Cation Mass Research Articles

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Molecular dynamics simulations show that the desolvation rates of isotopes of Li(+), K(+), Rb(+), Ca(2+), Sr(2+), and Ba(2+) may have a relatively strong dependence on the metal cation mass. This inference is based on the observation that the exchange rate constant, k(wex), for water molecules in the first hydration shell follows an inverse power-law mass dependence (k(wex) ∝ m(-γ)), where the coefficient γ is 0.05 ± 0.01 on average for all cations studied. Simulated water-exchange rates increase with temperature and decrease with increasing isotopic mass for each element. The magnitude of the water-exchange rate is different for simulations run using different water models [i.e., extended simple point charge (SPC/E) vs. four-site transferrable intermolecular potential (TIP4P)]; however, the value of the mass exponent γ is the same. Reaction rate theory calculations predict mass exponents consistent with those determined via molecular dynamics simulations. The simulation-derived mass dependences imply that solids precipitating from aqueous solution under kinetically controlled conditions should be enriched in the light isotopes of the metal cations relative to the solutions, consistent with measured isotopic signatures in natural materials and laboratory experiments. Desolvation effects are large enough that they may be a primary determinant of the observed isotopic fractionation during precipitation.

Lattice dynamics properties of XAs (X=Al, Ga and In) with zinc-blende structure from first-principle calculations

Band structures, density of states, dielectric and vibrational properties of XAs (X=Al, Ga and In) alloys with zinc-blende structure have been studied using the density functional theory (DFT). The calculated lattice constants, band gap, static dielectric constants and phonon frequencies are all in good agreement with the available experimental data and other theoretical results. The calculated results show that Born effective charges ZB increase with cation mass. A similar tendency has been observed for phonon frequencies ωTO and ωLO. Calculation results prove that static dielectric constants ε(0) increase with atomic weight, i.e. in the sequences AlAs–GaAs–InAs, and show an inverse sequence for band gap.

Formation and investigation of cobalt silicide ultrathin layers in Ti/Co/Ti-, TiN/Ti/Co-, and TiN/Co-on-silicon structures

The formation of ultrathin CoSi2 layers in Ti(8 nm)/Co(10 nm)/Ti(5 nm), TiN(18 nm)/Ti(2 nm)/Co(8 nm), and TiN(18 nm)/Co(8 nm) systems magnetron-sputtered on the Si(100) surface is studied. The systems are subjected to two-step rapid thermal annealing. In between the annealing steps, the “sacrificial” layer is chemically removed and the second and third systems are additionally covered by a 17-nm-thick amorphous silicon (α-Si) layer. In the course of the fabrication process, the structures are examined using time-of-flight secondary-ion (cation) mass spectrometry, Auger electron spectroscopy, and scanning electron microscopy combined with X-ray energy dispersion microanalysis. It is shown that the above complex of analytical investigation provides efficient physical control of ultrathin silicide layer formation.

Cross sections for ionization and ionic fragmentation of pyrimidine molecules by electron collisions

The electron impact mass spectroscopy and the total ion collection measurements were used to investigate the ionization and ionic fragmentation of the pyrimidine, C4H4N2, molecules in the gas phase. The cation mass spectra were measured in the 10−85 amu range and the observed mass peaks assigned to corresponding ionic fragments. The most abundant cation in the mass spectra is the parent cation, C4H4N \hbox{$_{\mathrm{2}}^{\mathrm{+}}$} + 2 , at 80 amu. The appearance energies of the ionic fragments were determined and the possible fragmentation processes are discussed. The electron impact absolute total and partial ionization cross sections in pyrimidine were obtained over the energy range from the respective ionization thresholds up to 150 eV.

