Emissive ‘zinc(II)-salphen’ core: building block for columnar liquid crystals

A series of half-discoid [N₂O₂]-donor tetradentate alkoxy substituted salicylaldimine ligands, [N,N′-di- (4-n-alkoxysalicylidene)-4-Cl-l,2-diamino-benzene] (L; n?=?12, 14, 16 and 18) have been prepared. The reaction of the ‘salphen’-type Schiff base ligand with Zn(OAc)₂.4H₂O afforded a series of mononuclear zinc(II) complexes. The ligands and the corresponding zinc(II) complexes were characterised by elemental analysis, Fourier transform infrared, proton nuclear magnetic resonance and ultraviolet-visible spectroscopy. Although the ligands are non-mesogenic, columnar mesomorphism is induced upon complexation with the metal. The p2gg symmetry of the rectangular columnar phase is confirmed by variable temperature powder X-ray diffraction study. Two ‘half-disc’-shaped molecules with four alkoxy legs are presumed to self-assemble via a dimeric interaction filling the space. In contrast to the ligands, the zinc(II) complexes all exhibited moderately intense green emission at room temperature both in solution and in the solid state. Density functional theory calculation, carried out using a DMol3 program, revealed a distorted square planar geometry for the complexes. The mesomorphic and photoluminescence property of the zinc complexes are collated as a function of spacer substituent, as well as alkoxy carbon chain length.     

Photoluminescent columnar zinc(II) bimetallomesogen of tridentate [ONO]-donor Schiff base ligand

A new zinc(II) bimetallomesogenic complex, [Zn₂L₂], of tridentate [ONO]-donor Schiff base ligand (L = N-(2-hydroxyethyl)-4-hexadecyloxysalicylaldimines) was synthesised and their mesomorphic and photoluminescence properties were investigated. The compounds were characterised by Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV-Vis) spectroscopy, elemental analyses and fast atom bombardment (FAB) mass spectrometry. The mesomorphic behaviour of the complex was investigated by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction (XRD) study. A rectangular or oblique columnar mesophase is conjectured on the basis of powder X-ray diffraction (PXRD) study. The complex is found to be blue light emitter in solution, in solid and in condensed states with broad emission maxima at ～427–464 nm. The density functional theory (DFT) calculations revealed a distorted square planar structure around each zinc(II) centre in the dinuclear framework. Time-dependent DFT spectral correlative study was undertaken to account for the electronic transition.     

Synthesis of polyphenylene ether and thioether ketones

The known polymerization of 4,4′-difluorobenzophenone (DFB) with the dianion of hydroquinone to poly(phenylene ether ether ketone) (PEEK) and polymerization of either DFB with the dianion of 4,4′-dihydroxybenzophenone or self polycondensation of the anion of 4-hydroxy-4′-fluoro-benzophenone to poly(phenylene ether ketone) (PEK) were studied in N-cyclohexyl-2-pyrrolidone (CHP), which is a high-boiling aprotic polar solvent. The formation of high-molecular weight PEEK and PEK in this solvent was very efficient. The reactivity in CHP can be ascribed to effective solvation of metal ions rendering the anion very reactive toward nucleophilic substitution. The polymerization was extended to 4,4′-bis(4-fluorobenzoyl)diphenyl ether and 1,4-bis[4-(4-fluorobenzoyl)phenoxy]benzene to give a high molecular weight polymer with PEK and PEEK repeating units and PEEK respectively. The polymerization of DFB with purified anhydrous sodium sulfide in CHP gave rapidly a high molecular weight poly(phenylene ketone sulfide) (PKS). In contrast, diphenyl sulfone (DPS) was not very effective in obtaining such a high molecular weight PKS even with prolonged heating, which suggests the uniqueness of CHP in promoting a high degree of polymerization.     

Electrochemical characterization of Ni-Co and Ni-Co-Fe for oxidation of methyl alcohol fuel w ith high energetic catalytic surface*简

 Non Pt based metals and alloys as electrode materials for methyl alcohol fuel cells have been investigated with an aim of finding high electrocatalytic surface property for the faster electrode reactions. Electrodes were fabricated by electrodeposition on pure Al foil, from an electrolyte of Ni, Co, Fe salts. The optimum condition of electrodeposition were found out by a series of experiments, varying the chemistry of the electrolyte, pH valve, temperature, current and cell potential. Polarization study of the coated Ni-Co or Ni-Co-Fe alloy on pure Al was found to exhibit high exchange current density, indicating an improved electro catalytic surface with faster charge-discharge reactions at anode and cathode and low overvoltage. Electrochemical impedance studies on coated and uncoated surface clearly showed that the polarization resistance and impedance were decreased by Ni-Co or Ni-Co-Fe coating. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and atomic absorption spectroscopy (AAS) studies confirmed the presence of alloying elements and constituents of the alloy. The morphology of the deposits from scanning electron microscope (SEM) images indicated that the electrode surface was a three dimensional space which increased the effective surface area for the electrode reactions to take place.     

Raman spectroscopy in experimental oral carcinogenesis: investigation of abnormal changes in control tissues

Oral cancer is a major cause of mortality in South Asian men owing to rampant tobacco abuse. Cancers are also reported in non‐tobacco habitués, especially women, attributed to chronic irritations from irregular/sharp teeth, improper fillings, and poorly fit dentures. Conventional screening approaches are shown to be effective for high‐risk groups (tobacco/alcohol habitués). Raman spectroscopy (RS) is being extensively explored as an alternate/adjunct tool for diagnosis and management of oral cancers. In a previous Raman study on sequential oral carcinogenesis using hamster buccal pouch model, misclassifications between spectra from control and carcinogen [7,12‐dimethylbenz(a)anthracene (DMBA)]‐treated tissues were observed. Histopathology of some control tissues suggested pathological changes, attributable to repeated forceps‐induced irritations/trauma during animal handling. To explore these changes, in the present study, we recorded spectra from three different types of controls – vehicle control (n = 45), vehicle contralateral (n = 45), and DMBA contralateral (n = 70) – exposed to varying degree of forceps handling, along with DMBA‐treated pouches (n = 70) using a 14‐week carcinogenesis protocol. Spectra certified on the basis of histopathology and abnormal cell proliferation (cyclin D1 expression) were used to build models that were evaluated by independent test spectra from an exclusive set of DMBA‐treated and control animals. Many DMBA‐contralateral, vehicle‐control, and vehicle‐contralateral spectra were identified as higher pathologies, which subsequently corroborated with histopathology/cyclin D1 expression. Repeated forceps‐mediated injuries/irritations, during painting and animal handling, may elicit inflammatory responses, leading to neoplasm. The findings of the study suggest that RS could identify micro‐changes. Further, RS‐based in vivo imaging can serve as a promising label‐free tool for screening even in the non‐habitué population where conventional screening is shown to be not effective. Copyright © 2016 John Wiley & Sons, Ltd.