Hetero dimer from tetrakisammonium cavitand and tetratopic crown ether cavitand

Hetero dimer between tetrakis(m-ammonium)cavitand and tetrakis(dibenzo-25-crown-8)cavitand 5 was formed in CDCl₃ at room temperature. The effects of solvent polarity and temperature on the stability of were studied and the thermodynamic parameters for the formation of are , ΔH⁰ = −67.4 kcal mol⁻¹ and ΔS⁰ = −201.6 cal mol⁻¹ K⁻¹.     

Determination of arsenic, iron and selenium in moss samples using hexapole collision cell, inductively coupled plasma-mass spectrometry

Different collision gases (H₂, He and premixed 7% H₂ in He) used in the hexapole collision cell of an inductively coupled plasma-mass spectrometer (ICP-MS) were compared, and the gas-flow rates were optimized for the determination of arsenic (), iron () and selenium (). The study showed that the argon-based interferences at mass-to-charge ratios (m/z) of 56, 75 and 80 can be overcome by the optimized gas flows (7.5 ml min⁻¹ premixed 7% H₂ in He and 2 ml min⁻¹ H₂) in the hexapole collision cell. Detection limits of 15.5 ng l⁻¹ for iron () and 29 ng l⁻¹ for selenium () in 2% (v/v) HNO₃ were obtained under optimized collision cell conditions. The detection limit for arsenic () obtained in difficult hydrochloride acid matrix (5% HCl (v/v)) was 153 ng l⁻¹. The accuracy of the optimized method was confirmed by analyzing two moss reference materials. The results obtained by ICP-MS for arsenic, selenium and iron from both moss reference samples were, in most cases, in good agreement with the certified values.     

Crystal growth, characterization and physical properties of PrNiSb3, NdNiSb3 and SmNiSb3

The crystal structures of three new intermetallic ternary compounds in the LnNiSb₃ (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb₃, NdNiSb₃ and SmNiSb₃ all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb₆ octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb₃), 4.6 K (NdNiSb₃), and 2.9 K (SmNiSb₃). Effective moments of 3.62 μ_B, 3.90 μ_B and 0.80 μ_B are found for PrNiSb₃, NdNiSb₃ and SmNiSb₃, respectively, and are consistent with Pr³⁺ (f ²), Nd³⁺ (f ³), and Sm³⁺ (f ⁴).     

Determination of sulfur-containing amino acids by capillary electrophoresis dynamic reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis dynamic reaction cell™ inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the determination of sulfur-containing amino acids is described. The sulfur-containing amino acids studied include l-cysteine, l-cystine, dl-homocystine and l-methionine. The species studied were well separated using a 70 cm length×75 μm i.d. fused silica capillary while the applied voltage was set at +22 kV and a 10 mmol l⁻¹ disodium tetraborate buffer (pH 9.8) containing 0.1 mmol l⁻¹ EDTA and 0.5 mmol l⁻¹ Triton X-100 was used as the electrophoretic buffer. The sulfur-selective electropherogram was determined at m/z 48 as by using its reaction with O₂ in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by and on by detecting as the oxide ion at m/z 48, which is less interfered. The detection limit of various species studied was in the range of 0.047-0.058 μg S ml⁻¹, which corresponded to the absolute detection limit of 1.3-1.6 pg S based on the injection volume of 27 nl. We determined the concentrations of selected sulfur-containing amino acids in urine and nutritive complement samples. The recovery was in the range of 92-128% for various species.     

The thermodynamic dissociation constants of ambroxol, antazoline, naphazoline, oxymetazoline and ranitidine by the regression analysis of spectrophotometric data

The mixed dissociation constants of five drug acids—ambroxol, antazoline, naphazoline, oxymetazoline and ranitidine—at various ionic strengths I of range 0.01 and 1.0 and at temperatures of 25 and 37 °C were determined using SQUAD(84) regression analysis of the pH-spectrophotometric titration data. A proposed strategy of efficient experimentation in a protonation constants determination, followed by a computational strategy for the chemical model with a protonation constants determination, is presented on the protonation equilibria of ambroxol. The thermodynamic dissociation constant pK_a^T was estimated by non-linear regression of {pK_a, I} data at 25 and 37 °C: for ambroxol and 8.25 (4), log  and 11.83 (8), for antazoline and 7.83 (6), and 9.55 (2), for naphazoline and 10.63 (1), for oxymethazoline and 10.77 (7), pK_a,2^T=12.03(3) and 11.82 (4) and for ranitidine and 1.77 (1). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates to be found.     

