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The [Ru(NH3)6]3+ complex is shown to be a two-electron catalyst for homogeneous as well as heterogeneous water oxidation to evolve dioxygen. The oxygen evolution is proposed to proceed by two molecules of the complex through a peroxo-bridged intermediate involving higher oxidation state [Ruv(NH3)6]5+.

The fluorescence of pyrene and five other aromatic hydrocarbons solubilized with caffeine in aqueous solution was quenched by 0.001–1mol dm−3 sulfuric acid; this quenching did not occur in the absence of caffeine. Exceptionally a non-alternative hydrocarbon, fluoranthene, showed an increase of the fluorescence intensity by the acid. The observed quenching rate was explained by the rate of energy transfer from the aromatic molecules to protonated caffeine in the complex.

Ethanol glasses were irradiated with high-LET ion beams of 18.0 MeV He, 59.2 MeV C, and 60.5 MeV N at 80K. In all these irradiations, the apparent G -value of the trapped electron decreases with increasing dose. The G -values corrected for the dose effects were evaluated at 0.83 for C ions, 0.91 for N ions, and 1.4 for He ions. The dose dependence for high-LET radiations and the LET effect are discussed.

SummaryLysozyme dimers produced on oxidation of lysozyme with in aqueous solutions exhibit a fluorescence spectrum (λmax=400 nm) closely similar to that of bi-tyrosine. This suggests that the dimer is likely to have a tyrosin–tyrosine bond resulting from the combination of tyrosine phenoxy radicals of two lysozyme molecules. Kinetic studies on dimer formation were made by measuring time-dependent fluorescence after pulsed-electron irradiation over wide pH range. The results lead to the following conclusions. The second-order growth of the dimer fluorescence observed at pH 10·7–12·5 reflects the combination process of the lysozyme radicals, which is rate-determining in the pH range. On the other hand, the first-order growth observed at pH 6·8–10·2 is attributable to the enolization of the keto-form of the dimer. A tentative reaction scheme is proposed for the dimer formation.

The catalytic oxidative decomposition of water has been achieved with the help of the dinuclear manganese complexes 1 and 2, which are models for compounds participating in photosynthesis. Whereas no reaction was observed in homogeneous solution, O 2 evolution took place almost immediately in the heterogeneous phase after addition of a Ce IV salt as oxidizing agent. This finding supports the assumption that a microheterogeneous environment and a large spatial proximity of the manganese centers are essential for the photosynthetic activity of manganese compunds (bpy=2,2'-bipyridyl; phen=1,10-phenanthroline).

The geometry of the radical ions of tetraphenylethylene was studied by means of electronic absorption spectroscopy. The spectrum of the anion radical produced by γ-ray irradiation in frozen 2-methyltetrahydrofuran changes markedly on controlled warming. The resultant spectrum resembles the spectra of the anion radical in fluid solutions produced by potassium reduction and by pulse radiolysis. These spectra are distinctly different from the spectra of diphenylmethanide ion and of diphenylmethyl radical. From these facts it is inferred that the relaxed anion radical has a geometry in which the central ethylenic bond is twisted by an angle considerably smaller than 90°, in contrast with the near 90° twist in the dianion, and in which each bond connecting a phenyl group with an ethylenic carbon atom is twisted by a smaller angle than in the molecule. The spectrum of the cation radical produced by γ-ray irradiation in frozen matrices is similar to that of the cation radical produced by pulse radiolysis in flui...

Oxygenated 2-mehyltetrahydrofuran glasses containing maleic anhydride (MA) were ..gamma..-irradiated at 77 K followed by warming, and optical and ESR spectra were measured. Two species peculiar to the presence of both MA and O/sub 2/ were found: one that appears at earlier stages is characterizied by both a broad optical absorption band at 432 nm and an ESR band with g/sub z/ = 2.047, and the other that follows this possesses an optical band at 640 nm and an ESR band with g/sub z/ = 2.055. the features of the observed ESR spectra including those for /sup 17/O/sub 2/ indicate that these species are most likely molecular complexes, O/sub 2//sup -/...(MA) and O/sub 2//sup -/...(MA)/sub 2/, respectively. Similar optical and ESR spectra were also observed for methyl- and dimethylmaleic anhydride, maleimide, and fumaronitrile. 8 figures, 1 table.

