Selective detection of F− by chromogenic tetrazole receptor

A chromogenic anion host 4, containing two amide functionalities linked to azo dye and tetrazole rings, was synthesised and its complexes with various anions were investigated. The results show that receptor 4 can recognise selectively biologically important F^?  ion. The binding affinity for F^?  was investigated by naked-eye colour change, UV–vis and ¹H NMR spectroscopy. Addition of F^?  ion in CH₃CN and Dimethyl sulfoxide to receptor 4 causes a change in colour of the solution from colourless to yellow. The stoichiometry for host:anion is 1:1. Furthermore, receptor 4 was used as an ion carrier in ion-selective membrane electrodes. Selectivity of this membrane was studied towards various anions in water solution. Binding behaviour of receptor 4 towards several anions (Cl^? , F^? , Br^? , I^? ) has been investigated using density functional theory calculations.     

Excited-state dynamics of trans,trans-1,3,5,7-octatetraene: estimation of decay rate constants of 1(1)B(u) ⇝ 2(1)A(g) and 2(1)A(g) ⇝ 1(1)A(g) internal conversions

The general expressions we previously derived for calculating internal conversion rate constants between two adiabatic displaced-distorted-rotated potential energy surfaces, by including all vibratinal modes, are applied to estimate the decay rate constants of 1(1)B(u) ? 2(1)A(g) and 2(1)A(g) ? 1(1)A(g) internal conversions in trans,trans-1,3,5,7-octatetraene molecule. The minimal models with respect to the number and types of vibrational modes are determined for these processes. Our calculations show that in the low temperature limit the 1(1)B(u) ? 2(1)A(g) internal conversion takes place on a 232-290 fs time scale in the condensed phase and 2 ps in the gas phase, whereas 2(1)A(g) ? 1(1)A(g) internal conversion takes place on a 2 μs time scale under the isolated conditions.     

A comparison of different types of gold–carbon composite electrode for detection of arsenic(III)

A study has been conducted using abrasively modified basal and edge-plane graphite, carbon-paste, and carbon–epoxy electrodes to create gold–carbon composite electrodes. Using either nano or micro-sized gold particles their suitability for use in detecting arsenic(III) is assessed. It was found that gold arrays prepared from micron-sized particles gave the best performance for arsenic detection. In particular micron arrays produced in carbon-paste electrodes with an easily renewable surface work well for detection of arsenic, producing a detection limit of 5(±2)×10^–9 mol L^–1, with a high sensitivity of 10(±0.1) A mol^–1 L.     

Decay of (Fe1−xNix)0.96S DSC investigation

The decay of a monosulphide solid solution (mss) with the composition (Fe_1?1Ni_x)_0.96S was investigated by means of differential scanning calorimetry in the temperature range, from 20 to 305?C. Thermal effects of various natures were detected:

1. Ordering-disordering in the Fe-Ni sublattice near 100?C.
2. Pentlandite exsolution (exothermal peak); the peak temperature varies from 180 to 240?C and depends on the initial composition; the higher the Ni content, the lower the exsolution temperature.
3. Magnetic-paramagnetic transition. The transition temperature decreases down to 220?C as the Fe∶Ni ratio is decreased from 10∶0 to 4∶6.

Ni atoms are the defects in the magnetic ordering of themss generated by the Fe atoms in the metal sublattice. Thus, the driving force for pentlandite exsolution is the removal of Ni atoms from the magneticmss into the nonmagnetic pentlandite. This is the reason why the Fe∶Ni ratio in the generated pentlandite is much higher than that in the initialmss.     

A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.     

The formation of the Ba(CuOx)1−y(CO3)y

Carbocuprate compounds are generally described as multiple perovskites with CO ₃ ² - and Cu-O alternating layers containing Ba and/or Sr; they have gained an unexpected importance in the high temperature superconductivity field, because many compounds with transition temperature above 100 K belong to this class of materials.We have started a systematic study on phase formation and stabilisation in the Ba-Cu-C-O system in the temperature range 20-600°C, by using thermal analysis techniques. Starting from a BaCO₃-BaO₂-CuO mixture (311 mol), a new phase isomorphic with BaCO₃ formed after heat treatment above 390°C in air. TG, DSC, EGA and high temperature XRD were employed to follow the complex interaction of the reactants with the atmosphere and the formation of the new phase.     

