D. Katakis

Interaction of thiamine and its phosphate esters with Pt(II) and Pd(II)

Abstract The reactions of Thiamine·HCl (ThH), Thiamine monophosphate·HCl (TMP) and Thiamine pyrophosphate (TPP) have been studied in aqueous solutions (pH ∼3–4) at room temperature. Two types of complexes have been characterized by elemental analyses, conductivity measurements, ir, 1 H nmr and 13 C nmr spectra: ionic 1:2 sults in which thiamine is present as a cation, and 1:1 complexes in which the organic ligand is directly coordinated to the metal ions. The formulae of the ionic salts that were prepared are [MX 4 ] 2− [Th] + 2 and MThX 3 . The salts can easily be converted into 1:1 products by stirring in water at room temperature, while the TPP analogs require excess of ligand. The 1:1 complexes appear to have a zwitterionic structure and the metal is bound through N′ 1 of the pyrimidine ring of thiamine. These solid and stable complexes of thinmine are the first examples reported having a direct metal-to-nitrogen bond.

Dispersion and Sorption of Oil Spills by Emulsifier-Modified Expanded Perlite

Abstract Three grain sizes of expanded perlite were modified with emulsifiers and their potential usefulness in combating oil spills was studied. The tests in the laboratory show that when this perlite is added to a water–oil mixture, the light perlite particles move on the surface spreading over it very quickly (in fractions of a second). It seems that the emulsifier disperses the oil, but at the same time it disperses the perlite particles. At the end there is an emulsion and also perlite particles saturated with it. The usefulness in combating oil spills at sea depends on the following characteristics: (a) With emulsifier-modified perlite some of the oil can be removed (in the form of emulsion), whereas with emulsifiers only this is not possible. Simultaneously the spill is dispersed quickly, before spreading. (b) The action is quick even with a calm sea. Self-mixing is inherent to the process. (c) The action is quick and limited to the surface, where the perlite particles float. There is little waste of the emulsifier in the bulk of the sea.

First-row transition metal complexes with 2-benzoylpyridine

Abstract The interaction of 2-benzoylpyridine with first row transition metal ions is studied in organic solvents and in the solid state. The isolated complexes are characterized by elemental analyses, magnetic susceptibility, conductivity measurements, IR spectra and UV-vis electronic spectra. It is found that 2-benzoylpyridine acts either as mono- or as a bidentate agent, depending on such factors as the halide used (Cl − or Br − ), the solvent and adduct formation between the complex and HCl or HBr. In the case of the Co(II) complexes studied, opening of the chelate ring is accompanied by a change from an octahedral to a tetrahedral arrangement. In all the other cases the complexes are octahedral. Aspects of the results that might have mechanistic implications are pointed out.

Photocatalytic splitting of water

Abstract The non-biomimetic splitting of water has been achieved using a single photocatalyst-catalyst (tris-[1-(4-methoxyphenyl-2-phenyl-1,2-ethylenodithiolenic-S,S′]tungsten), and a reversible electron acceptor (methylviologen). The average quantum yield (in equivalents) in the effective wavelength range in the visible (400–500 nm) is about 4%. The oxidation and reduction cycles of water are fully coupled, in fact they are integrated, in the sense that they are part of a single cycle, rather than of the separate hypothetical cycles with contact points proposed in the literature.

Photocatalytic splitting of water: increase in conversion and energy storage efficiency

Abstract The yield of the photocatalytic splitting of water using tris-[1-(4-methoxyphenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′] tungsten as a photocatalyst-catalyst increases by more than threefold on going from 20 to 70°C, and there is no indication that the effect levels off at this temperature. The intensity of light (within the error limits of our experiments) does not have appreciable effect. The nature of the reversible electron acceptor also influences the energy storage efficiency, e.g. 1,1-dibenzyl-4,4′-bipyridiniumdichloride gives an energy storage efficiency approximately 10% higher than methylviologen. The energy storage efficiency also depends on the presence of electron donors; if Ph 3 N is added, the energy storage efficiency increases by 20%. With ethylenediaminetetraacetic acid (EDTA) the results are even more spectacular; there is a twofold increase, but only initially. At longer times the system is unstable. Overall light energy storage efficiencies can be as high as 7%, and the expectations for further improvement are very good.

