Series Of Metalloporphyrins Research Articles

How the macrocyclic precursors influence the M-N-C catalysts? Preparation and their applications on the electrochemically catalyzed hydrogen evolutions

Herein, a series of metallo-porphyrins, corroles and phthalocyanines were applied as the key precursors to confirm the influence of macrocyclic cores on the preparation of single- and dual-metal nitrogen-doped carbon (M-N-C) catalysts, and the control the M-N-C catalyst preparation towards accelerating electrocatalyzed hydrogen evolutions could be rationally modulated. Due to the synergetic effect, the dual-metal Co0.97Cu0.03TPP@rGO-900 M-N-C catalyst has the best performance on the electrochemically catalyzed hydrogen evolution with onset potentials as −166 mV and Tafel 117 mV·dec−1. More importantly, these M-N-C catalysts could also be used in a wide range of pH values, such as PBS and KOH medias.

Metalloporphyrin-Decorated Titanium Dioxide Nanosheets for Efficient Photocatalytic Carbon Dioxide Reduction.

In photocatalysis, the most efficient way to separate photogenerated electron-hole pairs has been extensively studied. However, the methods to increase the quantities of free electrons are neglected. Herein, we used a self-assembly method to fabricate MTCPP/TiO2 composite materials with a series of metalloporphyrins (MTCPPs, M = Fe, Co, Zn) as sensitizers to modify TiO2 nanosheets. First, abundant carboxyl and hydroxyl on porphyrin were adsorbed by metal ions. Then, the remaining carboxyl and hydroxyl on porphyrin were anchored on the surface of TiO2 nanosheets. Finally, MTCPP/TiO2 was obtained by a layer-by-layer self-assembly process. MTCPP broadens the light response of TiO2 from ultraviolet light to visible light and enhances the CO2 adsorption ability. Moreover, metal ions coordinating with porphyrin regulate the electron density of the porphyrin ring and provide a stronger π feedback bond, which promote charge separation. Consequently, by optimizing the type of metal ion, the yield of ZnTCPP/TiO2 composites reached 109.33 μmol/(g h) of CO and 9.94 μmol/(g h) of CH4, which was more than 50 times that of pure TiO2. This study proposes a possible visible-light-induced CO2 reduction mechanism of metal-ion-based photocatalysis, which provides great insights into optimizing the designation of efficient photocatalysis.

An Undergraduate Experiment Using Microwave-Assisted Synthesis of First Raw Metalloporphyrins: Characterizations and Spectroscopic Study

There is a notable absence in the practical inorganic curricula for experiments in which students can synthesize and characterize series of inorganic complexes. This is possibility attributed to the long required time which is not normally available in regular lab sessions. To address this absence, this paper describes a two-part experiment for chemistry major students in which they prepare series of metalloporphyrins using microwave-assisted technique. In addition to its attractive simplicity, microwave-assisted preparation substantially reduces the needed reaction time to suit the lab session duration. The first lab session is dedicated to the characterization of the 5,10,15,20-tetraphenylporphyrin (TPP) as well as the synthesis of the corresponding Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes. The second session involves the spectroscopic characterization (UV-vis, 1H-NMR, and IR) of the prepared metalloprophyrins. The students relate the experimental results with the provided theoretical data based on quantum chemical calculations.

Achieving anti-oxygen-interference temperature sensing using phosphorescent metalloporphyrins

