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.     

Enantioselective binding of lambda- and delta-[Ru(bpy)(2)(HPIP)]Cl2 (HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline) to the hexanucleotide [d(5'-GTCGAC-3')2

Multidimensional NMR techniques (1D (1)HNMR, 2D DQF (1)H(1)H COSY and 2D (1)H(1)H NOESY), electrospray ionization mass spectrometry (ESI-MS) and electronic spectroscopy, were performed to study the interactions of the enantiomers lambda- and delta-[Ru(bpy)(2)(HPIP)]Cl(2), (HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthro-line) with the self complementary hexanucleotide duplex d(5'-GTCGAC-3')(2). The results show that the delta-[Ru(bpy)(2)(HPIP)]Cl(2) binds tightly to the oligonucleotide, by intercalation of the ligand HPIP, between the A5 and C6 base sequence of the same strand, probably through the minor groove. Lambda-enantiomer binds weakly, suggesting groove interactions with the hexanucleotide duplex. ESI-MS spectrometry and UV-vis spectroscopy also confirmed these observations.     

Interaction of Lambda- and Delta-[Ru(bpy)2(pbmz)](PF6)2 with the oligonucleotide duplex d(CGCGAATTCGCG)2

The interaction of the enantiomeric complexes Lambda- and Delta-[Ru(bpy)(2)(pbmz)](PF(6))(2) (bpy=2,2'-bipyridine, pbmz=2-(2'-pyridyl)benzimidazole) with the DNA duplex d(CGCGAATTCGCG)(2) was investigated by means of 2D NMR techniques. The synthesis of the enantiomers was based on the optically pure complexes Lambda- and Delta-[Ru(bpy)(2)(py)(2)](2+) and were characterized by CD and NMR spectroscopy. NMR data indicate that both enantiomers bind weakly to the oligonucleotide, approaching from the minor groove at the centre of the helix. The perturbation of the B-DNA conformation is minor with an apparent absence of enantioselectivity. Molecular modelling calculations in conjunction with the NOE data support the suggestion that more than one binding modes are present. The imidazole amine group of the pbmz ligand is probably hydrogen bonded to the DNA phosphodiesteric backbone at the AATT step, and this may provide an explanation for the diminished enantioselectivity observed.     

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.     

Characterization of dipyridophenazine complexes of ruthenium(II): the light switch effect as a function of nucleic acid sequence and conformation.

Spectroscopic parameters for two novel ruthenium complexes on binding to nucleic acids of varying sequences and conformations have been determined. These complexes, Ru(bpy)2dppz2+ and Ru(phen)2dppz2+ (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; dppz = dipyrido[3,2:a-2',3':c]-phenazine) serve as "molecular light switches" for DNA, displaying no photoluminescence in aqueous solution but luminescing intensely in the presence of DNA. The luminescent enhancement observed upon binding is attributed to the sensitivity of the excited state to quenching by water; in DNA, the metal complex, upon intercalation into the helix, is protected from the aqueous solvent, thereby preserving the luminescence. Correlations between the extent of protection (depending upon the DNA conformation) and the luminescence parameters are observed. Indeed, the strongest luminescent enhancement is observed for intercalation into DNA conformations which afford the greatest amount of overlap with access from the major groove, such as in triple helices. Differences are observed in the luminescent parameters between the two complexes which also correlate with the level of water protection. In the presence of nucleic acids, both complexes exhibit biexponential decays in emission. Quenching studies are consistent with two intercalative binding modes for the dppz ligand from the major groove: one in which the metal-phenazine axis lies along the DNA dyad axis and another where the metal-phenazine axis lies almost perpendicular to the DNA dyad axis. Ru(bpy)2dppz2+ and Ru(phen)2dppz2+ are shown here to be unique reporters of nucleic acid structures and may become valuable in the design of new diagnostics for DNA.     

