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Ionic Species (ionic + species)
Selected AbstractsAnalysis of Simulated Martian Regolith Using an Array of Ion Selective ElectrodesELECTROANALYSIS, Issue 15-16 2005Stefan Abstract A prototype miniature array of polymer membrane and solid state ion selective electrodes was developed for the purpose of performing an in-situ analysis of the soluble ionic species in Martian regolith (soil). The array contains a total of 27 electrodes for K+, Na+, Ca2+, Mg2+, NH, Ba2+, NO, Cl,, and Li+, each in triplicate. Barium electrodes were used to indirectly monitor sulfate through precipitation by the addition of barium chloride while the lithium electrodes served as a reference for the array by having a constant lithium concentration as a background for all solutions. The array was tested with several types of simulants, soils, and sawdust from a Mars meteorite, all with varying salt content, meant to approximate the various hypotheses regarding the ionic composition of the Martian soil. The activities of anions and cations determined with the array were compared to ion chromatography data. [source] Nanoparticle-Structured Ligand Framework as Electrode InterfacesELECTROANALYSIS, Issue 1-2 2004Nancy Abstract Nanostructured thin film assemblies derived from metal or oxide nanocrystal cores and functionalized molecular shells provide large surface-to-volume ratio and three-dimensional ligand frameworks. In this article, we report results of an investigation of the nanostructured materials for electroanalysis. Monolayer-capped gold nanoparticles of 2-nm core diameter and carboxylic acid-functionalized alkyl thiols were assembled on electrode surfaces via an exchange-crosslinking-precipitation reaction route, and were studied as a model system. The network assemblies exhibit open frameworks in which the void space forms channels with the nanometer sized cores defining its size and the shell structures defining its chemical specificity. Such nanostructures were exploited to demonstrate the viability of responsive materials for interfacial incorporation and fluxes of ionic species. The nanomaterials were characterized by an array of techniques, including cyclic voltammetry, electrochemical quartz-crystal nanobalance, flow injection analysis, and surface infrared reflection spectroscopy. The current responses and mass loading as a result of the incorporation of ionic species into the nanostructure have been analyzed. The potential application of the nanostructured thin films for electrochemical detection in microfluidic systems is also discussed. [source] Electric field-enhanced transport across phase boundaries and membranes and its potential use in sample pretreatment for bioanalysisELECTROPHORESIS, Issue 5 2010Pavel Kubá Abstract Separation techniques, such as electrodialysis, electroextraction, electro-membrane extraction and extraction across phase interfaces, are reviewed and discussed as methods for sample cleanup and preconcentration. This survey clearly shows that electromigration of ionic species across phase interfaces, especially across supported liquid membranes, may be very selective and is strongly dependent on the chemical composition of these interfaces. Thus, electric field-enhanced transport across chemically tailored liquid membranes may open new perspectives in preparative analytical chemistry. This review offers comprehensive survey of related literature and discussion of the topic, which may stimulate interest of experts and practitioners in bioanalysis. [source] Variations of chemical compositions in coarse aerosols and fine aerosols in two successive episodesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2006Chung-Yih Kuo Abstract Particulate matter with diameters less than 2.5 ,m (PM2.5) and ranging between 10 to 2.5 ,m (PM10-2.5) were simultaneously collected at four air-quality monitoring stations in the Taichung area of central Taiwan during the period of February 12 to 22, 2004. Two different types of PM10 episodes, a nonlocal dust-storm episode and a local episode, were observed in the present study. High concentrations of coarse aerosols occurred during the dust-storm episode, whereas high concentrations of fine aerosols were present during the local episode. Relatively high levels of Na+, Mg2+, Ca2+, and Cl, in coarse aerosols were observed during the dust-storm episode. Very high concentrations of secondary aerosols (NH+4, SO2,4, and NO,3) in fine aerosols were observed during the local episode. The nitrate ion demonstrated the greatest increase in the ratios of ionic species to PM2.5 and ionic species to PM10-2.5 during the local episode. Significantly