Search

An hybrid functional which includes a larger amount of pure exchange has been specially designed for the description of hydrogen-only systems. Both the H abstraction by H2 and the H2n + 1+ clusters have been investigated. Comparison with experimental values shows that the proposed functional gives dissociation energies and vibrational frequencies better than previous ab initio calculations. The results compare favorably with those obtained by a coupled clusters method [CCSD(T)], also performed in this work for sake of reference data.

Conformational flexibility of the ammonium complex of macrocyclic 18-crown-6 at 100 K � T � 300 K is studied using a positron microprobe in conjunction with molecular dynamics simulations. The ammonium cation, encapsulated in a three-pointed hydrogen-bonding perching arrangement, undergoes unhindered facile rotation inside the crown cavity, and the ether backbone adopts itself to the dynamic cation conformation. Preferential localization of the positron in the vicinity of the encapsulated cation results in the positron sensing changes in the local electron density distribution arising from the unrestricted rotational motion of the cation as well as from the slow motion of the crown backbone and hence sensing only an average conformation of the complex. ? 2005 American Chemical Society.

We present the synthesis of novel disk-shaped hexagonal Cu2Te nanocrystals with a well-defined stoichiometric composition and tunable diameter and thickness. Subsequent cation exchange of Cu to Cd at high temperature (180 C) results in highly fluorescent CdTe nanocrystals, with less than 1 mol % of residual Cu remaining in the lattice. The procedure preserves the overall disk shape, but is accompanied by a substantial reconstruction of the anion sublattice, resulting in a reorientation of the c-axis from the surface normal in Cu2Te into the disk plane in CdTe nanodisks. The synthesized CdTe nanodisks show a continuously tunable photoluminescence (PL) peak position, scaling with the thickness of the disks. The PL lifetime further confirms that the CdTe PL arises from band-edge exciton recombination; that is, no Cu-related emission is observed. On average, the recombination rate is about 25-45% faster with respect to their spherical quantum dots counterparts, opening up the possibility to enhance the emission rate at a given wavelength by controlling the nanocrystal shape. Finally, with a PL quantum efficiency of up to 36% and an enhanced PL stability under ambient conditions due to a monolayer of CdS formed on the nanocrystal surface during cation exchange, these flat quantum disks form an interesting enrichment to the current family of highly fluorescent, shape-controlled nanocrystals. © 2013 American Chemical Society.

Nd 1− x Sm x (Mg 0.5 Ti 0.5 )O 3 ( x = 0.0–1.0) samples were prepared by solid-state reaction method. Rietveld refinement of X-ray diffraction data was done using P 2 1 / n space group with monoclinic symmetry, which supports 1:1 B-site cation ordering. Long range ordering (LRO) parameter decreased up to x = 0.5 and then found to increase with further increase in Sm concentration. The A 1g -like mode in Raman spectra was observed to possess Briet–Wigner–Fano line shape. The variation in obtained line width of the A 1g -like mode supported LRO. Microwave dielectric characteristics such as dielectric constant ( ɛ r ), quality factor ( Q ) and temperature coefficient of resonant frequency ( τ f ) were measured in the range of 7–9 GHz. ɛ r decreased from 26.5 to 24.9 and τ f become less negative from −58 ppm/°C to −36 ppm/°C with increase in Sm concentration. Q × f decreased from 47,500 GHz (for x = 0) to 39,800 GHz (for x = 0.5) and then increased to 44,600 GHz (for x = 1).

The electrochemical, optical, and metal cation sensing properties of the triazole-tethered ferrocene-anthracene conjugates, C(48)H(40)FeO(2)N(6) (3) and C(52)H(40)FeO(2)N(6) (4), and the ferrocene-pyrene conjugates, C(29)H(25)FeON(3) (5) and C(31)H(25)FeON(3) (6), have been documented. All the compounds 3-6 behave as very selective redox, chromogenic, and "turn-on" fluorescent probes for Pb(2+) ion in an aqueous environment (CH(3)CN/H(2)O, 2/8). The significant changes in their absorption spectra are accompanied by a strong color change from yellow to greenish blue, which allows a prospective use for the "naked eye" detection of Pb(2+) ion over other competitor cations such as Hg(2+) and Cd(2+). These chemosensors present immense brightness and fluorescence enhancement (chelation-enhanced fluorescence = 85 for 3 and 92 for 4) following Pb(2+) coordination within the limit of detection at 2 ppb. Interestingly, their fluorescence, redox, and colorimetric responses are preserved in presence of water, which can be used for the selective colorimetric detection of Pb(2+) ion in aqueous environment over Hg(2+) and Cd(2+) cations. All the compounds have been characterized by (1)H, (13)C NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS) spectrometric analysis, and the solid-state structures of 5 and 6 have been unequivocally established by X-ray diffraction analysis.

