Copper Porphyrin Research Articles

Uptake and degradation of copper and cobalt porphyrins by indigenous microorganisms of Kupferschiefer (Fore-Sudetic Monocline, Poland)

To understand how natural metalloporphyrins from black shale may be transformed by indigenous microorganisms, a model experiment with synthetic copper and cobalt porphyrins was performed. Under laboratory conditions, microorganisms isolated from organic-rich metal-bearing black shale from the Fore-Sudetic Monocline were able to utilize both of these metalloporphyrins as their sole source of energy and carbon. The first step in metalloporphyrin biotransformation was identified as the highly efficient uptake of these compounds by bacterial cells. The further degradation of them in bacterial cells was also confirmed. Besides contributing to the important process of degrading and recycling organic and inorganic matter in the environment, the ability of microorganisms to transform metalloporphyrins has potential practical application in bioremediation of copper tailings as well as in the recovery of metals from organic-rich metal-bearing black shale ore, which is not possible using traditional hydrometallurgical procedures.

Spin−Spin Interactions in Porphyrin-Based Monoverdazyl Radical Hybrid Spin Systems

The spin-spin interactions in a complex consisting of a metalloporphyrin with a verdazyl radical attached at one of the beta positions of the porphyrin ring are investigated. The X-ray crystal structure of the copper porphyrin complex shows that the plane of the verdazyl moiety is oriented such that it is nearly perpendicular to the plane of the porphyrin ring so that weak magnetic interactions between the metal and radical are expected. Consistent with this expectation, magnetic susceptibility and continuous-wave electron paramagnetic resonance (EPR) measurements of the copper (d(9)) and vanadyl (d(1)) versions of the porphyrin show that the metal and radical are weakly antiferromagnetically coupled. Thus, the ground state is a singlet, but the triplet state is thermally accessible above approximately 5 K. Spin-polarized transient EPR measurements of the free-base analogue show that its lowest excited state is a quartet, indicating that the verdazyl radical couples ferromagnetically to the triplet excited state of the porphyrin. Low-temperature transient EPR measurements on the vanadyl porphyrin reveal that the lowest excited quintet state is populated. This implies that the antiferromagnetic coupling between the metal and radical observed in the ground state is switched to a ferromagnetic arrangement in the excited state by the presence of the unpaired electrons in the pi and pi* orbitals of the porphyrin.

Metal-complex formation and DNA interaction of 5, 10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphine: Study of the mechanistic aspects

The macrocyclic porphyrin 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphine is studied in its ability to coordinate Cu(II) even at very low pH values and to interact, as a copper complex, with calf-thymus (CT-DNA). The kinetics and equilibria for metal-ligand complexes formation are spectrophotometrically studied, particularly focussing on the mechanistic information provided by the kinetic approach. The rate constants of complex formation is much lower than that of water exchange at Cu(II); this behavior is ascribed to an equilibrium between two porphyrin populations, only one of them being reactive. Concerning the interaction of the copper–porphyrin complex (D) with CT-DNA, it has been found that the complex binds to G–C base pairs by intercalation while forms external complex with the A–T base pairs. The kinetic results agree with a reaction mechanism that takes into account the slow shuffling from an AT-bound form (DAT) to a GC-bound form (DGC) of the copper complex (D), finally leading to a more stable DGC* intercalated form. Kinetic and equilibrium parameters for the copper complex binding to the nucleic acid are obtained, and the binding mechanism is discussed. A mechanism is proposed where D reacts simultaneously with (G–C) and (A–T) base pairs. The resulting bound forms interconvert according to a “shuffling” process, which involves formation of an intermediate (DGC) form. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 79–89, 2010

Synthesis, Characterization, and Electrochemical Studies of New π‐Extended Metalloporphyrins

AbstractA doubly fused porphyrin has been synthesized by two successive cyclization reactions. The first meso‐phenyl group was fused by an intramolecular Cadogan reaction leading to an enamine‐functionalized porphyrin. After Vilsmeier–Haack formylation of the nickel enaminoporphyrin, an intramolecular Friedel–Crafts reaction followed by dehydration of the intermediate alcohol afforded the doubly fused aromatic nickel porphyrin, which could be demetalated. The free base and the copper and palladium porphyrins show extremely high absorbances in the 700–800 nm range. The palladium complex was a good catalyst for the oxidation of cholesterol with singlet oxygen, which makes this chromophore a potential candidate for photodynamic therapy.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Tris-ruthenium(II)/copper(II) multimetallic porphyrin: Synthesis, characterization, DNA binding and supercoiled DNA photocleavage studies

