Preparation of Pt<Subscript>core</Subscript>Ag<Subscript>shell</Subscript> nanoparticles: Catalytic reduction of Ag<Superscript>+</Superscript> ions by hydrogen

It is shown that the saturation of an aqueous solution containing silver ions with hydrogen in the presence of 9.5-nm platinum nanoparticles leads to the reduction of silver and the formation of Pt_coreAg_shell bimetal nanoparticles. An increase in the concentration of silver ions gives rise to a number of elementary silver layers that cover the platinum core. It is established that the concentration of silver ions does not substantially affect the rate of the formation of a silver shell on the surface of platinum nanoparticles.     

Photoreduction of Ag<Superscript>+</Superscript> cations in a perfluorosulfonic membrane

The two-stage synthesis of nanosize silver in the pore space of a perfluorosulfonic membrane by ion-exchange fixation of Ag⁺ cations with the subsequent photoreduction in formaldehyde vapor was fulfilled. The study of the obtained composites shows that they contain silver “near-wall” form and nanoparticles weakly connected with the membrane surface.     

Stability of Ag<Superscript>+</Superscript> Complexes with Cryptand 222 in Ionic Liquids

Stability constants of silver(I) complexes with cryptand 222 were measured in a number of ionic liquids, applying potentiometric titration. The ionic liquids were based on 1-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-1-methyl-pyrrolidinium and 1-methyl-1-propyl-pyrrolidinium cations, as well as on tetrafluoroborate, triflate and bis(trifluoromethane sulfonyl) imide. The stability constants, expressed in log K scale, were within the broad range of 8.4–17.2. The formation of the Ag⁺222 cryptates was not detected in ionic liquids based on halide anions. Free enthalpy of silver(I) transfer from dimethylsulfoxide as a reference molecular solvent to ionic liquids was calculated applying the cryptate assumption. The results were discussed in terms of the competition between silver(I) complexation by ion forming ionic liquid and its complexation by cryptand 222.in final form: 6 December 2004This revised version was published online in July 2005 with a corrected issue number.     

Energetic ion bombardment of Ag surfaces by C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack> and Ga<Superscript>+</Superscript> projectiles

The ion bombardment-induced release of particles from a metal surface is investigated using energetic fullerene cluster ions as projectiles. The total sputter yield as well as partial yields of neutral and charged monomers and clusters leaving the surface are measured and compared with corresponding data obtained with atomic projectile ions of similar impact kinetic energy. It is found that all yields are enhanced by about one order of magnitude under bombardment with the C60+ cluster projectiles compared with Ga+ ions. In contrast, the electronic excitation processes determining the secondary ion formation probability are unaffected. The kinetic energy spectra of sputtered particles exhibit characteristic differences which reflect the largely different nature of the sputtering process for both types of projectiles. In particular, it is found that under C60+ impact (1) the energy spectrum of sputtered atoms peaks at significantly lower kinetic energies than for Ga+ bombardment and (2) the velocity spectra of monomers and dimers are virtually identical, a finding which is in pronounced contrast to all published data obtained for atomic projectiles. The experimental findings are in reasonable agreement with recent molecular dynamics simulations.     

Conversion of Methane over Ag<Superscript>+</Superscript>-exchanged Zeolite in the Presence of Ethene

