Role of iron in Na <Subscript>1.5</Subscript>Fe <Subscript>0.5</Subscript>Ti <Subscript>1.5</Subscript>(PO <Subscript>4</Subscript>) <Subscript>3</Subscript>/C as electrode material for Na-ion batteries studied by operando Mössbauer spectroscopy

The role of iron in Na _1.5Fe _0.5Ti _1.5(PO ₄)₃/C electrode material for Na batteries has been studied by ⁵⁷Fe Mössbauer spectroscopy in operando mode. The potential profile obtained in the galvanostatic regime shows three plateaus at different voltages due to different reaction mechanisms. Two of them, at 2.2 and 0.3 V vs Na ⁺/Na ⁰, have been associated to redox processes involving iron and titanium in Na _1.5Fe _0.5Ti _1.5(PO ₄)₃. The role of titanium was previously elucidated for NaTi ₂(PO ₄)₃ and the effect of the substitution of Fe for Ti was investigated with ⁵⁷Fe Mössbauer spectroscopy. We show that iron is an electrochemically active center at 2.2 V with the reversible Fe ³⁺/Fe ²⁺ transformation and then remains at the oxidation state Fe ²⁺ along the sodiation until the end of discharge at 0 V.     

Polyvinylpyrrolidone and arsenic-induced changes in biological responses of model aquatic organisms exposed to iron-based nanoparticles

The efficiency of zero-valent iron particles used in the remediation of contaminated groundwater has, with the emergence of nanotechnology, stimulated interest on the use of nano-size particles to take advantage of high-specific surface area and reactivity characteristics of nanoparticles (NPs). Accordingly, engineered iron-NPs are among the most widely used nanomaterials for in situ remediation. However, while several ecotoxicity studies have been conducted to investigate the adverse impacts of these NPs on aquatic organisms, research on the implications of spent iron-based NPs is lacking. In this study, a comparative approach is used, in which the biological effects of three iron-based NPs (Fe₃O₄ and γ-Fe₂O₃ NPs with particle sizes ranging from 20 to 50 nm, and Fe⁰-NPs with an average particle size of 40 nm) on Raphidocelis subcapitata (formely known as Pseudokirchneriella subcapitata) and Daphnia magna were investigated using both as-prepared and pollutant-doped Fe-based NPs. For the latter, arsenic (As) was used as example sorbed pollutant. The results show that improved degree of NP dispersion by use of polyvinylpyrrolidone overlapped with both increased arsenic adsorption capacity and toxicity to the tested organisms. For R. subcapitata, Fe-oxide NPs were more toxic than Fe⁰-NPs, due primarily to differences in the degree of NPs aggregation and ability to produce reactive oxygen species. For the invertebrate D. magna, a similar trend of biological responses was observed, except that sorption of As to Fe⁰-NPs significantly increased the toxic response when compared to R. subcapitata. Overall, these findings point to the need for research on downstream implications of NP-pollutant complexes generated during water treatment by injection of NPs into aquatic systems.     

Tunneling in green tea: understanding the antioxidant activity of catechol-containing compounds. A variational transition-state theory study

The catechol functionality present in the catechins is responsible for the protective effects exerted by green tea against a wide range of human diseases. High-level electronic structure calculations and canonical variational transition-state theory including multidimensional tunneling corrections have allowed us to understand the key factors of the antioxidant effectiveness of the catechol group. This catechol group forms two hydrogen bonds with the two oxygen atoms of the lipid peroxyl radical, leading to a very compact reactant complex. This fact produces an extremely narrow adiabatic potential-energy profile corresponding to the hydrogen abstraction by the peroxyl radical, which makes it possible for a huge tunneling contribution to take place. So, quantum-mechanical tunneling highly increases the corresponding rate constant value, in such a way that catechins become able to trap the lipid peroxyl radicals in a dominant competition with the very damaging free-radical chain-lipid peroxidation reaction.     

