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Abstract A simple and sensitive spectrophotometric method for the determination of sulphamethoxazole in pure as well as in dosage form is described. The method is based on the reaction of sulphamethoxazole as electron donor with o-chloranil as electron acceptor to form violet colored charge transfer complex having maximum absorption band at 539 nm. Under the optimized reaction conditions, Beer’s law was obeyed in the range of 2-60 μg ml-1 with molar absorptivity 3.675×103 L mol−1cm−1. The limits of detection (LOD) and limit of quantitation (LOQ) were 0.371 and 1.236 μg ml-1 respectively. The accuracy and precision of the method were satisfactory; the average recovery % was 100.95 % and values of relative standard deviations ≤1.06 %. The stoichiometry of the reaction was studied, and the reaction mechanism was postulated. The proposed method was successfully applied to the determination of sulphamethoxazole in its pharmaceutical tablets and syrup with good accuracy and precisions. Keywords: Charge transfer; Spectrophotometry; o-chloranil; sulphamethoxazole

Abstract: To enhance the conversion efficiency of thin film photovoltaics, chalcopyrite based absorber materials are usually substituted in the cation and anion lattice to yield an absorber with a graded bandgap composed of mixed pentanary crystals Cu(In,Ga)(Se,S)2. Applying in-situ investigations during the crystallisation of the chalcopyrite is a prerequisite to understand the formation of inhomogeneities and elemental gradients caused by the growth process. The variation of anions yields a combined crystallisation path due to metal sulphoselenides with chalcogen exchange reactions upon heating, i.e. copper sulphoselenides act as a chalcogen buffer and afford substitution of S with Se during annealing. The extended chalcogen substitutions occur due to the complete solid solution of S and Se in Cu(S,Se) and Cu2−x(S,Se). On the contrary, different reaction paths are found for the cations. Although the metals show a good intermixture within the intermetallic alloys featuring In–Ga substitutions, no formation of a mixed or ternary (In,Ga)-chalcogenide is observed. This can be attributed to a narrow solid solution range of the (In,Ga)-chalcogenides. As a consequence the preceding formation of an In-rich and the delayed crystallisation of a Ga-rich chalcopyrite cause a vertical elemental gradient with Ga-accumulation near the back electrode. An interdiffusion of the In- and Ga-rich chalcopyrites is observed for increasing annealing time and temperature. The presented study is focused on quantification of the phase evolution, variation of lattice parameter and diffusion of elements as obtained by Rietveld refinements. [Copyright &y& Elsevier]

Abstract: The pentanary chalcogenide Cu2ZnSn(S,Se)4 (CZTSSe) compound is attracting considerable attention as a low-cost and high-efficient solar cell. The band gap can be tuned by adding Se to pure kesterite Cu2ZnSnS4, which influences the crystallization kinetics. The investigation of the crystallization of the pure selenium (Se) compound Cu2ZnSnSe4 can be helpful in understanding the reaction path between the elements of CZTSSe. Sputtered Cu-poor intermetallic Cu–Zn–Sn precursors were deposited on Mo-coated polyimide foil and sequentially capped by a thermally evaporated Se layer. Two different amounts of Se were deposited: amount that exactly matches the composition of Cu2ZnSnSe4; and that corresponding to twofold excess of the compound''s element ratio. These two compositions were chosen to investigate influences of the amount of Se on the reaction path and kinetics. Also, the reaction of pure metallic Sn with Se was studied by stacking Sn layers on Mo-coated foils for observing a Sn-loss phenomenon. It was also deposited with two different amounts of Se matching approximately the compositions of SnSe and SnSe2. Time-resolved X-ray diffraction was employed to measure the solid state reactions while increasing the sample temperature up to 550°C at a rate of 0.5K/s in an evacuated reaction chamber. After the experiment, sample is analyzed by Raman spectroscopy to distinguish the CZTSe from secondary phases. [Copyright &y& Elsevier]

Abstract: Chalcopyrite based photovoltaic materials Cu(InxGa1−x)(SySe1−y)2 (CIGSSe) are substituted in the cation and anion lattice to adopt the semiconductor bandgap to the terrestrial solar spectrum. In-situ X-ray diffraction (XRD) investigations on the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se)2 while annealing stacked elemental layers (SEL) show phase transitions proceeding during the chalcopyrite synthesis. Thin layers of metals with elemental ratio Cu:In:Ga=3:2:1 are deposited onto Mo-coated polyimide foil by DC-magnetron sputtering. The metal precursor is covered with S and subsequently Se by thermal evaporation of the elements in chalcogen excess (S+Se)/(Cu+In+Ga)=2.3. Investigated chalcogen ratios reach from pure Se to pure S. Crystalline phases formed during the annealing of SEL are qualitatively determined. The results are compared to conclusions drawn from previous experiments on Ga-free CuIn(S,Se)2 absorbers. The presence of Ga and S influences significantly the time-scale and the temperatures of phase transitions, i.e. the sulfoselenisation of precursor phases Cu16(In,Ga)9 and Cu9(Ga,In)4 proceeds faster with increasing S and is shifted to higher temperatures as compared to Ga-free Cu11In9/Cu16In9. [Copyright &y& Elsevier]