A temperature-sensing method immune to oxygen interference is established based on phosphorescent metalloporphyrins on regenerated cellulose (RC). A series of metalloporphyrins (hematoporphyrin monomethyl ether coordinated to Pd, Gd, and Lu ions: Pd-, Gd-, and Lu-HMME) are designed to be embedded in RC. The phosphorescence emissions of these metalloporphyrins are effectively enhanced on RC, affording phosphorescence quantum yields of 1.8%, 3.3%, and 2.2%, respectively. The phosphorescence emissions of these metalloporphyrins on RC (metalloporphyrins/RC) are independent of oxygen concentration because RC provides an oxygen-impermeable microenvironment. Meanwhile, the phosphorescence emissions are effectively quenched with increasing temperature. The phosphorescence lifetimes also decrease with temperature, indicating an increase in non-radiative relaxation, which weakens phosphorescence emission. The oxygen-independence and temperature-dependence of these metalloporphyrins/RC reveal that they could serve as promising anti-oxygen-interference temperature indicators. Temperature-response plots are obtained in the range from −75 to 50 °C. The temperature sensitivities of Pd-, Gd-, and Lu-HMME on RC are evaluated to be 0.50, 0.28, and 0.36%/°C based on the temperature-response plots. The temperature resolution values of Pd-, Gd-, and Lu-HMME on RC are 0.5, 1.3, and 1.2 °C. These temperature indicators have high photostability under extended irradiation, making them suitable for practical use. The method offers attractive new insights into phosphorescent temperature-sensing materials and the development of oxygen sensors with temperature compensation.

Can MP(P)4 Compounds Form Complexes with C60?

Numerous complexes between versatile derivatives of metalloporphyrins MP (with M being Mn, Co, Ni, Cu, Zn and Fe) and C60 have been synthesized and characterized recently. Favorable van der Waals attractions between the curved p-surface of the fullerene and the planar p-surface of MP assist in the supramolecular recognition, overcoming the necessity of matching a concave-shaped host with a convex-shaped guest structure. Recently, we reported the computational studies of the structures and electronic properties of the series of metalloporphyrins where all the four pyrrole nitrogen atoms are replaced with P-atoms, MP(P)4, M = Sc-Zn. Motivated by the numerous examples of the complex formation between regular planar or quasi-planar MP and C60, we computationally investigated possibility of the complex formation between two MP(P)4 species, ZnP(P)4 and NiP(P)4, and C60 without any linkers, using the CAM-B3LYP/6-31G* approach, both in the gas phase and with implicit effects from C6H6. We found that the binding energies in the MP(P)4-C60 complexes for these two MP(P)4 compounds are relatively low, ca. 1-1.6 kcal/mol and ca. 5 kcal/mol for M = Zn and Ni, respectively. The ZnP(P)4 species was found to be noticeably distorted in the ZnP(P)4-C60 complex whereas NiP(P)4 inside the NiP(P)4-C60 complex essentially retained its bowl-like shape. Thus, we showed the possibility of the formation of complexes between MP(P)4 species and C60 without any linkers and showed dependence of the complex stability on the transition metal M. Further investigations are in progress.

Enhancement of the room temperature phosphorescence of metalloporphyrins using imidazole as a triplet state protector

The enhancement of the room-temperature phosphorescence (RTP) emissions of phosphorescent metalloporphyrins is critical toward extending their applications in many fields. Imidazole is widely used as a molten solvent in the synthesis of metalloporphyrins and can influence their RTP emissions. Here, the effects of imidazole on the RTP emissions of a series of metalloporphyrins (hematoporphyrin monomethyl ether coordinated to gadolinium (Gd-HMME), lutetium (Lu-HMME), and palladium (Pd-HMME) ions) were studied. It was found that imidazole effectively enhanced the RTP emissions of these metalloporphyrins both on a solid matrix and in solution. For metalloporphyrins on a solid matrix (filter paper), the RTP intensities of samples immersed in an imidazole solution were much higher than those immersed in methanol. Imidazole enhanced the phosphorescence quantum yields (ΦP) of Gd-, Lu- and Pd-HMME on filter paper by 23-, 5.0-, and 3.5-fold, respectively. For metalloporphyrins in solution (methanol), the RTP intensities increased gradually with the concentration of imidazole. These results indicate that imidazole has potential as an RTP enhancer by protecting the triplet states of phosphorescent metalloporphyrins.