Motivated by the potential of using room temperature ionic liquids (RTILs) as electrolytes to replace traditional aqueous electrolytes for Zn-anode secondary batteries, Zn/Zn(II) redox reactions have been studied in four aprotic RTILs based on pyrrolidinium ([Pyrr]+) and imidazolium ([Im] +) cations, and bis(trifluoromethanesulfonyl)imide ([TFSI] -) and dicyanamide ([DCA]-) anions. Cyclic voltammetry results suggest a smaller overpotential for Zn redox in [Im]+ cation based and [DCA]- anion based RTILs than in [Pyrr]+ and [TFSI]- based RTILs. Potentiodynamic polarization experiments indicate a strong dependence of the electrode reaction mechanism for the Zn species on the RTIL anions. In [TFSI]- based RTILs, Zn2+ ions are the electroactive species, with the electrode reaction being a single-step, two-electron transfer process. In [DCA]- based RTILs, two-step, single-electron reactions account for the electrode mechanism. The exchange current densities derived from Tafel analysis for the Zn species in the four RTILs are greater than 10-3 mA/cm2, with the [Im]+ cation based RTIL possessing the highest value of 9.9 × 10-3 mA/cm2. The results obtained will assist in obtaining a better understanding of the electrochemical behavior of Zn in RTILs, shedding light on the development of RTILs for Zn-anode secondary batteries. © 2012 Elsevier Ltd. All Rights Reserved.

Density Functional Theory (UB3LYP/6-311++G(d,p)) calculations of the affinity of the pentaaqua nickel(II) complex for a set of phosphoryl [Oï£P(H)(CH3)(PhR)], imino [HNï£C(CH 3)(PhR)], thiocarbonyl [Sï£C(CH3)(PhR)] and carbonyl [Oï£C(CH3)(PhR)] ligands were performed, where Rï£NH2, OCH3, OH, CH3, H, Cl, CN, and NO2 is a substituent at the para-position of a phenyl ring.The affinity of the pentaaqua nickel(II) complex for these ligands was analized and quantified in terms of interaction enthalpy (ΔH), Gibbs free energy (ΔG298), geometric and electronic parameters of the resultant octahedral complexes. The ΔH and ΔG298 results show that the ligand coordination strength increases in the following order: carbonyl < thiocarbonyl < imino < phosphoryl. This coordination strength order is also observed in the analysis of the metal-ligand distances and charges on the ligand atom that interacts with the Ni(II) cation. The electronic character of the substituent R is the main parameter that affects the strength of the metal-ligand coordination. Ligands containing electron-donating groups (NH 2, OCH3, OH) have more exothermic ΔH and ΔG298 than ligands with electron-withdrawing groups (Cl, CN, NO2). The metal-ligand interaction decomposed by means of the energy decomposition analysis (EDA) method shows that the electronic character of the ligand modulates all the components of the metal-ligand interaction. The absolute softness of the free ligands is correlated with the covalent contribution to the instantaneous interaction energy calculated using the EDA method. © 2013 Wiley Periodicals, Inc. The interactions between metal cations and biomolecules are extensively studied in bioinorganic and coordination chemistry. Transition metal ions are present in many enzymes, metalloproteins, peptide hormones, and nucleic acids and are fundamental for their biological functions. In this work, the affinity of the pentaaqua nickel(II) complex toward a set of para-substituted ligands is evaluated. The electronic nature of the ligand modulates the magnitude of the electrostatic, covalent, and repulsion components of the interaction. © 2013 Wiley Periodicals, Inc.

Ring polymer molecular dynamics experiments have been carried out to examine effects derived from nuclear quantum fluctuations at ambient conditions on equilibrium and non-equilibrium dynamical characteristics of charge solvation by a popular simple, rigid, water model, SPC/E, and for a more recent, and flexible, q-TIP4P/F model, to examine the generality of conclusions. In particular, we have recorded the relaxation of the solvent energy gap following instantaneous, ±e charge jumps in an initially uncharged Lennard-Jones-like solute. In both charge cases, quantum effects are reflected in sharper decays at the initial stages of the relaxation, which produce up to a ∼20% reduction in the characteristic timescales describing the solvation processes. For anionic solvation, the magnitude of polarization fluctuations controlling the extent of the water proton localization in the first solvation shell is somewhat more marked than for cations, bringing the quantum solvation process closer to the classical case. Effects on the solvation response from the explicit incorporation of flexibility in the water Hamiltonian are also examined. Predictions from linear response theories for the overall relaxation profile and for the corresponding characteristic timescales are reasonably accurate for the solvation of cations, whereas we find that they are much less satisfactory for the anionic case. © 2013 AIP Publishing LLC. Fil:Videla, P.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

A study is made of the laws that govern the sorptive equilibrium of zinc, calcium, and magnesium in aqueous solutions on iminodiacetate commercial resin Lewatit TP 207. The relations that are obtained show that the cation sorption process is described by the Langmuir and Freundlich models. The selectivity series Zn2+ > Ca2+ > Mg2+ was established based on determination of the affinity constants in the corresponding equations. Thus, the resin can be used to remove zinc cations from waste water even when it contains high concentrations of hardness ions. © 2013 Springer Science+Business Media New York.

