proved to be convenient tools for the study of the comparative reactivity of this reagent toward different sequences of DNA. However, they showed a particular reactivity at their terminal base pairs (the "end effect") that biased their modeling capacity for double-helix-DNA models.

Oxidation of hydrocarbons with iodobenzene diacetate catalyzed by manganese(III) porphyrins in a room temperature ionic liquid

Abstract Efficient methods for oxidation of alkanes and alkenes were obtained by using two manganses(III) porphyrin catalysts in combination with iodobenzene diacetate in a room temperature ionic liquid [bmim]PF6 (1-n-butyl-3-methylimidazolium hexafluorophosphate). The effects of various organic solvents on the reactions and the role of axial ligands were examined. The recyclability of the catalyst remained in the oily ionic liquid phase was also investigated. A high-valent manganese-oxo porphyrin complex (MnV = O) was considered as a reactive oxidation intermediate according to investigation by stopped-flow rapid spectroscopy.

Oxidation of alkanes catalyzed by manganese(III) porphyrin in an ionic liquid at room temperature

Efficient oxidation of alkanes is achieved by using an electron-deficient manganese(III) porphyrin catalyst in combination with iodobenzene diacetate in an ionic liquid at room temperature; a high-valent manganese-oxo porphyrin complex (Mn VO) was considered as the reactive oxidation intermediate.

Olefins epoxidation by Ph 4PHSO 5 catalyzed by manganese porphyrins: A novel mechanistic proposal

The epoxidation of three olefins, cyclooctene, styrene and cis-stilbene by Ph 4PHSO 5, catalyzed by Mn(TMP)Cl, has been studied in dichloroethane at 0°C. In the absence of imidazole the reaction does not proceed. When the axial ligand is present the oxidation provides the corresponding epoxides. Cis-stilbene stereospecifically yields cis-stilbene oxide. The epoxidation rates linearly depend on Ph 4PHSO 5 and catalyst concentrations. By increasing the axial ligand concentration the rates increase up to a plateau. This occurs when all the manganese-porphyrin has been complexed by imidazole to form the bis-coordinated adduct. Also by increasing the olefin initial concentration the rates reach a plateau. This behavior, which might be taken as evidence of the formation of a Michaelis-Menten type intermediate, is alternatively rationalized here on the basis of a balance of the rates of the various steps of the overall process. In particular it is envisaged that at high olefin concentration the oxygen transfer to the double bond from the oxo-manganese porphyrin becomes at least as fast as the oxygen transfer from Ph 4PHSO 5 to the manganese porphyrin.

Formation and reactivity toward hydrocarbons of oxomanganese porphyrins in the presence of anionic bases

In dichloroethane oxygen transfer from Ph 4PHSO 5 to manganese (III) porphyrins forming the corresponding oxo-species, which then oxidize organic substrates, occurs only in the presence of basic species acting as axial ligands. Together with neutral nitrogen bases such as pyridines and imidazole, anionic bases, i.e., CIO, SO, and CH 3CO, promote the formation of oxo-manganese porphyrin species. However, on the basis of a comparison of the spectral properties and of the oxidative behaviors towards cis-stilbene and diphenylmethane, we suggest that the oxo-species formed in the presence of anionic oxygen bases is different from that formed in the presence of neutral bases. In particular, the former is suggested to be a manganese (IV) derivative behaving as a radical oxidant.

An Electron Paramagnetic Resonance Investigation of the Reaction of Some Radical Traps with Oxomanganese Porphyrins.

The reaction of 2-methyl-N-(phenylmethylene)-2-propanamine N-oxide, 2-methyl-2-nitrosopropane and nitrosobenzene with manganese (III) porphyrins and an oxygen donor system (iodosylbenzene or sodium hypochlorite/phase-transfer catalyst) has been studied using electron paramagnetic resonance investigations. In the reaction of 2-methyl-N-(phenylmethylene)-2-propanamine N-oxide with the oxomanganese porphyrin a t-butyl radical is generated which is trapped by 2-methyl-N-(phenylmethylene)-2-propanamine N-oxide; furthermore an acylaminoxyl radical is also observed. The reaction of 2-methyl-2-nitrosopropane and nitrosobenzene with the manganese (III) porphyrins and the oxygen donor system generates the corresponding di-t-butyl- and diphenyl-aminoxyl radicals, respectively; in the case of 2-methyl-2-nitrosopropane as the substrate an acylaminoxyl radical is also detected

