Solubility and dissolution enthalpy of xanthine

At a constant ionic strength corresponding to human urine (I_c =  0.300 mol · dm ^− 3), the solubilities of xanthine were measured as a function of  − lg{c (H ⁺ ) / c^o} (c^o =  1 mol · dm ^− 3) at the temperatures T =  298.15 K and T =  310.15 K, respectively. Highly reproducible solubility and dissociation constants were obtained. Also, for the first time, the dissolution enthalpy of xanthine was determined calorimetrically. The values of this quantity obtained from both calorimetric determination and temperature dependence of solubility equilibrium constants are thermodynamically consistent.     

Preparation and characterization of Al and Mn doped ZnO (ZnO: (Al,Mn)) transparent conducting oxide films

This paper presents the electro-optical, chemical and structural properties of doped-ZnO films deposited by DC-reactive magnetron sputtering at room temperature using the bi-dopant Al and Mn. A minimum resistivity of 3.46×10⁻⁴ Ω cm, exceeding 75.0% average transmittance (380–800 nm), and fundamental band gap of 3.48±0.01 eV have been obtained. XPS analyses show that Zn uniformly remains in the valence state of Zn²⁺; all of the Al and a little amount of Mn with valence state of Mn⁴⁺ are supposed to have donor effect, while dominant Mn²⁺ will induce to form more oxygen vacancies and this proposal has been verified by O 1s XPS results. It has been concluded that the presence of more oxygen vacancies will attenuate the effect of hybridization of p–d orbitals in the matrix of ZnO. It has been found that all the as-deposited films have c-axis preferred orientation with flat and smooth surface (RMS surface roughness is of the order of ∼3 nm over 5×5 μm² area).     

Conformational and stereoelectronic investigation of chloromethyl methyl sulfide and its sulfinyl and sulfonyl analogs

Three compounds based on polyoxometalate building blocks, [Cu(en)₂]{[Cu(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(PO₄)]} · 4H₂O (1), [Co(en)₂]{[Co(en)₂]₂[HMo^VI₄Mo^V₄V^IV₈O₄₀(PO₄)]} · 5H₂O (2) and [Ni(en)₂]{[Ni(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(VO₄)]} · 2H₂O (3) (en = ethylenediamine), have been synthesized and characterized by elemental analysis, IR, XPS, XRD, TGA and single-crystal X-ray diffraction analysis. The result of structure determination shows that isomorphic compounds 1, 2 and 3 feature a one-dimensional chain built from the reduced tetra-capped pseudo-Keggin polyoxoanion, which is further interconnected by [M(en)₂]²⁺ (M = Cu, Co and Ni) groups via the terminal oxygen atoms of polyoxoanions. The crystal data for these compounds are the following: 1, monoclinic, space group C2/c, a = 26.702(3) Å, b = 13.4539(14) Å, c = 19.5987(19) Å, β = 108.650(2)°, V = 6671.0(12) Å³, Z = 4; 2, monoclinic, space group C2/c, a = 26.244(3) Å, b = 13.5070(17) Å, c = 19.581(3) Å, β = 106.881(2)°, V = 6641.8(15) Å³, Z = 4; 3, monoclinic, space group C2/c, a = 26.2789(15) Å, b = 13.5408(6) Å, c = 19.6312(9) Å, β = 106.2590(10)°, V = 6706.1(6) Å³, Z = 4. Variable-temperature magnetic susceptibility measurements of compounds 1 and 3 reveal the feature of antiferromagnetic exchange in these compounds.     

