The Hydrolysis of Hydroxamic Acid Complexants in the Presence of Non-Oxidizing Metal Ions 2: Neptunium (IV) Ions

Hydroxamic acids are salt free, organic compounds with affinities for cations such as Fe³⁺, Np⁴⁺ and Pu⁴⁺, and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. The results of a UV-visible, near-IR spectrophotometric study of the 1:1 and 2:1 complexes formed between formo- and aceto-hydroxamic acids (FHA, AHA) and Np(IV) ions are interpreted using speciation diagrams for the identification of the species present at different pH and ligand to metal ratios. A kinetic model that describes the instability of the complex due to hydrolysis of the hydroxamate moiety, previously developed for the Fe(III)-AHA complexes (Andrieux et al. in J. Solution Chem. 36:1201–1217, [2007]), is tested here against experimental Np(IV)-FHA data. Consequently, the complexation constant for formation of the 1:1 Np(IV)-FHA complex in nitric acid is estimated at K ₁=2715 and indications are that complexation protects the ligand against hydrolysis at 0.1>pH>−0.1.     

The Binding Pocket at the Interface of Multimeric Telomere G-quadruplexes: Myth or Reality?

Human telomeric DNA with hundreds of repeats of the 5’-TTAGGG-3’ motif plays a crucial role in several biological processes. It folds into G-quadruplex (G4) structures and features a pocket at the interface of two contiguous G4 blocks. Up to now no structural NMR and crystallographic data are available for ligands interacting with contiguous G4s. Naphthalene diimide monomers and dyads were investigated as ligands of a dimeric G4 of human telomeric DNA comparing the results with those of the model monomeric G4. Time-resolved fluorescence, circular dichroism, isothermal titration calorimetry and molecular modeling were used to elucidate binding features. Ligand fluorescence lifetime and induced circular dichroism unveiled occupancy of the binding site at the interface. Thermodynamic parameters confirmed the hypothesis as they remarkably change for the dyad complexes of the monomeric and dimeric telomeric G4. The bi-functional ligand structure of the dyads is a fundamental requisite for binding at the G4 interface as only the dyads engage in complexes with 1 : 1 stoichiometry, lodging in the pocket at the interface and establishing multiple interactions with the DNA skeleton. In the absence of NMR and crystallographic data, our study affords important proofs of binding at the interface pocket and clues on the role played by the ligand structure.     

Synthesis of Graphene Oxide by Oxidation of Graphite with Ferrate(VI) Compounds: Myth or Reality?

It is well established that graphene oxide can be prepared by the oxidation of graphite using permanganate or chlorate in an acidic environment. Recently, however, the synthesis of graphene oxide using potassium ferrate(VI) ions has been reported. Herein, we critically replicate and evaluate this new ferrate(VI) oxidation method. In addition, we test the use of potassium ferrate(VI) for the synthesis of graphene oxide under various experimental routes. The synthesized materials are analyzed by a number of analytical methods in order to confirm or disprove the possibility of synthesizing graphene oxide by the ferrate(VI) oxidation route. Our results confirm the unsuitability of using ferrate(VI) for the oxidation of graphite on graphene oxide because of its high instability in an acidic environment and low oxidation power in neutral and alkaline environments.     

Flavonoids: A Myth or a Reality for Cancer Therapy?

Nutraceuticals are biologically active molecules present in foods; they can have beneficial effects on health, but they are not available in large enough quantities to perform this function. Plant metabolites, such as polyphenols, are widely diffused in the plant kingdom, where they play fundamental roles in plant development and interactions with the environment. Among these, flavonoids are of particular interest as they have significant effects on human health. In vitro and/or in vivo studies described flavonoids as essential nutrients for preventing several diseases. They display broad and promising bioactivities to fight cancer, inflammation, bacterial infections, as well as to reduce the severity of neurodegenerative and cardiovascular diseases or diabetes. Therefore, it is not surprising that interest in flavonoids has sharply increased in recent years. More than 23,000 scientific publications on flavonoids have described the potential anticancer activity of these natural molecules in the last decade. Studies, in vitro and in vivo, show that flavonoids exhibit anticancer properties, and many epidemiological studies confirm that dietary intake of flavonoids leads to a reduced risk of cancer. This review provides a glimpse of the mechanisms of action of flavonoids on cancer cells.     

Detection and Determination of Released Ions in the Presence of Nanoparticles: Selectivity or Strategy?

Metallic nanoparticles can release ionic species, but also both species can occur in the same samples. Therefore, there is a need of efficient and cost‐effective methods to determine these ionic species in the presence of the corresponding nanoparticles. Electroanalytical techniques open the door to this selective detection of NPs and their ions. In this work, a methodology that allows the direct determination of ionic silver (Ag⁺) in the presence of silver nanoparticles based on anodic stripping voltammetry was implemented. Silver nanoparticles were determined, after acidic digestion of the sample, by difference with respect to the total content of silver. The method was validated in terms of specific identification of silver ions, linearity, working range, limit of detection, limit of quantification, recovery, repeatability and ruggedness. All parameters are adequate for an analytical method following Eurachem recommendations. The validated method was used to determine the concentration of Ag⁺ and total silver in two commercial products of colloidal silver. The results were compared with those obtained by atomic absorption spectrometry in combination with an ultrafiltration step for isolation of ionic silver. There were no significant differences in the results. The proposed methodology benefits from the intrinsic selectivity of the electroanalysis methods, allowing to eliminate the steps of pretreatments of the samples, which are necessary in other techniques. The novelty of the article lies in the direct determination of Ag (I) ions in the presence of AgNPs, without the use of previous separation steps.     

