DNA binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline

Absorption spectroscopy and circular dichroism (CD) have been used to characterize the DNA binding of [Fe(phen)3]2+, [Fe(phen)2(DIP)]2+ and [Fe(phen)(DIP)2]2+ where phen and DIP stand for 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline, respectively. Both [Fe(phen)3]2+ and [Fe(phen)2(DIP)]2+ bind weakly to calf thymus DNA (CT-DNA) in an electrostatic mode, while [Fe(phen)(DIP)2]2+ binds more strongly to CT-DNA, possibly in an intercalation mode. The hypochromicity, red shift and Kb increase in the order [Fe(phen)3]2+ < [Fe(phen)2(DIP)]2+ < [Fe(phen)(DIP)2]2+ in accordance with the increase in size and hydrophobicity of the iron(II) complexes. The thermodynamic parameters obtained suggest that the DNA binding of both [Fe(phen)3]2+ and [Fe(phen)2(DIP)]2+ is entropically driven, while that of [Fe(phen)(DIP)2]2+ is enthalpically driven. A strong CD spectrum in the UV and visible region develops upon addition of CT-DNA into the racemate solution of each iron(II) complex (Pfeiffer effect). This has revealed that a shift in diastereomeric inversion equilibrium takes place in the solution to yield an excess of one of the DNA-complex diastereomers. The striking resemblance of the CD spectral profiles to those of the pure delta-enantiomer indicates that the delta-enantiomer of the iron(II) complexes is preferentially bound to CT-DNA. The mechanism of the development of Pfeiffer CD is proposed on the basis of kinetic studies on the DNA binding of the racemic iron(II) complexes.     

Synthesis and DNA binding of mu-[2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline]bis[1,10-phenanthrolinecopper(II)

A binuclear complex [(phen)Cu(mu-bipp)Cu(phen)](ClO(4))(4), where phen=1,10-phenanthroline and bipp=2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline, has been synthesized and its interaction with calf-thymus DNA in the buffer containing 5mM Tris and 50mM NaCl has been studied by means of electronic absorption titration, luminescence titration and viscometric measurements. The absorbance of the complex in the range of 320-400 nm, which is mainly based on bipp showed no obvious change upon addition of DNA, while the peak at 270 nm, which is determined by both phen and bipp decreased by up to 18%. The emission band of the complex around 360 nm decreased remarkably in presence of DNA. The emission quenching of this complex by [Fe(CN)(6)](4-) was depressed greatly when bound to DNA. The relative viscosity of DNA was increased by this complex more significantly than a bipp directed intercalating reagent. These results suggest that this complex binds to calf thymus DNA by intercalation of the two phenanthrolinecopper terminals. The apparent intrinsic binding constant of the complexes with DNA was 1.6 x 10(4)M(-1) as determined by UV-visible titration.     

Salt-dependent binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and dipyrido[3,2-a:2',3'-c]phenazine to calf thymus DNA

The salt-dependent binding of racemic iron(II) mixed-ligand complex containing 1,10-phenanthroline (phen) and dipyrido[3,2-a:2',3'-c]phenazine (dppz), [Fe(phen)2(dppz)]2+ to calf thymus DNA (ct-DNA) has been characterized by UV-VIS spectrophotometric titration. The equilibrium binding constant (Kb) of the iron(II) complex to ct-DNA decreases with the salt concentration in the solution. The slope, SK=(deltalog Kb/deltalog [Na2+]) has been found to be 0.49, suggesting that, in addition to intercalation, considerable electrostatic interaction is also involved in the ct-DNA binding of [Fe(phen)2(dppz)]2+. The calculation of non-electrostatic binding constant (Kt(o)) based on polyelectrolyte theory has revealed that the non-electrostatic contribution to the total binding constant (Kb) increases significantly with the increase in [Na+] and reaches 36% at 0.1 M NaCl. On the other hand, the contribution of the non-electrostatic binding free energy (DeltaGt(o)) to the total binding free energy change (DeltaGo) is considerably large, i.e. 87% at [Na+]=0.1 M, suggesting that the stabilization of the DNA binding is mostly due to the contribution of non-electrostatic process. Moreover, the effect of specific ligand substitutions on DeltaGo has been rigorously evaluated using the quantity DeltaDeltaGt(o), i.e. the difference in DeltaGt(o) relative to that of the parent iron(II) complex, [Fe(phen)3]2+, indicating that each substitution of phen by dip and dppz contributes 7.5 and 17.5 kJ mol(-1), respectively to more favorable ct-DNA binding.     