Study on the effects of cefotaxime on intracellular Ca^2＋ in human peripheral lymphocytes by fluoremetry

Characteristic of Fura-2-Ca~(2 )interaction was studied based on the fluorescence technique.The apparent dissociation constants(K_d)of the Fura-2-Ca~(2 )complex were determined at different temperature.The effect of cefotaxime(CEFA)on intracellular Ca~(2 )concentration([Ca~(2 )]_i)was discussed by using a ratiometric fluorescence dye Fura-2 as a probe.The basal[Ca~(2 )]_i in resting humanperipheral lymphocytes was 100 7 nmol/L but after treatment with cefotaxime,the changes of[Ca~(2 )]_i were observed in differentconditions.In the concentration range of 1-30 μmol/L of cefotaxime[Ca~(2 )]_i increased,as a result of releasing intracellular Ca2 stores.Higher concentration of cefotaxime(50-500 μmol/L)stimulated to decrease of[Ca~(2 )]_i.     

Synthesis,structure, and characterization of a new two-dimensional lead(II) vanadate,Ba3PbV4O14

A new two-dimensional lead(II) vanadate, Ba₃PbV₄O₁₄ has been synthesized by standard solid state techniques using BaCO₃, PbO, and V₂O₅ as reagents. The structure of Ba₃PbV₄O₁₄ was determined by single-crystal X-ray diffraction. Ba₃PbV₄O₁₄ crystallizes in the triclinic space group P-1 (no. 2), with a = 7.2997(15) (Å), b = 7.2932(15) (Å), c = 13.379(3) (Å), α = 93.68(3)°, β = 99.68(3)°, γ = 91.49(3)°, V = 700.2(2) (ų) and Z = 2. Ba₃PbV₄O₁₄ exhibits a novel two-dimensional layered structure consisting of corner shared VO₄ tetrahedra that are linked by edge shared PbO₇ polyhedra, in which the Ba²⁺ cations occupy the interlayer region. The Pb²⁺ cations are in asymmetric coordination environments attributable to its lone pair. Infrared, Raman, and UV–vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dipole moment calculations are also presented.     

Direct electron transfer of cytochrome c and its biosensor based on gold nanoparticles/room temperature ionic liquid/carbon nanotubes composite film

A robust and effective composite film based on gold nanoparticles (GNPs)/room temperature ionic liquid (RTIL)/multi-wall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode was prepared by a layer-by-layer self-assembly technique. Cytochrome c (Cyt c) was successfully immobilized on the RTIL-nanohybrid film modified GC electrode by electrostatic adsorption. Direct electrochemistry and electrocatalysis of Cyt c were investigated. The results suggested that Cyt c could be tightly adsorbed on the modified electrode. A pair of well-defined quasi-reversible redox peaks of Cyt c was obtained in 0.10 M, pH 7.0 phosphate buffer solution (PBS). RTIL-nanohybrid film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis currents increased linearly to the H₂O₂ concentration in a wide range of 5.0 × 10⁻⁵– 1.15 × 10⁻³ M. Based on the multilayer film, the third-generation biosensor could be constructed for the determination of H₂O₂.     

Hopping conductivity of distorted K2NiF4-type (Ca1+xNd1−x)CrO4

Orthorhombic distorted K₂NiF₄-type (Ca_1+xNd_1?x)CrO₄ (0.00 ≤ x ≤ 0.15) was synthesized using a standard ceramic technique. The cell parameters (a and c) decreased, whereas the cell parameter (b) increased with the increase in x. The variation in the global instability index (GII) indicated that the crystal stability of (Ca_1+xNd_1?x)CrO₄ was not influenced by the Cr⁴⁺ ion content. At all temperatures, the electrical conductivity (σ) of (Ca_1+xNd_1?x)CrO₄ increased with the increase in x. (Ca_1+xNd_1?x)CrO₄ was a p-type semiconductor and exhibited hopping conductivity in a small-polaron model in the temperature range of 290 K ≤ T ≤ 713 K. The Cr⁴⁺ ion acts as an acceptor, and the electron transfer through the Cr³⁺–O–Cr⁴⁺ path becomes active as a result of the Cr⁴⁺ ion content and the Cr–O(1) distance.     