The porphyrin, meso-5-(pentafluorophenyl)-10, 15, 20-tris(4-pyridyl)porphyrin has been used to synthesize two new metalloporphyrin complexes. Insertion of copper(II) into the porphyrin center gives the copper(II) porphyrin. Coordination of three [Ru(bipy) 2Cl] + moieties (where bipy = 2,2′-bipyridine) to the pyridyl nitrogens of the copper(II) porphyrin gives the target complex. Electronic transitions associated with the copper(II) porphyrin and the triruthenium copper(II) porphyrin include an intense Soret band and a less intense Q-band in the visible region of the spectrum. An intense π–π∗ transition in the UV region associated with the bipyridyl groups and a metal to ligand charge transfer (MLCT) band appearing as a shoulder to the Soret band are observed for the ruthenated copper(II) porphyrin. Electrochemical properties associated with the multimetallic complex include a redox couple in the cathodic region with E 1/2 = −0.86 V versus Ag/AgCl attributed to the porphyrin and a redox couple in the anodic region E 1/2 = 0.88 V versus Ag/AgCl due to the Ru III/II couple. DNA titrations indicate the triruthenium copper(II) porphyrin interacts with DNA potentially through a groove binding mechanism. Irradiation of aqueous solutions of the target complex and supercoiled DNA at a 10:1 base pair to complex ratio with visible light above 400 nm indicates that the complex causes nicking of the DNA helix.

Ultrafast all-optical light modulation in the near infrared region by phase sensitive polymer guided wave mode geometry containing porphyrin tapes

A phase sensitive detection was introduced into reflection type all-optical light modulation based on guided wave mode (GWM) geometry. A polymer film containing a copper porphyrin tape and a low refractive polymer film formed GWM at specific incident angle and wavelength. Sensitive changes of output intensity were observed upon femtosecond laser excitation depending on azimuthal angles of the analyzer, which was caused by phase changes at the GWM by Δk alone. The present system has a great advantage as compared with the conventional GWM or simple transmission methods for all-optical light modulation especially for materials showing the ground state absorption.

Extended X-ray Absorption Fine Structure of Copper(II) Complexes at the Air-Water Interface by a Polarized Total-Reflection X-ray Absorption Technique

Copper(II) complexes spread on an aqueous solution surface were studied by a polarized total-reflection X-ray absorption fine structure (TR-XAFS) technique. The polarized TR-XAFS spectra at the Cu-K edge for copper(II) porphyrins and copper(II) chlorophyllin in a monolayer were measured in situ at the air-water interface. The polarization dependences of X-ray absorption near-edge structure (XANES) involving a 1s-->4p(z) transition allowed us to estimate the molecular orientation and the local coordination structure around the copper(II) atom in the polarization plane selectively. The extended X-ray absorption fine structure (EXAFS) region of the polarized TR-XAFS spectra for the metal complexes present at the air-water interface was successfully analyzed for the first time. The relative coordination number for the copper center evaluated from the EXAFS analysis indicated larger values in the vertical polarization than in the horizontal one, in agreement with the standing-up molecular orientation at the air-water interface estimated from the XANES region.

Amphiphilic Porphyrins for Second Harmonic Generation Imaging

Amphiphilic donor-acceptor meso-ethynyl porphyrins with polar pyridinium electron-acceptor head groups and hydrophobic dialkyl-aniline electron donors have high molecular hyperpolarizabilities (as measured by hyper-Rayleigh scattering) and high affinities for biological membranes. When bound to water droplets in dodecane, or to the plasma membranes of living cells, they can be used for second harmonic generation (SHG) microscopy; an incident light of wavelength 840 nm generates a strong frequency-doubled signal at 420 nm. Copper(II) and nickel(II) porphyrin complexes give similar SHG signals to those of the free-base porphyrins, while exhibiting no detectable two-photon excited fluorescence.

Steric effects direct the binding of porphyrins to tetramolecular quadruplex DNA

The binding motifs of copper(II) porphyrins with G quadruplex DNA structures vary markedly depending on the steric demands of the ligand and the host structure.

