Synthesis and structural characterization of isolable phosphine coinage metal ��-complexes

The chemical community has recently witnessed a dramatic increase in the application of cationic gold(I)-phosphine complexes as homogeneous catalysts for organic synthesis. The majority of gold(I)-catalyzed reactions rely on nucleophilic additions to carbon–carbon multiple bonds, which have been activated by coordination to a cationic gold(I) catalyst. However, structural evidence for coordination of cationic gold(I) complexes to alkynes has been limited. Here, we report the crystal structure of a gold(I)-phosphine η²-coordinated alkyne. Related Ag(I) and Cu(I) complexes have been synthesized for comparison. The crystallization of these complexes was enabled by tethering a labile alkyne ligand to a strongly coordinating triarylphosphine. This approach also proved applicable to crystallization of the first gold(I)-phosphine η²-coordinated alkene.     

The influence of NH3-attaching on the NMR and NQR parameters in the (6,0) zigzag single-walled BPNTs: a density functional study

The structural properties, NMR and NQR parameters in the pristine and NH₃-attached (6,0) zigzag BPNTs model were calculated using DFT methods in order to evaluate the influence of NH₃-attached on the (6,0) zigzag BPNTs for the first time. Geometry optimizations were carried out at the BLYP, B3LYP/6-31G^* levels of theory using the Gaussian 03 program suites. The chemical shielding (CS) parameters for the sites of various ¹¹B and ³¹P atoms and quadrupole coupling constant (C_Q), and asymmetry parameter (η_Q) at the sites of various ¹¹B nuclei were calculated in the pristine and the NH₃-attached (6,0) zigzag BPNTs model. The values of dipole moments detect notable changes due to direct effect of the NH₃-attached on the BPNTs; however, the tip diameters are slightly significant changed in comparison to the pristine models and the gap energies of the NH₃-attached BPNT do not detect any changes in comparison to the pristine model. For the NH₃-attached BPNT, the NMR values for the ¹¹B₁₄ atom which is directly bonded to the NH₃ molecule and the ³¹P atoms that directly bonded to the ¹¹B₁₄ atom in the BPNT are significantly changed. CS^I parameters of the atoms are increased whereas CS^A parameters of the atoms are decreased. The NQR results showed that in BPNTs, the B atoms at the edges of nanotubes play dominant roles in determining the electronic behaviors of BPNTs and the average value of C_Q (¹¹B) and η_Q for the NH₃-attached (6,0) zigzag BPNTs is further in comparison to the pristine model.     

A cysteine-selective fluorescent probe for the cellular detection of cysteine

A series of coumarin fluorophores (1-3), each bearing a double bond conjugated quinoline unit that can undergo a Michael-type reaction with thiol-containing compounds, is reported. These systems, designed to provide so-called turn-on changes in fluorescence response when exposed to thiols, act as fluorescent chemical sensors for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). In the case of 1, selectivity for Cys over Hcy and GSH is observed, both in terms of analyte-induced signal enhancement and response time. On the basis of fluorescence spectroscopic analyses, DFT calculations, and pH dependent studies this substrate selectivity is ascribed to steric interactions between the substituents on the quinolone units present in 1 and the targeted thiols, as well as to the comparatively lower pK_a value of Cys relative to Hcy and GSH. In aqueous solution, probe 1 was found capable of detecting Cys with a detection limit of 10⁻⁷ m. This system was successfully applied to the fluorescence imaging of intracellular Cys in HepG2 cells.     

Successful prediction of a model pharmaceutical in the fifth blind test of crystal structure prediction

The range of target structures in the fifth international blind test of crystal structure prediction was extended to include a highly flexible molecule, (benzyl-(4-(4-methyl-5-(p-tolylsulfonyl)-1,3-thiazol-2-yl)phenyl)carbamate, as a challenge representative of modern pharmaceuticals. Two of the groups participating in the blind test independently predicted the correct structure. The methods they used are described and contrasted, and the implications of the capability to tackle molecules of this complexity are discussed.     

Nocturnal phantom shock cessation with zolpidem

A 77 year old man with a biventricular ICD-pacemaker complained of painful, electric jolts disturbing him nightly from sleep. Extensive work-up including device interrogation revealed no defibrillations or arrhythmia, and he was subsequently diagnosed with phantom shocks (PS). His nightly PS symptoms terminated after starting zolpidem 10 mg each night. To date, literature review reveals fifteen articles reporting 163 phantom shock (PS) cases. PS affects 5–9% of ICD recipients. Risk factors include psychiatric disease, atrial fibrillation, NYHA functional status III or greater, prior shock storm, and intraoperative awareness during ICD placement, with defibrillation threshold testing. This report describes a successful PS intervention, and reviews the current knowledge available in the pathophysiology and treatment of PS.     

The pristine BN nanocone as a toluene gas sensor: A computational study

Calculations based on the density functional theory have been used to investigate the reactivity of boron nitride nanocones (BNNCs) to toluene gas. The adsorption energy for the toluene gas was calculated about ?19.67 kcal/mol and based on this parameter, BNNCs are promising compounds for the detection of toluene gas. Furthermore, after adsorption of toluene gas the HOMO-LUMO gap of BNNCs was decrease significantly (from 4.59 to 3.25 eV), as a results, the electrical conductivity has also increased and it indicates that the BNNCs could be an appropriate electrical sensor for toluene gas. In addition, the work function of BNNCs is influenced by the toluene gas adsorption, which substantially alters the field emission electron current from its surface and reveals that it could also be a work function based sensor for the detection of toluene. The BNNCs have also the advantage of short recovery time about 3.10 ms for desorption of toluene gas.     