Interaction of bacteria with citrate-reduced silver nanoparticles (AgNPs) of size 25 nm � 8.5 nm is studied using Raman spectroscopy in conjunction with plasmon resonance imaging of single bacterial cells. Distribution of isolated nanoparticles (NPs) inside Escherichia coli (ATCC 25922; E. coli) is observed by hyperspectral imaging (HSI) as a function of incubation time. Time-dependent degradation of bacterial DNA upon incubation of AgNPs with E. coli is proven by Raman spectroscopic studies. While attachment of NPs is evident in HSI, molecular changes are evident from the surface-enhanced Raman spectra of adsorbed DNA and its fragments. Distinct enhancement of DNA features is observed upon interaction of AgNPs and the number of such distinct features increases with incubation time, reaches a maximum, and decreases afterwards. This systematic interaction of DNA with the NPs system and its gradual chemical evolution is proven by investigating isolated plasmid DNA. A comparative Raman study with silver ions has shown that DNA features are observable only when bacteria are incubated with AgNPs. Energetics of interaction examined with microcalorimetry suggests the exothermicity of -1.547 � 1010 cal mol-1 for the NP-bacteria system. Specific interaction of AgNPs with exocyclic nitrogen present in the bases, adenine, guanine, and cytosine, leads to the changes in DNA. The interactions of E. coli with citrate-reduced silver nanoparticles (AgNPs) are studied using Raman spectroscopy and plasmon resonance imaging of single bacterial cells. While attachment of nanoparticles to bacteria is evident in plasmonic hyperspectral imaging, molecular changes of the adsorbed DNA are seen in Raman spectra. Specific interactions of AgNPs with exocyclic nitrogen present in the bases, adenine, guanine, and cytosine leads to time-dependent changes in the DNA. � 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This article is devoted to investigation of cation self-diffusion mechanisms, taking place in UO2, UO2+x, and UO2-x crystals simulated under periodic (PBC) and isolated (IBC) boundary conditions using the method of molecular dynamics in the approximation of rigid ions and pair interactions. It is shown that under PBC the cations diffuse via an exchange mechanism (with the formation of Frenkel defects) with activation energy of 15-22 eV, while under IBC there is competition between the exchange and vacancy (via Schottky defects) diffusion mechanisms, which give the effective activation energy of 11-13 eV near the melting temperature of the simulated UO2.00 nanocrystals. Vacancy diffusion with lower activation energy of 6-7 eV was dominant in the non-stoichiometric crystals UO2.10, UO2.15 and UO1.85. Observations showed that a cation vacancy is accompanied by different number of anion vacancies depending on the deviation from stoichiometry: no vacancies in UO2.15, single vacancy in UO2.00 and four vacancies in UO1.85. The corresponding law of mass action formulas derived within the Lidiard-Matzke model allowed explaining the obtained activation energies and predicting a change in the activation energy within the temperature range of the superionic phase transition. The diffusion of cations on the surface of nanocrystals had activation energy of 3.1-3.6 eV., 22 pages, 6 tables, 15 figures

Cholera toxin (CT), the causative agent of cholera, displays a pentavalent binding domain that targets the oligosaccharide of ganglioside GM1 (GM1os) on the periphery of human abdominal epithelial cells. Here, we report the first GM1os-based CT inhibitor that matches the valency of the CT binding domain (CTB). This pentavalent inhibitor contains five GM1os moieties linked to a calix[5]arene scaffold. When evaluated by an inhibition assay, it achieved a picomolar inhibition potency (IC50 = 450 pM) for CTB. This represents a significant multivalency effect, with a relative inhibitory potency of 100000 compared to a monovalent GM1os derivative, making GM1os-calix[5]arene one of the most potent known CTB inhibitors. This journal is © The Royal Society of Chemistry 2013.

The separation of the nonaqueous azeotropic systems methyl acetate-methanol and ethyl acetate-ethanol was investigated with 13 cations and 27 anions as entrainers to identify suitable ionic liquids using the COSMO-RS model. It is observed that the cations best suited are imidazolium > pyridinium > methyl pyrrolidinium > octyl quinolinium. The lengthening of the alkyl chain of cations was also studied as well as whether the shorter the alkyl chain, the better is the separation. It was also noticed that the efficacy of the anions is in the order [OAc] > [Cl] > [DHP]. It was seen that the influence of anions is more significant on the behavior of ionic liquid solvation in alcohols. The effects of polarity, excess free energy, and excess enthalpy are addressed on nonaqueous systems containing ionic liquids. It is suggested that [EMIM][OAc], [EMIM][Cl], and [EMIM][DHP] can be used as promising entrainers for practical applications of ester-alcohol separation. � 2013 American Chemical Society.

