Ionic Shifts Research Articles

One- and two-electron transfer processes in ion-surface scattering

Abstract : A phenomenological description of one-electron transfer leading to ion neutralization in ion-surface scattering is summarized. A perturbative treatment using an effective interaction in the Anderson-Newns Hamiltonian is then reviewed, and tje conditions under which the perturbative series has fast convergence are explored in terms of the electronic and dynamical properties of the collision system. Calculational results are discussed for proton neutralization at different alkali-halide surfaces. In the case of negative-ion formation and hence two-electron transfer to the incoming projectile ion, the Anderson correlation energy U is included in the analysis. Calculations of the probability of negative-ion formation are in qualitative agreement with experiments on the conversion of H+ (D+) to H- (D-) by scattering from a cesiated W(110) surface. The interplay between temperature effects and U are discussed. Improvements on the calculations by incorporating the image potential into the ionic energy level shift are considered. Keywords include: ION-SURFACE Scattering, Electron Transfer, Anderson-Newns Hamiltonian, Proton Neutralization, Negative-ion Formation, Correlation Energy.

A dose dependence study of O2 adsorbed on large Ar clusters

An investigation of the behavior of O(2) molecules in and on O(2)-doped large (N approximately 8000) Ar host clusters has been performed by means of core and valence photoelectron spectroscopy. Data from pure O(2) and Ar clusters, as well as from O(2)-doped Ar clusters, are presented. The experimental data together with calculations of the binding energy shifts of oxygen molecular ions in and on the surface of a large host Ar cluster show that the diffusion behavior has a strong dependence on the doping pressure. We conclude that the oxygen molecules in the doped Ar host do not partake in band formation, since there is clear vibrational resolution in the spectral features stemming from screened O(2) (+) ions. This implies that valence photoelectron spectroscopy can be used to determine the geometrical structure of this and certain, similar, cluster systems.

Application of a hybrid ion trap/time-of-flight mass spectrometer in metabolite characterization studies: Structural identification of the metabolism profile of antofloxacin in rats rapidly using MS n information and accurate mass measurements

We describe herein, a very effective way in the rapid identification of metabolites for antofloxacin based on a hybrid ion trap (IT)/time-of-flight (TOF) mass spectrometer technique. The purified samples were separated by a reversed-phase C 18 column under a gradient elution, antofloxacin and its metabolites were detected by the on-line IT/TOF detector in scan mode. The identification of the metabolites and elucidation of their structure were performed by comparing the changes in molecular masses (Δ M), calculating compound-based component by Formula Predictor software, and defining sites of biotransformation based upon mass shifts of diagnostic fragment ions according to the accurate MS n spectral information. In this case, we used such strategies for the identification of the metabolism for antofloxacin, and six metabolites of antofloxacin were found in rats for the first time.

Compact variational wave functions for bound states in three-electron atomic systems

The variational procedure to construct compact and accurate wave functions for three-electron atoms and ions is developed. The procedure is based on the use of six-dimensional Gaussoids written in the relative four-body coordinates r 12, r 13, r 23, r 14, r 24, and r 34. The nonlinear parameters in each basis function have been carefully optimized. Using these variational wave functions, we have determined the energies and other bound state properties for the ground 12 S-states in a number of three-electron atoms and ions. The three-electron atomic systems considered in this work include the neutral Li atom and nine positively charged lithiumlike ions: Be+, B2+, C3+, ..., Na8+, and Mg9+. Our variational wave functions are used to determine the hyperfine structure splitting and field shifts for some lithium-like ions. The explicit formulas of the Q −1 expansion are derived for the total energies of these three-electron systems.

