Synthesis and Trapping of Iminoboranes by M=B/C=N Bond Metathesis

Although the metathesis of metal–boron double bonds with elemental chalcogenides is an established process, no similar reactivity has been observed with element–nitrogen bonds. Such a reaction would provide a new route to iminoborane compounds (RB≡NR′), which have recently experienced renewed synthetic interest. Herein, we present the first observation of M=B/C=N metathesis reactions, which led to the isolation of a stable iminoborane in addition to further iminoborane cycloaddition products.     

Imparting Multifunctionality by Utilizing Biporosity in a Zirconium-Based Metal–Organic Framework

In this work, we have synthesized nanocomposites made up of a metal–organic framework (MOF) and conducting polymers by polymerization of specialty monomers such as pyrrole (Py) and 3,4-ethylenedioxythiophene (EDOT) in the voids of a stable and biporous Zr-based MOF ( UiO-66 ). FTIR and Raman data confirmed the presence of polypyrrole ( PPy ) and poly3,4-ethylenedioxythiophene ( PEDOT ) in UiO-66-PPy and UiO-66-PEDOT nanocomposites, respectively, and PXRD data revealed successful retention of the structure of the MOF. HRTEM images showed successful incorporation of polymer fibers inside the voids of the framework. Owing to the intrinsic biporosity of UiO-66 , polymer chains were observed to selectively occupy only one of the voids. This resulted in a remarkable enhancement (million-fold) of the electrical conductivity while the nanocomposites retain 60–70 % of the porosity of the original MOF. These semiconducting yet significantly porous MOF nanocomposite systems exhibited ultralow thermal conductivity. Enhanced electrical conductivity with lowered thermal conductivity could qualify such MOF nanocomposites for thermoelectric applications.     

Stannylenes: structures, electron affinities, ionization energies, and singlet-triplet gaps of SnX2/SnXY and XSnR/SnR2/RSnR′ species (X; Y = H, F, Cl, Br, I, and R; R' = CH3, SiH3, GeH3, SnH3)

Systematic computational studies of stannylene derivatives SnX(2)/SnXY and XSnR/SnR(2)/RSnR' were carried out using density functional theory. The basis sets used for H, F, Cl, Br, C, Si, and Ge atoms are of double-ζ plus polarization quality with additional s- and p-type diffuse functions, denoted DZP++. For the iodine and tin atoms, the Stuttgart-Dresden basis sets, with relativistic small-core effective core potentials (ECP), are used. All geometries are fully optimized with three functionals (BHLYP, BLYP, and B3LYP). Harmonic vibrational wavenumber analyses are performed to evaluate zero-point energy corrections and to determine the nature of the stationary points located. Predicted are four types of neutral-anion separations, plus adiabatic ionization energies (E(IE)) and singlet-triplet energy gaps (ΔE(S-T)). The dependence of all three energetic properties upon choice of substituent is remarkably strong. The EA(ad(ZPVE)) values (eV) obtained with the B3LYP functional range from 0.70 eV [Sn(CH(3))(2)] to 2.36 eV [SnI(2)]. The computed E(IE) values lie between 7.33 eV [Sn(SnH(3))(2)] and 11.15 eV [SnF(2)], while the singlet-triplet splittings range from 0.60 eV [Sn(SnH(3))(2)] to 3.40 eV [SnF(2)]. The geometries and energetics compare satisfactorily with the few available experiments, while most of these species are investigated for the first time. Some unusual structures are encountered for the SnXI(+) (X = F, Cl, and Br) cations. The structural parameters and energetics are discussed and compared with the carbene, silylene, and germylene analogues.     

Synthesis, structural and optical characterization of nanocrystalline ZnS:Cu embedded in silica matrix

The synthesis of Cu doped ZnS nanoparticles inside the pore of an inorganic silica gel matrix is presented. The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). X-ray diffraction pattern reveals the crystalline wurtzite phase of ZnS. The existence of silica gel in modeling morphologies of the nanoparticles was characterized using Fourier transform infrared (FTIR) spectrometer. Thickness of the silica shell was also calculated. UV- absorption spectrum shows the appearance of an absorption peak at 273 nm which confirms the blue shift as compared to that of bulk ZnS. The photoluminescence (PL) emission spectrum of the sample showed a broad band in the range 465-510 nm due to the transition from the conduction band edge of ZnS nanocrystals to the acceptor like t₂ state of Cu.     

“Pointsource” Delivery of a Photosensitizer Drug and Singlet Oxygen: Eradication of Glioma Cells In Vitro

We describe a pointsource sensitizer‐tipped microoptic device for the eradication of glioma U87 cells. The device has a mesoporous fluorinated silica tip which emits singlet oxygen molecules and small quantities of pheophorbide sensitizer for additional production of singlet oxygen in the immediate vicinity. The results show that the device surges in sensitizer release and photokilling with higher rates about midway through the reaction. This was attributed to a self‐amplified autocatalytic reaction where released sensitizer in the extracellular matrix provides positive feedback to assist in the release of additional sensitizer. The photokilling of the glioma cells was analyzed by global toxicity and live/dead assays, where a killing radius around the tip with ~0.3 mm precision was achieved. The implication of these results for a new PDT tool of hard‐to‐resect tumors, e.g. in the brain, is discussed.     

Phosphine-free Suzuki cross-coupling reaction: a mild and selective method for the carbon–carbon bond formation in aqueous tea extract

A mild and selective protocol has been developed for the palladium-catalyzed phosphine-free Suzuki cross-coupling reaction of aryl bromides with arylboronic acids in aqueous tea extract at room temperature. It is noteworthy that the aqueous tea extract plays an important role in the reaction, and various functional groups are tolerated under the optimized conditions. The reactions proceeded with very good chemoselectivity in favor of the bromo instead of the chloro group even at higher temperatures. Furthermore, this protocol could be applied to the cross-coupling of 4-bromoindole without protecting the base sensitive amine group with arylboronic acids in moderate to excellent yields.     

Sulfinyl group as an intramolecular nucleophile: synthesis of bromohydrins from beta-methyl-gamma,delta-unsaturated sulfoxides with high 1,2-asymmetric induction

Bromohydrins have been prepared from beta-methyl-gamma,delta-unsaturated sulfoxides with high regio- and stereoselectivity. The reaction proceeds via neighboring group participation of the sulfinyl moiety with inversion of sulfoxide configuration as proven by an (18)O labeling study and X-ray crystallography.