Desorption chemical ionization tandem mass spectrometry of polyprenyl and dolichyl phosphates

Negative-ion desorption chemical ionization (DCI) tandem mass spectrometry was applied to the analysis of nanomole quantities of semisynthetic polyisoprenyl phosphates, the chain length of which ranged from 7 to 20 isoprene units. The DCI spectrum of all the compounds tested show the presence of independently generated ions [M-HPO₃-H]^?, [M-H₃PO₂-H]^? and [M-H₃PO₄-H]^? resulting from the loss of a part of or the entire phosphate group of a polyisoprenyl-P. In tandem mass spectrometry, the [M-H₃PO₄-H]^? fragment produces series of ions 68 mass units apart, indicative of the polyisoprenoid nature of a compound. Studies with deuterated and α-saturated polyisoprenyl phosphates demonstrated that fragmentations of the [M-H₃PO₄-H]^? ion proceed from both ends (α and ω) of a polyisoprenoid chain and may occur at either allylic (A) or vinylic (V) sites. Fragments of masses equal to [n×68 ? 1] and [n×68 ? 13] (where n is the number of isoprene units and 3≤n is less than the total number of isoprene residues within a polyisoprenoid chain) comprise the αA and ωV series, respectively, and represent the most abundant ions in tandem mass spectra of the [M-H₃PO₄-H]^? fragment of polyprenyl phosphates, α-Saturated dolichyl phosphates can be distinguished easily from corresponding polyprenyl phosphates not only on the basis of a 2-u shift of the [M-H₃PO₄-H]^? ion and the α series of fragments, but also because of the presence of an additional (A+14) series of ions 14 u heavier than fragments resulting from the allylic cleavages of an α-saturated polyisoprenoid chain. Possible mechanisms of the collision-induced dissociation reactions of polyprenyl phosphates are discussed.     

The Effect of Moisture on the Hydrolysis of Basic Salts

A great deal of information exists concerning the hydration of ions in bulk water. Much less noticeable, but equally ubiquitous is the hydration of ions holding on to several water molecules in nanoscopic pores or in natural air at low relative humidity. Such hydration of ions with a high ratio of ions to water molecules (up to 1:1) are essential in determining the energetics of many physical and chemical systems. Herein, we present a quantitative analysis of the energetics of ion hydration in nanopores based on molecular modeling of a series of basic salts associated with different numbers of water molecules. The results show that the degree of hydrolysis of basic salts in the presence of a few water molecules is significantly different from that in bulk water. The reduced availability of water molecules promotes the hydrolysis of divalent and trivalent basic ions (S₂^?, CO₃^2?, SO₃^2?, HPO₄^2?, SO₄^2?, PO₄^3?), which produces lower valent ions (HS^?, HCO₃^?, HSO₃^?, H₂PO₄^?, HSO₄^?, HPO₄^2?) and OH^?ions. However, reducing the availability of water inhibits the hydrolysis of monovalent basic ions (CN^?, HS^?). This finding sheds some light on a vast number of chemical processes in the atmosphere and on solid porous surfaces. The discovery has wide potential applications including designing efficient absorbents for acidic gases.     

Determination of sodium ion diffusion coefficients in sodium vanadium phosphate

Carbon-coated Na₃V₂(PO₄)₃ (NVP) was prepared by a standard sol–gel procedure. The apparent diffusion coefficients of sodium ions in the rhombohedral NVP have been determined by different techniques such as galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). It was found that the apparent diffusion coefficients range from 6?×?10^?13 cm² s^?1 to 2?×?10^?15 cm² s^-1. These sodium ion apparent diffusion coefficients follow a similar trend as observed for lithium ions in the closely related monoclinic modification of Li₃V₂(PO₄)₃, demonstrating a minimum at the potential where the ion extraction/insertion occurs.     

