Elucidating the radical kinetics involved in the radiolytic destruction of lanthanide-complexed DTPA

The reprocessing of nuclear fuels to extract the remaining actinides is one of the most important strategies for viable nuclear power in the future, as geologic waste disposal of high-level radioactive waste could have considerable negative impacts on the environment. As many of these strategies are based on solvent extraction processes, our aim is to establish the radiolytic stability of the component extraction ligands. The oxidative stability of the lanthanide metal-complexed extraction ligand DTPA (diethylenetriaminepentaacetic acid) has been investigated through its reaction rate constant with the hydroxyl radical under TALSPEAK acidic pH conditions, both for the free ligand and complexed with Eu³⁺, Lu³⁺ and Gd³⁺. Specific rate constants were obtained over a range of pH conditions using thiocyanate competition kinetics. The rate constants for the complexed metals are seen to be greater than the corresponding values determined for only the DTPA protonated ligands at these pHs.     

Exciton quenching in emitter blends for organic light emitting devices probed by electric field-dependent time-resolved luminescence

We investigate quenching mechanisms of excited states in emitter layers for organic light emitting diodes (LEDs). An extensive study of a strong electric field-induced modulation (over 50%) of the time-resolved luminescence in a diamine derivative (TPD): polycarbonate blend films doped with an organic complex of europium are presented as a typical example of an important class of emitters for organic monochromatic LEDs. Using this method allowed us to identify the quenched species as the excited ligand precursors of the emissive europium ion states. Manipulating the electrode materials and their electrical bias, the electric field-enhanced dissociation, and interaction with injected charge could be separated and found as principal quenching mechanisms. We show the first one to follow the three-dimensional Onsager theory of geminate recombination, and the second one raised by their interaction with the TPD-transported holes. The interaction rate constant is found to be underlain by the three-dimensional diffusion of excited ligand singlets, combining the exciton diffusion coefficient and long-range (Forster type) energy transfer parameters. The dynamic parameters of the hole-precursor excitons interactions, extracted from the experimental data, allow us to establish the criteria for identifying useful ligands and matrices in the optimized design of electrophosphorescent, linelike emitting molecules, and device structure for organic LEDs.     

Enhancement of second harmonic generation efficiency: Growth and characterization of magnesium(II)-doped tetrakis(thiourea)nickel(II) chloride crystals

The influence of magnesium doping on the properties of tetrakis(thiourea)nickel(II) chloride crystals has been described. The reduction in the intensity observed in powder X-ray diffraction of doped specimen and slight shifts in vibrational frequencies confirm the lattice stress as a result of doping. Surface morphological changes due to doping of the alkaline earth metal are observed by scanning electron microscopy. The incorporation of Mg(II) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy. Lattice parameters are determined by single crystal XRD analysis. The thermogravimetric and differential thermal analysis studies reveal the purity of the materials and no decomposition is observed up to the melting point. The crystal is further characterized by Kurtz powder technique and dielectric studies.     

Kinetic model for the radical degradation of tri-halonitromethane disinfection byproducts in water

The halonitromethanes (HNMs) are byproducts of the ozonation and chlorine/chloramine treatment of drinking waters. Although typically occurring at low concentrations HNMs have high cytotoxicity and mutagenicity, and may therefore represent a significant human health hazard. In this study, we have investigated the radical based mineralization of fully-halogenated HNMs in water using the congeners bromodichloronitromethane and chlorodibromonitromethane. We have combined absolute reaction rate constants for their reactions with the hydroxyl radical and the hydrated electron as measured by electron pulse radiolysis and analytical measurements of stable product concentrations obtained by ⁶⁰Co steady-state radiolysis with a kinetic computer model that includes water radiolysis reactions and halide/nitrogen oxide radical chemistry to fully elucidate the reaction pathways of these HNMs. These results are compared to our previous similar study of the fully chlorinated HNM chloropicrin. The full optimized computer model, suitable for predicting the behavior of this class of compounds in irradiated drinking water, is provided.     

The role of oxidizing radicals in neptunium speciation in γ-irradiated nitric acid

The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as ^?OH, ^?NO₃ and ^?NO₂. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.     

Fluidized and vibrofluidized shallow beds of fresh leaves

The fluid dynamics behavior of shallow fluidized and vibrofluidized beds operating with fresh leaves was investigated with the aim of exploring drying applications in a modified conveyor belt (MCB) system,which may be operated in a fixedor fluidized-bed mode.Leaves of the specimens Duranta repens,Schinus molle,Coleus barbatus,Buxus sempervirens,and Bougainvillea spectabilis were tested with a range of sphericities from 0.063 to 0.213,bulk densities from 0.038 to 0.251 g/cm 3,apparent densities from 0.52 to ...     

Thermal lensing in a supercritical water medium

A pulsed, two-beam, thermal lensing experiment was performed to determine the concentration of aqueous solutes above the critical point of water. Despite a very significant mirage effect due to thermal gradients in the cell and absorption by water itself, the thermal lensing signal strength for aqueous benzoic acid in supercritical water was found to be linear with concentration in the sub-millimolar range. Although thermal lensing experiments in aqueous media are notoriously insensitive, the sharp density gradient near the critical point considerably improves the signal intensity. In this study a short-pulse pump 266 nm YAG laser and continuous low-power probe Ar ion beam were both focused into a supercritical water cell, giving a lensing signal whose strength could be maximized by changing the overlap of the two beams.     

A7DB: a relational database for mutational,physiological and pharmacological data related to the α7 nicotinic acetylcholine receptor

Background  

Nicotinic acetylcholine receptors (nAChRs) are pentameric proteins that are important drug targets for a variety of diseases including Alzheimer's, schizophrenia and various forms of epilepsy. One of the most intensively studied nAChR subunits in recent years has been α7. This subunit can form functional homomeric pentamers (α7)₅, which can make interpretation of physiological and structural data much simpler. The growing amount of structural, pharmacological and physiological data for these receptors indicates the need for a dedicated and accurate database to provide a means to access this information in a coherent manner.