Modulations in the onoratoite system

The iodide form of the mineral onoratoite was synthesized, and like the Cl and Br based analogues, it displays super structure ordering, but for the iodide, the super structure is clearly incommensurate. Due to the poor quality of crystals attainable, the structure was solved by converting the solution of the Cl analogue to a super space formalism, and then using the structural elements from this solution to model the iodide. The structure is triclinic, crystallizing in the 3+1d super space group P-1(αβγ) with the (pseudomonoclinic) cell parameters a = 19.066(8) Å, b = 4.102(2) Å, c = 10.82(6) Å, β = 108.9(2)° and the modulation wave vector q = (0.4716a¹ + 0.25b¹ + 0.1679c¹) been changed accordingly.     

Low temperature synthesis of ferromagnetic (LaK)MnO3 from KCl,KBr and KI fluxes

Potassium doped lanthanum manganites have been synthesized from KCl, KBr and KI fluxes at 900, 850 and 750 °C respectively. While all the flux-grown oxides are ferromagnetic metals (T_c=290–330 K), the oxides grown from KCl and KBr fluxes crystallize in the rhombohedral structure and that synthesized from KI flux adopts the cubic structure. The enhancement in T_c correlates with the increasing tendency of the flux to get oxidized and decreasing melting points of the flux. Nearly stoichiometric (LaK)MnO₃ with 33 % of Mn⁴⁺ concentration could be prepared at temperature as low as 750 °C. Composition of all the phases have been obtained from the chemical analysis of the elements present.     

Substitution of Sr2+ by Eu3+ in Bi-2201 ceramics,effects on structure and physical properties

In this paper, we report the effects of the substitution of Sr by Eu on the properties of Bi-2201 ceramics. Samples with nominal compositions of Bi₂Sr_2?xEu_xCuO_y (x = 0–0.4) are elaborated in air by solid state reaction. They are characterized by means of X ray diffraction (XRD), scanning electron microscopy (SEM), magnetic and resistivity measurements. The undoped sample (x = 0) is monophasic and its structure belongs to phase A. No trace of superconductivity is observed down to 2 K for this sample and the variation of resistivity with temperature shows a semiconducting behaviour. As Eu is added and for x ≥ 0.2, the samples convert totally to B or Raveau phase and become superconducting. The highest T_c, obtained from both magnetic and resistivity measurements, is observed for x = 0.3. In the normal state, all the samples exhibit a semiconducting character which decreases as well as resistivity when the Eu content increases. The refinement of cell parameters is done with considering the structural modulation. The study shows that the substitution of Sr²⁺ by Eu³⁺ leads to an increase of a and b parameters, while c decreases similarly to those of the La doped phases. The a axis component of the modulation is observed to be independent of Eu content, while the c axis one increases slightly as this content increases. The XRD analysis has also revealed that the limit solubility of the used Eu₂O₃ oxide is situated between x = 0.3 and 0.4 of Eu content. The SEM micrographs show that the undoped sample consists of poorly connected grains with a random distribution. A quite different microstructure is obtained for the doped samples. The grains are more connected and have a flat shape which is characteristic of the Bi-based superconductors.     

On oxoacidic properties and solubilities of beryllium and magnesium oxides in molten (CsCs + KCl + NaCl) eutectic at T = 783 K

Reactions of Be²⁺ and Mg²⁺ with O^2– in molten eutectic mixture (CsCs + KCl + NaCl) (0.455:0.245:0.30) at T = 783 K were studied by a potentiometric method using Pt(O₂)|ZrO₂(Y₂O₃) indicator electrode. Addition of O^2– ions to the melt containing Mg²⁺ results in precipitation of MgO (pK_s,MgO = 11.89 ± 0.3, molality) whereas interaction of Be²⁺ with O^2– is accompanied with sequential formation of Be₂O²⁺ (pK = 15.68 ± 0.5, molality) and precipitation of BeO (pK_s,BeO = 9.62 ± 0.3, molality). On the basis of the obtained and known data pK_s,MgO–T⁻¹ dependence in molten (CsCs + KCl + NaCl) eutectic is constructed. The slope of the said dependence in T/K = (from 583 to 1073) range is in good agreement with the value predicted by the Shreder equation, that extends the range of use of the Shreder equation for predictions of metal oxide solubilities in molten halides.     