Activation of TonEBP by Calcium Controls β1,3-Glucuronosyltransferase-I Expression, a Key Regulator of Glycosaminoglycan Synthesis in Cells of the Intervertebral Disc

The goal of this investigation was to study the expression and regulation of beta1,3-Glucuronosyltransferase-I (GlcAT-I), a key enzyme regulating GAG synthesis in cells of the intervertebral disc. There was a robust expression of GlcAT-I in the nucleus pulposus in vivo. Treatment with the calcium ionophore ionomycin resulted in increased GlcAT-I expression, whereas GlcAT-I promoter constructs lacking TonE site or a mutant TonE were unresponsive to the ionophore. Experiments using TonEBP and DN-TonEBP constructs showed that TonEBP positively regulated GlcAT-I promoter activity. ChIP analysis confirmed binding of TonEBP to the promoter. We further validated the role of TonEBP in controlling GlcAT-I expression using mouse embryo fibroblasts from TonEBP null mice. GlcAT-I promoter activity in null cells was significantly lower than the wild type cells. In contrast to wild type cells, treatment with ionomycin failed to increase GlcAT-I promoter activity in null cells. We then investigated if calcineurin (Cn)-NFAT signaling played a regulatory role in GlcAT-I expression. Inhibition of Cn following ionomycin treatment did not block GlcAT-I and tauT, a TonEBP-responsive reporter activity. GlcAT-I promoter activity was suppressed by co-expression of Cn, NFAT2, NFAT3, and NFAT4. Moreover, following ionomycin treatment, fibroblasts from CnAalpha and CnAbeta null mice exhibited robust induction in GlcAT-I promoter activity compared with wild type cells. Results of these studies demonstrate that calcium regulates GlcAT-I expression in cells of the nucleus pulposus through a signaling network comprising both activator and suppressor molecules. The results suggest that by controlling both GAG and aggrecan synthesis, disc cells can autoregulate their osmotic environment and accommodate mechanical loading.

Synthesis and optical properties of mesoporous MCM-41 containing doped TiO 2 nanoparticles

Nanosized TiO 2 is a kind of high-performance and functional inorganic material, the widespread use of TiO 2 is impaired by some defects of its structure, wide band gap (3.2 eV), and agglomeration easily occurred during the synthesis process. Uniform ordered channels of mesoporous materials, such as MCM-41, can control the particle size of TiO 2 and efficiently prevent particles from agglomeration. Tetraethylorthosilicate (TEOS) and tetrabutyl titanate were used as the silica source and Ti source respectively to synthesize the TiO 2/MCM-41 (TM) doped with different ions. MCM-41 was synthesized using a hydrothermal route; metal ions were incorporated into the pore channels of MCM-41 via a sol–gel method. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–vis) spectrophotometry, N 2 adsorption–desorption measurements and X-ray photoelectron spectroscopy (XPS) confirmed the incorporation of TiO 2 nanoparticles inside the pores of the mesoporous MCM-41 host without destroying its integrity. Specific surface area of TM composites increased, but the pore size and the pore volume decreased compared with that of pure MCM-41. The UV–vis spectra demonstrate that all the absorbance peaks of TM composites have a blue shift. The absorbance peaks of TM composites doped with different metal ions shift again. Ce-doped TM shows red shift markedly, which provides the possibility for preparing visible-light reactive photocatalyst.

Thermodynamics, Interfacial Structure, and pH Hysteresis of Rb+ and Sr2+ Adsorption at the Muscovite (001)−Solution Interface