Production and characterization of a polyclonal antibody for Os(II) and Ru(II) polypyridyl complexes

The characterization of a polyclonal antibody produced via immunization with an [Os(bpy)(2)dcbpy] hapten is described. Bpy is 2,2'-bipyridine and dcbpy is 2,2'-bipyridine-4,4'-dicarboxylic acid. The cross-reactivity of the antibody for the Ru(II) analogue of the hapten was also investigated. Large increases in the emission and luminescent lifetime of a series of Os and Ru complexes were observed on binding of the antibody. Association equilibrium constants were derived from luminescence titration data and were found to be 5.6 x 10(8) and 5.0 x 10(8)M(-1) for [Os(bpy)(2)dcbpy] and [Ru(bpy)(2)dcbpy], respectively. Spectroscopic changes were likely due to the exclusion of H(2)O from the complex/antibody binding cleft and blocking of vibrational relaxation pathways of the Os/Ru excited state. D(2)O/H(2)O experiments confirmed that the antibody protected approx. 82% of [Os(bpy)(2)dcbpy] and 80% of [Ru(bpy)(2)dcbpy] from excited state deactivation by the aqueous solvent.     

Synthesis, characterization, X-ray structure and DNA photocleavage by cis-dichloro bis(diimine) Co(III) complexes

Complexes of the type [Co(LL)2Cl2]Cl, where LL = N,N'-ethylenediamine (en), 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (phendione) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) have been synthesized and characterized by elemental analyses, IR, UV-visible and NMR spectroscopy. Crystal structure of [Co(phendione)2Cl2]Cl x 0.5 HCl x 3.5 H2O has been solved and refined to R = 0.0552. The crystal is monoclinic with space group C2/c; a = 25.730(2) A, b = 12.375(1) A, c = 18.979(2) A, beta = 119.925(1) degrees and Z = 8. The DNA binding characteristics of the complexes, investigated by covalent binding assay, viscosity measurements and competitive binding fluorescence measurements show that the complexes interact with DNA covalently except the complex containing the planar dppz ligand which intercalates within the base pairs of DNA. The complexes containing en, phen and phendione cleave plasmid pBR 322 DNA upon irradiation under aerobic conditions while the complex containing the dppz ligand cleaves DNA upon irradiation under inert atmosphere. Molecular modeling studies show that the minimized structure of [Co(phendione)2Cl2]+, maintained the octahedral structure while binding to the N7 of guanines and the ligand fits into the major groove without disrupting the helical structure of the B-DNA.     

DNA mediated resonance energy transfer from 4',6-diamidino-2-phenylindole to [Ru(1,10-phenanthroline)2L]2+

The binding site of Delta- and Lambda-[Ru(phenanthroline)2L]2+ (L being phenanthroline (phen), dipyrido[3,2-a:2'3'-c]phenazine (DPPZ), and benzodipyrido[3,2-a:2'3'-c]phenazine (benzoDPPZ)), bound to poly[d(A-T)2] in the presence and absence of 4',6-diamidino-2-phenylindole (DAPI) was investigated by circular dichroism and fluorescence techniques. DAPI binds at the minor groove of poly[d(A-T)2] and blocks the groove. The circular dichroism spectrum of all Ru(II) complexes are essentially unaffected whether the minor groove of poly[d(A-T)2] is blocked by DAPI or not, indicating that the Ru(II) complexes are intercalated from the major groove. When DAPI and Ru(II) complexes simultaneously bound to poly[d(A-T)2], the fluorescence intensity of DAPI decreases upon increasing Ru(II) complex concentrations. The energy of DAPI at excited state transfers to Ru(II) complexes across the DNA via the F?rster type resonance energy transfer. The efficiency of the energy transfer is similar for both [Ru(phen)2DPPZ]2+ and [Ru(phen)2benzoDPPZ]2+ complexes, whereas that of [Ru(phen)3]2+ is significantly lower. The distance between DAPI and [Ru(phen)3]2+ is estimated as 0.38 and 0.64 F?rster distance, respectively, for the Delta- and Lambda-isomer.     

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.     