Syntheses and crystal structures of new vanadium(IV) oxyphosphates M(VO)2(PO4)2 with M = Co,Ni

We have extended our research interest on titanium oxyphosphates (M^II(TiO)₂(PO₄)₂, with M^II = Mg, Fe, Co, Ni, Cu, Zn) to vanadium oxyphosphates M^II(V^IVO)₂(PO₄)₂ (M^II = Co, Ni). For each compound two phases, named α and β according to synthesis conditions, have been stabilized at room temperature, then characterized. The four crystal structures M(VO)₂(PO₄)₂ (α and β for M = Co, Ni) have been determined in monoclinic P2₁/c space group using X-ray single crystals diffraction data. Structure of the α phase is derived from the Li(TiO)(PO₄) (orthorhombic Pnma) and LiNi_0.50(TiO)₂(PO₄)₂ (monoclinic P2₁/c) types, with cell parameters: a = 6.310(1) Å, b = 7.273(1) Å, c = 7.432(1) Å, β = 90.43(1)° for M = Co, and a = 6.297(2) Å, b = 7.230(2) Å, c = 7.421(2) Å, β = 90.36(2)° for M = Ni. Structure of the β phase is derived from the Ni(TiO)₂(PO₄)₂-type (monoclinic P2₁/c) with cell parameters: a = 7.2742(2) Å, b = 7.2802(2) Å, c = 7.4550(2) Å, β = 120.171(2)° for M = Co, and a = 7.2691(2) Å, b = 7.2366(2) Å, c = 7.4453(2) Å, β = 120.231(2)° for M = Ni. All these structures consist of a three dimensional (3D) framework built up of infinite chains of tilted corner-sharing [VO₆] octahedra, cross-linked by corner-sharing [PO₄] tetrahedra. The M²⁺ ion (M = Co, Ni) is located in a triangular based antiprism which shares faces with two [VO₆] octahedra. Structural filiation is discussed based on a common structural unit, a sheet where divalent cations M²⁺ (M = Co, Ni) are inserted. A thermal study of the α ? β transition is also presented.     

Complexation study and spectrofluorometric determination of the binding constant for diquat and p-sulfonatocalix[4]arene

The interactions between diquat (DQ) and p-sulfonatocalix[4]arene (C4S) were studied in an aqueous solution as a function of the ionic strength. Evidence for the formation of a complex between DQ and C4S was obtained using fluorescence measurements, while the stoichiometry of the complex was confirmed as 1:1 for DQ/C4S using UV–vis spectroscopy. The ionic strength had no influence on the stoichiometry of the complex, but exerted a significant influence on the complexation constant, K_c, decreasing with an increase in the ionic strength. The thermodynamic complexation constant, K_c′, was computed as 5.25±1.11×10⁷ using the extended Debye–Hückel law. The rate constants for the heterogeneous electron transfer for the reduction of DQ at an electrode surface were evaluated as 0.150±0.010 cm s^?1 in the absence of C4S and 0.065±0.010 cm s^?1 when C4S was added to the solution in a 1:1 ratio.     

The experimental and DFT studies of 1,3-dimethyl-2-[4-chloro-styryl]-benzimidazolium iodide

1,3-Dimethyl-2-[4-chloro-styryl]-benzimidazolium iodide (1) was synthesized and characterized by X-ray diffraction, ¹H NMR, MS, IR, UV–vis spectra and elemental analysis. The crystals are monoclinic, space group P2₁/c, with a = 12.507(3) Å, b = 7.3259(19) Å, c = 36.705(9) Å, V = 3358.9(15) Å³, and Z = 4 (at 296(2) K). Crystal stacking scheme indicates the face-to-face π?π aromatic stacking interactions. Molecular geometries, frequencies, IR, ¹H NMR and UV–vis were calculated at DFT/TD-DFT level using two hybrid exchange–correlation functionals, B3LYP and PBE1PBE. The stability of the molecule arising from hyperconjugative interaction and charge delocalization had been analyzed using natural bond orbital (NBO) analysis. These calculations on (1) provide deep insight into its electronic structure and properties.     