Water oxidation was achieved catalytically by the use of mononuclear ruthenium–ammine complexes and using Ce(IV) as an oxidant. Cyclic voltammetric studies of the mononuclear ruthenium–ammine complexes [Ru(NH3)5Cl]2+ and [Ru(NH3)5(H2O)]3+, have been carried out using Basal Plane Pyrolytic Graphite (BPG) coated with poly(p-styrenesulfonate), Nafion, or Kaolin clay. The electrochemical properties of these ruthenium–ammine complexes show that they can be used as two-electron oxidants for water oxidation. It has also been found that these complexes oxidize water to evolve oxygen in the presence of excess Ce(IV) under homogeneous as well as heterogeneous conditions. The oxygen evolution by means of water oxidation was confirmed by using the H218O isotope in the reaction medium. The water oxidation process was found to be dependent on the ionic strength of the medium. Higher acidic conditions gave higher O2 yields. Heterogeneous catalysis with the Ru complex adsorbed in Kaolin clay was as effective as the homog...

Oxygen evolution by electrochemical water oxidation has been studied. The reaction was carried out through electrochemical water oxidation mediated by polynuclear complexes embedded in a Nafion film. The polynuclear complexes used were the µ-oxo-trinuclear ruthenium complex, [(NH3)5 RuORu(NH3)4ORu(NH3)5]Cl6 and [graphic omitted]. These complexes are effective as mediators for enhanced oxygen evolution. The mediated water oxidation has been demonstrated by potential vs. current characteristics and by oxygen analysis by gas chromatography.

The electronic absorption spectra of anion radicals produced by γ-ray irradiation of (E)-stilbene (1), indeno[2,1-a]indene (2), 5,6,11,12-tetrahydrochrysene (3), (E)-1,1′-bi-indanylidene (4), and (E)-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-binaphthylidene (5) in glassy 2-methyltetrahydrofuran solution at 77 K have been measured. Examination of the spectra leads to the following conclusions. (a) The (E)-stilbene skeleton in the anion radical of (1) as well as of (2), (3), and (4) is planar or nearly planar; (b) in the anion radical of (5) immediately after its production, the ethylene bond and the C–Ph bonds are substantially twisted, and on controlled warming or on illumination, the twisting of the ethylene bond is increased.

The time evolution of optical absorptions of cationic species in sec-butyl chloride glasses at 77 K was observed over the range of 10/sup -5/ to 1 s after irradiation with electron pulses. A band tail newly found at wavelengths shorter than 420 nm in a pure glass is assignable to a precursor of the trapped hole characterized by the 480-nm band. In the presence of an aromatic solute, trapped holes decay over the above time range and solute cations grow concurrently. In biphenyl-pyrene solutions, the decay of biphenyl cations is accompanied by the growth of pyrene cations. The observed positive-charge transfer is consistent with long-range electron transfer. 6 figures.

The electrochemical studies of a trinuclear ruthenium complex (Ruthenium red) have been carried out. Di- and tri-nuclear ruthenium complexes were adsorbed onto clay and ion-exchange resin and were then used as homogeneous and heterogeneous (clay-and resin-adsorbed) catalysts for water oxidation to evolve oxygen. The gas-chromatographic and mass-spectral data clearly show that oxygen evolved by water oxidation is catalysed by the polynuclear ruthenium complexes in the presence of CeIV oxidant. The turnover numbers and stabilities of the catalysts were evaluated under various conditions. The observed data show that the trinuclear ruthenium complexes are more efficient towards water oxidation than the dinuclear ruthenium complexes. Based on these results, the four-electron water oxidation process is discussed.

The di-μ-oxo-tetrakis(2,2′-bipyridine)dimanganese complex was used as a heterogeneous phase catalyst for water oxidation by adsorbing into Kaolin clay. The oxygen evolved was analyzed by gas chromatography and mass spectrometry. The water oxidation reaction involving the four-electron process in a heterogeneous phase was discussed.

The crystal structure of the title compound was determined by X-ray diffraction. The crystals have monoclinic symmetry with a=13.481(5), b=8.285(5), c=l3.092(3) A. β=96.24(3)°, and space group P21⁄n with Z=4. The final R-factor was 0.065 for 2191 independent reflections. The torsion angles of the C–Ph bonds are 47.4(4) and 44.4(4)°. The cyclohexene rings have approximate twist-boat conformations. The molecular structure in the crystal is compared with that in the solution phase, that of (E)-stilbenes, and the results of the molecular mechanics calculations. It is also discussed in relation to the molecular packing.