Structural and Chemical Peculiarities of Natural Apatites as Revealed by Epr Spectra

Abstract

Apatite-Ca₅ (PO₄)₃ (F,Cl,OH) is a poligenic mineral widely-spread in nature. A number of important properties of this complex matrix was found by EPR studies. It was shown, that the paramagnetic centres can be used as original probe of crystallostructural and chemical peculiarities which are formed at a) isomorfous substitution, b) deflection of composition from stoichiometry. In natural apatites isomorfous admixtures of Mn²⁺, Cu²⁺, Fe³⁺, V⁴⁺ ions in CaI, CaII position are registered. The distribution regularities of the admixtures between two Ca-positions are considered. If the Ca-cations are substituted isomorphically by actionoide ions, PO^3- ₃-anions are destructed, namely one of the four oxygen atoms comes off and PO^? ₃ -group is formed. The capture of electron by PO^? ₃ -fragment under the effect of ionizing radiation results in the formation of paramagnetic PO^2- ₃-centre of electron type with peculiar EPR parameters. Depending on the P-OII(I) or P-OIII(III) the PO^3- ₄ -anion bond, which is broken, as well as on the nature of substi-tuting actinoide ion (U or Th) the variety of PO^2- ₄ -centres (four type) with different EPR parameters could be registered. A number of radical i.ons in the position PO^3- ₄ -anion-CO^3- ₃, CO^? ₃, SO^? ₃, SiO^? ₃ are observed. The spectrum of H° is identified in the group of nonstoichiometrical apatites with Ca/P <1,67. This spectrum can be used as the indicator of calcium deficiency and the presence of HPO^2- ₄ -group in the structure. The organic radical HCO is registered in the non-stoichiometric carbonate-apatites with phosphorus deficiency (Ca/P > 1,67). The presence of different ion-halogen (F, C1, OH) and oxygen in the form 0^? at the axes G₃ leads to the formation of different complexes: F^? -0^? -F^?, cl^? -O^? cl^? -O^? -Cl^? F^? -O^?-Cl^?, OH^? -O^?-. The EPR-spectrs parameters of the above-mentioned centres are presented.     

Radiotracer study of the adsorption of phosphoric acid on platinized platinum electrodes in the presence of different ions and oxalic acid

Radiotracer study of the adsorption of phosphoric acid on platinized platinum electrodes was carried out under different experimental conditions. The potential and concentration dependence of the adsorption was studied at low concentrations (5×10^?6–6×10^?3 mol dm^?3) in the presence of 1 M HClO₄ supporting electrolyte. A Freundlich type isotherm was found. The effect of different additives was studied. In the presence of Cl^? and HSO₄^? ions and oxalic acid the decrease of the adsorption of H₃PO₄ may be observed. On the other hand Cd²⁺ and Cu²⁺ ions induce the increase of the adsorption of H₃PO₄ in the potential range where their electrosorption takes place.     

Potassium-conducting solid electrolytes in the K3 − 2x Cd x PO4 system

New potassium-conducting solid electrolytes of the K_{3 ? 2x} Cd _x PO₄ system are synthesized and studied. A wide range of solid solutions reaching x ≈ 0.35 with the structure of high-temperature modification of potassium orthophosphate forms in the system. An addition of cadmium ions leads to an abrupt increase in the K₃PO₄ conductivity due to the formation of potassium vacancies. The highest conductivity is approximately 10^?2 S cm^?1 at 300°C and above 10^?1 S cm^?1 at 700°C.     

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate species H₃PO ₄ ⁰ (aq),H₂PO ₄ ^? (aq),HPO ₄ ^2? (aq) or PO ₄ ^3? (aq). Many divalent, trivalent and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation require comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier, with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ?mol^?1 per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq) ions at 298.15 K and p?° =1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S _m ^o (H₂PO ₄ ^? , aq, 298.15 K) = (90.6±1.5) J?K^?1?mol^?1 was obtained.     

Properties of A Phosphate Sensitive Solid State Electrode Based On Cerium-Iv-Hydrogenphosphate Mixed With Pvc

Abstract

The development of a phosphate sensitive electrode based on a heterogeneous (Ce-O-Ce) (HPO₄)₃·H₂O / PVC membrane is described. At a certain salt / PVC - mixture ratio an electrode for H₂PO₄ ^? with a slope of -50 mV/activity decade (AD) and a detection limit of approximately 20 ppm H₂PO₄ ^? is obtained. the selectivity coefficients for the interfering ions So₄ ^2?, cl^?, NO₃ ^?     