Abstract: The quaternary compound kesterite Cu2ZnSnS4 (CZTS) is a promising candidate for the production of low-cost thin film solar cells. Depending on the precursor composition and deposition technique several intermetallic precursor phases may appear, affecting the formation reactions during the crystallization process of the thin film absorber. A better understanding of these formation reactions in the system Cu–Zn–Sn–S is required for the optimization of CZTS absorbers and future development of solar modules. The crystallization of CZTS is completed by the reaction of Cu2SnS3 and ZnS. The formation of Cu2SnS3 itself depends on the different available precursor compounds after sulfur evaporation. Incomplete conversion of binary sulfides during annealing may lead to the formation of undesirable compounds, i.e. the transformation of Cu2SnS3 into Cu4SnS4 via reaction with Cu2-x S, which affect or even inhibit the crystallization of CZTS. Therefore a precise knowledge about formation reactions of binary and ternary Cu–Sn sulfides during annealing at low temperatures is important to crystallize a monophase CZTS absorber. Real-time investigations on the formation reactions in the quaternary and also the ternary subsystems of Cu–Zn–Sn–S while annealing stacked elemental layers elucidate the reaction paths of binary and ternary sulfides. We report on results of time-resolved and angle-dispersive XRD experiments during annealing comparing the formation reactions in sulfurized Cu–Sn precursors prepared by different deposition techniques. [Copyright &y& Elsevier]

Abstract: Thermal experiments were conducted using real boiler ash and fly ash samples from three types of municipal or industrial solid waste incineration plants to understand the formation reactions of polychlorinated dibenzo-p-dioxin and furans (PCDD/Fs) and related bromine compounds that were chlorinated–brominated dibenzodioxins and furans (PXDD/Fs) and polybrominated dibenzo-p-dioxin and furans (PBDD/Fs). The results obtained were as follows: The formation of PCDD/Fs was clearly shown, and fly ash containing abundant carbon matter had a significant potential for de novo synthesis. The homologous distribution change apparently showed that the formation of PXDD/Fs occurred from the substitution of a bromine atom with a chlorine atom in the PCDD/F molecules. This suggests that PXDD/Fs are usually formed with PCDD/Fs on the ash. PBDD/Fs might be formed from any reaction mechanism different from that of PXDD/Fs. The existence of carbonaceous matters always does not mean the potential formation of PCDD/Fs. However, any addition of catalytic copper may influence the nature of ash to increase the formation potential. The findings suggest that there are many instances that result in the unintended production of trace hazardous pollutants in the incineration process and show that careful and sophisticated control is required to prevent the formation of pollutants. [Copyright &y& Elsevier]

The reaction thermodynamic and kinetic equations for the non-reversible reactions are established. The enthalpy change of formation reaction of manganese(II) histidine (His) complex in water has been determined by microcalorimetry, using manganese chloride with L-a-histidine at 298.15-323.15 K. The standard enthalpy of formation of Mn(His)22+(aq) has been calculated. On the basis of experimental and calculated results, three thermodynamics parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constants, along with three kinetic parameters (the apparent activation energies, the pre-exponential constant and the reaction order) are obtained. The results show that the reaction easily takes place over the studied temperature range. The solid complex Mn(His)2Cl2·4H2O was prepared and characterized by IR and TG-DTG. [ABSTRACT FROM AUTHOR]

The enthalpy change of formation reaction of cobalt(II) histidine (His) complex in water has been determined by a microcalorimeter, using cobalt chloride with L-α-histidinein the temperature range of 25~50°C. On the basis of experimental and calculated results, three thermodynamics parameters (the activation enthalpies, the activation entropies, the activation free energies), the rate constant, three kinetic parameters (the activation energies, the pre-exponential constant and the reaction order) are obtained. The results show that the titled reaction easily took place in the studied temperature. [ABSTRACT FROM AUTHOR]

A highly diastereoselective synthesis of the C29–C41 fragment of karlotoxin 2 (KmTx2) is described by employing regio-selective epoxide opening, our own developed domino isomerization followed by C–O and C–C bond formation reaction and chelation-controlled Grignard reaction as key steps. The synthesis involves installation of seven stereocenters present in the C29–C41 fragment of karlotoxin 2. [ABSTRACT FROM AUTHOR]

• The standard molar thermodynamic properties of formation of HCl was studied. • A closed-form expression for the vibration part of the molecular partition function is used. • The internal interaction was modeled by an improved Manning-Rosen oscilator. • Results were compared with the harmonic and an-harmonic oscillator models. In this work, the thermodynamic properties of the formation reaction of hydrogen chloride from the reactants chlorine and hydrogen are studied by employing the developed Manning-Rosen potential. A closed-form expression for the vibration part of the molecular partition function is used to calculate the vibrational contribution of the thermodynamic properties. The results obtained are used to investigate the change in the thermodynamic functions for the formation reaction of HCl at a high temperature range. The predicted results are compared with the ones obtained from the other theoretical approaches based on the harmonic and an-harmonic oscillator models. [ABSTRACT FROM AUTHOR]