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Three novel Cr(III) complexes, [Cr(dafone) 2 (H 2 O) 2 ](NO 3 ) 3 ( 1 ), [Cr(opd) (dafone) 2 ](NO 3 ) 3 ( 2 ) and [Cr (phen-dione) (dafone) (H 2 O) 2 ].(NO 3 ) 3 ( 3 ) were synthesized and characterized by different techniques. Fluorescence spectroscopy, gel electrophoresis, viscosity measurement, and circular dichroism (CD) were applied to explore the interaction of Cr complexes with FS-DNA. The binding constant (K b ) was obtained from UV-Vis measurements. The obtained results exhibited the effective binding of target complexes to DNA double-strand. The fluorescence data appraised both binding and thermodynamic constants of complexes-DNA interactions. The measured thermodynamic factors (∆S˚, ∆H˚, ∆G˚) revealed that hydrogen bonding and van der Waals forces for DNA- Cr(III) complexes bear the most important roles. As well, the Stern-Volmer quenching constants (K sv ) and the binding constants (K b ) of synthesized compounds and DNA were calculated. The results of thermodynamic parameters showed that the binding of synthesized Cr(III) compounds to DNA was driven mainly through hydrogen bonds and van der Waals interactions. Viscosity measurement results showed that increasing the concentration of synthesized compounds, did not make any major changes in specific viscosity of FS-DNA. The data of viscosity and circular dichroism (CD) support the groove binding mode.

Bipyridine derivatives have shown different applications in chemistry such as electron transfer, catalysis, biological systems and artificial photosynthesis. Two cobalt(II) complexes with formula [Co(5,5'-dmbipy) 2 (NCS) 2 ] 1 and [Co(5,5'-dmbipy) 3 ] [Co(NCS) 4 ] 2 were prepared. The metal complexes 1 and 2 were characterized through FT-IR, electronic absorption, elemental analysis and 1 H-NMR. The interaction of complexes 1 and 2 with FS-DNA was investigated by fluorescence, UV-Vis and gel electrophoresis. The antibacterial properties have been studied in vitro against two gram-negative and two gram-positive standard bacterial strains. The synthesized complexes were further investigated against MCF-7 cells at 25, 50, 100 and 200 µM. The results revealed that the metal complexes can bind effectively to FS-DNA. The measured thermodynamic factors (Δ H °, Δ S ° and Δ G °) displayed that hydrogen bonding, van der Waals forces (for DNA-compound 1 ) and electrostatic binding (for DNA-compound 2 ) are the most important interactions. The binding forces in metal complexes 1 and 2 are spontaneous as suggested by the negative Δ G °. Specific viscosity of FS-DNA remained without significant changes while the concentration of complexes 1 and 2 increased. The results of molecular docking with FS-DNA illustrate the binding sites and binding modes that are in acceptable agreement with experimental results. The biological results determined that complexes 1 and 2 exhibit antibacterial activities that are better than those shown for their corresponding metal salt and free ligand. The target compounds showed low-to-moderate cytotoxicity activities. The obtained results revealed that the synthesized complexes are stronger antibacterial agents against the gram-positive than gram-negative bacteria. In the present study, for the first time we reported two Co(II) complexes bearing 5,5'-dimethyl-2,2'-bipyridine ligands.Communicated by Ramaswamy H. Sarma.