high ratios (0.444) of NO,3 to NO2 in fine aerosols were present during the local episode, indicating that the relatively high formation rate of NO,3 was one of the important factors leading to the increase of the NO,3 to PM2.5 ratio during the local episode. Results also showed that an abundant quantity of fine ammonium nitrate was formed during the local episode, and chloride depletion probably was the major pathway to form coarse NaNO3 during this episode. [source] Variations of nitrate and sulfate in the atmosphere on days of high and low particulate mattersENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2005Chung-Yih Kuo Abstract Particulate matters with aerodynamicdiameter less than 10 ,m (PM10) were collected with high-volume samplers for four periods of consecutive samplings. Each period included a high PM10 (defined as PM10 ,110 ,g/m3) episode. The concentrations of all ionic species of high PM10 day (HPD) samples were higher than those of low PM10 (defined as PM10 < 110,g/m3) d (LPD) samples. Using the ionic concentrations of HPD samples at each station divided by those of LPD samples at respective stations, the results showed thatNO increased most from LPD to HPD among the eight ionic species examined. A high mean value (3.15) of NO/elemental carbon (EC) ratio of HPD divided by that of LPD indicates that concentration variations due to chemical formation and nonchemical factors apparently were higher than those of the concentration variations due to nonchemical factors alone. The NO/SO ratio of HPD divided by that of LPD ranged from 1.62 to 3.92 for the four periods. The results indicate that more nitrate than sulfate had formed during high PM10 episodes. Multiple linear regression analysis showed that the percentage of NH associated with nitrate and sulfate decreased and the percentage that could be explained by Ca2+ and Na+ increased on HPD. The reactions of HNO3 and H2SO4 with sea salt particles and with aqueous carbonates on soil particles during HPD were considered the main causes leading to these variations. [source] The Polymerization of Tetrahydrofuran Initiated by Niobium(V) and Tantalum(V) HalidesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2008Fabio Marchetti Abstract The halides MX5 (M = Nb, Ta, X = F, Cl, Br) (1) are effective in promoting the polymerization of tetrahydrofuran (thf). The polymerization reactions promoted by MCl5 and MBr5 proceed via the ionic species 3, which forms from MX5(thf) (2) by attack of the incoming monomer to the metal-bonded thf. The metal-bonded thf of 3 is not involved in the immediately successive steps of the reaction. The [TaF6], anion is not formed when the polymerization is initiated by TaF5. The activities of the promoters increase according to the series TaBr5 < NbCl5 < TaCl5 < TaF5. The latter possesses high activity and produces high molar mass poly(tetrahydrofuran) (67100 g/mol). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Surface Physiochemistry Affects Protein Adsorption to Stoichiometric and Silicate-Substituted Microporous Hydroxyapatites,ADVANCED ENGINEERING MATERIALS, Issue 4 2010Katharina Guth An important factor in the bioactivity and success of a bone-graft substitute is the nature of the adsorbed protein layer, which plays a vital role in orchestrating cell attachment and development through the presence of adhesion proteins such as fibronectin (Fn) and vitronectin (Vn). In this study, microporous hydroxyapatite (HA) and silicate-substituted hydroxyapatite (SA) discs with matched porosity and surface morphology are developed to mimic the topography found in commercial bone-graft substitutes in order to identify whether the introduction of microporosity and associated surface roughness eliminates the beneficial effect that silicate substitution has on protein adsorption. The introduction of microporosity does not abolish the relative enrichment of the protein layer that is adsorbed to the microporous SA discs, as opposed to HA, but appears to accelerate it. Fibronectin and Vn adsorption in a range of competitive environments at physiological temperatures confirm that the microporous SA discs have a greater affinity for Fn and Vn compared with HA, suggesting differences in the mechanisms behind the surface affinity to SA. Thus, development of a surface protein layer on SA and HA is likely to be dependent on the nature of the local protein environment and a combination of factors that are associated with the addition of silicate: the surface charge, the nature of the ionic species at the interface and the resultant hydrophilicity of the surface. Total protein adsorption is not found to be a good indicator of potential implant