Synchronous fluorescence, UV-visible spectrophotometric, and voltammetric studies of the competitive interaction of bis(1,10-phenanthroline)copper(II) complex and neutral red with DNA

Constant wavelength synchronous fluorescence spectroscopy (CW-SFS), UV-visible absorption spectroscopy, and cyclic and differential pulse voltammetry were applied to investigate the competitive interaction of DNA with the bis(1,10-phenanthroline)copper(II) complex cation ([Cu(phen)(2)](2+)) and a fluorescence probe, neutral red dye (NR), in a tris-hydrogen chloride buffer (pH 7.4). The results show that both the [Cu(phen)(2)](2+)and the NR molecules can intercalate competitively into the DNA double-helix structure. The cyclic voltammetry method showed that both anodic and cathodic currents of [Cu(phen)(2)](2+) decreased on addition of the DNA and the intercalated [Cu(phen)(2)](2+)-DNA complex formed (beta = (4.14 +/- 0.24) x 10(3)). CW-SFS measurements were facilitated by the use of the three-way resolution of the CW-SFS for NR, [Cu(phen)(2)](2+), and NR-DNA. The important constant wavelength (CW) interval, Deltalambda, was shown to vary considerably when optimized (135, 58, and 98 nm for NR, NR-DNA, and [Cu(phen)(2)](2+), respectively). This approach clearly avoided the errors that otherwise would have arisen from the common assumption that Deltalambda is constant. Furthermore, a chemometrics approach, parallel factor analysis (PARAFAC), was applied to resolve the measured three-way CW-SFS data, and the results provided simultaneously the concentration information for the three reaction components, NR, [Cu(phen)(2)](2+), and NR-DNA, for the system at each equilibrium point. The PARAFAC analysis indicated that the intercalation of the [Cu(phen)(2)](2+) molecule into the DNA proceeds by exchanging with the NR probe and can be attributed to two parallel reactions. Comprehensive information was readily obtained; the replacement of the intercalated NR commenced immediately on introduction of [Cu(phen)(2)](2+), approximately 50% of NR was replaced by [Cu(phen)(2)](2+) at a concentration of 0.45 x 10(-5) mol L(-1), and nearly all of the NR was replaced at a [Cu(phen)(2)](2+) concentration of 2.50 x 10(-5) mol L(-1). This work has the potential to improve extraction of information from the fluorescence intercalator displacement (FID) assay.     

Crystal structure and nuclease activity of mono(1,10-phenanthroline) copper complex

The hydroxo-bridged dinuclear copper (II)/phen complex [Cu(2)(phen)(2)(OH)(2)(H(2)O)(2)][Cu(2)(phen)(2)(OH)(2)Cl(2)]Cl(2).6H(2)O (phen=1,10-phenanthroline) has been prepared and characterized by single crystal X-ray diffraction. The coordinated area of the complex shows two distorted [CuN(2)O(2)O(w)] and [CuN(2)O(2)Cl] square-pyramidal and one strictly planar configuration CuO(2)Cu involving two O atoms of hydroxo-bridged, Cu(2+) cations, N atoms of two phen ligands and disorder solvate water and chlorine anions. In the presence of H(2)O(2), the complex of mono(1,10-phenanthroline)copper exhibits higher activity as a nuclease than bis(1,10-phenanthroline)copper.     

DNA interactions of new mixed-ligand complexes of cobalt(III) and nickel(II) that incorporate modified phenanthroline ligands

Four new mixed-ligand complexes, namely [Co(phen)(2)(qdppz)](3+), [Ni(phen)(2)(qdppz)](2+), [Co(phen)(2)(dicnq)](3+) and [Ni(phen)(2)(dicnq)](2+) (phen=1,10-phenanthroline, qdppz=naptho[2,3-a]dipyrido[3,2-H:2',3'-f]phenazine-5,18-dione and dicnq=dicyanodipyrido quinoxaline), were synthesized and characterized by FAB-MS, UV/Vis, IR, 1H NMR, cyclic voltammetry and magnetic susceptibility methods. Absorption and viscometric titration as well as thermal denaturation studies revealed that each of these octahedral complexes is an avid binder of calf-thymus DNA. The apparent binding constants for the dicnq- and qdppz-bearing complexes are in the order of 10(4) and >10(6) M(-1), respectively. Based on the data obtained, an intercalative mode of DNA binding is suggested for these complexes. While both the investigated cobalt(III) complexes and also [Ni(phen)(2)(qdppz)](2+) affected the photocleavage of DNA (supercoiled pBR 322) upon irradiation by 360 nm light, the corresponding dicnq complex of nickel(II) was found to be ineffective under a similar set of experimental conditions. The physico-chemical properties as well as salient features involved in the DNA interactions of the cobalt(III) and nickel(II) complexes investigated here were compared with each other and also with the corresponding properties of the previously reported ruthenium(II) analogues.     