Micro- and nanostructure of (Sn1−xGex)S mixed crystals

Mixed crystals (Sn_1−xGe_x)S had been prepared by a reaction of solvochemically activated tin and activated germanium with elemental sulfur. The homogeneity of the samples and the sizes of the crystals depend on the annealing temperature. Nanocrystals and larger crystals exhibit characteristic planar defects. The defects real structure was reconstructed from HRTEM observations. Image simulations indicate that two models of the real structure are consistent with the experimental data. Both models are characterized by a combination of structural features of the high and low temperature phases of SnS.     

Adsorption of S2− and HS− ions on the (111) face of coinage metals: A quantum-chemical study

The interactions of S^2? and HS^? ions with gold, silver, and copper were studied by density functional theory using the cluster model of the metal surface. The geometrical and energy characteristics of the interactions of these ions with the surface metal atoms were evaluated. The S^2? ions form stronger chemical bonds with the surface metal atoms than HS^? ions. A significant charge transfer from anion to metal occurs during the adsorption. The adsorbability increased in the series Ag < Cu < Au for both anions. The HS^? ion showed greater ability to be transferred to the surface during the electrochemical adsorption due to the strong hydration of the S^2? ion. In alkaline media, however, the dissociation of the adsorbed HS^? leads to its conversion to S^2?.     

A Mössbauer spectroscopy investigation of SrFe1−xScxO3−δ perovskites

Polycrystalline samples of oxygen deficient perovskites SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5) have been synthesized by direct solid state reactions. Each compound has been stabilized with two different oxygen stoichiometries. The structural study shows, firstly, the good cationic homogeneity of the samples and, secondly, that the Sc and Fe atoms are randomly distributed over the same crystallographic site, whatever the scandium content. This implies that no anionic order is possible. A detailed Mossbauer spectroscopy study clearly shows that the substitution of scandium for iron involves an oxygen content decrease which decreases the tetravalent iron content until its total disappearance for x = 0.5. The evolutions of the isomer shift, the quadrupolar splitting and the relative intensity versus the Sc³⁺ content are depicted in the present paper.     

Facile synthesis of an optical sensor for CO32− and HCO3− detection

A novel fluorogenic signalling probe (E)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (6) for the carbonate and bicarbonate ions has been developed through microwave assisted Schiff base formation reaction. The anion recognition occurs through hydrogen bonding assessed by ¹H NMR titration experiments. The photophysical results of probe 6 corroborates its applicability as an optical sensing platform for carbonate as well as bicarbonate ions in mixed aqueous organic media depending on pH of reaction solution. The fluorescence emission signal enhancement at 424 nm and considerable shift in the signal position as well as molar absorptivity to the probe absorption bands upon CO₃^2? and HCO₃^? addition suggest the affinity of probe 6 towards these ions in comparison to a variety of competitive ions in aqueous/ethanol (7:3, v/v) at neutral pH and ambient temperature. From the fluorescence titration experiment, the limit of detection was calculated to be 1.91 μM.     

A full vibrational assignment (4000-50 cm−1) of 1, 10-phenanthroline and its perdeuterated analogue

Full infrared and Raman vibrational assignments (4000-50 cm⁻¹) of 1,10-phenanthroline are presented and full infrared assignments (4000-50 cm⁻¹) of 1,10-phenanthroline-d₈ are given. Four fundamentals are newly reported for 1,10-phenanthroline and several changes are recommended to earlier assignments for this compound. The assignments of the fully deuterated analogue are newly reported.     

[(CrGe9)Cr2(CO)13]4−: A disubstituted case of ten-vertex closo cluster with spherical aromaticity

We report the first disubstituted hetero-ten-vertex closo cluster [(CrGe₉)Cr₂(CO)₁₃]^4? with three adjacent Cr(CO)_n units adopting both η⁵ and η¹ coordination modes, which was synthesized through the reaction of “KGe_1.67” with (MeCN)₃Cr(CO)₃ and Cr(CO)₆ in ethylenediamine (en) solution. In contrast to the η¹-Cr atoms forming localized two-center two-elelctron (2c-2e) Cr-Ge bonds, the hetero atom η⁵-Cr exhibits versatile bonding mechanisms including three 5c-2e and five 8c-2e delocalized bonds which account for Hückel aromaticity. Intricate multi-center bonding patterns delineate the multiple local σ-aromatic characters of the title cluster displaying explicit spherical aromaticity.     

