Probing the binding of tetraplatinum(pyridyl)porphyrin complexes to DNA by means of surface plasmon resonance

Tetrapyridylporphyrins containing four chloro(2,2`-bipyridine)platinum(II) complexes attached at the meta (3-H(2)TPtPyP) and para (4-H(2)TPtPyP) positions of the peripheral pyridine ligands were synthesized and their interaction with DNA investigated. The compounds were isolated in the solid state and characterized by means of spectroscopic and analytical techniques. According to molecular simulations, the two isomers exhibit contrasting structural characteristics, consistent with a saddle shape configuration for 3-H(2)TPtPyP and a planar geometry for 4-H(2)TPtPyP. Surface plasmon resonance studies were carried out on the interaction of the complexes with calf thymus DNA, revealing a preferential binding of 3-H(2)TPtPyP, presumably at the DNA major grooves. (C) 2008 Elsevier Inc. All rights reserved.

On an Electrode Modified by a Supramolecular Ruthenium Mixed Valence (Ru(II)/Ru(III)) Diphosphine-Porphyrin Assembly

Three novel polymetallic ruthenium (III) meso-tetra(4-pyridyl)porphyrins containing peripheral ""RuCl(3)(dppb)"" moieties have been prepared and characterized. The X-ray structure of the tetraruthenated {NiTPyP[RuCl(3)(dppb)](4)} porphyrin complex crystallizes in the triclinic space group FT. This structure is discussed and compared with the crystal data for the mer-[RuCl(3)(dppb)(py)]. The {TPyP[RuCl(3)(dppb)](4)} and {CoTPyP[RuCl(3)(dppb)](4)} porphyrins were used to obtain electrogenerated films on ITO and glass carbon electrode surfaces, respectively. Such tetraruthenated porphyrins form films of a mixed-valence species {TPyP[Ru(dppb)](4)(mu Cl(3))(2)}(2)(4n2+) and {CoTPyP[Ru(dppb)](4)(mu Cl(3))(2)}(2n)(4n2+) on the electrode surface. The modified electrode with {CoTPyP[RuCl(3)(dppb)](4)} is very stable and can be used to detect organic substrates such as catechol.

Contrasting photoelectrochemical behaviour of two isomeric supramolecular dyes based on meso-tetra(pyridyl)porphyrin incorporating four (mu(3)-oxo)- triruthenium(III) clusters

A saddle shaped tetracluster porphyrin species containing four [Ru(3)O(OAc)(6)(py)(2)](+) clusters coordinated to the N-pyridyl atoms of 5,10,15,20-tetra(3-pyridyl)porphyrin, H(2)(3-TCPyP), has been investigated in comparison with the planar tetra(4-pyridyl) porphyrin analogue H(2)(4-TCPyP). The steric effects from the bulky peripheral complexes play a critical role in the H(2)(3-TCPyP) species, determining a non-planar configuration around the porphyrin centre and precluding any significant pi-electronic coupling, in contrast with the less hindered H(2)(4-TCPyP) species. Both systems exhibit a photoelectrochemical response in the presence of nanocrystalline TiO(2) films, involving the porphyrin excitation around 450 nm. However, only in the H(2)(4-TCPyP) case do the cluster moieties also contribute to the photoinduced electron injection process at 670 nm, reflecting the relevance of the electronic coupling between the porphyrin centre and the peripheral complexes.

The use of electrospray ionization tandem mass spectrometry on the structural characterization of novel asymmetric metallo-organic supermolecules, based on pentafluorophenylporphyrins and ruthenium complexes

