Cage Structure Formation of Singly Doped Aluminum Cluster Cations Al<Subscript><Emphasis Type="BoldItalic">n</Emphasis></Subscript><Emphasis Type="BoldItalic">TM</Emphasis><Superscript>+</Superscript> (<Emphasis Type="BoldItalic">TM</Emphasis> = Ti,V, Cr)

Structural information on free transition metal doped aluminum clusters, Al _n TM ⁺ (TM = Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n = 5 – 35) and temperature (T = 145 – 300 K) dependent investigations reveal that bare Al _n ⁺ clusters are inert toward argon, while Al _n TM ⁺ clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum cage. The critical size, n _crit , is found to be surprisingly large, namely n _crit = 16 and n _crit = 19 – 21 for TM = V, Cr, and TM = Ti, respectively. Experimental cluster–argon bond dissociation energies have been derived as function of cluster size from equilibrium mass spectra and are in the 0.1–0.3 eV range.     

Influence of Amino Acid Composition and Phosphorylation on the Ion Yields of Peptides in MALDI-MS

The influence of arginine (Arg), lysine (Lys), and phenylalanine (Phe) residues and phosphorylation on the molecular ion yields of model peptides have been quantitatively studied using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry in both positive- and negative-ion mode. The results obtained from these experiments have been interpreted from the standpoint of two different components, namely, desorption and ionization, on the basis of the physicochemical properties of constituent amino acids of the model peptides. The presence of basic residues such as Arg and Lys enhanced the ion yields of protonated molecules [M + H]⁺. An N-terminal rather than a C-terminal Arg residue was advantageous for the formation of both [M + H]⁺ and [M – H]^–. The presence of the Phe residue resulted in the increase of the ion yields of both [M + H]⁺ and [M – H]^–. In contrast, the presence of phosphate group(s) contributed to the suppression of the yields of both [M + H]⁺ and [M – H]^– due to the loss of phosphate group. The detection limits for both [M + H]⁺ and [M – H]^– of model peptides have been evaluated.     

TiCl, TiH, and TiH+ bond energies: a test of a correlation-consistent Ti basis set

Correlation-consistent basis sets are developed for the Ti atom. The polarization functions are optimized for the average of the ³F and ⁵F states. One series of correlation-consistent basis sets is for 3d and 4s correlation, while the second series includes 3s and 3p correlation as well as 3d and 4s correlation. These basis sets are tested using the Ti ³F–⁵F separation and the dissociation energies of TiCl X⁴Φ, TiH X⁴Φ, and TiH⁺ X³Φ. The CCSD(T) complete basis set limit values are determined by extrapolation. The Douglas–Kroll approach is used to compute the scalar relativistic effect. Spin-orbit effects are taken from experiment and/or are computed at the CASSCF level. The Ti³F–⁵F separation is in excellent agreement with experiment, while the TiCl, TiH, and TiH⁺ bond energies are in good agreement with experiment. Extrapolation with the valence basis set is consistent with other atoms, while including 3s and 3p correlation appears to make extrapolation more difficult. Received: 20 January 1999 / Accepted: 26 February 1999 / Published online: 7 June 1999     

Dissociative recombination of HeH+. I. Rovibrational spectrum of HeH Rydberg states

The repulsive ground electronic state X²Σ⁺ of HeH is strongly coupled to the Rydberg states at small interatomic distances. Such large couplings also occur between some of the Rydberg states. HeH⁺ ions that capture an electron in a Rydberg state end up in separated He and H atoms by indirect predissociation. This paper presents a study of potential functions and pertinent matrix elements involving the lowest electronic states: the ²Σ⁺ states, X, A, C, and D, and the ²Π states B and E. Individual transition rates as well as total radiative and non-radiative lifetimes have been computed for the lowest vibrational and rotational levels. Received: 22 June 1998 / Accepted: 21 August 1998 / Published online: 12 October 1998     

