Four new copper(II) complexes with 1,3-tpbd ligand: Synthesis, crystal structures, magnetism, oxidative and hydrolytic cleavage of pBR322 DNA

Four copper(II) complexes [Cu₂(1,3-tpbd)Cl₄]·EtOH (1), {[Cu₂(1,3-tpbd)(μ-Cl)₂](ClO₄)₂(H₂O)_4.5 (NaClO₄)}_∞ (2), [Cu₂(1,3-tpbd)(1,10-phen)₂(H₂O)₂](ClO₄)₄ (3) and [Cu₂(1,3-tpbd)(2,2′-bpy)₂(H₂O)₂](ClO₄)₄ (4) (1,3-tpbd = N,N,N′,N′-tetrakis(2-pyridylmethyl)benzene-1,3-diamine) have been synthesized and characterized by X-ray single crystal structure analysis. Variable-temperature magnetic susceptibility studies (2-300 K) indicate the existence of antiferromagnetic coupling between the copper(II) ions in complexes 2 and 3. The interactions of the four complexes with calf thymus DNA (CT-DNA) have been investigated by UV absorption, fluorescent spectroscopy, circular dichroism spectroscopy, viscosity and cyclic voltammetry, and the modes of CT-DNA binding to the complexes have been proposed. Furthermore, DNA cleavage activities by the four complexes were performed in the presence and absence of external agents, the results indicate that their cleavage activities have been promoted in the presence of external agents. Mechanism investigation shows that the four complexes could cleave DNA through both oxidative and hydrolytic processes. In the four copper(II) complexes, complex 2 showed highest cleavage activity with the pseudo-Michaelis-Menten kinetic paraments k_cat = 5.16 h⁻¹ and K_m = 3.6 × 10⁻⁵ M.     

Novel peptide-based copper(II) complexes for total hydrolytic cleavage of DNA

Stable Cu(II) complexes with histamine- and histidine-containing dipeptides histidylserine and histidylphenylalanine have been developed. Their interaction in solution has been investigated, and the stability of their complexes was determined. The nature of binding in these complexes has been explained with the help of potentiometric pH titrations and 1H-NMR spectroscopy. The geometry of these complexes has been established by electronic spectra. The DNA-binding and -cleavage abilities of these Cu(II) complexes have been probed by the absorption, thermal denaturation, fluorescence, and electrophoresis experiments. The results suggest that these peptide-based Cu(II) complexes effectively bind and efficiently cleave DNA under mild biological conditions. Since Cu(II) complexes are known to play an important role in phosphodiester bond cleavages, these results assume importance.     

DNA-binding and cleavage studies of macrocyclic copper(II) complexes

Three hexaaza macrocyclic copper (II) complexes with different functional groups have been synthesized and characterized by elemental analysis and infrared spectra. Absorption and fluorescence spectral, cyclic voltammetric and viscometric studies have been carried out on the interaction of [CuL(1)]Cl(2) (L(1)[double bond]3,10-bis(2-methylpyridine)-1,3,5,8,10,12-hexaazacyclotetradecane), [CuL(2)]Cl(2) (L(2)[double bond]3,10-bis(2-propionitrile)-1,3,5,8,10,12-hexaazacyclotetradecane) and [CuL(3)]Cl(2) (L(3)=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) with calf thymus DNA. The results suggest that three complexes can bind to DNA by different binding modes. The spectroscopic studies together with viscosity experiments and cyclic voltammetry suggest that [CuL(1)](2+) could bind to DNA by partial intercalation via pyridine ring into the base pairs of DNA. [CuL(2)](2+) may bind to DNA by hydrogen bonding and hydrophobic interaction while [CuL(3)](2+) may be by weaker hydrogen bonding. The functional groups on the side chain of macrocycle play a key role in deciding the mode and extent of binding of complexes to DNA. Noticeably, the three complexes have been found to cleave double-strand pUC18 DNA in the presence of 2-mercaptoethanol and H(2)O(2).     