Thermogravimetric analysis of different molar mass ammonium cations intercalated different cationic forms of montmorillonite

Different cationic forms of montmorillonite, mainly K-, Na-, Ca- and Mg-montmorillonites were intercalated in this study via ion exchange process with mono-, di-, and triethanolammonium cations. The developed samples were characterized by TG, XRD, and CHNS techniques. Thermogravimetric study of ammonium-montmorillonites shows three thermal transition steps, which are attributable to the volatilization of the physically adsorbed water and dehydration, followed by the decomposition of the intercalated ammonium cations and dehydroxylation of the structural water of the modified clay, respectively, while untreated and cationic forms of montmorillonite showed only two decomposition steps. The type of ammonium cation has affected both desorption temperature (Position) and the amount of the adsorbed water (intensity). XRD results show a stepwise change in the crystallographic spacings of montmorillonite with the molar mass of ammonium cation, reflecting a change in the structure of the clay. CHNS data confirm the intercalation of ammonium cations into the interlayer space of montmorillonite and corroborate the effect of the molar mass of ammonium cation on the amount adsorbed by the clay.

Experimental study of the diffusion-controlled acid degradation of Class H Portland cement

The rate of acid corrosion of Class H Portland cement was measured using time-lapse video over a range of temperature (T=30–80°C) and pH (0–3.7), both for hydrochloric acid and carbonic acid. The process was found to be diffusion-controlled, and the dependence of the slope, S, of corrosion depth vs square root of time was obtained as a function of T and pH. The slope decreases by about a factor of 3, if the leachate is allowed to accumulate on the corroded surface; however, a flow rate as low as 4cm/h is sufficient to flush the surface and establish an equilibrium rate. With or without accumulation of leachate, the cumulative cation mass loss is proportional to the depth of leaching, indicating that the phases extracted are very similar in both cases. The corrosion rate between 30 and 80°C is characterized by an activation energy of 39.6kJ/mol and a power-law dependence on acid concentration, S∼[H+]0.35. The resulting equation describes the present results, and agrees within a factor of 2 with rates reported in the literature by other workers. On the basis of this equation, estimates are provided of the leakage rates from a reservoir that is sealed with a sound plug of cement (where escape of the acid would take millions of years) or where an annular gap extends through the caprock. In the latter case, corrosion in small annuli (≤10μm diameter) is predicted to be concentrated near the bottom (i.e., near the reservoir-caprock boundary), so that penetration of acid into the overlying formation will take centuries.

Chemical characteristics of precipitation at Nanping Mangdang Mountain in eastern China during spring

To study the characteristics of precipitation in eastern China, an automatic sampler was used to collect rainwater samples from 19 precipitation events at Mangdang Mountain, Nanping City, Fujiang Province, in the spring of 2009. We used ion chromatography to analyze the ionic components and concentrations, and inductively coupled plasma mass spectrometry (ICP-MS) to analyze element compositions and contents. The results demonstrated remarkable acidic characteristics: in more than 80% of precipitation events the pH was less than 5.6, with an average of 4.81. Mass concentration results showed SO 4 2− was the main anionic component (36.2% of the total anion mass), while NH 4 + was the main cationic component (47.7% of the total cation mass) and main ion for acidity neutralization in the rainwater. Organic acid content accounted for 30.9% of total anion mass. The main trace metals were Ca, K, and Na. The SO 4 2−/NO 3 − ratio was 1.4, indicating that precipitation in this region was influenced by complex air pollution – the product of individual coal-burning combined with vehicle exhaust pollution. Correlation analysis of the chemical composition of the precipitation indicated that acidity in this region was determined by a combination of all acidic and neutralization ions rather than any single ion component. The results also showed that Na + and Cl − contributions were mainly by seawater; Mg 2+ by seawater and crustal materials; the NH 4 +, K +, Ca 2+, NO 3 − and SO 4 2− by anthropogenic sources; the trace metals were from the Earth's crust; and organic acids were potentially from combustion of biomass.

