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    ABSTRACT: A new hybrid catalyst has been prepared by tethering a palladium(II) Schiff-base complex via post-synthesis modification of mesoporous silica, MCM-41. The Schiff-base has been derived from o-vanillin and 3-[(2-aminoethylamino)propyl]trimethoxysilane (ATMS) which is chemically anchored on MCM-41 via silicon alkoxide route. The anchored Schiff-base imposed a stable planar coordination sphere on the central palladium ion. The catalyst has been characterized by elemental analysis, small angle Xray diffraction, FT-IR, UV-vis, N-2 sorption study, transmission electron microscopy (TEM) studies and scanning electron microscopy (SEM) studies. X-ray and TEM measurement showed the mesoporosity of the catalyst. The activity of the catalyst has been assessed in the Suzuki C-C cross coupling reaction using various phenyboronic acid in heterogeneous condition. High selectivity for the biaryl products containing both electron-donating and electron-withdrawing substituents, high turnover, mild reaction conditions and possibility of easy recycle makes the catalyst highly desirable to address the industrial needs and environmental concerns.
    Full-text · Article · Nov 2014 · Journal of Molecular Catalysis A Chemical
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    ABSTRACT: Span and Span-Tween mixed surfactants have been used to stabilize the silver nanoparticles synthesized chemically and photochemically. This synthetic process of silver sol preparation has the advantage of producing homogeneous particles of very small size (similar to 1.65 nm) and finally aggregate brilliantly in a symmetric manner to form cubic clusters. Electromagnetic interaction in the close-packed assembly of silver aggregates generates its optical property that has been explained in the light of Maxwell-Garnett effective medium theory. A small sized silver nanoparticle has quenching properties on the fluorophore probes of methylene blue and cresol red. The particle size dependent fluorescence quenching property has been rationalized considering its surface area. Steady state circular dichroism and time resolved spectroscopic studies of Ag nanoparticles with bovine serum albumin (BSA) and human adult hemoglobin (Hb) proves the formation of a ground state BSA-Ag complex. The effect of different sizes of silver nanoparticle on the rate of electron transfer reaction between [Co-III(NH3)(5)Br](NO3)(2) and Mohr's salt (Fe-II) has also been explained rationally.
    No preview · Article · Nov 2014 · Journal of Photochemistry and Photobiology A Chemistry
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    ABSTRACT: For high-fidelity selective and sensitive fluorescent detection of zinc ions (Zn2+), a new pyrimidine based Schiff-base ligand PyMD (2,2'-(1Z, 1'Z)-(2,2'-(pyrimidine-2,4-diyl)bis(hydrazin-2-yl-1-ylidene))bis(ethan-1-yl-1-ylidene))diphenol) was designed and synthesized. In 4:1 methanol (MeOH)-water mixture, zinc (Zn2+) binding was found to promote similar to 23 fold fluorescence enhancement of PyMD at wavelength 469 nm. The limit of detection (LOD) of Zn2+ was calculated to be 6.9 x 10(-7) M according to fluorometric titration. The 1:1 binding mode of the metal complex was established by combined UV-vis, fluorescence, NMR and HRMS spectroscopic methods. Photophysical investigations including steady-state and time resolved analysis suggested a mechanism for the fluorescent zinc response that involved a ligand-to-metal charge transfer (LMCT) pathway. The experimental observations were further confirmed by DFT (Density Functional Theory) calculations of the free sensor molecule (i.e., PyMD) and the complex structure (PyMD-Zn2+). Finally, newly synthesized PyMD was applied for detection of free zinc in real samples, e.g., cabbage, banana, banana stem juice and commercial fruit juice. Besides, fluorescence behavior of PyMD-Zn2+ complex was also employed for Escherichia coli bacterial cell imaging study.
    Full-text · Article · Oct 2014 · Sensors and Actuators B Chemical
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