Dielectric analysis of tungsten-phosphoniobate 20A2O-30WO3 -10Nb2O5 -40P2O5 (A = Li, Na) glass-ceramics

New phosphate glasses of the quaternary system A₂O-Nb₂O₅-WO₃-P₂O₅, where X = Li and Na were prepared by the melt-quenching method. The introduction of WO₃ in the glass composition was based on the proposal of analysing the effect of the diminishing of the molar amount of the alkaline oxide and thus decreasing the molar ratio between network modifiers and network formers (M/F).In the present work we present the preparation of 20A₂O-30WO₃-10Nb₂O₅-40P₂O₅ (A = Li, Na) transparent glasses. These glasses were heat-treated in air, at 550 °C and 650 °C for 4 h. The structure of the obtained samples was studied by X-ray powder diffraction (XRD) and Raman spectroscopy and the morphology by scanning electron microscopy (SEM). The dc (σ_dc), ac (σ_ac) conductivity and dielectric spectroscopy measurements were performed in the function of the temperature and were related with the structural changes of the glass structures.     

Fluorines in tetrafluoromethane as halogen bond donors: Revisiting address the nature of the fluorine's σhole

It has been demonstrated in several instances that the 0.001 a.u. (electrons per bohr³) isodensity mapped electrostatic surface potentials on the fluorines along the outermost extensions of the C? F covalent bonds in tetrafluoromethane (CF₄) are entirely negative, they are thereby unable to engage in σ_hole bonding interactions with the negative sites on another molecules. In this study, we have attempted at resolving this controversy by performing various high‐level electronic structure calculations with Quadratic Configuration Integrals of Singles and Doubles QCISD(full), second‐order Møller–Plesset MP2(full), and 12 other Density Functional Theory (DFT) based functionals with and without dispersion corrections, all in conjunction with the 6–311++G(2d,2p) basis set. The results achieved with all the levels of theory utilized suggest that the fluorine's σ_holes in CF₄ are positive regardless of the 0.001‐, 0.0015‐, and 0.002‐a.u. isodensity mapped electrostatic surfaces examined. Because of this specific quality, the fluorines in CF₄ have displayed their capacities to form not only 1:1 clusters with the Lewis bases such as water (H₂O), ammonia (NH₃), formaldehyde (H₂C?O), hydrogen fluoride (HF), and hydrogen cyanide (HCN), but also 1:2, 1:3, and 1:4 clusters with the latter three randomly chosen Lewis bases. Various topological and nontopological features obtained from applications of atoms in molecules, noncovalent interaction reduced‐density‐gradient and natural bond orbital analytical tools reveal that the N···F, O···F, and F···F long‐ranged interactions developed between the interacting monomers in H₃N···FCF₃, H₂O···FCF₃, and (Y? D)_n=1–4···F₄C (Y? D = H₂C?O, HCN, and HF) are reminiscent of halogen bonding. The nonadditive cooperative and anticooperative energetic effects emerged on cluster formations are discussed in detail. © 2015 Wiley Periodicals, Inc.     

Electropolymerized Diphenylamine on Functionalized Multiwalled Carbon Nanotube Composite Film and Its Application to Develop a Multifunctional Biosensor

Diphenylamine (DPA) monomers have been electropolymerized on the amino‐functionalized multiwalled carbon nanotube (AFCNT) composite film modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The surface morphology of PDPA‐AFCNT was studied using field‐emission scanning electron microscopy (FE‐SEM). The interfacial electron transfer phenomenon at the modified electrode was studied using electrochemical impedance spectroscopy (EIS). The PDPA‐AFCNT/GCE represented a multifunctional sensor and showed good electrocatalytic behavior towards the oxidation of catechol and the reduction of hydrogen peroxide. Rotating‐disk electrode technique was applied to detect catechol with a sensitivity of 1360 µA mM^?1 cm^?2 and a detection limit of 0.01 mM. Amperometric determination of hydrogen peroxide at the PDPA‐AFCNT film modified electrode results in a linear range from 10 to 800 µM, a sensitivity of 487.1 µA mM^?1 cm^?2 and detection limit of 1 µM. These results show that the nano‐composite film modified electrode can be utilized to develop a multifunctional sensor.     

Energy‐Level Alignment for Single‐Molecule Conductance of Extended Metal‐Atom Chains

The use of single‐molecule junctions for various functions constitutes a central goal of molecular electronics. The functional features and the efficiency of electron transport are dictated by the degree of energy‐level alignment (ELA), that is, the offset potential between the electrode Fermi level and the frontier molecular orbitals. Examples manifesting ELA are rare owing to experimental challenges and the large energy barriers of typical model compounds. In this work, single‐molecule junctions of organometallic compounds with five metal centers joined in a collinear fashion were analyzed. The single‐molecule i–V scans could be conducted in a reliable manner, and the E_FMO levels were electrochemically accessible. When the electrode Fermi level (E_F) is close to the frontier orbitals (E_FMO) of the bridging molecule, larger conductance was observed. The smaller |E_F?E_FMO| gap was also derived quantitatively, unambiguously confirming the ELA. The mechanism is described in terms of a two‐level model involving co‐tunneling and sequential tunneling processes.     

