Control of the evolution of iron peroxide intermediate in superoxide reductase from Desulfoarculus baarsii. Involvement of lysine 48 in protonation

Superoxide reductase is a nonheme iron metalloenzyme that detoxifies superoxide anion radicals O(2)(?-) in some microorganisms. Its catalytic mechanism was previously proposed to involve a single ferric iron (hydro)peroxo intermediate, which is protonated to form the reaction product H(2)O(2). Here, we show by pulse radiolysis that the mutation of the well-conserved lysine 48 into isoleucine in the SOR from Desulfoarculus baarsii dramatically affects its reaction with O(2)(?-). Although the first reaction intermediate and its decay are not affected by the mutation, H(2)O(2) is no longer the reaction product. In addition, in contrast to the wild-type SOR, the lysine mutant catalyzes a two-electron oxidation of an olefin into epoxide in the presence of H(2)O(2), suggesting the formation of iron-oxo intermediate species in this mutant. In agreement with the recent X-ray structures of the peroxide intermediates trapped in a SOR crystal, these data support the involvement of lysine 48 in the specific protonation of the proximal oxygen of the peroxide intermediate to generate H(2)O(2), thus avoiding formation of iron-oxo species, as is observed in cytochrome P450. In addition, we proposed that the first reaction intermediate observed by pulse radiolysis is a ferrous-iron superoxo species, in agreement with TD-DFT calculations of the absorption spectrum of this intermediate. A new reaction scheme for the catalytical mechanism of SOR with O(2)(?-) is presented in which ferrous iron-superoxo and ferric hydroperoxide species are reaction intermediates, and the lysine 48 plays a key role in the control of the evolution of iron peroxide intermediate to form H(2)O(2).     

Coupled radiation and turbulent multiphase flow in an aluminised solid propellant rocket engine

We present in this paper numerical simulations of coupled radiative transfer and turbulent flows at high temperature and pressure, typical of multiphase flows encountered in aluminised solid propellant rocket engines. The radiating medium is constituted of gases and of liquid or solid particles of oxidised aluminum. The turbulent flow of the gaseous phase is treated by using a four equation, low Reynolds number, boundary-layer-type turbulence model. The distributions of concentrations, temperatures, and temperature fluctuation variances of particles are calculated from a Lagrangian approach and a turbulence dispersion model. Thermal and mechanical non-equilibrium between the gas and different classes of particles is allowed. A locally one dimensional, iteratively based, radiative transfer solver is developed to compute wall fluxes and radiative source terms. It is shown that the thermal boundary layer attenuates significantly the radiative fluxes coming from the outer regions. Particle radiation is found to be much more important than gas radiation. Turbulent dispersion of particles in the boundary layer induces a decrease of particle concentration in the region of maximum turbulent kinetic energy, and then, decreases the attenuation effect of wall fluxes due to the boundary layer. The effects of turbulent temperature fluctuations are found to be small in the problem under consideration.     

Influence of relative humidity on electrical properties of alpha-Al2O3 powders: resistivity and electrochemical impedance spectroscopy

The influence of humidity on the electrical properties of alpha-Al2O3 powders has been investigated using adsorption isotherms, DC resistivity, and electrochemical impedance spectroscopy. Samples of two alpha-Al2O3 particle sizes were examined, both individually and mixed together. The results show that the grain-bed resistivity decreases with humidity, whereas the grain capacitance is almost constant. The resistivity difference between the two particle sizes is of several orders of magnitude, while the capacitance values are not very different. These results are interpreted in terms of the layer-by-layer growth of water adsorbed on the grain surfaces. The first, more tightly bound adsorbed layer does not provoke the same effects as those layers adsorbed at higher relative humidity.     

