Department of Chemistry

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A low density, highly compressible, porous foam of poly(dimethylsiloxane) (PDMS) incorporated with Au nanoparticles (10-50 nm) has been synthesized by using a single-step process with water as a medium. It exhibits high swelling ability (≈600 %) against benzene, toluene, ethylbenzene, and xylene (BTEX)-a property that has been exploited in the removal of oil spills from water. It is resistant to harsh chemical environments. It is also effective against odorous sulfur containing contaminants such as thioanisole. It works repeatedly and efficiently over many cycles. The regeneration of the foam is rather simple: heating in air to 300 °C for short time brings back its original activity. The fascinating properties of Au nanoparticles could be mingled with those of PDMS to provide a sustainable and practical solution for water treatment. It is also demonstrated to work effectively for deodorizing garlic extract with a promise as a food packaging material. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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ChemSusChem

Removal of organic compounds from water by using a gold nanoparticle-poly(dimethylsiloxane) nanocomposite foam

A simple, one-step direct micromolding process has been realised to produce highly conducting Pd μ-stripes over large areas on various substrates including flexible polyimide. Under a PDMS micromold, Pd octanethiolate served as a precursor at 250 °C, a temperature at which the precursor gets neatly metallised. Thus produced μ-stripes are robust under bending and can be utilised for flexible electronics. Hydrogen sensing by Pd μ-stripes is demonstrated. By electrolessly depositing Cu on the stripes, they can be made to peel off to form free standing Cu-Pd μ-ribbons. Copyright © 2011 American Scientific Publishers All rights reserved.

Journal of Nanoscience and Nanotechnology

Direct micromolding of Pd μ-stripes for electronic applications

Organocatalytic conjugate addition of thiols to R-substituted N-acryloyloxazolidin-2-ones followed by asymmetric protonation has been studied in the presence of cinchona alkaloid derived thioureas. Both of the enantiomers are accessible with the same level of enantioselectivity using pseudoenantiomeric quinine/quinidine derived catalysts. The addition/protonation products have been converted to useful biologically active molecules. ©2011 American Chemical Society.

Organic Letters

Enantioselective enolate protonation in sulfamichael addition to r-substituted n-acryloyloxazolidin-2-ones with bifunctional organocatalyst

The aim of this study was to develop topical hydrogels containing diclofenac potassium (DP) at 1% w/v concentration using conventional hydrophilic hydroxypropyl methyl cellulose (HPMC, 50cPs) and modified hydrophobic hydroxypropyl methyl cellulose (HPMC, 90L grade). The differences between in vitro release profiles of both types of polymer based hydrogels were studied using model dependent equations. Three formulations were prepared from hydrophobic HPMC at 1%, 1.5% and 2% (w/v) concentration. Other two formulations were prepared from hydrophilic HPMC at 12% and 15% (w/v) concentration. Hydrophobic formulations of higher viscosity with small quantity of polymer show higher release compared to hydrophilic formulations of lower viscosity with higher polymer concentration. Combined effect of swelling and erosion leads to anomalous diffusion in case of hydrophobic HPMC based hydrogels whereas only swelling leads to Fickian diffusion in case of hydrophilic HPMC based hydrogels. The formulations follow Higuchi release pattern as well as Weibull model.

Latin American Journal of Pharmacy

Formulation and characterization of both hydrophilic and hydrophobic HPMC based hydrogels containing diclofenac potassium

Cross coupling of aryl, alkenyl, and alkynyl magnesium compounds by using 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) as an environmentally benign organic oxidant is described. This coupling reaction can be performed without adding any transition metal on various ortho-substituted aryl and alkynyl Grignard reagents. Importantly, functional groups such as esters, amides, and cyanides are shown to be tolerated under the reaction conditions. © 2010 American Chemical Society.

Transition-metal-free sonogashira-type coupling of ortho-substituted aryl and alkynyl grignard reagents by using 2,2,6,6-tetramethylpiperidine-N-oxyl radical as an oxidant

We consider the Kramers problem for a long chain polymer trapped in a biased double-well potential. Initially the polymer is in the less stable well and it can escape from this well to the other well by the motion of its N beads across the barrier to attain the configuration having lower free energy. In one dimension we simulate the crossing and show that the results are in agreement with the kink mechanism suggested earlier. In three dimensions, it has not been possible to get an analytical 'kink solution' for an arbitrary potential; however, one can assume the form of the solution of the nonlinear equation as a kink solution and then find a double-well potential in three dimensions. To verify the kink mechanism, simulations of the dynamics of a discrete Rouse polymer model in a double well in three dimensions are carried out. We find that the time of crossing is proportional to the chain length, which is in agreement with the results for the kink mechanism. The shape of the kink solution is also in agreement with the analytical solution in both one and three dimensions. © 2010 IOP Publishing Ltd and SISSA.