DNA-binding and cleavage studies of novel binuclear copper(II) complex with 1,1'-dimethyl-2,2'-biimidazole ligand

DNA-binding properties of novel binulear copper(II) complex [Cu(2)(Dmbiim)(4)(H(2)O)(2)](ClO(4))(4).6H(2)O, where Dmbiim = 1,1'-Dimethyl-2,2'-biimidazole are investigated using electronic absorption spectroscopy, fluorescence spectroscopy, viscosity measurement and voltammetry. The results show that the copper(II) complex interacts with DNA through minor groove binding. The interaction between the complex and DNA has also been investigated by gel electrophoresis, interestingly, we found that the copper(II) complex can cleave circular plasmid pBR322 DNA efficiently in the presence of AH(2) (ascorbic acid) at pH 8.0 and 37 degrees C.     

DNA cleavage by novel copper (II) complex and the role of beta-cyclodextrin in promoting cleavage

A new cyclen derivative N-1-naphthyl-[4-amino-5-oxo-5-(1,4,7,10-tetraazacyclododecan-1-yl)]valeramide and the copper (II) complex were synthesized and characterized. The copper (II) complex showed DNA cleavage ability without the existence of other additives. The pUC19 plasmid DNA was cleaved to linear form by 0.71 microM of complex under physiological conditions. beta-Cyclodextrin was used to investigate the relationship of nuclease activity and DNA binding ability. The addition of beta-cyclodextrin exhibited an unexpected ability to promote the cleavage of DNA. The role of the beta-cyclodextrin in DNA cleavage process was studied by (1)H NMR and fluorescence spectrum. According to the data of viscosity measurement, it was confirmed that the binding of complex with DNA should be a groove binding model. All the results suggested that the increasing of the DNA cleavage ability was attributed to the interaction between beta-cyclodextrin and the naphthyl moieties. beta-Cyclodextrin could include the naphthyl moieties and keep it from the minor/major groove of DNA and decreased the DNA binding ability, therefore, the copper (II) center was activated to generate more reactive oxygen species, which was responsible for DNA cleavage.     

Investigation of DNA binding mechanism, photoinduced cleavage activity, electrochemical properties and biological functions of mixed ligand copper(II) complexes with benzimidazole derivatives: synthesis and spectral characterization

The benzimidazole derivative Schiff bases and their copper(II) (Cu(II)) mixed-polypyridyl complexes (1-4) have been synthesized and characterized by the spectral and analytical techniques. DNA binding/cleavage studies indicate a stronger binding capability for the complex 4 which is confirmed by the absorbance, viscometric and gel-electrophoresis studies. The photocleavage of plasmid pBR322 DNA reveals that hydroxyl radical (OH(?)) and singlet oxygen ((1)O(2)) are likely to be the reactive species. Analysis of the growth activity shows that the antimicrobial effect of these Schiff bases on Gram-negative bacteria is higher than that on Gram-positive. Furthermore, the complexes having nitro group show an increased antimicrobial effect.     

DNA binding, DNA cleavage, and cytotoxicity studies of two new copper (II) complexes

The DNA binding behavior of [Cu(phen)(phen-dione)Cl]Cl (1) and [Cu(bpy)(phen-dione)Cl]Cl (2) was studied with a series of techniques including UV-vis absorption, circular dichroism spectroscopy, and viscometric methods. Cytotoxicity effect and DNA unwinding properties were also investigated. The results indicate that the Cu(II) complexes interact with calf-thymus DNA by both partially intercalative and hydrogen binding. These findings have been further substantiated by the determination of intrinsic binding constants spectrophotometrically, 12.5?×?10(5) and 5?×?10(5) for 1 and 2, respectively. Our findings suggest that the type of ligands and structure of complexes have marked effect on the binding affinity of complexes involving CT-DNA. Circular dichroism results show that complex 1 causes considerable increase in base stacking of DNA, whereas 2 decreases the base stacking, which is related to more extended aromatic area of 1,10-phenanthroline in 1 rather than bipyridine in 2. Slow decrease in DNA viscosity indicates partially intercalative binding in addition to hydrogen binding on the surface of DNA. The second binding mode was also confirmed by additional tests: interaction in denaturation condition and acidic pH. Also, these new complexes induced cleavage in pUC18 plasmid DNA as indicated in gel electrophoresis and showed excellent antitumor activity against K562 (human chronic myeloid leukemia) cells.     