Fast screening immunoassay of sulfonamides in commercial fish samples

An indirect competitive enzyme-linked immunosorbent assay (ELISA) was developed in plate to detect three sulfonamide residues (sulfamerazine (SMR), sulfadimetoxine (SDM), and sulfadiazine (SDZ)) in gilthead sea bream (Sparus aurata) samples. Different extraction methodologies—using methanol/water 1:1 (v/v) + ethylene diamine tetraacetic acid (EDTA) 0.5% (m/v), acetonitrile, phosphate-buffered saline (PBS) 10 mmol L⁻¹ pH 7 and acetate buffer 100 mmol L⁻¹ pH 5—and cleanup steps, based on solid-phase extraction (C₁₈, SCX, Si) or liquid extraction with hexane, were assayed. As optimum, a fast and simple method using acetonitrile was selected to extract the sulfonamide residues from the edible muscle of fish. Due to matrix effects, a standard addition calibration curve in fish extract is necessary for quantification purposes. Sulfonamide-free samples were spiked at different concentration levels (between 30 and 90 ng g⁻¹, 5–15 ng mL⁻¹ in plate) and average recoveries (n = 8), ranging from 71% to 95%, 65% to 79%, and 72% to 95%, were obtained for SMR, SDM, and SDZ, respectively. The assay detection limits for these antibiotics were lower than 100 μg kg⁻¹ (maximum residue level established by the European Union). The accuracy was evaluated by spiking blank fish extracts at different concentrations (10–40 ng mL⁻¹, 5–20 ng mL⁻¹ in plate), and the relative errors ranged between ±20%. Finally, in order to confirm the utility of the developed ELISA as a screening methodology, fish samples from different supermarkets were analyzed, and results were compared with those obtained by a validated high-performance liquid chromatography (HPLC) method. The correlation between the results obtained by both ELISA and HPLC methods is satisfactory.      

Enhanced electrochemical properties of polyethylene oxide-based composite solid polymer electrolytes with porous inorganic–organic hybrid polyphosphazene nanotubes as fillers

Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO₄, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity values of 1.5 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.8 × 10⁻⁴ S cm⁻¹ at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO₁₀–LiClO₄–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries.     

Preparation and Crystal Structure of K2Ag12Te7

Summary.  Single crystals of K₂Ag₁₂Te₇ (a = 11.460(2), c = 4.660(1) ?; V = 530.01 ?³; space group: P6₃/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver and tellurium. The crystal structure is characterized by trigonal prismatic KTe₆ polyhedra, connected via two common faces to KTe₃ rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K₂Ag₁₂Te₆)^2 + and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit cell, distributed over two independent positions. Received May 17, 2001. Accepted (revised) July 3, 2001     

Preparation and Crystal Structure of K2Ag12Te7

 Single crystals of K₂Ag₁₂Te₇ (a = 11.460(2), c = 4.660(1) ?; V = 530.01 ?³; space group: P6₃/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver and tellurium. The crystal structure is characterized by trigonal prismatic KTe₆ polyhedra, connected via two common faces to KTe₃ rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K₂Ag₁₂Te₆)^2 + and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit cell, distributed over two independent positions.     

Construction of a Triphenyltetrazolium Liquid Membrane Ion Selective Electrode and its Analytical Application to the Assay of Vitamin C

 The construction of a liquid triphenyltetrazolium cation (TT⁺) ion-selective electrode (ISE) based on [TT⁺]₃[P(W₃O₁₀)₄] salt dissolved in 2-nitrotoluene is described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to triphenyltetrazolium cations in the concentration range from 2×10⁻⁴ to 1×10⁻² mol l⁻¹. The Nernstian slope is 56–58 mV decade⁻¹ which remains constant for at least two months. The response is virtually unaffected by pH changes in the range 3–12. Major interferents are periodate and malate. Deviation from linearity is also observed in the presence of bromide, iodide and thiocyanate, due to their precipitation with triphenyltetrazolium cations. Analytical applications such as direct potentiometry for the determination of TT⁺ in aqueous solutions and indirect potentiometry for the assay of ascorbic acid (vitamin C) in pharmaceutical preparations are described. Ascorbic acid in the range of 150–500 mg l⁻¹, under specified experimental conditions, can be determined with mean relative error of 1.9%. Received February 25, 2000. Revision April 4, 2000.     