New methods of preparation of hydroxy-closo-decaborates [B10H10 − n (OH) n ]2− (n = 1, 2)

New methods of preparation of hydroxy-closo-decaborates [B₁₀H_{10 ? n} (OH) _n ]^2? (n = 1, 2) that are based on the reaction of anions [B₁₀H_{10 ? n} (OAc) _n ]^2? and alkoxyethylidenoxonio-closo-decaborates [2-B₁₀H₉OC(OR)CH₃]^? with aqueous solution of hydrazine are proposed. The obtained compounds were characterized by IR, ESI/MS, and NMR (¹H, ¹¹B, ¹³C) spectroscopy.     

Behavior of Mn3+ ions in four-layered hexagonal (Sr1−x−yLaxBay)MnO3

Stoichiometric four-layered hexagonal (4H) (Sr_1?x?yBa_xLa_y)MnO₃ was synthesized using a standard ceramic technique. Rietveld analysis at room temperature indicated that the Mn–O(1) distance increased and the Mn–O(2) distance decreased with the increase in x. The samples were n-type semiconductors and exhibited hopping conductivity in a small-polaron model below 533 K. The Mn³⁺ ion acted as a donor and the electron transfer became active through the Mn³⁺–O–Mn⁴⁺ path. The samples were antiferromagnetic and the Néel temperature (T_N) was constant regardless of y when x was fixed to 0.3, whereas T_N shifted to a high temperature when y was fixed to 0.02. The face-sharing Mn³⁺–O(2)–Mn⁴⁺ interaction strengthened as the Mn–O(2) distance decreased, and T_N shifted to a high temperature as a result.     

Gram scale synthesis of the C(1)–C(9) fragment of amphidinolide C

An allylic cis-epoxide prepared by Sharpless asymmetric epoxidation was transformed in nine steps and 41% overall yield to the cyclization precursor 4 via a key one carbon homologation. Cobalt-catalyzed aerobic oxidative cyclization of 4 gave the trans-THF in 94% yield at gram scale. Subsequent manipulations, including a Still–Gennari olefination, Sharpless asymmetric dihydroxylation, Corey–Fuchs alkynylation, and Kazmaier hydrostannylation provided the fully functionalized C(1)–C(9) fragment 2 suitable for cross-coupling. The sequence is readily scalable and provides gram quantities of 2.     

Sintering, microstructures and dielectric properties of Ba1−xPbx(Ti1−xLix)O3−3xF3x ferroelectric ceramics

Various compositions (1−x)BaTiO₃ + xPbF2 + xLiF were prepared, shaped to pellets then sintered at 900°C for 2 h in gold sealed tubes. The purity and the symmetry of the obtained samples were checked by X-ray diffraction. A new solid solution with Ba_1−x Pb _x (Ti_1−x Li _x ) O_3−3x F_3x formula occurs in the composition range 0 ≤ x ≤ 0.20. SEM observations were performed on polished and fractured ceramics. The complex permittivity was measured as a function of temperature (−120°C ≤ T ≤ 250°C) and frequency (50 Hz ≤ f ≤ 4 × 10⁷ Hz). The dielectric performances are the best for ceramic Ba_0.97Pb_0.03(Ti_0.97Li_0.03)O_2.91F_0.09. The real component ε′, exhibits a maximum of approximately 7500 at the ferroelectric Curie temperature T _C ≈ -18°C, the dielectric losses tan δ value being 0.012. At room temperature, the relaxation frequency f _r is around 40 MHz for this ceramic. This novel ferroelectric oxifluoride is a promising material for applications, in particular in the field of Z5U multilayer capacitors.      

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

A highly selective fluorescent chemosensor for successive detection of Fe3+ and CN− in pure water

A water-soluble fluorescent chemosensor (D) based on 1, 8-naphthalimide derivative has been designed and synthesised as a new fluorescent sensor for successive detection of Fe³⁺ and CN^?. Fluorescence measurements show that chemosensor D has excellent fluorescent-specific selectivity and high sensitivity for Fe³⁺ over many other metal ions in pure water. Moreover, the complex of D and Fe³⁺ (D–Fe³⁺) displayed high sensitivity for CN^? over many other anions in the same medium. Even more important, the recognition of the sensor D for Fe³⁺ and D–Fe³⁺ complex for CN^- could be used successfully in pure water. The test strips based on D and D–Fe³⁺ exhibited good selectivity to Fe³⁺ and CN,^- respectively, we believe the test strips could serve as convenient and efficient Fe³⁺ and CN^? test kits.