Synthesis, DNA binding, photo-induced DNA cleavage, cytotoxicity and apoptosis studies of copper(II) complexes

Two new Cu(II) complexes, [Cu(acac)(dpq)Cl] () and [Cu(acac)(dppz)Cl] () (acac = acetylacetonate, dpq = dipyrido[3,2-d:20,30-f]quinoxaline, dppz = dipyrido[3,2-a:20,30-c] phenazine), have been synthesized and their DNA binding, photo-induced DNA cleavage activity and cell cytotoxicity are studied. The complexes show good binding propensity to calf thymus DNA in the order: 2(dppz) > 1(dpq). Furthermore, two complexes exhibit efficient DNA cleavage activity on natural light or UV-A (365 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The photo-induced DNA cleavage activity of the dppz complex 2 is found to be more efficient than its dpq analogue. In vitro study of the photocytotoxicity of two complexes on HeLa cells indicate that both of them have the potential to act as effective anticancer drugs, with IC₅₀ values of 5.25 ± 0.83 μM (1) and 4.40 ± 0.52 μM (2) in the natural light, and 2.57 ± 0.92 μM (1) and 2.18 ± 0.52 μM (2) in UV-A light. In addition, to detect an apoptotic HeLa body, cells were stained with Hoechst 33342 dye.     

Interaction of two new mixed ligand copper(II) complexes with DNA probed by thermodynamic and spectroscopic studies

The DNA binding behavior of [Cu(4,7-dmp)(phen-dione)Cl]Cl (1) and [Cu(2,9-dmp)(phen-dione)Cl]Cl (2) where dmp and phen-dion stand for dimethyl-1,10-phenanthroline and 1,10-phenanthroline-5,6-dion, respectively, was studied with a series of techniques including Viscometry, UV–Vis absorption, circular dichroism and fluorescence spectroscopy. Cytotoxicity effect was also investigated. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van’t Hoff equation, which indicated that both reactions are predominantly enthalpically driven. However, these two complexes show different behavior in fluorescence, circular dichroism and viscometry methods which indicate the Cu(II) complexes interact with calf-thymus DNA by different mode of binding. These have further been verified by competition studies using Hoechst as a distinct groove binder. All these results indicate that these two complexes (1) and (2) interact with CT-DNA via groove binding and partially intercalative mode, respectively and the binding affinity of the complex 1 is higher than that of complex 2. Finally, our findings suggest that the type of ligands and structure of complexes have marked effect on the binding affinity of complexes involving CT-DNA. Also, these new complexes showed excellent antitumor activity against human T lymphocyte carcinoma-Jurkat cell line.     

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.     

Aminoalcohols incorporating a piperazine ring: Synthesis, complexation of a hexadentate ligand and DNA cleavage capability of copper(II) complexes

The facility of aminoalcohol ligand synthesis via ring opening of cyclohexene oxide with polyamines including a piperazine ring is illustrated here with the syntheses and characterization of (2′-hydroxycyclohexyl)piperazine (1), bis(2′-hydroxycyclohexyl)-piperazine (2), 4-{(2″-hydroxycyclohexyl)-2′-aminoethyl)}piperazine (3), 1-(2″-hydroxycyclohexyl)-4-{(2″-hydroxycyclohexyl)-2′-aminoethyl)}piperazine (4), and 1,4-bis[(2″-hydroxycyclohexyl)-3′-aminopropyl]piperazine (5) described, along with an analogue of 4 in which a single -CH₂-CH₂- alkyl chain replaces the piperazine ring, 1,5-bis[(2′-hydroxycyclohexyl)amine]-3-azapentane (6). The viability of 5 as a hexadentate ligand was established by preparation of its copper(II) complex and subsequent X-ray crystal structure analysis. The complex [Cu(5)](ClO₄)₂ cation lies in a distorted octahedral environment with the four nitrogen donors in an approximate plane also incorporating the copper (Cu-N_tert 2.058(4) A; Cu-N_sec 2.072(4) A) and the two alcohol groups occupying axial sites with elongated bonds (Cu-O 2.415(3) A). The piperazine ring adopts a ‘butterfly wing’ geometry, whereas the two cyclohexane rings are in chair conformations. Significant bond angle distortions occur around the copper, exacerbated by the axial Jahn-Teller bond length distortion. The ability of the copper(II) complexes of the aminoalcohols to promote DNA cleavage was examined. Complexes of 2, 3 and 5 are effectively inactive whereas 4 is an efficient single strand cleavage promoter; however, the more flexible close analogue of 4, 6, also proved ineffective. Such observations for a closely related series indicate the subtle influences of spectator ligand rigidity and steric congestion on DNA cleavage promotion.     