Membranes composed of multilayer poly(4-styrenesul- fonate) (PSS)/protonated poly(allylamine) (PAH) fi lms on porous alumina supports exhibit high monovalent/divalent cation selectivities. Remarkably, the di ff usion dialysis K + /Mg 2+ selectivity is >350. However, in nano fi ltration this selectivity is only 16, suggesting some convective ion transport through fi lm imperfections. Under MgCl 2 concentration gradients across either (PSS/PAH) 4 - or (PSS/ PAH) 4 PSS-coated alumina, transmembrane potentials indicate Mg 2+ transference numbers approaching 0. The low Mg 2+ transference numbers with both polycation- and polyanion-terminated fi lms likely stem from exclusion of Mg 2+ due to its large size or hydration energy. However, these high anion/cation selectivities decrease as the solution ionic strength increases. In nano fi ltration, the high asymmetry of membrane permeabilities to Mg 2+ and Cl − creates transmembrane di ff usion potentials that lead to negative rejections (the ion concentration in the permeate is larger than in the feed) as low as − 200% for trace monovalent cations such as K + and Cs + . Moreover, rejection becomes more negative as the mobility of the trace cation increases. Knowledge of single-ion permeabilities is vital for predicting the performance of polyelectrolyte fi lms in the separation and puri fi cation of mixed salts.

Nucleic acid sample storage is of paramount importance in biotechnology and forensic sciences. Very recently, hydrated ionic liquids (ILs) have been identified as ideal media for long-term DNA storage. Hence, understanding the binding characteristics and molecular mechanism of interactions of ILs with DNA is of both practical and fundamental interest. Here, we employ molecular dynamics simulations and spectroscopic experiments to unravel the key factors that stabilize DNA in hydrated ILs. Both simulation and experimental results show that DNA maintains the native B-conformation in ILs. Simulation results further suggest that, apart from the electrostatic association of IL cations with the DNA backbone, groove binding of IL cations through hydrophobic and polar interactions contributes significantly to DNA stability. Circular dichroism spectral measurements and fluorescent dye displacement assay confirm the intrusion of IL molecules into the DNA minor groove. Very interestingly, the IL ions were seen to disrupt the water cage around DNA, including the spine of hydration in the minor groove. This partial dehydration by ILs likely prevents the hydrolytic reactions that denature DNA and helps stabilize DNA for the long term. The detailed understanding of IL-DNA interactions provided here could guide the future development of novel ILs, specific for nucleic acid solutes. � 2012 American Chemical Society.

Er3+ doping at the La site in La0.8Sr0.2MnO3 showed an unusual increase in Curie/peak resistivity temperature (TC/TP) above a certain nominal dopant concentration (x⩾0.086). This increase is attributed to the presence of a cation-deficient ErMnO3 phase. Further, with increase in TP the overall resistivity of these compounds also decreases. We explain these results assuming the presence of a nanoscale mixture of charge-ordered antiferromagnetic insulating (CO-AFMI) phase in a ferromagnetic metallic matrix, wherein the increase in TC/TP with increase in Er3+ content is due to the local destruction of the CO-AFMI phase by the presence of the cation-deficient ErMnO3 phase. We thus provide an indirect evidence of electronic phase separation in these compounds.

In this communication, a comprehensive literature survey has been performed to provide a data set for the normal melting temperature ( T m ) of 799 ionic liquids (ILs) from various 143 references. Using this data set, an accurate group contribution method has been developed to estimate the T m of ILs. The model employs a total of 80 sub-structures to predict the T m of ILs. To better distinct the effects of anion and cation on the latter property, 31 sub-structures related to chemical structure of anion, and 49 substructures related to the chemical structure of cation have been implemented. The results of this method show a low average relative deviation (AARD%) of 5.82% for a data set including 799 ILs.

We report synthetic routes to both cubic and hexagonal phase Cu 2-x(S ySe 1-y) alloy nanocrystals exhibiting a well-defined near-infrared valence band plasmon resonance, the spectral position of which is dependent mainly on x, i.e. on Cu stoichiometry, and to a lesser extent on the crystal phase of the NCs. For cubic Cu 2-x(S ySe 1-y) nanocrystals y could be varied in the 0.4-0.6 range, while for hexagonal nanocrystals y could be varied in the 0.3-0.7 range. Furthermore, the Cu 2-x(S ySe 1-y) nanocrystals could be transformed into the corresponding Cd-based alloy nanocrystals with comparable S ySe 1-y stoichiometry, by cation exchange. The crystal phase of the resulting Cd(S ySe 1-y) nanocrystals was either cubic or hexagonal, depending on the phase of the starting nanocrystals. One sample of cubic Cu 2-x(S ySe 1-y) nanocrystals, with S 0.5Se 0.5 chalcogenide stoichiometry, was then evaluated as the anode material in Li-ion batteries. The nanocrystals were capable of undergoing lithiation/delithiation via a displacement/conversion reaction (Cu to Li and vice versa) in a partially reversible manner. © 2012 The Royal Society of Chemistry.