Electrochemiluminescence of dipicolinic acid (DPA) and (bpy)(2)Ru(DPA)(+) (bpy = 2,2'-bipyridine).

The spectroscopic and electrochemiluminescence (ECL) properties of dipicolinic acid (DPA), (bpy)(2)Ru(2+) (bpy = 2,2'-bipyridine) and the species formed when DPA and (bpy)(2)Ru(2+) [abbreviated to (bpy)(2)Ru(DPA)(+)] are allowed to react are reported. The UV-Vis absorption maxima for (bpy)(2)Ru(2+) and (bpy)(2)Ru(DPA)(+) are 493 and 475 nm, respectively, indicating the in situ formation of a complex between DPA and (bpy)(2)Ru(2+). DPA, (bpy)(2)Ru(2+) and (bpy)(2)Ru(DPA)(+) display ECL upon oxidation in the presence of the oxidative-reductive co-reactant tri-n-propylamine (TPrA). The ECL of (bpy)(2)Ru(DPA)(+) is at least two-fold higher than either of the parent species. An ECL spectrum of (bpy)(2)Ru(DPA)(+) displays a peak maximum 40 nm red-shifted from the photoluminescence peak maximum, suggesting that the excited state formed electrochemically is different from that formed spectroscopically.     

Photooxidation of d(TpG) by riboflavin and methylene blue. Isolation and characterization of thymidylyl-(3',5')-2-amino-5-[(2-deoxy-beta-D- erythro-pentofuranosyl)amino]-4H-imidazol-4-one and its primary decomposition product thymidylyl-(3',5')-2,2-diamino-4-[(2-deoxy-beta-D- erythro-pentofuranosyl)amino]-5(2H)-oxazolone.

The major initial product of riboflavin- and methylene blue-mediated photosensitization of 2'-deoxyguanosine (dG) in oxygen-saturated aqueous solution has previously been identified as 2-amino-5-[(2-deoxy-beta-D-erythro-pentofuranosyl)amino] 4H-imidazol-4-one (dlz). At room temperature in aqueous solution dlz decomposes quantitatively to 2,2-diamino-4-[(2-deoxy-beta-D-erythro- pentofuranosyl)amino]-5(2H)-oxazolone (dZ). The data presented here show that the same guanine photooxidation products are generated following riboflavin- and methylene blue-mediated photosensitization of thymidylyl-(3',5')-2'-deoxyguanosine [d(TpG)]. As observed for the monomers, the initial product, thymidylyl-(3',5')-2-amino-5-[(2-deoxy- beta-D-erythro-pentofuranosyl)amino]-4H-imidazol-4-one [d(Tplz)], decomposes in aqueous solution at room temperature to thymidylyl-(3',5')-2,2-diamino-4- [(2-deoxy-beta-D-erythro-pentofuranosyl)amino]-5(2H)-oxazolone [d(TpZ)]. Both modified dinucleoside monophosphates have been isolated by HPLC and characterized by proton NMR spectrometry, fast atom bombardment mass spectrometry, chemical analyses and enzymatic digestions. Among the chemical and enzymatic properties of these modified dinucleoside monophosphates are: (i) d(Tplz) and d(TpZ) are alkali-labile; (ii) d(Tplz) reacts with methoxyamine, while d(TpZ) is unreactive; (iii) d(Tplz) is digested by snake venom phosphodiesterase, while d(TpZ) is unaffected; (iv) relative to d(TpG), d(TpZ) and d(Tplz) are slowly digested by spleen phosphodiesterase; (v) d(Tplz) and d(TpZ) can be 5'-phosphorylated by T4 polynucleotide kinase. The first observation suggests that dlz and dZ may be responsible for some of the strand breaks detected following hot piperidine treatment of DNA exposed to photosensitizers.     