performance, particularly at early time points. [source] Novel Engineered Ion Channel Provides Controllable Ion Permeability for Polyelectrolyte Microcapsules Coated with a Lipid MembraneADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Andrew R. Battle Abstract The development of nanostructured microcapsules based on a biomimetic lipid bilayer membrane (BLM) coating of poly(sodium styrenesulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) polyelectrolyte hollow microcapsules is reported. A novel engineered ion channel, gramicidin (bis-gA), incorporated into the lipid membrane coating provides a functional capability to control transport across the microcapsule wall. The microcapsules provide transport and permeation for drug-analog neutral species, as well as positively and negatively charged ionic species. This controlled transport can be tuned for selective release biomimetically by controlling the gating of incorporated bis-gA ion channels. This system provides a platform for the creation of "smart" biomimetic delivery vessels for the effective and selective therapeutic delivery and targeting of drugs. [source] A three-scale computational model of reactive pollutant transport in smectitic claysINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 8 2006Márcio A. Murad Abstract A three-scale model of dual-porosity type is proposed to describe contaminant transport in swelling clays. The swelling medium is characterized by three separate length scales (nano, micro and macro) and two levels of porosity (micro- and macro-pores). At the nanoscale the medium is composed of charged clay particles saturated by a binary monovalent aqueous electrolyte solution occupying the micro-pores. At the intermediate (micro) scale the two-phase system is represented in a homogenized fashion with averaged microscopic equations governing the behaviour of the clay clusters (or aggregates) regarded a two-phase mixture composed of clay particles and electrolyte solution. At the macroscale, the microscale mixture of clay clusters is homogenized with the bulk solution containing non-electrolyte species lying in the macro-pore system. The resultant macroscopic picture appears governed by a dual-porosity model wherein the clay clusters act as sources/sinks of mass to the macro-pore system. Under a local equilibrium assumption between the clay clusters and macro-pores, a quasi-steady version of the dual-porosity model is derived. This framework combined with a three-scale picture of the colloidal system allows to provide nanoscopic representations for the retardation coefficient, governing the instantaneous adsorption/desorption of the ionic species in the micro-pores, in terms of the local behaviour of the electrical double layer potential which satisfies a Poisson,Boltzmann-type problem at the nanoscale. Copyright © 2006 John Wiley & Sons, Ltd. [source] Coupled lattice-Boltzmann and finite-difference simulation of electroosmosis in microfluidic channelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004Dzmitry Hlushkou Abstract In this article we are concerned with an extension of the lattice-Boltzmann method for the numerical simulation of three-dimensional electroosmotic flow problems in porous media. Our description is evaluated using simple geometries as those encountered in open-channel microfluidic devices. In particular, we consider electroosmosis in straight cylindrical capillaries with a (non)uniform zeta-potential distribution for ratios of the capillary inner radius to the thickness of the electrical double layer from 10 to 100. The general case of heterogeneous zeta-potential distributions at the surface of a capillary requires solution of the following coupled equations in three dimensions: Navier,Stokes equation for liquid flow, Poisson equation for electrical potential distribution, and the Nernst,Planck equation for distribution of ionic species. The hydrodynamic problem has been treated with high efficiency by code parallelization through the lattice-Boltzmann method. For validation velocity fields were simulated in several microcapillary systems and good agreement with results predicted either theoretically or obtained by alternative numerical methods could be established. Results are also discussed with respect to the use of a slip boundary condition for the velocity field at the surface. Copyright © 2004 John Wiley & Sons, Ltd. [source] Charge and Mass Transfer Across the Metal/Solution InterfaceISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Eliezer Gileadi Electrode reactions are characterized by charge transfer across the interface. The charge can be carried by electrons or by ions. It is shown