The extreme-ultraviolet (XUV) and strong-field valence ionization of cytosine and uracil is considered. We examine some simple estimates of the relative yields of the cation states populated following ionization and compare these to the results of a recently developed ab initio-type numerical model designed to compute strong-field ionization of molecules, the so-called time-dependent resolution in ionic states (TD-RIS) method. In analogy with one-photon XUV ionization, where the photoionization matrix elements can be related to the Dyson orbitals, we construct estimates for the yield of strong-field ionization (SFI) to different cation states based on the Dyson orbital norms and the Keldysh tunneling ionization rate. In the case of XUV ionization, the Dyson norms are shown to be good predictors of the relative cation yields when compared with the TD-RIS yields. The Dyson- and Keldysh-based models underestimate the yield to excited cation states in the case of SFI. The increased yield to the excited cation states in the TD-RIS results is attributed to the inclusion of multielectron effects and continuum structure not present in the simple models. The molecular Ammosov-Delone-Krainov (MO-ADK) method of calculating SFI is also considered. This later method is seen to agree more closely with the Dyson- and Keldysh-based estimates as it also fails to capture the multielectron effects and continuum structure included in the TD-RIS approach. ©2012 American Physical Society.

Ca 1-xCd xMoO 4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) ceramics were prepared by solid-state reaction method. Tetragonal scheelite structure with I4 1/a space group was observed in all these compositions. Microwave dielectric properties such as quality factor (Q � f), dielectric constant (? r), and temperature coefficient of resonant frequency ( f) were measured in the microwave frequency range. Rietveld refinement was performed on all these compositions and bond valences of A-, B-site cation, and oxygen were calculated. Influence of these structural parameters on the microwave dielectric properties was examined. Q � f was correlated with the average covalence of A-, B-site cations. The variation in ? r was explained with ionic polarizability of Cd +2 ions. The deviation of observed polarizability from theoretical polarizability and f of all these compositions were explained with oxygen bond valence. The well-sintered Ca 1-xCd xMoO 4 ceramics showed highly promising microwave dielectric properties (? r = 8-10, Q � f = 46000-53000 GHz and f = -22 to -57 ppm/�C). � 2012 The American Ceramic Society.

The amino- and metal-ion sensing capability of a novel type of well-defined block copolymers based on 9-anthrylmethyl methacrylate (AnMMA; hydrophobic, fluorescent) and 2-(acetoacetoxy)ethyl methacrylate (AEMA; hydrophobic, metal chelating) has been investigated in organic media. AEMAx-b-AnMMAy diblock copolymers were prepared for the first time using reversible addition-fragmentation chain transfer (RAFT) polymerization. All polymers were characterized in terms of molecular weights, polydispersity indices and compositions by size exclusion chromatography and 1H NMR spectroscopy, respectively. The glass transition (Tg) temperatures of the AEMAx and AnMMAx homopolymers and the AEMAx-b-AnMMAy diblock copolymers were determined using differential scanning calorimetry. These systems were evaluated toward their ability to act as effective dual chemosensors (i.e., amino- and metal-ion sensors) in an organic solvent (chloroform). More precisely, the fluorescence intensity of both the AnMMAx homopolymers and the AnMMAx-b-AEMAy diblock copolymers in solution exhibited a significant decrease in the presence of triethylamine. Moreover, the presence of iron (III) cations were also found to significantly affect the fluorescence signal of the anthracene moieties when those were combined in a block copolymer structure with the AEMA units, due to complex formation occurring between the β-ketoester groups of the AEMAx segment and the cations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

We report the first vibrational study of NO bound to an oxidized heme-copper oxidase. Cytochrome cbb3 oxidase from P. stutzeri reduces both O2 and NO to H2O and N2O, respectively. The ferric nitrosyl complex of cbb3 exhibits v(N-O) at 1903 cm-1. This frequency is very similar to v(NO) of nitric oxide reductase, the acidic form of Met Mb-NO, but 18 cm-1 lower than that of neutral Met Mb-NO. By monitoring the NO intensity, we estimate that NO dissociates from the heme b3 pocket, without binding to CuB, with k = 1.8 × 10-3 s-1. Therefore, NO binding occurs at the heme site and not at CuB, generating a nitrosonium CuB1+-NO+ species as proposed recently (Torres J. Cooper, C.E. Wilson, M.T. J. Biol. Chem. 1998, 273, 8756-8766). The coordination of NO to cbb3 oxidase and to nitric oxide reductase and Mb is compared and discussed. 106 50 12860 12862 Cited By :18

In this work, we characterized the surface damage layer and sputtering yield of polycrystalline L-leucine films before and after irradiation with Ar cluster or monomer ion beams with x ray photoelectron spectroscopy and ellipsometry. Irradiation with Ar monomer ion beams induced heavy damage on the surface of L-leucine films, such as bond breaking and carbonization. In contrast, no significant surface damage was observed in the films irradiated with Ar cluster ion beams. The sputtering yield of L-leucine decreased dramatically with increasing fluence of monomer Ar ions and approached the value of the sputtering yield of graphite; but under irradiation with Ar cluster ion beams, the sputtering yield remained constant with fluence. The differences in sputtering yield behavior were explained in relation with the surface damage layer on organic materials. Thus, cluster ion beams could potentially be used to mill down biological materials without significant damage on the surface and could contribute to various applications in the analysis and processing of life matter.

