Electrochemical and Photochemical Conversion of [Ru3Ir(μ 3-H)(CO)13] into [Ru3Ir(μ-H)3(CO)12]

Electrochemical and photochemical properties of the tetrahedral cluster [Ru₃Ir( ₃-H)(CO)₁₃] were studied in order to prove whether the previously established thermal conversion of this cluster into the hydrogenated derivative [Ru₃Ir(-H)₃(CO)₁₂] also occurs by means of redox or photochemical activation. Two-electron reduction of [Ru₃Ir( ₃-H)(CO)₁₃] results in the loss of CO and concomitant formation of the dianion [Ru₃Ir( ₃-H)(CO)₁₂]^2–. The latter reduction product is stable in CH₂Cl₂ at low temperatures but becomes partly protonated above 283K into the anion [Ru₃Ir(-H)₂(CO)₁₂]^– by traces of water. The dianion [Ru₃Ir( ₃-H)(CO)₁₂]^2– is also the product of the electrochemical reduction of [Ru₃Ir(-H)₃(CO)₁₂] accompanied by the loss of H₂. Stepwise deprotonation of [Ru₃Ir(-H)₃(CO)₁₂] with Et₄NOH yields [Ru₃Ir(-H)₂(CO)₁₂]^– and [Ru₃Ir( ₃-H)(CO)₁₂]^2–. Reverse protonation of the anionic clusters can be achieved, e.g., with trifluoromethylsulfonic acid. Thus, the electrochemical conversion of [Ru₃Ir( ₃-H)(CO)₁₃] into [Ru₃Ir(-H)₃(CO)₁₂] is feasible, demanding separate two-electron reduction and protonation steps. Irradiation into the visible absorption band of [Ru₃Ir( ₃-H)(CO)₁₃] in hexane does not induce any significant photochemical conversion. Irradiation of this cluster in the presence of CO with _irr>340nm, however, triggers its efficient photofragmentation into reactive unsaturated ruthenium and iridium carbonyl fragments. These fragments are either stabilised by dissolved CO or undergo reclusterification to give homonuclear clusters. Most importantly, in H₂-saturated hexane, [Ru₃Ir( ₃-H)(CO)₁₃] converts selectively into the [Ru₃Ir(-H)₃(CO)₁₂] photoproduct. This conversion is particularly efficient at _irr >340nm.     

Emission of volatile sesquiterpenes and monoterpenes in grapevine genotypes following Plasmopara viticola inoculation in vitro

The grapevine (Vitis vinifera) is one of the most widely cultivated fruit crops globally, and one of its most important diseases in terms of economic losses is downy mildew, caused by Plasmopara viticola. Several wild Vitis species have been found to be resistant to this pathogen and have been used in breeding programs to introduce resistance traits to susceptible cultivars. Plant defense is based on different mechanisms, and volatile organic compounds (VOCs) play a major role in the response to insects and pathogens. Although grapevine resistance mechanisms and the production of secondary metabolites have been widely characterized in resistant genotypes, the emission of VOCs has not yet been investigated following P. viticola inoculation. A Proton Transfer Reaction‐Time of Flight‐Mass Spectrometer (PTR‐ToF‐MS) was used to analyze the VOCs emitted by in vitro‐grown plants of grapevine genotypes with different levels of resistance. Downy mildew inoculation significantly increased the emission of monoterpenes and sesquiterpenes by the resistant SO4 and Kober 5BB genotypes, but not by the susceptible V. vinifera Pinot noir. Volatile terpenes were implicated in plant defense responses against pathogens, suggesting that they could play a major role in the resistance against downy mildew by direct toxicity or by inducing grapevine resistance. The grapevine genotypes differed in terms of the VOC emission pattern of both inoculated and uninoculated plants, indicating that PTR‐ToF‐MS could be used to screen hybrids with different levels of downy mildew resistance. Copyright © 2015 John Wiley & Sons, Ltd.     

Persistence of zero velocity fronts in reaction diffusion systems

Steady, nonpropagating, fronts in reaction diffusion systems usually exist only for special sets of control parameters. When varying one control parameter, the front velocity may become zero only at isolated values (where the Maxwell condition is satisfied, for potential systems). The experimental observation of fronts with a zero velocity over a finite interval of parameters, e.g., in catalytic experiments [Barelko et al., Chem. Eng. Sci., 33, 805 (1978)], therefore, seems paradoxical. We show that the velocity dependence on the control parameter may be such that velocity is very small over a finite interval, and much larger outside. This happens in a class of reaction diffusion systems with two components, with the extra assumptions that (i) the two diffusion coefficients are very different, and that (ii) the slowly diffusing variables has two stable states over a control parameter range. The ratio of the two velocity scales vanishes when the smallest diffusion coefficient goes to zero. A complete study of the effect is carried out in a model of catalytic reaction. (c) 2000 American Institute of Physics.     

Herleitung des Gaußschen Fehlergesetzes aus einer Funktionalgleichung

Ohne Zusammenfassung     

Topological charge quantization via path integration: An application of the Kustaanheimo-Stiefel transformation

Editorial note: The complete text of this paper, dedicated to Professor Asim O. Barut, will appear in the August 1993 issue ofFoundations of Physics.     

Über die Annäherung einer stetigen Funktion durch die Cesàroschen Mittel ihrer Fourierreihe

Ohne Zusammenfassung     

“Brown-Ring”-Related Coordination Polymers of the Quartet-{FeNO}7 Chromophore

A conspicuous detail of the so-called brown-ring test (the analytical test on nitrate) is the reddish color of the bottom layer of concentrated sulfuric acid, which develops upon the bleeding of the brown layer into the acid. Crystals of the same color form from a solution of ferrous sulfate in concentrated sulfuric acid on saturation with gaseous nitric oxide. The structure of this H₃O[{Fe(NO)(μ₄-SO₄)(μ₂-SO₄)_0.5}_n/n] ( 1a ) is made up from infinite chessboard-type layers with sulfur on the field junctions and Fe(NO) moieties below the black and above the white fields. An Fe–N–O angle of about 160° causes disorder in the tetragonal space group I4/mmm. A similar crystal pathology was found in the related [{Fe(MeOH)(NO)(μ₄-SO₄)}_n/n] ( 1b ) in the same crystal class. A one-dimensional coordination polymer is formed in crystals of a third compound that comprises the Fe(NO)O₅ coordination pattern, namely the brown oxalato species [{Fe(H₂O)(NO)(μ₂-ox)}_n/n · H₂O] ( 2 ). A still larger NO tilt of about 156° is not obscured by disorder in the triclinic crystals of 2 .