The new Co(ii) compound [Co(5,5'-dmbpy) 2 (NCS) 2 ] (a1) was prepared by reacting Co(NO 3 ) 2 ·6H 2 O, 5,5'-dimethyl-2,2'-bipyridine ligand, and Na(SCN). The nano-scale size of [Co(5,5'-dmbpy) 2 (NCS) 2 ] (a1) was synthesized using sonochemical process. The size of the nanoparticles (a2) was ∼13 ± 2 nm. We have also provided a new platform of electrochemical sensing for simultaneous detection of acetaminophen and naproxen using (a2) surface modified graphite screen printed electrode (SPE) in 0.1 M phosphate buffer solution (PBS, pH 7.0). In contrast to bare SPE, the modified SPE could significantly improve the electrooxidation activity of acetaminophen along with the rise in the current of an anodic peak. The peak currents acquired using differential pulse voltammetry (DPV) raised linearly with the raising of acetaminophen concentration and the sensor had a detection range over the concentration range of 0.009-325.0 μM, with a detection limit of 5.0 nM (S/N = 3). In the case of naproxen peak, currents of naproxen oxidation at the modified SPE were linearly dependent on the naproxen amounts in the range of 1.0-500.0 μM. The detection limit (S/N = 3) was calculated to be 0.03 μM. The DPV responses show that the peaks of acetaminophen and naproxen oxidation were vividly separated from one other with a potential difference of 410 mV between them. The low detection limit, high sensitivity, and stability made the relevant electrode applicable for the analysis of acetaminophen and naproxen in real samples. Further, its practical applicability was reliable and desirable in the analysis of pharmaceutical compounds and biological fluids. The benefits of using this modified electrode for the determination of analytes are compared with other works in the manuscript., Competing Interests: The authors declare no competing interests., (This journal is © The Royal Society of Chemistry.)

The binuclear iron(III) complex (1), namely, {[Fe(5,5'-dmbpy) 2 (OH 2) ] 2 (µ-O)}(NO 3 ) 4 with a distorted octahedral coordination, formed by four nitrogen and two oxygen atoms, was previously reported by our team. In this study the DNA-binding and cytotoxicity evaluation for target complex were studied. The results indicated strong cytotoxicity activity against A549 cells comparable to cisplatin values. The binding interaction between complex 1 and FS-DNA was investigated by UV-Vis, fluorescence spectroscopy, and gel electrophoresis at physiological pH (7.2). The DNA binding investigation has shown groove binding interactions with complex 1, therefore the hydrogen binding plays an important role in the interaction of DNA with complex 1. The calculated thermodynamic parameters (ΔH°, ΔS° and ΔG°) show that hydrogen bonding and Vander-Waals forces have an important function in Fe(III) complex-DNA interaction. Moreover, DNA cleavage was studied using agarose gel electrophoresis. Viscosity measurements illustrated that relative viscosity of DNA was unchanged with the adding concentrations of Fe(III) complex. Molecular docking simulation results confirmed the spectroscopic and viscosity titration outcomes.

A mononuclear cadmium(II) complex of formula [Cd(5,5'-dmbipy) 2 (OAc) 2 ]·2H 2 O (5,5'-dmbipy = 5,5'-dimethyl-2,2'-bipyridine and OAc = acetato ligand) has been synthesized and characterized by FT-IR, UV-Vis, 1 H-NMR, elemental analysis and single-crystal X-ray structure analysis. The molecular structure of the complex shows a distorted tetragonal antiprism CdN 4 O 4 coordination geometry around the cadmium atom, resulting in coordination by four nitrogen atoms from two 5,5'-dmbipy ligands and four oxygen atoms from two acetate anions. The interaction of this complex to FS-DNA (fish sperm DNA) has also been studied by electronic absorption, fluorescence and gel electrophoresis techniques. Binding constant ( K b ), Stern-Volmer constant ( K sv ), number of binding sites ( n ) and bimolecular quenching rate constant ( k q ) have been calculated from these spectroscopic data. These results have revealed that the metal complex can bind effectively to FS-DNA via groove binding. The calculated thermodynamic parameters (Δ H °, Δ S ° and Δ G °) show that hydrogen bonding and van der Waals forces have an important function in the Cd(II) complex-DNA interaction. The antibacterial effects of the synthesized cadmium complex have also been examined in vitro against standard bacterial strains: one Gram-positive ( Staphylococcus aureus , ATCC 25923) and one Gram-negative ( Escherichia coli, ATCC 25922) bacteria, using disk diffusion and macro-dilution broth methods. The obtained results show that the Cd(II) complex exhibits a marked antibacterial activity which is significantly better than those observed for its free ligand and metal salt for both Gram-positive and Gram-negative bacteria. However, this metal complex is a more potent antibacterial agent against the Gram-positive than that of the Gram-negative bacteria.Communicated by Ramaswamy H. Sarma.