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At least 253 records · Page 14Linked to original sources
PubMed2002

Copper ion redox state is critical for its effects on ion transport pathways and methaemoglobin formation in trout erythrocytes.

We have studied the mechanism of copper uptake by the cells, its oxidative action and effects on ion transport systems using rainbow trout erythrocytes. Cupric ions enter trout erythrocytes as negatively charged complexes with chloride and hydroxyl anions via the band 3-mediated Cl-/HCO3- exchanger. Replacement of Cl- by gluconate, and complexation of cupric ions with histidine abolish rapid Cu2+ uptake. Within the cell cupric ions interact with haemoglobin, causing methaemoglobin formation by direct electron transfer from heme Fe2+ to Cu2+, and consecutive proton release. Ascorbate-mediated reduction of cupric ions to cuprous decreases copper-induced metHb formation and proton release. Moreover, cuprous ions stimulate Na+H+ exchange and residual Na+ transport causing net Na+ accumulation in the cells. The effect requires copper binding to an externally facing thiol group. Copper-induced Na+ accumulation is accompanied by K+ loss occurring mainly via K+-Cl- cotransporter. Taurine efflux is also stimulated by copper exposure. However, net loss of osmolytes is not as pronounced as Na+ uptake and modest swelling of the cells occurs after 5 min of copper exposure. Taken together the results indicate that copper toxicity, including copper transport into the cells and its interactions with ion transport processes, depend on the valency and complex formation of copper ions.

Animals↗
PubMed2005

Secondary ion MS imaging of lipids in picoliter vials with a buckminsterfullerene ion source.

Investigation of the spatial distribution of lipids in cell membranes can lead to an improved understanding of the role of lipids in biological function and disease. Time-of-flight secondary ion mass spectrometry is capable of molecule-specific imaging of biological molecules across single cells and has demonstrated potential for examining the functional segregation of lipids in cell membranes. In this paper, standard SIMS spectra are analyzed for phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine, phosphatidylinositol, cholesterol, and sulfatide. Importantly, each of the lipids result in signature mass spectral peaks that allow them to be identified. These signature peaks are also useful for imaging experiments and are utilized here to simultaneously image lipids on a micrometer scale in picoliter vials. Because the low secondary ion signal achieved for lipids from an atomic primary ion source makes cell-imaging experiments challenging, improving signal with cluster primary ion sources is of interest. Here, we compare the secondary ion yield for seven lipids using atomic (Ga+ or In+) ion sources and a buckminsterfullerene (C60+) primary ion source. A 40-1000-fold improvement in signal is found with C60+ relative to the other two ion sources, indicating great promise for future cellular imaging applications using the C60+ probe.

Fullerenes↗
PubMed2000

Differential ion accumulation and ion fluxes in the mesophyll and epidermis of barley.

In barley (Hordeum vulgare L.) leaves, differential ion accumulation commonly results in inorganic phosphate (Pi) being confined to the mesophyll and Ca(2+) to the epidermis, with preferential epidermal accumulation of Cl(-), Na(+), and some other ions. The pattern was confirmed in this study for major inorganic anions and cations by analysis of barley leaf protoplasts. The work focused on the extent to which differences in plasma membrane ion transport processes underlie these observations. Ion transport across the plasma membrane of barley epidermal and mesophyll protoplasts was investigated electrophysiologically (by microelectrode impalement and patch clamping) and radiometrically. Data from both approaches suggested that similar types of ion-selective channels and membrane transporters, which catalyze the transport of Ca(2+), K(+), Na(+), and Pi, exist in the plasma membrane of the two cell types. In general, the simple presence or absence of ion transporters could not explain cell-type-specific differences in ion accumulation. However, patch-clamp data suggested that differential regulation of instantaneously activating ion channels in the plasma membrane could explain the preferential accumulation of Na(+) in the epidermis.

Calcium↗
PubMed2006

Selective and simultaneous determination of phosphate and silicate ions in leaching process waters for ceramics glaze raw materials of narutal origin by ion-exclusion chromatography coupled with UV-detection after postcolumn derivatization.