Naked Eye Detection of Carbonate,Hydroxide, and Cyanide Ions with 1,4′‐Diazaflavonium Bromides: A Simple Spectrophotometric Method for Cyanide Determination

Anion sensor properties of N‐alkyl‐substituted 1,4′‐diazaflavonium bromides in methanol–water were evaluated by UV–vis spectrometry. Pronounced changes were observed in the absorption spectra of all compounds for only OH^?, CO₃^2?, and CN^? among F^?, Cl^?, Br^?, I^?, OH^?, CO₃^2?, NO₃^?, PO₄^3?, CN^?, SO₄^2?, HSO₄^?, HCO₃^?, SCN^?, NO₂^?, and P₂O₇^2? ions. Two new absorption bands at 385 and 685 nm accompanying the distinct color change for OH^?, CO₃^2?, and CN^? ions were observed in case of all compounds. The color changes were from pink to blue for CO₃^2? and OH^? ions and from pink to purple for CN^? ion. Thanks to the distinct color change, the compounds can be used as selective colorimetric anion sensors. Linear changes of absorbance of N‐heptyl‐substituted compound at 385 nm as a function of the ion concentration were used to determine CN^? ion in water samples. Detection and quantification limits of the proposed method were 0.94 and 2.82 mg/L, respectively.     

A Fluorescent Chemosensor for Dihydrogen Phosphate Ion Based on 2‐[2‐Hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine‐Fe3+ Ensemble

A long wavelength emission fluorescent (612 nm) chemosensor with high selectivity for H₂PO₄^? ions was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). The sensor can exist in two tautomeric forms ('keto' and 'enol') in the presence of Fe³⁺ ion, Fe³⁺ may bind with the 'keto' form of the sensor. Furthermore, the in situ generated GY‐Fe³⁺ ensemble could recover the quenched fluorescence upon the addition of H₂PO₄^? anion resulting in an off‐on‐type sensing with a detection limit of micromolar range in the same medium, and other anions, including F^?, Cl^?, Br^?, I^?, AcO^?, HSO₄^?, ClO₄^? and CN^? had nearly no influence on the probing behavior. The test strips based on 2‐[2‐hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine and Fe³⁺ metal complex ( GY‐Fe³⁺ ) were fabricated, which could act as convenient and efficient H₂PO₄^? test kits.     

Acenaphthenequinone based simple colorimetric anion sensor with only one binding site

Quinonehydrazone compound 1 was designed to be a simple chromogenic anion sensor with one anion binding site. The sensor 1 was easily obtained in 83% yield by the condensation of acenaphthenequinone with 4-nitrophenylhydrazine in ethanol solution. In DMSO, sensor 1 could high selectively and visually detect anions with strong basicity (e.g., AcO^?, F^? and H₂PO₄ ^?) from chloride, bromide, and iodide ions with weak basicity.     

Über die Chemie der Oberfläche des Titandioxids. III. Reaktionen der basischen Hydroxylgruppen auf der Oberfläche

Adsorption of various acids on anatase of high surface area was studied. Phosphoric, arsenic, sulphuric and acetic acid are specifically adsorbed; hydrochloric and perchloric acid are not adsorbed. Phosphate ions are bound on the TiO₂ surface also from NaH₂PO₄ and Na₂HPO₄ solutions; sodium ions are adsorbed at the same time. OH^? ions on the surface are replaced by anions such as H₂PO in these reactions. The bonding of adsorbed phosphate ions is not purely ionic. Infrared spectra show that adsorbed acetic acid is bound as acetate. NO₂ reacts with the basic OH^? ions undergoing disproportionation; OH^? ions are replaced by NO ions. Phophoric acid adsorption corresponded always to half the total OH population on five different TiO₂ samples. The TiO₂ surface is not completely covered by OH groups. The maximum coverage is ca. 7.5 μMol OH/m².     

