DNA-binding studies of mixed-ligand (ethylenediamine)ruthenium(II) complexes

A series of mixed-ligand ruthenium(II) complexes of the type [Ru(en)(2)bpy](2+) (bpy=2,2-bipyridine; 1), [Ru(en)(2)phen](2+) (phen=1,10-phenantroline; 2), [Ru(en)(2)IP](2+) (IP=imidazo[4,5-f][1,10]phenanthroline; 3), and [Ru(en)(2)PIP](2+) (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline; 4) have been isolated and characterized by UV/VIS, IR, and (1)H-NMR spectral methods. The binding of the complexes with calf thymus DNA has been investigated by absorption, emission spectroscopy, viscosity measurements, DNA melting, and DNA photo-cleavage. The spectroscopic studies together with viscosity measurements and DNA melting studies support that complexes 1 and 2 bind to CT DNA (=calf thymus DNA) by groove mode. Complex 2 binds more avidly to CT DNA than complex 1, complexes 3 and 4 bind to CT DNA by intercalation mode, 4 binds more avidly to CT DNA than 3. Noticeably, the four complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.     

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.     

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.     

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.     

Synthesis, antitumor activity and structure-activity relationships of a series of Ru(II) complexes

A series of octahedral Ru(II) polypyridyl complexes, [Ru(phen)(2)L](2+) (L=R-PIP and PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline) were synthesized and characterized by elementary analysis, (1)H NMR and ES-MS, as well as UV-visible spectra and emission spectra. The antitumor activities of these complexes and their corresponding ligands were investigated against mouse leukemia L1210 cells, human oral epidermoid carcinoma KB cells, human promyelocytic leukemia cells (HL-60) and Bel-7402 liver cancer cells by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. It was found that the complexes [Ru(phen)(2)L](2+) (L=R-PIP) exert rather potent activities against all of these cell lines, especially for the KB cells (IC(50)=4.7+/-1.3 microM). The binding affinities of these Ru(II) complexes to CT-DNA (calf thymus DNA), as well as the DNA-unwinding properties on supercoiled pBR322 DNA were also investigated. The results showed that these Ru(II) polypyridyl complexes not only had an excellent DNA-binding property but also possessed a highly effective DNA-photocleavage ability. The structure-activity relationships and antitumor mechanism were also carefully discussed.     

Synthesis, characterization, nucleic acid binding, and cytotoxic activity of a Ru(II) polypyridyl complex

The binding properties of [Ru(bpy)(2)(H(2)IIP)](2+) (1) {bpy=2,2'-bipyridine, H(2)IIP=2-(indole-3-yl)-imidazolo[4,5-f][1,10]phenanthroline} with calf thymus DNA (CT-DNA) and yeast tRNA have been investigated comparatively by different spectroscopic and viscosity measurements. The results suggest that the affinity of complex 1 binding with yeast tRNA is stronger than that of complex 1 binding with CT-DNA, and complex 1 is a better enantioselective binder to yeast tRNA than to CT-DNA. The toxicity of complex 1 was concentration dependent, and HL-60 cells are more sensitive to complex 1 than Hep-G2 cells; complex 1 could induce Hep-G2 cell apoptosis.     

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.     

DNA binding studies of ruthenium(II) complexes containing asymmetric tridentate ligands

Absorption spectroscopy, fluorescence spectroscopy and viscosity measurements have been used to characterize the DNA binding of [Ru(tpy)(dppt)](2+) (tpy=2,2':6',2"-terpyridine, dppt=3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine), [Ru(tpy)(pta)](2+) (pta=3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]acenaphthylene) and [Ru(tpy)(ptp)](2+) (ptp=3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]-phenanthrene). The results indicate that [Ru(tpy)(pta)](2+) and [Ru(tpy)(ptp)](2+) bind with CT-DNA in an intercalative mode, while [Ru(tpy)(dppt)](2+) binds with DNA by partial intercalation. The ligand planarity of the complex has a significant effect on DNA binding affinity increases in the order [Ru(tpy)(dppt)](2+)<[Ru(tpy)(pta)](2+)<[Ru(tpy)(ptp)](2+).     

