Study of DNA Light Switch Ru(II) Complexes : Synthesis,Characterization, Photocleavage and Antimicrobial Activity

The three Ru(II) complexes of [Ru(phen)₂dppca]²⁺ (1) [Ru(bpy)₂dppca]²⁺ (2) and [Ru(dmb)₂dppca]²⁺ (3) (where phen = 1,10 phenanthroline, bpy = 2,2-bipyridine, dmb = 2 ,2-dimethyl 2′,2′-bipyridine and polypyridyl ligand containing a single carboxylate functionality dppca ligand (dipyridophenazine-11-carboxylic acid) have been synthesized and characterized. These complexes have been shown to act as promising calf thymus DNA intercalators and a new class of DNA light switches, as evidenced by UV-visible and luminescence titrations with Co²⁺ and EDTA, steady-state emission quenching by [Fe(CN)₆]⁴⁻ and KI, DNA competitive binding with ethidium bromide, viscosity measurements, and DNA melting experiments. The results suggest that 1, 2, and 3 complexes bind to CT-DNA through intercalation and follows the order 1 > 2 > 3. Under irradiation at 365 nm, the three complexes have also been found to promote the photocleavage of plasmid pBR322 DNA.     

Identification of statistical regimes and crossovers in coherent random laser emission

We measure intensity statistics and identify statistical regimes and crossovers in random lasers based on nonresonant feedback. A single parameter extracted from an α-stable Levy fit is used to characterize the intensity distributions in all regimes. Measurements made over a range of scattering strengths, excitation energies, and sample sizes enable us to demarcate three regimes of intensity statistics and the corresponding crossovers. An initial subthreshold Gaussian regime abruptly transits into a Levy regime at the random lasing threshold, which is followed by a continuous gradual crossover toward a second Gaussian regime. We find that the prominence of the Levy regime depends upon the sample size.     

Aerosol-based coherent random laser

We demonstrate coherent random lasing from an aerosol of dye-doped microdroplets in air. The aerosol is in the form of a linear array of polydisperse, arbitrarily shaped, and randomly spaced microdroplets with average dimensions of about 30 μm. Upon optical excitation, ultranarrow lasing modes were observed in the emission along the axis of the linear array, while the transverse emission exhibited intrascatterer resonance peaks. Direct spatiospectral imaging and lasing threshold studies confirmed the origin of the lasing peaks to be from spatial modes that extended over the array of the polydisperse microdroplets.     

Biomimetic Model of Coenzyme B12: Aquabis(ethane‐1,2‐diamine‐κN,κN′)ethylcobalt(III) – Its Kinetic and Binding Studies with Imidazoles and Amino Acids and Interactions with CT DNA

Pseudo‐first‐order reaction kinetics and binding studies of trans‐[Co(en)₂(Et)H₂O] complex with 1H‐imidazole, substituted 1H‐imidazoles, histidine, histamine, glycine and glycine ethyl ester were investigated by means of spectrophotometric techniques. Equilibrium constants were determined as a function of pH at 25°. Binding and kinetic studies were correlated to basicity and steric hindrance. From the equilibrium data, it was found that the entering nucleophile is participating in the transition state, an I_d mechanism is proposed. The effect of the incoming ligands on the complex was studied by molecular mechanics. The interaction of trans‐[Co(en)₂(Et)H₂O] with CT DNA was studied spectrophotometrically.     

Synthesis, characterization and DNA-binding characteristics of Ru(II) molecular light switch complexes

A series of four polypyridyl Ru(II) complexes such as [Ru(L)₄(PIP)]²⁺ and [Ru(L)₄PPIP]²⁺ where L is 4-amino pyridine and Pyridine (PIP?=?2-phenylimidazo[4,5-f] [1, 10] phenanthroline), (PPIP?=?2-(4??-phenoxy-phenyl) imidazo[4,5-][1, 10]phenanthroline) have been synthesized and characterized by elemental analysis, physicochemical methods such as UV?Cvis, IR and NMR spectroscopic techniques. The DNA-binding behavior of these complexes was investigated by electronic absorption titrations, fluorescence spectroscopy, viscosity measurements and salt-dependent studies. The experimental results indicate that all these complexes can bind to DNA through an intercalation mode, the DNA-binding affinities of these complexes follow the order [Ru(4-APy)₄(PPIP)]²⁺(1)?>?[Ru(Py)₄PPIP]²⁺(2)?>?[Ru(4-APy)₄(PIP)]²⁺(3)?>?[Ru(Py)₄PIP]²⁺(4). Noticeably, these complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA. Further, all four complexes screened for their antimicrobial activity indicate that the complexes show appreciable activity against Escherichia coli and Neurospora Crassa. In addition, in the presence of Co²⁺, the emission of DNA-[Ru(L₄)PPIP/PIP]²⁺ can be quenched and recovered by the addition of EDTA, which exhibited the DNA ??light switch?? properties.     