The novel asymmetric metallo-organic triads cis- and trans-[B(4-py)BPFPH(2){Ru(3)O(Ac)(6)(py)(2)}(Ru(bpy)(2)Cl}](PF(6))(2) (5a,b) for which cis- and trans-B(4-py)BPFPH(2)=5,10-bis(pentafluorophenyl)-15,20-bis(4-pyridyl)porphyrin and 5,15-bis(pentafluorophenyl)-10,20-bis(4-pyridyl)porphyrin, respectively; Ac = acetate; py = pyridine and bpy = 2,2`-bipyridine, as well as their corresponding monosubstituted dyads cis- and trans-[B(4-py)BPFPH(2){Ru(3)O(Ac)(6)(py)(2)}]PF(6) (4a,b) have been structurally characterized via electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS). The ESI-MS of dyads 4a,b display two characteristic Ru-multicomponent clusters of isotopologue ions corresponding to singly charged ions 4a,b(+) of m/z 1629 and doubly charged ions [4a,b+H](2+) of m/z 815 and the triads 5a,b are detected by ESI-MS as the intact doubly charged cluster of isotopologue ions of m/z 1039 [5a,b](2+). The ESI-MS/MS of 4a,b(+), [4a,b+H](2+) and [5a,b](2+) reveal characteristic dissociation pathways, which confirm the structural assignments providing additional information on the intrinsic binding strengths of the gaseous ions. Although the gas-phase behavior of each pair of isomers was rather similar, the less symmetric dyads 4a,b are distinguished via the (1)H NMR spectral profile of the pyrrolic signals. Exploratory photophysical assays have shown that both modifying motifs alter the porphyrinic core emission profile, opening the possibility to use these asymmetric systems as photophysical devices. (C) 2008 Elsevier Ltd. All rights reserved.

Tetra-crowned porphyrin as P450 biomimetic model for carbamazepine oxidation

A substituted porphyrin bearing four crown ether units, H(2)(TCP), was synthesized from the reaction between (5,10,15,20-tetra(o-aminophenyl) porphyrin) and the acyl derivative of the ether (4-carboxy-18-crown-6). The free-base porphyrin was characterized by C, N, and H elemental analysis; UV-vis and IR spectroscopies; and (1)H NMR. The corresponding ironporphyrin, Fe(TCP)Cl, was obtained via iron insertion into H(2)(TCP). Fe(TCP)Cl was employed as catalyst for carbamazepine (CBZ) oxidation by iodosylbenzene (PhIO), 3-chloroperoxybenzoic acid (m-CPBA) or sodium hypochlorite (NaOCl), in methanol or in a biphasic water/dichloroethane system. The crowned ironporphyrin proved to be a highly efficient and selective catalyst for CBZ epoxidation even in the biphasic dichloroethane /H(2)O system, with no need for an additional phase transfer agent.

Novel manganese (III) porphyrin containing peripheral [RuCl(dppb)(X-bipy)](+) cations [dppb=1,4-bis(diphenylphosphino) butane and X = -CH3, -OMe, -Cl]. X-ray structure of the cis-[RuCl(dppb)(bipy)(4-Mepy)]PF6 complex

New tetraruthenated manganese (III) porphyrins were synthesized and characterized (P-31 NMR, cyclic voltammetry, UV-Vis). This new system presents four units of cationic ``[RuCl(dppb)(X-bipy)](+)``. The electrochemical and catalytic properties of the central manganese (III) show dependence on the characteristics of the peripheral ruthenium complexes as evidenced by the Mn-(III)/Mn-(II) reduction potential. The catalytic oxidation reactions of olefins, cyclohexene and cyclohexane, were carried out in the presence of tetrapyridyl manganese (III) porphyrins containing cationic ruthenium complex and using iodosylbenzene as oxygen donor. The performance of these new tetraruthenated porphyrins systems were evaluated and compared with the manganese porphyrin. (C) 2007 Elsevier Ltd. All rights reserved.

Vanadium oxide-porphyrin nanocomposites as gas sensor interfaces for probing low water content in ethanol

Vanadium pentoxide xerogels (VXG) incorporating meso(3- and 4-pyridyl)porphyrin cobalt(III) species coordinated to four [Ru(bipy)(2)Cl](+) complexes were employed as gas sensing materials capable of detecting small amounts of water in commercial ethanol and fuel supplies. According to their X-ray diffraction data, the original VXG lamellar framework was maintained in the nanocomposite material, but the interlamellar distance increased from 11.7 to 15.2 angstrom, reflecting the intercalation of the porphyrin species into the vanadium pentoxide matrix. The films generated by direct deposition of the nanocomposite aqueous suspensions exhibited good electrical and electrochemical performance for application in resistive sensors. The analysis of water in ethanol and fuels was carried out successfully using an especially designed electric setup incorporating a laminar gas flow chamber and interdigitated gold electrodes coated with the nanocomposites. (C) 2010 Elsevier B.V. All rights reserved.