Ferromagnetic-phase transition in the spinel-type CuCr2Te4

Ferromagnetic-phase transition in spinel-type CuCr₂Te₄ has been clearly observed. CuCr₂Te₄ is a telluride-spinel with the lattice constant , which has been synthesized successfully. The heat capacity exhibits a sharp peak due to the ferromagnetic-phase transition with the Curie temperature . This value of T_C corresponds exactly to that of the negative peak of dM/dT in low field of 1.0 Oe. The magnetic susceptibility shows the Curie-Weiss behavior between 380 and 650 K with the effective magnetic moment /Cr-ion and the Weiss constant . The low temperature magnetization indicates the spin-wave excitations, where the existence of first term of Bloch T^3/2 law and the next T^5/2 term are verified experimentally. This spin-wave excitation is detected up to approximately 250 K which is a fairly high temperature.     

Determination of chromium, cadmium and lead in food-packaging materials by axial inductively coupled plasma time-of-flight mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) with a time-of-flight (TOF) analyser was used for the determination of chromium, cadmium and lead in six food-packaging materials (paper and paper board). The samples (0.20-0.25 g) were digested in concentrated nitric acid in a high pressure microwave oven at 180 °C within 15 min. Two different plasma conditions were applied: cool plasma conditions (0.76 kW; 0.85, 0.89 and 15.5 l min⁻¹ nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of chromium and normal plasma conditions (1.21 kW; 0.66, 0.68 and 13.6 l min⁻¹ nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of cadmium and lead. External calibration was used in combination with rhodium (40 ng g⁻¹) as an internal standard. The detection limits (DL = 3S.D./sensitivity) under the conditions used corresponded to 0.01 ng g⁻¹ (), 0.06 ng g⁻¹ (), 0.07 ng g⁻¹ (), 0.03 ng g⁻¹ () and 0.02 ng g⁻¹ ( and ). The precision (R.S.D.) for six replicate determinations (10 s integration time) of 1 and 10 ng g⁻¹ of each analyte varied from 0.72% () to 4.43% (). The contents of chromium, cadmium and lead in the examined materials were evaluated using the signals of , and . They were in the range: 0.25-0.50 μg g⁻¹ for Cr, not detected (nd) to 0.12 μg g⁻¹ for Cd and 0.28-0.35 μg g⁻¹ for Pb in paper and 0.50-0.64 μg g⁻¹ for Cr, nd to 0.09 μg g⁻¹ for Cd and 0.67-0.99 μg g⁻¹ for Pb in paper board.     

Synthesis and crystal structure of a novel ternary oxoborate, PbBiBO4

A novel ternary borate oxide, lead bismuth boron tetraoxide, PbBiBO₄, has been prepared by solid-state reaction at temperature below 800 °C. The single-crystal X-ray structural analysis showed that PbBiBO₄ crystallizes in the monoclinic space group P2₁/n with , , , β=91.48(1), Z=4. It represents a new structure type in which distorted BiO₆⁹⁻ octahedra are connected to each other in corner- and edge-sharing manner to form two-dimensional layers that are bridged by B atoms of BO₃ triangles giving rise to a three-dimensional framework, with channels parallel to the [0 1 0] direction accommodating the pyramidally coordinated Pb²⁺ cations.     

The disordered structures and low temperature dielectric relaxation properties of two misplaced-displacive cubic pyrochlores found in the Bi2O3-MO-Nb2O5 (M=Mg, Ni) systems

The disordered structures and low temperature dielectric relaxation properties of Bi_1.667Mg_0.70Nb_1.52O₇ (BMN) and Bi_1.67Ni_0.75Nb_1.50O₇ (BNN) misplaced-displacive cubic pyrochlores found in the Bi₂O₃-M^IIO-Nb₂O₅ (M=Mg, Ni) systems are reported. As for other recently reported Bi-pyrochlores, the metal ion vacancies are found to be confined to the pyrochlore A site. The B₂O₆ octahedral sub-structure is found to be fully occupied and well-ordered. Considerable displacive disorder, however, is found associated with the O′A₂ tetrahedral sub-structure in both cases. The A-site ions were displaced from Wyckoff position 16d (, , ) to 96 h (, , ) while the O′ oxygen was shifted from position 8b (, , ) to Wyckoff position 32e (, , ). The refined displacement magnitudes off the 16d and 8b sites for the A and O′ sites were 0.408 Å/0.423 Å and 0.350 Å/0.369 Å for BMN/BNN, respectively.     