The coverage and average height of adsorbed Rb+ and Sr2+ at the muscovite (001)-solution interface were measured with resonant anomalous X-ray reflectivity (RAXR) as a function of cation concentration (10-8 < [Sr2+] < 10(-1) m, 10-6 < [Rb+] < 10(-1) m at pH 5.5 and 3.5) and pH (1.5 to 5.5 at [Me(n+)] = 10(-3) m) without background electrolyte. At pH 5.5, Rb+ uptake approximately follows a Langmuir isotherm with deltaG(Rb)(o) = -23.5 +/- 4.0 kJ x mol(-1) and a saturation coverage of Tmax = 0.94 +/- 0.06 Rb+ per unit cell area, Auc = 46.72 A2, compensating the nominal surface charge density (1 e-/Auc). The Sr2+ isotherm has a saturation coverage of 0.47 +/- 0.05 Sr2+/Auc that also compensates the muscovite's charge, but the adsorption edge is both more abrupt and shifted significantly to lower concentration than that for Rb+. The uptake of Sr2+ is consistent with a Frumkin isotherm with an intrinsic adsorption constant, deltaG(Sr)(o) = -28.8 +/- 6.0 kJ x mol(-1) and a correlation energy, gamma(Sr) = -7.2 +/- 3.7 kJ x mol(-1). The average height of each adsorbed cation, corresponding to inner-sphere dominant Rb+ and coexisting inner- and outer-sphere Sr2+ distributions, was independent of ion coverage at pH 5.5. At pH 3.5, the adsorption edges of both ions shift to higher cation concentration, indicating competition with hydronium, and the shifts are accompanied by an irreversible reduction in the saturation coverage. The inner-sphere dominant mode of Rb+ adsorption did not change at pH 3.5, while that of Sr2+ changed to an outer-sphere dominant distribution. Hysteresis in both the amount and height of the adsorbed ion was observed as a function of the direction in which pH was changed, indicating that the intrinsic surface charge density decreased after reaction with acidic solutions. These results suggest new and unexpected interrelationships among the distribution of adsorbed ions, competitive adsorption of hydronium, and surface charge density at the mineral-solution interface.

Reexamining blackbody shifts for hydrogenlike ions

We investigate blackbody-induced energy shifts for low-lying levels of atomic systems, with a special emphasis on transitions used in current and planned high-precision experiments on atomic hydrogen and ionized helium. Fine-structure- and Lamb-shift-induced blackbody shifts are found to increase with the square of the nuclear charge number, whereas blackbody shifts due to virtual transitions decrease with increasing nuclear charge as the fourth power of the nuclear charge. We also investigate the decay width acquired by the ground state of atomic hydrogen, due to interaction with blackbody photons. The corresponding width is due to an instability against excitation to higher excited atomic levels, and due to blackbody-induced ionization. These effects limit the lifetime of even the most fundamental, a priori absolutely stable, ``asymptotic'' state of atomic theory, namely, the ground state of atomic hydrogen.

Use of EDTA to minimize ionic strength dependent frequency shifts in the 1H NMR spectra of urine

The 1H NMR spectrum of urine exhibits a large number of detectable metabolites and is, therefore, highly suitable for the study of perturbations caused by disease, toxicity, nutrition or environmental factors in humans and animals. However, variations in the chemical shifts and intensities due to altered pH and ionic strength present a challenge in NMR-based studies. With a view towards understanding and minimizing the effects of these variations, we have extensively studied the effects of ionic strength and pH on the chemical shifts of common urine metabolites and their possible reduction using EDTA (ethylenediaminetetraacetic acid). 1H NMR chemical shifts for alanine, citrate, creatinine, dimethylamine, glycine, histidine, hippurate, formate and the internal reference, TSP (trimethylsilylpropionic acid-d4, sodium salt) obtained under different conditions were used to assess each effect individually. EDTA minimizes the frequency shifts of the metabolites that have a propensity for metal binding. Chelation of such metal ions is evident from the appearance of signals from EDTA complexed to divalent metal ions such as calcium and magnesium. Not surprisingly, increasing the buffer concentration or buffer volume also minimizes pH dependent frequency shifts. The combination of EDTA and an appropriate buffer effectively minimizes both pH dependent frequency shifts and ionic strength dependent intensity variations in urine NMR spectra.

Structural Transformation of LiVOPO4 to Li3V2(PO4)3 with Enhanced Capacity

In the present investigation, we report the transformation of alpha-LiVOPO 4 to alpha-Li 3V 2(PO 4) 3, leading to an enhancement of capacity. The alpha-LiVOPO 4 sample was synthesized by a sol-gel method, followed by sintering at 550-650 degrees C in a flow of 5% H 2/Ar. The structural transformation of a triclinic alpha-LiVOPO 4 structure to a monoclinic alpha-Li 3V 2(PO 4) 3 structure was observed at higher sintering temperatures (700-800 degrees C in a flow of 5% H 2/Ar). The alpha-Li 3V 2(PO 4) 3 phase was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and X-ray absorption near edge spectrum (XANES) techniques. The valence shift of vanadium ions from +4 to +3 states was observed using in situ XANES experiments at V K-edge. The structural transformation is ascertained by the shape changes in pre-edge and near edge area of X-ray absorption spectrum. It was observed that the capacity was enhanced from 140 mAh/g to 164 mAh/g via structural transformation process of LiVOPO 4 to Li 3V 2(PO 4) 3.

