Mixed ligand copper(II)-diimine complexes of 2-formylpyridine-N4-phenylthiosemicarbazone: diimine co-ligands tune the in vitro nanomolar cytotoxicity.

Recently, mixed-ligand copper(II) complexes have received much attention in searching for alternative metallodrugs to cisplatin. A series of mixed ligand Cu(II) complexes of the type [Cu(L)(diimine)](ClO4) 1-6, where the HL is 2-formylpyridine-N4-phenylthiosemicarbazone and the diimine is 2,2'-bipyridine (1), 4,4'-dimethyl-2,2'-bipyridine (2), 1,10-phenanthroline (3), 5,6-dimethyl-1,10-phenanathroline (4), 3,4,7,8-tetramethyl-1,10-phenanthroline (5) and dipyrido-[3,2-f:2',3'-h]quinoxaline (6), has been synthesized and their cytotoxicity in HeLa cervical cancer cells examined. In the molecular structures of 2 and 4, as determined by single-crystal X-ray studies, Cu(II) assumes a trigonal bipyramidal distorted square-based pyramidal (TBDSBP) coordination geometry. DFT studies reveal that the axial Cu-N4diimine bond length, interestingly, varies linearly with the experimental CuII/CuI reduction potential as well as the trigonality index τ of the five-coordinate complexes, and that methyl substitution on diimine co-ligands tunes the extent of the Jahn-Teller distortion at the Cu(II). While 4 is involved in strong DNA groove binding with a hydrophobic interaction of methyl substituents, 6 is involved in stronger binding through partial intercalation of dpq with DNA. Complexes 3, 4, 5, and 6 efficiently cleave supercoiled DNA into NC form in ascorbic acid by generating hydroxyl radicals. Interestingly, 4 exhibits higher DNA cleavage in hypoxic than at normoxic conditions. Notably, except for [CuL]+, all the complexes were stable in 0.5% DMSO-RPMI (without phenol red) cell culture medium up to 48 h at 37 °C. Remarkably, all the complexes show time-dependent cytotoxicity at nanomolar concentrations (IC50, 7.0-182 nM) in HeLa cervical cancer cells compared with uncoordinated ligand HL (IC50 > 10 000 nM). Except for 2 and 3, all the complexes exhibit higher cytotoxicity than [CuL]+ at 48 h. 4 shows (57.2 nM) higher cytotoxicity than 1 (181.5 nM) at 24 h incubation; however, notably, 1 demonstrates phenomenal cytotoxicity (7.0 nM) higher than 4 (13.6 nM) at 48 h incubation. The selectivity index (SI) reveals that complexes 1 and 4 are 53.5 and 37.3, respectively, times less toxic to HEK293 normal cells than to cancerous cells. Except for [CuL]+, all the complexes generate ROS to different extents at 24 h, with 1 producing the highest amount, which is consistent with their redox properties. Also, 1 and 4 exhibit, respectively, sub-G1 and G2-M phase cell arrest in the cell cycle. Therefore, complexes 1 and 4 have the potential to emerge as promising anticancer agents.

Crystal structure of [2-({[2-(dimethylamino-κN)ethyl]imino-κN}methyl)phenolato-κO](1,10-phen-anthroline-κ2 N,N')copper(II) perchlorate.

The title compound, [Cu(C11H15N2O)(C12H8N2)]ClO4 or [Cu(L)(phen)](ClO4) {where L refers to the deprotonated form of 2-[(2-di-methyl-amino-ethyl-imino)-meth-yl]phenol} and phen is 1,10-phenanthroline) is a mononuclear mixed ligand copper(II) complex. The CuII atom is coordinated by two N and one O atoms of the tridentate Schiff base ligand (HL) and two N atoms of the 1,10-phenanthroline ligand, resulting in a five-coordinate complex. The asymmetric unit of the title complex contains two crystallographically independent complex cations (a and b) with a slightly different geometry around the CuII ion. The value of the trigonality index τ, indicates that in both cations a and b, the CuII atoms display a square-pyramidal distorted trigonal-bipyramidal (SPDTBP) geometry, although the distortion is greater for cation a.