Standard enthalpy of formation of aqueous titanyl chloride, TiOCl2(aq), at T = 298.15 K

Enthalpies of solution of TiCl₄(l) in aqueous perchloric acid have been measured in an isothermal calorimeter at T = 298.15 K at ionic strengths of (1.964, 3.002, and 4.062) mol · kg⁻¹. These results were extrapolated to zero ionic strength using an extended Debye-Hückel equation, to yield the standard enthalpy of solution ; from which the standard partial molar enthalpy of formation of the titanyl ion was derived: .     

Quaternary ammonium salt-based chromogenic and fluorescent chemosensors for fluoride ions

Chemosensors 5-7 possessing a quaternary ammonium cation (for electrostatic interactions) and an N-H group(s) (for H-bonding) as recognition sites and an anthracene-9,10-dione as both a chromogenic and fluorescent moiety exhibit absorption and emission changes with fluoride ions only. No significant response to other anions such as Cl⁻, Br⁻, I⁻, , CH₃COO⁻, , and is observed. The dual emission at λ_max 580 nm (free 5/6) and λ_max 510 and 540 nm (5/6 + F⁻) in chemosensors 5 and 6 enables ratiometric analysis of fluoride ions.     

Thermodynamic studies on the interactions of diglycine with magnesium chloride in aqueous medium at different temperatures

Apparent molar heat capacities (C_P2,?), apparent molar volumes (V_2,?), and viscosities (η) of diglycine in water and in aqueous magnesium chloride (MgCl₂) solutions of molality m_S ≈ (0.05 to 0.70) mol · kg⁻¹ over the temperature range T = (288.15 to 328.15) K have been determined using high sensitivity micro-differential scanning calorimeter, vibrating-tube digital density meter, and automatic viscosity measuring unit (AVS 350), respectively. The data have been used to calculate the partial molar heat capacities and partial molar volumes at infinite dilution. The viscosity B-coefficients have also been obtained from viscosity data using Jones-Dole equation. The and values of diglycine in aqueous MgCl₂ solutions are higher than those in water and thus exhibit positive transfer functions ( and ), which are indicative of strong interactions between diglycine and MgCl₂. Corresponding viscosity B-coefficients of transfer are also generally positive. The transfer functions decrease with increase in temperature and increase with the concentration of MgCl₂. The free energies, enthalpies and entropies of activation for viscous flow of diglycine in aqueous MgCl₂ solutions have been obtained by using the Feakins transition-state theory. Partial molar expansibilities and at infinite dilution along with their temperature dependence, the interaction coefficients from the volume, heat capacity, and viscosity B-coefficients have been used to divulge the various kinds of plausible interactions between solute (diglycine) and cosolute (MgCl₂) in solutions.     

Comparison of methods for the determination of total selenium in plasma by magnetic sector inductively coupled plasma mass spectrometry

Three sample preparation methods (dilution, microwave digestion and ethanol addition) were evaluated for the determination of Se in human plasma using magnetic sector inductively coupled plasma mass spectrometry (ICP-MS). A number of instrumental parameters were also considered, namely the choice of internal standard (Sc, Rh, In) and pre-defined spectral resolution (m/Δm ∼300 (low resolution, LR) and ∼7500 (high resolution, HR)). The isotopes and were selected for analysis avoiding the major and unresolvable Ar dimer interferences associated with other Se isotopes.Ethanol addition was found to be the most suitable and reliable sample preparation method. The optimum ethanol concentration for a 1+9 dilution of the plasma sample was 0.5% (v/v). Indium or Sc were selected over Rh as internal standards as Seronorm™ Level 1 target values were achieved at lower concentrations of ethanol modifier. Representative ICP-MS detection limits for this method using (HR) and (HR), were 0.1 and 0.2 μg l⁻¹.Accurate analysis of Se in Seronorm™ Level 1 (MI0181) was found using either or and HR (86±5 and 83±5 μg l⁻¹ respectively, n=5, In internal standard, target value=83±6 μg l⁻¹). Although offering improved precision (e.g. LR: 0-3% versus HR: 1-6%), accurate results were only obtained with LR for the Seronorm™ Level 1 sample when using (86±1 μg l⁻¹). The major interference precluded accurate Se analysis using and LR for all samples considered. Reliable Se concentrations were only found for a “real” pooled sample when using (HR), in part a result of non-negligible and unresolved interference when using LR. Consistently elevated Se concentrations were found under all conditions when Seronorm™ Level 2 (NO0371) was analysed. These results were confirmed by independent GF-AAS analysis.Magnetic sector ICP-MS with (HR), in combination with the ethanol addition sample preparation method, was used for the analysis of Se in human plasma samples as part of a small pilot study. Average measured selenium concentrations were 102±18 μg l⁻¹ (n=18).     

