Synthesis, characterization and photocatalytic properties of novel zinc germanate nano-materials

We report the first instance of a hydrothermal synthesis of zinc germanate (Zn₂GeO₄) nano-materials having a variety of morphologies and photochemical properties in surfactant, template and catalyst-free conditions. A systematic variation of synthesis conditions and detailed characterization using X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy and small angle X-ray scattering led to a better understanding of the growth of these particles from solution. At 140 °C, the zinc germanate particle morphology changes with pH from flower-shaped at pH 6.0, to poly-disperse nano-rods at pH 10 when the Zn to Ge ratio in the synthesis solution is 2. When the Zn to Ge ratio is reduced to 1.25, mono-disperse nano-rods could be prepared at pH 7.5. Nanorod formation is also independent of the addition of cetyltrimethylammonium bromide (CTAB), in contrast to previous reports. Photocatalytic tests show that Zn₂GeO₄ nano-rods (by weight) and flower shaped (by surface area) are the most active for methylene blue dye degradation among the synthesized zinc germanate materials.     

Pyrochlore “dynamic spin-ice” Pr2Sn2O7 and monoclinic Pr2Ti2O7: A comparative temperature-dependent Raman study

Here we report a temperature-dependent Raman study of the pyrochlore “dynamic spin-ice” compound Pr₂Sn₂O₇ and compare the results with its non-pyrochlore (monoclinic) counterpart Pr₂Ti₂O₇. In addition to phonon modes, we observe two bands associated with electronic Raman scattering involving crystal field transitions in Pr₂Sn₂O₇ at ∼135 and 460 cm⁻¹ which couple strongly to phonons. Anomalous temperature dependence of phonon frequencies that are observed in pyrochlore Pr₂Sn₂O₇ are absent in monoclinic Pr₂Ti₂O₇. This, therefore, confirms that the strong phonon-phonon anharmonic interactions, responsible for the temperature-dependent anomalous behavior of phonons, arise due to the inherent vacant sites in the pyrochlore structure.     

HPLC method development and validation of cytotoxic agent phenyl‐heptatriyne in Bidens pilosa with ultrasonic‐assisted cloud point extraction and preconcentration

Extraction and pre‐concentration of a bioactive marker compound, phenyl‐1,3,5‐heptatriyne from Bidens pilosa, prior to HPLC has been demonstrated using both organic and ecofriendly solvents. Non‐ionic surfactants, viz. Triton X‐100, Triton X‐114 and Genapol X‐80, were used for extraction. No back‐extraction or liquid chromatographic steps were required to remove the target phytochemical from the surfactant‐rich extractant phase. The optimized cloud point extraction procedure has been shown to be a potentially useful methodology for the preconcentration of the target analyte, with a preconcentration factor of 4–99. Moreover, the method is simple, sensitive, rapid and consumes lesser solvent than traditional methods. An isocratic chromatographic separation and quantitation was accomplished on a C₁₈ column with acetonitrile–acidified aqueous as mobile phase at a flow rate of 1.0 mL/min, UV detection at 254 nm and specificity with photo diode‐array detector (PDA) and MS. Under the optimum experimental conditions recovery was satisfactory (99.18–100.33%) without interference from the surfactant. The method seems to be reliable with intraday precision and interday precision below 2.0%. Good linearity was obtained in the working range from 7.5 to 30 µg/mL with correlation coefficient >0.99. The limits of detection and quantitation were 1.84 and 6.13 µg/mL, respectively. The method was validated following international guidelines and successfully applied for quantitative assays of cytotoxic compound phenyl‐1,3,5‐heptatriyne in Bidens pilosa. Copyright © 2010 John Wiley & Sons, Ltd.     

Associative and segregative phase separations of poly(N-tert-butylacrylamide)/poly(acrylic acid) mixtures. Effect of solvent

Poly(N-tert-butylacrylamide) (PNtBAm) and poly(acrylic acid) (PAA) form interpolymer complexes in 1- and 2-propanol, blend in ethanol, whereas a segregative phase separation is observed when using methanol as solvent as shown by Fourier transform infrared (FTIR) spectrometry and elemental analysis studies. The composition of PNtBAm/PAA complexes has been determined. Thermal studies demonstrated that all complexes show unique glass transition temperatures, higher than those of the polymer components. Complexation of PAA with PNtBAm results in an improvement of its thermal stability. Solvent effects and specific interactions in the system PNtBAm/PAA have been studied by FTIR, revealing that differences in the polymer–solvent interactions are a decisive factor governing complex formation in solution.     

Amorphous structure heat: Heats of solution versus temperature for polysulfone in o-dichlorobenzene

The data presented for polysulfone in o-dichlorobenzene support previous observations on other systems in which the heats of solution decrease linearly with increasing temperature of measurement. Consistent with similar measurements on polycarbonate and polyphenylene oxide, a dramatic slope change from 0.078 cal/g-C° below 120°C to 0.019 cal/g-C° above 120°C occur for the data on polysulfone. The source of these heats is due primarily to the enthalpy difference between the solid polymer and its corresponding liquid amorphous state at the measurement temperature since the heats of mixing are rationalized to be small.     

Constructing a composite indicator with multiplicative aggregation under the objective of ranking alternatives

Composite indicators (CIs), constructed on the basis of the ‘benefit of the doubt’ criterion, are characterized by endogenously determined vectors of weights. In this paper, a new procedure to construct CIs is proposed in an attempt to overcome the main weakness of this family of procedures: the determination of an individual weighting vector for each alternative, which makes comparisons between alternatives difficult and the existence of multiple ties. A new procedure is proposed which, while maintaining the essence of DEA-inspired procedures determines a common weighting vector to evaluate the complete set of alternatives and includes the discrimination between alternatives as an objective of the procedure.     

Bulk universality for Wigner matrices

We consider N × N Hermitian Wigner random matrices H where the probability density for each matrix element is given by the density ν(x) = e^?U(x). We prove that the eigenvalue statistics in the bulk are given by the Dyson sine kernel provided that U ∈ C⁶( \input amssym $\Bbb R$ ) with at most polynomially growing derivatives and ν(x) ≥ Ce^?C|x| for x large. The proof is based upon an approximate time reversal of the Dyson Brownian motion combined with the convergence of the eigenvalue density to the Wigner semicircle law on short scales. © 2010 Wiley Periodicals, Inc.     

Structural and spectroscopic studies on 2-pyranones

Experimental methods of infrared, Raman and electronic absorption spectroscopy and DFT calculations using B3LYP functionals and 6-31G** and 6-311++G** basis sets have been used to understand the structural and spectral characteristics of 2-pyranones, 6-phenyl-4-methylsulfanyl-2-oxo-2H-pyran and 6-phenyl-4-methylsulfanyl-2-oxo-2H-pyran-3-carbonitrile in the electronic ground (S₀) and first excited (S₁) states. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). Based on TD-DFT calculations using 6-31+G**5D basis set, an assignment of absorption peaks in the UV–VIS region has been suggested. The S₁ state is found to be a ¹(π,π*) state. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra and calculated frequency and intensity of the vibrational bands and potential energy distribution over the internal coordinates. Characteristic vibrational bands of the 2-pyranone ring and methylsulfanyl and carbonyl groups have been identified.