Induction of Redox-Mediated Cell Death in ER-Positive and ER-Negative Breast Cancer Cells by a Copper(II)-Phenolate Complex: An In Vitro and In Silico Study.

This research was aimed at finding the cytotoxic potential of the mixed ligand copper(II) complex [Cu(tdp)(phen)](ClO4)-where H(tdp) is the tetradentate ligand 2-[(2-(2-hydroxyethylamino)-ethylimino)methyl]phenol, and phen is 1,10-phenanthroline-to two genotypically different breast cancer cells, MCF-7 (p53+ and ER+) and MDA-MB-231 (p53- and ER-). The complex has been already shown to be cytotoxic to ME180 cervical carcinoma cells. The special focus in this study was the induction of cell death by apoptosis and necrosis, and its link with ROS. The treatment brought about nuclear fragmentation, phosphatidylserine externalization, disruption of mitochondrial trans-membrane potential, DNA damage, cell cycle arrest at sub-G1 phase, and increase of ROS generation, followed by apoptotic death of cells during early hours and a late onset of necrosis in the cells surviving the apoptosis. The efficacy of the complex against genotypically different breast cancer cells is attributed to a strong association through p53-mitochondrial redox-cell cycle junction. The ADMET properties and docking of the complex at the active site of Top1 are desirable attributes of a lead molecule for development into a therapeutic. Thus, it is shown that the copper(II)-phenolate complex[Cu(tdp)(phen)]+ offers potential to be developed into a therapeutic for breast cancers in general and ER-negative ones in particular.

Metalloporphyrin Nanoparticles: Coordinating Diverse Theranostic Functions.

Metalloporphyrins serve key roles in natural biological processes and also have demonstrated utility for biomedical applications. They can be encapsulated or grafted in conventional nanoparticles or can self-assemble themselves at the nanoscale. A wide range of metals can be stably chelated either before or after porphyrin nanoparticle formation, without the necessity of any additional chelator chemistry. The addition of metals can substantially alter a range of behaviors such as modulating phototherapeutic efficacy; conferring responsiveness to biological stimuli; or providing contrast for magnetic resonance, positron emission or surface enhanced Raman imaging. Chelated metals can also provide a convenient handle for bioconjugation with other molecules via axial coordination. This review provides an overview of some recent biomedical, nanoparticulate approaches involving gain-of-function metalloporphyrins and related molecules.

Assessing Photosensitizer Targeting Using Meso-Tetra(Carboxyphenyl) Porphyrin.

Mesotetra(4-carboxyphenyl)porphyrin (mTCPP) is a commercially available small molecule fluorophore and photosensitizer with four free carboxylic acid groups. mTCPP can readily be conjugated with amines for facile attachment of functional groups. In this work, we synthesized and assessed tetravalent, lysine-conjugated mTCPP, for its potential applications in targeted imaging and photodynamic therapy. Fmoc-protected d-lysine or l-lysine was conjugated to mTCPP via amide coupling with the epsilon amine group of lysine, followed by Fmoc deprotection. The resulting compounds did not dissolve well in aqueous solvent, but could be solubilized with the assistance of surfactants, including cholic acid. The l-amino acid transporter (LAT1) can uptake diverse neutral l-amino acids. In vitro studies with U87 cells revealed a non-specific uptake of the hydrophobic Fmoc-protected lysine-conjugated mTCPP precursors, but not d- or l-lysine mTCPP. Likewise, only the Fmoc-protected compounds induced substantial phototoxicty in cells following incubation and irradiation with blue light. These experimental results do not provide evidence to suggest that lysine-mTCPP is able to specifically target cancer cells. However, they do highlight mTCPP as a convenient and accessible framework for assessing molecular targeting of photosensitizers.

New [Ru(5,6-dmp/3,4,7,8-tmp)2(diimine)]²âº complexes: non-covalent DNA and protein binding, anticancer activity and fluorescent probes for nuclear and protein components.