here that when both mass and charge cross the interface, the charge must be carried by the ionic species, not by the electrons, as a result of the very large difference in the time scale for electron and ion transfer. A prime example of charge transfer by ions is metal deposition. It is proposed that ion transfer occurs by migration of the ions across the interface, under the influence of the high electrostatic field in the double layer. The rate constants observed for metal deposition are comparable to those for outer-sphere charge transfer. These unexpectedly high rate constants for metal deposition are explained by a model in which removal of the solvation shell and reduction of the effective charge on the metal ion occur in many small steps, and a make-before-break mechanism exists, which lowers the total Gibbs energy of the system as it moves along the reaction coordinate from the initial to the final state. [source] A further investigation on a MALDI-based method for evaluation of markers of renal damageJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2009Annunziata Lapolla Abstract The validity of the urinary protein profile to characterize the pathological states of diabetic, nephropathic and diabetic,nephropathic patients was considered on the basis of previously obtained results by MALDI/MS, showing a different abundance ratio of the collagen ,1 and ,5 chain precursor fragments at m/z 1219 and 2049 and of the uromodulin precursor fragment at m/z 1912 observed in healthy subjects and patients; a larger number of subjects was examined and the obtained results were statistically evaluated. The p values related to the observed differences indicate that they are statistically significant when comparing all patients versus healthy controls, diabetic with normo or microalbuminuria versus nephropathic with advanced renal disease patients and diabetic with normo or microalbuminuria versus diabetic with advanced nephropathy patients. The scatter plot matrix gives evidence of the strict inverse relationship between the abundances of ions at m/z 1912 and 1219, the correlation coefficient being particularly high (r = 0.921, p < 0.001). The relationship between the true positive rate (sensitivity) and false positive rate (1,specificity) for every possible cutoff value in abundance of the considered ionic species was investigated through the receiver-operating characteristic (ROC) curve. The obtained data indicate that a good differentiation of nephropathic patients with advanced renal disease and diabetic patients with advanced nephropathy versus healthy subjects can be easily obtained by this approach. Copyright © 2009 John Wiley & Sons, Ltd. [source] Gas phase behavior of radical cations of perfluoroalkyl-1,2,4-triazines: an experimental and theoretical studyJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009Gianluca Giorgi Abstract Electron ionization mass spectrometry and low-energy collision-induced decomposition reactions occurring in a tridimensional ion trap, together with density functional theory (DFT) calculations on neutrals, even- and odd-electron cations, have been used to study the gas-phase ion chemistry of a series of perfluoroalkyl-1,2,4-triazines. Loss of oxygen, due to thermal degradation occurring before ionization, likely involving the hydroxylamino group, has been observed. Compounds having a carbonyl group at position 6 of the triazine ring fragment in the source by elimination of NO followed by HF or CO. The decomposition pathways occurring due to CID experiments have shown interesting features depending on the nature and structure of precursor ions. Most of them involve elimination of endocyclic atoms, thereby producing contraction of the original six-membered ring or formation of acyclic structures. DFT (B3LYP/6-31G(d,p)) calculations have been used for evaluating structure, stability and properties of neutral and ionic species involved in gas-phase processes. In particular, it has been calculated that in the molecular ion the unpaired electron is mainly located on the exocyclic nitrogen, while the positive charge is on the C(6) carbon atom. Copyright © 2009 John Wiley & Sons, Ltd. [source] Do collisions inside the collision cell play a relevant role in CID-LIFT experiments?,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2007Gloriano Moneti Abstract Collision experiments are a valid approach to characterize the ionic species generated by matrix assisted laser desorption ionization (MALDI). When a time-of-flight analyzer is employed, three different approaches are available for these experiments: the postsource decay (PSD), the LIFT and the MALDI-TOF/TOF. The last two are of