Tb(lll) and Ca(ll) Ion Equilibria in the Presence of Glutamic Acid and Glutamine

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Polymerization of Methyl Methacrylate in the Presence of N-Acetyl-ε-aminocaproic Acid Acetylamide

The effect of N-acetyl--aminocaproic acid acetylamide on radical polymerization of methyl methacrylate initiated with lauroyl peroxide was studied.     

Voltammmetric Determination of Uric Acid in the Presence of Ascorbates Using Overoxidized Polypyrrol

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Kinetic Determination of Iodide Traces Based on the Manganese(III) Metaphosphate–Arsenic(III) Reaction in the Presence of Orthophosphoric Acid

The kinetics of the iodide-catalyzed Mn(III) metaphosphate–As(III) reaction was studied in the presence of orthophosphoric acid. The reaction rate was followed spectrophotometrically at 516nm. It was established that orthophosphoric acid increased the reaction rate and that the extent of the non-catalytic reaction was extremely small. A kinetic equation was postulated and the apparent rate constant calculated. The dependence of the reaction rate on temperature was investigated and the energy of activation and other kinetic parameters determined. Iodide was determined under the optimal experimental conditions in the range 0.6–2.5ng·mL^–1 with a relative standard deviation of up to 6.7% and a detection limit of 0.12ngmL^–1. The effect of foreign ions on the accuracy of the determinations was also investigated.     

Addition of α-Halocarboxylic Acid Esters to para-Substituted Benzaldehydes in the Presence of Pentacarbonyliron

Pentacarbonyliron promotes addition of -halocarboxylic acid esters at the carbonyl group of benzaldehyde and its para-substituted analogs. The substituent in the benzene ring strongly affects the process.     

Differences in actinide metal-ligand orbital interactions: comparison of U(IV) and Pu(IV) β-ketoiminate N,O donor complexes

Syntheses and characterization of UCl(2)((Ar)acnac)(2), UI(2)((Ar)acnac)(2), and PuI(2)((Ar)acnac)(2) are reported ((Ar)acnac denotes a bis-phenyl β-ketoiminate ligand where Ar = 3,5-(t)Bu(2)C(6)H(3)). Structural analyses and computations show significant metal-ligand orbital interaction differences in U(IV) vs. Pu(IV) bonding.     

X-Ray Microanalysis in the Environmental SEM: A Challenge or a Contradiction?

 In this paper, the application of X-ray energy dispersive spectroscopy in the environmental scanning electron microscope is reviewed. Various techniques that have been used to remove the effects of the beam spreading in the gaseous environment are discussed, specifically the pressure variation techniques and the beam-stop method. The results of the application of modified versions, developed at the University of Michigan, are also presented. It is shown that quantitative analysis in the environmental SEM, operating at 30 kV, is possible at short working distances (6 mm to 7.2 mm, gas path length 1.2 mm to 2.2 mm) in the 70 to 350 Pa range.     

Interaction of thorium(IV) with nitrate in aqueous solution: medium effect or weak complexation?

Microcalorimetric titrations were performed to study the Th(IV)/nitrate interaction in aqueous solution. The results show the formation of a weak mononuclear complex of Th(IV) with nitrate and allow the determination of the complexation thermodynamic parameters at 298 K and ionic strength 1.0 mol dm(-3). The reaction is endothermic and entropy driven. Data and comparison with similar actinide(IV) complexes allow to confirm the inner-sphere nature of the Th(NO(3))(3+) complex.     

Polymerization of Methyl Methacrylate by the System Ribonucleic Acid–Water in the Presence of Carbon Tetrachloride and Copper(11) Ion

Polymerization of methyl methacrylate (MMA) was carried out in the presence of ribonucleic acid (RNA), water, carbon tetrachloride, and copper(II) ion. The overall activation energy for the polymerization is proportional to the square root of the amount of RNA. The rate increased at first with the amount of MMA, but then became independent of the amount of MMA.

Polymerization was inhibited by the presence of air. Carbon tetrachloride and copper(II) ion are able to give RNA the ability to initiate polymerization. Conversion of MMA is accelerated by the addition of tertiary amine derivatives instead of carbon tetrachloride.     

Dianionic complexes with hexacoordinate silicon(IV) or germanium(IV) and three bidentate ligands of the salicylato(2–) type: Syntheses and structural characterization in the solid state and in solution

Reaction of tetramethoxysilane or tetramethoxygermane with salicylic acid and morpholine (molar ratio 1:3:2) in tetrahydrofuran yielded morpholiniummer-tris[salicylato(2–)-O¹,O³]silicate(mer -5) and morpholiniummer-tris[salicylato(2–)-O¹,O³]germanate (mer-8), respectively. Treatment of tetramethoxysilane with 5-chlorosalicylic acid and piperidine (molar ratio 1:3:2) in tetrahydrofuran afforded piperidinium mer-tris[5-chlorosalicylato(2–)-O¹,O³]silicate–ditetrahydrofuran (mer-6·2THF). Triethylammonium mer-tris[3-methylsalicylato(2–)-O¹,O³]silicate (mer-7) was obtained analogously by reaction of tetramethoxysilane with three molar equivalents of 3-methylsalicylic acid and two molar equivalents of triethylamine in dichloromethane/diethyl ether. The racemic compounds mer-5, mer-6· 2THF,mer-7, and mer-8 were characterized by elemental analyses (C, H, N), single-crystal X-ray diffraction, as well as solid-state (²⁹Si) and solution(¹H, ¹³C, ²⁹Si) NMR studies. The structural characterizationwas complemented by computational studies (HF studies, TZVP level) of thefac- and mer-tris[salicylato(2–)-O¹,O³]silicatedianion. In addition, the behavior of mer-7 in solution was studied by VT ¹HNMR experiments.