High-throughput investigation and characterization of strontium-phosphonatoethanesulfonates

Using the polyfunctional ligand 2-phosphonethanesulfonic acid (H₃L) a high-throughput (HT) study was started for the systematic investigation of the system SrCl₂/H₃L/NaOH/H₂O. The HT experiment comprising 48 individual reactions were performed to systematically investigate the influence of pH of the starting mixture as well as the molar ratio Sr²⁺:H₃L. Two new compounds SrH(O₃P–C₂H₄–SO₃) (1) and Sr₃(O₃P–C₂H₄–SO₃)₂(H₂O)₂ (2) were obtained and structurally characterized by single-crystal X-ray diffraction. The reaction products synthesized under hydrothermal conditions always contain traces of SrSO₄, which are due to the decomposition of small amounts of the ligand. While compound 2 could only be obtained under hydrothermal conditions, the synthesis of 1 could be accomplished under milder reaction conditions and a reaction scale-up could be performed. Compound 1 crystallizes in a monoclinic system with space group C2/c (no. 15), a = 534.73(11) pm, b = 1648.7(3) pm, c = 825.43(17) pm, β = 105.34(3)°, V = 701.8(2)–10⁶ pm³, Z = 4, R1 = 0.0268, and wR₂ = 0.0642 for I > 2σ(I). Compound 2 crystallizes in a triclinic system with space group P-1 (no. 2), a = 700.97(14) pm, b = 1008.5(2) pm, c = 1274.8(3) pm, α = 97.63(3)°, β = 92.03(3)°, γ = 92.03(3)°, V = 843.7(3)–10⁶ pm³, Z = 2, R1 = 0.0360, and wR₂ = 0.0896 for I > 2σ(I). In the structure of compound 1 the phosphorous and sulfur atoms cannot be distinguished due to identical crystallographic positions. Thus, an averaged structure was obtained which is built up by edge-sharing SrO₈ polyhedra that form infinite M–O–M chains. Compound 2 contains corner-, edge-, and face-sharing SrO₈ polyhedra which form inorganic M–O–M layers. These M–O–M chains (1) and layers (2) are connected to a three-dimensional network by the –CH₂CH₂– group of the ligand, respectively. Additional characterization by thermogravimetric analysis and IR-spectroscopy for compound 1 is also presented.     

Measurements of the critical parameters for {xNH3 + (1 − x)H2O} with x = (0.9098, 0.7757, 0.6808)

Measurements of the critical parameters for {xNH₃ + (1 ? x)H₂O} with x = (0.9098, 0.7757, 0.6808) were carried out by using a metal-bellows variable volumometer with an optical cell. The expanded uncertainties (k = 2) in temperature, pressure, density, and composition measurements have been estimated to be less than 3.2 mK, 3.2 kPa, 0.3 kg · m^?3, and 8.8 · 10^?4, respectively. In each mole fraction, the critical temperature T_c was first determined on the basis of the intensity of the critical opalescence. The critical pressure p_c and critical density ρ_c were then determined as the point at which the meniscus disappears on the isotherm at T = T_c. The expanded uncertainties (k = 2) in the present critical parameters have also been estimated. Comparisons of the present values with the literature data as well as the calculated values afforded using the equation of state are also presented.     

The three-body dissociation dynamics of Cl2O at 248 and 193 nm

The photodissociation of Cl₂O has been studied at 248 and 193 nm using photofragment translational spectroscopy (PTS) experiments with tunable VUV photoionization detection. The sole products observed were Cl, O and ClO fragments. Based on the derived translational energy distributions for the ClO and Cl photofragments we conclude that at 248 nm 15% of Cl₂O excitation results in three-body dissociation. At 193 nm no Cl₂ fragments are observed and we conclude that the oxygen atoms arise solely from three-body dissociation. Dissociation geometries derived from forward convolution fitting suggest two qualitatively distinct three-body dissociation pathways: asymmetric concerted dissociation and symmetric concerted dissociation in agreement with recent theoretical predictions.     

