Synthesis and thermal behaviour of salicylaldimine-based liquid crystalline symmetrical dimers

A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C₈) while the number of methylene units in the central spacer was varied from C₃ to C₁₁. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C₉ to C₁₁ methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced.     

Improved highly efficient synthesis of α,β-acetylenic ketones. Nature of the intermediate from the reaction of lithium acetylide with boron trifluoride etherate

A wide variety of α,β-acetylenic ketones were synthesized in very high yields via an exceptionally facile intermolecular reaction of lithium alkynyltrifluoroborates and carboxylic acid anhydrides.     

A revised structure for hermonionic acid

Hermonionic acid and its decarboxylated product have been isolated from $\text{Garcinia}$$\text{quaesita}$. ¹³C NMR spectral and chemical evidence indicate that hermonionic acid is 2-0-[2-(3-methylbut-2-enyl)-3-methoxy- 4-hydroxy-5-(3,7-dimethylocta-2,6-dienyl]-4-methoxy-5-(3-methylbut-2-enyl-6-hydroxybenzoic acid. The previously assigned dienone structure for this acid is incorrect.     

Purification and Characterization of Gum-Derived Polysaccharides of Moringa oleifera and Azadirachta indica and Their Applications as Plant Stimulants and Bio-Pesticidal Agents

Plant gums are bio-organic substances that are derived from the barks of trees. They are biodegradable and non-adverse complex polysaccharides that have been gaining usage in recent years due to a number of advantages they contribute to various applications. In this study, gum was collected from Moringa oleifera and Azadirachta indica trees, then dried and powdered. Characterizations of gum polysaccharides were performed using TLC, GC-MS, NMR, etc., and sugar molecules such as glucose and xylose were found to be present. Effects of the gums on Abelmoschus esculentus growth were observed through root growth, shoot growth, and biomass content. The exposure of the seeds to the plant gums led to bio stimulation in the growth of the plants. Poor quality soil was exposed to the gum polysaccharide, where the polysaccharide was found to improve soil quality, which was observed through soil analysis and SEM analysis of soil porosity and structure. Furthermore, the plant gums were also found to have bio-pesticidal activity against mealybugs, which showed certain interstitial damage evident through histopathological analysis.     

High‐mobility solution‐processed zinc oxide thin films on silicon nitride

A high effective electron mobility of 33 cm² V^–1 s^–1 was achieved in solution‐processed undoped zinc oxide (ZnO) thin films. The introduction of silicon nitride (Si₃N₄) as growth substrate resulted in a mobility improvement by a factor of 2.5 with respect to the commonly used silicon oxide (SiO₂). The solution‐processed ZnO thin films grown on Si₃N₄, prepared by low‐pressure chemical vapor deposition, revealed bigger grain sizes, lower strain and better crystalline quality in comparison to the films grown on thermal SiO₂. These results show that the nucleation and growth mechanisms of solution‐processed films are substrate dependent and affect the final film structure accordingly. The substantial difference in electron mobilities suggests that, in addition to the grain morphology and crystalline structure effects, defect chemistry is a contributing factor that also depends on the particular substrate. In this respect, interface trap densities measured in high‐κ HfO₂/ZnO MOSCAPs were about ten times lower in those fabricated on Si₃N₄ substrates. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

     

Assessment of sandwich models for the prediction of sound transmission loss in unidirectional sandwich panels

The consistent higher-order approach and the two-parameter foundation formulation are used for the derivation of sound transmission loss in symmetric unidirectional (infinitely wide) sandwich panels with isotropic face sheets. In both models, transmission loss is calculated using decoupled equations representing symmetric and anti-symmetric motions of a sandwich panel. The closed-form expressions for impedances and transmission coefficient of a symmetric sandwich panel with an isotropic core are derived for the two-parameter foundation model. A comparison between the numerical predictions based on the two sandwich models and available experimental data shows that the consistent higher-order formulation can be used to predict the transmission loss in symmetric sandwich panels with both honeycomb and isotropic cores. For prediction of transmission loss of symmetric sandwich panels with an isotropic core, the two-parameter foundation model is more convenient, while the consistent higher-order approach is more accurate.     

Radiation chemistry of tris(acetylacetonato) cobalt(iii) in aqueous solutions

Abstract

On radiolysis tris(acetylacetonato) cobalt(III) in aqueous solutions is found to get reduced by reaction with (1) hydrated electrons, (2) H atoms, (3) OH radicals and (4) C₂H₂OH radicals. The bimolecular rate constants for the first three reactions, determined by competition kinetics are: 4 × 10¹⁰, 2.3 × 10⁹ and 4.7 × 10⁹ M^?1sec^?1 respectively. Absorption spectra of the irradiated solutions indicate the formation of bis(acetylacetonato) cobalt(II) from reaction (1), but not from (3). The total cobaltous yield in air-free solutions is given byG(Co⁺⁺) = 5.6 and 6.5 at pH 6.5 and 1 respectively. It appears that G_eaq- ∽ _H ⁺ G_oH ∽ 2.8 in neutral solutions. Considerations of material balance for the primary yields of radiolysis of water suggest the possibility that the so-called independent H-atoms in neutral solutions are probably excited water molecules or ion-pairs.     

Radiation induced polymerization of Vinylbenzoate–II. Study of the molecular weights of polymers

Abstract

In this study, the molecular weights of the polymer from vinyl benzoate has been reported for different dose rates and different temperatures. The mol.wt. remains around 4000. With increasing dose, the molecular weight increases to about 14,000. The degrees of polymerization and the kinetic chain lengths calculated from the experimentally determined G _R values have been compared which show that the kinetic chain length is larger than the D ^? Pn.

From a plot of the (D ^? Pn)^?1 vs. R _p , an intercept is obtained which is equal to 3.25 × 10^?2 which is higher than obtained in conventional polymerization. By examining the effect of temperature on mol.wt., the dependence of R _p on dose rate and the absence of induction period it has been concluded that chain transfer occurs to impurities that are generated during radiolysis.