Characterization of Several Metalloporphyrins in Unusual Oxidation States. The Effect of Axial and Equatorial Ligands

The effect of axial and equatorial ligands on the generation of unusual oxidation states in metalloporphyrins is discussed. Selected examples have been taken from the literature. These include the generation of Ni(III) and Ru(III) porphyrins from Ni(II) and Ru(II) complexes containing specific axial and equatorial ligands as well as the generatoin of a Cu(I) metalloporphyrin dianion which is produced upon the overall three-electron reduction of Cu(II) tetracyanoporphyrin. Special emphasis is placed on the oxidation and reduction of σ bonded iron phenyl porphyrins. These complexes, which are stable as Fe(III), may be oxidized by a single electron to yield unstable compounds characterized as containing a great deal of Fe(IV) character, or reduced by a single electron to produce stable species which resemble, in part, radical anions of Fe(III). This singly deduced species may be described by a resonance equilibria between an Fe(III) porphyrin anion radical and an Fe(II) porphyrin anion. Likewise, the singly oxidized complex may be described by a resonance equilibria between an Fe(IV) porphyrin cation and an Fe(III) cation radical.     

Novel meso-substituted porphyrins: Synthesis, characterization and photocatalytic activity of their TiO2-based composites

Two series of novel meso-substituted porphyrins, namely 5,10,15,20-tetra[4-(3-phenoxy)-propoxy]phenyl porphyrin, the structural analogue 5,10,15,20-tetra[2-(3-phenoxy)-propoxy]phenyl porphyrin and their Co(II) Cu(II) and Zn(II) complexes were synthesized. The compounds were characterized using various spectroscopic techniques and their molecular structure was proposed based on density functional theory calculations. The diverse properties of the porphyrin derivatives result from the different stereochemistry of the particular substituents at the meso site on the macrocycle and are controlled also by the coordinated metal. The ¹H NMR spectrum of the free-base porphyrin showed a complicated spin-splitting. The photocatalytic activities in degradation of 4-nitrophenol were investigated using polycrystalline TiO₂ impregnated with the porphyrins and metalloporphyrins. The Cu(II) porphyrin was a more effective sensitizer than other metal containing compounds (M = Co, Zn) as well as the free-base. Photocatalytic activity was also influenced by spatial positions of the substitutions on the porphyrin molecules.     

Reduced texaphyrin: A ratiometric optical sensor for heavy metals in aqueous solution

We report here a water-soluble metal cation sensor system based on the as-prepared or reduced form of an expanded porphyrin, texaphyrin. Upon metal complexation, a change in the redox state of the ligand occurs that is accompanied by a color change from red to green. Although long employed for synthesis in organic media, we have now found that this complexation-driven redox behavior may be used to achieve the naked eye detectable colorimetric sensing of several number of less-common metal ions in aqueous media. Exposure to In(III), Hg(II), Cd(II), Mn(II), Bi(III), Co(II), and Pb(II) cations leads to a colorimetric response within 10 min. This process is selective for Hg(II) under conditions of competitive analysis. Furthermore, among the subset of response-producing cations, In(III) proved unique in giving rise to a ratiometric change in the ligand-based fluorescence features, including an overall increase in intensity. The cation selectivity observed in aqueous media stands in contrast to what is seen in organic solvents, where a wide range of texaphyrin metal complexes may be prepared. The formation of metal cation complexes under the present aqueous conditions was confirmed by reversed phase high-performance liquid chromatography, ultra-violet-visible absorption and fluorescence spectroscopies, and high-resolution mass spectrometry.     

