Unsymmetrical trimesogens exhibiting the undulated twist grain boundary (UTGBC*) mesophase

A new set of trimesogens consisting of a cholesteryl ester, a biphenyl and an azobenzene mesogenic segment joined together through either odd-even, even-even or odd-odd central alkylene spacers has been synthesized and the liquid crystalline properties investigated. The trimesogens having even-even and odd-odd central alkylene spacers exhibit the undulated twist grain boundary phase (UTGBC*) mesophase over a temperature range of ~40-50°C.     

Simultaneous determination of titanium and molybdenum in steel samples using derivative spectrophotometry in neutral micellar medium

A simple, selective and sensitive spectrophotometric method has been developed for the individual and simultaneous determination of Ti(IV) and Mo(VI) using resacetophenone p-hydroxybenzoylhydrazone (RAPHBH) in presence of Triton X-100, without any prior separation. Beer's law is obeyed between 0.13-1.2 microg mL-1 and 0.18-1.90 microg mL-1 concentration of Ti(IV) and Mo(VI) at 455 nm and 405 nm, respectively. The molar absorptivity and Sandell's sensitivity of the coloured complexes at pH 3.0 are 3.1x10(4) L mol-1 cm-1, 4.2x10(4) L mol-1 cm-1, and 1.6 ng cm-2, 2.3 ng cm-2 for Ti(IV) and Mo(VI), respectively. The stoichiometry of the complexes were found to be 1:2 and 1:1 (metal:ligand) for Ti(IV) and Mo(VI), respectively. These metal ions interfere with the determination of each other in zero-order spectrophotometry. The first derivative spectra of these complexes permitted a simultaneous determination of Ti(IV) and Mo(VI) at zero crossing wavelengths of 500.0 nm and 455.0 nm, respectively. The effect of foreign ions in the determination of Ti(IV) and Mo(VI) were investigated. The proposed method has been successfully applied for the determination of titanium and molybdenum in standard alloy steel, mineral and soil samples.     

The first examples of monodispersive liquid crystalline tetramers possessing four non-identical anisometric segments

The molecular design, synthesis and thermal behaviour of the first liquid crystalline tetramers composed of four non-identical mesogenic entities connected covalently through paraffinic spacers are presented. These new molecular structures consisting of a tolan (half disc-shaped), azobenzene (photoactive), biphenyl and cholesteryl ester (thermochromic) cores, connected through either an even-even-odd or an odd-even-odd paraffinic spacer, exhibit features of a columnar mesophase.     

Pyridoxinium picrate

The title compound [systematic name: 3‐hydr­oxy‐4,5‐bis­(hydroxy­meth­yl)‐2‐methyl­pyridinium 2,4,6‐trinitro­phenolate], C₈H₁₂NO₃⁺·C₆H₂N₃O₇⁻, is a complex of picric acid with pyridoxine. The asymmetric part of the unit cell contains one pyridoxinium cation and one picrate anion. The aromatic rings of the picrate anion and the pyridoxinium cation are inclined with a dihedral angle of 83.19 (7)°. An intra­molecular hydrogen bond between OH and a nearby CH₂OH group is observed in the cation. The hydro­phobic layers at y = are packed between the hydro­philic layers at y = 0.     

Salicylaldimine-based symmetric dimers: synthesis and thermal behaviour

Several symmetrical dimers comprised of salicylaldimine-moieties connected through ester linkages to the termini of odd-parity alkanediols have been synthesized and investigated for their thermal behaviour. In order to understand the structure-property relations, the lengths of the central alkylene spacers (C₃ and C₅) as well as those of the terminal alkoxy chains (C₆ to C₂₂) have been varied. The dimers with a C₃-alkylene spacer are non-liquid crystalline, while some of the compounds having a C₅-alkylene spacer exhibit liquid crystalline properties. The dimer, with a C₅-alkylene spacer and C₆-alkoxy tails, shows an intercalated smectic C (SmC_c) phase, whereas the C₈, C₁₀, C₁₁, and C₁₂ homologues are non-mesomorphic. The higher homologues of this series with C₁₆, C₁₈, C₂₀ and C₂₂ alkoxy tails show a mesophase that has the signatures of a two-dimensional banana (B₁) phase. This mesophase is enantiotropic in the C₁₆ and C₁₈ homologues while it is monotropic in the other homologues. In these dimers, the spacer length has a remarkable influence on the thermal behaviour.     

