Browsing by Author "Namrata Dixit"

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A hetero-bimetallic(Cu-Ru) chromogenic and fluorogenic complex as receptor of soft metal ions
(2013) Namrata Dixit; Mohammad Shahid; Arvind Misra; Lallan Mishra
A hetero-bimetallic complex of type [Cu(bpy)(NCS)(μ-NCS)Ru(bpy) 2Cl]·PF6 is synthesized and characterized using spectroscopic studies, elemental analyses and ESI-MS data. Owing to the presence of sulphur donor ligand in the complex, its affinity towards soft metal ions is monitored. It detects selectively Hg2+ and Ag+ ions over a number of environmentally relevant cations including Mn2+, Pb 2+, Zn2+, Cd2+, Ni2+, Cu 2+, and Co2+. The naked eye response is more pronounced for Hg2+ as compared to Ag+ ions. The detection limit for Hg2+ ions is 1.0 ppm while for Ag+ ions are 10 ppm. However, fluorescence response is exclusive to Ag+ ions. The complex shows a tenfold enhancement in the fluorescence intensity upon addition of Ag+ ions while no change in emission intensity is observed upon addition of other cations including Hg2+. Competitive binding experiments using fluorescence spectrometry reveal that the complex binds Ag+ selectively even in presence of tenfold excess of other cations exclusive of Hg2+ ions. The emission from the complex obtained by addition of Ag+ ions is quenched upon addition of Hg2+ ions, displaying fluorescence on-off behavior. Graphical Abstract: [Figure not available: see fulltext.] © 2012 Springer Science+Business Media B.V.
Binding of urea and thiourea with a barbiturate derivative: Experimental and theoretical approach
(2010) Namrata Dixit; P.K. Shukla; P.C. Mishra; Lallan Mishra; Herbert W. Roesky
A barbiturate derivative [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]- 2H-chromeno[2,3-d] pyrimidine- 2,4(3H)-dione)] (L1) possesses functionalities complementary to amide and thioamide. Hence its binding with urea and thiourea, is monitored using UV-vis and fluorescence titrations as well as isothermal titration calorimetry (ITC) study. Theoretical studies on hydrogen-bonded complexes of Ll-urea and Ll-thiourea in the gas phase, aqueous, and DMSO medium are carried out using density functional theory (DFT) at the B3LYP/6-31G** level. The theoretical calculations support the experimental results. © 2010 American Chemical Society.
Cytotoxicity of Cu(II) and Zn(II) 2,2′-bipyridyl complexes: Dependence of IC50 on recovery time
(2010) Yi Shi; Bonnie B. Toms; Namrata Dixit; Niraj Kumari; Lallan Mishra; Jerry Goodisman; James C. Dabrowiak
We measure the cytotoxicity of three metal complexes containing the 2,2′-bypyridine ligand, Cu(bpy)(NCS)2, 1, [Cu(bpy) 2(H2O)](PF6)2, 2, and Zn(bpy) 2(NCS)2, 3, toward neuroblastoma cells (SK-N-SH) and ovarian cancer cells (OVCAR-3) using two different cell assays. The cells were exposed to various concentrations of the compounds for 1 h and the percent inhibition of cell growth, I, measured for various times after exposure, i.e., as a function of the recovery time t. After developing the theory showing the relationship between I and t, the cytotoxicity data were analyzed to reveal that the two copper complexes, 1 and 2, cause the cells to divide at a slower rate than the controls during the recovery period, but the zinc complex, 3, had little or no effect on cell division during the recovery period. The usual metric for reporting cytotoxicity is IC50, which is the concentration of agent required to inhibit cell growth to 50% of the control population. However, since IC50 can depend on the recovery time, t, as is the case for 1 and 2, reporting IC50 for a single recovery time can hide important information about the long-time effects of a cytotoxic agent on the health of the cell population. Mechanistic studies with the compounds revealed that the copper complexes, 1 and 2, cleave closed circular pBR322 DNA in the presence of ascorbate, while the zinc complex, 3, does not facilitate DNA cleavage under the same conditions. This difference in DNA cleavage activity may be related to the fact that Cu(II) is redox active and can readily change its oxidation state, while Zn(II) is redox inert and cannot participate in a redox cycle with ascorbate to break DNA. © 2010 American Chemical Society.
