Two mononuclear fluorophore-labeled copper(II) complexes [Cu(nip)(acac)](+)(2) and [Cu(nip)2](2+) (3), where fluorophore is 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (nip) (1) and acac is acetylacetone, have been synthesized and characterized by various techniques. The ligand 1 and complex 2 are structurally characterized by single-crystal X-ray diffraction. The coordination geometries around the copper are square planar in solid as well as solution state as evidenced by electron paramagnetic resonance (EPR) spectroscopy. The density functional calculations carried out on 1-3 have shown that electron-rich regions in the highest occupied orbital are localized on the naphthalene and partly on the phenanthroline moiety. Both complexes 2 and 3 in dimethyl sulfoxide (DMSO) exhibit near square planar structure around the metal ion in their ground state. Time-dependent density functional theory (TD-DFT) calculations reveal that Cu(II) ion in complex 2 shows tetrahedral coordination around the metal while 3 retains its square planar geometry in the lowest excited state. The interaction of complexes with calf-thymus DNA (CT DNA) has been explored by using absorption, emission, thermal denaturation, and viscosity studies, and the intercalating mode of DNA binding has been proposed. The complexes cleave DNA oxidatively without any exogenous additives. The protein binding ability has been monitored by quenching of tryptophan emission in the presence of complexes using bovine serum albumin (BSA) as model protein. The compounds showed dynamic quenching behavior. Further, the anticancer activity of the complexes on MCF-7 (human breast cancer), HeLa (human cervical cancer), HL-60 (human promyelocytic leukemia), and MCF-12A (normal epithelial) cell lines has been studied. It has been observed that 3 exhibits higher cytotoxicity than 2, and the cells undergo apoptotic cell death.

Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

Free radical generation is an inevitable consequence of aerobic existence and is implicated in a wide variety of pathological conditions including cancer, cardiovascular disease, ageing and neurodegenerative disorder. Free radicals can, however, be used to our advantage since their production is catalysed by synthetic inorganic molecules—termed artificial metallonucleases—that cut DNA strands by oxidative cleavage reactions. Here, we report the rational design and DNA binding interactions of a novel di-Cu2+ artificial metallonuclease [Cu2(tetra-(2-pyridyl)-NMe-naphthalene)Cl4] (Cu2TPNap). Cu2TPNap is a high-affinity binder of duplex DNA with an apparent binding constant (Kapp) of 107 M(bp)−1. The agent binds non-intercalatively in the major groove causing condensation and G-C specific destabilization. Artificial metallonuclease activity occurs in the absence of exogenous reductant, is dependent on superoxide and hydrogen peroxide, and gives rise to single strand DNA breaks. Pre-associative molecular docking studies with the 8-mer d(GGGGCCCC)2, a model for poly[d(G-C)2], identified selective major groove incorporation of the complex with ancillary Cu2+-phosphate backbone binding. Molecular mechanics methods then showed the d(GGGGCCCC)2 adduct to relax about the complex and this interaction is supported by UV melting experiments where poly[d(G-C)2] is selectively destabilized.

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Complexes of the type [Ru(N-N)(2)(bxbg)]Cl(2) where N-N is 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), dipyrido [3,2-d:2',3f] quinoxaline (dpq) (3), and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (4) which incorporate the bis(o-xylene)bipyridine glycoluril (bxbg) as the ancillary ligand have been synthesized and characterized by IR, NMR, UV-visible, luminescence, ESI-MS, cyclic voltammetry, and spectroelectrochemistry. The bis(o-xylene)bipyridine glycoluril initiates a head to head association which act as the nucleation point for the further growth in two direction by head-to-head and tail-to-tail self-association resulting in formation of aggregates in water which have been investigated by (1)H NMR, NOESY, steady state luminescence dilution experiments, and electron microscopy studies. The self-association has been confirmed by single crystal X-ray analysis of complex 2. Electrochemical and spectroelectrochemical studies in acetonitrile show that these complexes undergo reversible one electron oxidation from Ru(II) to Ru(III). The binding of these complexes with calf thymus DNA (CT-DNA) has been studied by absorption titration, steady-state and time-resolved emission measurement experiments, to investigate the influence of the ancillary ligand. The binding ability of these complexes to DNA is dependent on the planarity of the intercalative polypyridyl ligand which is further affected by the bis(o-xylene)bipyridine glycoluril ancillary ligand.

Two novel water soluble ruthenium(II) complexes [Ru(bpy)(2)(bqbg)](2+) and [Ru(phen)(2)(bqbg)](2+) have been structurally characterized and their DNA condensation activity, cytotoxicity, and cellular uptake studies of DNA condensates as potential non-viral DNA carriers were evaluated.

Complexes of the type [Ru(bxbg)(2) (N-N)](2+), where N-N denotes 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), dipyrido[3,2-d:2',3-f] quinoxaline (dpq) (3), and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (4), incorporating bis(o-xylene)bipyridine-glycoluril (bxbg) as an ancillary "molecular clip" ligand, have been synthesized and characterized. These ruthenium(II) complexes of bis(o-xylene)bipyridine-glycoluril self-associate in water through specific molecular recognition processes to form polycationic arrays. These arrays containing electrostatic binders as well as intercalator ligands at micromolar doses rapidly condense free DNA into globular nanoparticles of various sizes. The DNA condensation induced by these complexes has been investigated by electrophoretic mobility assay, dynamic light scattering, and transmission electron microscopy. The cellular uptake of complex-DNA condensates and the low cytotoxicity of these complexes satisfy the requirements of a gene vector.

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