Comparison of the chemical properties of iron and cobalt porphyrins and corrins

Density functional calculations have been used to compare various geometric, electronic and functional properties of iron and cobalt porphyrin (Por) and corrin (Cor) species. The investigation is focussed on octahedral M(II/III) complexes (where M is the metal) with two axial imidazole ligands (as a model of b and c type cytochromes) or with one imidazole and one methyl ligand (as a model of methylcobalamin). However, we have also studied some five-coordinate M(II) complexes with an imidazole ligand and four-coordinate M(I/II) complexes without any axial ligands as models of other intermediates in the reaction cycle of coenzyme B12. The central cavity of the corrin ring is smaller than that of porphine. We show that the cavity of corrin is close to ideal for low-spin Co(III), Co(II), and Co(I) with the axial ligands encountered in biology, whereas the cavity in porphine is better suited for intermediate-spin states. Therefore, the low-spin state of Co is strongly favoured in complexes with corrins, whereas there is a small energy difference between the various spin states in iron porphyrin species. There are no clear differences for the reduction potentials of the octahedral complexes, but [Co(I)Cor] is more easily formed (by at least 40 kJ mole(-1)) than [Fe(I)Por]. Cobalt and corrin form a strong Cobond;C bond that is more stable against hydrolysis than iron and porphine. Finally, Fe(II/III) gives a much lower reorganisation energy than Co(II/III); this is owing to the occupied d(z2) orbital in Co(II). Altogether, these results give some clues about how nature has chosen the tetrapyrrole rings and their central metal ion.     

Self-assembly of novel tris(p-carboxyphenyl) porphyrin monomer and its copolymers with acrylamide in aqueous media

The novel porphyrin monomer 5-(4-acryloyloxylphenyl)-10,15,20-tris(4-carboxyphenyl)porphyrinate zinc(II) (ZnAOTCPP) and its corresponding sodium salt (ZnAOTCPP-Na) were synthesized. The latter compound exhibited a new band in excitation spectra due to formation of porphyrin aggregates in water, which were derived from its surface-activity when the concentration was higher than its critical association concentration (CAC). The porphyrins were copolymerized with acrylamide (AM) to prepare water-soluble copolymers with random and micro-blocky structures, which all displayed very new absorption and fluorescence emission bands in the long wavelength region compared with the porphyrin monomer. Furthermore, the micro-blocky copolymer exhibited an additional new absorption band at even longer wavelength region compared with the random copolymer. The experimental results and analysis showed that the porphyrin units in the random copolymer chains self-assembled to form porphyrin association complexes by hydrophobic association and π-π stacking interactions, and covalent restrictions of polymer chains in the micro-blocky copolymer.     

Catalytic destruction of paraoxon by metallomicelle layers of Co(II) and Cr(III)

Two micellized ion complexes, Co(II) and Cr(III), were synthesized and found to possess good catalytic activity in cleaving the paraoxon/cobalt (chromate) complex phosphate ester. The complexes orm metallomicelles, which bind the substrate by coordinating with the phosphorus in the paraoxon (which is chemically similar to the nerve agents sarin and soman). Possible reasons for the acceleration include enhanced electrophilicity of the micellized metals, enhanced surface activity, and the recognized ability of cationic micelles to accelerate the cleavage of phosphate ester. The results of kinetic data (half-lives) for paraoxon degradation were 16.5 and 28.9 min in the presence of Co(II) and Cr(III) metallomicelle layers, respectively. The higher the value of the stability constant, the more stable the Co(II) and Cr(III) complexes.     

Mechanism toward Turn-on of Polysaccharide-Porphyrin Complexes for Fluorescence Probes and Photosensitizers in Photodynamic Therapy in Living Cells

β-(1,3-1,6)-D-Glucan, λ-carrageenan, tamarind gum, and pullulan can dissolve various porphyrin derivatives via the formation of complexes in water using a high-speed vibration milling method. The aqueous solutions of the resulting complexes exhibit long-term stability. Despite the adverse effects of the self-quenching process, notable fluorescence and improved photodynamic activity of the polysaccharide-complexed porphyrin derivatives were observed in the presence of liposomes, micelles, cyclodextrins, and HeLa cells. It was noted that the type of porphyrins was more important than the type of polysaccharides present in the complex. Porphyrin self-aggregates were monodispersed in the lipid membranes of the liposomes and lysosomes. The polysaccharide-complexed porphyrin derivatives showed increased photodynamic activity toward HeLa cells under photoirradiation between 610 and 740 nm.     

