Sivakumar Shanmugam

Tetraphenylethene-2-Pyrone Conjugate: Aggregation-Induced Emission Study and Explosives Sensor.

Design and synthesis of a novel tetraphenylethene-2-pyrone (TPEP) conjugate exhibiting donor-acceptor characteristics is reported. The localized frontier molecular orbitals (DFT studies) and the solvent polarity dependent photoluminescence characteristics directly corroborate the presence of intramolecular charge transfer character in TPEP. TPEP is poorly emissive in the solution state. In contrast, upon aggregation (THF/water mixtures), TPEP exhibits aggregation-induced emission enhancement. Upon aggregation, dyad TPEP forms a fluorescent nanoaggregate which was confirmed by transmission electron microscopy imaging studies. The luminescence nanoaggregates were elegantly exploited for selective detection of nitro aromatic compounds (NACs). It was found that nanoaggregates of TPEP were selectively sensing the picric acid over the other NACs. Efficiency of the quenching process was further evaluated by the Stern-Volmer equation. TPEP-based low-cost fluorescent test strips were developed for the selective detection of picric acid.

Convenient one-pot multicomponent strategy for the synthesis of 6-pyrrolylpyrimidines

We have developed an easy method to construct diheteroaryls from α-aroylidineketene dithioacetals in a multicomponent manner. The reaction proceeded with high chemo/regioselectivity to yield 4-alkoxy-6-(4-aryl-1H-pyrrol-3-yl)pyrimidin-2-amines under milder conditions. It is found that α-aroylidineketene dithioacetals (2) undergo cycloaddition with (p-tolylsulfonyl)methyl isocyanide (3) [TosMIC], guanidine nitrate (5) and alcohol in the presence of NaH/THF to furnish the target 6-pyrrolylpyrimidines (8) in excellent yields.

One-pot synthesis of hydrazono-sulfonamide adducts using Cu(BTC) MOF catalyst and their remarkable AIEE properties: unprecedented copper(II)-catalyzed generation of ketenimine

An efficient, four-component reaction for the synthesis of hydrazono-sulfonamide adducts via in situ generated ketenimine was discovered. Highly porous copper benzenetricarboxylate [Cu(BTC)], a metal–organic framework (MOF), was used as a heterogeneous catalyst for the four-component coupling reaction involving aldehyde, alkyne, tosyl azide, and phenylhydrazine in a one pot process. For the first time, a copper(II) catalyst was utilized to generate a ketenimine intermediate. The Cu(BTC) catalyst was recycled and reused six times without any substantial loss in the yield. In addition, pyrene adduct (5r) shows remarkable aggregation induced emission enhancement (AIEE) properties, and was studied in detail using THF : water solvent mixtures. Adduct 5r is almost non-emissive in pure THF solution, however, it emits a greenish-yellow colour in the aggregated state. Formation of nano-aggregates was confirmed by TEM analysis. A theoretical DFT study supports the observed photophysical changes.

Metal catalyst free one-pot synthesis of 2-arylbenzimidazoles from α-aroylketene dithioacetals

An efficient green synthetic approach has been developed towards the synthesis of 2-aryl substituted benzimidazoles from α-aroylketene dithioacetals (AKDTAs) 1 and o-phenylenediamine (OPD) 2. The reaction has been achieved in water with a catalytic amount of acetic acid. 2-Arylbenzimidazoles have been synthesized in remarkable yields under both thermal and microwave conditions. The metal catalyst free condition makes this transformation very green, practical and attractive.

One-pot chemo/regio/stereoselective generation of a library of functionalized spiro-oxindoles/pyrrolizines/pyrrolidines from α-aroylidineketene dithioacetals

An efficient chemo/regio/stereoselective synthesis of novel and functionalized spiro-oxindole/pyrrolizine/pyrrolidine scaffolds has been achieved. The in situ generated azomethine ylide from isatin & L-proline/phenyl alanine underwent 1,3-dipolar cycloaddition with α-aroylidineketene dithioacetals under simple reaction conditions affording spiro-oxindole derivatives. This protocol exhibits an interesting double bond selectivity of α-aroylidineketene dithioacetals. Furthermore, utilizing this spiro-oxindoles scaffold, biologically important benzimidazole and pyrimidine based poly heterocycles were also synthesized.