The Cr2O72−CrO42−HCrO4− system revisited

Abstract The electronic spectra of aqueous CrVI solutions in the pH range 3–11 have four isosbestic points, located at 246, 293, 338 and 441 nm. These positions are independent of the total concentration of CrVI. The existence of the isosbestic points indicates that only two species are present, namely CrO42− and Cr2O72−, and that HCrO4− is spectrophotometrically undetectable. This conclusion is further supported by factor analysis, which gives the number of linearly independent species in solution to be two, and also by the method of spectral displacement. At the isosbestic points absorbance in linear in total CrVI concentration. In this sense Beers law is valid, and the results can be used for analytical purposes.

The interaction of oxomolybdenum(VI) with nucleic acid bases and nucleosides

Abstract The reactions have been studied of the nucleic acid bases, adenine, cytosine, guanine, purine, hypoxanthine, mercaptopurine and the nucleosides, guanosine, cytidine and adenosine with sodium molybdate in aqueous solutions. Compounds of the type (AH+)4 Mo8O26·4H2O (where A = adenine, cytosine, guanine, hypoxanthine, purine, mercaptopurine, adenosine and cytidine) were isolated at pH values around 4 and compounds of the type (AH+)2Mo6O19 (where A = Adenosine, cytidine or guanosine) at around pH 2. The compounds prepared were characterized by elemental analysis, infrared, Raman, electronic and 1H NMR spectroscopy, conductivity measurements and pH tirations.

Dithiolenes: A cheap alternative to platinum for catalytic dihydrogen formation. The case of tris-[1-(4-methoxyphenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′] tungsten

Abstract The monoanion of the title compound acts as a catalyst in the production of H2 from water. The reaction was studied using the free radical derived from methyl viologen as the source of the required electrons, in mixed water-acetone solutions. The kinetics are first order in the concentration of the free radical, and in the concentration of the catalyst. The dependence on hydrogen ion concentration, and on the water content of the solvent is complex. This, and the activation parameters indicate parallel paths. The proposed catalytic cycle involves the sequence: (1) Electron transfer, (2) Proton transfer, (3) Electron transfer, (4) Proton transfer. It is postulated that the rate-determining step is the transfer of the second electron or a concerted combination of this and of the transfer of the second proton.

New catalysts in the photo-oxidation of water

Abstract Of the 20 dithiolene complexes investigated, only three were effective in the photo-oxidation of water to O2 in the visible region and at the same time sufficiently stable: tris-[1-(4-dimethylaminophenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′]tungsten, tris-[1-(4-methoxy-phenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′]tungsten and tris-[1-(4-methoxyphenyl)-1,2-ethylenodithiolenic-S,S′]tungsten. Four more produced oxygen, but were not sufficiently stable for the reaction to be truly catalytic. The three successful catalysts are non-symmetrical and have phenyl rings with para electron-donating substituents. The metals used were W, Mo, Re and Ni. The dithiolene complexes of the first three are trigonal prismatic and of nickel are square planar. The best results in terms of yield and stability were obtained with tungsten, and specifically with tris-[1-(4-dimethylaminophenyl)-2-phenyl-1,2-ethylenodithiolenic-S,S′] tungsten; the light storage efficiency for this catalysts was estimated to be better than 9%. As indicated by the oxidation potentials, the excited states of the dithiolenes used were powereful oxidizing agents, sufficient to oxidize water.

Homogeneous catalytic action of a nickel dithiolene complex, leading to dihydrogen formation from N,N'-dimethyl-4,4'-dipyridinium radical ion solutions

Abstract Bis(2-chlorodithiobenzyl)nickel(II) reacts with the methylviologen free-radical ion and is reduced to its mono-anion. The second-order rate constant for this reaction was found to be greater than 10 7 M −1 s −1 . The mono-anion of the complex acts as a homogeneous catalyst for the electron transfer reaction between the remaining excess of the methylviologen free-radical ion and water, leading to dihydrogen production. The kinetics and mechanism of the catalytic reaction were studied in acetone-water solutions. The reaction is second order with respect to the catalyst and depends on the water content of the solutions. The value of k 2 is 8.2 ± 0.3 M −2 s −1 at 21 °C and at a 30:70 water: acetone ratio. The Arrhenius activation energy is 77 ± 3 kJ mol −1 . A mechanism is proposed for the reaction.