A novel polycondensate containing cyclodextrin and lactose: Synthesis, metal-complexing properties, and degradation

The synthesis and characterization of the novel water-soluble polycondensate from β-cyclodextrin triazine and d-lactose are described, which represents the first copolymer containing cyclodextrin and lactose in the main-chain. In addition, the metal complex forming properties of the novel polymer for different metal ions such as Cr(III), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Cd(II), Pb(II), and Al(III) were studied using the liquid-phase polymer-based retention (LPR) method and compared with those of β-cyclodextrin. According to the retention profiles obtained by the LPR method, all 10 metal ions investigated showed a strong interaction with this polymer. Finally, this polycondensate was shown to be microbiologically degradable with exponential microbial growth of 45 CFU (10⁸ mL⁻¹) by using conventional microbiological methods.     

Metal-complex compounds as components of initiating systems for the controlled radical polymerization of vinyl monomers

The effect of initiating systems based on substituted and unsubstituted metallocenes; polynuclear macrocyclic semi- and clathrochelates of Fe(II); and metal complexes of Ti(IV), Zr(IV), Fe(III), and Co(III) porphyrins on the free-radical polymerization of MMA and styrene is analyzed. Experimental data are systematized, general relationships are ascertained, and specific features of the process related to the structure of metal-complex compounds and the nature of initiators and monomers are revealed.     

Phototoxic Activity and DNA Interactions of Water‐Soluble Porphyrins and Their Rhenium(I) Conjugates

In the search for alternative photosensitizers for use in photodynamic therapy (PDT), herein we describe two new water‐soluble porphyrins, a neutral fourfold‐symmetric compound and a +3‐charged tris‐methylpyridinium derivative, in which either four or one [1,4,7]‐triazacyclononane (TACN) units are connected to the porphyrin macrocycle through a hydrophilic linker; we also report their corresponding tetracationic Re^I conjugates. The in vitro (photo)toxic effects of the compounds toward the human cell lines HeLa (cervical cancer), H460M2 (non‐small‐cell lung carcinoma), and HBL‐100 (non‐tumorigenic epithelial cells) are reported. Three of the compounds are not cytotoxic in the dark up to 100 μm , and the fourfold‐symmetric couple revealed very good phototoxic indexes (PIs). The intracellular localization of all derivatives was studied in HeLa cells by confocal fluorescence microscopy. Although low nuclear localization was observed for some of them, it still prompted us to investigate their capacity to bind both quadruplex and duplex DNA; we observed significant selectivity in the tris‐methylpyridinium derivatives for G‐quadruplex interactions.     

Metal complexes of diisopropylthiourea: synthesis, characterization and antibacterial studies

Co(II), Cu(II), Zn(II) and Fe(III) complexes of diisopropylthiourea have been synthesized and characterized by elemental analyses, molar conductivity, magnetic susceptibility, FTIR and electronic spectroscopy. The compounds are non-electrolytes in solution and spectroscopic data of the complexes are consistent with 4-coordinate geometry for the metal(II) complexes and six coordinate octahedral for Fe(III) complex. The complexes were screened for their antibacterial activities against six bacteria: Escherichia coli, Pseudomonas auriginosa, Klebsiella pneumoniae, Bacillus cereus, Staphylococcus aureus and Bacillus pumilus. The complexes showed varied antibacterial activities and their minimum inhibitory concentrations (MICs) were determined.     