Pre-clinical therapeutic development of a series of metalloporphyrins for Parkinson's disease

Reactive oxygen species are a well-defined therapeutic target for Parkinson's disease (PD) and pharmacological agents that catalytically scavenge reactive species are promising neuroprotective strategies for treatment. Metalloporphyrins are synthetic catalytic antioxidants that mimic the body's own antioxidant enzymes i.e. superoxide dismutases and catalase. The goal of this study was to determine if newly designed metalloporphyrins have enhanced pharmacodynamics including oral bioavailability, longer plasma elimination half-lives, penetrate the blood brain barrier, and show promise for PD treatment. Three metalloporphyrins (AEOL 11216, AEOL 11203 and AEOL 11114) were identified in this study as potential candidates for further pre-clinical development. Each of these compounds demonstrated blood brain barrier permeability by the i.p. route and two of three compounds (AEOL 11203 and AEOL 11114) were orally bioavailable. All of these compounds protected against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity, including dopamine depletion in the striatum, dopaminergic neuronal loss in the substantial nigra, and increased oxidative/nitrative stress indices (glutathione disulfide and 3-nitrotyrosine) in the ventral midbrain of the mice without inhibiting MPTP metabolism. Daily therapeutic dosing of these metalloporphyrins were well tolerated without accumulation of brain manganese levels or behavioral alterations assessed by open field and rotarod tests. The study identified two orally active metalloporphyrins and one injectable metalloporphyrin as clinical candidates for further development in PD.

Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation.

The heme oxygenase-1 (HO-1) enzyme system remains an attractive therapeutic target for the treatment of inflammatory conditions. HO-1, a cellular stress protein, serves a vital metabolic function as the rate-limiting step in the degradation of heme to generate carbon monoxide (CO), iron, and biliverdin-IXα (BV), the latter which is converted to bilirubin-IXα (BR). HO-1 may function as a pleiotropic regulator of inflammatory signaling programs through the generation of its biologically active end products, namely CO, BV and BR. CO, when applied exogenously, can affect apoptotic, proliferative, and inflammatory cellular programs. Specifically, CO can modulate the production of proinflammatory or anti-inflammatory cytokines and mediators. HO-1 and CO may also have immunomodulatory effects with respect to regulating the functions of antigen-presenting cells, dendritic cells, and regulatory T cells. Therapeutic strategies to modulate HO-1 in disease include the application of natural-inducing compounds and gene therapy approaches for the targeted genetic overexpression or knockdown of HO-1. Several compounds have been used therapeutically to inhibit HO activity, including competitive inhibitors of the metalloporphyrin series or noncompetitive isoform-selective derivatives of imidazole-dioxolanes. The end products of HO activity, CO, BV and BR may be used therapeutically as pharmacologic treatments. CO may be applied by inhalation or through the use of CO-releasing molecules. This review will discuss HO-1 as a therapeutic target in diseases involving inflammation, including lung and vascular injury, sepsis, ischemia-reperfusion injury, and transplant rejection.

Coordination of a neutral thiazyl radical to Co(II) tetraphenylporphyrin

The 1,2,3,5-dithiadiazolyl radicals (R-CNSSN) are of considerable interest due to their potential as building blocks for materials with interesting magnetic or conducting properties. The behaviour of these neutral radicals as ligands has also been investigated [1]. Reactions with Pt(0) and Pd(0) have been shown to yield complexes where coordination to the metal is through sulfur, and the S-S bond in the radical is broken [2]. More recent work has shown that coordination through the radical nitrogen is possible with 2'-pyridyl-substituted dithiadiazolyl in combination with strongly electron-withdrawing ligands. Several of these complexes show magnetic coupling between the radical and the metal centre [3]. We have recently begun investigating the coordination of dithiadiazolyls to metalloporphyrins. The crystal structure of a coordination polymer formed between 4-(4'-pyridyl)-1,2,3,5-dithiadiazolyl and cobalt(II) tetraphenylporphyrin has been determined. The radical in this complex is coordinated through one sulfur atom, a coordination mode for dithiadiazolyls that has not previously been observed. Formation of the complex in solution has been investigated using EPR and UV-vis. Irradiation of a solution of the diamagnetic complex with intense white light leads to homolysis of the radical-ligand bond, observed by EPR. Our investigations of complex formation involving other dithiadiazolyl derivatives with a series of metalloporphyrins will also be presented.

