Silver nanoparticles (AgNPs) were synthesized through a green chemical approach using the piperine isolated from black pepper. The physicochemical properties of Triton X-100 coated silver nanoparticles (Triton X-100/Ag NPs) were well characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). The TEM images confirmed the spherical shape of silver nanoparticles. The powder X-ray diffraction analysis revealed the silver nanoparticles exhibiting face-centered cubic (fcc) crystal structure with an average crystallite size of 15 nm. The cytotoxicity effects on HepG2 cells were also evaluated with a series of 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. The effective toxic concentration of Triton X-100/piperine with silver nanoparticles was too low to damage HepG2 cells. The antibacterial activity results showed that the Triton X-100/piperine/AgNPs efficiently inhibited the two bacteria namely S. aureus and E. coli. The Triton X-100/piperine/AgNPs nanoconjugates were effective in inhibiting the growth of both gram-positive and gram-negative bacteria S. aureus and E. coli.

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A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.

Multicomponent, highly efficient, catalytic synthesis of some polysubstituted imidazole under solvent-free condition is reported. Characterization of polysubstituted imidazole have been carried out by X-ray diffraction (XRD) and spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on both the absorption and emission spectral results have been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazole fit satisfactorily to a single exponential kinetics. The prototropic studies of N,N-dimethyl-4-(1,4,5-triphenyl-1H-imidazol-2-yl)naphthalen-1-amine (DTINA) reveal that two monocations [imidazole nitrogen protanated (MC1) and dimethylamino nitrogen protanated (MC2)] and a dication [both imidazole nitrogen and dimethylamino nitrogen protanated (DC)] are formed by protonation in both ground and excited states. These observations are in consistent with quantum chemical calculations.

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