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 effectiv...

A series of mononuclear mixed ligand copper(II) complexes [Cu(bba)(diimine)](ClO(4))(2)1-4, where bba is N,N-bis(benzimidazol-2-ylmethyl)amine and diimine is 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (3), or dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (4), have been isolated and characterized by analytical and spectral methods. The coordination geometry around copper(II) in 2 is described as square pyramidal with the two benzimidazole nitrogen atoms of the primary ligand bba and the two nitrogen atoms of phen (2) co-ligand constituting the equatorial plane and the amine nitrogen atom of bba occupying the apical position. In contrast, the two benzimidazole nitrogen atoms and the amine nitrogen atom of bba ligand and one of the two nitrogen atoms of 5,6-dmp constitute the equatorial plane of the trigonal bipyramidal distorted square based pyramidal (TBDSBP) coordination geometry of 3 with the other nitrogen atom of 5,6-dmp occupying the apical position. The structures of 1-4 have been optimized by using the density functional theory (DFT) method at the B3LYP/6-31G(d,p) level. Absorption spectral titrations with Calf Thymus (CT) DNA reveal that the intrinsic DNA binding affinity of the complexes depends upon the diimine co-ligand, dpq (4) > 5,6-dmp (3) > phen (2) > bpy (1). The DNA binding affinity of 4 is higher than 2 revealing that the π-stacking interaction of the dpq ring in between the DNA base pairs with the two bzim moieties of the bba ligand stacked along the DNA surface is more intimate than that of phen. The complex 3 is bound to DNA more strongly than 1 and 2 through strong hydrophobic interaction of the methyl groups on 5,6-positions of the phen ring in the DNA grooves. The extent of the decrease in relative emission intensities of DNA-bound ethidium bromide (EB) upon adding the complexes parallels the trend in DNA binding affinities. The large enhancement in relative viscosity of DNA upon binding to 3 and 4 supports the DNA binding modes proposed. Interestingly, the 5,6-dmp complex 3 is selective in exhibiting a positive induced CD band (ICD) upon binding to DNA suggesting that it induces a B to A conformational change. In contrast, 2 and 4 show induced CD responses indicating their involvement in strong DNA binding. Interestingly, only the dpq complex 4, which displays the strongest DNA binding affinity and is efficient in cleaving DNA in the absence of an activator with a rate constant of 5.8 ± 0.1 h(-1), which is higher than the uncatalyzed rate of DNA cleavage. All the complexes exhibit oxidative DNA cleavage ability, which varies as 4 > 2 > 3 > 1 (ascorbic acid) and 3 > 2 > 4 > 1 (H(2)O(2)). Also, the complexes cleave the protein bovine serum albumin in the presence of H(2)O(2) as an activator with the cleavage ability varying in the order 3 > 4 > 2 > 1. The highest efficiency of 3 to cleave both DNA and protein in the presence of H(2)O(2) is consistent with its strong hydrophobic interaction with the biopolymers. The IC(50) values of 1-4 ag...

The dinuclear copper(II) complexes [Cu(2)(LH)(2)(diimine)(2)(ClO(4))(2)](ClO(4))(2) (1-4), where LH = 2-hydroxy-N-[2-(methylamino)ethyl]benzamide and diimine = 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. The X-ray crystal structure of complex 1 contains two copper(II) centers bridged by the phenolate moiety of the amide ligand. All of the complexes display a ligand-field band (630-655 nm) and the PhO(-)-to-Cu(II) ligand-to-metal charge-transfer band (405-420 nm) in solution. Absorption and emission spectral studies and viscosity measurements indicate that complex 4 interacts with calf thymus DNA more strongly than all of the other complexes through strong partial intercalation of the extended planar ring (dpq) with a DNA base stack. Interestingly, 3 exhibits a DNA binding affinity higher than 2, suggesting the involvement in hydrophobic interaction of coordinated 5,6-dmp with the DNA surface. In contrast to the increase in relative viscosities of DNA bound to 2-4, a decrease in viscosity of DNA bound to 1 is observed, indicating a shortening of the DNA chain length through formation of kinks or bends. All of the complexes exhibit an ability to cleave DNA (pUC19 DNA) in a 5% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an oxidant at 100 μM complex concentration, which varies as 4 > 2 > 1 > 3. The order of DNA the cleavage ability at 30 μM concentration in the presence ascorbic acid is 4 > 2 > 1 > 3, and, interestingly, 4 alone shows an ability to convert supercoiled DNA into nicked-coiled DNA even at 6 μM concentration, beyond which complete degradation is observed and the pathway of oxidative DNA cleavage involves hydroxyl radicals. In the presence of distamycin, all of the complexes, except 3, show decreased DNA cleavage activity, suggesting that the complexes prefer to bind in the DNA minor groove. All of the complexes exhibit prominent DNA cleavage even at very low concentrations (nM) in the presence of H(2)O(2) as an activator, with the order of cleavage efficiency being 3 > 2 > 4 > 1. Studies on the anticancer activity toward HEp-2 human larynx cell lines reveal that the ability of the complexes to kill the cancer cell lines varies as 3 > 4 > 2 > 1. Also, interestingly, the IC(50) value of 3 is lower than that of cisplatin, suggesting that the hydrophobicity of methyl groups on the 5 and 6 positions of the complex enhances the anticancer activity. The mode of cell death effected by the complex has been explored by using various biochemical techniques like comet assay, mitochondrial membrane potency, and Western blotting. The complex has been found to induce nuclear condensation and fragmentation in cell lines. Also, it triggers activation of caspases by releasing cytochrome c from mitochondria to cytosol, suggesting that it induces apoptosis in cells via the mitochondrial pathway.

Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO 4 ) 2 , where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g || and A || values of ~2⋅22 and 185 × 10 -4 cm -1 respectively, suggesting the presence of a square-based coordination geometry for the CuN 5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dmp. This suggests the involvement of the diimine rather than the dipica 'face' of the complexes in DNA binding. An intercalative mode of DNA interaction, which involves the insertion of dpq and to a lesser extent the phen ring of the complexes in between the DNA base pairs, is proposed. However, interestingly, the 5,6-dmp complex is involved in hydrophobic interaction of the 5,6-dmp ring in the grooves of DNA. The large enhancement in the relative viscosity of DNA on binding to the dpq and 5,6-dmp complexes supports the proposed DNA binding modes. Further, remarkably, the 5,6-dmp complex is selective in exhibiting a positive-induced CD band on binding to DNA suggesting the transition of the B form of CT DNA to A-like conformation. The variation in relative emission intensities of DNA-bound ethidium bromide observed upon treatment with the complexes parallels the trend in DNA binding affinities.

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The complexes [Cu(phen)(3)](ClO(4))(2) 1, [Cu(5,6-dmp)(3)](ClO(4))(2) 2, [Cu(dpq)(3)](ClO(4))(2) 3, [Zn(phen)(3)](ClO(4))(2) 4, [Zn(5,6-dmp)(3)](ClO(4))(2) 5 and [Zn(dpq)(3)](ClO(4))(2) 6, where phen = 1,10-phenanthroline, 5,6-dmp = 5,6-dimethyl-1,10-phenanthroline and dpq = dipyrido[3,2-d:2',3'-f]quinoxaline, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Cu(5,6-dmp)(3)](ClO(4))(2) and rac-[Zn(5,6-dmp)(3)](ClO(4))(2) have been determined. While 2 possesses a regular elongated octahedral coordination geometry (REO), 5 possesses a distorted octahedral geometry. Absorption spectral titrations of the Cu(II) complexes with CT DNA reveal that the red-shift (12 nm) and DNA binding affinity of 3 (K(b), 7.5 x 10(4) M(-1)) are higher than those of 1 (red-shift, 6 nm; K(b), 9.6 x 10(3) M(-1)) indicating that the partial insertion of the extended phen ring of dpq ligand in between the DNA base pairs is deeper than that of phen ring. Also, 2 with a fluxional Cu(II) geometry interacts with DNA (K(b), 3.8 x 10(4) M(-1)) more strongly than 1 suggesting that the hydrophobic forces of interaction of 5,6 methyl groups on the phen ring is more pronounced than the partial intercalation of phen ring in the latter with a static geometry. The DNA binding affinity of 1 is lower than that of its Zn(ii) analogue 4, and, interestingly, the DNA binding affinity 2 of with a fluxional geometry is higher than that of its Zn(II) analogue 5 with a spherical geometry. It is remarkable that upon binding to DNA 3 shows an increase in viscosity higher than that the intercalator EthBr does, which is consistent with the above DNA binding affinities. The CD spectra show only one induced CD band on the characteristic positive band of CT DNA upon interaction with the phen (1,4) and dpq (3,6) complexes. In contrast, the 5,6-dmp complexes 2 and 5 bound to CT DNA show exciton-coupled biphasic CD signals with 2 showing CD signals more intense than 5. The Delta-enantiomer of rac-[Cu(5,6-dmp)(3)](2+) 2 binds specifically to the right-handed B-form of CT DNA at lower ionic strength (0.05 M NaCl) while the Lambda-enantiomer binds specifically to the left-handed Z-form of CT DNA generated by treating the B-form with 5 M NaCl. The complex 2 is stabilized in the higher oxidation state of Cu(II) more than its phen analogue 1 upon binding to DNA suggesting the involvement of electrostatic forces in DNA interaction of the former. In contrast, 3 bound to DNA is stabilized as Cu(I) rather than the Cu(II) oxidation state due to partial intercalative interaction of the dpq ligand. The efficiencies of the complexes to oxidatively cleave pUC19 DNA vary in the order, 3> 1 >> 2 with 3 effecting 100% cleavage even at 10 microM complex concentration. However, interestingly, this order is reversed when the DNA cleavage is performed using H(2)O(2) as an activator and the highest cleavage efficiency of 2 is ascribed to its electrostatic interaction with the exterior phos...