Synthesis,characterization, and catalytic activity of 4 mol % N,N′‐methylene bisacrylamide crosslinked poly(acrylic acid)–metal complexes

The metal‐ion complexation behavior and catalytic activity of 4 mol % N,N′‐methylene bisacrylamide crosslinked poly(acrylic acid) were investigated. The polymeric ligand was prepared by solution polymerization. The metal‐ion complexation was studied with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) ions. The metal uptake followed the order: Cu(II) > Cr(III) > Mn(II) > Co(II) > Fe(III) > Zn(II) > Ni(II). The polymeric ligand and the metal complexes were characterized by various spectral methods. The catalytic activity of the metal complexes were investigated toward the hydrolysis of p‐nitrophenyl acetate (NPA). The Co(II) complexes exhibited high catalytic activity. The kinetics of catalysis was first order. The hydrolysis was controlled by pH, time, amount of catalyst, and temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 272–279, 2004     

Nitric oxide synthase-like activity of ion exchange resins modified with iron (III) porphyrins in the oxidation of l-arginine by H2O2: Mechanistic insights

Resin supported iron (III) porphyrins, prepared by strong electrostatic interactions between the ionic iron (III) porphyrins and counter ionic groups on the surface of the support, were found to be very efficient catalysts for H₂O₂ mediated oxidation of l-arginine with the formation of citrulline and nitric oxide, and the yields of these products were remarkably higher than those obtained with corresponding soluble iron (III) porphyrins. No leaching of iron porphyrin or uncomplexed iron ions was observed. A high-valent iron–oxo porphyrin complex was suggested as a reactive intermediate for this oxidation reaction.     

Electrical properties of macromolecular complexes of coordinated polymers with mixed valence of Co(II), Co(III) and Co(II–III)

Electrical properties of bis‐ethylenediamine Co(II), Co(III) and Co(II–III) mixed valence complexes and polyethylenediaminecarbosilazane (PEDCSZ) [Co(II), Co(III) and Co(II–III)] macromolecules were measured at room temperature in a frequency range between 1 Hz and 10⁶ Hz. Electrical modulus, permittivity and ac conductivity were calculated using ac impedance and phase‐angle measurements. It was found that the overall conductivity of PEDCSZ macromolecules with Co is much higher than that for Co monomers. In addition, the conductivity of PEDCSZ Co(III) and Co(II–III) mixed valence compounds are higher than those containing Co(II) where the electronic conduction is dominant. The relaxation time increases from about 2.7 × 10^?6 s for Co(II) chloride to a value of 2.9 × 10^?4 s for Co(II–III) chloride monomers. Copyright © 2003 Society of Chemical Industry     

两种新的水溶性卟啉的离解常数测定及酸碱诱导聚合

研究了ｍｅｓｏ－四卟啉和ｍｅｓｏ－四卟啉的离解常数。ＴＢＰｈＰ的离解常数为：ｐＫａ４＝１．１３．ｐＫａ３＝１．８８，ｐＫＡ２＝１２．２１；ＴＴＰＳ的离解常数为：ｐＫａ４＝４．４７，ｐＫａ３＝６．２６。外还发现了两卟啉的酸碱诱导聚合。     

Thermal properties of poly(N-maleyl glycine), poly(N-maleyl glycine-co-acrylic acid), and their metal complexes

The thermal properties of two water-soluble polymers; poly(N-maleyl glycine) and poly(N-maleyl glycine-co-acrylic acid) as well as their metal complexes with Co(II), Zn(II), Ni(II), Cu(II), Fe(III), Cd(II), Pb(II), and Hg(II) ions were investigated. The copolymer-metal ion complexes were obtained in aqueous phase by using the Liquid Phase Polymer-Based Retention (LPR) technique in conjunction with membrane filtration. The water-soluble P(MG) and P(MG-co-AA) are shown to be useful for the retention of different metal ions and their separation from elements not bound to the polymeric reagent. The thermal stability of the copolymer-metal ion complexes under nitrogen atmosphere at 20–500°C was also investigated. The complexes with different transition were characterized with FT-IR and thermogravimetry (TGA). From the TGA data the thermal decomposition temperature (TDT) and kinetic parameters such as activation energy (Ea) and reaction order (n) were determined. Received: 21 April 1998/Revised version: 16 July 1998/Accepted: 22 July 1998     

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) ≈ Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) can be easily achieved by varying of the metal center. In addition, mechanism speculation is also presented to elucidate the dependence of catalytic behaviors on metal and cocatalyst.     