Exploration of enzyme-ligand interactions in CYP2D6 & 3A4 homology models and crystal structures using a novel computational approach

New crystal structures of human CYP2D6 and CYP3A4 have recently been reported, and in this study, we wanted to compare them with previously used homology models with respect to predictions of site of metabolism and ligand-enzyme interactions. The data set consisted of a family of synthetic opioid analgesics with the aim to cover both CYP2D6 and CYP3A4, as most of these compounds are metabolized by both isoforms. The program MetaSite was used for the site of metabolism predictions, and the results were validated by experimental assessment of the major metabolites formed with recombinant CYP450s. This was made on a selection of 14 compounds in the data set. The prediction rates for MetaSite were 79-100% except for the CYP3A4 homology model, which picked the correct site in half of the cases. Despite differences in orientation of some important amino acids in the active sites, the MetaSite-predicted sites were the same for the different structures, with the exception of the CYP3A4 homology model. Further exploration of interactions with ligands was done by docking substrates/inhibitors in the different structures with the docking program GLUE. To address the challenge in interpreting patterns of enzyme-ligand interactions for the large number of different docking poses, a new computational tool to handle the results from the dockings was developed, in which the output highlights the relative importance of amino acids in CYP450-substrate/inhibitor interactions. The method is based on calculations of the interaction energies for each pose with the surrounding amino acids. For the CYP3A4 structures, this method was compared with consensus principal component analysis (CPCA), a commonly used method for structural comparison to evaluate the usefulness of the new method. The results from the two methods were comparable with each other, and the highlighted amino acids resemble those that were identified to have a different orientation in the compared structures. The new method has clear advantages over CPCA in that it is far simpler to interpret and there is no need for protein alignment. The methodology enables structural comparison but also gives insights on important amino acid substrate/inhibitor interactions and can therefore be very useful when suggesting modifications of new chemical entities to improve their metabolic profiles.     

Extraction of Cu(II) with Acorga M5640 using hollow fibre liquid membrane

The extraction of copper from sulphuric/sulphate solutions using a hollow fibre module as contactor was studied. The aldoxime Acorga M5640 was used as an extractant. The effects on the extraction rate of the flow-rates, the concentrations of copper and extractant, pH, and the presence of Na₂SO₄ in the feed phase were investigated. The overall mass transfer coefficient for copper extraction was calculated from the experimental data and was compared with the value evaluated by the resistance in the series model. The extraction process was found to be governed by the diffusion in the boundary aqueous layer and also by the chemical reaction. The kinetic data obtained were used to simulate the extraction of copper with the pseudo-emulsion-based hollow fibre with strip dispersion technique. The accordance between the results thus calculated and the experimental data was found to be satisfactory, particularly for dilute feed solutions.     

Dye-labeled polystyrene latex microspheres prepared via a combined swelling-diffusion technique

A series of water-insoluble, biologically compatible dyes, meso-tetraphenylchlorin, meso-tetraphenylporphyrin and chlorophyll-a, were successfully incorporated into beads composed of linear polystyrene (PS) via a tunable combined swelling-diffusion process. Dyed PS beads were prepared by the addition of a dye solution in tetrahydrofuran to an aqueous suspension of 10 μm PS beads in the presence of a poly((ethylene glycol)-b-(propylene glycol)-b-(ethylene glycol)) block copolymer surfactant. The presence of surfactant was found to be beneficial to prevent particle aggregation, especially at tetrahydrofuran contents above 30%. Dye loading was shown to be tunable by simple adjustments in dye composition. Confocal fluorescence microscopy indicated that dyes were distributed uniformly throughout the entire PS bead, but heterogeneously with ~500 nm diameter droplets, indicative of a separate dye phase within the PS matrix. The stability of dyed beads, indicated by resistance to dye leaching in solvent, was found to be governed by the degree of swelling of PS in the solvent medium. Hence, no leaching was observed even when a good solvent for the dye was used (ethanol), as long as that solvent did not swell the carrier particle, PS. No leaching of dyes from the beads was observed during long-term (2 years) storage in water.     

8-Alkenylborondipyrromethene dyes. General synthesis, optical properties, and preliminary study of their reactivity

A new series of 8-alkenylBODIPY dyes were prepared via the Liebeskind-Srogl cross-coupling starting from 8-thiomethyl-substituted BODIPY. Ten derivatives were prepared using alkenylboronic acids in good to excellent yields (79-97%), and one additional example was prepared from an alkenylstannane in 74% yield. The products display Michael acceptor-like reactivity. The alkenyl fragment quenches the fluorescence of the BODIPY core, which is turned back on by reducing the double bond.     

Synthesis of 6-bromo-2-arylindoles using 2-iodobenzoic acid as precursor

The synthesis of 6-bromo-2-arylindoles starting from readily available 2-iodobenzoic acid is presented. Regioselective bromination of the latter was followed by Curtius rearrangement and trapping of the isocyanate with benzyl alcohol led to the benzyl carbamate of 2-iodo-5-bromoaniline. Chemoselective Sonogashira coupling of this compound with arylacetylenes followed by TBAF induced 5-endo-dig cyclization gave the desired bromo indoles. The method allows selective introduction of a bromine atom at the indole C-6 position.