Methane is shown to react with ethene over silver-exchanged zeolites at around 673 K to form higher hydrocarbons. Methane conversion of 13.2% is achieved at 673 K over Ag–ZSM−5 catalyst. Under these conditions, H–ZSM−5 does not catalyze the methane conversion, only ethene being converted into higher hydrocarbons. Zeolites with extra-framework metal cations such as In and Ga also activate methane in the presence of ethene. Using ¹³C-labeled methane as a reactant, propene is shown to be a primary product from methane and ethane. ¹³C atoms were not found in benzene molecules produced, indicating that benzene is entirely originated from ethane. On the other hand, in toluene, ¹³C atoms are found in both the methyl group and the aromatic ring. This implies that toluene is formed by the reaction of propene with butenes formed by the dimerization of ethene, and also by the reaction of benzene with methane. The latter path was confirmed by direct reaction of ¹³CH₄ with benzene. In this case, ¹³C atoms are found only in methyl groups of toluene produced. The heterolytic dissociation of methane over Ag⁺-exchanged zeolites is proposed as a reaction mechanism for the catalytic conversion of methane, leading to the formation of silver hydride and CH₃^δ+ species, which reacts with ethene and benzene to form propene and toluene, respectively. The conversion of methane over zeolites loaded with metal cations other than Ag⁺ is also described. The reaction of methane with benzene over indium-loaded ZSM−5 afforded toluene and xylenes in yields of up to 7.6% and 0.9% at 623 K when the reaction was carried out in a flow reactor.     

Interaction energies of histidine with cations (H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>)

The imidazol side group of histidine has two nitrogen atoms capable of being protonated or participating in metal binding. Hence, histidine can take on various metal-bound and protonated forms in proteins. Because of its variable structural state, histidine often functions as a key amino acid residue in enzymatic reactions. Ab initio (HF and MP2) calculations were done in modeling the cation (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) interaction with side chain of histidine. The region selectivity of metal ion complexation is controlled by the affinity of the side of attack. In the imidazol unite of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity. The complexation energies with the model systems decrease in the following order: Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.     

High temperature Ag<Superscript>+</Superscript>β”-alumina in situ sensor for sulfur-containing gases

The paper reports the development of high temperature in situ fully solid electrochemical sensor for sulfur-containing gases monitoring. The sensor is based on Ag⁺β”-Al₂O₃ membrane with Ag₂S or Ag₂SO₄ layer on its surface. Silver beta alumina was manufactured by high temperature ion exchange technique in AgNO₃ melt. The original design of the in situ sensor was developed. Three types of galvanic cells were used for the investigation of electromotive force (EMF) response on SO₂ partial pressure both in oxygen-free and oxygen-containing atmosphere in the temperature range 673–923 K. The data obtained was compared with following Nernst equations. The applicability of the sensor for in situ measurements in industrial processes is discussed.     

Photoreduction of Ag<Superscript>+</Superscript> ions and coalescence of silver nanoparticles in aqueous polyacrylate solutions

It is shown that changes in the spectral composition of irradiating light makes it possible to realize the competing photoreduction of Ag⁺ ions by polyacrylate anions in the bulk of an aqueous solution and on the surface of silver nanoparticles, which is accompanied by their coalescence.     

Synthesis,characterisation and photocatalytic activity of Ag<Superscript>+</Superscript>- and Sn<Superscript>2+</Superscript>-substituted KSbTeO<Subscript>6</Subscript>

Ag⁺- and Sn²⁺-substituted KSbTeO₆ were prepared by a facile ion-exchange method at ambient temperature. All the samples were characterised by scanning electron microscopy, energy-dispersive spectra, thermogravimetric analysis, powder X-ray diffraction, Raman spectra and UV-VIS diffuse reflectance spectra. Both Sn²⁺- and Ag⁺-substituted KSbTeO₆ were crystallised in a cubic lattice with the \(Fd\bar 3m\) space group. The band-gap energy of all the samples was deduced from their UV-VIS diffuse reflectance spectral profiles. The visible light-induced photocatalytic oxidation of the methylene blue (MB) dye was examined in the presence of all the as-prepared materials. The Ag⁺- and Sn²⁺-substituted KSbTeO₆ exhibited a higher photocatalytic activity than the parent KSbTeO₆ in degradation of the MB dye under visible light irradiation.     