Electrostatic interactions between double layers: influence of surface roughness, regulation, and chemical heterogeneities

Electrostatic interactions between two surfaces as measured by atomic force microscopy (AFM) are usually analyzed in terms of DLVO theory. The discrepancies often observed between the experimental and theoretical behavior are usually ascribed to the occurrence of chemical regulation processes and/or to the presence of surface chemical or morphological heterogeneities (roughness). In this paper, a two-gradient mean-field lattice analysis is elaborated to quantifying double layer interactions between nonplanar surfaces. It allows for the implementation of the aforementioned sources of deviation from DLVO predictions. Two types of ion-surface interaction ensure the adjustment of charges and potentials upon double layer overlap, i.e., specific ionic adsorption at the surfaces and/or the presence of charge-determining ions for the surfaces considered. Upon double layer overlap, charges and potentials are adjusted via reequilibrium of the different ion adsorption processes. Roughness is modeled by grafting asperities on supporting planar surfaces, with their respective positions, shapes, and chemical properties being assigned at will. Local potential and charge distributions are derived by numerically solving the nonlinear Poisson-Boltzmann equation under the boundary conditions imposed by the surface profiles and regulation mechanism chosen. Finite size of the ions is taken into account. A number of characteristic situations are briefly discussed. It is shown how the surface irregularities are reflected in the Gibbs energy of interaction.     

Nouvelle méthode d'accès aux benzo[h]furo[3,2-c]quinoléines,analogues isostériques des benzo[c]phénanthridines

A convenient synthesis of the benzo[h]furo[3,2-c]quinoline ring is reported. Hydrogenation of dienic adducts 5 gives comppounds 6. Successive pyrolysis and alcaline hydrolysis of 6 provide diacids 9 which in the presence of anhydrous ammonium acetate and acetic acid undergoes intramolecular cyclisation to give benzo[h]furo[3,2-c]quinolone derivatives 12. The modulation of the 7-carboxy group and introduction of amino groups in the 6 position are then realized.     

Étude physico-chimique des substances thermomètres

Résumé Les auteurs ont donné un résumé de leurs recherches sur la pyrolyse de 32 substances qui changent de couleur entre 35 et 450° C et qui peuvent s'utiliser comme indicateurs de température. Les courbes de thermolyse ne sont pas reproduites à cause de leur simplicité. Les causes des changements de couleur sont variables. Dans quelques cas, il s'agit d'un changement d'état allotropique (dérivés du mercure) et l'on observe une réversibilité parfaite. Dans d'autres cas, sous l'action d'une reprise d'humidité, on revient à la teinte initiale. Enfin, comme la température de destruction dépend beaucoup du mode de préparation, de la vitesse de chauffe, de l'atmosphère environnante, certaines températures de virage ne doivent pas être considérées comme absolues. C'est pourquoi certaines de nos valeurs s'écartent de celles des auteurs précédents.

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Summary The writers have given a résumé of their investigations of the pyrolysis of 32 substances which change color between 35 and 450° C and which can be employed as temperature indicators. The thermolysis curves are not reproduced because of their simplicity. There are various reasons for these changes in color. In some instances a change in allotropic state is involved (mercury derivatives) and a perfect reversibility is observed. In other cases, the initial color is restored because of the recovery of moisture. Finally, since the temperature of destruction depends greatly on the method of preparation, the rate of heating and the surrounding atmosphere, certain color change temperatures should not be regarded as absolute. This explains the divergence of our values from those of previous workers.

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Zusammenfassung Über die Untersuchungen der Pyrolyse von 32 Substanzen, die zwischen 35 und 450° C ihre Farbe ändern und daher als Wärmeindikatoren dienen können, wird zusammenfassend berichtet. Die Thermolysekurven sind ihrer Einfachheit wegen nicht wiedergegeben. Die Ursachen der Farbänderung sind unterschiedlich. Mitunter handelt es sich um Polymorphien (Quecksilberverbindungen), die vollständig reversibel sind. In anderen Fällen führt die Wiederaufnahme von Wasser auch zur ursprünglichen Farbe. Da die Zersetzungstemperatur weitgehend von der Art der Darstellung des Präparates, der Geschwindigkeit des Erhitzens, der umgebenden Atmosphäre abhängt, sind manche Umwandlungspunkte nicht als Absolutwerte anzusehen. Aus diesem Grund ergaben sich auch Abweichungen gegenüber Angaben anderer Autoren.

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En l'honneur du ProfesseurFrite Feigl, pour son 70^e anniversaire.