Triisopropoxyniobium(V) and tantalum(V)bis-O,O′-dialkyl dithiophosphates

Summary Triisopropoxy bis(O,O-dialkyl dithiophosphates), (i-PrO)₃M[S₂P(OR)₂]₂ (M = Nb^v, Ta^v; R = n-Pr, i-Pr, i-Bu and Ph) have been prepared by reacting the appropriate triisopropoxymetal(V)dichloride, (i-PrO)₃MCl₂ (1 mol) with sodium/ammonium dialkyl dithiophosphates (2 mols)in THF. The monomeric products which are viscous liquids, soluble in common organic solvents and highly susceptible to hydrolysis, were characterized by i.r. and n.m.r. spectra which indicate a bidentate mode of attachment of dithiophosphato groups to the metal.     

Synthesis of Mannich type products via a three-component coupling reaction

The reactions of alkyl nitriles, acetyl chloride, aldehydes and β-ketoesters or simple ketones was studied for the one-pot synthesis of β-acetamido carbonyl compounds. It was observed that the reaction proceeds in the absence of Lewis acids. However, a Lewis acid catalyzes the reaction and several were tested. It was found that whereas Cu(OTf)₂ is suitable for the coupling of β-ketoesters with aldehydes, Sc(OTf)₃ is the best for ketones. A possible mechanism is proposed based on the isolation and characterization of an intermediate.     

Confinement and controlled release of quinine on chitosan–montmorillonite bionanocomposites

To accomplish the controlled‐release systems based on layered clay minerals, one of the best ways is to intercalate organic molecules into the interlayer gallery of clay minerals. Into a series of chitosan (CS) intercalated montmorillonite (MMT) nanocomposites, prepared via ion‐exchange route, antimalarial drug [quinine (QUI)] was loaded to act as effective drug delivery systems. Among the CS–MMT nanocomposites, higher drug adsorption with decreasing CS concentration was observed. CS–MMT and CS–MMT/QUI intercalated compounds were characterized by powder X‐ray diffraction, Fourier transform infrared spectroscopy, and thermal analysis. The synthesized nanocomposites, filled in the gelatin capsules followed by coating of Eudragit® L 100, were tested for in vitro drug release performance in the sequential buffer environments at 37 ± 0.5 °C. As no drug release (0%) was observed in the gastric fluid, the coating of Eudragit® L 100 to the capsules is highly adequate. However, the drug release rate was comparatively faster from the CS intercalated clay with compare with pure clay. The drug release kinetic data revealed that the release of QUI from the nanocomposites can be explained by modified Freundlich model. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Modified sub-population teaching-learning-based optimization for design of truss structures with natural frequency constraints

In this paper, a modified sub-population teaching-learning-based optimization (MS-TLBO) algorithm is proposed to improve the exploration and exploitation capacities by including the concept of number of teachers, adaptive teaching factor, learning through tutorial, and self-motivated learning in the basic TLBO algorithm. The multiple frequency responses to the structural optimization problems are challenging due to its search space, which is implicit, nonconvex, nonlinear, and often leading to divergence. The viability and efficiency of the proposed method are tested by five structural benchmark problems of shape and size optimization with multiple natural frequency constraints on the planar and space trusses. The results reveal that MS-TLBO is more effective as compared to the original TLBO and other state-of-the-art algorithms.     

Dip-coated HNR120 photoresists thin-film optical waveguides

We report on our systematic and detailed study of fabrication and characterization of HNR120 photoresists thin-film optical waveguides. Various waveguide properties, such as refractive index, optical losses as a function of temperature, waveguide thickness, dispersion and birefringence have been studied. The optical loss are found to be <1.4 dB cm⁻¹.     

Rh-B doped polymeric optical waveguide for integrated optics

A systematic study of fabrication and characterization of rhodamine-blue (Rh-B) doped polystyrene waveguide is presented. Optical absorption and mode effective refractive index measurement was performed on the waveguides fabricated on glass substrate prepared by dip coating technique. It is observed that doping of dye increase the index of refraction of waveguides. The losses, however, decrease initially for dye concentration upto 0.1% and thereafter increase rapidly.     

Adsorption of atomic oxygen on cubic PbTiO3 and LaMnO3 (001) surfaces: A density functional theory study

We present and discuss density functional theory calculations addressing the electronic structure and energetics of isolated oxygen ad-atoms at the (001) surfaces of PbTiO₃ (PTO) and LaMnO₃ (LMO) cubic perovskites. Both AO- and BO₂-type of surface terminations are considered for each perovskite. Difference electron density analysis has been carried out for each surface to probe local electronic charge redistribution upon oxygen adsorption. Our results show that the (001) surfaces of the two perovskites behave quite differently towards oxygen adsorption. In the case of the PTO (001) surfaces, the adsorbate oxygen atom was found to form a peroxide-type molecular species along with a surface lattice oxygen atom on both PbO- and TiO₂-terminated surface facets. On the other hand, the most stable oxygen adsorption site for the LMO (001) surfaces corresponds to the one expected from a natural continuation of the perovskite lattice. Moreover, the dissociative adsorption of molecular oxygen varies from being only slightly exothermic on the PTO (001) facets to being highly exothermic on the LMO (001) facets. The AO-terminated facets, in general, showed a stronger binding to the adsorbed oxygen.     

Access to 2‐Arylindoles via Decarboxylative C−C Coupling in Aqueous Medium and to Heteroaryl Carboxylates under Base‐Free Conditions using Diaryliodonium Salts

Easily accessible heteroaromatic carboxylic acids and diaryliodonium salts were successfully employed to construct valuable 2‐arylindoles and heteroaryl carboxylates in a regioselective fashion. C2‐arylated indoles were produced using a Pd‐catalyzed decarboxylative strategy in water without any base, oxidant, or ligand. Heteroaryl carboxylates were prepared under metal and base‐free conditions. This protocol was successfully utilized to synthesize Paullone, a cyclin‐dependent kinase (CDK) inhibitor.