Koiti Araki

Supramolecular assemblies of ruthenium complexes and porphyrins

Abstract The build-up of polymetallic supermolecules based on porphyrins and ruthenium bipyridine complexes has been pursued with great interest. A relevant series of symmetric polynuclear species has been obtained by attaching four [Ru II (bipy) 2 Cl] groups to the pyridyl substituents of meso -tetra(4-pyridyl)porphyrin and its metallated derivatives. These compounds display a rich electrochemistry and versatile catalytic and photochemical properties, associated with the ruthenium–bipyridine and metalloporphyrin complexes. The supermolecular species interact very strongly with DNA, yielding by irradiation with visible light, very efficient single-strand breaks and formation of 8-oxo-7,8-dihydroxo-2′-deoxyguanosine. Another interesting property of the supramolecular porphyrins is their ability to form homogeneous and adherent molecular films by dip-coating. When combined with anionic porphyrins, self-assembled films can be generated, layer-by-layer, in a controlled way. Both types of films display photoaction response in the presence of visible light. The modified electrodes exhibit rectifying response in the presence of reducing species, demonstrating excellent performance as FIA detectors for biological and environmentally relevant substrates such as dopamine, NADH, ascorbic acid and sulfite ions.

Monomeric and extended oxo-centered triruthenium clusters

Abstract The chemistry of μ-oxo-centered trinuclear ruthenium-carboxylate clusters, of general formula [Ru 3 O(RCO 2 ) 6 L 3 ] n , has been dealt with special emphasis on their spectroscopic and electrochemical properties, as well as their capability to form ligand-bridged oligomeric structures exhibiting pronounced electronic delocalization. Mixed systems containing trinuclear ruthenium clusters attached to transition metal complexes and porphyrins are also focused upon in this review article, from the point of view of cooperative interactions and supramolecular chemistry. The role of the trinuclear clusters as electron donor/acceptor groups, and their relevance in biomimetic systems, redox catalysis and molecular devices have been discussed.

Electrochemistry of a tetraruthenated cobalt porphyrin and its use in modified electrodes as sensors of reducing analytes

Abstract The properties and analytical applications of a new polymetallic species containing four [Ru(bipy) 2 Cl] + (bipy = 2,2′-bipyridine) groups coordinated to the pyridine residues of the meso -tetra(pyridyl)porphynate cobalt(III) complex are reported. The cyclic voltammograms of the tetraruthenated cobalt porphyrin, in DMF solution, exhibit an intense reversible wave at E 1 2 = 0.93 V associated with the Ru III II redox couple, and two irreversible cathodic waves at E pc = −1.37 and −1.63 V, involving the stepwise reduction of the bipyridine ligands in each peripheral ruthenium complex. Three successive reductions of the cobalt porphyrin center can be detected in the −0.5 to −0.7 V range, using spectroelectrochemical techniques. Stable, homogeneous films of the polymetallic porphyrin can be generated by dip-coating on to electrode surfaces, exhibiting pronounced electrochemical activity. The modified electrodes have been successfully employed for analytical purposes, using conventional and flow injection methods, showing excellent performance in the determination of reducing analytes, such as nitrite and sulphite ions, even at ppb levels.

Ultrasensitive SERS nanoprobes for hazardous metal ions based on trimercaptotriazine-modified gold nanoparticles.

Trimercaptotriazine-modified gold nanoparticles exhibit strong SERS effects, yielding vibrational profiles very sensitive to the presence of heavy metal ions. Because of the contrasting response observed for selected vibrational bands in the SERS profiles, they provide useful nanoprobes for Hg2+ and Cd2+ ions, allowing direct quantitative assays by employing relative peak intensity ratios instead of using internal standards.