Electrochemical reactions at a porphyrin–copper interface

The structure and reactivity of a Cu(100) single crystal electrode surface covered with free base meso-tetra (N-methyl-4-pyridinium) porphyrin (abbreviated as H(2)TMPyP) as a function of electrode potential have been investigated with cyclic voltammetry (CV), electrochemical scanning tunneling microscopy (ECSTM), and UV-Vis and Raman spectroscopy. The well-ordered self-assembled layer of the porphyrin is consistent with the adsorption of the reduced porphyrin species after the first two-electron reduction step. The copper dissolution reaction in the presence of the stable self-assembled porphyrin layer starts at step edges on both upper and lower terraces and coincides with the preferential oxidation of reduced porphyrin species at step sites. The dissolved copper cations are incorporated into the free base porphyrin molecules leading to the formation of CuTMPyP. As a consequence this new species accumulates in the solution with time and a copper redeposition in the cathodic potential scan is lacking.

Solvent effects on photophysical properties of copper and zinc porphyrins

The photophysics of Zn(tetraphenylporphyrin,TPP), Zn(tetra-2,4,6-trimethylphenyl porphyrin, TMP), Zn (tetra-(o-dichlorophenyl) porphyrin, TPPCl8), Cu(tetraphenylporphyrin,TPP), Cu(tetra-2,4,6-trimethylphenyl porphyrin,TMP), and Cu(tetra-(o-dichlorophenyl) porphyrin, TPPCl8, TPPCl8) in several solvents have been investigated on steady state and time-resolved spectroscopy. The Cu(TPPCl8 ) is normal and shows no evidence of CT transition in the visible or near UV regions in nonpolar solvent. However, Cu(TPPCl8)shows a blue shift in the absorption spectrum and intramolecular CT bands at absorption spectra in polar solvent, which shows a fluorescence maximum emission at 650 nm and 8.4 ns lifetime. The reason can be attributed to two points. Firstly, the increase of solvent polarity can enlarge outer reorganisational energy, which is favorable to reduce the activation free energy of charger-transfer transition based on Marcus theory of electron transfer. Moreover, the internal heavy-atom effect on Cu(TPPCl8) is encouraging to stabilize the 2T1 state also, which increases the possibility of population to CT band from 2T1 state. This result is in accord with an earlier estimate of a 10 ns lifetime and CT absorption at 640 nm bands for the CT state of Cu (II) octethylporphyrins. Other possible reasons arousing unusual fluorescence like H-bonding, axial ligands, molecular aggregation are excluded.

Prominent Electron Transport Property Observed for Triply Fused Metalloporphyrin Dimer: Directed Columnar Liquid Crystalline Assembly by Amphiphilic Molecular Design

A triply fused copper porphyrin dimer, when site-specifically modified on its periphery with hydrophobic and hydrophilic wedges (1C12/TEG), self-assembles into a columnar liquid crystalline (LC) mesophase over a wide-temperature range from -17 to 99 degrees C but gives rise to an amorphous solid when modified with only hydrophobic (1C12/C12) or hydrophilic wedges (1TEG/TEG). A LC film of 1C12/TEG displays at 16 degrees C a top-class one-dimensional electron mobility (0.27 cm2/V x s), as evaluated from its maximum flash-photolysis time-resolved microwave conductivity.

Laser induced gratings enhanced by surface-charge mediated electric field in doped nematic liquid crystals

The optically induced grating enhanced by dc electric field in nematic liquid crystal (LC) doped with copper porphyrin is studied. The reorientational effect of the LC was not observed for the writing beams with the intensity up to 500 mW/mm2, but the threshold of the reorientation was reduced to 1 mW/mm2 with the assistance of an electric pulse applied to the LC. The low threshold for the induced grating can be retained even after switching off the dc pulse, indicating that an induced field inside the LC is present to sustain the low threshold operation for the induced grating. The low threshold operation does not persist by short circuiting of LC electrodes. The underlying mechanism is explained by an optical surface-charge mediated effect.

