Solid‐phase preconcentration and determination of mercury(II) using activated carbon in drinking water by X‐ray fluorescence spectrometry

A novel and simple method was developed for the preconcentration and determination of mercury(II) from hydrochloric acid solutions through their adsorption on Aliquat 336 (tri‐octylmethylammonium chloride)‐activated carbon. The determinations were made directly on the solid by X‐ray fluorescence spectrometry, which had the advantage of eliminating the step of elution of the mercury retained. This preconcentration system enabled the determination of Hg(II) in drinking water samples at µg l^?1 levels. A 1700‐fold enrichment factor was obtained. The described methodology showed excellent reproducibility, accuracy, and detection limits improvement by eliminating the step of elution of the analyte, replacing those methods based on cold vapor generation, reducing reagent consumption, and handling of samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Dilaton Quantum Cosmology with a Schrödinger-like Equation

A quantum cosmological model with radiation and a dilaton scalar field is analyzed. The Wheeler–DeWitt equation in the minisuperspace induces a Schrödinger equation, which can be solved. An explicit wavepacket is constructed for a particular choice of the ordering factor. A consistent solution is possible only when the scalar field is a phantom field. Moreover, although the wavepacket is time-dependent, a Bohmian analysis allows to extract a bouncing behavior for the scale factor.     

Boron Difluoride Curcuminoid Fluorophores with Enhanced Two‐Photon Excited Fluorescence Emission and Versatile Living‐Cell Imaging Properties

The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time‐dependent (TD)‐DFT calculations confirm the charge‐transfer character of the second lowest‐energy transition band and ascribe the lowest energy band to a “cyanine‐like” transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV–visible absorption and fluorescence spectra. Two‐photon‐excited fluorescence and Z‐scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two‐photon cross section, reaching 5000 GM, with predominant two‐photon absorption from the S₀–S₂ charge‐transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two‐photon active band for the curcuminoid derivatives has the same intramolecular charge‐transfer character and therefore arises from a dipolar structure. Overall, this structure–relationship study allows the optimization of the two‐photon brightness (i.e., 400–900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission.     

NMR study of the comonomer effect in metallocene poly(propylene‐co‐1‐pentene) copolymers synthesized at low temperature

The influence of the comonomer in the synthesis of poly(propylene‐co ?1‐pentene) copolymers, with rac‐(dimethylsilylbis(1‐indenyl))ZrCl₂/Methylaluminoxane at low temperature, has been studied. Changes in the catalyst activity and molecular weight have been analyzed as a function of copolymer composition, and associated with both content and nature of chain defects. The thorough characterization of chain‐end double bonds by means of the ¹H NMR technique highlights the particular chain termination pathway, which underlies the so‐called comonomer effect. A specific termination mechanism is proposed based on the preferential regio‐irregular interaction of the active site with 1‐pentene molecules, instead of the one related to the β‐H atom of the last regular inserted unit, either propene or 1‐pentene. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 843–854     

Platinum trans‐Bis(borirene) Complexes Displaying Coplanarity and Communication Across a Platinum Metal Center

Ambient‐temperature photolysis of the aminoborylene complex [(OC)₅Cr?B?N(SiMe₃)₂] in the presence of a series of trans‐bis(alkynyl)platinum(II) precursors of the type trans‐[Pt(CCAr)₂(PEt₃)₂] (Ar=Ph, p‐C₆H₄OMe, and p‐C₆H₄CF₃) successfully leads to twofold transfer of the borylene moiety [ : B?N(SiMe₃)₂] onto the alkyne functionalities. The alkynyl precursors and resultant bis(borirene)platinum(II) complexes formed are of the type trans‐[Pt(B{?N(SiMe₃)₂}C?CAr)₂(PEt₃)₂] (Ar=Ph, p‐C₆H₄OMe, and p‐C₆H₄CF₃). These species have all been successfully characterized by NMR, IR, and UV/Vis spectroscopy as well as by elemental analysis. Single‐crystal X‐ray diffraction has verified that these trans‐bis(borirene)platinum(II) complexes display coplanarity between the twin three‐membered rings across the platinum core in the solid state and stand as the first examples of coplanar conformations of twin borirene systems. These complexes were modeled using density functional theory (DFT), providing information helpful in determining the ability of the transition metal core to interact with each individual borirene ring system and allowing for the observed coplanarity of these rings in the solid state. This proposed transition metal interaction with the twin borirene systems is manifested in the electronic characterization of these borirene species, which display divergent photophysical UV/Vis spectroscopic profiles compared to a previously published mono(borirene)platinum(II) complex.     

Reduction of Organoselenium and Tellurium Halides and Oxides with Thiourea Dioxide

Aryltellurium trihalides, arylselenium trihalides, organyltellurium and selenium dichlorides and organylselenoxides and telluroxides were reduced in high yield to the corresponding diaryl ditellurides and selenides with thiourea dioxide in a two phase system.