DFT/TD-DFT studies on structural and spectroscopic properties of metalloporphyrin complexes: A design of ruthenium porphyrin photosensitizer

Given their efficacy in photosynthesis, a series of metalloporphyrins were examined using density functional theory (DFT) and time-dependent DFT. An experimentally known zinc porphyrin has been calculated to evaluate performance of various functionals, basis sets, computational models of solvent effect and solvent sorts. With an alternative approach, absorption spectra of complexes (MLx, M=Zn, Cd and Hg, x=1–4) varying substituted porphyrin Lx and metal center were investigated. It was shown that the strongest peak at about 400nm for MLx was attributed to the intra-porphyrin π→π* transition. Substitution of benzoic acid at the β-position of porphyrin core allows an extra intense peak at 450nm in ML3 and ML4, but ML2 with the meso-substituted benzoic acid only displays some very weak low-energy absorptions. Additionally, we theoretically designed [Ru(NCS)2Lx]2− and expected their possession of advantages of polypyridyl ruthenium and porphyrin-based sensitizers. The present study reveals that the L4 complex, [Ru(NCS)2L4]2−, exhibits extra intense absorption peaks at 500 and 582nm, allowing for its promising application in dye-sensitized solar cells (DSSCs).

Hetero-multimetallic Tetrakis(SCS-pincer palladium)−(Metallo)porphyrin Hybrids. Tunable Precatalysts in a Heck Reaction

A series of meso-tetrakis(SCS-pincer PdCl)−(metallo)porphyrin hybrids have been synthesized using two distinct synthetic routes. Manganese and nickel were introduced into the porphyrin macrocycle prior to peripheral electrophilic palladation, whereas magnesium was introduced thereafter in light of its acid sensitivity. When these complexes were used as precatalysts in the Heck reaction between iodobenzene and styrene, different catalytic activities were observed for each hybrid complex. The catalytic activity increased for the metalloporphyrin series MnCl < 2H < Ni < Mg, which interestingly coincides with an increase of electron richness of the porphyrin ring. Control experiments on model compounds confirmed that an intramolecular effect rather than an intermolecular effect was responsible for this influence. We postulate that, in analogy with related NCN-pincer metal complexes, the electron density on the palladium atom in SCS-pincer palladium complexes is influenced by the electronic properties of the para-substituent, i.e., the metalloporphyrin in this case. This in turn influences the rate of palladium leaching and, hence, of catalysis.

Remote site photosubstitution in metalloporphyrin–rhenium tricarbonylbipyridine assemblies: photo-reactions of molecules with very short lived excited states

The synthesis is reported of a series of metalloporphyrins (and the corresponding free-base porphyrin), mono-meso-substituted with a bipyridyl group via an amide link at the 4-position of one phenyl group: [Re(CO)(3)(Pic)Bpy-MTPP][OTf], where M = Mg, Zn, Pd or 2H, Pic = 3-picoline, Bpy = 2,2'-bipyridine, TPP = tetraphenylporphyrin. The photochemical reactions of the assemblies with the sacrificial electron donor triethylamine have been investigated by IR spectroscopy and compared to the behaviour of analogues of the type Bpy-MTPP without rhenium. Selective long-wavelength irradiation of the metalloporphyrin unit in the presence of excess picoline leads to reduction at the rhenium bipyridine centre. In the absence of 3-picoline, the latter is not reduced, but substituted by added halide or by the THF solvent. Mechanistic analysis highlights the differences between the zinc and magnesium chelate on the one hand and the palladium porphyrin on the other. The free-base assembly, [Re(CO)(3)(Pic)Bpy-H(2)TPP][OTf] is unreactive. The zinc and magnesium porphyrin assemblies initially coordinate Et(3)N before undergoing photo-induced inner-sphere electron transfer from the triethylamine to form a charge-shifted excited state of the assembly. In contrast, the palladium-based dyad reacts via outer-sphere reductive quenching of a porphyrin-based excited state. The substitution products are postulated to form by a mechanism involving an electron-transfer chain.