Synthesis, characterization, DNA-binding and cleavage studies of [Ru(bpy)2(actatp)]2+ and [Ru(phen)2(actatp)]2+ (actatp=acenaphthereno[1,2-b]-1,4,8,9-tetraazariphenylence)

New ligand acenaphthereno[1,2-b]-1,4,8,9-tetraazariphenylence (actatp) and its complexes [Ru(bpy)(2)(actatp)](ClO(4))(2).2H(2)O (1) (bpy=2,2'-bipyridine) and [Ru(phen)(2)(actatp)](ClO(4))(2).2H(2)O (2) (phen=1,10-phenanthroline) have been synthesized and characterized by UV-vis, 1H NMR, and mass spectra. The electrochemical behavior of the two complexes was studied by cyclic voltammetry. The interaction of the two complexes with calf thymus DNA has been investigated by spectrophotometric methods and viscosity measurements. The experimental results suggest that both complexes bind to DNA through an intercalative mode. The circular dichroism signals of the dialysates of the racemic complexes against calf thymus DNA are discussed. When irradiated at 302 nm, both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA.     

Synthesis, characterization and DNA binding of ruthenium(II) complexes containing the atatp ligand

Acenaphtheno[1,2-b]-1,4,8,9-tetraazatriphenylene (atatp) and its complexes [Ru(L)2atatp](ClO4)2 x nH2O (L = 2,2'-bipyridine (bpy), n=2 (1); 1,10-phenanthroline (phen), n=2 (2); and 2,9-dimethyl-1,10-phenanthroline (dmp), n=1 (3)) have been synthesized and characterized by elemental analyses and 1H NMR. The spectral and electrochemical properties of these complexes are also examined. Complexes 1 and 2 display bright luminescence in acetonitrile but very weak luminescence in water solution. However, complex 3 is not luminescent in either solvent. The interaction of the complexes with calf thymus DNA (CT-DNA) has been studied by absorption, emission and viscosity measurements. The intrinsic binding constants of complexes 1 and 2 are 7.6 x 10(4) and 8.8 x 10(4) M(-1) respectively. The relatively low affinities of complexes 1 and 2 with DNA may arise from the atatp ligand, indicating that the size and shape of the intercalated ligand have a marked effect on the strength of interaction. Complexes 1 and 2 bind with CT-DNA in an intercalative mode but complex 3 in a non-intercalative one, showing that changing the ancillary ligand affects not only the binding magnitude, but also the binding mode of the interaction.     

The light switch effect upon the association of [Ru(1,10-phenanthroline)2dipyrido[3,2-a:2',3'-c]phenazine]2+ with single stranded poly(dA) and poly(dT)

Large enhancement in the luminescence intensity of the Delta- and Lambda-Ru(phenanthroline)(2)dipyrido[3,2-a:2',3'-c]phenazine](2+) ([Ru(phen)(2)DPPZ](2+)) complexes upon their association with single stranded poly(dA) and poly(dT) is reported in this work. As the mixing ratio ([[Ru(phen)(2)DPPZ](2+)]/[DNA base]) increases, the luminescence intensity increase in a sigmoidal manner, indicating that the enhancement involves some cooperativity. At a high mixing ratio, the luminescence properties are affected by the nature of the DNA bases and not by the absolute configuration of the [Ru(phen)(2)DPPZ](2+) complex, indicating that the single stranded poly(dA) and poly(dT) do not recognize the configuration of the metal complex. In the case of the Lambda-[Ru(phen)(2)DPPZ](2+)-poly(dT) complex, the manner of the enhancement is somewhat different from the other Ru(II) complex-polynucelotide combinations: the luminescence intensity reached a maximum at an intermediate mixing ratio of 0.32, and gradually decreased as the mixing ratio increased. In contrast to other complexes at high mixing ratios, an upward bending curve was found in the Stern-Volmer plot, which indicates that the micro-environment of the Lambda-[Ru(phen)(2)DPPZ](2+) is heterogeneous. In the Delta-[Ru(phen)(2)DPPZ](2+)-poly(dT) complex case, formation of this highly luminescent species at an intermediate mixing ratio is far less effective.     

