Syntheses of Molybdenum and Tungsten Imido Alkylidene Complexes that Contain a Bidentate Oxo/Thiolato Ligand

3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl[1,1′-biphenyl]-2-ol (H₂[^tBu₄OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H₂[^tBu₄OS] to Mo(NAr)(CHCMe₂Ph)(2,5-dimethylpyrrolide)₂ led to formation of Mo(NAr)(CHCMe₂Ph)[^tBu₄OS], which was trapped with PMe₃ to give Mo(NAr)(CHCMe₂Ph)[^tBu₄OS](PMe₃) ( 1 (PMe₃)). An X-ray crystallographic study of 1 (PMe₃) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1 (PMe₃)_A and 1 (PMe₃)_B are disordered. Mo(NAd)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 2 (PMe₃); Ad=1-adamantyl) and W(NAr)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 3 (PMe₃)) were prepared using analogous approaches. 1 (PMe₃) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(^tBu₄OS)(C₂H₄) ( 4 ) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for the ethylene ligand in 4 are like those found for bisalkoxide ethylene complexes of the same general type. Complex 1 (PMe₃) in the presence of one equivalent of B(C₆F₅)₃ catalyzes the homocoupling of 1-decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature. 1 (PMe₃), 2 (PMe₃), and 3 (PMe₃) all catalyze the ROMP of rac-endo,exo-5,6-dicarbomethoxynorbornene (rac-DCMNBE) in the presence of B(C₆F₅)₃, but the polyDCMNBE that is formed has a random structure.     

Convex fuzzy mapping with differentiability and its application in fuzzy optimization

The concepts of differentiability, convexity, generalized convexity and minimization of a fuzzy mapping are known in the literature. The purpose of this present paper is to extend and generalize these concepts to fuzzy mappings of several variables using Buckley–Feuring approach for fuzzy differentiation and derive Karush–Kuhn–Tucker condition for the constrained fuzzy minimization problem.     

Solid state white light emitting systems based on CeF3: RE3+ nanoparticles and their composites with polymers

A series of doped CeF(3): RE(3+) (RE(3+): Tb(3+), Eu(3+) and Dy(3+)) nanoparticles were synthesized, with the aim of obtaining a white light emitting composition, by a simple polyol route at 160°C and characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. Uniformly distributed and highly water-dispersible rectangular nanoparticles (length ~15-20 nm, breadth ~5-10 nm) were obtained. The steady state and time resolved luminescence studies confirmed efficient energy transfer from the host to activator ions. Lifetime studies revealed that optimum luminescence is observed for 2.5 mol% Dy(3+) and 7.5 mol% Tb(3+). The energy transfer efficiencies (Ce(3+) to activators) were found to be 89% for CeF(3): Tb(3+) (7.5 mol%) nanoparticles and 60% for CeF(3): Dy(3+) (2.5 mol%) nanoparticles. Different concentrations of Tb(3+), Eu(3+) and Dy(3+) were doped to achieve a white light emitting phosphor for UV-based LEDs (light emitting diodes). Finally CeF(3), triply doped with 2.0 mol%Tb(3+), 4.5 mol% Eu(3+) and 3.5 mol% Dy(3+), was found to have impressive chromaticity co-ordinates, close to broad day light. The colloidal solutions of doped CeF(3) nanoparticles emitted bright green (Tb(3+)), blue (Dy(3+)) and white (triply doped) luminescence upon host excitation. Composites of poly methyl methacrylate (PMMA) and poly vinyl alcohol (PVA) were made with CeF(3): 5.0 mol%Tb(3+), CeF(3): 5.0 mol% Dy(3+) and triply doped white light emitting composition. The CeF(3)/PMMA (PVA) nanocomposite films, so obtained, are highly transparent (in the visible spectral range) and exhibit strong photoluminescence upon UV excitation.     

Surface functionalized silver nanoparticle conjugates: demonstration of uptake and release of a phototherapeutic porphyrin dye

A facile supramolecular approach to prepare surface functionalized silver nanoparticle conjugates has been established and their enhanced molecular recognition features have been explored to demonstrate the uptake and stimulus responsive release of a phototherapeutic porphyrin dye, the TMPyP.     

An easily accessible Re-based catalyst for the selective conversion of methanol: evidence for an unprecedented active site structure through combined operando techniques

Heterogeneous Re/SiO(2) catalysts prepared using a one pot sol-gel synthesis were found to display high activity in the direct, selective methanol conversion to methylal, which is correlated to an unprecedented rhenium oxide structure.     