Hybrid A-B-A type nanowires (NWs) with Ag 5Te 3-HgTe- Ag 5Te 3 composition have been created by the reaction of Hg 2+ with Ag 2Te NWs. The NW morphology of Ag 2Te is preserved upon reaction with minor changes and the two separate phases formed are spatially separated within the same NW. The reaction of Hg 2+ with Ag 2Te NWs was monitored at different concentrations and the reactivity was attributed to cationic exchange depending on solubility products. Hybrid NWs were formed by partial cation exchange only at low concentrations (below 50 ppm) resulting in Ag 5Te 3 and HgTe within the same NW. However, at high concentrations (above 100 ppm), the HgTe phase alone was formed. These studies have been extended to other metal ions such as Pb 2+, Cd 2+, and Zn 2+ whose reactivity towards Ag 2Te NWs is different from that of Hg 2+. These ions form a passivating Te oxide layer upon reaction with other metal ions. The mechanism of reactivity of Hg 2+ is explained on the basis of free energy of formation of the ionic solid. Phase transition of Hg 2+-reacted NWs occurs at a lower temperature than the parent (Ag 2Te NWs) and other metal ions-reacted Ag 2Te NWs. Details of the process were elucidated using microscopic and spectroscopic investigations. The physical and chemical properties of the individual components within a NW are expected to provide a novel functionality to the metal chalcogenide systems. � 2011 The Royal Society of Chemistry.

A new preconcentration method was developed for the determination of trace amounts of Cu(II), Fe(III), Pb(II), Ni(II), and Cd(II) on a double-walled carbon nanotube disk. 4-(2-Thiazolylazo) resorcinol was used as a complexing reagent. The effects of parameters, including pH of the solutions, amounts of complexing reagent, eluent type, sample volume, flow rates of solutions, and matrix ions were examined for quantitative recoveries of the studied analyte ions. The retained metal ions were eluted by 2 M HNO3. The LOD values for the analytes were in the range of 0.7–4.4 μg/mL. Natural water samples and standard reference materials were analyzed by the presented method.

Recently non-uniform distribution of dopants in transparent optical ceramics was observed. It was demonstrated that dopants with low segregation coefficients (K3+ and Y3+ host cations in Ce3+-doped (Gd,Y)3Al5O12 ceramic sample demonstrated that no detectable redistribution of Gd3+ and Y3+ cations in the vicinity of the grain boundaries was detected. These results are in good agreement with comparable segregation behavior of Gd3+ and Y3+ [K(Y3+)≈K(Gd3+)] when the garnet solidification is performed from liquid phase. This observation also confirms qualitative match of segregation in liquid and solid states.

The Journal of Chemical Physics, 135 (20), ISSN:0021-9606, ISSN:1089-7690

Utilizing Langmuir-Blodgett deposition and scanning probe microscopy, we have investigated the extent to which cations alter the self-assembly processes of hybrid polyoxometalates (POMs) on surfaces. The well-defined 2D hexagonal nanostructures obtained were extensively characterized and their properties were studied, and this has revealed fascinating dielectric behavior and reversible capacitive properties. The nanostructures are extremely stable under ambient conditions, and yet exhibit fascinating self-patterning upon heating. These findings present POMs as effective smart nanodielectrics and open up a new field for future POM applications. (c) 2011 American Chemical Society.

The set of 1:1 and 2:1 complexes of XOOX′ (X, X′ H, CH 3) with lithium cation has been studied to determine if they are suitable candidates for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. Conventional nuclear magnetic resonance is unable to distinguish between enantiomers in the absence of a chiral solvent. The criterion for experimental detection is valuated by the isotropic part of nuclear shielding polarisability tensors, related to a pseudoscalar of opposite sign for two enantiomers. The study includes calculations at coupled Hartree-Fock and density functional theory schemes for 17O nucleus in each compound. Additional calculations for 1H are also included for some compounds. A huge static homogeneous electric field, perpendicular to the magnetic field of the spectromer, as big as ≈1.7 108 V m -1 should be applied to observe a shift of ≈1 ppm for 17O magnetic shielding in the proposed set of complexes. © 2011 American Institute of Physics.

A novel ScVO 3 perovskite phase has been synthesized at 8 GPa and 1073 K from the cation-disordered bixbyite-type ScVO 3. The new perovskite has orthorhombic symmetry at room temperature, space group Pnma, and lattice parameters a = 5.4006(2) Å, b = 7.5011(2) Å, and c = 5.0706(1) Å with Sc 3+ and V 3+ ions fully ordered on the A and B sites of the perovskite cell. The vanadium oxygen octahedra [V-O 6] display cooperative Jahn-Teller (JT) type distortions, with predominance of the tetragonal Q 3 over the orthorhombic Q 2 JT modes. The orthorhombic perovskite shows Arrhenius-type electrical conductivity and undergoes a transition to triclinic symmetry space group P-1 close to 90 K. Below 60 K, the magnetic moments of the 4 nonequivalent vanadium ions undergo magnetic long-range ordering, resulting in a magnetic superstructure of the perovskite cell with propagation vector (0.5, 0, 0.5). The magnetic moments are confined to the xz plane and establish a close to zigzag antiferromagnetic mode. © 2011 American Chemical Society.

