Carboxyl-Functionalized Task-Specific Ionic Liquids for Solubilizing Metal Oxides

Imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium, and quaternary ammonium bis(trifluoromethyl-sulfonyl)imide salts were functionalized with a carboxyl group. These ionic liquids are useful for the selective dissolution of metal oxides and hydroxides. Although these hydrophobic ionic liquids are immiscible with water at room temperature, several of them form a single phase with water at elevated temperatures. Phase separation occurs upon cooling. This thermomorphic behavior has been investigated by H-1 NMR, and it was found that it can be attributed to the temperature-dependent hydration and hydrogen-bond formation of the ionic liquid components. The crystal structures of four ionic liquids and five metal complexes have been determined.

Task-specific ionic liquid for solubilizing metal oxides

Protonated betaine bis(trifluoromethylsulfonyl) imide is an ionic liquid with the ability to dissolve large quantities of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium( II) oxide, mercury( II) oxide, nickel( II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide, manganese( II) oxide, and silver( I) oxide. Insoluble or very poorly soluble are iron(III), manganese(IV), and cobalt oxides, as well as aluminum oxide and silicon dioxide. The metals can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution. After transfer of the metal ions to the aqueous phase, the ionic liquid can be recycled for reuse. Betainium bis( trifluoromethylsulfonyl) imide forms one phase with water at high temperatures, whereas phase separation occurs below 55.5 degrees C ( temperature switch behavior). The mixtures of the ionic liquid with water also show a pH-dependent phase behavior: two phases occur at low pH, whereas one phase is present under neutral or alkaline conditions. The structures, the energetics, and the charge distribution of the betaine cation and the bis( trifluoromethylsulfonyl) imide anion, as well as the cation-anion pairs, were studied by density functional theory calculations.

Catalytic hydrogenation of tertiary amides at low temperatures and pressures using bimetallic Pt/Re-based catalysts

Hydrogenation of tertiary amides, in particular, N-methylpyrrolidin-2-one, can be efficiently facilitated by a TiO(2)-supported bimetallic Pt/Re catalyst at low temperatures and pressures. Characterisation of the catalysts and kinetic tests have shown that the close interaction between the Re and Pt is crucial to the high activity observed. DFT calculations were used to examine a range of metal combinations and show that the role of the uncoordinated Re is to activate the C=O and that of the Pt is as a hydrogenation catalyst, removing intermediates from the catalyst surface. The rate enhancement observed on the TiO(2) support is thought to be due to the presence of oxygen vacancies allowing adsorption and weakening of the C=O bond. (C) 2011 Elsevier Inc. All rights reserved.

Evaluation of Pt and Re oxidation state in a pressurized reactor: difference in reduction between gas and liquid phase

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.

Holothurians – potential biomonitors for metal levels in deep-sea sediments

Levels of cadmium, copper, aluminium, iron, manganese and zinc (Cd, Cu, Al, Fe, Mn and Zn) in deep-sea sediments and sediment-feeding holothurians are reported. Profiles of metals were found to vary with depth in the sediment. Holothurian foregut metal values are generally closer to surficial sediment levels, whereas body wall levels, with the exception of Cd and Cu, were generally lower. Holothurians are presented as potential biomonitors of metal concentrations in the deep-sea floor environment.

Versatile N,C,N coordination behavior of a monoanionic aryldiamine ligand in ruthenium(II) complexes: Syntheses and crystal structures of [Ru-II(C6H3(CH(2)NMe(2))(2)-2,6)X(L)] (L equals norbornadiene, X=Cl, SO3CF3; L=PPh(3), X=I) and [Ru-II{C6H3(CH(2)NMe(2))(2)-2,6}(2,2':6:2''-terpyridine)]Cl

The monoanionic ligand [C6H3(CH(2)NMe(2))(2)-2,6](-), a potentially terdentate N,C,N bonding system, has been employed to synthesize a series of new ruthenium(II) complexes [Ru{C6H3(CH(2)NMe(2))(2)-2,6}X(L)] (L = PPh(3) X = Cl (2a), I (2b); L = norbornadiene (nbd), X = Cl (4), eta(1)-OSO2CF3 (5)) and [Ru{C6H3(CH(2)NMe(2))(2)-2,6}(2,2':6',2 ''-terpyridine)]Cl (3). X-ray crystal structures of 2b and 3-5 have been determined, in which the N,C,N coordination geometry with respect to the metal center is found to differ considerably. In each complex the aryldiamine ligand is terdentate, eta(3)-N,C,N-bonded as a six electron donor system. However, depending on the other ligands in the Ru(II) coordination sphere, this ligand demonstrates considerable flexibility in adopting coordination geometries which range from meridional in 3 through pseudomeridional in 2b to pseudofacial in 4 and 5. In the structures of 4 and 5 significant distortions of the aryl ring, involving bending of the six-membered ring into a boatlike conformation, are found. The different combinations of the N,C,N ligand with sets of other ligands lead to a range of metal geometries, i.e. square pyramidal in 2b, octahedral in 3, and bicapped tetrahedral in 4 and 5.