The selective and simultaneous ion-exclusion chromatography (IEC) with UV-detection on a weakly acidic cation-exchange resin column in the H+ -form (TSKgel Super IC-A/C) was developed and applied for the simultaneous determination of phosphate and silicate ions as the water quality parameters required for optimizing the water-leaching process for ceramics glaze raw materials of natural origin including feldspar, woods-ash, and straw-ash. Phosphate and silicate ions in these water-leaching process water samples were separated selectively from the coexisting anions such as sulfate, chloride, nitrate and carbonate ions, based on the ion-exclusion separation mechanism. They were detected selectively and simultaneously by a postcolumn derivatization with molybdenum-yellow using the UV-detector. Under the optimized separation and detection conditions (eluent, 0-1 mM sulfuric acid; reactant, 10 mM sodium molybdate-25 mM sulfuric acid; detector, UV at 370 nm; temperature, 45 degrees C), the linearity of calibration was in the range 0.1 - 10 ppm for both phosphate and silicate ions, and the detection limits at S/N = 3 were 2.58 ppb for silicate ions and 4.75 ppb for phosphate ions. The effectiveness of this method was demonstrated in practical applications to the water-leaching process for some ceramics glaze raw materials.

Aluminum Silicates↗
PubMed1999

Role of ions and ion channels in capacitation and acrosome reaction of spermatozoa.

Capacitation and acrosome reaction are important prerequisites of the fertilization process. Capacitation is a highly complex phenomenon occurring in the female genital tract, rendering the spermatozoa capable of binding and fusion with the oocyte. During capacitation various biochemical and biophysical changes occur in the spermatozoa and the spermatozoal membranes. Ions and ion channels also play important roles in governing the process of capacitation by changing the fluxes of different ions which in turn controls various characteristics of capacitated spermatozoa. Along with the mobilization of ions the generation of free radicals and efflux of cholesterol also plays an important role in the capacitation state of the spermatozoa. The generation of free radical and efflux of cholesterol change the mechanodynamic properties of the membrane by oxidation of the polyunsaturated lipids and by generating the cholesterol free patches. The process of capacitation renders the spermatozoa responsive to the inducers of the acrosome reaction. The glycoprotein zona pellucida 3 (ZP3) of the egg coat zona pellucida is the potent physiological stimulator of the acrosome reaction; progesterone, a major component of the follicular fluid, is also an inducer of the acrosome reaction. The inducers of the acrosome reaction cause the activation of the various ion-channels leading to high influxes of calcium, sodium and bicarbonate. The efflux of cholesterol during the process of capacitation alters the permeability of the membrane to the ions and generate areas which are prone to fusion and vesiculation process during the acrosome reaction. This review focuses mainly on effects of the ion and ion-channels, free radicals, and membrane fluidity changes during the process of capacitation and acrosome reaction.

Acrosome Reaction↗
PubMed2000

Enhanced gas-phase hydrogen-deuterium exchange of oligonucleotide and protein ions stored in an external multipole ion reservoir.

Rapid gas-phase hydrogen-deuterium (H-D) exchange from D(2)O and ND(3) into oligonucleotide and protein ions was achieved during storage in a hexapole ion reservoir. Deuterated gas is introduced through a capillary line that discharges directly into the low-pressure region of the reservoir. Following exchange, the degree of H-D exchange is determined using Fourier transform ion cyclotron resonance mass spectrometry. Gas-phase H-D exchange experiments can be conducted more than 100 times faster than observed using conventional in-cell exchange protocols that require lower gas pressures and additional pump-down periods. The short experimental times facilitate the quantitation of the number of labile hydrogens for less reactive proteins and structured oligonucleotides. For ubiquitin, we observe approximately 65 H-D exchanges after 20 s. Exchange rates of > 250 hydrogens s(-1) are observed for oligonucleotide ions when D(2)O or ND(3) is admitted directly into the external ion reservoir owing to the high local pressure in the hexapole. Partially deuterated oligonucleotide ions have been fragmented in the reservoir using infrared multiphoton dissociation (IRMPD). The resulting fragment ions show that exchange predominates at charged sites on the 5'- and 3'-ends of the oligonucleotide, whereas exchange is slower in the core. This hardware configuration is independent of the mass detector and should be compatible with other mass spectrometric platforms including quadrupole ion trap and time-of-flight mass spectrometers.