Synthesis and characterization of water-soluble free-base, zinc and copper porphyrin–oligonucleotide conjugates

We describe the synthesis and characterization of a series of water-soluble free-base, zinc, and copper porphyrin–oligonucleotide (ODN) conjugates. A non-charged tetraarylporphyrin was directly attached to the 5′-position of thymine via a short amide linker. Such a linker should allow for rigid connection to the adjacent nucleobases, thus increasing the sensitivity for monitoring conformational changes of the ODNs by electronic circular dichroism due to capping effects or ligand binding. Two complementary synthetic approaches have been used to incorporate porphyrin chromophores into the DNA. In the first approach a porphyrin carboxylic acid is conjugated to 5′-amino-ODN. In the second approach the phosphoramidite of the porphyrin-amido-thymidine is coupled to 5′-hydroxy-ODN using standard automated phosphoramidite chemistry. In both cases a spontaneous metallation of the free-base porphyrin in porphyrin–DNA conjugates was observed during the porphyrin–DNA conjugate cleavage from the solid support and its consequent deprotection using concentrated aqueous ammonia. Zinc and copper porphyrin–DNA conjugates were isolated by HPLC and characterized together with the anticipated free-base porphyrin–DNA conjugate. Authentic zinc and copper porphyrin–DNA conjugates were intentionally prepared from intentionally metallated porphyrins to compare their spectroscopic and HPLC characteristics with isolated metallospecies and to confirm the spontaneous metallation.

PELDOR Measurements on a Nitroxide-Labeled Cu(II) Porphyrin: Orientation Selection, Spin-Density Distribution, and Conformational Flexibility

Metal ions are functionally or structurally important centers in metalloproteins or RNAs, which makes them interesting targets for spectroscopic investigations. In combination with site-directed spin labeling, pulsed electron-electron double resonance (PELDOR or DEER) could be a well-suited method to characterize and localize them. Here, we report on the synthesis, full characterization, and PELDOR study of a copper(II) porphyrin/nitroxide model system. The X-band PELDOR time traces contain besides the distance information a convolution of orientational selectivity, conformational flexibility, exchange coupling, and spin density distribution, which can be deconvoluted by experiments with different frequency offsets and simulations. The simulations are based on the known experimental and spin Hamiltonian parameters and make use of a geometric model as employed for structurally similar bis-nitroxides and spin density parameters as obtained from density functional theory calculations. It is found that orientation selection with respect to dipolar angles is only weakly resolvable at X-band frequencies due to the large nitrogen hyperfine coupling of the copper porphyrin. On the other hand, the PELDOR time traces reveal a much faster oscillation damping than observed for structurally similar bis-nitroxides, which is mainly assigned to a small distribution in exchange couplings J. Taking the effects of orientation selectivity, distribution in J, and spin density distribution into account leads finally to a narrow distance distribution caused solely by the flexibility of the structure, which is in agreement with distributions from known bis-nitroxides of similar structure. Thus, X-band PELDOR measurements at different frequency offsets in combination with explicit time trace simulations allow for distinguishing between structural models and quantitative interpretation of copper-nitroxide PELDOR data gives access to localization of copper(II) ions.

Comparison between the electrocatalytic properties of different metal ion phthalocyanines and porphyrins towards the oxidation of hydroxide

This work reports on the electrocatalytic oxidation of hydroxide using different central metal ion phthalocyanines and porphyrins immobilized on gold electrodes. The apparent electrocatalytic activity of cobalt phthalocyanine or porphyrin modified electrodes was found to be the greatest among the present series of metal ion macrocycles investigated. Copper and unmetallated phthalocyanine or porphyrin modified electrodes show no electrocatalytic behaviour towards hydroxide, such as bare gold. A possible mechanism for the enhanced reactivity of cobalt ion macrocycles towards the oxygen evolution is given. It is also stated that the electrocatalytic activity towards an adsorbate involves several aspects, such as the coordination state of the central metal ion, the nature of the ligand, the stability of the complexes, the number of d electrons, the energy of orbitals and the strength of the bonding between the central metal ion and the axial ligand.

Similarities and Differences among Monolayers of a Free Base Porphyrin and Its Copper Complex: Synthesis and Characterization of a Luminescent Copper(II) Porphyrin Monolayer

Silica substrates were functionalized with a covalent 4-ClCH2C6H4SiCl3 monolayer. Additional covalent bonding of the 5,10,15-tri-(p-dodecanoxyphenyl)-20-(p-hydroxyphenyl) copper porphyrin to the silylated substrates was further achieved. The optical properties of this robust monolayer system were studied at room temperature by both UV−vis and photoluminescence measurements. The UV−vis spectrum reveals the presence of the Soret band and of a Q-band envelope only. The surface chemical characterization was carried out by X-ray photoelectron measurements. The N 1s spectrum shows two peaks in tune with the copper porphyrin axial grafted to the silylated substrate. Luminescence measurements gave emission intensity values larger than those observed for the free base monolayer.

