Tilak Raj

Fluorescent Organic Nanoparticles of Biginelli-Based Molecules: Recognition of Hg2+ and Cl– in an Aqueous Medium

Biginelli-based molecules (1-3) have been synthesized and developed as a new class of fluorescent organic nanoparticle-based chemosensors. Chemosensor 2 has shown excellent selectivity and sensitivity for detection of Hg(2+) in an aqueous medium. It can detect Hg(2+) up to 1 nM, and the resultant 2Hg(2+) complex can detect Cl(-) ions (micromolar level) in an aqueous medium.

Design, synthesis and antimicrobial evaluation of dihydropyrimidone based organic–inorganic nano-hybrids

Substituted dihydropyrimidone derivatives were synthesized through one pot multicomponent Zn(ClO4)2 catalysed Biginelli reactions between differently substituted aromatic aldehydes, urea and ethylacetoacetate. Purified products were characterized and further engineered into metal inorganic conjugates of silver, copper and gold. Size, morphology and stability of nanoaggregates were analysed using FTIR, EDX, TEM, XRD and TGA analysis. Antimicrobial activities of all the synthesized compounds and their metal conjugates were evaluated against various bacterial and fungal strains. Results of investigations revealed that metal nanoaggregate Au@4c has shown maximum inhibition of MIC 8 against bacteria S. aureus. Further, bacterial SEM cell imaging carried out against S. aureus before and after treatment of Au@4c advocates that formation of blebs due to the accumulation of the cytoplasm are possible cause of bacterial cell death.

Nanoaggregates of benzothiazole-based amidine-coupled chemosensors: a chemosensor for Ag+ and the resultant complex as a secondary sensor for Cl−

Nanoaggregates of benzothiazole-based amidines were prepared for study as sensors in aqueous medium. Sensor N2 was found to behave as a selective primary sensor for Ag+, and the subsequent complex N2·Ag+ acted as a secondary sensor for Cl− in aqueous medium through a cation displacement mechanism. The cation displacement mechanism was further supported by a CV titration of complex N2·Ag+ with Cl−.

A Biginelli-based organic nanoprobe for simultaneous estimation of tyramine and 1,2-diaminopropane: application in real samples

The detrimental effects caused by the presence of biogenic amines in food samples render them an important parameter for evaluating food quality. In the current report, a facile fluorescent Biginelli based receptor 1 has been prepared through a multicomponent reaction between pyridine-2-carbaldehyde, methyl acetoacetate and 2-aminobenzimidazole in a single pot using a zinc perchlorate catalyst. Subsequently, the receptor 1 was processed to obtain aqueous phase organic nanoparticles, N1, which were characterized using DLS and TEM. Fluorescence spectroscopy studies in aqueous media revealed that the organic nanoparticles show interesting potential for Ag(I) recognition with a fluorescence “turn-off” mechanism. The resultant Ag–receptor complex, N1.Ag(I), was further found to bind with tyramine (limit of detection: 3.91 nM) and 1,2-diaminopropane (limit of detection: 4.21 nM) through unquenching of fluorescence.

Nano molar detection of Al3+ in aqueous medium and acidic soil using chromone based fluorescent organic nanoparticles (FONPs)

Compounds 1 (1,2-bis[4-oxo-4H-1-benzopyran-3-ylmethylenamino]-ethanes) and 2 (3-((E)-(3-(dimethylamino) propylimino)methyl)-4H-chromen-4-one) were synthesized using a one pot condensation reaction between 3-formylchromone and ethylenediamine/N,N-dimethylpropylamine, respectively. Compounds 1 and 2 were purified and characterized using 1H and 13C NMR, IR, mass and CHN analysis. Fluorescent organic nanoparticles (FONPs) were developed from the compounds 1 and 2 using a reprecipitation technique. The size and morphology of nano-aggregates 1 and 2 was analysed using DLS and TEM analysis. Nanoaggregates of 1 and 2 were further exploited for chemosensory applications in an aqueous medium. An efficient nanoaggregate of compound 1 has shown an excellent detection limit of 100 nM for Al3+ in an aqueous medium. The stoichiometry of the complex formation of 1 with Al3+ was found to be 1:1 using Jobs plot method. The sensor 1 was further checked for its practical applications, e.g., soil and water analysis (drinking, tap and river water). Results of Al3+ determination in soil and water were well coordinated with the existing methods. Finally, the mechanism of fluorescence recognition is supported with DFT calculations, which shows the effective binding of Al3+ with chromone leading to the lowering in the energy and thus stability. The present approach is the first report on the fabrication and chemosensory applications of chromone-based FONPs for the nanomolar detection of Al3+ in an aqueous medium.

Highly Selective and Efficient Reduction of Nitroarenes by Imidazolium Salt Stabilized Copper Nanoparticles in Aqueous Medium

Imidazolium salt stabilized copper nanoparticles were developed and characterized using TEM, DLS and EDX studies. Copper nanoparticles were further utilized as heterogeneous catalyst for the highly selective and efficient reduction of nitroarenes (1a–10a) to the corresponding aromatic amines (1b–10b) in aqueous medium. Imidazolium salt stabilized copper nanoparticles are not only causing the stability of the copper nanoparticles but also greatly enhancing the reactivity and selectivity of reduction reaction in presence of several functional group (–OH, –CHO and –NH2) in aqueous medium with higher yield.Graphical Abstract

Unusual transformation of substituted-3-formylchromones to pyrimidine analogues: Synthesis and antimicrobial activities of 5-(o-hydroxyaroyl)pyrimidines

Substituted-3-formylchromones (4a-e) on reaction with 1,3-bis-dimethylaminomethylene-thiourea (5) in refluxing toluene solution give novel substituted 5-(o-hydroxyaroyl)pyrimidines (6a-e) in high yields. A mechanistic rationalization of the formation of products (6a-e) is proffered. Antimicrobial activities of all the synthesized compounds (6a-e) were evaluated against various fungal and bacterial strains. Compound 6d display significant antifungal activity (MIC 15) against Geotrichum candidum in comparison fluconazole used as positive control. Some of the compounds also display good antibacterial activity. Cytotoxic profile of compound 6d against HeLa cells indicates that at concentration (20 μM) no significant cell death (~2%) was observed.

4‐Substituted thieno[2,3‐d]pyrimidines as potent antibacterial agents: Rational design, microwave‐assisted synthesis, biological evaluation and molecular docking studies

In an attempt to discover a new class of antibacterial agents with improved efficacy and to overcome the drug‐resistant problems, some novel 4‐substituted thieno[2,3‐d]pyrimidines have been synthesized via microwave‐assisted methodology and evaluated for their in vitro antibacterial activity against various pathogenic bacterial strains. Compounds 12b and 13c showed the promising inhibitory potencies against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli with MICs ranging from 2 to 10 μg/ml. Compound 13c was also found to be highly potent against methicillin‐resistant S. aureus (MRSA) with MIC value of 4 μg/ml. Docking simulation studies have been performed to unravel the mode of action and association study indicate the binding of potent compounds with DHPS enzyme. In silico ADME studies suggest the drug‐like characteristics of the potent compounds.