Facile synthesis and characterization of bio-organometallic compounds and their biological activity contour against human pathogens

We have reported the synthesis of novel di & trisubstituted pyrroles and their biological activity. Most of the compounds show antibacterial activity towards gram positive and gram negative bacteria. The agar-diffusion method was used for prelude screening studies, which showed a hopeful broad range of antibacterial activity. The minimum inhibitory concentration (MIC) for bacteria was determined by the micro dilution method of selected active compounds. For the same compounds cytotoxicity assay was also performed. The photophysical properties were studied for the selected compounds and their results were suitably supported by DFT computation.

Aggregates of a hydrazono-sulfonamide adduct as picric acid sensors

A novel hydrazono-sulfonamide adduct (AVM) was designed and synthesized. Due to the inhibition of CN isomerization with a higher water content, the adduct shows remarkable aggregation induced emission enhancement (AIEE) properties in a THF:water solvent system. The formation of nanoaggregates was confirmed by transmission electron microscopy (TEM) analysis. Theoretical DFT calculations supported the observed photophysical changes. These aggregates of AVM act as selective and sensitive sensors for picric acid via a fluorescence quenching mechanism. The efficiency of the quenching process was calculated using the Stern–Volmer equation. The detection limit was found to be 80 nM. In addition, contact mode detection using fluorescent test strips was developed to demonstrate the solid phase sensing of picric acid.

Iodine catalyzed one-pot synthesis of highly substituted N-methyl pyrroles via [3 + 2] annulation and their in vitro evaluation as antibacterial agents

A new class of highly substituted pyrroles have been synthesized via a simple, fast, and efficient method using environmentally friendly iodine catalyzed [3 + 2] annulation. N-Methyl-N-[(E)-1-(methylsulfanyl)-2-nitro-1-ethenyl]amine (NMSM) 1 and β-nitrostyrenes 3 underwent cycloaddition to afford the desired products 4 in excellent yields under solvent and metal free conditions. All the pyrrole derivatives were evaluated for their in vitro anti-bacterial activity. Among the synthesized pyrrole derivatives, 4b, 4c, 4e, 4g, 4i, 4j, 4l, 4m and 4n displayed good inhibitory properties against a panel of Gram positive and negative infectious pathogens.

One-pot synthesis of boron diketonate complexes: photophysical properties and sensor for picric acid

Boron diketonate complexes were synthesized via a one-pot method. The method focused on the selective synthesis of unsymmetric boron diketonate by involving BF3–OEt2 and β-ketothiolester intermediates generated in situ from α-aroylketene dithioacetals using p-toluenesulfonic acid as a catalyst. The unsymmetrical boron diketonate complexes are emissive both in solution and in the solid state with high quantum yield and large Stokes shift. The boron diketonate 6e selectively senses picric acid over other nitroaromatic compounds with a detection limit of 21.5 μM.

Live cell imaging of bacterial cells: Pyrenoylpyrrole-based fluorescence labeling

A novel substituted pyrenoylpyrroles was synthesized by the reaction of pyrenoyl chalcone, TosMIC and methyl iodide under mild condition. All the synthesized compounds were screened for their bioactivity, and the MIC was determined, among which few compounds showed moderate antibacterial activity toward Gram‐positive as well as Gram‐negative bacteria. Further, cytotoxicity assay ascertained that these compounds were non‐toxic to mammalian cells as well. The pyrene chromophore in the synthesized compounds (3a–e) and (5a–e) is responsible for the good photophysical properties which have an absorbance at λ 340 nm and emission at λ 410 nm. Hence, two of the selected novel synthesized compounds with non‐cytotoxic nature prospected for bio‐imaging of bacterial cells using high‐content screening analysis show that the molecule is suitable for microbial imaging in pathological diagnostic studies.