particular interest because of the overcoming of the PSD problems related to mass calibration of the product ion spectra. Experiments performed by LIFT on linear or cyclic peptides, in presence or in absence of collision gas in the collision cell, gave evidence of an unexpected behavior: the two spectra were practically superimposable, and in the former case only a few new fragmentation channels were activated with low yield. These results mean that the selected ion exhibits a large amount of internal energy, capable of promoting fragmentation processes in the time window corresponding to the flight time between ion source and the acceleration electrode placed after the collision cell. Experiments performed by varying the plume density show that this internal energy uptake occurs in the expanding plume, through multiple collisions. The LIFT data have been compared with those achieved by collisions of ESI-generated [MH]+ ions of angotensin II performed under ,in-source' conditions and by triple-quadrupole experiments. The obtained results show a strong similarity among the spectra, indicating that the internal energy uptake in a MALDI source is comparable with that of 40-eV ions colliding with Ar in a triple-quadrupole instrument. Copyright © 2006 John Wiley & Sons, Ltd. [source] Multivariate analysis approach to the plasma protein profile of patients with advanced colorectal cancer,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2006Eugenio Ragazzi Abstract The aim of the present study was to identify the pattern of plasma protein species of interest as markers of colorectal cancer (CRC). Using matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), the plasma protein profile was determined in nine stage IV CRC patients (study group) and nine clean-colon healthy subjects (control group). Multivariate analysis methods were employed to identify distinctive disease patterns at protein spectrum. In the study and control groups, cluster analysis (CA) on the complete MALDI-MS spectra plasma protein profile showed a distinction between CRC patients and healthy subjects, thus allowing the identification of the most discriminating ionic species. Principal component analysis (PCA) and linear discriminant analysis (LDA) yielded similar grouping results. LDA with leave-one-out cross validation achieved a correct classification rate of 89% in both the patients and the healthy subjects. Copyright © 2006 John Wiley & Sons, Ltd. [source] Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxidesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2003David Rondeau Abstract Organic peroxides such as the cumene hydroperoxide I (Mr = 152 u), the di- tert -butyl peroxide II (Mr = 146 u) and the tert -butyl peroxybenzoate III (Mr = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water,methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (,50 °C) and probe temperature (70,200 °C). The mass spectra of these compounds show the formation of (i) an [M + H]+ ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH3OH2]+ ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH3OH2+, i.e. thermochemical parameters () and two kinetic factors such as the capture constant of the initial stable ion,dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster. Copyright © 2003 John Wiley & Sons, Ltd. [source] The discovery of two kinds of ion pairsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2004Johannes Smid Abstract The discovery and implications of the existence of two kinds of ion pairs in solutions of carbanion salts is described. Also discussed are the factors controlling tight,loose ion pair equilibrium: the nature of the carbanion and its counterion, temperature, pressure, solvent, and cation-complexing additives. A few examples are presented of the effect of these ionic species on the mechanisms of anionic polymerization and proton transfer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3655,3667, 2004 [source] Low-oxidation-potential conducting polymers derived from 3,4-ethylenedioxythiophene and dialkoxybenzenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2001Jennifer A. Irvin Abstract Monomers derived from 3,4-ethylenedioxythiophene and phenylenes with branched or oligomeric ether dialkoxy substituents were prepared with the Negishi coupling technique. Electrooxidative polymerization led to the corresponding dialkoxy-substituted 3,4-ethylenedioxythiophene,phenylene polymers, with extremely low oxidation potentials (E1/2,p = ,0.16 to ,0.50 V vs Ag/Ag+) due to the highly electron-rich nature of these materials. The polymers were electrochromic, reversibly switching from red to blue upon oxidation, with bandgaps at about 