Single-crystal Raman spectra of YAlO3 and GdAlO3: comparison to several orthorhombic ABO3 perovskites

Room-temperature-polarized single-crystal Raman spectra have been measured for both GdAlO3 and YAlO3. Both aluminates crystallize in the orthorhombic (Pbnm) perovskite structure. Of the 24 possible Raman modes in 4 symmetries, 20 and 17 modes were observed for gadolinium and yttrium aluminates, respectively. Comparisons of the Raman spectra of these two aluminates to those of 28 other orthorhombic ABO3 perovskites revealed remarkably similar spectral patterns, regardless of chemistry or valency of the cations. Closer examination of the effect of mass, valencies, and size of the cations on the Raman spectra versus composition revealed that for the observed modes, the A cation plays the dominant role in determining the Raman shift. In particular, the one to two lowest energy modes in each symmetry are determined by cation mass and valency no matter what the chemistry. For some perovskites with common A cations, higher energy modes were also strikingly similar. In particular, the calcium perovskites had almost all Ag modes at the same energies despite the greatly varying B cations. The second to the lowest mode in Ag and B1g depended only on A cation mass for all perovskites. The volume plays a minor role throughout but is hard to separate from mass effects because the most massive cations are also the largest. However, if the B-cation is common, for example, aluminates or ferrites, the volume has a minor effect on the higher energy modes. These trends were not observed for all perovskites. Notable exceptions were found if a perovskite is near a phase transition or metastable, as found for three manganites. The effect of increased valency of the A cation from 2–4 to 3–3 perovskites expresses itself as relatively larger Raman shifts for the lowest energy modes. Analog studies of MgSiO3 perovskites should be undertaken with only 2–4 perovskites. The increased understanding for the mode distributions of perovskites allows for better estimates of their thermodynamic properties through vibrational modeling.

Ionization and ionic fragmentation of tetrahydrofuran molecules by electron collisions

Electron impact ionization and ionic fragmentation of tetrahydrofuran molecules in the gas phase were studied in the energy range from ionization threshold up to 150 eV using the technique of mass spectrometry. The cation mass spectra, ionization and ionic fragmentation efficiencies were measured over this energy range. Well-resolved mass peaks were detected in the mass range 10–72 amu and assigned to corresponding ionic molecular fragments. The most abundant cation in the mass spectra is at 42 amu. Appearance energies of selected ionic fragments were also determined. Possible ionic fragmentation processes are discussed.

New neutral cesium evaporation chamber and UHV suitcase

AbstractIt is well known that the use of Cs+ primary ions results in an important increase of the negative ionization probability during SIMS analyses. Moreover, Cs+ bombardment allows working in the MCsx+ mode, which is a widely used technique to reduce the matrix effect. A major drawback of Cs+ primary ion bombardment is that the Cs+ beam serves both for the incorporation of Cs and for the sputtering of the surface. Therefore, the sputtering yield, and consequently the cesium surface concentration, are constricted by the primary bombardment conditions.To overcome this problem, the Cation Mass Spectrometer (CMS), equipped with an evaporator delivering a collimated and adjustable stream of neutral Cs onto the sample, has been developed at the SAM department. By continuous Cs0 deposition during the SIMS analysis, optimal Cs surface concentrations, and thus optimal ionization probabilities are obtained.1In order to make the Cs0 deposition technique available for other analysis instruments, a standalone UHV instrument for Cs evaporation prior to SIMS analyses has been developed. Furthermore, a suitcase for the transfer under UHV conditions of the samples in‐between the Cs0 evaporation chamber and the analysis instruments has been designed, to avoid any contaminations. In this work, we present this new Cs0 evaporation chamber, as well as our new UHV suitcase in terms of their characteristics and handling. Copyright © 2010 John Wiley & Sons, Ltd.

ELECTRA: Electrostatic lens calculation tool with real time adjustment. A virtual optics bench for rapid determination of optical parameters using pre-characterized lenses

A software for dynamically displaying basic optical parameters of a system of pre-characterized lenses (ELECTRA) has been written. The lens characterization may be carried out with any charged particle optics program. In this study the pre-characterization was carried out using SIMION versions 7.0.5 and 8.0. The ELECTRA software has been benchmarked against SIMION using a well known lens (the 3 cylinder Einzel lens) and used to determine the configuration of new transfer optics for the cation mass spectrometer. Good agreement has been achieved between the ELECTRA software and SIMION for basic optical parameters.