A series of Ru(II) complexes of the type [Ru(5,6-dmp)(2)(diimine)](2+)1-3 and [Ru(tmp)(2)(diimine)](2+)4-6, where 5,6-dmp is 5,6-dimethyl-1,10-phenanthroline, tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline and diimine is dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq), dipyrido[3,2-a:2',3'-c]phenazine (dppz) and 11,12-dimethyl-dipyrido[3,2-a:2',3'-c]phenazine (11,12-dmdppz), has been isolated and the DNA binding mode of the complexes studied by using emission and circular dichroic (CD) spectral techniques. All the complexes exhibit induced circular dichroism upon binding to calf thymus (CT) DNA and show preferential binding to AT and mixed (d(CGCGATCGCG)(2)) sequences rather than to GC sequences. The complex [Ru(tmp)(2)(dpq)](2+)4 exhibits enhancement in luminescence higher than [Ru(5,6-dmp)(2)(dpq)](2+)1 upon binding to DNA. In contrast, [Ru(5,6-dmp)(2)(dppz)](2+)2 and [Ru(5,6-dmp)(2)(dmdppz)](2+)3 exhibit luminescence enhancement higher than [Ru(tmp)(2)(dppz)](2+)5 and [Ru(tmp)(2)(dmdppz)](2+)6 respectively upon DNA binding, illustrating the importance of hydrophobic forces of interaction in determining the DNA binding affinity. Among the complexes, 4 exhibits the highest enhancement in fluorescence intensity upon binding to the protein bovine serum albumin (BSA). The cytotoxicity of the complexes has been studied by screening them against non-small lung carcinoma (NCI-H460) cell line. It is noteworthy that the complex showing the strongest DNA binding affinity exhibits the highest cytotoxicity. The efficiency of the complexes as fluorescent probes for detection of nuclear morphology and proteins has been evaluated by using fluorescence microscopy. Remarkably, 4, which shows strong hydrophobic forces of interaction when bound to DNA and protein, acts as fluorescent probes for detection of nuclear components in the head, and proteins in the tail, of sperms.

[Ru(phen)2(dppz)]2+ as an efficient optical probe for staining nuclear components.

The 'molecular light switch' complexes [Ru(bpy)(2)(dppz)](2+) (1) and [Ru(phen)(2)(dppz)](2+) (2), where bpy=2,2'-bipyridine, phen=1,10-phenanthroline and dppz=dipyrido[3,2-a:2',3'-c]phenazine, have been explored as probes for diagnosing and staining nuclear components. The phen complex acts as a better staining agent for nonviable cells than for viable cells and exhibits a staining efficiency in tail region of comet more specific and stronger than the already known dye Hoechst 33258.

Induction of cell death by ternary copper(II) complexes of L-tyrosine and diimines: role of coligands on DNA binding and cleavage and anticancer activity.

