Solvatochromism and fluoride sensing of thienyl-containing benzodiazaboroles

Static and time-resolved fluorescence studies were carried out to investigate the photophysical properties and fluoride sensing abilities of highly fluorescent thienyl-containing 1,3-diethyl-1,3,2-benzodiazaboroles. Absorption and fluorescence spectra were measured in various solvents, showing the fluorophores to emit in the visible wavelength region with colors varying from blue to orange and quantum yields ranging between 0.21 and 1. Measured Stokes shifts of 2898 cm(-1) to 9308 cm(-1) were used to calculate the difference between excited- and ground-state dipole moments of the fluorophores. Values up to 18.8 D are of the same magnitude as for designed polarity probes such as PRODAN, supporting the idea of internal charge transfer transitions. Quenching studies with pyridine observing static and time-resolved fluorescence revealed a purely dynamic quenching mechanism and low Lewis acidity of the boron within the benzodiazaborolyl moiety compared to other triarylboranes. In contrast to this, quenching with fluoride was shown to stem from adduct formation. Reversible complexation of fluoride follows a simple mechanism for multi-functionalized benzodiazaboroles 2b and 2c, while those containing only one benzodiazaborole moiety (1 and 2a) show a more complicated behaviour, which might be explained by aggregation. Combining a benzodiazaborole group and a dimesitylborane function results in spectrally switchable fluoride sensors 3a and 3b, since the two boron sides can be deactivated for fluorescence in a stepwise manner.     

Liquid crystalline polymers XVI*. Thermotropic liquid crystalline copoly(arylidene-ether)/TiO2 Nanocomposites: synthesis,characterisation and applications

ABSTRACT

Polymer nanocomposites are already a part of many important worldwide businesses. Among many nanocomposite precursors, titanium dioxide (TiO₂) nanopowder is increasingly being investigated due to its special properties. In this work, the feasibility of synthesising a new series of materials, copoly(arylidene-ether)/titanium dioxide nanocomposites, using in-situ copolymerisation technique has been investigated. This can be performed by the interaction of both cyclohexanone and 4-tert-butylcyclohexanone monomers with 4,4′-diformyl-2,2′-dimethoxy-α,ω-diphenoxyalkanes Ia–e, respectively, using different additions of titanium dioxide-P25. The structure of the prepared nanocomposites IIa–e/TiO₂ (0.2–3.0%) was confirmed by elemental analysis (energy dispersive X-ray spectroscopy) and spectral data (Fourier transform-infrared [FT-IR]). FT-IR verified the dispersion of nanofillers in the copolymer. Then, the characterisation and applications of these nanocomposites are extensively discussed depending on the investigation of how the addition of titanium dioxide nanoparticles affected on their properties using various techniques, such as X-ray diffraction, SEM, transmission electron microscopy, Water Contact Angle (WCA), thermogravimetric analysis, differential thermogravimetric, differential thermal analysis (DTA), polarising optical microscope and UV–vis absorption spectroscopy. The nanoparticles affected on the copolymer thermal behaviour in different ways (discrepancy results) depending on how these nanoparticles are dispersed in the copolymer matrix. UV–vis absorption spectra displayed a decrease in the optical band gap of some nanocomposites, which resulted from the addition of titanium dioxide to these copolymers, and this can improve the efficiency of them as organic emitting materials.     

A wet chemical preparation of transparent conducting thin films of Ga-doped ZnO nanoparticles

Crystalline gallium doped zinc oxide (GZO) nanopowders were synthesized using hydrothermal treatment processing. The doping concentration affected the phase structure as well as the shape of the nanopowder from nano rod-like structure to nanoparticulate one. The specific BET surface area increases with increasing the gallium doping concentration. Transparent conducting films were deposited on borosilicate glass substrate by spin coating using sols containing GZO nanoparticles dispersed in 1-propanol. The films are crystalline with a hexagonal structure. The effect of Ga doping concentration, sintering temperature and thickness of the layers has been investigated. The lowest resistivity achieved was 6.4 × 10^?2 Ω cm for a thickness of 150 nm. The films present a transmittance in the visible range as high as 90 %.     

Tunable Spin‐Crossover Behavior of the Hofmann‐like Network {Fe(bpac)[Pt(CN)4]} through Host–Guest Chemistry

A study of the spin‐crossover (SCO) behavior of the tridimensional porous coordination polymer {Fe(bpac)[Pt(CN)₄]} (bpac=bis(4‐pyridyl)acetylene) on adsorption of different mono‐ and polyhalobenzene guest molecules is presented. The resolution of the crystal structure of {Fe(bpac)[Pt(CN)₄]} ? G (G=1,2,4‐trichlorobenzene) shows preferential guest sites establishing π???π stacking interactions with the host framework. These host–guest interactions may explain the relationship between the modification of the SCO behavior and both the chemical nature of the guest molecule (electronic factors) and the number of adsorbed molecules (steric factors).     