Synthesis, DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes: [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+)

Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+).     

DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes containing 2-(2-chloro-5-nitrophenyl)imidazo [4,5-f][1,10]phenanthroline

The ligand 2-(2-chloro-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline(CNOIP) and its complexes [Co(bpy)(2)(CNOIP)](3+) (1) and [Co(phen)(2)(CNOIP)](3+) (2) (bpy=2,2'-bipyridine; phen=1,10-phenanthroline) have been synthesized and characterized. Binding of the two complexes with calf thymus DNA has been investigated by spectroscopic methods, cyclic voltammetry, viscosity, and electrophoresis measurements. The experimental results indicate that both complexes bind to DNA through an intercalative mode. In comparison with their parent complexes containing PIP ligand (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline), the introduction of NO(2) and Cl groups to the PIP ligand decreased the binding affinity of complexes 1 and 2 to CT DNA. Both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA, the hydroxyl radical (OH*) is suggested to be the reactive species responsible for the cleavage.     

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.     

Synthesis, DNA-binding and photocleavage studies of ruthenium(II) complex with 2-(3'-phenoxyphenyl)imidazo[4,5-f][1,10]phenanthroline

A new polypyridyl ligand MPPIP {MPPIP=2-(3'-phenoxyphenyl)imidazo[4,5-f]-[1,10]phenanthroline} and its ruthenium(II) complexes, [Ru(bpy)(2)MPPIP](2+) (1) (bpy=2,2'-bipyridine) and [Ru(phen)(2)MPPIP](2+) (2) (phen=1,10-phenanthroline) have been synthesized and characterized. The binding of the two complexes to calf thymus DNA (CT-DNA) has been investigated with spectrophotometric methods, viscosity measurements, as well as equilibrium dialysis and circular dichroism spectroscopy. The results suggest that both complexes bind to CT-DNA through intercalation, and enantioselectively interact with CT-DNA in a way. However, complex 2 is a much better candidate as an enantioselective binder to CT-DNA than complex 1. When irradiated at 365nm, both complexes have also been found to promote the photocleavage of plasmid pBR322 DNA.     

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).     

Synthesis, characterization, DNA-binding and photocleavage studies of [Ru(bpy)2(PPIP)]2+ and [Ru(phen)2(PPIP)]2+

A novel ligand 2-(4'-phenoxy-phenyl)imidazo[4,5-f][1,10]phenanthroline (PPIP) and its complexes [Ru(bpy)(2)(PPIP)](2+) (1) (bpy = 2,2'-bipyridine) and [Ru(phen)(2)(PPIP)](2+) (2) (phen = 1,10-phenanthroline) have been synthesized and characterized by mass spectroscopy, (1)H NMR and cyclic voltammetry. The interaction of two complexes with calf thymus DNA (CT-DNA) was investigated by spectroscopic and viscosity measurements. The results suggest that both complexes bind to DNA via an intercalative mode. Both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA under irradiated.     

Probing site specificity of DNA binding metallointercalators by NMR spectroscopy and molecular modeling