The mononuclear mixed ligand copper(II) complexes of the type [Cu(L-tyr)(diimine)](ClO(4)), where tyr is L-tyrosine and diimine is 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (3), and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (4), have been isolated and characterized by analytical and spectral methods. In the X-ray crystal structure 3 Cu(II) possesses a distorted square pyramidal coordination geometry with the two nitrogen atoms of 5,6-dmp ligand and the amine nitrogen and carboxylate oxygen atoms of L-tyrosine located at the equatorial sites and the coordinated water molecule present in the apical position. The electronic absorption and electron paramagnetic resonance (EPR) spectral parameters reveal that the complexes retain their square-based geometries even in solution. All of the complexes display a ligand field band in the visible region (600-700 nm) in Tris-HCl/NaCl buffer (5:50 mM) at pH 7.2 and also axial EPR spectra in acetonitrile at 77 K with g(parallel) > g(perpendicular) indicating a d(x(2)-y(2)) ground state. The g(parallel) and A(parallel) values of 2.230 and (170-180) x 10(-4) cm(-1), respectively, conform to a square-based CuN(3)O coordination chromophore, which is consistent with the X-ray crystal structure of 3. The interaction of the complexes with calf thymus DNA (CT DNA) has been explored by using physical methods to propose modes of DNA binding of the complexes. Absorption (K(b)) and emission spectral studies and viscosity measurements indicate that 4 interacts with DNA more strongly than all of the other complexes through partial intercalation of the extended planar ring of dpq with DNA base stack. Interestingly, complex 3 exhibits a DNA binding affinity that is higher than that of 2, which suggests the involvement of 5,6-dimethyl groups on the phen ring in hydrophobic interaction with DNA surface. In contrast with the increase in relative viscosities of DNA bound to 2-4, the viscosity of DNA bound to 1 decreases, indicating the shortening of the DNA chain length by means of the formation of kinks or bends. All complexes exhibit effective DNA (pUC19 DNA) cleavage at 100 microM complex concentrations, and the order of DNA cleavage ability varies as 3 > 2 > 4 > 1. Interestingly, 3 exhibits a DNA cleavage rate constant that is higher than that of the other complexes only at 100 microM concentration, whereas 4 exhibits the highest cleavage rate constant at 80 microM complex concentration. The oxidative DNA cleavage follows the order 4 > 3 > 2 > 1. Mechanistic studies reveal that the DNA cleavage pathway involves hydroxyl radicals. Interestingly, only 4 displays efficient photonuclease activity upon irradiation with 365 nm light, which occurs through double-strand DNA breaks involving hydroxyl radicals. Furthermore, cytotoxicity studies on the nonsmall lung cancer (H-460) cell line show that the IC(50) values of 2-4 are more or less equal to cisplatin for the same cell line, indicating that they have the potential to act as very effective anticancer drugs in a time-dependent manner. The study of cytological changes reveals the higher induction of apoptosis and mitotic catastrophe for 4 and 3, respectively. The alkaline single-cell gel electrophoresis (comet assay), DNA laddering, and AO/EB and Hoechst 33258 staining assays have also been employed in finding the extent of DNA damage. Flow cytometry analysis shows an increase in the percentage of cells with apoptotic morphological features in the sub-G(0)/G(1) phase for 4, whereas it shows mitotic catastrophe for 3.

Mixed ligand ruthenium(II) complexes of bis(pyrid-2-yl)-/bis(benzimidazol-2-yl)-dithioether and diimines: study of non-covalent DNA binding and cytotoxicity.

A series of mixed ligand ruthenium(II) complexes [Ru(pdto)(diimine)](ClO4)2/(PF6)2 1-3 and [Ru(bbdo)(diimine)](ClO4), 4-6, where pdto is 1,8-bis(pyrid-2-yl)-3,6-dithiooctane, bbdo is 1,8-bis(benzimidazol-2-yl)-3,6-dithiooctane and diimine is 1,10-phenanthroline (phen), dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz), have been isolated and characterised by analytical and spectral methods. The complexes [Ru(pdto)(phen)](PF6)2 la, [Ru(pdto)(dpq)(Cl](PF6) 2a, [Ru(bbdo)(phen)](PF6)2 4a and [Ru(bbdo)(dpq)](ClO4)2 5 have been structurally characterized and their coordination geometries around ruthenium(II) are described as distorted octahedral. In la, 4a and 5 the two thioether sulfur and two py/bzim nitrogen atoms of the tetradentate pdto/bbdo ligand are folded around Ru(II) to give predominantly a "cis-alpha" configuration. (I)H NMR spectral data of the complexes support this configuration in solution. In [Ru(pdto)(dpq)Cl](PF6) 2a with a distorted octahedral coordination geometry, one of the two py nitrogens of pdto is not coordinated. The DNA binding constants (Kb: 2, 2.00 +/- 0.02 x 10(4) M(-1), s = 1.0; 3, 3.00 +/- 0.01 x 10(6) M(-1), s = 1.3) determined by absorption spectral titrations of the complexes with CT DNA reveal that 3 interacts with DNA more tightly than 2 through partial intercalation of the extended planar ring of coordinated dppz with the DNA base stack. The DNA binding affinities of the complexes increase with increase in the number of planar aromatic rings in the co-ligand, and on replacing both the py moieties in pdto complexes (1-3) by bzim moieties to give bbdo complexes (4-6). Upon interaction with CT DNA the complexes 1, 2, 5 and 6 show a decrease in anodic current in the cyclic voltammograms. On the other hand, interestingly, 3 and 4 show an increase in anodic current suggesting their involvement in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 6 alters the superhelicity of DNA upon binding with supercoiled pBR322 DNA. The cytotoxicities of the dppz complexes 3 and 6, which avidly bind to DNA, have been examined by screening them against cell lines of different cancer origins. It is noteworthy that 6 exhibits selectivity with higher cytotoxicity against the melanoma cancer cell line (A375) than other cell lines, potency approximately twice that of cisplatin and toxicity to normal cells 3 and 90 times less than cisplatin and adriamycin respectively.