Ab‐initio calculations on oxomanganese porphyrin chloride. II. An explanation of its reactions with alkenes

AbstractMinimal‐basis‐set gradient‐SCF calculations on oxomanganese porphyrin chloride in which the oxygen atom bridges a metal‐nitrogen bond (Cs structure) are reported. In comparison with the earlier reported results of similar calculations on a C4v structure, a lower energy is found for the Cs structure. Electronic and steric arguments are brought forward to explain available experimental information on the reactions of the complex with alkenes.

Observations and comments on the mechanism of epoxidation of alkenes by manganese(III) porphyrins with hypochlorite.

The kinetics of olefin epoxidation in a methylene chloride/water biphase containing a phase-transfer agent with hypochlorite as oxygen transfer reagent and manganese(III) tetraphenylporphyrin catalysts has been reinvestigated. The results do not support the accumulation of an intermediate composed of an alkene and a hypervalent metaloxo porphyrin. Second-order rate constants for oxygen transfer from hypochlorite to the manganese porphyrin, comproprotionation of the hypervalent manganese-oxo porphyrin with manganese(III) porphyrin, and olefin epoxidation by the hypervalent manganese-oxo porphyrin were obtained from experiments in a wet organic monophase.

Kinetics and mechanism of oxygen transfer in the reaction of p-cyano-N,N-dimethylaniline N-oxide with metalloporphyrin salts. 5. The influence of imidazole ligation of (meso-tetrakis(2,6-dimethylphenyl)porphinato)manganese(III) chloride on the rates of oxygen transfer from N-oxide to metalloporphyrin salt and the efficiency of oxidations by the intermediate higher valent manganese-oxo species

Equilibrium constants for mono- and bisligation of imidazole (ImH) with (meso-tetrakis(2,6-dimethylphenyl)porphinato)manganese(III) chloride ((Me/sub 8/TPP)Mn/sup III/Cl) have been determined so that the concentrations (dry CH/sub 2/Cl/sub 2/) of the three species (Me/sub 8/TPP)Mn/sup III/Cl, ((Me/sub 8/TPP)Mn/sup III/(ImH))Cl, and ((Me/sub 8/TPP)Mn/sup III/(ImH)/sub 2/)Cl may be calculated at different ImH concentrations. The equilibrium constants for ligation of the one and two imidazoles are K/sub 1/ = 245 M/sup -1/ and ..beta../sub 2/ = 1.80 x 10/sup 5/ M/sup -1/. The reaction of p-cyano-N,N-dimethylaniline N-oxide (NO) with the manganese(III)porphyrin (under the pseudo-first-order conditions of (NO)/sub i/ >> ((Me/sub 8/TPP)Mn/sup III/Cl)/sub i/ and in the presence and absence of ImH) is first order in both NO and manganese(III) porphyrin, and the rate-controlling step involves oxygen transfer with formation of higher valent manganese-oxo porphyrin species plus p-cyano-N,N-dimethylaniline (DA). From the dependence of the pseudo-first-order rate constants (k/sub obsd/) upon (ImH)/sub i/ and a knowledge of the equilibrium constants for imidazole ligation there has been calculated the second-order rate constants for the kinetic terms k/sub 1/(NO)((Me/sub 8/TPP)Mn/sup III/Cl), k/sub 2/(NO)((Me/sub 8/TPP)Mn/sup III/(ImH))Cl, and k/sub 3/(NO)((Me/sub 8/TPP)Mn/sup III/(ImH)/sub 2/)Cl). Comparison of the second-order rate constants (k/sub 1/ = 3.3 x 10/sup -2/ M/sup -1/ s/sup -1/, k/sub 2/more » = 5.53 M/sup -1/ s/sup -1/, and k/sub 4/ = 7.32 x 10/sup -2/ M/sup -1/ s/sup -1/) establishes that ligation by one imidazole increases the rate of reaction of the manganese(III) porphyrin with NO by approx. 166-fold.« less