Diffuse Scattering and Monte Carlo Studies of Relaxor Ferroelectrics

A renewed interest in the field of ferroelectricity has taken place in recent years since the finding of exceptional piezoelectric properties in the lead-oxide class of relaxor ferroelectric materials typified by the disordered perovskite PbZn1/3Nb2/3O3 (PZN). Although PZN and numerous related materials have been extensively studied over a long period, a detailed understanding of the exact nature of their polar nanostructure has still not emerged. In this article, we describe the development of Monte Carlo computer models, which seek to account for the detailed three-dimensional (3-D) diffuse neutron scattering data that have been recorded from a single crystal of PZN. It has been established that the observed diffuse patterns are due to planar nanodomains oriented normal to the six \( \left\langle {{\text{110}}} \right\rangle \) directions, but there is still some uncertainty concerning the direction of the local Pb ionic shifts, which remains an area of controversy. It is argued that further detailed analysis and experiments in which data are recorded with the crystal in an applied field should allow these remaining issues to be resolved.

Molecular Dynamics Study on Ion Diffusion in LiFePO4 Olivine Materials

Molecular dynamics (MD) simulations have been employed to investigate the ionic diffusion and the structure of LiFePO 4 cathode material. The results correspond well with the published experimental observations. The simulation results indicated that the diffusion of lithium ions was thermally activated and more significant than those of other ions. Compared with other cathode materials, the shifts of ions were less significant in LiFePO 4. This suggested that LiFePO 4 was more thermally stable. The snapshots of the positions of lithium atoms over a range of the steps provided a microscopic picture and the picture showed the lithium ions migrated through one-dimension channels.

High‐throughput, accurate mass liquid chromatography/tandem mass spectrometry on a quadrupole time‐of‐flight system as a ‘first‐line’ approach for metabolite identification studies

Throughput for drug metabolite identification studies has been increased significantly by the combined use of accurate mass liquid chromatography/tandem mass spectrometry (LC/MS/MS) data on a quadrupole time-of-flight (QTOF) system and targeted data analysis procedures. Employed in concert, these tools have led to the implementation of a semi-automated high-throughput metabolite identification strategy that has been incorporated successfully into lead optimization efforts in drug discovery. The availability of elemental composition data on precursor and all fragment ions in each spectrum has greatly enhanced confidence in ion structure assignments, while computer-based algorithms for defining sites of biotransformation based upon mass shifts of diagnostic fragment ions have facilitated identification of positions of metabolic transformation in drug candidates. Adoption of this technology as the 'first-line' approach for in vitro metabolite profiling has resulted in the analysis of as many as 21 new chemical entities on one day from diverse structural classes and therapeutic programs.

Effects of irradiation on intestinal cells in vivo and in vitro.

The effects of irradiation on intestinal epithelial cells were analyzed in vivo and in vitro. The in vivo study was carried out on the rat small intestine and for the in vitro study the intestinal crypt cell-line IEC-6 was used. Rat intestine and IEC-6 cells were irradiated with X-ray doses ranging between 1-16 Gy. Energy-dispersive X-ray microanalysis was used for detection of the elemental changes in the cells. Cell morphology was investigated in the scanning electron microscope, DNA-synthesis by autoradiography of 3H-thymidine incorporating nuclei and proliferation by cell counting. Our results indicate that in vivo, in the crypt cells, the increasing doses of irradiation led to increased sodium and lowered potassium and phosphorus concentrations. Corresponding ion shifts were found in the irradiated IEC-6 cells. Cells continued to proliferate up to the dose of 8 Gy, although the proliferation rate became lower with increasing dose of irradiation. The increasing dose of irradiation significantly reduced DNA-synthesis (16 Gy decreased DNA-synthesis by 50%) which resulted in a complete inhibition of cell proliferation. Analysis of goblet cells also showed characteristic radiation-dependent elemental changes. Scanning electron microscopical investigation of cells in culture revealed that most of the control cells were flat and had rather smooth cell membranes. Irradiation led to the appearance of numerous different membrane manifestations (microvilli of varying length and distribution, and blebs). Frequency of differences in the topology of the cells was related to the dose of irradiation. Our study clearly demonstrates that even low doses of irradiation cause changes in the ionic composition of the cells and inhibit DNA-synthesis and cell proliferation. The effects observed in the crypt cells in vivo were the same as in the intestinal cell line in vitro, which indicates that IEC-6 cells can be used for investigation of side effects of radiation to the abdomen.