Porphyrin—Aminoquinoline Conjugates as Telomerase Inhibitors.

A series of metalloporphyrins was prepared in order to target the G-quadruplex structure of telomeric DNA for the design of antitelomerase compounds. The initial cationic tetramethylpyridiniumyl porphyrin was modified by the replacement of one or two methylpyridiniumyl groups by one or two 4-aminoquinoline moieties, at the meso position, in order to increase the cell penetration and the quadruplex affinity. The porphyrins were either metallated by manganese or by nickel. The degradation of quadruplex DNA was assayed in vitro with the manganese redox-active derivatives. All porphyrins complexes were capable of inhibiting the telomerase enzyme with IC50 values in the micromolar range (TRAP assay).

Porphyrin-aminoquinoline conjugates as telomerase inhibitors.

A series of metalloporphyrins was prepared in order to target the G-quadruplex structure of telomeric DNA for the design of antitelomerase compounds. The initial cationic tetramethylpyridiniumyl porphyrin was modified by the replacement of one or two methylpyridiniumyl groups by one or two 4-aminoquinoline moieties, at the meso position, in order to increase the cell penetration and the quadruplex affinity. The porphyrins were either metallated by manganese or by nickel. The degradation of quadruplex DNA was assayed in vitro with the manganese redox-active derivatives. All porphyrins complexes were capable of inhibiting the telomerase enzyme with IC50 values in the micromolar range (TRAP assay).

Electrochemical metalloporphyrin-catalyzed reduction of chlorite.

We measured the redox stoichiometry and rate constants for the electrochemical reduction of ClO(2)(-) at pH 7, catalyzed by a series of metalloporphyrins of Mn, Fe, and Co with different proximal and distal environments. A clean four-electron reduction was observed. The catalytic activity correlates well with that observed in reduction of H(2)O(2). The axial imidazole and/or a redox-active distal metal (Cu or Co) increases the turnover frequency in several compounds. The metalloporphyrins were inert to ClO(x)(-) (x = 3,4) and IO(3)(-) but catalyzed facile two-electron reduction of IO(4)(-); six-electron reduction of BrO(3)(-) was also observed.

Matrix assisted laser desorption/ionisation (MALDI)-TOF mass spectrometry of supramolecular metalloporphyrin assemblies: a survey †

Analysis of a representative series of metalloporphyrins and of their supramolecular assemblies using laser desorption/ionisation time of flight mass spectrometry (LDI-TOF MS) revealed that non-covalent metal–ligand interactions in the complexes remain effective in the gas phase. Detectable assemblies range from simple ruthenium( II) porphyrin complexes with N- or P-donor ligands, or tin( IV) and zirconium( IV) porphyrin complexes with O-donor ligands, up to trimeric arrays. Crucial to successful recording of intact complexes is avoiding protic matrices which interfere with Lewis acidic analytes and which may induce ligand exchange reactions to form complexes with the matrix itself. Also described is the in situ generation of a series of ruthenium( II) porphyrin dimers via laser induced vaporisation of the corresponding monomers and the suppression of dimerisation by nitrogen and phosphorus ligands. Careful adjustment of instrument parameters such as incident laser energy requires special attention. Relative affinities in complexation reactions are found to be consistent with liquid phase chemistry, therefore LDI-MS can provide a fast and simple, yet effective screening method for reactivity exploration. However, it also induces side-reactions such as iodine abstraction/transfer reactions. Furthermore, structurally different porphyrins show variations up to 90% in relative ion formation. Extreme caution is therefore required in the interpretation, and particularly in the quantitation, of such mass spectra.