Developing red-emissive ruthenium(II) complex-based luminescent probes for cellular imaging

Ruthenium(II) complexes have rich photophysical attributes, which enable novel design of responsive luminescence probes to selectively quantify biochemical analytes. In this work, we developed a systematic series of Ru(II)-bipyrindine complex derivatives, [Ru(bpy)(3-n)(DNP-bpy)(n)](PF(6))(2) (n = 1, 2, 3; bpy, 2,2'-bipyridine; DNP-bpy, 4-(4-(2,4-dinitrophenoxy)phenyl)-2,2'-bipyridine), as luminescent probes for highly selective and sensitive detection of thiophenol in aqueous solutions. The specific reaction between the probes and thiophenol triggers the cleavage of the electron acceptor group, 2,4-dinitrophenyl, eliminating the photoinduced electron transfer (PET) process, so that the luminescence of on-state complexes, [Ru(bpy)(3-n)(HP-bpy)(n)](2+) (n = 1, 2, 3; HP-bpy, 4-(4-hydroxyphenyl)-2,2'-bipyridine), is turned on. We found that the complex [Ru(bpy)(DNP-bpy)(2)](2+) remarkably enhanced the on-to-off contrast ratio compared to the other two (37.8 compared to 21 and 18.7). This reveals a new strategy to obtain the best Ru(II) complex luminescence probe via the most asymmetric structure. Moreover, we demonstrated the practical utility of the complex as a cell-membrane permeable probe for quantitative luminescence imaging of the dynamic intracellular process of thiophenol in living cells. The results suggest that the new probe could be a very useful tool for luminescence imaging analysis of the toxic thiophenol in intact cells.     

Characterization of synthetic oxomanganese complexes and the inorganic core of the O2-evolving complex in photosystem II: evaluation of the DFT/B3LYP level of theory

The capabilities and limitations of the Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional are investigated as applied to studies of mixed-valent multinuclear oxomanganese complexes. Benchmark calculations involve the analysis of structural, electronic and magnetic properties of di-, tri- and tetra-nuclear Mn complexes, previously characterized both chemically and spectroscopically, including the di-mu-oxo bridged dimers [Mn(III)Mn(IV)(mu-O)(2)(H(2)O)(2)(terpy)(2)](3+) (terpy=2,2':6,2'-terpyridine) and [Mn(III)Mn(IV)(mu-O)(2)(phen)(4)](3+) (phen=1,10-phenanthroline), the Mn trimer [Mn(3)O(4)(bpy)(4)(H(2)O)(2)](4+) (bpy=2,2'-bipyridine), and the tetramer [Mn(4)O(4)L(6)](+) with L=Ph(2)PO(2)(-). Furthermore, the density functional theory (DFT) B3LYP level is applied to analyze the hydrated Mn(3)O(4)CaMn cluster completely ligated by water, OH(-), Cl(-), carboxylate and imidazole ligands, analogous to the '3+1 Mn tetramer' of the oxygen-evolving complex of photosystem II. It is found that DFT/B3LYP predicts structural and electronic properties of oxomanganese complexes in pre-selected spin-electronic states in very good agreement with X-ray and magnetic experimental data, even when applied in conjunction with rather modest basis sets. However, it is conjectured that the energetics of low-lying spin-states is beyond the capabilities of the DFT/B3LYP level, constituting a limitation to mechanistic studies of multinuclear oxomanganese complexes where until now the performance of DFT/B3LYP has raised little concern.     

DNA intercalating studies of [Ru(bpy)2dmt]2+ with two vacant nitrogen atoms by introducing copper(II) ions

A novel, yet effective method for identifying DNA-binding modes of [Ru(bpy)(2)dmt](2+) (where bpy?=?2,2'-bipyridine and dmt?=?2,3-dimethyl-1,4,8,9-tetra-aza-triphenylene) on an indium tin oxide electrode has been successfully developed by introducing Cu(2+) ion and ethylenediaminetetraacetic acid. The results from emission spectra and fluorescence microscopic images suggested that [Ru(bpy)(2)dmt](2+) not only associates with Cu(2+) ion in both the absence and presence of DNA but also shows strong affinity with DNA in the presence of Cu(2+). Evidence for the strong binding of [Ru(bpy)(2)dmt](2+) to DNA was determined from the interface studies using electrochemical methods. The present study suggests that a combination of photoluminescence measurement with electrochemical methods identifies the DNA-binding behavior of luminescent molecules with redox activities. [Ru(bpy)(2)dmt](2+) binds to DNA via an intercalative mode.     