Amperometric detection of nitrite and nitrate at tetraruthenated porphyrin-modified electrodes in a continuous-flow assembly

The modification of a glassy carbon surface by coating with an electrostatically assembled film of tetraruthenated cobalt porphyrin/(meso-tetra(4-sulphonatephenyl)porphyrinate zinc(II) yields an indicator electrode that allows the determination of nitrite to be performed with a limit of detection of 0.1 μM in a flow injection configuration. The dynamic range extends up to 1000 μM and the repeatability of the measurements was evaluated to be 1.5% with a throughput of 50 samples per hour. The efficiency of the bilayered film to mediate the electron transfer allows the determinations to be performed at a less positive potential (+0.75 V) with enhanced sensitivity. The coating also prevents the surface poisoning and its stability is maintained over several weeks. The same detector was used for determination of nitrate after reduction to nitrite in a reductor column containing copperised cadmium. This method was used for the determination of nitrate and nitrite in mineral water, saliva and cured meats, the results being in agreement with certified values and those obtained by using recommended procedures.

Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry

Travelling wave ion mobility mass spectrometry (TWIM-MS) with post-TWIM and pre-TWIM collision-induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM-MS. CID performed after TWIM separation (post-TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N-protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH(3) , whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co-existing protomers of two isomeric porphyrins were also separated and characterized via post-TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO(2) loss, but a CID-resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups.

SYNTHESIS AND CHARACTERIZATION OF A MULTIBRIDGED PORPHYRIN COMPLEX CONTAINING PERIPHERAL BIS(BIPYRIDINE)-RUTHENIUM(II) GROUPS

The synthesis and characterization of a new meso-tetrapyridylporphyrin (TPyP) modified with four [Ru(bipy)2Cl]+ groups is reported. Cyclic voltammograms of this species in N,N′-dimethylformamide ex...

Supramolecular cationic tetraruthenated porphyrin induces single-strand breaks and 8-oxo-7,8-dihydro-2'-deoxyguanosine formation in DNA in the presence of light.

Abstract— The aim of this investigation is the evaluation of DNA interaction of with tetraruthenated porphyrin (TRP) and of DNA damage in the presence of light. Direct‐fluorescence and electronic absorption measurements after incubation of DNA with TRP indicate strong binding between pBR322 DNA or calf thymus DNA with the modified porphyrin. Exposure of pBR322 DNA to TRP (up to 3 μM) and light leads to single‐strand break formation as determined by the conversion of the supercoiled form (form I) of the plasmid into the nicked circular form (form II). Oxidative DNA base damage was evaluated by the detection of 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐oxodGuo) after irradiation of calf thymus DNA in the presence of the TRP. The data demonstrated a dose and time dependence with each type of DNA damage. These data indicate (1) a specificity of the binding mode and (2) type I and II photoinduced mechanisms leading to strand scission activity and 8‐oxodGuo formation. Accordingly, singlet molecular oxygen formation, after TRP excitation, was confirmed by near‐infrared emission. From these investigations a potential application of TRP in photodynamic therapy is proposed.

The coordination chemistry at gold nanoparticles

In gold nanoparticles the surface metal atoms play a major role, determining their chemical and physical properties by interacting with donor-acceptor species or ligands in a similar way as the related metal complexes. In addition, coherent oscillations of the metal electrons in resonance with the frequency of the exciting light give rise to localized surface plasmons responsible for an enhancement of the local electric field and SERS effect, allowing a wide range of applications in chemistry, biology and nanotechnology. Multifunctional bridging ligands can be employed for simultaneously binding metal ions and surface atoms. The attractive point of this approach is the possibility of exploiting the charge controlled stabilization by the metal complexes, while imparting new characteristics and properties to the modified nanoparticles. As a matter of fact, a new, exciting field of coordination chemistry can be envisaged, combining metal nanoparticles and metal complexes, in the light of supramolecular and surface plasmon resonance effects.

Determination of sulfur dioxide in wines by gas-diffusion flow injection analysis utilizing modified electrodes with electrostatically assembled films of tetraruthenated porphyrin

Abstract Reported is a new method for the determination of both free and total SO 2 in wine, specially designed for FIA. The method involves separation of the analyte using a flow through gas diffusion unit, in line with an amperometric detector consisting of a glassy carbon electrode modified with electrostatically assembled films of a tetraruthenated porphyrin. The results demonstrate a good accuracy, comparable with those obtained using the conventional iodometric method. In addition, the method can be readily applied to red, white and rose wines; it is free from interference of the other compounds of wine, consumes small amounts of sample and is faster than the iodometric method.