Retention of toxic chromium from aqueous phase by H3PO4-activated lignin: Effect of salts and desorption studies

In this study, the feasibility of using H₃PO₄-activated lignin for hexavalent chromium adsorption has been investigated. The composite of activated lignin was characterized using FTIR, XRD and SEM with EDAX analysis. It was observed that the pH had a strong effect on the adsorption capacity; adsorption of Cr(VI) was more favorable at acidic pH with maximum uptake at pH 2. The adsorption equilibrium data were best represented by Koble-Corrigan isotherm. The monolayer sorption capacity obtained from the Langmuir model was found to be 77.85 mg/g. Adsorption showed pseudo-second order rate kinetics and the process involving the rate-controlling step is complex as it involves both film and intraparticle diffusion processes. The NaOH desorbing agent was able to release approximately 84% of metal ions. Thermodynamic parameters showed that the sorption process is exothermic and non-spontaneous. The overall Cr(VI) retention on the activated lignin surface perhaps includes both the physical adsorption of Cr(VI) and the consequent reduction of Cr(VI) to Cr(III). (C) 2011 Elsevier B.V. All rights reserved.

Selectivity control in hydrogenation reactions by nanoconfinement of polymetallic nanoparticles in mesoporous thin films

A one-pot sol-gel synthesis method has been developed for the incorporation of metal nanoparticles into mesoporous oxide thin films deposited on various plane substrates by spin-coating and on the inner surface of fused silica capillaries by dip-coating. The size, the metal loading and the stoichiometry of the metal nanoparticles could be precisely controlled by following this methodology. In the first step, polymer stabilized Pt50Sn50 and Pt90Sn10 nanoparticles were obtained by a solvent-reduction method. Then, the nanoparticles were added to a metal oxide precursor sol, which was destabilized by solvent evaporation. After calcination, the obtained materials were tested in the hydrogenation of citral in both batch and continuous modes. The highest selectivity of 30% towards the unsaturated alcohols was obtained over supported Pt90Sn10 nanoparticles with a preferential formation of the cis-isomer (nerol) due to a unique confinement of the bimetallic nanoparticles in the mesoporous framework. The selectivity towards the unsaturated alcohols was further improved to 56% over the PtRu5Sn nanoparticles supported by impregnation onto mesoporous silica films. (C) 2009 Elsevier B.V. All rights reserved.

Controlling Assembly of Mixed Thiol Monolayers on Silver Nanoparticles to Tune Their Surface Properties

Modifying the surfaces of metal nanoparticles with self-assembled monolayers of functionalized thiols provides a simple and direct method to alter their surface properties. Mixed self-assembled monolayers can extend this approach since, in principle, the surfaces can be tuned by altering the proportion of each modifier that is adsorbed. However, this works best if the composition and microstructure of the monolayers can be controlled. Here, we have modified preprepared silver colloids with binary mixtures of thiols at varying concentrations and modifier ratios. Surface-enhanced Raman spectroscopy was then used to determine the effect of altering these parameters on the composition of the resulting mixed monolayers. The data could be explained using a new model based on a modified competitive Langmuir approach. It was found that the composition of the mixed monolayer only reflected the ratio of modifiers in the feedstock when the total amount of modifier was sufficient for approximately one monolayer coverage. At higher modifier concentrations the thermodynamically favored modifier dominated, but working at near monolayer concentrations allowed the surface composition to be controlled by changing the ratios of modifiers. Finally, a positively charged porphyrin probe molecule was used to investigate the microstructure of the mixed monolayers, i.e., homogeneous versus domains. In this case the modifier domains were found to be <2 nm.

The WaaL O-antigen lipopolysaccharide ligase has features in common with metal ion-independent inverting glycosyltransferases(*)

WaaL is a membrane enzyme that catalyzes a key step in lipopolysaccharide (LPS) synthesis: the glycosidic bonding of a sugar at the proximal end of the undecaprenyl-diphosphate (Und-PP) O-antigen with a terminal sugar of the lipid A-core oligosaccharide (OS). Utilizing an in vitro assay, we demonstrate here that ligation with purified Escherichia coli WaaL occurs without adenosine-5'-triphosphate (ATP) and magnesium ions. Furthermore, E. coli and Pseudomonas aeruginosa WaaL proteins cannot catalyze ATP hydrolysis in vitro. We also show that a lysine substitution of the arginine (Arg)-215 residue renders an active protein, whereas WaaL mutants with alanine replacements in the periplasmic-exposed residues Arg-215, Arg-288 and histidine (His)-338 and also the membrane-embedded aspartic acid-389 are nonfunctional. An in silico approach, combining predicted topological information with the analysis of sequence conservation, confirms the importance of a positive charge at the small periplasmic loop of WaaL, since an Arg corresponding to Arg-215 was found at a similar position in all the WaaL homologs. Also, a universally conserved H[NSQ]X(9)GXX[GTY] motif spanning the C-terminal end of the predicted large periplasmic loop and the membrane boundary of the transmembrane helix was identified. The His residue in this motif corresponds to His-338. A survey of LPS structures in which the linkage between O-antigen and lipid A-core OS was elucidated reveals that it is always in the beta-configuration, whereas the sugars bound to Und-PP are in the alpha-configuration. Together, our biochemical and in silico data argue that WaaL proteins use a common reaction mechanism and share features of metal ion-independent inverting glycosyltransferases.

