The key role of hydrogen bonding in the nuclearity of three copper(II) complexes with hydrazone-derived ligands and nitrogen donor heterocycles

Peculiar DNA partial threading intercalative ability of tetradentate copper complex based on ONO hydrazone backbone and an ancillary ligand

Multidentate copper metal complexes have been in the limelight in the area of DNA interaction studies exhibiting intercalation, groove binding and cross linking modes. Design of metal complex based on the versatile ligands decides their mode of DNA binding behavior. Based on this, a tetradentate Copper (II) complex, [Cu(L)(4,4'-bpy)], is synthesized using ONO hydrazone ligand and ancillary ligand, 4,4'-bipyridine. It is characterized by physico-chemical and UV-Visible, FTIR, Mass and EPR spectroscopic techniques. The binding pattern of the characterized complex with DNA has been assessed by UV absorption and fluorescence spectral titrations as well as viscosity studies and it has exhibited peculiar threading intercalation. The binding constant, Kb value of the synthesized complex was found to be (4.38 ± 0.09) × 104 M-1, greater than that of the hydrazone ligand (Kb = 2.29 × 104 M-1) and lesser than the classical intercalator ethidium bromide - EtBr (Kb = 107). The fluorescence quenching assays in the presence of ethidium bromide and viscometric studies show threading intercalative mode of binding of the complex to the DNA base pairs. Molecular docking studies further supports such a binding pattern with the bipyridine ring of the complex intercalating with deoxycytosine nucleobase of DNA. ADME (Absorption, Distribution, Metabolism and Excretion) parameters of the complex and ligand were predicted to get an idea of drug likeliness and to correlate the structural properties with semi DNA intercalative pattern of the same.

A highly selective colorimetric and fluorescent probe for quantitative detection of Cu2+/Co2+: The unique ON-OFF-ON fluorimetric detection strategy and applications in living cells/zebrafish

Identifying and detecting similar target cations through combining "turn on" and "turn off" fluorescence mechanism is effective and challenging. Now a new colorimetric and ON-OFF-ON fluorescent probe N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)-3-hydroxy-2-naphthohydrazide (L) was reported, which could detect Cu²⁺ and Co²⁺ in phosphate buffered CH₃CH₂OH-H₂O solvent system. With the assistance of glutathione and pH adjustment, a unique ON-OFF-ON fluorescence detection strategy could be achieved for distinguishing Cu²⁺ and Co²⁺. The emission of probe could recover from the L-Cu²⁺ and L-Co²⁺ system by addition of GSH or adjusting pH value to 4, respectively, which is due to the abolishment of paramagnetic Cu²⁺/Co²⁺. Based on fluorescence titration experiments, the limit of detection was determined as 3.84 × 10^-9 M and 4.55 × 10^-9 M for Cu²⁺ and Co²⁺, respectively. Meanwhile, the detection limit reached 6.21 × 10^-8 M for Cu²⁺ and 6.96 × 10^-8 M for Co²⁺ according to absorbance signal output. Fast recognition of Cu²⁺/Co²⁺ can be achieved by obvious color changes from green to colorless under UV light, as well as from yellow to orange-red in room light. The binding mode of L toward Cu²⁺ and Co²⁺ have been systematically studied by Job's plot analysis, ESI-MS, IR and density functional theory calculations. Most strikingly, further practical applications of the probe L in fluorescence imaging were investigated in MCF-7 cells and zebrafish due to its low cytotoxicity and good optical properties, suggesting that L could serve as a fluorescent sensor for tracking Cu²⁺ and Co²⁺in vivo.

DNA/protein interaction, cytotoxic activity and magnetic properties of amino-alcohol Schiff base derived Cu(ii)/Ni(ii) metal complexes: influence of the nuclearity and metal ions

The reactions of amino-alcohol derived Schiff-base ligands with Cu(ii) and Ni(ii) salts have afforded four novel polynuclear complexes, which exhibited interesting magnetic and cytotoxic properties.