Can mass dissociation patterns of transition-metal complexes be predicted from electrochemical data?

The Cooks kinetic method has been very convenient to correlate the relative dissociation rates obtained by collision-induced fragmentation experiments with the energies of two related bonds in molecules and complexes in the gas phase. Reliable bond energy data are, however, not always available, particularly for polynuclear transition-metal complexes, such as the triruthenium acetate clusters of the general formula [Ru(3) (mu(3)-O)(mu-CH(3)COO)(6)(py)(2)(L)](+), where L = ring substituted N-heterocyclic ligands. Accordingly, their gas-phase collision-induced tandem mass spectrometry (CID MS/MS) dissociation patterns have been analyzed pursuing a relationship with the more easily accessible redox potentials (E(1/2)) and Lever`s E(L) parameters. In fact, excellent linear correlations of In(1/2A(L)/A(py)), where A(py) and A(L) are the abundance of the fragments retaining the pyridine (py) and L ligand, respectively, with E(1/2) and E(L) were found. This result shows that those electrochemical parameters are correlated with bond energies and can be used in the analysis of the dissociation data. Such modified Cooks method can be used, for example, to determine the electronic effects of substituents on the metal-ligand bonds for a series of transition-metal complexes. Copyright (C) 2008 John Wiley & Sons, Ltd.

Biological activity of metal-edds (ethylenediaminedisuccinate) complexes in K562 and PBMC cells

The effect of S,S-ethylenediaminedisuccinic acid (edds) on the quenching of metal-catalyzed (metal = Mn, Fe, Co, Ni, Cu, Zn) oxidation of ascorbic acid was tested in vitro via oxidation of the fluorescent probe 1,2,3-dihydrorhodamine dihydrochloride. The pro-oxidant activity of iron was not fully suppressed, even at a four-fold molar excess of the ligand. The effect of serum on the toxicity to peripheral blood mononuclear cells (PBMC) and K562 cells was investigated. The cytotoxic effect of Fe-edds was abrogated in the presence of Trolox or serum proteins. The probable pathways of cell toxicity were investigated through blocking of the monocarboxylate transporters (MCT) in association with cell cycle studies by flow cytometry. Cells treated with metal complexes and alpha-cyano-4-hydroxycinnamic acid, a known MCT inhibitor, showed recovery of viability, suggesting that MCT proteins may be involved in the internalization of metal-edds complexes. The free acid induced cell cycle arrest in G0/G1 (PBMC) and S (K562) phases, suggesting direct DNA damage or interference in DNA replication.

Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

Herein, the immobilization of some Schiff base-copper(II) complexes in smectite clays is described as a strategy for the heterogenization of homogeneous catalysts. The obtained materials were characterized by spectroscopic techniques, mostly UV/Vis, EPR, XANES and luminescence spectroscopy. SWy-2 and synthetic Laponite clays were used for the immobilization of two different complexes that have previously shown catalytic activity in the dismutation of superoxide radicals, and disproportionation of hydrogen peroxide. The obtained results indicated the occurrence of an intriguing intramolecular redox process involving copper and the imine ligand at the surface of the clays. These studies are supported by computational calculations.

Oxidative DNA damage induced by S(IV) in the presence of Cu(II) and Cu(I) complexes