Ruthenium(II)-phenanthroline-biotin complexes: synthesis and luminescence enhancement upon binding to avidin

We report the synthesis, characterization, and avidin-binding properties of two novel ruthenium complexes, [Ru(bpy)(2)(phen-biotin)][PF(6)](2) 1 and [Ru(phen)(2)(phen-biotin)][PF(6)](2) 2 (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline, phen-biotin = 5-(10-amidobiotinyl)-1,10-phenanthroline)). We demonstrate that both biotinylated compounds bind to avidin through their biotin moieties with high affinity and in a 4:1 ratio. The binding of compounds 1 and 2 to avidin results in an enhancement in luminescence intensity ( approximately 1.4x, approximately 1.6x, respectively), relative to the unbound biotinylated ruthenium complexes. This behavior is markedly different from biotinylated organic dyes, whose fluorescence is quenched upon binding to avidin. Thus, ruthenium-biotin complexes 1 and 2 can form the basis of new, simplified biotin-avidin assays, which involve luminescence detection of the relevant biotinylated molecule through cross-linking with avidin.     

Rotation of periphery methylpyridine of meso-tetrakis(n-N-methylpyridiniumyl)porphyrin (n = 2, 3, 4) and its selective binding to native and synthetic DNAs

By utilizing circular and linear dichroism, the binding mode of meso-tetrakis(n-N-methylpyridiniumyl)porphyrin (n = 2, 3, 4) to various DNAs was studied in this work. 2-N-(methylpyridiniumyl)porphyrin(o-TMPyP), in which rotation of the periphery pyridinium ring is prevented, exhibits similar spectral properties when bound to DNA, poly[d(G-C)(2)] and poly[d(A-T)(2)], suggesting a similar binding mode. Close analysis of the spectral properties led us to conclude that o-TMPyP sits in the major groove. However, both 3-N- and 4-N-(methylpyridiniumyl)porphyrin (m- and p-TMPyP), of which the periphery pyridinium ring is free to rotate, intercalate between the basepairs of DNA and poly[d(G-C)(2)]. In the presence of poly[d(A-T)(2)], m-TMPyP exhibits a typical bisignate excitonic CD spectrum in the Soret band, while p-TMPyP shows two positive CD bands. The excitonic CD spectrum of the m-TMPyP-poly[d(A-T)(2)] complex and the positive CD band of the o-TMPyP-poly[d(A-T)(2)] complex were not affected by the presence of the minor groove binding drug, 4',6-diamidino-2-phenylindole (DAPI), indicating that this porphyrin is bound in the major groove. In contrast, two positive CD bands of the p-TMPyP-poly[d(A-T)(2)] complex altered in the presence of DAPI. From the changes in CD spectrum and other spectral properties, a few possible binding modes for p-TMPyP to poly[d(A-T)(2)] are suggested.     

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.     

Luminescent pH sensing and DNA binding properties of a novel ruthenium(II) complex

A new Ru(II) complex, [Ru(bpy)(2)(dhipH3)](ClO4)(2) (in which bpy=2,2'-bipyridine, dhipH(3)=3,4-dihydroxy-imidado[4,5-f][1,10]-phenanthroline), was synthesized and characterized, and the pH effect on the emission spectra of the complex was studied. The interaction of the complex with calf thymus DNA was investigated by UV-visible and emission spectroscopy, and viscosity measurements. The results suggest that the complex acted as a sensitive luminescent pH sensor and a strong ct-DNA intercalator with an intrinsic binding constant of (4.0+/-0.7) x 10(5) M(-1) in buffered 50 mM NaCl.     

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.     

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.