Synthesis, characterization, and DNA binding and cleavage properties of copper(II)-tryptophanphenyl-alanine-1,10-phenanthroline/2,2'-bipyridine complexes

The mononuclear dipeptide‐based Cu^II complexes [Cu^II(trp‐phe)(phen)(H₂O)] ⋅ ClO₄ ( 1 ) and [Cu^II(trp‐phe)(bpy)(H₂O)] ⋅ ClO₄ ( 2 ) (trp‐phe=tryptophanphenylalanine, phen=1,10‐phenanthroline, bpy=2,2′‐bipyridine) were isolated, and their interaction with DNA was studied. They exhibit intercalative mode of interaction with DNA. The intercalative interaction was quantified by Stern Volmer quenching constant (K_sq=0.14 for 1 and 0.08 for 2 ). The Cu^II complexes convert supercoiled plasmid DNA into its nicked circular form hydrolytically at physiological conditions at a concentration as low as 5 μM (for 1 ) and 10 μM (for 2 ). The DNA hydrolysis rates at a complex concentration of 50 μM were determined as 1.74 h⁻¹ (R=0.985) for 1 and 0.65 h⁻¹ (R=0.965) for 2 . The rate enhancement in the range of 2.40–4.10×10⁷‐fold compared to non‐catalyzed double‐stranded DNA is significant. This was attributed to the presence of a H₂O molecule in the axial position of the Cu complexes.     

DNA-binding and cleavage studies of novel copper(II) complex with L-phenylalaninate and 1,4,8,9-tetra-aza-triphenylene ligands

DNA-binding properties of novel copper(II) complex [Cu(l-Phe)(TATP)(H(2)O)](+), where L-Phe=L-phenylalaninate and TATP=1,4,8,9-tetra-aza-triphenylene are investigated using electronic absorption spectroscopy, fluorescence spectroscopy, voltammetry and viscosity measurement. It is found that the presence of calf thymus DNA results in a hypochromism and red shift in the electronic absorption, a quenching effect on fluorescence nature of ethidium bromide-DNA system, an enhanced response on voltammograms of [Co(phen)(3)](3+/2+)-DNA system, and an obvious change in viscosity of DNA. From absorption titration, fluorescence analysis and voltammetric measurement, the binding constant of the complex with DNA is calculated. The latter two methods reveal the stronger binding of [Cu(l-Phe)(TATP)(H(2)O)](+) complex to double strand DNA by the moderate intercalation than [Co(phen)(3)](3+). Such a binding induces the cleavage of plasmid pBR322 DNA in the presence of H(2)O(2).     

Interactions of mixed ligand ruthenium(II) complexes containing an amino acid and 1,10-phenanthroline with DNA

Mixed ligand ruthenium(II) complexes containing an amino acid (AA) and 1,10-phenanthroline (phen), i.e. [Ru(AA)(phen)₂]ⁿ⁺ (n=1,2, AA=glycine (gly), l-alanine (l-ala), l-arginine (l-arg)) have been synthesized. The interactions of these complexes and [Ru(phen)₃]²⁺ with DNA have been examined by absorption, luminescence, and circular dichroism spectroscopic methods. Absorption spectral properties revealed that [Ru(AA)(phen)₂]⁺ (AA=gly, l-ala) interacted with CT-DNA by the electrostatic binding mode. [Ru(l-arg)(phen)₂]²⁺ exhibited the greatest hypochromicity, red shift, and binding constant, indicating that this complex may partially intercalate into the base-pairs of DNA. These results were also suggested by luminescence spectroscopy. CD spectral properties have been examined to understand the detailed interactions of the ruthenium(II) complexes with artificial DNA. In the case of Δ-[Ru(l-arg)(phen)₂]²⁺, the solution on adding [poly(dG-dC)]₂ exhibited two well-defined positive peaks, which the shorter and longer wavelength peaks were assigned as originating from the major and the minor groove binding modes, respectively. Then, the solution on adding [poly(dA-dT)]₂ exhibited only one positive peak, which was assigned as a peak corresponding to the minor groove binding mode.     