The transport properties of two ion-exchange membranes in the presence of tin, as Sn(II) and Sn(IV), were investigated by chronopotentiometry and current–voltage curves. Since tin forms positively or negatively charged complex species in solution, the effect of the counterions on the transport phenomena through both cation- and anion-exchange membranes was evaluated. The speciation diagrams of Sn(II) and Sn(IV) as a function of the chloride concentration and pH were calculated for all the tin and HCl concentrations in order to explain the values of parameters like the limiting current ( I lim ), the resistance of the ohmic region ( R 1st ) and the resistance of the overlimiting region ( R 3rd ). In the case of the anion-exchange membrane (AEM), the chloride ions were the species responsible for current transfer through the membrane in the cases of both Sn(II) and Sn(IV). The formation of a Sn(IV) precipitate at low HCl concentration was reflected by a diffusion relaxation behaviour characteristic of the bipolar membranes. Protons are the main counterions capable of crossing the cation exchange membrane (CEM) for both tin oxidation sates. The contribution of Sn(II) to the water splitting phenomenon was evident for every HCl concentration by the increase of the membrane potential in the chronopotentiometric curves and by the appearance of a Sn(OH) 2 precipitate located at the anodic side of the CEM.

The transport properties of a cation-exchange membrane in the presence of nickel sulphate solutions were investigated by means of chronopotentiometry. The interest of this study relies on the application to the treatment of chromium plating rinse baths. The presence of chromic acid in the solutions and the initial concentration of nickel sulphate affect significantly the shape of the chronopotentiograms. The different shape of chronopotentiograms as well as the values of different parameters is thereby justified by the calculation of the speciation diagrams of Ni(II).Parameters like the limiting current density, resistance of the ohmic region, plateau length, and nickel transport numbers through the cation-exchange membrane were calculated from the chronopotentiometric and the current-voltage curves. The obtained results show an important competence between Ni2+ and H+ ions, with increases of the nickel transport numbers when the [Ni2+]/[H+] ratio corresponding to the initial equilibrium exceeds the unity. The increase in the Ni2+ concentration brings about a facilitated arising of electroconvection, which promotes overlimiting currents and additional mixing at the membrane surface. © 2011 Elsevier B.V., The authors of this work would like to express their gratitude to Ministerio de Ciencia e Innovacion (Spain) for their financial support (CTQ2008-06750-C02-01/PPQ) and to Universitat Politecnica de Valencia for a postgraduate grant (Ref. 2010-12).

A series of crown ethers carrying a pyrene group with nitrogen-sulfur donor atoms, that differ in having three, four and five sulfur atoms in the macrocycle was designed and synthesized by the reaction of the corresponding macrocyclic compound and 1-bromomethylpyrene. The influence of metal cations such as Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+ and Al3+ on the spectroscopic properties of the ligands was investigated in acetonitrile-dichloromethane (1:1) by means of absorption and emission spectrometry. Absorption spectra show isosbestic points in the spectrophotometric titration of Fe2+, Zn2+, Cu2+, Pb2+ and Hg2+. The results of spectrophotometric titration experiments disclosed the complexation compositions and complex stability constants of the novel ligands with Fe2+, Zn2+, Cu2+, Pb2+ and Hg2+ cations. The monoazatetrathia crown ether showed good sensitivity for Cu2+ with linearity in the range 5.0 x 10(-7)-2.5 x 10(-6) M and detection limit of 1.6 x 10(-8) M. (C) 2010 Elsevier B.V. All rights reserved.

Ionic conductivity, diffusion coefficients, mobility and ionic concentration for lithium salts dissolved in polymer electrolytes are determined by the modeling of the dielectric loss and spectra. Cation and anion diffusion coefficients are quantified using the Trukhan model depending on the assumed ratio of the cation to anion diffusion coefficients. Measurements are performed for polymer electrolytes consisting of polyethylene oxide (PEO) with dissolved LiClO 4 salts for different sample thicknesses and temperatures ranging from 5 to 105 °C, which comprises both the crystalline and amorphous phases of the composite electrolyte. A good phenomenological description of the dielectric loss spectra is obtained for both the semi-crystalline and amorphous phases. The fraction of mobile ions is estimated to vary from 0.002% at 25 °C (semi-crystalline phase) up to 0.05% at 80 °C (amorphous phase)., This research has been supported by the IMIDIC/2009/152 project, granted by the Generalitat Valenciana (Valencia, Spain) through the Institute for Small and Medium Industry (IMPIVA) and the European Union by FEDER funds. Dr. A. Munar acknowledges the support of the Ramon y Cajal programme08-18-463B-750, and Grant MAT2009-14602, Ministerio de Ciencia e Innovacion, Spain.

International audience; Lithium cation insertion and extraction in LiFePO4 were electrochemically studied with a cavity microelectrode (CME). Cyclic voltammetry measurements were used to characterize the kinetics of the material. LiFePO4 was successfully cycled from 0.1 mV s-1 up to 1 V s-1 and is therefore a suitable material to be used in high power applications, such as asymmetric hybrid supercapacitors. Several kinetic behaviors were observed depending on the sweep rate. The LiFePO4 was found to follow different kinetics behaviors depending of the sweep rate. The charge storage mechanisms were investigated for Liþ extraction/insertion.

