Oxygen centered radicals in iodine chemical oscillators

The existence of free radicals in iodine-based oscillatory systems has been debated for some time. Recently, we have reported the presence of reactive oxygen species (ROS) in the iodide-peroxide system in acidic medium, which is common to all iodine--based oscillatory systems ( J. Phys. Chem. A 2011 , 115 , 2247--2249 ). In this work, the goal was to identify the ROS produced in this system using an EPR spin trap which can distinguish between hydroxyl (HO(?)) and hydroperoxyl (HOO(?)) radicals. The formation of the hydroperoxyl radical was observed and a possible explanation for the low EPR signal of hydroxyl radical was proposed.     

Photocatalytic degradation of metoprolol in water suspension of TiO<Subscript>2</Subscript> nanopowders prepared using sol–gel route

Nanocrystalline titanium dioxide (TiO₂) powders have been synthesized by sol–gel method using titanium tetrachloride (TiCl₄) or tetrabutyl titanate (Ti(OC₄H₉)₄ as precursors, different alcohols and calcination temperatures in the range from 400 to 650 °C. The photocatalytic activity of as-prepared powders has been tested for the degradation of metoprolol tartrate salt, a selective β-blocker used to treat a variety of cardiovascular diseases, and compared to photocatalytic activity obtained from Degussa P25. Nanosized TiO₂ powders prepared from TiCl₄ and amyl-alcohol, calcined at 550 °C, displayed an activity comparable to Degussa P25, whereas the sample from the same series, calcined at 650 °C, showed higher photocatalytic activity in the whole range of the catalyst loading. Structural, morphological and surface properties of synthesized TiO₂ nanopowders have been investigated by XRD, SEM, EDS and BET measurements, as well as FTIR and Raman spectroscopy, in order to find out the material properties which enable rapid an efficient decomposition of metoprolol under UV radiation.     

Microwave-assisted polyol synthesis of carbon-supported platinum-based bimetallic catalysts for ethanol oxidation

High surface area carbon-supported Pt, PtRh, and PtSn catalysts were synthesized by microwave-assisted polyol procedure and tested for ethanol oxidation in perchloric acid. The catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning tunnelling microscopy (STM), TEM, and EDX techniques. STM analysis of unsupported catalysts shows that small particles (～2?nm) with a narrow size distribution are obtained. TEM and XRD examinations of supported catalysts revealed an increase in particle size upon deposition on carbon support (diameter?～?3?nm). The diffraction peaks of the bimetallic catalysts in X-ray diffraction patterns are slightly shifted to lower (PtSn/C) or higher (PtRh/C) 2θ values with respect to the corresponding peaks at Pt/C catalyst as a consequence of alloy formation. Oxidation of ethanol is significantly improved at PtSn/C with the onset potential shifted for?～?150?mV to more negative values and the increase of activity for approximately three times in comparison to Pt/C catalyst. This is the lowest onset potential found for ethanol oxidation at PtSn catalysts with a similar composition. Chronoamperometric measurements confirmed that PtSn/C is notably less poisoned than Pt/C catalyst. PtRh/C catalyst exhibited mild enhancement of overall electrochemical reaction in comparison to Pt/C.     

A joint application of spectroscopic, electrochemical and theoretical approaches in evaluation of the radical scavenging activity of 3-OH flavones and their iron complexes towards different radical species

Combined spectroscopic (UV/visible, MS and EPR), electrochemical (CV) and theoretical approaches were used to evaluate the relevant interactions of morin and quercetin, as well as their respective iron(III) complexes with DPPH, tempone, hydroxyl and superoxide radicals. The results on iron complexation specify the stoichiometry and the relevant structural forms entering the chelation of the molecules. The spectroscopic DPPH assay shows better antioxidant activity of quercetin and its iron complex both in terms of EC(50) values and stoichiometry. The results of 2-deoxyribose degradation suggest that antioxidant activities of morin and quercetin may originate from their combined effect of iron chelation and radical scavenging. The distinctive difference in the EPR spectra of morin and quercetin radicals suggests different positions of the radical centers which may account for different sequences of their activities towards investigated radicals. Activity ranking of quercetin and morin, established by cyclic voltammetry, confirms their activity sequence obtained by EPR results and is also in agreement with the results of conformational analysis. The equilibrium geometries, optimized with the M052X functionals and 6-311G(d,p) basis set, predict structural modifications between the ligand molecules in the free state and in the complex structures. The arguments gained through experimental results can also be rationalized in terms of overall molecular geometry and structural features governing antioxidant behavior i.e. substitution pattern of the ring B.     

Universally balanced photonic interferometers

A new general class of optical interferometers is proposed, and the physical principle of their operation is explained. They split the spectrum entering one input port among the interferometer arms in an arbitrarily chosen wavelength- and/or time-dependent manner but guarantee broadband constructive interference into a single output port by symmetry. The design relies only on time reversibility of Maxwell's equations and a phase condition that holds for lossless, reflectionless four-ports. As an application, a new Vernier scheme is proposed to multiply the tuning and free spectral range of microphotonic add-drop filters. It provides effective suppression of both the amplitude and the phase response of unwanted resonant passbands.     

Infrared reflectivity spectra of <Emphasis Type="Italic">η</Emphasis>-Na<Subscript>1.3</Subscript>V<Subscript>2</Subscript>O<Subscript>5</Subscript> in the charge disordered and ordered phase

We have measured the far-infrared reflectivity spectra of the sodium vanadium oxide η-Na_1.3V₂O₅ polycrystals in the wide temperature (80–300 K) and frequency (150–1500 cm⁻¹) range. Appearance of new phonon oscillators, phonon oscillator mode splitting and step-like shift of TO and LO frequencies at low temperatures are correlated with the charge-ordering phase transition, which takes place at about 120 K in this vanadium oxide.     

Low-frequency Raman scattering from CeO<Subscript>2</Subscript> nanoparticles

Raman scattering measurements were performed on CeO₂ nanoparticles at room temperature. Low-frequency modes are assigned to confined acoustic vibrations of spherical CeO₂ nanoparticles. Frequencies of these vibrational modes have been calculated in the elastic continuum approximation, which considers a nanoparticle as a homogeneous elastic sphere. We assumed stress-free boundary conditions. The specific dependence of the vibrational frequency on the particle diameter enables the determination of the particle size from the experimental Raman frequency. The particle size value calculated in this way agrees well with the value acquired from the phonon confinement model. PACS 61.46.Df; 73.63.Bd; 63.22.+m     

A structural investigation of tris(ethyl acetoacetate)aluminium (III)

Aluminium tris(ethyl acetoacetate), Al(C₆H₉O₃)₃ has been prepared and characterized by means of ¹H and ¹³C nuclear magnetic resonance spectroscopy, scanning electron microscopy and X-ray powder diffraction (XRPD). It was determined that two stereoisomeric complexes can be distinguished in the solution: meridional and facial. The crystal structure of Al(C₆H₉O₃)₃ has been determined from XRPD data. The compound crystallizes in the monoclinic space group P2₁/n.