Two-Dimensional ZnS/SnS2 Heterojunction as a Direct Z-Scheme Photocatalyst for Overall Water Splitting: A DFT Study

Direct Z-scheme photocatalysts have attracted extensive attention due to their strong redox ability and efficient separation of photogenerated electron-hole pairs. In this study, we constructed two types of ZnS/SnS₂ heterojunctions with different stacking models of ZnS and SnS₂ layers, and investigated their structures, stabilities, and electronic and optical properties. Both types of heterojunctions are stable and are direct Z-scheme photocatalysts with band gaps of 1.87 eV and 1.79 eV, respectively. Furthermore, their oxidation and reduction potentials straddle the redox potentials of water, which makes them suitable as photocatalysts for water splitting. The built-in electric field at the heterojunction interface improves the separation of photogenerated electron-hole pairs, thus enhancing their photocatalytic efficiency. In addition, ZnS/SnS₂ heterojunctions have higher carrier mobilities and light absorption intensities than ZnS and SnS₂ monolayers. Therefore, the ZnS/SnS₂ heterojunction has a broad application prospect as a direct Z-scheme visible-light-driven photocatalyst for overall water splitting.     

Water Splitting on Multifaceted SrTiO3 Nanocrystals: Calculations of Raman Vibrational Spectrum

Various photocatalysts are being currently studied with the aim of increasing the photocatalytic efficiency of water splitting for production of hydrogen as a fuel and oxygen as a medical gas. A noticeable increase of hydrogen production was found recently experimentally on the anisotropic faces (facets) of strontium titanate (SrTiO₃, STO) nanoparticles. In order to identify optimal sites for water splitting, the first principles calculations of the Raman vibrational spectrum of the bulk and stepped (facet) surface of a thin STO film with adsorbed water derivatives were performed. According to our calculations, the Raman spectrum of a stepped STO surface differs from the bulk spectrum, which agrees with the experimental data. The characteristic vibrational frequencies for the chemisorption of water derivatives on the surface were identified. Moreover, it is also possible to distinguish between differently adsorbed hydrogen atoms of a split water molecule. Our approach helps to select the most efficient (size and shape) perovskite nanoparticles for efficient hydrogen/oxygen photocatalytic production.     

Effects of Mono-Vacancies of Oxygen and Manganese on the Properties of the MnO2/Graphene Heterostructure

The effects of the monovacancies of oxygen (V_O) and manganese (V_Mn) on the structural and electronic properties of the 1T–MnO₂/graphene heterostructure are investigated, within the framework of density functional theory (DFT). We found that the values of the formation energy for the heterostructure without and with vacancies of V_O and V_Mn were −20.99 meVÅ2, −32.11meVÅ2, and −20.81 meVÅ2, respectively. The negative values of the formation energy indicate that the three heterostructures are energetically stable and that they could be grown in the experiment (exothermic processes). Additionally, it was found that the presence of monovacancies of V_O and V_Mn in the heterostructure induce: (a) a slight decrease in the interlayer separation distance in the 1T–MnO₂/graphene heterostructure of ~0.13% and ~1.41%, respectively, and (b) a contraction of the (Mn−O) bond length of the neighboring atoms of the V_O and V_Mn monovacancies of ~2.34% and ~6.83%, respectively. Calculations of the Bader charge for the heterostructure without and with V_O and V_Mn monovacancies show that these monovacancies induce significant changes in the charge of the first-neighbor atoms of the V_O and V_Mn vacancies, generating chemically active sites (locales) that could favor the adsorption of external atoms and molecules. From the analysis of the density of state and the structure of the bands, we found that the graphene conserves the Dirac cone in the heterostructure with or without vacancies, while the 1T–MnO₂ monolayer in the heterostructures without and with V_O monovacancies exhibits half-metallic and magnetic behavior. These properties mainly come from the hybridization of the 3d–Mn and 2p–O states. In both cases, the heterostructure possesses a magnetic moment of 3.00 μ_β/Mn. From this behavior, it can be inferred the heterostructures with and without V_O monovacancies could be used in spintronics.     

Effect of Boron Doping on the Interlayer Spacing of Graphite

Boron-doped graphite was prepared by the heat treatment of coke using B₄C powder as a graphitization catalyst to investigate the effects of the substitutional boron atoms on the interlayer spacing of graphite. Boron atoms can be successfully incorporated into the lattice of graphite by heat treatment, resulting in a reduction in the interlayer spacing of graphite to a value close to that of ideal graphite (0.3354 nm). With an increase in the catalyst mass ratio, the content of substituted boron in the samples increased significantly, causing a decrease in the interlayer spacing of the boron-doped graphite. Density functional theory calculations suggested that the effects of the substitutional boron atoms on the interlayer spacing of the graphite may be attributed to the transfer of Π electrons between layers, the increase in the electrostatic surface potential of the carbon layer due to the electron-deficient nature of boron atoms, and Poisson contraction along the c-axis.