Deuterium↗
PubMed2004

Different behavior of dextrans in positive-ion and negative-ion mass spectrometry.

A mass spectrometric (MS) comparative study of dextran samples using two different ionization techniques (matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI)) in both positive- and negative-ion modes is reported. The experiments were carried out with two polydisperse dextrans (1000 and 8800 Da) and isomaltotriose. In the positive-ion mode, the expected alkali metal ion adducts of dextrans were observed in both techniques. In contrast, the expected preferential formation of deprotonated molecules [M - H](-) was not confirmed in negative mode MALDI time-of-flight (TOF) MS, where the series of ions [M(x)- H +42](-) or [M(x+1)- H - 120](-), coming either from some addition or fragmentation, were observed. In both ionization techniques, these ions formed the main distributions of dextrans in the negative-ion mode. It seems that the negative molecular ions formed from the alpha1 --> 6 linkage of polyglucose oligomers easily decompose, and the product ions [M - H - 120](-) markedly dominate. The fragmentation experiments and especially the investigation of the fundamental role of the nozzle-skimmer potential in ESI-MS supported our explanation of the observed behavior because its higher values caused higher fragmentation. The experiments with isomaltotriose excluded any addition of 42 Da during the MS procedures, which is not distinguishable from the loss of 120 Da in the case of polydisperse dextrans. MALDI-TOFMS was found to be more sensitive for the detection of higher oligosaccharides and ESI-MS more useful for structural studies.

Dextrans↗
PubMed2003

Probing the mechanisms of the self ion-molecule reactions of dopamine in an ion trap mass spectrometer.

Our previous work was the first to report [M+CH](+) and [M+C(2)H(3)](+) ions in the self ion-molecule reactions (SIMR) of two aza-crown ethers in an ion trap mass spectrometer (ITMS). In this study, the CH and C(2)H(3) addition ions were also found in the SIMR of dopamine. The SIMR of dopamine lead to the formation of the protonated molecules ([M+H](+)), of adduct ions ([M+F](+), where F represents fragment ions), and of [M+CH](+), [M+C(2)H(3)](+) and [2M+H](+) ions. Based on the combination of the results of isolation experiments and semi-empirical calculations, the reactive site for the formation of the [M+H](+) and [M+CH](+) ions of dopamine is proposed to be the amino group.

Dopamine↗
PubMed2004

Formation of c1 fragment ions in collision-induced dissociation of glutamine-containing peptide ions: a tip for de novo sequencing.

A c1 ion was observed with significant yield in the tandem mass (MS/MS) spectra of peptide ions containing glutamine as the second amino acid residue from the N-terminus. The c1 fragment was generated independently of the N-terminal residue of the peptide, but its abundance was strongly dependent on the side-chain identity. This ion is not a common fragmentation product in low-energy collision-induced dissociation of peptide ions, but it assists in identification of the first two amino acid residues, often difficult due to a low or absent signal from the heaviest y ion. A consecutive fragmentation mechanism is proposed, involving a b2 ion with a six-membered ring as an intermediate, to explain the exceptional stability of the c1 fragment ion. The utility of this information is discussed, especially in de novo sequencing of peptide ions.

Amino Acid Sequence↗
PubMed2002

Ligand and metal-ion effects in metal-ion clusters used for chiral analysis of alpha-hydroxy acids by the kinetic method.