The response of the local structure of various types of spinel aluminates, ZnAl2O4 (normal spinel), MgAl2O4 (partly inverse spinel), and Li0.5Al2.5O4 (fully inverse spinel), to mechanical action through high-energy milling is investigated by means of 27Al MAS NMR. Due to the ability of this nuclear spectroscopic technique to probe the local environment of Al nuclei, valuable quantitative insight into the mechanically induced changes in the spinel structure, such as the local cation disorder and the deformation of the polyhedron geometry, is obtained. It is revealed that, independent of the ionic configuration in the initial oxides, the mechanical action tends to randomize cations over the two non-equivalent cation sublattices provided by the spinel structure. The response of the spinels to mechanical treatment is found to be accompanied by the formation of a non-uniform core-shell nanostructure consisting of an ordered crystallite surrounded by a structurally disordered interface/surface shell region. Based on the comparative NMR studies of the non-treated and mechanically treated spinels, an attempt is made to separate the surface effects from the bulk effects in spinel nanoparticles. The non-equilibrium cation distribution and the deformed polyhedra are found to be confined to the near-surface layers of spinel nanoparticles with the thickness extending up to about 0.7 nm. The cation inversion parameter of the mechanically treated spinel is compared with that of the non-treated material at non-ambient conditions. © 2011 The Royal Society of Chemistry.

15 pags. ; 11 figs. ; 2 Appendix ; 4 tabs., In this work a reliable full nine-dimensional potential energy surface for studying the dynamics of H5+ is constructed, which is completely symmetric under any permutation of the nuclei. For this purpose, we develop a triatoms-in-molecules method as an extension of the more common diatoms-in-molecules one, which allows a very accurate description of the asymptotic regions by including correctly the charge-induced dipole and quadrupole interactions. Moreover, this treatment provides a semiquantitative description of all the topological features of the global potential compared with coupled cluster results. In particular, the hop of the proton between two H2 fragments produces a double well in the potential. This resonant structure involving the five atoms produces a stabilization, lowering the barrier, and the triatoms-in-molecules yields to a barrier significantly higher than the ab initio results. Therefore, to improve the triatomics-in-molecules potential surface, two five-body terms are added, which are fitted to more than 110 000 coupled-cluster ab initio points. The global potential energy surface thus obtained in this work has an overall root mean square error of 0.079 kcal/mol for energies below 27 kcal/mol above the global well. The features of the potential are described and compared with previous available surfaces., We acknowledge Professor J. Bowman for providing us the program of their potential energy surface. This work has been supported by Ministerio de Ciencia e Innovación under Grant Nos. CTQ2007-62898, CTQ2007-63332, and FIS2007-62006 and by Comunidad Autónoma de Madrid under Grant No. S-2009/MAT-1467. It has also been founded by the program CONSOLIDER-INGENIO 2010 of Ministerio de Ciencia e Innovación under Grant No. CSD2009-00038 entitled “Molecular Astrophysics: The Herschel and Alma Era.” The calculations have been performed at CESGA and IFF computing centers.

A new cobalt(II) complex, [Co(H2O)4(nia)2](suc)·(H2suc) [nicotinamide = nia, succinate = suc2−], has been synthesized and characterized by elemental analysis, IR, TG-DTA and single-crystal X-ray diffraction. It contains [Co(H2O)4(nia)2]2+ complex cations, uncoordinated suc2− anios and H2suc species. In the complex cation the cobalt(II) ion is coordinated by four aqua and two nia ligands in a distorted octahedral geometry. The suc2− dianion acts as a counter-ion, while H2suc is present as a molecule of solvation. A three-dimensional network is formed by O-H· · ·O and N-H· · ·O hydrogen bonds. The title complex exhibits luminescence in the solid state at room temperature. The magnetism of the complex was studied over the temperature range 1.8 - 300 K.

In this paper we use density functional theory corrected for on-site Coulomb interactions (DFT + U) to study the defects formed in the ceria (111) and (110) surfaces doped with La. To describe consistently the defect formed with substitutional La(3+) doping at a Ce(4+) site we use DFT and DFT + U, with U = 5 eV for Ce 4f states and U = 7 eV for O 2p states. When La(3+) substitutes on a Ce(3+) site, an La(Ce)' + O(O)(center dot) defect state, with an oxygen hole, is formed at both surfaces, but only with the DFT + U approach. The formation energy of an oxygen vacancy in a structure with two La dopants in their most stable distribution is reduced over the undoped surfaces but remains positive. Formation of an oxygen vacancy results in the appearance of a reduced Ce(3+) cation and a compensated oxygen hole, instead of compensation of both oxygen holes, which is typical of metal oxides doped with lower valence cations. We tentatively suggest that the key role in the formation of this unusual defect is played by cerium and arises from the ease with which cerium can be reduced, as compared to other metal oxides. Experimental confirmation of these results is suggested.