Single‐Cell Investigations of Silver Nanoparticle–Bacteria Interactions

Interaction of bacteria with citrate‐reduced silver nanoparticles (AgNPs) of size 25 nm ± 8.5 nm is studied using Raman spectroscopy in conjunction with plasmon resonance imaging of single bacterial cells. Distribution of isolated nanoparticles (NPs) inside Escherichia coli (ATCC 25922; E. coli) is observed by hyperspectral imaging (HSI) as a function of incubation time. Time‐dependent degradation of bacterial DNA upon incubation of AgNPs with E. coli is proven by Raman spectroscopic studies. While attachment of NPs is evident in HSI, molecular changes are evident from the surface‐enhanced Raman spectra of adsorbed DNA and its fragments. Distinct enhancement of DNA features is observed upon interaction of AgNPs and the number of such distinct features increases with incubation time, reaches a maximum, and decreases afterwards. This systematic interaction of DNA with the NPs system and its gradual chemical evolution is proven by investigating isolated plasmid DNA. A comparative Raman study with silver ions has shown that DNA features are observable only when bacteria are incubated with AgNPs. Energetics of interaction examined with microcalorimetry suggests the exothermicity of ?1.547 × 10¹⁰ cal mol^?1 for the NP–bacteria system. Specific interaction of AgNPs with exocyclic nitrogen present in the bases, adenine, guanine, and cytosine, leads to the changes in DNA.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Probing of surface Eu ions present in ZnO:Eu nanoparticles by covering ZnO:Eu core with Y2O3 shell: Luminescence study

Eu³⁺ doped ZnO nanoparticles are known to have significance extent of surface Eu³⁺ ions due to a large difference in ionic radii. Effect of such Eu³⁺ ions on the luminescence properties of ZnO:Eu nanoparticles has been understood from the luminescence studies of ZnO:Eu nanoparticles covered with Y₂O₃ shell. Based on the asymmetric ratio of luminescence and extent of energy transfer, it is established that when ZnO:Eu nanoparticles are covered with Y₂O₃ shell, a part of Eu³⁺ ions present with ZnO:Eu core migrate to Y₂O₃ shell and occupy Y³⁺ lattice positions.     

Multinuclear solid-state NMR spectroscopy of doped lanthanum fluoride nanoparticles

Multinuclear solid-state NMR spectroscopy and powder X-ray diffraction (XRD) experiments are applied to comprehensively characterize a series of pure and lanthanide-doped LaF3 nanoparticles (NPs) that are capped with di-n-octadectyldithiophosphate ligands (Ln3+ = diamagnetic Y3+ and Sc3+ and paramagnetic Yb3+ ions), as well as correlated bulk microcrystalline materials (LaF3, YF3, and ScF3). Solid-state 139La and 19F NMR spectroscopy of bulk LaF3 and the LaF3 NPs reveal that the inorganic core of the NP retains the LaF3 structure at the molecular level; however, inhomogeneous broadening of the NMR powder patterns arises from distributions of 139La and 19F NMR interactions, confirming a gradual change in the La and F site environments from the NP core to the surface. 139La and 19F NMR experiments also indicate that low levels (5 and 10 mol %) of Ln3+ doping do not significantly change the LaF3 structure in the NP core. Similar doping levels of paramagnetic Yb3+ ions severely broaden 19F resonances, but only marginally effect 139La powder patterns, suggesting that the dopant ions are uniformly distributed throughout the NP core and occupy vacant La sites. Measurements of 139La T1 and T2 relaxation constants are seen to vary between the bulk material and NPs and between samples with diamagnetic and paramagnetic dopants. 45Sc NMR experiments confirm that the dopants are integrated into the La sites of the LaF3 core. Solid-state 1H and 31P magic-angle spinning (MAS) NMR spectra aid in probing the nature of the capping ligands and their interactions at the NP surface. 31P cross-polarization (CP)/MAS NMR experiments identify not only the dithiophosphate head groups but also thiophosphate and phosphate species which may form during NP synthesis. Finally, 19F-31P CP/MAS and 1H MAS experiments confirm that ligands are coordinated to the NP surface.     

Selective coulometric release of ions from ion selective polymeric membranes for calibration-free titrations

Coulometry belongs to one of the few known calibration-free techniques and is therefore highly attractive for chemical analysis. Titrations performed by the coulometric generation of reactants is a well-known approach in electrochemistry, but suffers from limited selectivity and is therefore not generally suited for samples of varying or unknown composition. Here, the selective coulometric release of ionic reagents from ion-selective polymeric membrane materials ordinarily used for the fabrication of ion-selective electrodes is described. The selectivity of such membranes can be tuned to a significant extent by the type and concentration of ionophore and lipophilic ion-exchanger and is today well understood. An anodic current of fixed magnitude and duration may be imposed across such a membrane to release a defined quantity of ions with high selectivity and precision. Since the applied current relates to a defined ion flux, a variety of non-redox active ions may be accurately released with this technique. In this work, the released titrant's activity was measured with a second ionophore-based ion-selective electrode and corresponded well with expected dosage levels on the basis of Faraday's law of electrolysis. Initial examples of coulometric titrations explored here include the release of calcium ions for complexometric titrations, including back titrations, and the release of barium ions to determine sulfate.