Synthesis and the crystal and electronic structure of Hg4AsI5

New mercury arsenide iodide Hg₄AsI₅ was synthesized and its crystal and electronic structure was determined. The crystal structure is layered. The layers are composed of alternating AsHg₄ tetrahedra and IHg₈ Archimedean antiprisms and are bound by the iodine atoms, which form short Hg-I bonds with all mercury atoms. Band structure calculations provided evidence for very weak interactions between the iodine atoms of the adjacent layers and the ionic character of the iodine atom centering the Archimedean antiprism. Hence, individual [AsHg₄I₄]⁺ clusters and I⁻ anions can be distinguished. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 736–739, May, 2006. Additional details of the crystal structure study (deposition number CSD-416238) can be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany, fax: +(49)7247-808-666; e-mail: crysdata@fiz-karlsruhe.de.     

X-ray diffraction study of benzothiacrown compounds and their complexes with heavy metal cations

The structures of a series of substituted benzothiacrown compounds containing the dithia-15-crown-5, dithia-18-crown-6, or monothia-15-crown-5 fragment and their complexes with Ag⁺ and Pb2⁺ ions were studied by X-ray diffraction. In free benzothiacrown compounds, the sulfur atoms are preferably located outside the macrocyclic cavity, and their lone electron pairs (LEPs) point away from the center of the macrocycle, which is unfavorable for the formation of inclusion complexes. Flexible macrocyclic fragments can change their conformations in accord with the coordination requirements of heavy metal cations. As a result, benzothiacrown compounds involved in complexes adopt a crown conformation, in which LEPs of all hetero-atoms point toward the cation. The sulfur atoms are involved in coordination of Ag⁺ to a greater degree than the oxygen atoms due to high affinity of soft sulfur atoms for silver cations. On the contrary, the sulfur and oxygen atoms are involved to approximately the same degree in coordination of Pb2⁺ ions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 967–976, May, 2007.     

Quantitative WDXS Microanalysis of Bismuth-Based BaBi4Ti4O15 Perovskites Doped with Nb and Fe

 Quantitative electron-probe microanalysis was used to determine the chemical composition of an Fe- and Nb-doped bismuth-based BaBi₄Ti₄O₁₅ perovskite compound. Elemental concentrations of Fe, Nb, Bi, Ba and Ti were accurately measured using wavelength-dispersive X-ray spectroscopy that was optimised for the analysis of a complex oxide matrix containing minor concentrations of dopants. Measurements were performed with a JEOL JXA 840A electron probe microanalyser at 20 and 26 kV, 50 nA beam current, 100 s maximum counting time and 0.3% preset counting deviation (σ_c) using both PET and LiF crystals. K-ratios were quantified by the ZAF and the φ(ρz) PAP matrix-correction procedures. The results showed that dopants incorporate into the BaBi₄Ti₄O₁₅ at Ti^4 + sites according to the Ba_1−4XBi_4 + 4XTi_4−4XFe_4XO₁₅ and Ba_1 + 4XBi_4−4XTi_4−4XNb_4XO₁₅ solid-solution formulae. The majority of the excess charge introduced by the substitution of Ti^4 + with Fe^3 + or Nb^5 + is compensated for the change in the Ba^2 +/Bi^3 + ratio.     

The effect of bias-temperature stress on Na<Superscript>+</Superscript> incorporation into thin insulating films

The action of Na⁺ incorporation into thin insulating films and transport therein under influence of a bias voltage and temperature (BT stress) is the subject of this work. Deposited onto highly n-doped Si wafers, the insulators get BT stressed and subsequently investigated by means of time-of-flight–secondary ion mass spectrometry (ToF-SIMS). A thin PMMA film, spin-coated onto the insulator, serves as host matrix for a defined amount of Na⁺, provided via sodium triflate. Combining BT stress and ToF-SIMS depth profiling enables the unambiguous detection of Na⁺, incorporated into the insulating material. The insulators of interest vary in their nitride content: SiO₂, SiO_xN_y, and Si₃N₄. For SiO₂, it is shown that once a threshold BT stress is exceeded, Na⁺ gets quantitatively incorporated from PMMA into the underlying insulator, finally accumulating at the SiO₂/Si interface. A quantitative assessment by combination of Butler–Volmer kinetics with hopping dynamics reveals activation energies of E _a = 1.55 − 2.04 eV for Na⁺ transport in SiO₂ with varying thickness. On the other hand, SiO_xN_y and Si₃N₄ films show a different Na⁺ incorporation characteristic in this type of experiment, which can be explained by the higher coordination of nitrogen and hence the reduced Na⁺ permeability within these insulators.     