The DNA damage induced by S(IV) in the presence of some Cu(II) complexes in air saturated solution was investigated. The addition of S(IV) to an air saturated solution containing CuII GGA (GGA = glycylglycyl-L-alanine), CuII G3 (G3 = triglycine) or CuII G4 (G4 = tetraglycine) and Ni(II) traces, causes rapid formation of the respective Cu(III) complex, with simultaneous O2 uptake and S(IV) oxidation. SO3•- and HO• were detected by EPR-spin trapping experiments. The DNA strand breaks were attributed to the oxysulfur radicals formed. In the reduction of Cu(II)/BCA (BCA = 4,4' dicarboxy-2-2'-biquinoline) by S(IV), with CuI BCA complex formation, there is the possible formation of carbon centered radical of BCA or peroxyl radical (ROO•) capable of oxidizing DNA bases. The intensity of DNA damage in the presence of these Cu(II) complexes and S(IV) (10-300 µmol L-1) followed the order: CuII BCA ∼ CuII G4 ∼ Cu(II) (added as Cu(NO3)2) > CuII G3 ∼ CuII GGA. Specifically for CuII BCA the damage occurred even at lower S(IV) concentration (0.1 µmol L-1). For the Cu(II) complexes with glycylglycylhistidine, glycylhistidylglycine, glycylhistidyllysine and glycylglycyltyrosylarginine the Cu(III) formation and the DNA damage was not observed.

Electronic properties and hyperfine fields of nickel-related complexes in diamond

We carried out a first-principles investigation on the microscopic properties of nickel-related defect centers in diamond. Several configurations, involving substitutional and interstitial nickel impurities, have been considered either in isolated configurations or forming complexes with other defects, such as vacancies and boron and nitrogen dopants. The results, in terms of spin, symmetry, and hyperfine fields, were compared with the available experimental data on electrically active centers in synthetic diamond. Several microscopic models, previously proposed to explain those data, have been confirmed by this investigation, while some models could be discarded. We also provided insights into the microscopic structure of several of those centers.

Effect of zinc insertion and hydrophobicity on the membrane interactions and PDT activity of porphyrin photosensitizers

A series of photosensitizers (PS), which are meso-substituted tetra-cationic porphyrins, was synthesized in order to study the role of amphiphilicity and zinc insertion in photodynamic therapy (PDT) efficacy. Several properties of the PS were evaluated and compared within the series including photophysical properties (absorption spectra, fluorescence quantum yield Phi(f), and singlet oxygen quantum yield Phi(Delta)), uptake by vesicles, mitochondria and HeLa cells, dark and phototoxicity in HeLa cells. The photophysical properties of all compounds are quite similar (Phi(f) <= 0.02; Phi(Delta) similar to 0.8). An increase in lipophilicity and the presence of zinc in the porphyrin ring result in higher vesicle and cell uptake. Binding in mitochondria is dependent on the PS lipophilicity and on the electrochemical membrane potential, i.e., in uncoupled mitochondria PS binding decreases by up to 53%. The porphyrin substituted with octyl groups (TC8PyP) is the compound that is most enriched in mitochondria, and its zinc derivative (ZnTC8PyP) has the highest global uptake. The stronger membrane interaction of the zinc-substituted porphyrins is attributed to a complexing effect with phosphate groups of the phospholipids. Zinc insertion was also shown to decrease the interaction with isolated mitochondria and with the mitochondria of HeLa cells, an effect that has been explained by the particular characteristics of the mitochondrial internal membrane. Phototoxicity was shown to increase proportionally with membrane binding efficiency, which is attributed to favorable membrane interactions which allow more efficient membrane photooxidation. For this series of compounds, photodynamic efficiency is directly proportional to the membrane binding and cell uptake, but it is not totally related to mitochondrial targeting.

Pulse train fluorescence technique for measuring triplet state dynamics

We report on a method to study the dynamics of triplet formation based on the fluorescence signal produced by a pulse train. Basically, the pulse train acts as sequential pump-probe pulses that precisely map the excited-state dynamics in the long time scale. This allows characterizing those processes that affect the population evolution of the first excited singlet state, whose decay gives rise to the fluorescence. The technique was proven to be valuable to measure parameters of triplet formation in organic molecules. Additionally, this single beam technique has the advantages of simplicity, low noise and background-free signal detection. (C) 2011 Optical Society of America

Intermolecular energy transfer and photostability of luminescence-tuneable multicolour PMMA films doped with lanthanide-beta-diketonate complexes

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)(3)(H(2)O)(2)] and [Tb(acac)(3)(H(2)O)(3)] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln(3+)-beta-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand-Ln(3+) intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the (5)D(4) emitting level of the Tb(3+) ion to the excited triplet state T(1) of the tta ligand coordinated to the Eu(3+) ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.