One pot synthesis of Cu(II) 2,2′-bipyridyl complexes of 5-hydroxy-hydurilic acid and alloxanic acid: Synthesis, crystal structure, chemical nuclease activity and cytotoxicity
(2011) Namrata Dixit; R.K. Koiri; B.K. Maurya; S.K. Trigun; Claudia Höbartner; Lallan Mishra
A barbiturate derivative [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]- 2H-chromeno[2,3-d] pyrimidine-2,4(3H)-dione] (LH4) was allowed to react with 2,2′-bipyridyl-dinitrato-Copper(II)-dihydrate which provides two complexes, characterized as [Cu(bpy)(L1)]•3H2O (1) and [Cu(bpy)(L2)]•H2O (2), where bpy = 2,2′-bipyridine, L1 = 5-hydroxy-hydurilic acid and L2 = alloxanic acid. In a separate reaction of LH4 with Cu(NO3)2•H2O another type of complex [Cu(LH3)2•(H2O) 2]•4H2O (3) is formed. The complexes were characterized by single crystal X-ray crystallography, physicochemical and electrochemical studies. The interaction of complexes 1 and 3 with DNA was monitored using absorption and emission titrations as well as circular dichroism spectroscopy. The complexes were found to cleave supercoiled plasmid DNA to nicked circular and linear DNA. Complexes 1 and 3 were also tested against T-cell lymphoma (Dalton lymphoma DL) and showed significant cytotoxic activity with IC50 values of ∼ 9.0 nM and 0.6 nM. © 2010 Elsevier Inc.
Reversible and pH dependent photophysical properties of mixed-ligand Ru(II) complexes containing 2,2′-bipyridine and nitrosobarbiturate: Experimental and theoretical approach
(Elsevier S.A., 2013) Namrata Dixit; Stanislav Záliš; Biswajit Maiti; Lallan Mishra
A ruthenium(II) complex of type [Ru(bpy)2(L′H)] ·PF6 1 (L′H = 5-Nitroso-pyrimidine-2,4,6-trione, is prepared by the reaction of [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]-2H- chromeno[2,3-d] pyrimidine- 2,4(3H)-dione)]) LH4 with [Ru(bpy) 2(NO3)2] (prepared in situ). It is characterized using elemental analyses, spectroscopic and single crystal X-ray diffraction techniques. This complex is converted in another complex of type [Ru(bpy)2(L′)] 2 by the addition of an aqueous solution of NaOH. The complex 2 turns back to complex 1 after its neutralization by the addition of an aqueous solution of HCl. The reversible conversion of complexes 1 and 2 in each other is monitored using their UV-Vis and luminescence spectra. Quantum chemical calculations using density functional theory (DFT) method corroborates transfer of electron density from nitrosobarbiturate to metal ion leading the formation of complex 2. © 2013 Elsevier B.V.
Synthesis of a ruthenium(II) bipyridyl complex coordinated by a functionalized Schiff base ligand: Characterization, spectroscopic and isothermal titration calorimetry measurements of M2+ binding and sensing (M2+ = Ca2+, Mg2+)
(2009) Namrata Dixit; Lallan Mishra; Sourajit M. Mustafi; Kandala V.R. Chary; Hirohiko Houjou
Bis-[methylsalicylidine-4′benzoic acid]-ethylene (LH2) complexed with cis-Ru(bpy)2Cl2·2H2O provides a complex of composition [Ru(bpy)2L]·2NH4PF6 (1), which has been characterized spectroscopically. Its binding behaviour towards Mg2+ and Ca2+ ions is monitored using 1H NMR titration, isothermal titration calorimetry (ITC) and luminescence microscopy. The luminescent ruthenium complex binds Ca2+ in a more selective manner as compared to Mg2+. © 2009 Elsevier B.V. All rights reserved.