Non-covalent DNA binding and cytotoxicity of certain mixed-ligand ruthenium(II) complexes of 2,2'-dipyridylamine and diimines.

A series of mixed ligand ruthenium(II) complexes [Ru(Hdpa)2(diimine)](ClO4)2, 1-5 where Hdpa is 2,2'-dipyridylamine and diimine is 1,10-phenanthroline (phen) and a modified/extended 1,10-phenanthroline such as, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), 5-methyldipyrido[3,2-d:2',3'-f]quinoxaline (mdpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) have been isolated and characterized by analytical and spectral methods. The complex [Ru(Hdpa)2(phen)](PF6)2 1 has been structurally characterized and the coordination geometry around Ru(II) in it is described as distorted octahedral. 1H NMR spectral data reveal that 1-5 should have a C2 symmetry lying on the diimine plane due to the rapid flapping of the coordinated Hdpa ligands. The interaction of the complexes with calf thymus (CT) DNA has been explored by using absorption and emission spectral and viscometry and electrochemical techniques and the mode of DNA binding of the complexes has been proposed. The DNA binding affinity of the complexes decreases with decrease in number of planar aromatic rings in the co-ligand supporting the intercalation of the diimine co-ligands in between the DNA base pairs. Circular dichroic spectral studies reveal that the complexes 3-5 exhibit induced circular dichroism upon binding to CT DNA. Interestingly, upon interaction with CT DNA all the complexes show an increase in anodic current in the cyclic voltammograms suggesting that they are involved in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 5 alters the DNA superhelicity upon binding with supercoiled pBR322 DNA, which is consistent with its higher DNA binding affinity. Further, the cytotoxicities of the complexes against human cervical epidermoid carcinoma cell line (ME180) have been examined. Interestingly, 5 exhibits a cytotoxicity against ME180 higher than other complexes with potency approximately 8 times more than cisplatin for 24 h incubation but 4 times lower than cisplatin for 48 h incubation.

Cleavage of proteins by a mixed-ligand copper(II) phenolate complex: hydrophobicity of the diimine co-ligand promotes cleavage.

The mixed-ligand copper(II) complex [Cu(tdp)(tmp)](ClO4), where H(tdp) is 2-[(2-(2-hydroxyethylamino)ethylimino)methyl]phenol and tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline, exhibits cleavage of the proteins bovine serum albumin and lysozyme, producing approximately 5 and 4 kDa protein fragments respectively within a few minutes at micromolar concentrations. The hydrophobic tmp ligand recognizes the hydrophobic site and enhances protein binding and cleavage even at physiological pH and temperature.

Mixed-ligand copper(II)-phenolate complexes: effect of coligand on enhanced DNA and protein binding, DNA cleavage, and anticancer activity.