Chiral recognition of alpha-hydroxy acids has been achieved, and mixtures of enantiomers have been quantified in the gas phase, by using the kinetics of competitive unimolecular dissociation of singly-charged transition metal ion-bound trimeric complexes, [M(II)(A)(ref*)(2)-H](+) (M(II)=divalent transition metal ion; A=alpha-hydroxy acid; ref*=chiral reference ligand), to form the dimeric complexes [M(II)(A)(ref*)-H](+) and [M(II)(ref*)(2)-H](+). Chiral selectivity, the ratio of these two fragment ion abundances for the complex containing the analyte in one enantiomeric form expressed relative to that for the fragments of the corresponding complex containing the other enantiomer, ranges from 0.65 to 7.32. Chiral differentiation is highly dependent on the choice of chiral reference compound and central metal ion. The different coordination geometry of complexes resulting from the different d-orbital electronic configurations of these transition metal ions plays a role in chiral discrimination. Of all the transition metal ions examined chiral recognition is lowest for Cu(II), because of large distortion of the coordination complexes, and hence weak metal-ligand interactions and small stereochemical effects. It seems that two independent pi-cation interactions occur when N-acetyl-substituted aromatic amino acids used as the reference ligands and this accounts for improved chiral discrimination. If both metal-ligand and ligand-ligand interactions are optimized, large chiral selectivity is achieved. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, which are intrinsic to the kinetic method, enable mixtures to be analyzed for small enantiomeric excess ( ee) by simply recording the ratios of fragment ion abundances in a tandem mass spectrum.

Calibration↗
PubMed1991

Ion chromatographic analysis of the purity and synthesis of sulfonium and selenonium ions.

The use of single-column ion chromatography with conductometric detection was shown to be useful for the analysis of sulfonium and selenonium ions. A Hamilton PRP X-200 cation column was eluted with either solvent A (5 mM nitric acid in 30% methanol) or solvent B (4 mM nitric acid). With solvent B, trimethylsulfonium ion was separated from trimethylselenonium ion. With solvent A, amounts of trimethylsulfonium ion from 2 to 250 nmol were detected with a linear response. The retention times and response factors for a series of sulfonium ions with various organic groups were determined. In general the ions with more hydrophobic groups eluted later, but all had similar response factors. The method was shown to be useful for optimizing conditions for the synthesis of methylsulfonium ions, specifically the reaction of methyl iodide with diallyl sulfide.

Allyl Compounds↗
PubMed1987

Effects of Ca(II) ions on Cu(II) ion-phytic acid interactions.

In vitro interactions among phytic acid (PA), Cu(II) ions, and Ca(II) ions were examined as functions of PA:Cu(II):Ca(II) molar ratios and pH. Ca(II) ions competed with Cu(II) ions for binding by the soluble phytate species for PA:Cu(II) molar ratios ranging from 10:1 to 1:6 and pH values in the 2.4-5.9 range. At pH values where precipitation occurred, Ca(II) ions potentiated Cu(II) ion binding by the precipitated phytate species for PA:Cu(II) molar ratios of 10:1 to 1:3. At lower PA:Cu(II) molar ratios, Ca(II) ions competed with Cu(II) ions for binding by the precipitated phytate species. Compositions of the precipitated copper-calcium phytates are reported.

Calcium↗
PubMed1976

Thermodynamic and kinetic parameters of ion condensation to polynucleotides. Outer sphere complex formed by Mg++ions.

