Upgrading and expanding the electro-Fenton and related processes

The Fenton-based electrochemical advanced oxidation processes are currently recognized as the most effective technologies to achieve fast and complete degradation of target organic contaminants in water. Electro-Fenton was the pioneering process, but a larger mineralization is attained via UV and solar photoelectro-Fenton processes due to the occurrence of key photoreduction reactions. In practice, the decontamination effectiveness turns out to be limited as solution pH increases and the two-electron oxygen reduction reaction occurring at the cathode becomes inefficient or insufficient. Here, we focus on the current opinion in two crucial features of the reviewed processes: (i) trends in cathodic H₂O₂ electrogeneration, showing the oxygen reduction reaction upgrading upon use of new and/or more sustainable electrocatalysts, cathode configurations and reactor designs; and (ii) advances in iron-based catalysts, with the main purpose of expanding the application to a much wider pH range, eventually surpassing the classical acidic limitation associated to conventional Fenton's reaction.     

Carbon nanotube/polysulfone composite screen-printed electrochemical enzyme biosensors

The fabrication, evaluation and attractive performance of multiwall carbon nanotube(MWCNT)/polysulfone biocomposite membrane modified thick-film screen-printed electrochemical biosensors are reported. The fabricated carbon nanotube/polysulfone (CNT/PS) strips combine the attractive advantages of carbon nanotube materials, polysulfone matrix and disposable screen-printed electrodes. Such thick-film carbon nanotubes/polysulfone sensors have a well defined performance, are mechanically stable, and exhibit high electrochemical activity. Furthermore, biocompatibility of CNT/PS composite allows easy incorporation of biological functional moiety of horseradish peroxidase by phase inversion technique. The comparison of graphite with MWCNT as conductor material is described in this paper. The proposed H(2)O(2) biosensor exhibited a linear range (applied potential, -0.2 V) from 0.02 to 0.5 mM and a K(M)(app) of 0.71 mM.     

Intramolecular mixed-valence state through silicon or germanium double bridges in rigid bis(tetrathiafulvalenes)

The synthesis and characterization of two ortho-dimethyltetrathiafulvalene (o-DMTTF)-based rigid dimers containing dimethylsilicon (Me(2)Si) or dimethylgermanium (Me(2)Ge) linkers are described. Single-crystal X-ray analysis reveals planar geometry for the central 1,4-disilicon or 1,4-digermanium six-membered rings. DFT calculations provide optimized conformations in agreement with the experimental ones, and also emphasize the role of the heteroatomic linkers in the conjugation between the two redox active units. Cyclic voltammetry measurements show sequential oxidation into radical cation, and then dication species. Solution EPR measurements on the radical-cation species indicate full delocalization of the unpaired electron over both electroactive TTF units, with an associated coupling of 0.42 G with twelve equivalent protons. DFT calculations afford fully planar geometry for the radical-cation species and confirm the experimental isotropic coupling constant. Single-crystal X-ray analyses of two charge-transfer compounds obtained upon chemical oxidation, formulated as [(Me(2)Si)(2)(o-DMTTF)(2)].1/2[TCNQ].1/2[TCNQF(4)] and [(Me(2)Ge)(2)(o-DMTTF)(2)].[TCNQ], demonstrate the occurrence of genuine mixed-valence radical-cation species, as well as a three-dimensional network of short S...S intermolecular contacts. Temperature-dependent conductivity measurements demonstrate semiconducting behavior for both charge-transfer compounds, with an increase of the absolute value of the conductivity upon applying external pressure. Band structure calculations reveal peculiar pseudo-two-dimensional electronic structures, also confirming electronic interactions through SiMe(2) and GeMe(2) bridges.     

Chiral molecular metals: syntheses, structures, and properties of the AsF(6)(-) salts of racemic (+/-)-, (R)-, and (S)-tetrathiafulvalene-oxazoline derivatives

A metallic behavior characterizes a first complete series of 2:1 AsF6- mixed-valence chiral salts of (R)-, (S)-, and racemic (+/-)-tetrathiafulvalene methyl-oxazoline derivatives. The enhanced conductivity of the pure enantiomeric salts, when compared with that of the racemic one, is the likely consequence of the structural disorder observed in the latter.     

DTPA-bisamide-based MR sensor agents for peroxidase imaging

[reaction: see text] The synthesis and some properties of two novel DTPA-bisamides are reported. These derivatives were designed as enzyme-activated contrast agents (CA) for magnetic resonance imaging. Both derivatives bear tyramido or 5-hydroxytryptamido groups that could be oligomerized in situ in the presence of peroxidase/H(2)O(2) pair resulting in a net increase in longitudinal (R1) relaxivity.     

Electronic Band Structure Study of the Transport Properties of the Intermetallic Compounds ZrRuP and ZrRuSi

Electrical properties of the intermetallic superconductors h-ZrRuP, o-ZrRuP, and h-ZrRuSi were examined by calculating their electronic structures on the basis of the extended Hückel tight-binding method. To a first approximation, the electronic structure of ZrRuP is well described in terms of the oxidation state Zr(4+)(RuP)(4)(-). This picture provides simple explanations for why both h-ZrRuP and o-ZrRuP have low N(E(f)) values and why h-ZrRuP has a nearly half-filled one-dimensional (1D) band dispersive along the c direction. A charge density wave instability associated with such a 1D band probably causes a c-axis doubling structural distortion in h-HfRuAs and h-TiRuAs. We discussed probable reasons for why the intermetallic phases with the c-axis doubling distortion are not superconductors and why h-ZrRuP has a higher T(c) than does o-ZrRuP.     

Assigning students to course sections using tabu search

In this paper we describe a new student registration system which has been developed at the University of Valencia, Spain. The system has two steps. First, the students make a computer-aided course selection from the courses available at the University. Thereafter, an assignment procedure allocates students to sections in order to respect two criteria: to provide the students with satisfactory schedules and to get balanced section enrollments. The assignment process has two phases. In Phase I, we obtain a set of the best solutions for each student. The algorithm is based on the construction of maximum cardinality independent sets. In Phase II, these solution sets are put together and a tabu search algorithm looks for a satisfactory balance between course sections without causing the solution obtained for each student to worsen significantly. The system was used at the beginning of the academic year 1996/97 in the Faculty of Mathematics and could be extended in the near future to the rest of the University. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spacelike Fluctuations of the Stress Tensor for de Sitter Vacuum

The two-point function characterizing the stresstensor fluctuations of a massless, minimally coupledfield for an invariant vacuum state in de Sitterspacetime is discussed. This two-point function is explicitly computed for spacelike-separatedpoints which are geodesically connected. We show thatthese fluctuations are as important as the expectationvalue of the stress tensor itself. These quantum field fluctuations will induce fluctuations inthe geometry of de Sitter spacetime. This paper is afirst step toward the computation of such metricfluctuations, which may be of interest for large-scale structure formation in cosmology. The relevanceof our results in this context is brieflydiscussed.     

Surface Probing with Streaming Potential: The Polymer Flooding Scenario

Transport in Porous Media - The first experimental evidence of polymer adsorption in natural carbonates obtained from streaming potential measurements is presented. The surface probing of the...