Effect of iron salt on the color removal of water containing the azo-dye reactive blue 69 using photo-assisted Fe(II)/H2O2 and Fe(III)/H2O2 systems

The effect of chloride, sulfate and nitrate anions on the color removal of water containing the azo-dye reactive blue 69 (RB69) in acidic solution, by using photo-assisted Fenton process with Fe(II)/H₂O₂ and Fe(III)/H₂O₂ systems was investigated. Experiments were conducted in a batch reactor irradiated during 5 h with a domestic 15 W lamp with emission in the visible spectra. Experimental results showed color disappearance in the first 5 min of reaction in the photo-assisted process for all of the different salts, greatly enhancing the reaction rate with respect to the corresponding systems under dark conditions. The exception of the general trend was the Fe₂(SO₄)₃/H₂O₂/UV system, where the decolorization process is slower probably because the oxidative species generated by rupture of Fe(III)–peroxo complexes are less reactive. Total organic matter depletion and mineralization of the effluent were also tested during the experimental runs by means of total organic carbon (TOC) showing that, for most of the photo-assisted experiments high mineralization was reached after 3 h of reaction.     

Hyperfine anomaly measurements in francium isotopes and the radial distribution of neutrons

We have performed precision measurements in a magneto-optical trap of the 7P_1/2 hyperfine structure of the isotopes ^209-210Fr. The ratio of these hyperfine constants to the previously measured 7S_1/2 ground state values reveals a significant hyperfine anomaly. This anomaly results from the different radial dependence of the electron density in the two atomic levels. The measurements are sensitive to changes in the radial distribution of the neutron magnetism. This revised version was published online in August 2006 with corrections to the Cover Date.     

Total synthesis and mechanism of action of the antibiotic armeniaspirol A

Emerging antimicrobial resistance urges the discovery of antibiotics with unexplored, resistance-breaking mechanisms. Armeniaspirols represent a novel class of antibiotics with a unique spiro[4.4]non-8-ene scaffold and potent activities against Gram-positive pathogens. We report a concise total synthesis of (±) armeniaspirol A in six steps with a yield of 20.3% that includes the formation of the spirocycle through a copper-catalyzed radical cross-coupling reaction. In mechanistic biological experiments, armeniaspirol A exerted potent membrane depolarization, accounting for the pH-dependent antibiotic activity. Armeniaspirol A also disrupted the membrane potential and decreased oxygen consumption in mitochondria. In planar lipid bilayers and in unilamellar vesicles, armeniaspirol A transported protons across membranes in a protein-independent manner, demonstrating that armeniaspirol A acted as a protonophore. We provide evidence that this mechanism might account for the antibiotic activity of multiple chloropyrrole-containing natural products isolated from various origins that share a 4-acylphenol moiety coupled to chloropyrrole as a joint pharmacophore. We additionally describe an efflux-mediated mechanism of resistance against armeniaspirols.

The antibiotic armeniaspirol A depolarized bacterial and mammalian cell membranes through a protonophore activity, that accounts for its potent antibiotic effects. A total synthesis of (±) armeniaspirol A was achieved in six steps.     

Polarization effects in generalized molecular interaction potential: New Hamiltonian for reactivity studies and mixed QM/MM calculations

A strategy to introduce multipole-induced polarization effects into quantum mechanical particles is presented. The strategy takes advantage of perturbation theory, and allows one to introduce polarization effects into the generalized molecular interaction potential (GMIP) previously defined by our group. The resulting parameter provides a complete and accurate picture of molecular interactions at a reduced computational cost. It is suggested that this polarized potential (GMIPp) can be used as an effective Hamiltonian for mixed QM/MM calculations. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 866–881, 1998     

Suitability of density functional methods for calculation of electrostatic properties