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.

Synthesis and Properties of Metalloporphyrin Monolayers and Stacked Multilayers Bound to an Electrode via Site Specific Axial Ligation to a Self-Assembled Monolayer

A general method has been developed for the immobilization of metalloporphyrins at a gold electrode surface coated with a self-assembled monolayer (SAM). SAMs containing imidazole-terminated adsorbates are shown to bind a series of metalloporphyrins, including bis-acetonitrile octaethylporphyrinatoruthenium(II), Ru(OEP)(CH3CN)2; bis-acetonitrile octaethyltetraazaporphyrinato ruthenium(II), Ru(OETAP)(CH3CN)2; bis-acetonitrile tetra-(p-chlorophenyl)porphyrinatoruthenium(II), Ru(Tp-ClPP)(CH3CN)2; bis-acetonitrile octaethylporphyrinatoosmium(II), Os(OEP)(CH3CN)2; and carbonyl meso-tetramesitylporphyrinatoruthenium(II), Ru(TMP)(CO). The SAM/metalloporphyrin films have been characterized by optical ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy, grazing angle FT-IR spectroscopy, transmission visible spectroscopy, and electrochemistry. The results indicate that the metalloporphyrins are chemisorbed via axial ligand substitution of the metal center with the porphyrin ring parallel to the surface and the second axial ligand position normal to the surface. Scanning tunneling microscopy images of Ru(TMP)(CO) bound to the SAM corroborate this model. Axial ligation of metalloporphyrins to SAMs serves as the basis for an iterative, defined approach to the preparation of stacked single component and mixed metalloporphyrin multilayers on SAMs. In these materials, the bidentate ligand pyrazine serves as a bridge between successive metalloporphyrins in the stacks.

Comparison of metalloporphyrins interacting with DNA

AbstractA series of metalloporphyrins (CuTMpyP, CuTMAP. CuTPPS, NiTMpyP, ZnTMpyP and CdTMpyP) reacting with DNA were compared. The interaction of metalloporphyrin with DNA shows different binding modes and electrochemical behavior when either the metal ion or porphyrin ligand is different. Due to electrostatical repulsion interaction between the anionic substitute group and a phosphate group on DNA molecular backbone, it is difficult for the anionic porphyrin to interact with DNA. The ability of cationic porphyrins to react with DNA depends on the size of the substitute group and the metal ion in the porphyrin plane center. Metalloporphyrin with or without axial ligand, which depends on the metal ion, results in outside binding or intercalating modes, and shows different interaction capability with DNA. The conditional binding constants of NiTMpyP, CuTMpyP and CuTMAP, which mainly show intercalating mode to DNA, were evaluated.

Electron Transfer Function of Metalloporphyrins and Their Fixation in Polymer Gel Beads for Constructing Hydrogen Evolution System.

Two series of metalloporphyrins, meso-tetra(p-sulfonatephenyl) porphine and meso-tetra (p-carboxyphenyl) porphine were prepared as their manganese-, tin-, and zinc-complexes for purpose of their fixation in polymer beads. The functions of these metalloporphyrins as an electron carrier instead of viologen derivatives and/or a photosensitizer for constructing the photoinduced hydrogen evolution system were investigated both in free and in polymer-fixed systems. Manganese- and tin-porphyrins could be photoreduced by zinc-porphyrins in the presence of electron donor, and hydrogen was generated efficiently in the system applying tin-porphyrin as an electron carrier in aqueous solutions. Among the beads-fixed heterogeneous systems, only metalloporphyrins/chitosan gel beads could act in the photoinduced hydrogen evolution system.