Potentiometric study of acid–base equilibria in the {KCl + LiCl} eutectic melt at temperatures in the range (873 to 1073) K

Some heterogeneous reactions of oxide ion exchange (carbonate ion dissociation and magnesium oxide dissolution) in the molten {KCl + LiCl} eutectic at temperatures of (873, 973 and 1073) K were studied using an electrochemical cell with an oxygen membrane electrode Pt(O₂)|ZrO₂(Y₂O₃). The dissociation constant of the CO₃²⁻ was found to increase with increasing temperature: pK (873 K)=(2.39 ± 0.05); pK (973 K)=(1.81 ± 0.09); pK (1073 K)=(1.53 ± 0.08). Removal of CO₂ from the gas above the melt allows the complete transformation of CO₃²⁻ to O²⁻. pP_MgO values decrease more from (6.99 ± 0.08) to (5.41 ± 0.04). The oxobasicity indices, pI_(KCl+LiCl), were calculated from the solubility data to be 3.2 at 873 K, 3.4 at 973 K, and 3.6 at 1073 K. This trend suggests an increase in acidity with increasing temperature of {KCl + LiCl}.     

Syntheses and structures of the MOF-type series of metal 1,4,5,8,-naphthalenetetracarboxylates M2(OH)2[C14O8H4] (Al,Ga, In) with infinite trans-connected M–OH–M chains (MIL-122)

Three new isostructural MOF-type compounds (named MIL-122) have been obtained from the hydrothermal reaction at 210 °C for 24 h of the 1,4,5,8-naphthalenetetracarboxylic acid with aluminum, gallium or indium source in water. The structures of the compounds M₂(OH)₂[C₁₄H₄O₈] (M = Al, Ga, In) have been solved ab initio from powder X-ray diffraction analysis using the synchrotron radiation (Soleil; station CRISTAL). The three-dimensional organic–inorganic framework exhibits infinite straight chains of metal-centered octahedra sharing trans corners linked to each other through the 1,4,5,8-naphthalenetetracarboxylate ligand. The cations Al, Ga or In, are coordinated by four oxygen atoms coming from the carboxyl groups and two bridging hydroxyl groups μ₂-OH, located in trans position in the octahedral surrounding. The compounds characterized by thermogravimetric and thermodiffraction analyses are thermally stable up to 440, 460 and 380 °C, for Al, Ga and In, respectively. Crystal data: monoclinic cell; P2₁/c (n°14); for MIL-122 (Al): a = 9.5174(2), b = 10.0706(1), c = 6.6465(2) Å, β = 91.2614(5)°, V = 636.878(2) Å³, Z = 2; for MIL-122 (Ga): a = 9.6501(1), b = 10.0585(1), c = 6.75069(9) Å, β = 92.4786(9)°, V = 654.65(1) Å³, Z = 2; for MIL-122 (In): a = 9.92359(5), b = 10.19765(7), c = 7.19357(4) Å, β = 727.034(8)°, V = 727.034(8)ų, Z = 2.     

Quantum chemical calculations and X-ray crystallographic studies of cis-dioxomolybdenum(VI) Schiff base complex

Treatment of the Schiff base 2-((E)-(2-hydroxy propylimino)methyl)phenol with MoO₂(acac)₂ in dry methanol gave the mononuclear complex (methanol{6-[(2-oxidopropyl)iminometh-yl]phenolato}dioxidomolybdenum(VI), which was characterized by X-ray crystal analysis, and it has monoclinic space group p2₁/c, and a = 10.330(17) Å, b = 9.397(15) Å, c = 13.695(2) Å, V = 1252.1(3) Å³, and Z = 4. B3LYP theoretical method with DZP basis sets calculations nicely reproduces the X-ray experimental geometry, molecular orbital levels and the other structural properties for this complex.