DNA-binding and photoactivated enantiospecific cleavage of chiral polypyridyl ruthenium(II) complexes

A series of enantiomeric polypyridyl ruthenium(II) complexes Delta- and Lambda-[Ru(bpy)2CNOIP](PF6)2 (Delta-1 and Lambda-1; BPY=2,2'-bipyridine, CNOIP=2-(2-chloro-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline), Delta- and Lambda-[Ru(bpy)2HPIP](PF6)2 (Delta-2 and Lambda-2; HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline), Delta- and Lambda-[Ru(bpy)2DPPZ](PF6)2 (Delta-3 and Lambda-3; DPPZ=dipyrido[3,2:a-2',3':c]-phenazine), Delta- and Lambda-[Ru(bpy)2TAPTP](PF6)2 (Delta-4 and Lambda-4; TAPTP=4,5,9,18-tetraazaphenanthreno[9,10-b] triphenylene) have been synthesized. Binding of these chiral complexes to calf thymus DNA has been studied by spectroscopic methods, viscosity, and equilibrium dialysis. The experimental results indicated that all the enantiomers of these complexes bound to DNA through an intercalative mode, but the binding affinity of each chiral complex to DNA was different due to the different shape and planarity of the intercalative ligand. After binding to DNA, the luminescence property of complex 1 was distinctly different from complexes 2 to 4. Upon irradiation at 302 nm, complexes 2-4 were found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II, and obvious enantioselectively was observed on DNA cleavage for the enantiomers of complexes 2 and 4. The mechanisms for DNA cleavage by these enantiomeric complexes were also proposed.     

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.     

Synthesis, characterization, and DNA-binding of chiral complexes delta- and lambda-[Ru(bpy)2(pyip)]2+

New chiral Ru(II) complexes delta and lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) [(bpy = 2,2'-bipyridine; pyip = (2-(1-pyrenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline] were synthesized and characterized by elemental analysis, (1)H NMR, ESI-MS, IR, and CD spectra. Their DNA-binding properties were studied by means of UV-vis, emission spectra, CD spectra and viscosity measurements. A subtle but detectable difference was observed in the interaction of both enantiomer with CT-DNA. Spectroscopy experiments indicated that each of these complexes could interact with the DNA. The DNA-binding of the Delta-enantiomer was stronger than that of Lambda-enantiomer. DNA-viscosity experiments provided evidence that both Delta- and Lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) bound to DNA by intercalation. At the same time, the DNA-photocleavage properties of the complexes were investigated too. Under irradiation with UV light, Ru(II) complexes showed different efficiency of cleaving DNA.     

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.     

Enantiomeric ruthenium(II) complexes binding to DNA: binding modes and enantioselectivity

A series of enantiomerically pure polypyridyl ruthenium(II) complexes, delta- and lambda-[Ru(bpy)2 (HPIP)](PF6)2 (delta-1 and lambda-1; bpy=2,2'-bipyridine, HPIP = 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline), delta and lambda-[Ru(bpy)2(HNAIP)](PF6)2 (delta-2 and lambda-2; HNAIP = 2-(2-hydroxy-1-naphthyl)imidazo[4,5-f][1,10]phenanthroline), delta- and lambda-[Ru(bpy)2 (HNOIP)](PF6)2 (delta-3 and lambda-3; HNOIP = 2-(2-hydroxy-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline), and delta- and lambda-[Ru(bpy)2(DPPZ)](PF6)2 (delta-4 and lambda-4; DPPZ= dipyridophenazine), have been synthesized. Binding behavior of these chiral complexes to calf thymus DNA (CT-DNA) has been investigated by electronic absorption, steady-state emission, and circular dichroism spectroscopies, as well as by viscosity measurements and equilibrium dialysis binding studies. Several points came from the results. (1) The DNA-binding properties were distinctly different for the [Ru(bpy)2L]2+ (L=HPIP, HNAIP, HNOIP) series of ruthenium(II) complexes, which indicates that the photophysical behavior of the complexes on binding to DNA can be modulated through ligand design. (2) Different binding rates of individual enantiomers of complexes 1 and 4 to DNA were observed through dialysis experiments. The lambda enantiomer bound more rapidly than the lambda enantiomer and their different intercalative binding geometries were suggested to be responsible. (3) Both delta-2 and lambda-2 bound weakly to CT-DNA; delta-2 may bind through a partial intercalation mode, whereas lambda-2 may bind in the DNA groove. (4) There was no noticeable enantioselectivity for complexes 1, 3, and 4 on binding to CT-DNA. Both of their enantiomers can intercalate into DNA base pairs. It is noted that delta-3 and lambda-3 exhibited almost identical spectral changes on addition of CT-DNA, and a similar binding manner of the isomers to the double helix was proposed.     