Biased sample holder for complete correction of SIMS transmission losses with tilted samples

For investigation of fundamental aspects of secondary ion mass spectrometry (SIMS) such as secondary ion distributions, roughness formation or simply for optimisation of a particular analysis, the ability to tilt a sample is vital. However many instruments suffer transmission losses when the sample is tilted. This phenomenon has been investigated for the Cation Mass Spectrometer (CMS) instrument using Monte Carlo simulations and the cause determined to be modification of the extraction field arising from the sample tilt. A new sample holder incorporating biasing electrodes has been developed to eliminate transmission losses during SIMS analysis when using tilted samples. Simulations and experimental result confirm complete elimination of transmission losses for sample tilts of up to 20°.

Intrinsic Linear Heterogeneity of Amyloid β Protein Fibrils Revealed by Higher Resolution Mass-per-length Determinations

Amyloid β proteins spontaneously form fibrils in vitro that vary in their thermodynamic stability and in morphological characteristics such as length, width, shape, longitudinal twist, and the number of component filaments. It is vitally important to determine which variant best represents the type of fibril that accumulates in Alzheimer disease. In the present study, the nature of morphological variation was examined by dark-field and transmission electron microscopy in a preparation of seeded amyloid β protein fibrils that formed at relatively low protein concentrations and exhibited remarkably high thermodynamic stability. The number of filaments comprising these fibrils changed frequently from two to six along their length, and these changes only became apparent when mass-per-length (MPL) determinations are made with sufficient resolution. The MPL results could be reproduced by a simple stochastic model with a single adjustable parameter. The presence of more than two primary filaments could not be discerned by transmission electron microscopy, and they had no apparent relationship to the longitudinal twist of the fibrils. However, the pitch of the twist was strongly affected by the pH of the negative stain. We conclude that highly stable amyloid fibrils may form in which a surprising amount of intrinsic linear heterogeneity may be obscured by MPL measurements of insufficient resolution, and by the negative stains used for imaging fibrils by electron microscopy.

Interactions of metal cations with anionic groups on the cell wall of the macroalga Vaucheria sp.

AbstractThe aim of this article was to investigate the interactions of metal cations in aqueous solutions with the biomass of the freshwater macroalga Vaucheria sp. This problem is important when elaborating new applications of biosorption, e.g. the production of mineral feed additives for livestock from the biomass of algae enriched with microelement ions. Potentiometric titration was applied as a quick and cheap screening test to search for new efficient biosorbents. It revealed a variety of functional groups capable of cation exchange on the macroalgal surface, including carboxyl, phosphate, hydroxyl or amino groups. Fourier transform infrared spectroscopy on natural and chromium‐loaded Vaucheria sp. confirmed that carboxyl groups played a dominant role in the biosorption. The study also showed that Ca(II), Na(I), K(I), and Mg(II) ions were released from the biomass after biosorption of Cu(II), Mn(II), Zn(II), and Co(II) ions, indicating that ion exchange was a key mechanism in the biosorption of metal ions by Vaucheria sp. biomass. It was noticed that the mass of the microelement cations bound by the macroalga was proportional to the total mass of light metal ions [Na(I), K(I), Ca(II), and Mg(II)] released from the biomass.

Structural Characterization of Unsaturated Phosphatidylcholines Using Traveling Wave Ion Mobility Spectrometry

A number of phosphatidylcholine (PC) cations spanning a mass range of 400-1000 Da are investigated using electrospray ionization mass spectrometry coupled with traveling wave ion mobility spectrometry (TWIMS). A high correlation between mass and mobility is demonstrated with saturated phosphatidylcholine cations in N(2). A significant deviation from this mass-mobility correlation line is observed for the unsaturated PC cation. We found that the double bond in the acyl chain causes a 5% reduction in drift time. The drift time is reduced at a rate of approximately 1% for each additional double bond. Theoretical collision cross sections of PC cations exhibit good agreement with experimentally evaluated values. Collision cross sections are determined using the recently derived relationship between mobility and drift time in TWIMS stacked ring ion guide (SRIG) and compared to estimated collision cross sections using an empiric calibration method. Computational analysis was performed using the modified trajectory (TJ) method with nonspherical N(2) molecules as the drift gas. The difference between estimated collision cross sections and theoretical collision cross sections of PC cations is related to the sensitivity of the PC cation collision cross sections to the details of the ion-neutral interactions. The origin of the observed correlation and deviation between mass and mobility of PC cations is discussed in terms of the structural rigidity of these molecules using molecular dynamic simulations.