Effect of inorganic ions on the photocatalytic degradation of humic acid

The article studies on the effects of six inorganic ions (Ca²⁺, Mg²⁺, Cl^?, SO ₄ ^2? , H₂PO ₄ ^? , and HCO ₃ ^? ) on titanium dioxide (TiO₂)-based photocatalytic degradation of humic acid (HA). We focus on the effects of the inorganic ions on HA characters, adsorption of HA on TiO₂ and photocatalytic degradation of HA. The results indicate that Ca²⁺ and Mg²⁺ with HA can form complexes which can decrease the solubility of HA, and then increase the HA adsorbed on TiO₂. However, the complex is more difficult to be degraded than HA. The effects of Cl^? and SO ₄ ^2? are closely related to their influences on HA solubility. The solubility changes of HA to some extent can enhance the adsorption of HA on TiO₂, and promote the photocatalytic degradation. Nevertheless, great solubility decreasing of HA can weaken the photocatalytic degradation. HCO ₃ ^? and H₂PO ₄ ^? can inhibit the photocatalytic degradation process seriously, because HCO ₃ ^? and H₂PO ₄ ^? are the strong scavengers of hydroxyl radicals, and can weaken the adsorption of HA on TiO₂ due to adsorption competition.     

Comparative investigations of LiVPO4F/C and Li3V2(PO4)3/C synthesized in similar soft chemical route

Triclinic LiVPO₄F and monoclinic Li₃V₂(PO₄)₃ are synthesized through a soft chemical process with mechanical activation assist, followed by annealing. In this process, ascorbic acid is used as reducing agent as well as carbon source. The as-prepared samples are coated with amorphous carbon. XPS analysis results show the expected valency states of ions in LiVPO₄F and Li₃V₂(PO₄)₃. The electrochemical properties of the prepared LiVPO₄F/C and Li₃V₂(PO₄)₃/C cathodes are evaluated. The as-prepared LiVPO₄F/C cathode shows an initial discharge specific capacity of 140?±?3 mAh?g^?1 at 30 mA?g^?1 in the voltage range of 3.0~4.4 V, compared with that of 138?±?3 mAh?g^?1 possessed by Li₃V₂(PO₄)₃/C. Both samples exhibit good cycle performance at different current densities. The capacity delivered by LiVPO₄F remains 95.5 and 91.7 % of its initial discharge capacity after 50 cycles at 150 and 750 mA?g^?1, respectively, while 97.4 and 90.6 % for Li₃V₂(PO₄)₃/C. But the rate capability of LiVPO₄F/C is not so good compared with as-prepared Li₃V₂(PO₄)₃/C.     

Negative ion fragmentations of deprotonated peptides containing post‐translational modifications. An unusual cyclisation/rearrangement involving phosphotyrosine; a joint experimental and theoretical study

The characteristic fragmentations of a pTyr group in the negative ion electrospray mass spectrum of the [M–H]^? anion of a peptide or protein involve the formation of PO (m/z 79) and the corresponding [(M‐H)^?–HPO₃]^? species. In some tetrapeptides where pTyr is the third residue, these characteristic anion fragmentations are accompanied by ions corresponding to H₂PO and [(M‐H)^?–H₃PO₄]^? (these are fragmentations normally indicating the presence of pSer or pThr). These product ions are formed by rearrangement processes which involve initial nucleophilic attack of a C‐terminal ‐CO [or ‐C(?NH)O^?] group at the phosphorus of the Tyr side chain [an S_N2(P) reaction]. The rearrangement reactions have been studied by ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory. The study suggests the possibility of two processes following the initial S_N2(P) reaction. In the rearrangement (involving a C‐terminal carboxylate anion) with the lower energy reaction profile, the formation of the H₂PO and [(M‐H)^?–H₃PO₄]^? anions is endothermic by 180 and 318 kJ mol^?1, respectively, with a maximum barrier (to a transition state) of 229 kJ mol^?1. The energy required to form H₂PO by this rearrangement process is (i) more than that necessary to effect the characteristic formation of PO from pTyr, but (ii) comparable with that required to effect the characteristic α, β and γ backbone cleavages of peptide negative ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Complexation of the [Rh(NH3)5H2O]3+ ion in aqueous solutions of H3PO4 based on 31P NMR data