DNA binding, oxidative DNA cleavage, cytotoxicity, and apoptosis-inducing activity of copper(II) complexes with 1,4-tpbd (N,N,N',N'-tetrakis(2-yridylmethyl)benzene-1,4-diamine) ligand

Three new binuclear copper(II) complexes have been synthesized and structurally characterized by X-ray crystallography, [Cu₂(1,4-tpbd)(dafo)₂(MeOH)₂](ClO₄)₄·2.5H₂O (1), [Cu₂(1,4-tpbd) (DMSO)₂(ClO₄)₂](OH)₂·6H₂O (2) and [Cu₂(1,4-tpbd)(OAC)₂(ClO₄)₂]·5H₂O (3) (1,4-tpbd = N,N,N′,N′-tetrakis(2-pyridylmethyl)benzene-1,4-diamine). Complex 1 to 3 shows similar binuclear structure and each Cu atom adopts five-coordinated square-pyramidal geometry. The interactions of the three complexes with CT-DNA (Calf-thymus DNA) have been investigated by UV absorption, fluorescence spectroscopy, circular dichroism spectroscopy and viscosity. Furthermore, the three complexes display oxidative cleavage of supercoiled DNA in the presence of external agents. Complex 3 shows higher DNA affinity and nuclease activity may be attributed to its cis structural configuration and labile acetate and perchlorate anions. The cleavage mechanisms between the complexes and plasmid DNA are likely to involve singlet oxygen or singlet oxygen-like entity as reactive oxygen species. In addition, in vitro cytotoxicity studies on the Hela cell line show that the IC₅₀ values of complexes 1-3 are 14.75, 13.67 and 16.58 μM, respectively. The apoptosis-inducing activity was also assessed by AO/EB (Acridine Orange/Ethidium bromide) staining assay, indicating they have the potential to act as effective metal-based anticancer drugs.     

DNA binding and cleavage properties of certain tetrammine ruthenium(II) complexes of modified 1,10-phenanthrolines--effect of hydrogen-bonding on DNA-binding affinity

A series of ruthenium(II) mixed ligand complexes of the type [Ru(NH(3))(4)(L)](2+), where L=imidazo[4,5-f][1,10]phenanthroline (ip), 2-phenylimidazo[4,5-f][1,10]phenanthroline (pip), 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline (hpip), 4,7-diphenyl-1,10-phenanthroline (dip), naphtha[2,3-a]dipyrido[3,2-h:2',3'-f]phenazine-5,18-dione (qdppz), 5,18-dihydroxynaphtho[2,3-a]dipyrido[3,2-H:2',3'-f]phenazine (hqdppz), have been isolated and characterized. The interaction of these complexes with calf thymus DNA (CT DNA) has been explored by using absorption, emission, and circular dichroic spectral methods, thermal denaturation studies and viscometry. All these studies suggest the involvement of the modified phenanthroline 'face' rather than the ammonia 'face' of the complexes in DNA binding. An intercalative mode of DNA binding, which involves the insertion of the modified phenanthroline ligands in between the base pairs, is suggested. The results from absorption spectral titration and circular dichroism (CD), thermal denaturation and viscosity experiments indicate that the qdppz and hqdppz complexes (K(b) approximately 10(6) and Delta T(m)=11-13 degrees C) bind more avidly than the ip, pip and hpip complexes (K(b) approximately 10(5), Delta T(m)=6-8 degrees C). Intramolecular hydrogen bonding in the hpip and hqdppz complexes increases the surface area of the intercalating diimines and enhances the DNA binding affinity substantially. The ammonia co-ligands of the complexes are possibly involved in hydrogen bonding with the intrastrand nucleobases to favour intercalation of the extended aromatic ligands. Circular dichroism spectral studies reveal that all the complexes effect certain structural changes on DNA duplex; [Ru(NH(3))(4)(ip)](2+) induces a B to A transition while [Ru(NH(3))(4)(qdppz)](2+) a B to Psi conformational change on CT DNA. Cleavage efficiency of the complexes were determined using pBR322 supercoiled plasmid DNA. All the complexes, except hqdppz complex, promote the cleavage of supercoiled plasmid (form I) to relaxed circular form (form II).     