2 eV. The electrochemical behavior of the oligomeric ether-substituted polymer was investigated in the presence of different metal ions. Films of the polymer exhibited electrochemical recognition for several alkali and alkaline-earth cations with selectivity in the order Li+ > Ba2+ > Na+ > Mg2+. Cyclic voltammetry showed a decrease in the oxidation potential and an improvement in the definition of the voltammetric response, as well as an increase in the overall electroactivity of the polymer films when the concentration of the cations in the medium was increased. These results are discussed in terms of the electrostatic interactions between the complexed cation and the redox center, as well as the diffusion of the ionic species into the polymer matrix. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2164,2178, 2001 [source] Raman spectroscopy of hydrotalcites with phosphate in the interlayer: implications for the removal of phosphate from waterJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2006Ray L. Frost Abstract Hydrotalcites with phosphate in the interlayer were prepared at different pH values. At pH > 11.0 (PO4)3, was the intercalated ionic species, whereas at pH < 11.0 a mixture of (PO4)3, and (HPO4)2, ions was intercalated. Powder X-ray diffraction shows that the hydrotalcite formed at pH 9.5 is poorly diffracting with a d-spacing of 11.9 Ĺ; whereas the d(003) spacing for the phosphate interlayered hydrotalcite formed at pH 11.9 and 12.5 was 8.0 and 7.9 Ĺ respectively. The addition of a thermally activated ZnAl-HT to a phosphate solution resulted in the uptake of the phosphate and the reformation of the hydrotalcite. Raman spectroscopy of the phosphate interlayered hydrotalcites shows that the interlayered anion is pH dependent and only above pH 11.9 is the orthophosphate anion intercalated. At lower pH, the monohydrogen phosphate anion is intercalated. Raman spectroscopy shows that upon addition of the thermally activated hydrotalcite to an aqueous phosphate solution, results in the uptake of phosphate anion from the solution. Copyright © 2006 John Wiley & Sons, Ltd. [source] The Laser Two-photon Photolysis of Liquid Carbon Tetrachloride,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006G. Zhang ABSTRACT The two-photon photolysis of liquid CCl4 with 25 ps pulses of 266 nm light has been studied and compared with similar studies with high energy radiation. Both neutral and ionic species are produced from excited states and ionization. The emphasis of the study is on the ionic processes, while some data related to excited states and free radicals are presented. In both radiolysis and photolysis, a solvent separated charged pair, CCl3+, Cl - , exhibiting a ,max at 475 nm, is observed that exhibits a total growth over 38 to 100 ps. Solutes with ionization potentials less than that of CCl4 (11.47 eV) reduce the yield of the 475 nm species producing radical cations of the solute. The efficiency of this process is about 10-fold larger in radiolysis compared with photolysis. Analysis of the data suggest that the lower energy of two-photon photolysis produces a charge pair CCl4+, CCl4 - , which decays in about 3 ps to CCl4+, Cl - . This species then decays to CCl3+, Cl - . The lifetime of the growth of the 475 nm is measured as 46 ps. These studies clearly show areas where radiolysis and photolysis can be quite similar and also areas where the vast difference in excitation energy introduces stark differences in the observed radiation and photoinduced chemistry. [source] Investigation of p-type macroporous silicon formationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005C. Lévy-Clément Abstract Nanopores and macropores can be formed electrochemically on p-type silicon depending on the silicon resistivity and composition of the electrolyte. In order to understand if the structural dimensionality of the porous p-type Si, either nanopore or macropore formation, depends on the electrochemical process at the Si/electrolyte interface, in situ pulsed surface photovoltage (SPV) and photoluminescence (PL) measurements have been undertaken. The SPV and PL studies have been made as a function of the applied current density as well as the electrolyte composition (aqueous or in presence of organic solvent) and the silicon doping density. Main results show that the Si surface is well passivated with preferential formation of ionic species and the Si band bending is around 100 mV, during porous Si formation. It varies slightly with the doping density, but is not affected by the composition of the electrolyte (HF/water and HF/organic solvent). This demonstrates that the chemistry of the electrolyte plays a major role in the formation of macroporous and nanoporous Si, but has still to be determined. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New isotope ratio mass spectrometric method of precise ,37Cl determinationsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2009Stanislaw Halas The most precise method of chlorine isotope analysis described to date is based on the isotope ratio mass spectrometry (IRMS) of chlorine quantitatively converted into chloromethane, CH3Cl. This gas can be produced from several chlorine-containing compounds and analyzed by IRMS. However, the mass spectrum of chloromethane is rather complicated and the ratio of the most abundant ions (mass-52/mass-50) differs from the 37Cl/35Cl isotope ratio. This difference becomes significant when the , exceeds 10,. Moreover, the electron ionization source yields approximately 80% of all the ionic species at the useful masses 50 and 52. To overcome these drawbacks, we have devised a negative ion mass spectrometer which retains all the best features of IRMS, including a dual-inlet system with changeover valve, dual collector assembly and CH3Cl gas as analyte. In the modified ion source we have replaced the ionization chamber with an electron beam by a metal tube with a hot metal filament inside it. Within this tube the 35Cl, and 37Cl, ions are produced with an efficiency dependent on the filament material and its temperature. No other ionic species were found in the mass spectrum except of traces at masses 26 and 28 at ppm levels, probably due to the formation of CN, and CO,. The minimal amount of Cl used in our method is of the order of 5,µmol (3,mg AgCl) and the precision is better than 0.005, (1,). Copyright © 2009 John Wiley & Sons, Ltd. [source] Mass spectrometry in the characterization of ambers.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2008Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers. Copyright © 2008 John Wiley & Sons, Ltd. [source] Energy-resolved in-source collisionally induced dissociation for the evaluation of the relative stability of noncovalent complexes in the gas phaseRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2005Nataliya Lyapchenko Energy-resolved in-source collisionally induced dissociation (CID) studies on the complexation of alkali metal cations by some crown ethers, nucleic acid bases, and amino acids have been performed. It has been shown that the cone voltage corresponding to the maximum ion abundance (Vc,Imax) of the breakdown curve is characteristic of a given ion and not influenced by the cone desolvation process or the composition of the solution. Very good agreement of the Vc,Imax value with the bond strength of the ion has been observed. Determination of the Vc,Imax values for different ionic species is a useful, simple, and inexpensive way to obtain their relative stabilities in in-source CID conditions. Copyright © 2005 John Wiley & Sons, Ltd. [source] {4-[(Carbamimidoylhydrazono)methyl-,2N1,N4]-5-hydroxymethyl-2-methylpyridinium-3-olate-,O}(methanol-,O)copper(II) dinitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Vukadin M. Leovac The title compound, [Cu(C9H13N5O2)(CH4O)](NO3)2, consists of square-planar cationic complex units where the CuII centre is coordinated by an N,N,,O -tridentate pyridoxal,aminoguanidine Schiff base adduct and a methanol molecule. The tridentate ligand is a zwitterion exhibiting an almost planar conformation. The dihedral angles between the mean planes of the pyridoxal ring and the six- and five-membered chelate rings are all less than 2.0°. The charge on the complex cation is neutralized by two nitrate counter-ions. Extensive N,H...O and C,H...O hydrogen bonding connects these ionic species and leads to the formation of layers. The pyridoxal hydroxy groups are the only fragments that deviate significantly from the flat layer structure; these groups are involved in O,H...O hydrogen bonding, connecting the layers into a three-dimensional crystal structure. [source] An unusual two-dimensional hydrogen-bonding network in bis(2,9-dimethyl-1,10-phenanthrolin-1-ium) peroxodisulfate dihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2008Miguel Angel Harvey The title compound, 2C14H13N2+·S2O82,·2H2O, is a protonated amine salt which is formed from two rather uncommon ionic species, namely a peroxodisulfate (pds2,) anion, which lies across a crystallographic inversion centre, and a 2,9-dimethyl-1,10-phenanthrolin-1-ium (Hdmph+) cation lying in a general position. Each pds2, anion binds to two water molecules through strong water,peroxo O,H...O interactions, giving rise to an unprecedented planar network of hydrogen-bonded macrocycles which run parallel to (100). The atoms of the large R88(30) rings are provided by four water molecules bridging in fully extended form (...H,O,H...) and four pds2, anions alternately acting as long (...O,S,O,O,S,O...) and short (...O,S,O...) bridges. The Hdmph+ cations, in turn, bind to these units through hydrogen bonds involving their protonated N atoms. In addition, the crystal structure also contains ,,, and aromatic,peroxo C,H...O interactions. [source] Bis(acetonitrile-,N)[(1RS,4RS,8SR,11SR)-1,4,8,11-tetraazatetradecane-,4N]copper(II) bis{tetrakis[3,5-bis(trifluoromethyl)phenyl]borate} 0.31-hydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2003Janet M. S. Skakle The title compound, [Cu(C2H3N)2(C10H24N4)](C32H12BF24)2·0.31H2O, crystallizes as an ionic species with no interactions between the ions. The [CuII(cyclam)(MeCN)2]2+ dication (cyclam is 1,4,8,11-tetraazatetradecane), located on a 2/m symmetry site, forms as a distorted octahedral species with four Cu,Ncyclam bonds of 2.013,(2),Ĺ and two C,NMeCN bonds of 2.499,(4),Ĺ. The [B{C6H3(CF3)-3,5}4], anion, located on a twofold axis, is a distorted octahedral species. A small amount of water is present, occupying sites between columns of ions. [source] Use of complementary cation and anion heavy-atom salt derivatives to solve the structure of cytochrome P450 46A1ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2008Mark Andrew White Human cytochrome P450 46A1 (CYP46A1) is one of the key enzymes in cholesterol homeostasis in the brain. The crystallization and heavy-atom structure solution of an active truncated CYP46A1 in complex with the high-affinity substrate analogue cholesterol-3-sulfate (CH-3S) is reported. The 2.6,Ĺ structure of CYP46A1,CH-3S was solved using both anion and cation heavy-atom salts. In addition to the native anomalous signal from the haem iron, an NaI anion halide salt derivative and a complementary CsCl alkali-metal cation salt derivative were used. The general implications of the use of halide and alkali-metal quick soaks are discussed. The importance of using isoionic strength buffers, the titration of heavy-atom salts into different ionic species and the role of concentration are considered. It was observed that cation/anion-binding sites will occasionally overlap, which could negatively impact upon mixed RbBr soaks used for multiple anomalous scatterer MAD (MMAD). The use of complementary cation and anion heavy-atom salt derivatives is a convenient and powerful tool for MIR(AS) structure solution. [source] Decomposition of Formic Acid Catalyzed by a Phosphine-Free Ruthenium Complex in a Task-Specific Ionic LiquidCHEMCATCHEM, Issue 10 2010Jackson D. Scholten Abstract The dehydrogenation of formic acid is effectively catalyzed by the Ru complex [{RuCl2(p -cymene)}2] dissolved in the ionic liquid (IL) 1-(2-(diethylamino)ethyl)-3-methylimidazolium chloride at 80,°C without additional bases. This catalytic system gives TOF values of up to 1540,h,1. Preliminary kinetic insights show formal reaction orders of 0.70(±0.15), 0.78(±0.03) and 2.00(±0.17) for the Ru catalyst, IL,1, and formic acid, respectively. The apparent activation energy of this process is estimated to be (69.1±7.6),kJ,mol,1. In addition, dimeric Ru hydride ionic species involved in the reaction, such as [{Ru(p -cymene)}2{(H),-(H)-,-(HCO2)}]+ and [{Ru(p -cymene)}2{(H),-(Cl),-(HCO2)}]+, are identified by mass spectrometry. The presence of water in large amounts inhibits higher conversions. Finally, a remarkable catalytic activity is observed during recycles, indicating this system's potential for hydrogen gas production. [source] Synthesis of Gold Microplates Using Bovine Serum Albumin as a Reductant and a StabilizerCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2010Leslie Au Abstract Gold microplates were synthesized in aqueous solutions by reducing HAuCl4 with the hydroxyl groups in both serine and threonine of bovine serum albumin (BSA), which is a globular protein in its native state. In this article, we systematically investigated the effects of temperature, pH value, the concentration of BSA, and ionic species on the reduction kinetics and thus the size and morphology of the final product. The optimal experimental conditions for producing uniform Au microplates include the following: an elevated temperature in the range of 55,65,°C, an acidic solution with pH,3, and the presence of NaCl (0.14,M). We found that if any one of these parameters was deviated from the optimal condition, Au microplates would not be formed in high yields. We also found that the surfaces of the as-synthesized Au microplates were covered by a dense array of BSA bumps. [source] | ||||||||||||||||||||||||||||||||||