Potentiostatic Electrochemical Preparation of Bismuth Nanoribbons and its Application in Biologically Poisoning Lead and Cadmium Heavy Metal Ions Detection

A simple and elegant electrochemical potentiostatic method has been described for the preparation of highly stable and electrocatalytically active bismuth nanoribbons (BiNRs). The average length and width of the BiNRs were of 100±50 nm and 10±5 µm, respectively. Here, disodium ethylene diamine tetraacetate was employed as a scaffold for the growth of BiNRs. The formation of BiNRs was confirmed by surface morphological, elemental and cyclic voltammetric analyses. The BiNRs exhibited excellent electrocatalytic ability in detecting biologically poisoning heavy metal ions such as lead and cadmium. The described BiNRs based sensor presents good linear dependence on lead and cadmium ions in the concentration range of 1–50 µg/L for both metal ions with a detection limit of 0.104 µg/L for lead and 0.145 µg/L for cadmium.     

Combining ligand-based and structure-based drug design approaches to study the structure-activity relationships of a β-carboline derivative series

In this study, we investigated the structure-activity relationships of a series of β-carboline alkaloid derivatives using the 2D-QSAR and molecular docking, in order to identify the mode of interaction between β-carboline derivatives and the PLK1 kinase, and determine their key substituents responsible for the cytotoxic activity. The obtained QSAR models using multiple linear regression (MLR) and partial least squares (PLS) methods showed a high correlation between the experimental activity and the predicted one by PLS (R²_PLS?=?0.82, q²?=?0.72) and MLR (R²_MLR?=?0.82, q²?=?0.72). An external dataset was used to test the extrapolation power of the models which resulted in an R²_PLS (EV)?=?0.76; RMSE?=?0.39. The 2D-QSAR analysis reveals that lipophilicity plays an important role in the cytotoxic activity of this group of β-carboline derivatives. Indeed, the molecular docking study into the active site of the polo-like kinase (PLK1) revealed that the most active ligand 57 shows higher binding energy and interacts, especially by H-bonds and hydrophobic interactions, with the active site of the PLK1 kinase. Consequently, the results obtained from the 2D-QSAR and docking studies provided a useful tool to design new and potent β-carboline derivatives as cytotoxic agents.     

Investigations of molybdenum redox phenomenon in Li2O-MoO3-P2O5 phosphate glasses

Two series of glasses have been prepared and characterized. One with varying Li₂O/P₂O₅ ratio and the other with varying Mo/P ratio. The relationship between the formation of the reduced state of molybdenum in phosphate glasses and the type of gases released in heating batch materials has been investigated. Effect of temperature on the valence state of molybdenum is also studied. Oxidation-reduction (redox) equilibrium of Mo⁵⁺/Mo⁶⁺ and environment of molybdenum (V) in these series of lithium-molybdenum-phosphate glasses are related to the glass composition and the possible structural units formation in the glasses.     

Separation and characterization of silybin, isosilybin, silydianin and silychristin in milk thistle extract by liquid chromatography-electrospray tandem mass spectrometry

A selective and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for the characterization of silymarin in commercially available milk thistle extract. In this study, six main active constituents, including silydianin, silychristin, diastereomers of silybin (silybin A and B) and diastereomers of isosilybin (isosilybin A and B) in silymarin, were completely separated on a YMC ODS-AQ HPLC column using a gradient mobile phase system comprised of ammonium acetate and methanol/water/formic acid. Identification and characterization of the major constituents were based not only on the product ion scan, which provided unique fragmentation information of a selected molecular ion, but also on the specific fragmentation of multiple reaction monitoring (MRM) data, which confirmed the retention times of LC chromatographic peaks. The method was applied in the analysis of human plasma samples in the presence of silymarin and appeared to be suitable for the pharmacokinetic studies in which the discrimination of silymarin constituents is essential.     

Thermal Study of A2O–(MoO3)2–P2O5 (A=Li, Na) Glasses

Alkali phosphomolybdate glasses have been prepared by quenching melted mixtures of P₂O₅, MoO₃ and A₂O(A=Li, Na). The composition dependence of the transition temperature of glasses belonging to ternary A₂O–(MoO₃)₂–P₂O₅ (A=Li, Na) systems is studied for several series of glasses corresponding to either a fixed A₂O rate or a constant Mo/P ratio. The interpretation of the results is based on the presence of different types of molybdenum and phosphorous structural groups and P–O–M (M=P, Mo) linkages in glasses. This revised version was published online in August 2006 with corrections to the Cover Date.