Phenol degradation by powdered metal ion modified titanium dioxide photocatalysts

Conventional water purification and disinfection generally involve potentially hazardous substances, some of which known to be carcinogenic in nature. Titanium dioxide photocatalytic processes provide an effective route to destroy hazardous organic contaminants. This present work explores the possibility of the removal of organic pollutants (phenol) by the application of TiO2 based photocatalysts. The production of series of metal ions doped or undoped TiO2 were carried out via a sol–gel method and a wet impregnation method. Undoped TiO2 and Cu doped TiO2 showed considerable phenol degradation. The efficiency of photocatalytic reaction largely depends on the photocatalysts and the methods of preparation the photocatalysts. The doping of Fe, Mn, and humic acid at 1.0 M% via sol–gel methods were detrimental for phenol degradation. The inhibitory effect of initial phenol concentration on initial phenol degradation rate reveals that photocatalytic decomposition of phenol follows pseudo zero order reaction kinetics. A concentration of > 1 g/L TiO2 and Cu doped TiO2 is required for the effective degradation of 50 mg/L of phenol at neutral pH. The rise in OH- at a higher pH values provides more hydroxyl radicals which are beneficial of phenol degradation. However, the competition among phenoxide ion, Cl- and OH- for the limited number of reactive sites on TiO2 will be a negative influence in the generation of hydroxyl radical. The dependence of phenol degradation rate on the light intensity was observed, which also implies that direct sunlight can be a substitute for the UV lamps and that photocatalytic treatment of organic pollutants using this technique shows some promise.

The distribution of arsenic in soils affected by the Aznalcóllar mine spill, SW Spain

In April 1998, a holding lagoon containing pyrite ore processing waste, failed and released an estimated 5-6 million m(3) of metal rich sludge and acidic waters into the Rio Guadiamar, SW Spain. Over 2700 ha of the internationally important Doñana National and Natural Parks were contaminated. The sludge component of the waste contained up to 0.6% arsenic. This paper presents an extensive set of 0-5 cm soil analyses results from samples taken 6-8 months after the spill. Data are presented on pseudo-total arsenic levels in these samples, and on arsenic removed by both single batch and sequential extraction techniques. Pseudo-total levels of arsenic in the sludge ranged from 1521 to 3510 mg kg(-1), and a mean 4.4% of this was found to be extractable using 2.5% acetic acid. Soils in the Guadiamar Valley and Entremuros areas (those worst affected by the spill) were found to contain 85.4-782 mg kg(-1) and 7.1-196 mg kg(-1) pseudo-total arsenic, respectively. The mean acetic acid extractable component in these areas was 2.5% and 4.9%, respectively. Background pseudo-total arsenic levels in the soils of the area have been found to be 4.2-13.6 mg kg(-1). Rapid input of acidic waters, and the acidic nature of the sludge itself, may have caused depletion of Mg, Na and K, and to a lesser extent Mn, Ca and PO(4) in the upper 5 cm of the worst affected soils. Sequential extraction results suggest clear As-Fe associations, and possible As-Mn associations within the more soluble phases.

Coordination Properties of Ionic Liquid-Mediated Chromium(II) and Copper(II) Chlorides and Their Complexes with Glucose

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with diallrylimidazolium chloride (RMlm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl42- species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMlm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl- ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl ligands by a hydroxyl group of glucose is only favorable for CrCl42-. For Cu2+ complexes, the formation of hydrogen bonded complexes between CuCl42- and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results.

The Use of Electrospray Mass Spectrometry to Determine Speciation in a Dynamic Combinatorial Library for Anion Recognition

The composition of a dynamic mixture of similar 2,2'-bipyridine complexes of iron(II) bearing either an amide (5-benzylamido-2,2'-bipyridine and 5-(2-methoxyethane)amido-2,2'-bipyridine) or an ester (2,2'-bipyridine-5-carboxylic acid benzylester and 2,2'-bipyridine-5-carboxylic acid 2-methoxyethane ester) side chain have been evaluated by electrospray mass spectroscopy in acetonitrile. The time taken for the complexes to come to equilibrium appears to be dependent on the counteranion, with chloride causing a rapid redistribution of two preformed heteroleptic complexes (of the order of 1 hour), whereas the time it takes in the presence of tetrafluoroborate salts is in excess of 24^^h. Similarly the final distribution of products is dependent on the anion present, with the presence of chloride, and to a lesser extent bromide, preferring three amide-functionalized ligands, and a slight preference for an appended benzyl over a methoxyethyl group. Furthermore, for the first time, this study shows that the distribution of a dynamic library of metal complexes monitored by ESI-MS can adapt following the introduction of a different anion, in this case tetrabutylammonium chloride to give the most favoured heteroleptic complex despite the increasing ionic strength of the solution.