The kinetics of the reaction between the [Rh(NH₃)₅H₂O]³⁺ ion and H₃PO₄ was studied by ³¹P NMR at 323?C343 K (E _a = 100.9 ± 0.3 kJ/mol, lnA = 35.7 ± 0.1). An empirical dependence of the ³¹P chemical shift on the equilibrium pH was found. The acid dissociation constants of the coordinated H₂PO ₄ ^? (3.9) and H PO ₄ ^2? ions (9.1) were estimated. The chemical shifts of the [Rh(NH₃)₅H₂PO₄]²⁺, [Rh(NH₃)₅HPO₄]⁺, and [Rh(NH₃)₅PO₄]⁰ complex ions were 8.38 ± 0.03, 10.76 ± 0.05, and 13.63 ± 0.05 ppm, respectively.     

Evaluation of phosphate removal capacity of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–ZVINPs from aqueous solution: optimization using response surface analysis

The present research aims to optimize the removal of phosphate (PO₄ ^3?) from aqueous solution by Fe₃O₄ stabilized zero-valent iron nanoparticles (Fe₃O₄–ZVINPs). A three-factor, three-level, Box–Behnken design combined with response surface methodology was applied to design the experiments, to develop a mathematical model, and for evaluating the individual and also the interactive effects of the operating variables like pH, temperature, and PO₄ ^3? concentration on removal efficiency. The analysis of variance has been used to evaluate the adequacy of the developed mathematical model in order to predict the optimal conditions of independent process variables, and to get maximum removal efficiency. Three-dimensional response surface plots were constructed to visualize the simultaneous interactive effects between two process variables. All three factors had a significant impact on removal of PO₄ ^3?. The predicted value of the model (166.0 mg g^?1PO₄ ^3?) was in good agreement with the experimental value (164.92 mg g^?1 PO₄ ^3?) under the optimum conditions of temperature 49.2 °C; pH 3.5; and PO₄ ^3? concentration 79.8 mg L^?1. The removal of PO₄ ^3? in the presence of environmental matrix (other ions) was also investigated at optimum conditions as predicted by the model. The results suggest that the presence of these ions had no significant effect on PO₄ ^3? removal. In addition, the adsorbed PO₄ ^3? can be effectively desorbed at higher pH of the solution. The findings suggest that removal of PO₄ ^3? from aqueous solution using Fe₃O₄–ZVINPs can be an effective method.     

Selective “naked-eye” sensing of acetate ion based on conformational flexible amide-pyridinium receptor

A simple pincer-shape anion receptor L1 containing amide-pyridinium as binding unit was synthesized and its anion binding properties were investigated by UV–Vis, NMR titration spectra and molecular simulation. L1 displayed better affinity toward AcO^? ion with visible color change compared with other investigated anions, including F^?, H₂PO₄ ^?, Cl^?, Br^?, I^?, NO₃ ^? and HSO₄ ^? ions. The selectivity was ascribed to the synergistic effects arising from hydrogen bonding, electrostatic interaction and induced-fit process.     

Mercuric chloranilate as solid colorimetric reagent in microanalysis of complex ions

The colorless complex anions triphenylcyanoborate ((C₆H₅)₃CNB^?), azide (N₃^?), and monothiophosphate (PO₃S^3?) have been determined in an acidic aqueous medium through colorimetric exchange on solid mercuric chloranilate surface. The released colored chloranilate ion absorbing at 530 nm responds linearly in the range 3–100 ppm for PO₃S^3? and N₃^? ions and in the range 8–200 ppm for (C₆H₅)₃CNB^? ion. The reaction is pH dependent and equilibration is achieved within an hour.