Subcellular mass determination by <Superscript>4</Superscript>He<Superscript>+</Superscript> energy-loss micro-spectrometry

The scanning transmission ion microscope (STIM) has been used to determine the intracellular mass of human cultured cells. A 4He+ microbeam of 2.0 MeV energy was chosen to obtain enhanced ion-energy-loss sensitivity through the micron-thick freeze-dried cells. Local sample mass calculation, based on energy-loss conversion by use of appropriate matrix stopping powers, was performed by use of dedicated software. The method was validated with epoxy resin sections and polymer foil as analogues of biological samples in the range of (intra)cellular thickness, 150 to 3000 nm. STIM analysis resulted in less than 5% error in mass determination. 4He+ energy-loss micro-spectrometry was performed on freeze-dried human ovarian cancer cells, the mean areal mass obtained was 120 microg cm(-2) (200 microg cm(-2) in the nucleus and 250 microg cm(-2) in nucleoli). This method is particularly useful for mass normalization of X-ray fluorescence yields resulting from particle-induced X-ray emission microanalysis (micro-PIXE). When performed successively these two ion-beam micro-analytical methods enable the mapping of true element concentrations within single cells.     

Kinetics of solid-phase H<Superscript>+</Superscript>/M<Superscript>+</Superscript> ion exchange on hafnium hydrogen phosphate

The kinetics of solid-phase reactions between hafnium hydrogen phosphate and alkali metal chlorides were studied by thermogravimetry with subsequent analysis of leaving gases. For sodium and potassium chlorides, the reaction occurs in two stages; the first stages produces MHHf(PO₄)₂, and the second yields the MHf₂(PO₄)₃ NASICON phosphate. For rubidium chloride, the reaction is one stage and produces Rb₂Hf(PO₄)₂. For cesium chloride, the reaction is an analogue of the reaction for rubidium chloride, but has two stages. Kinetic data were used to determine interdiffusion coefficients for hydrogen and alkali-metal ions at various temperatures and the activation energies of interdiffusion.     

Hydration of the H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, and Cs<Superscript>+</Superscript> ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes modified with inorganic dopants

The hydration, state, and mobility of protons and Li⁺, Na⁺, and Cs⁺ ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes doped with silicon dioxide and phosphotungstic acid have been investigated by NMR and impedance spectroscopy. The dopants increase the moisture content of the membrane and change the system of pores and channels in which ion transport takes place. At low humidities, the dopant particles are involved in ion transport. The greatest effect is observed for the membranes doped with both SiO₂ and phosphotungstic acid. The water molecules sorbed by dopant particles as a material participate in the hydration of alkali metal cations in the membrane.     

Enhanced detection of olefins using ambient ionization mass spectrometry: Ag<Superscript>+</Superscript> adducts of biologically relevant alkenes

Spray solvent doped with silver ions increases the ease of olefin detection by desorption electrospray ionization (DESI). Characteristic silver adducts were generated in up to 50 times greater abundance when compared to conventional DESI spray solvents for the biologically significant olefin, arachidonic acid, in the positive ion mode. In the analysis of 26 lipids, silver adduct formation was highly favorable for fatty acids, fatty acid esters and prostaglandins but not applicable to some other classes (e.g., polar lipids such as ceramide and its derivative cerebroside sulfate). An investigation exploring competitive Ag⁺ cationization with a mixture of components demonstrated that polyunsaturated compounds form Ag⁺ adducts most readily. Silver cationization allowed the distinction between three sets of isomers in the course of multiple-stage collision-induced dissociation, so providing insight into the location of the olefin bonds. A silver ion-doped solvent was used in DESI imaging of normal and tumor canine bladder tissue sections. The Ag⁺ fatty acid adducts permitted post facto differentiation between the normal and tumor regions. In addition, silver adduct formation in the course of DESI imaging of tissue sections revealed the presence of triacylglycerides, a class of compounds not previously identified through DESI imaging. A simple silver nitrate spray solvent has the potential to further improve DESI analysis of unsaturated biomolecules and other molecules containing π-bonds through selective silver cationization.     