DNA-Binding and cytotoxicity of the cobalt(III) ethylenediamine pyrazole complex [Co(en)2(pyz)2]3+

The complex of cobalt(III) ethylenediamine was synthesized, isolated and characterized by UV-Vis, IR, and 1H NMR spectral methods. The binding of the complex with calf thymus DNA was investigated by absorption and emission spectroscopy, viscosity measurements, DNA melting and DNA photocleavage. The spectroscopic studies together with the viscosity measurements and DNA melting studies indicated that the complex binds to calf thymus DNA in a nonintercalative mode. This complex is found to promote photocleavage of the DNA plasmid pBR322 and shows a cytotoxic effect against CHO cells.     

Synthesis,Characterization, DNA Binding Properties,Fluorescence Studies and Toxic Activity of Cobalt(III) and Ruthenium(II) Polypyridyl Complexes

The new ligand 4-(isopropylbenzaldehyde)imidazo[4,5-f ][1,10]phenanthroline (ippip) and its complexes [Ru(phen)₂(ippip)]²⁺(1),[Co(phen)₂(ippip)]³⁺(2),[Ru(bpy)₂(ippip)]²⁺(3),[Co(bpy)₂(ippip)]³⁺(4)(bpy=2,2-bipyridine) and (phen=1,10-phenanthroline) were synthesized and characterized by ES⁺-MS, ¹H and ¹³C NMR. The DNA binding properties of the four complexes were investigated by different spectrophotometric methods and viscosity measurements. The results suggest that complexes bind to calf thymus DNA (CT-DNA) through intercalation. When irradiated at 365 nm, the complexes promote the photocleavage of pBR322 DNA, and complex 1 cleaves DNA more effectively than 2, 3, 4 complexes under comparable experimental conditions. Furthermore, photocleavage studies reveal that singlet oxygen (¹O₂) plays a significant role in the photocleavage.     

Analytical Techniques Used to Detect DNA Binding Modes of Ruthenium(II) Complexes with Extended Phenanthroline Ring

This review describes the analytical techniques used to detect DNA-probes such as Ru(II) complexes with hetero cyclic imidazo phenanthroline (IP) ligands. Studies on drug-DNA interactions are useful biochemical techniques for visualization of DNA both in vitro and in vivo. The interactions of small molecules that binds to DNA are mainly classified into two major classes, one involving covalent binding and another non-covalent binding. Covalent binding in DNA can be irreversible and may leads to inhibition of all DNA processes which subsequently leads to cell death. Usually, covalent interactions leads to permanent changes in the structure of nucleic acids. The non-covalent interaction of molecules with DNA can be due to electrostatic interaction, intercalation and groove binding. These interactions of DNA probes can be explored by various spectroscopic techniques viz. UV–visible, emission, emission quenching spectroscopy, viscosity and thermal denaturation measurements.     

Influence of Gold Nanoshell on Hyperthermia of Super Paramagnetic Iron Oxide Nanoparticles (SPIONs)

Gold nanoshell around super paramagnetic iron oxide nanoparticles (SPIONs) was synthesized and small angle X-ray scattering (SAXS) analysis suggests a gold coating of approximately 0.4 to 0.5 nm thickness. On application of low frequency oscillating magnetic fields (44 - 430 Hz), a four- to five-fold increase in the amount of heat released with gold-coated SPIONs (6.3 nm size) in comparison with SPIONs (5.4 nm size) was observed. Details of the influence of frequencies of oscillating magnetic field, concentration and solvent on heat generation are presented. We also show that, in the absence of oscillating magnetic field, both SPIONs and SPIONs@Au are not particularly cytotoxic to mammalian cells (MCF-7 breast carcinoma cells and H9c2 cardiomyoblasts) in culture, as indicated by the reduction of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium by viable cells in a phenazine methosulfate-assisted reaction.