Binay K. Ghorai

One-pot three-component synthesis of quinoxaline and phenazine ring systems using Fischer carbene complexes

Summary One-pot three-component coupling of o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes and dienophiles leading to the synthesis of quinoxaline and phenazine ring systems has been investigated. This involves the generation of furo[3,4-b]pyrazine and furo[3,4-b]quinoxaline as transient intermediates, which were trapped with Diels–Alder dienophiles. This is the first report on furo[3,4-b]pyrazine intermediates.

Solvent Retention, Thermodynamics, Rheology and Small Angle X-ray Scattering Studies on Thermoreversible Poly(vinylidene fluoride) Gels

Solvent retention power of poly(vinylidene fluoride) (PVDF) gels has been studied for various homologues of phthalate (aromatic diesters). The thermal stability has been examined for gels of varying morphology. Solvent evaporation, gelation, gel melting, and polymer degradation temperatures have increased with increasing aliphatic chain length of phthalates. The thermodynamics and polymer-solvent compound formations in the PVDF-phthalate gels have been explored. The weight fraction of polymer in compound has decreased with increasing aliphatic chain length. SAXS studies have confirmed the lamellar organization inside the fibrils, and interlamellar distance increases with aliphatic chain length of diesters. The scattering patterns follow the power law behavior (I(q) approximately q(-alpha)), and polymer gels consist of high-density mass (fibril), voids, and interlamellar region. Dynamic mechanical properties indicate the splintering and reformation of network structure in gels whose percolation frequency has reduced for higher aliphatic chain length phthalate. Morphology-dependent moduli have been observed, and greater mechanical strength has been verified for thicker fibrillar gels both for steady and dynamic measurements.

Planar–rotor architecture based pyrene–vinyl–tetraphenylethylene conjugated systems: photophysical properties and aggregation behavior

Four pyrene-vinyl-tetraphenylethylene based conjugated materials were synthesized and characterized by FT-IR, NMR, and mass spectroscopy. The photophysical (including absorption, fluorescence, and fluorescence lifetime) and aggregation properties in tetrahydrofuran were investigated. The photophysical and aggregation behavior depends on the spacer, substituent, and also the architecture (mono or tetra-branched) of the molecule. The vinyl spacer mono-branched compound is aggregation induced emission (AIE) active (αAIE = ∼6). Vinyl spacer tetra-branched compounds are AIE inactive, but their emitting efficiency is good in both solution (Φfl = 63%) phase and in the aggregated state (Φfl = 43%). Phenylvinyl spacer tetra-branched compounds emit light strongly in solution (Φfl = 92%), but not in the aggregated state (Φfl = 8%). They are shown to be thermally stable and emit light in the green region (500-550 nm). The results of cyclic voltammetry measurements of these materials showed irreversible oxidation waves, and have high HOMO energy levels (-5.66 to -5.53 eV).

Functionalized chitosan with self-assembly induced and subcellular localization-dependent fluorescence ‘switch on’ property

Chitosan-based polymers are commonly used as drug delivery carriers and for functional modification of nanoparticle/polymers. Herein, we report a functional chitosan oligosaccharide with a self-assembly-induced fluorescence ‘switch on’ property, and that also exhibits a similar type fluorescence ‘off’ to ‘on’ state via subcellular localization. Specifically, chitosan oligosaccharide was conjugated with aggregation induced emission (AIE) active tetraphenylethene (TPE) and lipophilic–cationic triphenylphosphonium (TPP) molecules. The resultant functional chitosan self-assembles into 50–200 nm particles, whereby TPE offers a self-assembly induced fluorescence ‘switch on’ property and TPP offers cell uptake via lipophilic–cationic surface properties. The self-assembled chitosan nanoparticle enters into the cell predominately by lipid-raft endocytosis and exhibit a fluorescence ‘off’ to ‘on’ state upon localization at the lysozome. We have shown that adjustment of the number of TPP/TPE molecules bound to each chitosan is critical for the self-assembly induced fluorescence ‘switch on’ property and the subcellular localization-dependent fluorescence ‘off’ to ‘on’ state performance. Other fluorescence ‘switch on’ type sub-cellular imaging probe could be designed with appropriate functional modification of chitosan oligosaccharide or similar macromolecules.

Metallation of 2,4-Dialkoxy-5-bromopyrimidine and Formylation with Dimethylformamide: Isolation of 2,6-Dialkoxy-5-dimethylaminopyrimidine-4-carboxaldehyde

Direct metallation of 2,4-dialkoxy-5-bromopyrimidine with lithium diisopropylamide and consequent trapping by dimethylformamide resulted unexpectedly in the formation of 2,6-dialkoxy-5-dimethylaminopyrimidine-4-carboxaldehyde via displacement of bromine by dimethylamine moiety of dimethylformamide.

Coupling of β-Cyanocarbene-Chromium Complexes with 2-Alkynylbenzoyl Derivatives: A [5+5]-Cycloaddition Approach to Phenanthridines

The coupling of β-cyanocarbene complexes and 2-alkynylbenzoyl derivatives has been examined. The reaction afforded phenanthridine derivatives in a complex tandem process involving carbene-alkyne coupling, isobenzofuran formation, intramolecular Diels-Alder reaction using a nitrile dienophile, and deoxygenation. The chemistry could not be reproduced in non-chromium-based systems.