Electrochemically-driven conformational shift in mono- and di-copper constrained macrotricyclic cyclen receptors

An electrochemical study of mono- and di-copper constrained cyclen macrotricycles is presented. Electrochemical data in DMF solution indicate that the reduction of dinuclear complexes occurs in two steps in the -0.4 to -0.8 V vs.AgCl/Ag potential range yielding CuII CuI and CuI CuI species further reduced to Cu metal at highly negative potentials. Mononuclear complexes are reduced in two steps to CuI and Cu metal. Electrochemical data suggest that reduction of both mononuclear and dinuclear complexes approach a square scheme involving electrochemically-driven conformational shifts for metal ions. The presence of endo- and exo-forms of the complexes are revealed by changes in the electrochemical response of the complexes in the presence of tetraethylammonium chloride, 1-azabicyclo[2.2.2]octane and diazabicyclo[2.2.2]octane competing ligands.

Flow-dependent versus spreading-like impairment of brain tissue integrity during focal cerebral ischemia and its consequences for neuroprotective strategies

Focal cerebral ischemic lesions demonstrate a gradual reduction of blood flow from the rim to the core. Flow reduction induces irreversible damage in the core region, whereas more peripheral tissue, i.e. penumbral tissue, is applicable to therapeutic interventions. Secondary mechanisms for lesion growth involve excitotoxicity, extracellular ion shifts, lactate generation, tissue acidosis, inflammation, spreading depolarization and many other processes. These toxic mediators accumulate in the ischemic core and endanger the still viable rim by diffusion or other spreading-like mechanisms, probably in part largely independent from blood flow. A substantial proportion of hemodynamic penumbral tissue could be demonstrated both in experimental settings and in clinical practice, whereas the precise spatial and temporary contribution of secondary mechanisms is much more difficult to investigate in our patients. Diffusion or spreading-mediated neurotoxicity will affect a small rim around the necrotic lesion. Due to the third power of volumetric analysis this would contribute to a large amount in small experimental lesions, but to a negligible amount of tissue in large clinical lesions and could therefore explain the difference in efficacy of neuroprotective strategies between experimental and clinical setups. Therefore, we discuss the likelihood of direct flow-dependent versus diffusion- or spreading-mediated impairment of endangered tissue in focal cerebral ischemia.

Tandem Mass Spectrometry Characteristics of Silver-Cationized Polystyrenes: Internal Energy, Size, and Chain End versus Backbone Substituent Effects

The Ag(+) adducts of polystyrene (PS) oligomers with different sizes (6-19 repeat units) and initiating (alpha) or terminating (omega) end groups mainly decompose via free radical chemistry pathways upon collisionally activated dissociation. This reactivity is observed for ions formed by matrix-assisted laser desorption/ionization as well as electrospray ionization. With end groups lacking weak bonds (robust end groups), dissociation starts with random homolytic C-C bond cleavages along the PS chain, which lead to primary and benzylic radical ions containing either of the chain ends. The primary radical ions mainly depolymerize by successive beta C-C bond scissions. For the benzylic radical ions, two major pathways are in competition, namely, depolymerization by successive beta C-C bond scissions and backbiting via 1,5-H rearrangement followed by beta C-C bond scissions. The extent of backbiting decreases with internal energy. With short PS chains, the primary radical ions also undergo backbiting involving 1,4- and 1,6-H rearrangements; however, this process becomes negligible with longer chains. If the polystyrene contains a labile substituent at a chain end, this substituent is eliminated easily and, thus, not contained in the majority of observed fragments. Changes in the PS backbone structure can have a dramatic effect on the resulting dissociation chemistry. This is demonstrated for poly(alpha-methylstyrene), in which backbiting is obstructed due to the lack of benzylic H atoms; instead, this backbone connectivity promotes 1,2-phenyl shifts in the primary radical ions formed after initial C-C bond homolyses as well as H atom transfers between the incipient primary and benzylic radicals emerging from these homolyses.