Journal of Statistical Mechanics: Theory and Experiment

Barrier crossing in one and three dimensions by a long chain

(Figure Presented) Monosubstituted acyclic (E)-1,3-dienes undergo efficient hydrovinylation giving (Z)-3-alkylhexa-1,4-dienes upon treatment with catalytic amounts of bidentate phosphine-CoCl2 complexes {[P̃P](CoCl 2)} and Me3Al in an atmosphere of ethylene. The regioselectivity of the reaction (i.e., 1,4- or 1,2-addition) depends on the nature of the ligand and temperature at which the reaction is carried out. Complexes derived from (RR)-DIOP and (SS)-BDDP at -45 °C give very high enantioselectivities for several prototypical 1,3-dienes. In sharp contrast to the corresponding Ni(II)-catalyzed hydrovinylation, 1-aryl-substituted 1,3-dienes give almost exclusively achiral linear 1,4-addition products, unless the 2-position is also substituted. Solid-state structures of the precatalysts are presented. Copyright © 2010 American Chemical Society.

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Journal of the American Chemical Society

Asymmetrie hydrovinylation of unactivated linear 1,3-dienes

"Chemical Equation Presented" A cinchona alkaloid-derived urea was found to be an efficient organocatalyst for catalyzing enantioselective conjugate addition between thiols and various α,β-unsaturated ketones to provide optically active sulfides with high chemical yields (up to >99%) and enantiomeric excess (up to > 99% ee). The reaction was performed with 0.1 mol % of catalyst in toluene at room temperature. A transition state model has been proposed to explain the stereochemical outcome of the reaction. © 2010 American Chemical Society.

Journal of Organic Chemistry

Highly enantioselective organocatalytic sulfa-michael addition to α, β-unsaturated ketones

The deuterium isotope effect on the solvation dynamics and the anisotropy decay of coumarin 480 (C480) in a room temperature ionic liquid (RTIL) microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the RTIL 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF4]) in triton X-100 (TX-100)/benzene. Replacement of H 2O by D2O in the microemulsion causes retardation of solvation dynamics. The average solvation time of C480 (-s) in RTIL microemulsion with 5 wt % D2O is ∼1.5-1.7 times slower compared to that in the H2O containing RTIL microemulsion. This suggests that the main species in the microemulsion responsible for solvation is the water molecules. In both D2O and H2O containing RTIL microemulsion, the solvation dynamics exhibits marked dependence on the excitation wavelength (λex) and becomes about 15 times faster as λex increases from 375 to 435 nm. This is ascribed to the structural heterogeneity in the RTIL microemulsion. For λex = 375 nm, the region near the TX-100 surfactant is probed where bound water molecules cause slow solvation dynamics. At 435 nm, the RTIL pool is selected where the water molecules are more mobile and hence gives rise to faster solvation. The average time constant of anisotropy decay shows opposite dependence on λex and increases about 2.5-fold from 180 ps at λex = 375 nm to 500 ps at λex = 435 nm for D2O containing RTIL microemulsion. The slower anisotropy decay at λex = 435 nm is ascribed to the higher viscosity of RTIL which causes greater friction at the core. © 2010 American Chemical Society.

Journal of Physical Chemistry B

Deuterium isotope effect on femtosecond solvation dynamics in an ionic liquid microemulsion: An excitation wavelength dependence study

Excited state proton transfer (ESPT) of pyranine (8-hydroxypyranine-1,3,6- trisulfonate, HPTS) in room temperature ionic liquid (RTIL) mixed micelles is studied by femtosecond up-conversion. The mixed micelle consists of a triblock copolymer, (PEO)20-(PPO)70-(PEO)20 (Pluronic P123), and one of the two RTILs, 1-pentyl-3-methyl-imidazolium bromide ([pmim][Br]) and 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF4]). The size and structure of the mixed micelle vary with the relative amount of the RTIL. For [pmim][Br], the hydrodynamic diameter of the mixed micelle is 26 nm in 0.3 M RTIL and 3500 nm in 3.0 M RTIL. The time constant of initial proton transfer (τPT) in P123 micelle (65 ps) is 10 times slower than that (5 ps) in water, while the time constants of recombination (τrec) and dissociation (τdiss) are 2-3 times slower in P123 micelle. On addition of the RTIL, the rate of ESPT is markedly modified. In 0.3 M RTIL-P123 mixed micelle, τPT is shorter than that in P123 micelle. In the mixed micelle, τPT increases with an increase in the concentration of the RTIL (230 ps in 3 M [pmim][Br] and 55 ps in 0.9 M [pmim][BF4]). This is attributed to large scale penetration of the P123 micelle by RTIL replacing water molecules. The time constants of proton transfer (τPT, τrec, and τdiss) are faster than the slowest component (200-500 ps) of solvation dynamics. It seems that the ultrafast component of solvation (&lt;0.3 ps and &lt;5 ps) is enough for inducing proton transfer. The time constant of the proton transfer (τPT) in [pmim][BF4]-P123 mixed micelle is longer (∼20%) than that in [pmim][Br]-P123 mixed micelle for the same concentration of RTIL. The counterion dependence of ESPT is attributed to the difference in the structure and greater hydrophobicity of the [pmim][BF 4]. © 2010 American Chemical Society.