A systematic analysis was performed on the suitability of the molecular electrostatic potential (MEP) and MEP-derived properties determined by means of density functional (DFT) methods. Attention was paid to the electrostatic potential (ESP) derived charges, the ESP and exact quantum mechanical dipole moments, the depth of MEP minima, and the MEP distribution in layers around the molecule for a large series of molecules. The electrostatic properties were determined at either local or nonlocal DFT levels using different functionals. The results were compared with the values estimated from quantum mechanical calculations performed at Hartree–Fock, Møller–Plesset up to fourth order, and CIPSI levels. The suitability of the MEP-derived properties estimated from DFT methods is discussed for application in different areas of chemical interest. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 980–991, 1997     

Monitoring of bentonite pore water with a probe based on solid-state microsensors

Repositories for the disposal of radioactive waste generally rely on a multi-barrier system to isolate the waste from the biosphere. This multi-barrier system typically comprises the natural geological barrier provided by the repository host rock and its surroundings and an engineered barrier system (EBS). Bentonite is being studied as an appropriated porous material for an EBS to prevent or delay the release and transport of radionuclides towards biosphere. The study of pore water chemistry within bentonite barriers will permit to understand the transport phenomena of radionuclides and obtain a database of the bentonite-water interaction processes. In this work, the measurement of some chemical parameters in bentonite pore water using solid-state microsensors is proposed. Those sensors are well suited for this application since in situ measurements are feasible and they are robust enough for the long periods of time that monitoring is needed in an EBS. A probe containing an ISFET (ion sensitive field effect transistor) for measuring pH, and platinum microelectrodes for measuring conductivity and redox potential was developed, together with the required instrumentation, to study the chemical changes in a test cell with compacted bentonite. Response features of the sensors’ probe and instrumentation performance in synthetic samples with compositions similar to those present in bentonite barriers are reported. Measurements of sensors stability in a test cell are also presented.     

Parametrization of the magnetic behavior of the triangular spin ladder chains organically templated: (C2N2H10)[M(HPO3)F3] (M(III) = Fe, Cr, and V). Crystal structure and thermal and spectroscopic properties of the iron(III) phase

A new iron(III) phosphite templated by ethylenediamine has been synthesized using solvothermal conditions under autogenous pressure. The (C2N2H10)[Fe(HPO3)F3] compound has been characterized by single-crystal X-ray diffraction data and spectroscopic and magnetic techniques. The crystal structure is formed by chains extended along the c axis and surrounded by ethylenediammonium cations. A study by diffuse-reflectance spectroscopy has been performed, and the calculated Dq, B, and C parameters for the Fe(III) cations are 1030, 720, and 3080 cm(-1), respectively. The M?ssbauer spectrum at room temperature is characteristic of Fe(III) ions. The electron spin resonance (ESR) spectra carried out at different temperatures show isotropic signals with a g value of 2.00(1). The thermal evolution of the intensity of the ESR signals indicates the existence of antiferromagnetic interactions for the Fe(III) phase. The magnetic susceptibility data of the Cr(III) and V(III) compounds show antiferromagnetic couplings. The J-exchange parameters of the Fe(III) and Cr(III) compounds have been calculated by using a model for a triangular spin ladder chain. The values are J1 = -1.63(1) K and J2 = -0.87(2) K with g = 2.02 for the Fe(III) phase and J(1) = -0.56(2) K and J2 = -0.40(2) K with g = 1.99 for the Cr(III) compound. In the case of the V(III) phase, the fit has been performed considering a linear chain with the magnetic parameters D = 2.5 cm(-1) and J = -1.15(1) K.     

Super-accelerating bouncing cosmology in asymptotically free non-local gravity

Application of the effective action approach to amplitudes with loop integration is studied for collisions on two and three centers with possible gluon emission. A rule is formulated for the integration around pole singularities in the induced vertices which brings the results in agreement with the QCD. It is demonstrated that the amplitudes can be restored from the purely transverse picture by introducing the standard Feynman propagators for intermediate gluons and quarks.