Diatomic potential well depths from analyses of high-resolution electron energy spectra for autoionizing collision complexes

High-resolution energy spectra of electrons released in Penning ionization collisions of metastable rare gas atoms Rg*(ns) (Rg = He, Ne, Ar, Kr, Xe) with several open-shell and closed-shell atoms are analyzed to determine the well depth of the potential energy curve which describes the respective autoionizing collision complex. We thereby elucidate trends in the chemical interaction of Rg* with closed-shell target atoms A(ns ²) and establish a basis for detailed comparison with the respective interactions involving open-shell, ground state alkali atoms A(ns). From electron energy spectra due to␣associative ionization (RgH⁺ formation) in Rg* + H(1s) collisions, we determine binding energies for the RgH⁺(¹Σ) ground state potential (Rg = Ne, Ar, Kr, Xe) with uncertainties around 0.03 eV. Received: 30 June 1998 / Accepted: 5 August 1998 / Published online: 28 October 1998     

EPMA and Quantitative MCs+-SIMS of Metal-DLC Coating Materials

 Compositional characterization of metal-DLC (metal-containing diamond-like carbon) hard coatings is carried out by (WDS)-EPMA and MCs⁺-SIMS. EPMA enables accurate (± 5% relative) quantitative analysis including minor concentrations (0.1–10 at%) of N, O and Ar. Under conditions of “near-surface” EPMA (E₀ < 10 keV) the influence of surface oxide films on “pure” metal standards may be a limiting factor in respect of accuracy. Depth profiling of sufficiently “thick” layered structures (film thickness ≥ 2 μm) is carried out by EPMA-line scans along mechanically prepared bevels. The depth resolution is about 0.2 μm. SIMS in the MCs⁺-mode enables high resolution (< 20 nm) depth profiling of metal-DLC layered structures including the determination of H (1–20 at%). MCs⁺-SIMS, i.e. employing Cs⁺ primary ions and monitoring MCs⁺ molecular secondary ions (M is the element of interest) is presented as a promising route towards sufficiently accurate (10–20%) SIMS-quantification. Matrix-independent relative sensitivity factors for MCs⁺-SIMS are derived from homogeneous coating materials defined by EPMA. EPMA proves to be also useful to detect problems related to SIMS of Ar in metal-DLC materials. The combination EPMA-SIMS is demonstrated as an effective analytical strategy for quality control in industrial production and to support the development of metal DLC layered structures with optimum tribological properties.     

Bismuth compounds [Ph3BuP]+I?, [Ph3BuP] 2+ [Bi2I8 · 2Me2C=O]2?, and [Ph3BuP] 2+ [Bi2I8 · 2Me2S=O]2?: Syntheses and crystal structures

The complexes [Ph₃BuP]₂⁺[Bi₂I₈ · 2Me₂C=O]²⁻ (II) and [Ph₃BuP]₂⁺[Bi₂I₈ · 2Me₂S=O]²⁻ (III) are synthesized by the reactions of triphenyl(n-butyl)phosphonium iodide (I) with bismuth iodide in acetone and dimethyl sulfoxide. In the cations of complexes I–III, the P atoms have a distorted tetrahedral coordination (CPC angles 106.3(2)°–112.0(3)°). The butyl group in cation I is disordered over two positions. In the binuclear centrosymmetric anions of structures II and III, the octahedrally coordinated bismuth atoms are linked in pairs by two bridging (br) iodine atoms (Bi-I_br 3.1508(7) and 3.2824(8) ? in compound II, 3.1961(3) and 3.3108(3) ? in complex III), which are coplanar to four terminal (t) iodine atoms (Bi-I_t 2.9260(7) and 2.9953(6) ? in complex II, 2.9206(3) and 2.9786(3) ? in complex III). The two remaining positions at the bismuth atom are occupied by the iodine atom (Bi-I_t 2.8531(7) ? in complex II, 2.8984(3) ? in complex III) and O atom of the organic molecule (Bi-O 2.747(6) ? in complex II, 2.507(3) ? in complex III). Original Russian Text ? V.V. Sharutin, I.V. Egorova, N.N. Klepikov, E.A. Boyarkina, O.K. Sharutina, 2009, published in Koordinatsionnaya Khimiya, 2009, Vol. 35, No. 3, pp. 188–192.     