The copper(II) complex [Cu(tdp)(ClO4)].0.5H2O (1), where H(tdp) is the tetradentate ligand 2-[(2-(2-hydroxyethylamino)ethylimino)methyl]phenol, and the mixed ligand complexes [Cu(tdp)(diimine)]+ (2-5), where diimine is 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) (4), and dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) (5), have been isolated and characterized by analytical and spectral methods. Complexes 1 and [Cu(tdp)(phen)]ClO4 (3) have been structurally characterized, and their coordination geometries around copper(II) are described as distorted octahedral. The equatorially coordinated ethanolic oxygen in 1 is displaced to an axial position upon incorporating the strongly chelating phen, as in 3. The solution structures of all the complexes have been assessed to be square-based using electronic absorption and electron paramagnetic resonance (EPR) spectroscopy. The interaction of the complexes with calf thymus DNA (CT DNA) has been explored by using absorption, emission, and circular dichroic spectral and viscometric studies, and modes of DNA binding for the complexes have been proposed. Absorption spectral (Kb = 0.071 +/- 0.005 (2), 0.90 +/- 0.03 (3), 7.0 +/- 0.2 (4), 9.0 +/- 0.1 x 10(5) M(-1) (5)), emission spectral (Kapp = 4.6 (1), 7.8 (2), 10.0 (3), 12.5 (4), 25.0 x 10(5) M(-1) (5)), and viscosity measurements reveal that 5 interacts with DNA more strongly than the other complexes through partial intercalation of the extended planar ring of the coordinated dpq with the DNA base stack. Interestingly, only complex 4 causes a B to A conformational change upon binding DNA. All the complexes hydrolytically cleave pBR322 supercoiled DNA in 10% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an activating agent, and the cleavage efficiency varies in the order 5 > 3 > 2 > 4 > 1 with 5 displaying the highest Kcat value (5.47 +/- 0.10 h(-1)). The same order of cleavage is observed for the oxidative cleavage of DNA in the presence of ascorbic acid as a reducing agent. Interestingly, of all the complexes, only 5 displays efficient photonuclease activity through double-strand DNA breaks upon irradiation with 365 nm light through a mechanistic pathway involving hydroxyl radicals. The protein binding ability of 1-5 has been also monitored by using the plasma protein bovine serum albumin (BSA), and 4 exhibits a protein binding higher than that of the other complexes. Further, the anticancer activity of the complexes on human cervical epidermoid carcinoma cell line (ME180) has been examined. Interestingly, the observed IC50 values reveal that complex 4, which effects conformational change on DNA and binds to BSA more strongly, exhibits a cytotoxicity higher than the other complexes. It also exhibits approximately 100 and 6 times more potency than cisplatin and mitomycin C for 24 and 48 h incubation times, respectively, suggesting that 4 can be explored further as a potential anticancer drug. Complexes 4 and 5 mediate the arrest of S and G2/M phases in the cell cycle progression at 24 h harvesting time, which progress into apoptosis.

Interaction of rac-[Ru(5,6-dmp)3]2+ with DNA: enantiospecific DNA binding and ligand-promoted exciton coupling.

The X-ray crystal structure of the complex rac-[Ru(5,6-dmp)(3)]Cl(2) (5,6-dmp = 5,6-dimethyl-1,10-phenanthroline) reveals a distorted octahedral coordination geometry with the Ru-N bond distances shorter than in its phen analogue. Absorption spectral titrations with CT DNA reveal that rac-[Ru(5,6-dmp)(3)](2+) interacts (K(b), (8.0 +/- 0.2) x 10(4) M(-1)) much more strongly than its phen analogue. The emission intensity of the 5,6-dmp complex is dramatically enhanced on binding to DNA, which is higher than that of the phen analogue. Also, interestingly, time-resolved emission measurements on the DNA-bound complex shows biexponential decay of the excited states with the lifetimes of short- and long-lived components being higher than those for the phen analogue. The CD spectral studies of rac-[Ru(5,6-dmp)(3)](2+) bound to CT DNA provide a definite and elegant evidence for the enantiospecific interaction of the complex with B-form DNA. Competitive DNA binding studies using rac-[Ru(phen)(3)](2+) provide support for the strong binding of the complex with DNA. The Delta-enantiomer of rac-[Ru(5,6-dmp)(3)](2+) binds specifically to the right-handed B-form of poly d(GC)(12) at lower ionic strength (0.05 M NaCl), and the Lambda-enantiomer binds specifically to the left-handed Z-form of poly d(GC)(12) generated by treating the B-form with 5 M NaCl. The strong electronic coupling of the DNA-bound complex with the unbound complex facilitates the change in its enantiospecificity upon changing the conformation of DNA. The (1)H NMR spectra of rac-[Ru(5,6-dmp)(3)](2+) bound to poly d(GC)(12) reveal that the complex closely interacts most possibly in the major grooves of DNA. Electrochemical studies using ITO electrode show that the 5,6-dmp complex stabilizes CT DNA from electrocatalytic oxidation of its guanine base more than the phen analogue does.