The complexes [Co(diimine)(3)](ClO(4))(2)1-3 and [Ni(diimine)(3)](ClO(4))(2)4-6, where diimine = 1,10-phenanthroline (phen) (1,4), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (2,5) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (3,6), have been isolated, characterized and their interaction with CT DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Co(5,6-dmp)(3)](ClO(4))(2)2 and rac-[Ni(5,6-dmp)(3)](ClO(4))(2)5 have been determined and the isostructural and also isomorphous complex cations possess distorted octahedral coordination geometries. The absorption spectral titrations of the complexes with DNA reveal that the CT DNA binding affinity (K(b)) of the complexes varies as 3>2>1; 6>5>4. The Ni(II) complexes display DNA binding stronger than the corresponding Co(II) analogues, which is expected of their bigger sizes. The higher DNA binding affinity of 3 and 6 is due to the involvement in partial insertion of the extended phen ring in between the DNA base pairs. In contrast, 2 and 5 interact with DNA in the major groove through hydrophobic forces involving the methyl groups on the 5,6 positions of phen ring. An enhancement in relative viscosities of DNA upon binding to 1-6 is consistent with the DNA binding affinities. The CD spectral studies show only an induced CD band on the characteristic positive band of CT DNA for both the phen (1,4) complexes. In contrast, the 5,6-dmp (2,5) and dpq (3,6) complexes bound to CT DNA exhibit biphasic CD signals in place of the positive CD band and the negative helicity band disappears. This reveals that the complexes bind to DNA enantiopreferentially and effect changes in secondary structure of DNA. The CV and DPV responses indicate that the DNA-bound dpq complexes are stabilized in the lower oxidation state of Co(II) more than in the Co(III) oxidation state. The prominent DNA cleavage abilities of 1-3 observed in the presence of H(2)O(2) (200 μM) follows the order 2>1>3 with efficiencies of more than 90% even at 10 μM complex concentration. Interestingly, Ni(II) complexes 4-6 exhibit higher cytotoxicity (IC(50): 1, 28.0; 2, 15.0; 3, 20.0; 4, 8.0; 5, 2.0; 6, 2.0 μM at 48 h; IC(50): 1, 30.0; 2, 20.0; 3, 25.0; 4, 10.0; 5, 3.0; 6, 3.0 μM at 24 h) against human breast cancer (MCF 7) cell lines than the Co(II) complexes 1-3 as well as cisplatin in spite of their inability to cleave DNA. Also, the 5,6-dmp complex 5 shows cytotoxicity higher than the dpq complex 6 at 24 h incubation time and both 5 and 6 display apoptotic and necrotic modes of cell death.

The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 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, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structure of rac-[Fe(5,6-dmp)(3)](ClO(4))(2)3 has been determined and the packing diagram shows the presence of two enantiomeric forms of the complex cations in the same unit cell. The structures of 1-4 in solution have also been studied using UV-Visible, Cyclic Voltammetry and ESI-MS data and all data available suggests that they retain their solid state structures even in solution. The absorption spectral titrations of the iron(ii) complexes with CT DNA reveal that the DNA binding affinities of the complexes vary in the order, 4 (K(b): 9.0 × 10(3)) > 2 (6.8 × 10(3)) > 3 (4. 8 × 10(3)) > 1 (2.9 × 10(3) M(-1)). The DNA interaction of dpq complex (4) involves partial insertion of the extended phen ring in between the DNA base pairs, which is deeper than that of phen (2). The 5,6-dmp (3) complex is involved in groove binding in the major groove of DNA. The lower DNA binding affinity of 1 is due to electrostatic interaction of the cationic complexes with exterior phosphates of DNA. The EthBr displacement assay and DNA viscosity study support these DNA binding modes and the above trend in DNA binding affinities. The complexes of 1 and 2 show induced CD (ICD) upon interaction with CT DNA while 3 and 4 bound to DNA exhibit inversion in the positive band with the helicity band showing very small changes, which implies that 3 and 4 bind enantiopreferentially to DNA. The DNA cleavage abilities of 1-4 have been observed at 10 μM concentration of complexes in the presence of 100 μM H(2)O(2) and the DNA cleavage efficiency (> 90%) follows the order 3 > 1 > 2 > 4. The anticancer activity of 1-4 against human breast cancer cell line (MCF-7) has also been studied. The IC(50) values of the complexes at different incubation time intervals of 24 and 48 h follow the order, 3 (0.8, 0.6) < 4 (20.0, 17.0) < 2 (28.0, 22.0) < 1 (32.0, 29.0 μM). Interestingly, 3 exhibits anticancer activity more potent than 1, 2 and 4 and cisplatin for both 24 and 48 h. It induces cell death both through apoptosis and necrosis mechanisms, as revealed by morphological assessment data obtained by using AO/EB and Hoechst 33258 fluorescence staining methods.