Foundations of lens ion transport

Abstract Purpose: Prof. George Duncan began work on the lens almost 40 years ago. His studies laid the foundation for our understanding of the mechanisms that regulate lens electrolyte content. Methods: In the late 1960s Prof. Duncan conducted microelectrode and tracer flux studies that illustrated a link between ion transport, osmotic balance and lens transparency. Results: His work defined the permeability properties of lens membranes and the requirement for equilibrium between passive ion movement and active ion transport. Later, Prof. Duncan and his colleagues at the University of East Anglia carried out an analysis of human cataractous lenses that revealed abnormal sodium, potassium, calcium and water levels in lenses with cortical opacification. Prof. Duncan presented the argument that the lens swells, calcium rises and cellular organization is disrupted if active sodium‐potassium transport fails to balance cation leakage. Over the course of several years, the University of East Anglia group discovered evidence for a high degree of cooperativity between fiber and epithelial cells. Prof. Duncan’s discoveries became the foundation for later studies by his group and others that showed certain lens cells are specialized for active ion transport and shift ions for the entire lens. Conclusions: In recent years more has been learned regarding expression and regulation of Na,K‐ATPase in lens epithelium and fibers. Recent studies by Tamiya, Okafor and Delamere (Am. J. Physiol. 2007 In Press) point to alterations of Na,K‐ATPase activity subsequent to stimulation of purinergic receptors. It is interesting that one of the earliest reports on functional purinergic receptors in lens epithelium came from Prof. Duncan and the University of East Anglia group.

Significance of Experimental Infarct Size as an Indicator of Therapeutic Efficacy in Humans

To the Editor: We would like to make a comment not in particular to the article by Shimamura et al1 but to the use of infarct size in animal experiments as a guide to human cerebrovascular research. Many human studies of treatments with neuroprotective agents for acute ischemic stroke, which had good experimental potential, had disappointing clinical results. This failure can be attributed to many factors.2 One of the main problems is that reliance on infarct size measurement alone in animals can be misleading as an indicator of therapeutic efficacy in humans.3 We know for example that nitric oxide synthase (NOS) inhibitors have provided significant neuroprotection in experimental animals subjected to focal ischemia.4,5 Tirilazad mesylate is a potent inhibitor of lipid peroxidation caused by …

Electrochemical Recognition of Metalloproteins by Bromide-modified Silver Electrode - A New Method

A bromide–modified silver electrode is reported, in the present study, to catalyzethe redox reactions of metalloproteins. This study describes that the bromide ions showvery good redox behavior with silver electrode. The cathodic and anodic peak potentialswere related to the concentration of bromide ions involved in making bromide-modifiedsilver electrode. The electrode reaction in the bromine solution was a diffusion-controlledprocess. Positive potential shift of the bromide ions was seen when different proteins wereadded to the solution using a silver electrode. New cathodic and anodic peaks wereobserved at different potential ranges for myoglobin, cytochrome c and catalase. A linearlyincreasing cathodic peak current of bromide ions was seen when the concentration ofsuperoxide dismutase was increased in the test solution. However, no change for albuminwas observed when its concentration was increased in the test solution. Present data provesour methodology as an easy-to-use analysis for comparing the redox potentials of differentmetalloproteins and differentiating the metallo- from non-metalloproteins. In this study, weintroduced an interesting method for bio-electrochemical analyses.