The molecular recognition of oligonucleotides by chiral ruthenium complexes has been probed by NMR spectroscopy using the template Delta-cis-alpha- and Delta-cis-beta-[Ru(RR-picchxnMe(2)) (bidentate)](2+), where the bidentate ligand is one of phen (1,10-phenanthroline), dpq (dipyrido[3,2-f:2',3'-h]quinoxaline), or phi (9,10-phenanthrenequinone diimine) and picchxnMe(2)() is N,N'-dimethyl-N,N'-di(2-picolyl)-1,2-diaminocyclohexane. By varying only the bidentate ligand in a series of complexes, it was shown that the bidentate alone can alter binding modes. DNA binding studies of the Delta-cis-alpha-[Ru(RR-picchxnMe(2))(phen)](2+) complex indicate fast exchange kinetics on the chemical shift time scale and a "partial intercalation" mode of binding. This complex binds to [d(CGCGATCGCG)](2) and [d(ATATCGATAT)](2) at AT, TA, and GA sites from the minor groove, as well as to the ends of the oligonucleotide at low temperature. Studies of the Delta-cis-beta-[Ru(RR-picchxnMe(2))(phen)](2+) complex with [d(CGCGATCGCG)](2) showed that the complex binds only weakly to the ends of the oligonucleotide. The interaction of Delta-cis-alpha-[Ru(RR-picchxnMe(2))(dpq)](2+) with [d(CGCGATCGCG)](2) showed intermediate exchange kinetics and evidence of minor groove intercalation at the GA base step. In contrast to the phen and dpq complexes, Delta-cis-alpha- and Delta-cis-beta-[Ru(RR-picchxnMe(2))(phi)](2+) showed evidence of major groove binding independent of the metal ion configuration. DNA stabilization induced by complex binding to [d(CGCGATCGCG)](2) (measured as DeltaT(m)) increases in the order phen < dpq and DNA affinity in the order phen < dpq < phi. The groove binding preferences exhibited by the different bidentate ligands is explained with the aid of molecular modeling experiments.     

Mixing ratio-dependent energy transfer from DNA-bound 4',6-diamidino-2-phenylindole to [Ru(1,10-phenanthroline)(2)dipyrido[3,2-a:2',3'-c]phenazine](2+)

The binding mode of Delta- and Lambda-[Ru(1,10-phenanthroline)(2)dipyrido[3,2-a:2',3'-c]phenazine](2+) ([Ru(phen)(2)DPPZ](2+)) to DNA in the presence of 4',6-diamidino-2-phenylindole (DAPI) at a low and high [DAPI]/[DNA base] ratio (0.02 and 0.20, respectively) was investigated using electric absorption and circular dichroism spectroscopy. The spectral properties of both the Delta- and Lambda-[Ru(phen)(2)DPPZ](2+) were not altered in the presence of DAPI disregarding the [DAPI]/[DNA] ratio, suggesting that the presence of DAPI in the minor groove of DNA does not affect the binding mode of the [Ru(phen)(2)DPPZ](2+) complex to DNA. The transferring excited energy of DAPI to both Delta- and Lambda-[Ru(phen)(2)DPPZ](2+) occurs through F?rster type resonance when they both spontaneously bound to DNA. At a high [DAPI]/[DNA] ratios, an upward bending curve in the Stern-Volmer plot, and a shortening the DAPI fluorescence decay time with increasing [Ru(phen)(2)DPPZ](2+) concentration were found. These results indicate that the quenching of the DAPI's fluorescence occurs through both the static and dynamic mechanisms. In contrast, the quenching mechanism at a low [DAPI]/[DNA] ratios was found to be purely static. The static quenching constant decreased linearly with respect to the [DAPI]/[DNA] ratio. Decrease in quenching efficiency can be explained by the association constant of [Ru(phen)(2)DPPZ](2+) to DNA while being within a quenchable distance from a DAPI molecule.     

Oxidative DNA damage of mixed copper(II) complexes with sulfonamides and 1,10-phenanthroline. Crystal structure of [Cu(N-quinolin-8-yl-p-toluenesulfonamidate)2(1,10-phenanthroline)

Mixed coordination compounds of Cu(II) with sulfonamides and 1,10-phenanthroline as ligands have been prepared and characterised. Single crystal structural determination of the complex [Cu(N-quinolin-8-yl-p-toluenesulfonamidate)(2)(phen)] shows Cu(II) ions are located in a highly distorted octahedral environment, probably as a consequence of the Jahn-Teller effect. The FT-IR and electronic paramagnetic resonance (EPR) spectra are also discussed. The mixed complexes prepared undergo an extensive DNA cleavage in the presence of ascorbate and hydrogen peroxide. Two of the complexes have higher nucleolytic efficiency than the bis(o-phenanthroline)copper(II) complex.     