Synthesis, crystal structure, and electronic structure of RbVSe2

RbVSe₂ has been synthesized at 773 K through the reaction of V and Se with a Rb₂Se₃ reactive flux. The compound crystallizes in the orthorhombic space group D_2h²⁴-Fddd with 16 formula units in a cell of dimensions , , and at . The structure possesses infinite one-dimensional chains of edge-sharing VSe₄ tetrahedra separated from the Rb⁺ ions. These chains distort slightly to chains. The V-V distance within these chains is 2.8362(4) Å. First-principles total energy calculations indicate that a non-magnetic configuration for the V³⁺ cations is the most stable.     

Synthesis, structure, band gap, and electronic structure of CsAgSb4S7

The compound CsAgSb₄S₇ has been synthesized by the reaction of the elements in a Cs₂S₃ flux at 773 K. The compound crystallizes in a new structure type with eight formula units in space group C2/c of the monoclinic system in a cell at 153 K of dimensions , , , β=97.650(1)°, and . The structure contains two-dimensional layers separated by Cs atoms. Each layer is built from edge-sharing one-dimensional and chains. Each Ag atom is tetrahedrally coordinated to four S atoms. Each Sb³⁺ center is pyramidally coordinated to three S atoms to form an SbS₃ group. CsAgSb₄S₇ is insulating with an optical band gap of 2.04 eV. Extended Hückel calculations indicate that the band gap in CsAgSb₄S₇ is dominated by the Sb 5s and S 3p states above and below the Fermi level.     

The H2O-D2O solvent isotope effects on the molar volumes of alkali-chloride solutions at T = (288.15, 298.15, and 308.15) K

Densities of LiCl, NaCl, KCl, and CsCl in normal and heavy water solutions have been measured using a vibrating-tube densitometer with (1-2) · 10⁻⁶ precision at T = (288.15, 298.15, and 308.15) K over a wide concentration range from (0.1 to 5) molal, m. Solvent isotope effects (IE) on apparent molar volumes, as well as both on solute- and solvent-partial molar volumes were evaluated to establish their trend with cationic size in a systematic way. With the exception of the LiCl, both the “normal” standard IEs, , and the “inverse” excess IEs of the solutes, , increase linearly with the electrostriction effect of the cations (1/r_ion), while with increasing temperature and/or concentration, the excess effects become almost the same.In contrast to the solute excess IEs, which show linear m^1/2-dependence over the whole concentration range, except for LiCl, the “inverse” excess IEs of the solvent, , hardly change over the lower concentration range (, m ? 1). However, with further increase of the concentration, these IEs significantly decrease. Individual ionic standard and excess volume contributions are derived and the results are discussed in terms of structural concepts of ionic hydration.     

Structural characterization and ferroelectric ordering in (C3N2H5)5Sb2Br11

A ferroelectric crystal (C₃N₂H₅)₅Sb₂Br₁₁ has been synthesized. The single crystal X-ray diffraction studies (at 300, 155, 138 and 121 K) show that it is built up of discrete corner-sharing bioctahedra and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P2₁/n with: , and and β=96.19^°. The crystal undergoes three solid-solid phase transitions: ) discontinuous, continuous and discontinuous. The dielectric and pyroelectric measurements allow us to characterize the low temperature phases III and IV as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations.     

Preparation, structures, and band gaps of RbInS2 and RbInSe2

The two compounds RbInS₂ and RbInSe₂ have been synthesized at 773 K by means of the reactive flux method. These isostructural compounds crystallize in space group C2/c of the monoclinic system with 16 formula units in a cell at 153 K of dimensions , , , and β=100.244(1)° for RbInS₂, and , , , and β=100.16(2)° for RbInSe₂. The In atoms are four-coordinated. The structure consists of two-dimensional (Q=S, Se) layers perpendicular to [001] separated from the Rb⁺ cations. Adamantane-like In₄Q₁₀ units are connected by common corners to form the layers. Band structure calculations indicate that these compounds are direct band-gap semiconductors with the smallest band gap at the Γ point. The calculated band gaps are 2.8 eV for RbInS₂ and 2.0 eV for RbInSe₂, values that are consistent with the colors of the compounds.