A novel lectin with antiproliferative activity from the medicinal mushroom Pholiota adiposa.

Little was known about biological activities of compounds from the medicinal mushroom of the genus Pholiota. A lectin from the Pholiota adiposa has now been isolated and its properties tested. The isolation procedure included ion exchange chromatography on DEAE-cellulose and CM-cellulose, and fast protein liquid chromatography-gel filtration (FPLC) on Superdex 75. The lectin was composed of two identical subunits, each with a molecular mass of 16 kDa. Its N-terminal amino-acid sequence showed little similarity to sequences of other Agaricales lectins. The hemagglutinating activity of the lectin was stable at temperatures up to 50 degrees C, and in NaOH and HCl solutions with concentrations less than 25 mM. It was inhibited by inulin (12.5-200 mM), but enhanced by Cu(2+) (6.25-25 mM), Fe(2+) (12.5-25 mM), and Al(3+) (6.25-25 mM) ions. The lectin showed antiproliferative activity toward hepatoma Hep G2 cells and breast cancer MCF7 cells with an IC(50) of 2.1 microM and approximately 3.2 microM, respectively. It exhibited HIV-1 reverse transcriptase inhibitory activity with an IC(50) of 1.9 microM. When compared with P. aurivella lectin, the only Pholiota lectin published to date, P. adiposa lectin differs in chromatographic behavior, molecular mass, N-terminal sequence, and effect of cations on hemagglutinating activity. In the case of the lectin from P. aurivella, its antifungal, antiproliferative, and HIV-1 reverse transcriptase inhibitory activities have not been determined.

Size distributions of nano/micron dicarboxylic acids and inorganic ions in suburban PM episode and non-episodic aerosol

The distribution of nano/micron dicarboxylic acids and inorganic ions in size-segregated suburban aerosol of southern Taiwan was studied for a PM episode and a non-episodic pollution period, revealing for the first time the distribution of these nanoscale particles in suburban aerosols. Inorganic species, especially nitrate, were present in higher concentrations during the PM episode. A combination of gas-to-nuclei conversion of nitrate particles and accumulation of secondary photochemical products originating from traffic-related emissions was likely a crucial cause of the PM episode. Sulfate, ammonium, and oxalic acid were the dominant anion, cation, and dicarboxylic acid, respectively, accounting for a minimum of 49% of the total anion, cation or dicarboxylic acid mass. Peak concentrations of these species occurred at 0.54 μm in the droplet mode during both non-episodic and PM episode periods, indicating an association with cloud-processed particles. On average, sulfate concentration was 16–17 times that of oxalic acid. Oxalic acid was nevertheless the most abundant dicarboxylic acid during both periods, followed by succinic, malonic, maleic, malic and tartaric acid. The mass median aerodynamic diameter (MMAD) of oxalic acid was 0.77 μm with a bi-modal presence at 0.54 μm and 18 nm during non-episodic pollution and an MMAD of 0.67 μm with mono-modal presence at 0.54 μm in PM episode aerosol. The concomitant formation of malonic acid and oxalic acid was attributed to in-cloud processes. During the PM episode in the 5–100 nm nanoscale range, an oxalic acid/sulfate mass ratio of 40.2–82.3% suggested a stronger formation potential for oxalic acid than for sulfate in the nuclei mode. For total cations (TC), total inorganic anions (TIA) and total dicarboxylic acids (TDA), major contributing particles were in the droplet mode, with least in the nuclei mode. The ratio of TDA to TIA in the nuclei mode increased greatly from 8.40% during the non-episodic pollution period to 28.08% during the PM episode, favoring dicarboxylic acid formation in the nuclei mode. The evidence suggests stronger formation strength and contribution potential exists for dicarboxylic acids than for inorganic salts in nanoscale particles, especially in PM episode aerosol.

