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.     

Catalytic activation of the leaving group in the S(N)2 reaction

A novel catalytic activation of the leaving group in the S(N)2 reaction is achieved as an extension of our mercuric triflate-catalyzed reactions. Derivatives of anilinoethyl 4-pentynoate reacted smoothly with catalytic amounts of Hg(OTf)(2) to give indoline derivatives in excellent yield with efficient catalytic turnovers under very mild conditions. The reaction of optically pure secondary alcohol derivatives resulted in inversion of stereochemistry, which is a definitive feature of the S(N)2 reaction. The procedure is applicable for benzoazepine synthesis.     

Thermal decomposition mechanism of 1-ethyl-3-methylimidazolium bromide ionic liquid

In order to better understand the volatilization process for ionic liquids, the vapor evolved from heating the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIM(+)Br(-)) was analyzed via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and thermogravimetric analysis mass spectrometry (TGA-MS). For this ionic liquid, the experimental results indicate that vaporization takes place via the evolution of alkyl bromides and alkylimidazoles, presumably through alkyl abstraction via an S(N)2 type mechanism, and that vaporization of intact ion pairs or the formation of carbenes is negligible. Activation enthalpies for the formation of the methyl and ethyl bromides were evaluated experimentally, ΔH(?)(CH(3)Br) = 116.1 ± 6.6 kJ/mol and ΔH(?)(CH(3)CH(2)Br) = 122.9 ± 7.2 kJ/mol, and the results are found to be in agreement with calculated values for the S(N)2 reactions. Comparisons of product photoionization efficiency (PIE) curves with literature data are in good agreement, and ab initio thermodynamics calculations are presented as further evidence for the proposed thermal decomposition mechanism. Estimates for the enthalpy of vaporization of EMIM(+)Br(-) and, by comparison, 1-butyl-3-methylimidazolium bromide (BMIM(+)Br(-)) from molecular dynamics calculations and their gas phase enthalpies of formation obtained by G4 calculations yield estimates for the ionic liquids' enthalpies of formation in the liquid phase: ΔH(vap)(298 K) (EMIM(+)Br(-)) = 168 ± 20 kJ/mol, ΔH(f,?gas)(298 K) (EMIM(+)Br(-)) = 38.4 ± 10 kJ/mol, ΔH(f,?liq)(298 K) (EMIM(+)Br(-)) = -130 ± 22 kJ/mol, ΔH(f,?gas)(298 K) (BMIM(+)Br(-)) = -5.6 ± 10 kJ/mol, and ΔH(f,?liq)(298 K) (BMIM(+)Br(-)) = -180 ± 20 kJ/mol.     

Laser photolysis studies of hydrazine vapor: 193 and 222-nm H-atom primary quantum yields at 296 K,and the kinetics of H + N2H4 reaction over the temperature range 222–657 K

The primary quantum yield of H-atom production in the pulsed-laser photolysis of hydrazine vapor, N₂H₄ + hν → H + N₂H₃, was measured to be (1.01 ± 0.12) at 193 nm relative to HBr photolysis, and (1.06 ± 0.16) at 222 nm relative to 248-nm N₂H₄ photolysis, in excess He buffer gas at 296 K. The H-atoms were directly monitored in the photolysis by cw-resonance fluorescence detection of H(²S) at 121.6 nm. The high H-atom yield observed in the photolysis is consistent with the continuous ultraviolet absorption spectrum of N₂H₄ involving unit dissociation of the diamine from repulsive excited singlet state(s). The laser photodissociation of N₂H₄ was thus used as a ‘clean’ source of H-atoms in excess N₂H₄ and He buffer gas to study the gas-phase reaction, H + N₂H₄ → products; (k₁), in a thermostated photolysis reactor made of quartz or Pyrex. The pseudo-first-order temporal profiles of [H] decay immediately after photolysis were determined for a range of different hydrazine concentrations employed in the experiments to calculate the absolute second-order reaction rate coefficient, k₁. The Arrhenius expression was determined to be k₁ = (11.7 ± 0.7) × 10^?12 exp[?(1260 ± 20)/T] cm³ molec^?1 s^?1 in the temperature range 222–657 K. The rate coefficient at room temperature was, within experimental errors, independent of the He buffer gas pressure in the range 24.5–603 torr. The above temperature dependence of k₁ is in excellent agreement to that we determine in our discharge flow-tube apparatus in the temperature range 372–252 K and in 9.5 torr of He pressure. The Arrhenius parameters we report are consistent with a metathesis reaction mechanism involving the abstraction of hydrogen from N₂H₄ by the H-atom. © 1995 John Wiley & Sons, Inc.