The effects of grafting of 2-pyridyl to [Ru(bpy)(2)(Hpip)](2+) on acid-base and DNA-binding properties: experimental and DFT studies

A new Ru(II) complex of [Ru(bpy)(2)(Hpip)](2+) {bpy = 2,2'bipyridine; Hppip = 2-(4-(pyridin-2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} has been synthesized by grafting of 2-pyridyl to parent complex [Ru(bpy)(2)(Hpip)](2+) {Hppip = 2-(4-phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline}. The acid-base properties of [Ru(bpy)(2)(Hpip)](2+) studied by UV-visible and luminescence spectrophotometric pH titrations, revealed off-on-off luminescence switching of [Ru(bpy)(2)(Hpip)](2+) that was driven by the protonation/deprotonation of the imidazolyl and the pyridyl moieties. The complex was demonstrated to be a DNA intercalator with an intrinsic DNA binding constant of (5.56 ± 0.2) x 10(5) M-1 in buffered 50 mM NaCl, as evidenced by UV-visible and luminescence titrations, reverse salt effect, DNA competitive binding with ethidium bromide, steady-state emission quenching by [Fe(CN)6]4-, DNA melting experiments and viscosity measurements. The density functional theory method was also used to calculate geometric/electronic structures of the complex in an effort to understand the DNA binding properties. All the studies indicated that the introduction of 2-pyridyl onto Hpip ligand is more favorable for extension of conjugate plane of the main ligand than that of phenyl, and for greatly enhanced ct-DNA binding affinity accordingly.     

The dichotomy in the DNA-binding behaviour of ruthenium(II) complexes bearing benzoxazole and benzothiazole groups

The substituted tris(bipyridine)ruthenium(II) complexes {[Ru(bpy)(2)(4,4'-bbob)](2+) and [Ru(bpy)(2)(5,5'-bbob)](2+) [where bpy=2,2'-bipyridine and bbob=bis(benzoxazol-2-yl)-2,2'-bipyridine] have been prepared and compared to the previously studied complex [Ru(bpy)(2)(4,4'-bbtb)](2+) [where bbtb=bis(benzothiazol-2-yl)-2,2'-bipyridine]. From the UV/VIS titration studies, Delta-[Ru(bpy)(2)(4,4'-bbob)](2+) displays a stronger association than the Lambda-isomer with calf-thymus DNA (ct-DNA). For [Ru(bpy)(2)(5,5'-bbob)](2+), there appears to be minimal interaction with ct-DNA. The results of fluorescence titration studies suggest that [Ru(bpy)(2)(4,4'-bbob)](2+) gives an increase in emission intensity with increasing ct-DNA concentrations, with an enantiopreference for the Delta isomer, confirmed by membrane dialysis studies. The fluorescent intercalation displacement studies revealed that [Ru(bpy)(2)(4,4'-bbob)](2+) and [Ru(bpy)(2)(5,5'-bbob)](2+) display a preference for more open DNA structures such as bulge and hairpin sequences. While Lambda-[Ru(bpy)(2)(4,4'-bbtb)](2+) has shown the most significant affinity for all the oligonucleotides sequences screened in previous studies, it is the Delta isomer of the comparable benzoxazole ruthenium(II) complex (Delta-[Ru(bpy)(2)(4,4'-bbob)](2+)) that preferentially binds to DNA.     

Interaction of polypyridyl ruthenium (II) complex containing asymmetric ligand with DNA

A novel asymmetric bidentate ruthenium (II) complex, [Ru(bpy)(2)(PYNI)](2+) (bpy=2,2'-bipyridine, PYNI=2-(2'-pyridyl)naphthoimidazole), has been synthesized and characterized by elemental analysis, ES-MS (electrospray mass spectra) and (1)H NMR. The electrochemical behaviors of this complex were studied by cyclic voltammetry. DNA interaction studies suggest that [Ru(bpy)(2)(PYNI)](2+) binds to calf thymus DNA (CT-DNA) in an intercalative mode. Interestingly, this new Ru(II) complex has also been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation.     

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+).