Photodegradation of azo‐dyes in aqueous solution by polyacrylonitrile nanofiber mat‐supported metalloporphyrins

Electrospinning has been employed to fabricate uniform polyacrylonitrile and polyacrylonitrile copolymer nanofiber mats supporting metalloporphyrins (MTPP; M: Zn(II), Cu(II), Ni(II), Co(II), Fe(III) and Pd(II); TPP: meso‐tetraphenylporphyrin). The nanofiber mat‐supported metalloporphyrins are shown as efficient photocatalysts for the degradation of various azo‐dyes in aqueous solutions under visible light irradiation. The effect of transition metals on azo‐dye photodegradation has been examined. The nanofiber mat‐supported copper–porphyrin and iron–porphyrin complexes are among the most effective photocatalysts for azo‐dye degradation. Immobilization of the metalloporphyrins onto the nanofiber mats greatly facilitates the recovery and reuse of the expensive and toxic photocatalysts. Most interestingly, there are no significant degradations of the photocatalytic activities of the recycled photocatalysts. © 2012 Society of Chemical Industry     

Role of Cobalt(III) Cationic Complexes in the Self-Assembling Process of a Water Soluble Porphyrin

Under moderate acidic conditions, the cationic (+3) complexes ions tris(1,10-phenanthroline)cobalt(III), [Co(phen)₃]³⁺, and hexamminecobalt(III), [Co(NH₃)₆]³⁺, efficiently promote the self-assembling process of the diacid 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H₂TPPS₄) into J-aggregates. The growth kinetics have been analyzed according to a well-established autocatalytic model, in which the rate determining step is the initial formation of a nucleus containing m porphyrin units (in the range 2–3), followed by a stage whose rate constant k_c evolves as a power of time. The observed catalytic rate constants and the extent of J-aggregation increase on increasing the metal complex concentration, with the phen complex being the less active. The UV/Vis extinction spectra display quite broad envelops at the J-band, especially for the amino-complex, suggesting that electronic dipolar coupling between chromophores is operative in these species. The occurrence of spontaneous symmetry breaking has been revealed by circular dichroism and the measured dissymmetry g-factor decreases on increasing the aggregation rates. The role of these metal complexes on the growth and stabilization of porphyrin nano-assemblies is discussed in terms of the different degree of hydrophilicity and hydrogen bonding ability of the ligands present in the coordination sphere around the metal center.     

Development of antimicrobial aminoacid-modified bisphenol-A formaldehyde resin and its transition-metal complexes

A polymeric ligand (BFG), containing glycine moiety was synthesized by the polycondensation reaction of bisphenol-A and formaldehyde with amino acid (glycine) in alkaline medium. The polymer–metal complexes were synthesized with transition metal ions. The polymer and its metal complexes were characterized by elemental analysis and other spectroscopic techniques. The analytical data revealed that the coordination polymers of Cr(III), Co(II), and Ni(II) were coordinated with two water molecules, which are further supported by FTIR spectra and TGA data. The amino acid was found to act as bidentate ligand toward metal ions via the nitrogen of the NH group and carboxyl oxygen of the respective amino acid. The in-vitro preliminary antimicrobial activities of all the synthesized polymers were investigated against some bacteria and fungi. The polymer–metal complexes showed excellent antimicrobial activities against both types of microorganisms. Interestingly the polymeric ligand was found antimicrobial in nature but less effective as compared the polymer–metal complexes. On the basis of the antimicrobial behavior, these polymers hold potential in their application as antifungal and antifouling coating materials in medical devices as well as antimicrobial packaging material.