Binding and oxidative cleavage studies of DNA by mixed ligand Co(III) and Ni(II) complexes of quinolo [3,2-b]benzodiazapine and 1,10-phenanthroline

Two mixed ligand complexes of the type [M(phen)(2)(qbdp)](PF(6))n.xH(2)O where M = Co(III) and Ni(II), qbdp = quinolo[3,2-b] benzodiazepine and phen = 1,10-phenanthroline, n = 3 or 2, x = 2 or 3 have been synthesized and characterized by employing analytical and spectral methods. The DNA binding property of the complexes with calf thymus-DNA has been investigated by using absorption spectra, viscosity measurements as well as thermal denaturation studies. The absorption spectral results indicate that the Co(III) and Ni(II) complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA binding constant of 6.4 x 10(4) and 4.8 x 10(4) M(-1) in Tris HCl buffer containing 50 mM NaCl, respectively. The large enhancement in the relative viscosity of DNA on binding to the quinolo [3,2-b] benzodiazepine supports the proposed DNA binding modes. The complexes on reaction with super coiled (SC) DNA shows nuclease activity.     

DNA-binding and photocleavage studies of mixed polypyridyl ruthenium(II) complexes with calf thymus DNA

New mixed polypyridyl {NMIP = 2′-(2″-nitro-3″,4″-methylenedioxyphenyl)imidazo-[4′,5′-f][1,10]-phenanthroline, dmb = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine} ruthenium(II) complexes [Ru(dmb)₂(NMIP)]²⁺ (1) and [Ru(bpy)₂(NMIP)]²⁺ (2) have been synthesized and characterized. The binding of these complexes to calf thymus DNA (CT-DNA) has been investigated with spectroscopic methods, viscosity and electrophoresis measurements. The experimental results indicate that both complexes could bind to DNA via partial intercalation from the minor/major groove. In addition, both complexes have been found to promote the single-stranded cleavage of plasmid pBR 322 DNA upon irradiation. Under comparable experimental conditions compared with [Ru(phen)₂(NMIP)]²⁺, during the course of the dialysis at intervals of time, the CD signals of both complexes started from none, increased to the maximum magnitude, then no longer changed, and the activity of effective DNA cleavage dependence upon concentration degree lies in the following order: [Ru(phen)₂NMIP]²⁺ > complex 2 > complex 1.     

Synthesis, characterization and DNA binding studies of two mixed ligand complexes of ruthenium(II)

Two mixed ligand complexes [Ru(bpy)(2)(DMHBT)]Cl(2)(1) and [Ru(phen)(2)(DMHBT)]Cl(2) (2) (where DMHBT is 11,13-dimethyl-13H-4,5,9,11,14-hexaaza-benzo[b]triphenylene-10,12-dione) have been synthesized and characterized by electrospray ionization (ESI) mass, (1)H-(1)H correlation spectroscopy (COSY), electronic spectroscopy, fluorescence spectroscopy and cyclic voltammetry. Spectroscopic titration and viscosity changes of calf thymus (CT)-DNA in the presence of incremental amount of complexes 1 and 2 clearly demonstrate that both these complexes bind intercalatively to DNA, with binding constant 2.87+/-0.20 x 10(4)M(-1) and 1.01+/-0.20 x 10(5)M(-1) for complexes 1 and 2, respectively. All the experimental evidences suggest that the ancillary ligand 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) influences the intercalative binding of these complexes to DNA.     

Synthesis, characterization, crystal structures, and photophysical properties of a series of room-temperature phosphorescent copper(I) complexes with oxadiazole-derived diimine ligand

In this paper, we report four phosphorescent Cu(I) complexes of [Cu(OP)(PPh₃)₂]BF₄, [Cu(Me-OP)(PPh₃)₂]BF₄, [Cu(OP)(POP)]BF₄, and [Cu(Me-OP)(POP)]BF₄ with oxadiazole-derived diimine ligands, where OP = 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine, Me-OP = 2-(5-p-tolyl-[1,3,4]oxadiazol-2-yl)-pyridine, POP = bis(2-(diphenylphosphanyl)phenyl) ether, and PPh₃ = triphenylphosphane, including their synthesis, crystal structures, photophysical properties, and electronic nature. The Cu(I) center has a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the inter-molecular sandwich structure triggered by inter- and intra-molecular pi-stacking within solid state Cu(I) complexes is highly effective on restricting the geometric relaxation that occurs in excited states, and thus greatly enhances the photoluminescence (PL) performances, including PL quantum yield improvement, PL decay lifetime increase, and emission blue shift.