Small-angle neutron-scattering study of bis(quaternaryammonium bromide) surfactant micelles in water. Effect of the long spacer chain on micellar structure

The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br⁻(CH₃)₂N⁺(C _m H_{2 m +1})-(CH₂) _S  -(C _m H_{2 m +1})N⁺(CH₃)₂Br⁻, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12). Received: 15 June 1998 Accepted: 22 July 1998     

Electrocatalytic oxidation of pyridoxine (vitamin B<Subscript>6</Subscript>) on aluminum electrode modified by metallic palladium particles/iron (III) hexacyanoferrate (II) film

The electrocatalytic activity of a Prussian blue (PB) film on the aluminum electrode by taking advantage of the metallic palladium characteristic as an electron-transfer bridge (PB/Pd–Al) for electrooxidation of 2-methyl-3-hydroxy-4,5-bis (hydroxyl–methyl) pyridine (pyridoxine) is described. The catalytic activity of PB was explored in terms of Fe^III [Fe^III (CN)₆]/Fe^III [Fe^II (CN)₆]¹⁻ system. The best mediated oxidation of pyridoxine (PN) on the PB/Pd–Al-modified electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 6 at scan rate of 20 mV s⁻¹. The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The charge transfer-rate limiting reaction step is found to be a one-electron abstraction, whereas a two-electron charge transfer reaction is the overall oxidation reaction of PN by forming pyridoxal. The value of α, k, and D are 0.5, 1.2 × 10² M⁻¹ s⁻¹, and 1.4 × 10⁻⁵ cm² s⁻¹, respectively. Further examination of the modified electrodes shows that the modifying layers (PB) on the Pd–Al substrate have reproducible behavior and a high level of stability after posing it in the electrolyte or Pyridoxine solutions for a long time.     

Behaviour of cationic polyelectrolytes upon binding of electrolytes: effects of polycation structure, counterions and nature of the solvent

 The effects of polycation structure, counterions and the nature of the solvent on the interaction between low-molecular-weight salts with some cationic polyelectrolytes in water and methanol were investigated. The polyelectrolytes used in this study were cationic polymers with quaternary nitrogen atoms in the backbone with or without a nonpolar side chain (polymer type PCA₅H₁, PCA₅D₁ and PCA₅) or tertiary amine nitrogen atoms in the main chain (polymer type PEGA). LiCl, NaCl, KCl, NaBr, NaI and Na₂SO₄ were used as low-molecular-weight salts. The interaction between polycations and salts was followed by viscometric and conductometric measurements. The study of the interaction of monovalent counterions with cationic polyelectrolytes emphasized an increase in the interaction with the decrease in the radius of the hydrated counterion, both for strong polycations and for weak polycations, suggesting that counterion binding is nonspecific. In the case of SO²⁻ ₄ anions, the Λ_m−c ^1/2 curve passes through a minimum at c _p values between 1 × 10⁻³ and 3 × 10⁻³ unit mol/l; this phenomenon can be explained by the maximum counterion interaction owing to the capacity of the polyvalent counterion to bind two charged groups by intra- or interchain bridges. The investigation of the influence of the polycation structure on the counterion binding indicated an increase in charged group–counterion interactions with a decrease in the nonpolar chain length and an increase in the quaternary ammonium salt group content (charge density) in the chain. The polyelectrolyte with tertiary amine groups in the chain, PEGA, showed, on one hand, a cation adsorption order as K⁺>Na⁺>Li⁺ and, on the other hand, a stronger association between ions and PEGA chains in methanol than in water owing to the poorer solvating effect of methanol on the cations. Received: 20 February 2001 Accepted: 29 June 2001     

Liquid–Liquid Equilibria of Oxygenate Fuel Additives with Water: Two Quaternary Aqueous Systems of Diisopropyl Ether + 2,2,4-Trimethylpentane with Methyl <Emphasis Type="Italic">tert</Emphasis>-Butyl Ether or Toluene

Experimental tie-line data for two quaternary systems, water + diisopropyl ether + 2,2,4-trimethylpentane + methyl tert-butyl ether or toluene, were investigated at 298.15 K and atmospheric pressure. The experimental liquid–liquid equilibrium data were correlated using a modified UNIQUAC activity coefficient model with ternary and quaternary parameters, in addition to the binary ones. The calculated results were further compared with those obtained with an extended UNIQUAC model from Nagata [Fluid Phase Equilib. 54, 191–206 (1990)].