Bi-functional gold-coated magnetite composites with improved biocompatibility

The effect of gold attachment on the physical characteristics, cellular uptake, gene expression efficiency, and biocompatibility of magnetic iron oxide (MNP) vector was investigated in vitro in BHK21 cells. The surface modification of magnetite with gold was shown to alter the morphology and surface charge of the vector. Nonetheless, despite the differences in the surface charge with and without gold attachment, the surface charge of all vectors were positive when conjugated with PEI/DNA complex, and switched from positive to negative when suspended in cell media containing serum, indicating the adsorption of serum components onto the composite. The cellular uptake of all MNP vectors under the influence of a magnetic field increased when the composite loadings increased, and was higher for the MNP vector that was modified with gold. Both bare magnetite and gold-coated magnetite vectors gave similar optimal gene expression efficiency, however, the gold-coated magnetite vector required a 25-fold higher overall loading to achieve a comparable efficiency as the attachment of gold increased the particle size, thus reducing the surface area for PEI/DNA complex conjugation. The MNP vector without gold showed optimal gene expression efficiency at a specific magnetite loading, however further increases beyond the optimum loading decreased the efficiency of gene expression. The drop in efficiency at high magnetite loadings was attributed to the significant reduction in cellular viability, indicating the bare magnetite became toxic at high intracellular levels. The gene expression efficiency of the gold-modified vector, on the other hand, did not diminish with increasing magnetite loadings. Intracellular examination of both bare magnetite and gold-coated magnetite vectors at 48h post-magnetofection using transmission electron microscopy provided evidence of the localization of both vectors in the cell nucleus for gene expression and elucidated the nuclear uptake mechanism of both vectors. The results of this work demonstrate the efficacy of gold-modified vectors to be used in cellular therapy research that can function both as a magnetically-driven gene delivery vehicle and an intracellular imaging agent with negligible impact on cell viability.     

An engineering predictive approach of fatigue crack growth behavior: The case of the lug-type joint

The present attempt proposes a predictive approach of the fatigue crack growth (FCG) behavior of a lug-type joint used in an aeronautic context. The crack tip residual stress distribution and material dispersions are considered. The developed approach was implemented by coupling the Extended Finite Element Method (XFEM), the Residual Corrected Stress Intensity Factor (RC-SIF), developed by the authors, and the Monte Carlo simulation (MCS) method. The Lemaitre–Chaboche model, developed upon the ABAQUS commercial code, was considered for characterizing material behavior. The developed approach treats FCG life by considering the stochastic behavior of material parameters and the crack tip residual stress field during propagation. Comparing with experimental data, the proposed approach exhibits a good ability in evaluating the FCG reliability of a cracked lug-type joint subjected to different loading conditions. The iso-probabilistic P–a–N curves can be used as an efficient tool for ensuring the safety behavior of cracked components.     

Electrochemical determination of sulfaguanidine using COOH-MWCNT coated GC electrode

The electrochemical behavior of sulfaguanidine was investigated in PBS buffer aqueous solutions. Cyclic voltammograms have shown that (1) the Sg provided a well-defined irreversible oxidation peak (2) the signal-to-background current ratio is 3 times higher at COOH-MWCNT coated GCE than that of bare GCE and (3) the modifying GCE surface by COOH-MWCNT led to a significant improvement (2.7 folds) of the electrochemical response. It has been shown that Sg oxidizes according to a diffusion-controlled mechanism. A linear calibration curve was obtained for the oxidation of Sg at 10–70 μM. The COOH-MWCNT coated GCE has also been successfully used for the determination of Sg in real samples.     

Vibrational study of tin-containing siloxane ring compounds

By a condensation reaction of (t-Bu)₂Si(OH)₂ (L) with tin tetrachloride (SnCl₄), two different compounds were obtained: a condensation product between two molecules of L and a tin-containing siloxane bicycloheptane ring compound formed by a subsequent reaction between partially hydrolysed SnCl₄ and L. The latter was identified by x-ray diffraction. The Raman spectra of both isolated compounds were recorded and confirmed the structure obtained for the ring compound. © 1997 John Wiley & Sons, Ltd.     

ChemInform Abstract: Dots versus Antidots: Computational Exploration of Structure,Magnetism, and Half‐Metallicity in Boron‐Nitride Nanostructures

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