The coupling of ion binding to the single strand helix-coil transition in poly (A) and poly (C) is used to obtain information about both processes by ion titration and field-jump relaxation methods. Characterisation of the field-jump relaxation in poly (C) at various concentrations of monovalent ions leads to the evaluation of a stability constant K = 71 M(-1) for the ion binding to the polymer. the rate constant of helix formation is found to be 1.3 X 10(7)s(-1), whereas the dissociation rate is 1.0 X 10(6)s(-1). Similar data are preseented for poly (A) and poly (dA). The interaction of Mg(++) and Ca(++) with poly (A) and poly (C) is measured by a titration method using the polymer absorbance for the indication of binding. The data can be represented by a model with independent binding "sites". The stability constants increase with decreasing salt concentration from 2.7 X 10(4) M(-1) at medium ionic strengths up to 2.7 X 10(7) M(-1) at low ionic strength. The number of ions bound per nucleotide residue is in the range 0.2 to 0.3. Relaxation time constants associated with Mg(++) binding are characterised over a broad range of Mg(++) concentrations form 5 muM to 500 muM. The observed concentration dependence supports the conclusion on the number of binding places inferred from equilibrium titrations. The rate of Mg(++) and Ca(++) association to the polymer is close to the limit of diffusion control kR =1 X 10(10) to 2 X 10(10) M(-1) s(-1)). This high rate demonstrates that Mg(++) and Ca(++) ions do not form inner-sphere complexes with the polynucleotides. Apparently the distance between two adjacent phosphates is too large for a simultaneous site binding of Mg(++) or Ca(++), and inner sphere complexation at a single phosphate seems to be too weak. The data support the view that the ions like Mg(++) and Ca(++) surround the polynucleotides in the form of a mobile ion cloud without site binding.

Ions↗
PubMed1993

Remeasurement of ions using quadrupolar excitation Fourier transform ion cyclotron resonance spectrometry.

Ions formed by a single laser desorption event can be remeasured more than 500 times in a Fourier transform ion cyclotron resonance spectrometer. Quadrupolar excitation and collisional axialization are used to move ions located in any region of the ICR cell to the center of the cell, where they can be effectively detected. With this method, the signal from ions formed by a single laser desorption event is averaged for 200 remeasurement cycles with an efficiency in excess of 99.5% per cycle. Collisions of ions with helium are found to give higher remeasurement efficiencies than collisions with methane, due to reduced scattering losses by the lighter collision gas. With this method, ions that are stored in the analyzer cell for more than 1 hour can be detected. This technique is shown to be compatible with high-resolution data acquisition. Ions formed by one laser desorption event are remeasured at eight bandwidths, demonstrating low-resolution, wide-mass-range analysis and high-resolution, narrow-mass-range analysis of the same group of ions.

Amino Acid Sequence↗
PubMed2002

A quadrupole ion trap mass spectrometer with three independent ion sources for the study of gas-phase ion/ion reactions.

An instrument for the study of gas-phase ion/ion reactions in which three independent sources of ions, namely, two electrospray ionization sources and one atmospheric sampling glow discharge ionization source, are interfaced to a quadrupole ion trap mass analyzer is described. This instrument expands the scope of gas-phase ion/ion reaction studies by allowing for manipulation of the charge states of multiply charged reactant and product ions. Examples are provided involving the formation of protein-protein complexes in the gas phase. Complexes with charge states that cannot be formed from reactant ion charge states present in the normal electrospray charge state distributions can be formed in the new apparatus. Strategies that rely on both reactant ion charge state manipulation and product ion charge state manipulation are demonstrated. In addition, simplification of product ion spectra generated from dissociation of complexes formed via ion/ion reactions can be effected by using the discharge source to reduce the charge state of the product ions to primarily 1+.

Amino Acid Sequence↗
PubMed2006

Analysis of nitrate ion in nettle (Urtica dioica L.) by ion-pair chromatographic method on a C30 stationary phase.

Nitrate ion is a frequent pollutant not only in soil and natural water resources but in vegetables and foods as well. In our study we focused on nettle due to its increased ability to accumulate nitrate ions. A new, simple method for the separation and determination of nitrate ion based on reversed-phase ion-pair chromatography has been elaborated. A new four-step sample pretreatment method enables the precipitation of proteins and oxidative degradation of compounds that may disturb the identification of the nitrate ion: (1) extraction of the total nitrate content, (2) precipitation of proteins with acetonitrile, (3) oxidative degradation of the organic contaminants with H2O2, (4) evaporation of the solvent and taking up of the residue in water. The chromatographic separations were carried out on a high-density C30 stationary phase under isocratic conditions. The optimal mobile-phase composition was 10% (v/v) acetonitrile and 90% (v/v) 20 mmol L(-1) phosphate buffer, containing 2 mmol of tetrabutylammonium hydroxide at pH 6.0. The method could also be used for the separation of IO3(-), SeO3(2-), BrO3(-), NO2(-), Br-, SeO4(2-), and I- ions. The validated method is sensitive (the detection limit is 0.18 ng of nitrate ion). The method is linear in a high concentration range (0.031-30.66 microg mL(-1)). Recoveries varied between 98% and 103%. Reproducibility of the elaborated sample pretreatment method showed 1.54%. The method can be used for the determination of nitrate ion from different plants.