Synthesis and radiosensitizing properties of brominated tetrapyridine porphyrins

Brominated derivatives of tetrapyridinium copper porphyrin were prepared via bromination of the β-positions (pyrrole rings) and/or the peripheral alkyl side-chains attached to the pyridine moieties. The radiosensitizing properties of these new cationic, brominated porphyrins were tested on MDA-MB-231 breast cancer cells in vitro using a 60 Co source or an X-ray irradiator. The non-brominated porphyrin and the porphyrin containing bromines at β-positions only were devoid of any radiosensitizing activity. However, a pronounced radiosensitizing effect was observed with the porphyrin containing bromo atoms at both β-positions and the peripheral side-chains. A similar radiosensitizing effect was detected for different radiation energies, suggesting that high energy photons could be used to treat tumors in conjunction with this novel brominated, porphyrin-based radiosensitizer.

DNA Binding Studies of a New Dicationic Porphyrin. Insights into Interligand Interactions

Cationic porphyrins have an affinity for DNA and potential for applications in the fields of photodynamic therapy and cellular imaging. This report describes a new dicationic porphyrin, 5,15-dimethyl-10,20-di(N-methylpyridinium-4-yl)porphyrin, abbreviated H2tMe2D4. Although tetrasubstituted, H2tMe2D4 presents modest steric requirements and forms in reasonable yield by a "2+2" synthetic method. Accordingly, studies of the zinc(II)- and copper(II)-containing derivatives, Zn(tMe2D4) and Cu(tMe2D4), have also been possible. Methods used to characterize DNA-binding motifs include absorption, emission, linear, and circular dichroism spectroscopies, as well as viscometry. An unusually detailed picture of porphyrin uptake emerges. As the ratio of DNA to porphyrin increases during a typical titration, H2tMe2D4 or Cu(tMe2D4) initially aggregates on the host and then shifts to intercalative binding at close quarters before finally dispersing into non-interacting intercalation sites of the host. Emission studies of the copper(II) porphyrin have been very valuable. The existence of a measurable signal is diagnostic of intercalative binding, and the saturation behavior establishes that internalization typically monopolizes approximately three base pairs. In the moderate loading regime, emission data are most telling because dipole-dipole interactions between near-neighbor porphyrins tend to confuse other spectroscopic assays. The third ligand, Zn(tMe2D4), behaves differently in that the uptake is a strictly cooperative process. The mode of binding also varies with the base content of the DNA host. When the DNA is rich in A=T base pairs, the porphyrin remains five-coordinate and binds externally; however, Zn(tMe2D4) loses its axial ligand and binds by intercalation if the host contains only G[triple bond]C base pairs.

Efficient degradation of 4-nitrophenol by using functionalized porphyrin-TiO2 photocatalysts under visible irradiation

The novel porphyrins 5,10,15,20-tetra-[4-(3-phenoxy)-propoxy]phenyl porphyrin, H2Pp(a) and 5,10,15,20-tetra-[2-(3-phenoxy)-propoxy]phenyl porphyrin, H2Pp(b) and their corresponding copper(II) complexes CuPp(a), CuPp(b) were synthesized and characterized by using various spectroscopic techniques. The photocatalytic activity of polycrystalline TiO2 samples impregnated with H2Pp(a), H2Pp(b), CuPp(a) and CuPp(b) as sensitizers have been investigated by carrying out the photo-degradation of 4-nitrophenol (4-NP) as a probe reaction in aqueous suspension and under visible light. The maximum photocatalytic activity was obtained using TiO2 loaded with a monolayer of the copper porphyrin CuPp(b) in the amount of 18μmol per gram of TiO2.The photocatalytic efficiency decreased in the following order: TiO2-CuPp(b), TiO2-CuPp(a), TiO2-H2Pp(b), TiO2-H2Pp(a). A possible mechanism of the photocatalytic degradation is also proposed.