Structures, spectra, and DNA-binding properties of mixed ligand copper(II) complexes of iminodiacetic acid: the novel role of diimine co-ligands on DNA conformation and hydrolytic and oxidative double strand DNA cleavage.

The coordination geometry around copper(II) in [Cu(imda)(phen)(H2O)] (1) (H2imda = iminodiacetic acid, phen = 1,10-phenanthroline) is described as distorted octahedral while those in [Cu(imda)(5,6-dmp)] (2) (5,6-dmp = 5,6-dimethyl-1,10-phenanthroline) and [Cu(imda)(dpq)] (3) (dpq = dipyrido-[3,2-d:2',3'-f]-quinoxaline) as trigonal bipyramidal distorted square-based pyramidal with the imda anion facially coordinated to copper(II). Absorption spectral (Kb: 1, 0.60+/-0.04x10(3); 2, 3.9+/-0.3x10(3); 3, 1.7+/-0.5x10(4) M(-1)) and thermal denaturation studies (deltaTm: 1, 5.70+/-0.05; 2, 5.5+/-10; 3, 10.6+/-10 degrees C) and viscosity measurements indicate that 3 interacts with calf thymus DNA more strongly than 1 and 2. The relative viscosities of DNA bound to 1 and 3 increase while that of DNA bound to 2 decreases indicating formation of kinks or bends and/or conversion of B to A conformation as revealed by the decrease in intensity of the helicity band in the circular dichroism spectrum of DNA. While 1 and 3 are bound to DNA through partial intercalation, respectively, of phen ring and the extended planar ring of dpq with DNA base stack, the complex 2 is involved in groove binding. All the complexes show cleavage of pBR322 supercoiled DNA in the presence of ascorbic acid with the cleavage efficiency varying in the order 3 > 1 > 2. The highest oxidative DNA cleavage of dpq complex is ascribed to its highest Cu(II)/Cu(I) redox potential. Oxidative cleavage studies using distamycin reveal minor groove binding for the dpq complex but a major groove binding for the phen and 5,6-dmp complexes. Also, all the complexes show hydrolytic DNA cleavage activity in the absence of light or a reducing agent with cleavage efficiency varying in the order 1 > 3 > 2.

Synthesis, characterization and DNA-binding properties of rac-[Ru(5,6-dmp)2(dppz)]2+--enantiopreferential DNA binding and co-ligand promoted exciton coupling.

The new mixed ligand complex [Ru(5,6-dmp)2(dppz)]Cl2 [5,6-dmp = 5,6-dimethyl-1,10-phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine] has been isolated and its DNA-binding properties studied by employing UV-visible (UV-Vis), steady-state and time-resolved emission and circular dichroism spectral methods, viscometry, thermal denaturation and cyclic/differential pulse voltammetric techniques. The complex acts as a 'molecular light-switch' on binding to DNA, but the enhancement in emission intensity is only 75% of that of the parent complex [Ru(phen)2(dppz)]2+ (phen = 1,10-phenanthroline). The emission decay curves and quenching studies suggest two different DNA-binding modes both involving intercalation of the dppz ligand of [Ru(5,6-dmp)2(dppz)]Cl2. The characteristic red-shift of the induced CD signal, which is not observed for the phen analogue, arises from exciton coupling. The hydrophobicity and polarizability of 5,6-dmp co-ligand strongly favour the formation of a stable structural and electronic scaffold on the DNA surface for the unbound molecules to couple with the DNA-bound complexes facilitating spontaneous assembly of novel extended molecular aggregates using DNA as a helical nanotemplate. This observation is consistent with the shift in Ru(II)/Ru(III) redox potential to more positive values with a dramatic drop in peak current on binding of the 5,6-dmp complex to calf thymus (CT) DNA. Equilibrium dialysis experiments monitored by CD spectroscopy unambiguously reveal the preferential binding of the delta-enantiomer to the right-handed calf thymus (CT) DNA. The 5,6-dmp complex exhibits preferential binding to [d(AT)6]2 over [d(GC)6]2 and the complex aggregates formed consist of six [Ru(5,6-dmp)2(dppz)]2+ cations per base pair of [d(AT)6]2; however, only one [Ru(phen)2(dppz)]2+ cation per base pair is involved in DNA binding.