First Stereoselective Total Synthesis of Gallicynoic Acids G and H

A stereoselective convergent total synthesis of two acetylenic acids, gallicynoic acid G ( 1 ) and H ( 2 ), is reported, involving asymmetric reduction of alkynones 3 and 4 , respectively, with the Corey? Bakshi? Sibata (CBS) catalyst as a key step (Scheme 3), 3 and 4 being obtained from a common intermediate, the chiral alkynol 12 (Scheme 2).     

Analytical expression of the steady-state catalytic current of mediated bioelectrocatalysis and the application of He’s Homotopy perturbation method

A mathematical model of mediated bioelectrocatalysis is restudied in this paper. Here He’s Homotopy perturbation method is implemented to give approximate and analytical solutions of steady-state non-linear reaction diffusion equation containing a non-linear term related to Michaelis–Menten kinetics of the enzymatic reaction. Approximate analytical expressions for mediator concentration and current have been derived for all values of saturation parameter α and reaction diffusion parameter k for the various types of boundary conditions. The Homotopy perturbation method which produces the solutions in terms of convergent series, requiring no linearization or small perturbation. These analytical results are compared with numerical results (Matlab program) and are found to be in good agreement.     

Control of the PEO chain conformation on nanoparticles by adsorption of PEO-block-poly(L-lysine) copolymers and its significance on colloidal stability and protein repellency

The physical adsorption of PEO(n)-b-PLL(m) copolymers onto silica nanoparticles and the related properties of poly(ethylene oxide) (PEO)-coated particles were studied as a function of the block copolymer composition. Copolymers adopt an anchor-buoy conformation at the particle surface owing to a preferential affinity of poly(L-lysine) (PLL) blocks with the silica surface over PEO blocks when a large excess of copolymer is used. The interdistance between PEO chains at particle surface is highly dependent on the size of PLL segments; a dense brush of PEO is obtained for short PLL blocks (DP = 10), whereas PEO chains adopt a so-called interacting "mushroom" conformation for large PLL blocks (DP = 270). The size of the PEO blocks does not really influence the copolymer surface density, but it has a strong effect on the PEO layer thickness as expected. Salt and protein stability studies led to similar conclusions about the effectiveness of a PEO layer with a dense brush conformation to prevent colloidal aggregation and protein adsorption. Besides, a minimal PEO length is required to get full stabilization properties; as a matter of fact, both PEO(45)-b-PLL(10) and PEO(113)-b-PLL(10) give rise to a PEO brush conformation but only the latter copolymer efficiently stabilizes the particles in the presence of salt or proteins.     

Twist Sensitivity of Cladding-Mode Resonances and Its Cross-Sensitivity to Strain and Temperature in a Mechanically Induced Long-Period Fiber Grating

Abstract

Twist sensitivity of cladding-mode resonances in a mechanically induced long-period fiber grating formed over a single-mode fiber is experimentally demonstrated and theoretically analyzed. Of the two usual cladding-mode resonances corresponding to LP₁₁ and LP₁₂, higher-order mode LP₁₂ is more sensitive to twist in comparison with the lower-order mode LP₁₁. The extent of down-shifting of resonant wavelengths depends on twist-induced circular birefringence and the modal field distribution of the cladding-modes inside the fiber. When the fiber is severely twisted to 3.5 rad/cm, a shift sensitivity is observed of 1 nm/(rad/cm) for the LP₁₁ mode and 4.23 nm/(rad/cm) for the LP₁₂ mode. The fiber breaks when the twist rate exceeds 3.5 rad/cm. In comparison with LP₁₂, the LP₁₁ resonance is almost independent of the axial strain variation with an ultra-low sensitivity of 0.18 pm/με, and it is also almost insensitive to the temperature variation with a coefficient of 35 pm/°C. Forming the LP₁₁ resonance far away from its cut-off wavelength, a widely tunable band-pass filter is also demonstrated with a very high twist sensitivity of 8.75 nm/(rad/cm) and negligible cross-sensitivity to strain and temperature. The experimental and theoretical results are very useful in selecting sensitive and stable cladding-mode resonances in the design of new mechanically induced long-period fiber gratings based torsion sensors and tunable band-pass filters.