Synthesis and photoswitching properties of azobenzene liquid crystals with a pentafluorobenzene terminal

The fluorine-substituted benzoate ester rod-shaped liquid crystals containing an azobenzene side chain linked with terminal double bonds were synthesized and characterized.The mesophase and photoswitching properties were determined by polarizing optical microscopy(POM),differential scanning calorimetry(DSC) and UV-visible spectrometry.The rod-shaped compound 4a having an odd number of carbon atoms in the alkyl chains exhibits nematic phase and SmA type phase whereas compound 4b having an even number of carbon atoms showed only nematic phase.Both fluorinecontaining compounds 4c and 4d showed only SmA type phases.The photoswitching properties of these compounds showed a rate of trans to cis isomerization ranging 19-20 s,whereas reverse process took around 230 min in solution.These materials may be ideal in the field of optically rewritable applications where both on and off rates should be crucial.     

Photo-induced formation of silver nanoparticles and polymerization of acrylamide derivatives

The effect of silver ions and silver nanoparticles on the rate of polymerization of acrylamide and N-isopropylacylamide was investigated. Composites of silver particles of diameter around 30 nm and polyacrylamide were prepared by the photochemical method in the absence of any photosensitizer. The particles formed were characterized by UV–visible spectrophotometry, XRD, and TEM. It was shown that the presence of metal ions such as Ag⁺, Co²⁺, and Ni²⁺ in the acrylamide monomer is essential for photoinduced polymerization.     

Conformation and diffusion behavior of ring polymers in solution: a comparison between molecular dynamics, multiparticle collision dynamics, and lattice Boltzmann simulations

We have studied the effect of chain topology on the structural properties and diffusion of polymers in a dilute solution in a good solvent. Specifically, we have used three different simulation techniques to compare the chain size and diffusion coefficient of linear and ring polymers in solution. The polymer chain is modeled using a bead-spring representation. The solvent is modeled using three different techniques: molecular dynamics (MD) simulations with a particulate solvent in which hydrodynamic interactions are accounted through the intermolecular interactions, multiparticle collision dynamics (MPCD) with a point particle solvent which has stochastic interactions with the polymer, and the lattice Boltzmann method in which the polymer chains are coupled to the lattice fluid through friction. Our results show that the three methods give quantitatively similar results for the effect of chain topology on the conformation and diffusion behavior of the polymer chain in a good solvent. The ratio of diffusivities of ring and linear polymers is observed to be close to that predicted by perturbation calculations based on the Kirkwood hydrodynamic theory.     

Synthesis of novel molecular probes inspired by harringtonolide

A novel harringtonolide-inspired scaffold containing a cycloheptatriene ring and two fused cyclopentane rings has been synthesised from simple starting materials. The scaffold, containing a similar substitution pattern and relative stereochemistry to the complex diterpenoid, has been enumerated into a small library of derivatives. One of these library members has been converted into a sub-library of substituted triazoles using copper-catalysed azide-alkyne cycloaddition (click) chemistry. The scaffold may be useful in drug discovery or in the preparation of additional molecular probes for chemical biology.     

Synthesis and photoswitching properties of bent-shaped liquid crystals containing azobenzene monomers

Three novel bent-shaped monomers, namely 1,3-phenylene bis-{4-[4-(n-allyloxyalkyloxy)phenylazo]benzoate} 5a–c, containing azobenzene as side arms, resorcinol as central units and terminal double bonds as polymerisable functional groups were synthesised and characterised. The mesophase behaviour was investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements and it was found that all three compounds display SmA_intercal mesophases. These bent-shaped molecules exhibit strong photoisomerisation behaviour in solutions in which trans to cis isomerisation takes about 50 seconds whereas the reverse process takes almost 31 hours.     

Cost-effective bio-derived mesoporous carbon nanoparticles-supported palladium catalyst for nitroarene reduction and Suzuki–Miyaura coupling by microwave approach

A new heterogeneous catalyst was synthesized by immobilizing Pd on areca nut kernel-derived carbon nanospheres (CNSs). The CNSs, without any further activation processes, accommodated 3% of Pd on their surface. The new Pd/CNS material was used for the reduction of nitroarenes and Suzuki–Miyaura coupling of bromoarenes with aryl boronic acids. The reactions were conducted under microwave irradiation at 160 °C using 12 mol% of Pd/CNS (0.36% actual Pd content). The reduction of nitroarenes into their respective amino compounds was achieved in 10–20 min (conversion up to 100%); by contrast, the Suzuki–Miyaura reactions yielded up to 98% at 150 °C with 10 mol% of Pd/CNS catalyst. The products were identified using gas chromatography and nuclear magnetic resonance spectroscopy. The catalyst was isolated from reaction mixture and reused without any significant loss in the activity. Thus, the present work introduces one-pot-derived porous CNSs as efficient catalytic support to Pd, establishing an alternative to existing Pd/C in terms of cost and efficiency.     

Imperviousness of the hydrophobic silica aerogels against various solvents and acids

The experimental results on the imperviousness of the silica aerogels against various organic solvents and acids, are reported. Various types of hydrophobic silica aerogels were prepared using methyltrimethoxysilane (MTMS); tetraethoxysilane (TEOS) with ethyltriethoxysilane (ETES) and phenyltriethoxysilane (PTES) as co-precursors. The organic solvents used were: methanol, ethanol and acetone, and the acids used were: hydrochloric acid (HCl), nitric acid (HNO₃) and sulphuric acid (H₂SO₄). The imperviousness of the aerogels against these solvents and acids were tested with the variation of the percentage of organic solvents and acids in water from 10 to 100% and was characterized by the contact angle measurements. It was observed that in all the cases, the contact angle decreased with an increase in the percentage of solvent in water. While there was no absorption of the solvent up to 20% in water by the ETES and PTES modified aerogels, the MTMS-based aerogels showed the imperviousness up to 60% of the solvent in water. The MTMS aerogels were also impervious against all the three acids up to 100%, while the ETES and PTES modified aerogels could withstand only up to 80% of acids in water.