Copper(II) complexes of tridentate pyridylmethylethylenediamines: role of ligand steric hindrance on DNA binding and cleavage.

Copper(II) complexes of three linear unsymmetrical tridentate ligands viz. N-methyl-N'-(pyrid-2-ylmethyl)ethylenediamine (L1), N,N-dimethyl-N'-(pyrid-2-ylmethyl)ethylenediamine (L2) and N,N-dimethyl-N'-((6-methyl)pyrid-2-ylmethyl)ethylenediamine (L3) have been isolated and characterized by elemental analysis, electronic absorption and EPR spectroscopy and cyclic and differential pulse voltammetry. Of these complexes [Cu(L2)Cl2] and [Cu(L3)Cl2] have been structurally characterized by X-ray crystallography. The [Cu(L2)Cl2] complex crystallizes in the monoclinic space group P2(1)/n with a=11.566(2) A, b=7.369(1) A, c=15.703(3) A, alpha=90 degrees , beta=109.68(8) degrees , gamma=90 degrees and Z=4 while [Cu(L3)Cl2] crystallizes in the triclinic space group P1 with a=9.191(2) A, b=12.359(3) A, c=14.880(3) A, alpha=79.61(13) degrees , beta=86.64(13) degrees , gamma=87.28(8) degrees and Z=2. The coordination geometries around copper (II) in these two complexes are best described as trigonal bipyramidal distorted square based pyramidal (TBDSBP). The distorted CuN3Cl basal plane in them is comprised of three nitrogen atoms of the meridionally coordinated ligand and a chloride ion and the axial position is occupied by the other chloride ion. The interaction of these complexes with Calf Thymus DNA (CT DNA) has been studied by using absorption, emission and circular dichroic spectral methods, thermal denaturation studies, viscometry and cyclic and differential pulse voltammetry. A strong blueshift in the ligand field band and a redshift in the ligand based bands of the copper(II) complexes on binding to DNA imply a covalent mode of DNA binding of the complexes, which involves coordination of most possibly guanine N7 nitrogen of DNA to form a CuN4 chromophore. This is supported by studying the interaction of the complexes with N-methylimidazole (N-meim), guanosine monophosphate (GMP), adenosine monophosphate (AMP) and cytidine (cytd) by ligand field and EPR spectral methods, which indicate the formation of a CuN4 chromophore only in the case of the more basic N-meim and GMP. The DNA melting curves obtained in the presence of copper(II) complexes reveal a monophasic and irreversible melting of the DNA strands and the high positive DeltaTm values (12-21 degrees C) also support the formation of strong Cu-N bonds by the complexes with DNA, leading to intra- and/or interstrand crosslinking of DNA. Competitive ethidium bromide (EthBr) binding studies show that the L2 and L3 complexes are less efficient than the L1 complex in quenching EthBr emission, which is consistent with their forming DNA crosslinking preventing the displacement of the DNA-bound EthBr. A very slight decrease in relative viscosity of DNA is observed on treating the L1 and L2 complexes with CT DNA; however, a relatively significant decrease is observed for the L3 complex suggesting that the length of the DNA fiber is shortened. DNA cleavage experiments show that all the complexes induce the cleavage of pBR322 plasmid DNA, the complex of L1 being more efficient than those of sterically hindered L2 and L3 ligands.