Synthesis, characterization, DNA-binding and photocleavage of complexes [Ru(phen)2(6-OH-dppz)]2+ and [Ru(phen)2(6-NO2-dppz)]2+

Two new complexes, ([Ru(phen)(2)(6-OH-dppz)](2+)) (1) and ([Ru(phen)(2)(6-NO(2)-dppz)](2+)) (2) (phen=1,10-phenanthroline; 6-OH-dppz=6-hydroxyl-dipyrido[3,2-a:2',3'-c]phenazine; 6-NO(2)-dppz=6-nitro-dipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized by elemental analysis, ES-MS (electrospray mass spectra), (1)H NMR, UV-Vis (UV-visible) and CV (cyclic voltammetry). The DNA-binding behaviors of both complexes have been studied by spectroscopic methods and viscosity measurements. The results indicate that the two complexes all bind to calf thymus DNA (CT-DNA) in an intercalative mode, and the DNA-binding affinity of complex 2 is greater than that of complex 1. In addition, complex 1 can promote photocleavage of pBR322 DNA upon irradiation, whereas complex 2 can promote cleavage of pBR322 DNA both upon irradiation and in the dark, with more efficient cleavage occurring upon irradiation. Theoretical studies for these complexes have been also carried out with the density functional theory (DFT) method. The difference in the DNA-binding behaviors of the two complexes can be reasonably explained by the DFT calculations.     

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.     

Syntheses and DNA-binding studies of two ruthenium(II) complexes containing one ancillary ligand of bpy or phen: [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)2

Two new ruthenium(II) complexes of [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)(2) (bpy=2,2'-bipyridine, phen=1,10-phenanthroline, pp[2,3]p=pyrido[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline) have been synthesized and characterized by elemental analysis and 1H NMR spectra. The calf thymus DNA-binding properties of the two complexes were investigated by UV-visible and emission spectroscopy, competitive binding experiments with ethidium bromide and viscosity measurements. The results indicate that the two complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA-binding constants of 3.08 x 10(6) and 6.53 x 10(6) M(-1) in buffered 50 mM NaCl, respectively, which are much larger than 6.9 x 10(5) M(-1) for [Ru(bpy)2(pp[2,3]p)](ClO4)2 containing two ancillary ligands of bpy.     

Ruthenium(II) mixed-ligand complex containing 2-(4'-benzyloxy-phenyl)imidazo[4,5-f][1,10]phenanthroline: synthesis, DNA-binding and photocleavage studies

A novel polypyridyl ligand 2-(4'-benzyloxyphenyl)imidazo[4,5-f][1,10]phenanthroline (BPIP) and its complex [Ru(bpy)2(BPIP)]2+ (1) (bpy=2,2'-bipyridine) and (2) [Ru(phen)2(BPIP)]2+) (phen=1,10-phenanthroline) have been synthesized and characterized by elemental analysis, electrospray mass spectra and 1H NMR. The DNA-binding properties of the two complexes were investigated by spectroscopic and viscosity measurements. The results suggest that both complexes bind to DNA via an intercalative mode. Both complexes can enantioselectively interact with calf thymus DNA (CT-DNA) in a way. The Lambda enantiomer of complex 1 is slightly predominant for binding to CT-DNA to the Delta enantiomer. Under irradiation at 365 nm, both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA. Inhibitors studies suggest that singlet oxygen ((1)O2) and hydroxyl radical (*OH) play a significant role in the cleavage mechanism for both complexes. Moreover, the DNA-binding and photocleavage properties of both complexes were compared with that of [Ru(bpy)2(BPIP)]2+ and [Ru(phen)2(BPIP)]2+. The experimental results indicate that methene group existence or not have a significant effect on the DNA-binding and cleavage mechanism of these complexes.     

Homoleptic ruthenium (II) complexes containing asymmetric tridentate 2-(benzimidazole-2-yl)-1,10-phenanthroline likes ligands: syntheses, characterization and DNA binding

Two novel homoleptic ruthenium (II) complexes containing asymmetric tridentate ligands, 2-(benzimidazole-2-yl)-1,10-phenanthroline (PHBI) and 2-(naphtho[2,3-d]imidazole-2-yl)-1,10-phenanthroline (PHNI) have been synthesized and characterized by elemental analysis, mass spectra, (1)H NMR, and electronic spectroscopy. The DNA-binding properties of the complexes have been investigated by spectroscopic methods and viscosity measurements. The results indicate that the two complexes interact with DNA via electrostatic interaction, and the mechanisms of DNA binding with the complexes have also been discussed.