Beverages↗
PubMed2005

Catalysis of the ethanolysis of aryl methyl phenyl phosphinate esters by alkali metal ions: transition state structures for uncatalyzed and metal ion-catalyzed reactions.

This paper reports on a spectrophotometric kinetic study of the effects of the alkali metal ions Li+ and K+ on the ethanolysis of the aryl methyl phenyl phosphinate esters 3a-f in anhydrous ethanol at 25 degrees C. Rate data obtained in the absence and presence of complexing agents afford the second-order rate constants for the reaction of free ethoxide (k(EtO-)) and metal ion-ethoxide ion pairs (k(MOEt)). The sequence k(EtO-) < k(MOEt) is established for all the substrates, contrary to the generally observed reactivity order in nucleophilic substitution processes. The quantities deltaG(ip), deltaG(ts) and DeltaG(cat), which quantify the observed alkali metal ion effect in terms of transition state stabilization through chelation of the metal ion, give the order deltaG(ts) > deltaG(ip) for Li+ and K+. Hammett plots show significantly better correlation of rates with sigma and sigma(o) substituent constants than with sigma-, yielding moderately large rho(rho(o)) values that are consistent with a stepwise mechanism in which formation of a pentacoordinate (phosphorane) intermediate is the rate-limiting step. The range of the values of the selectivity parameter, rho(n) (= rho]/rho(eq)), 1.3-1.6, obtained for the uncatalyzed and alkali metal ion catalyzed reactions indicates that there is no significant perturbation of the transition state (TS) structure upon chelation of the metal ions. This finding is relevant to the mechanism of enzymatic phosphoryl transfer involving metal ion co-factors. The present results enable one to compare structural effects for nucleophilic reactions of several series of organophosphorus substrates. It is shown that the order of reactivity of the substrates: 4-nitrophenyl dimethyl phosphinate (2) > 3a > 4-nitrophenyl diphenyl phosphinate (1) is determined mainly by the steric effects of the alkyl/aryl substituents around the central P atom in the TS of the reaction.

Catalysis↗
PubMed1985

An ion's view of the potassium channel. The structure of the permeation pathway as sensed by a variety of blocking ions.

We have studied the block of potassium channels in voltage-clamped squid giant axons by nine organic and alkali cations, in order to learn how the channel selects among entering ions. When added to the internal solution, all of the ions blocked the channels, with inside-positive voltages enhancing the block. Cesium blocked the channels from the outside as well, with inside-negative voltages favoring block. We compared the depths to which different ions entered the channel by estimating the "apparent electrical distance" to the blocking site. Simulations with a three-barrier, double-occupancy model showed that the "apparent electrical distance," expressed as a fraction of the total transmembrane voltage, appears to be less than the actual value if the blocking ion can pass completely through the channel. These calculations strengthen our conclusion that sodium and cesium block at sites further into the channel than those occupied by lithium and the organic blockers. Our results, considered together with earlier work, demonstrate that the depth to which an ion can readily penetrate into the potassium channel depends both on its size and on the specific chemical groups on its molecular surface. The addition of hydroxyl groups to alkyl chains on a quaternary ammonium ion can both decrease the strength of binding and allow deeper penetration into the channel. For alkali cations, the degree of hydration is probably crucial in determining how far an ion penetrates. Lithium, the most strongly hydrated, appeared not to penetrate as far as sodium and cesium. Our data suggest that there are, minimally, four ion binding sites in the permeation pathway of the potassium channel, with simultaneous occupancy of at least two.

Animals↗