Selective ion-exchange sorption of K<Superscript>+</Superscript> from aqueous solutions containing Na<Superscript>+</Superscript>-K<Superscript>+</Superscript> mixture on Sn(IV) hydrophosphate

Ion-exchange sorption of K⁺ and Na⁺ from their mixture on X-ray-amorphous and crystalline Sn(IV) hydrophosphates was studied. These sorbents exhibit a high selectivity for K⁺. Amorphous Sn(IV) hydrophosphate can be used for efficient purification of aqueous sodium salt solutions to remove potassium impurity.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1275–1278.Original Russian Text Copyright © 2004 by Smirnov, Dimova, Redchenko.     

Structural role of large cations in sulfides with Cs<Superscript>+</Superscript> and Tl<Superscript>+</Superscript>

The results of a crystallographic analysis of the structures of CsFe₂S₃, Tl₂PbZrS₄, and Tl₂PbGeS₄ with a 1:1 cation–anion ratio are used to identify a joint F sublattice for Cs and S in the first compound and two separate F sublattices for cations and anions in the second compound (the PbS structural type). The substitution of the small Ge⁴⁺ (with its tetrahedral coordination by sulfur) for Zr⁴⁺ in the composition results in an increase in the unit cell volume, i.e., a decrease in the packing density for both cations and anions in the structure of the third compound. In the absence of regular F sublattices, there are “two-dimensional” orderings, typical of the PbS type, for the atomic positions in the projections of this structure.     

The solvation dynamics of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> ions in liquid methanol

The structure of the solvation shell of Na⁺ and K⁺ in fully deuterated liquid methanol has been studied by ab initio Car-Parrinello molecular dynamics simulations. The solvent cage has been found relatively stable and this property has been explained by means of charge transfer and electrostatic interactions as was previously done for Li⁺ in the same solvent. The differences with Li⁺ such as the increase of the coordination number going from Li⁺ to K⁺ and the reduced stability of the cage have been ascribed to the increase in the ionic radius.     

Borohydride reduction of Ag<Superscript>+</Superscript> in aqueous poly(acrylic acid-<Emphasis Type="Italic">co</Emphasis>-acrylamide) solutions

Silver clusters stabilized with poly(acrylic acid-co-acrylamide) are chemically synthesized via reduction of silver cations with sodium borohydride. Metallopolymer systems obtained at different concentrations of sodium borohydride in reaction mixtures are studied spectrophotometrically, and the effect of reductant content on the composition of the products is investigated.     

Time-dependent inhibition of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase induced by single and simultaneous exposure to lead and cadmium

Time-dependent interactions of Na⁺/K⁺-ATPase, isolated from rat brain synaptic plasma membranes (SPMs), with Cd²⁺ and Pb²⁺ ions in a single exposure and in a mixture were investigated in vitro. The interference of the enzyme with these metal ions was studied as a function of different protein concentrations and exposure time. The aim of the work was to investigate the possibility of selective recognition of Cd²⁺ and Pb²⁺ ions in a mixture, on the basis of the different rates of their protein-ligand interactions. Decreasing protein concentration increased the sensitivity of Na⁺/K⁺-ATPase toward both metals. The selectivity in protein-ligand interactions was obtained by variation of preincubation time (incubation before starting the enzymatic reaction). The text was submitted by the authors in English.     

Structures of the nearest surroundings of the K<Superscript>+</Superscript>, Rb<Superscript>+</Superscript>, and Cs<Superscript>+</Superscript> ions in aqueous solutions of their salts

Published data on structural characteristics of hydration of K⁺, Rb⁺, and Cs⁺ ions in aqueous solutions of their salts under standard conditions, including authors’ X-ray diffraction data, are summarized and correlated. The structural parameters of the nearest surrounding of the K⁺, Rb⁺, and Cs⁺ ions, such as the coordination numbers, interparticle distances, and types of ionic association, are discussed. It is noted that, because of weak tendency of these cations to hydration, the parameters of their coordination spheres strongly depend on the concentration and chemical nature of counterions.