Water Molecule Coupling to MeCl+ and MeClO4 + Ions Studied by the Electrospray Ionisation Mass Spectrometry

Abstract The binding stability of water molecules with MeCl+ and MeClO4 + ions has been studied by the electrospray ionisation mass spectrometry (ESI-MS). The Me ions studied were the typical transition metals (Me = Fe, Co, Ni, Cu, Zn, or Cd) and the typical alkaline-earth metals (Me = Mg, Ca, Sr, or Ba). The increasing voltage between the skimmer cones (referred to as the cone voltage) induced the abstraction of water molecules from MeCl+ and MeClO4 + ions. The binding stability of water molecules with MeCl+ and MeClO4 + ions has been correlated with the Me cation mass and with the heat capacity of hydration of Me cations. Moreover, the physicochemical properties of the ions studied have been compared by the cluster analysis and the principal component analysis of the experimental curves obtained for the [MeCl-H2O]+ and [MeClO4-nH2O]+ ions, where n is 1 or 2. Our results can be useful in examination of the ion dehydration process.

Lattice dynamics of chalcopyrite semiconductors LiAlTe2, LiGaTe2 and LiInTe2

AbstractWithin density functional perturbation theory using norm‐conserving pseudopotentials and a plane‐wave basis set calculations of phonon dispersion relations and densities of states of LiAlTe2, LiGaTe2 and LiInTe2 compounds being crystallized into the tetragonal chalcopyrite structure have been performed. Theoretical values of phonon mode frequencies in LiGaTe2 and LiInTe2 are in good agreement with the experimental data available for these crystals obtained by the methods of Raman and infrared spectroscopies. The similarity of the physical and chemical properties of the crystals concerned manifests itself in the similarity of their phonon spectra that are especially close to each other in low‐ and high‐frequency ranges. Phonon modes of the upper phonon band are predominantly caused by the lithium sublattice vibrations and have an upper bound of 350–370 cm–1. In a mid‐frequency range a significant downshift of the vibrational frequencies is observed on going from LiAlTe2 to LiGaTe2 and LiInTe2 that is a consequence of the third group cation mass reduction. From calculated electron density maps it follows that Li‐containing chalcopyrites are characterized by a less pronounced bond between the first group cation and anion as compared with the Cu‐ and Ag‐based analogs due to the absence of pd‐hybridization. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of heating temperature on the properties of vermiculites from Tanzania with respect to potential agronomic applications

This study was carried out to assess the properties of vermiculites from Tanzania with respect to the temperature used to expand them. Vermiculites from five locations in the Mozambique Belt of Tanzania were sampled and heated at 15, 200, 400, 600 and 800 °C in a muffle furnace. Palabora Europe Ltd provided one sample for comparison from their South Africa deposit which provides vermiculite used worldwide as a soil amendment. Water release characteristic, cation exchange capacity, pH, mass loss, and bulk density were among the properties assessed. All six vermiculites responded differently on heating, and had a significant variation in their agronomic properties. Water release characteristic varied with the degree of exfoliation and phase composition. Although vermiculites from Tanzania expanded on heating, their capacity to retain plant available water was relatively low as compared to vermiculite from Palabora. Disintegration on heating and the presence of a high amount of iron could be among the factors affecting their water release characteristic. Loss of hydroxyl water was higher in vermiculites than in hydrobiotites. Dehydroxylation enhanced the availability of exchangeable K + and reduced significantly the cation exchange capacity of vermiculites. The optimum exchangeable K + was obtained on heating at a temperature of 600 °C. The pH was unaffected by heating to a temperature of less than 600 °C. At higher temperature, the pH increased in some samples and was accompanied by substantial amounts of exchangeable Mg 2+. Thus, it was concluded that initial characterization of vermiculites is essential prior to potential agricultural applications in order to optimize their agronomic potential.