Synthesis,characterization, and DNA binding of ruthenium(II) complexes with 2-benzo[b] furan-2-yl-1H-imidazo[4,5f][1,10]phenanthroline as an intercalative ligand

DNA-binding properties of a number of ruthenium complexes with different polypyridine ligands are reported. The new polypyridine ligand BFIP (=2-benzo[b] furan-2-yl-1H-imidazo[4,5-f][1,10]phenanthroline) and its ruthenium complexes [Ru(bpy)₂BFIP]²⁺ (bpy = 2,2′-bipyridine), [Ru(dmb)₂BFIP]²⁺ (dmb = 4,4′-dimethyl-2,2′-bipyridine), and [Ru(phen)₂BFIP]²⁺ (phen = 1,10-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra, IR, UV-Vis, ¹H- and ¹³C-NMR, and cyclic voltammetry. The DNA binding of these complexes to calf-thymus DNA (CT-DNA) was investigated by spectrophotometric, fluorescence, and viscosity measurements. The results suggest that ruthenium(II) complexes bind to CT-DNA through intercalation. Photocleavage of pBR 322 DNA by these complexes was also studied, and [Ru(phen)₂BFIP]²⁺ was found to be a much better photocleavage agent than the other two complexes.     

Characterization of Binding Properties of Cr(Phen)33+ and Ru(Phen)32+ Complexes with Human Lactoferrin

This work presents research about [Cr(phen)₃]³⁺ and [Ru(phen)₃]²⁺ interaction with human lactoferrin (HLf), a key carrier protein of ferric cations. The photochemical and photophysical properties of [Cr(phen)₃]³⁺ and [Ru(phen)₃]²⁺ have been widely studied in the last decades due to their potential use as photosensitizers in photodynamic therapy (PDT). The behavior between the complexes and the protein was studied employing UV–visible absorption, fluorescence emission and circular dichroism spectroscopic techniques. It was found that both complexes bind to HLf with a large binding constant (K_b): 9.46 × 10⁴ for the chromium complex and 4.16 × 10⁴ for the ruthenium one at 299 K. Thermodynamic parameters were obtained from the Van't Hoff equation. Analyses of entropy (ΔS), enthalpy (ΔH) and free energy changes (ΔG) indicate that these complexes bind to HLf because of entropy-driven processes and electrostatic interactions. According to circular dichroism experiments, no conformational changes have been observed in the secondary and tertiary structure of the protein in the presence of any of the studied complexes. These experimental results suggest that [Cr(phen)₃]³⁺ and [Ru(phen)₃]²⁺ bind to HLf, indicating that this protein could act as a carrier of these complexes in further applications.     

Experimental and Theoretical Studies on DNA‐Binding and Spectral Properties of ‘Light Switch’ Complexes [Ru(L)2(ppn)]2+ (L=2,2′‐Bipyridine and 1,10‐Phenanthroline; ppn=Pteridino[6,7‐f] [1,10]phenanthroline‐11,13‐diamine)

The ligand pteridino[6,7‐f] [1,10]phenanthroline‐11,13‐diamine (ppn) and its Ru^II complexes [Ru(bpy)₂(ppn)]²⁺ ( 1 ; bpy=2,2′‐bipyridine) and [Ru(phen)₂(ppn)]²⁺ ( 2 ; phen=1,10‐phenanthroline) were synthesized and characterized by elemental analysis, electrospray MS, ¹H‐NMR, and cyclic voltammetry. The DNA‐binding behaviors of 1 and 2 were studied by spectroscopic and viscosity measurements. The results indicate that both complexes strongly bind to calf‐thymus DNA in an intercalative mode, with DNA‐binding constants K_b of (1.7±0.4)?10⁶ M ^?1 and (2.6±0.2)?10⁶ M ^?1, respectively. The complexes 1 and 2 exhibit excellent DNA‐‘light switch’ performances, i.e., they do not (or extremely weakly) show luminescence in aqueous solution at room temperature but are strongly luminescent in the presence of DNA. In particular, the experimental results suggest that the ancillary ligands bpy and phen not only have a significant effect on the DNA‐binding affinities of 1 and 2 but also have a certain effect on their spectral properties. [Ru(phen)₂(ppn)]²⁺( 2 ) might be developed into a very prospective DNA‐‘light switch’ complex. To explain the DNA‐binding and spectral properties of 1 and 2 , theoretical calculations were also carried out applying the DFT/TDDFT method.     

Mononuclear Polypyridylruthenium(II) Complexes with High Membrane Permeability in Gram‐Negative Bacteria—in particular Pseudomonas aeruginosa

Ruthenium(II) complexes containing the tetradentate ligand bis[4(4′‐methyl‐2,2′‐bipyridyl)]‐1,n‐alkane (“bb_n”; n=10 and 12) have been synthesised and their geometric isomers separated. All [Ru(phen)(bb_n)]²⁺ (phen=1,10‐phenanthroline) complexes exhibited excellent activity against Gram‐positive bacteria, but only the cis‐α‐[Ru(phen)(bb₁₂)]²⁺ species showed good activity against Gram‐negative species. In particular, the cis‐α‐[Ru(phen)(bb₁₂)]²⁺ complex was two to four times more active than the cis‐β‐[Ru(phen)(bb₁₂)]²⁺ complex against the Gram‐negative strains. The cis‐α‐ and cis‐β‐[Ru(phen)(bb₁₂)]²⁺ complexes readily accumulated in the bacteria but, significantly, showed the highest level of uptake in Pseudomonas aeruginosa. Furthermore, the accumulation of the cis‐α‐ and cis‐β‐[Ru(phen)(bb₁₂)]²⁺ complexes in P. aeruginosa was considerably greater than in Escherichia coli. The uptake of the cis‐α‐[Ru(phen)(bb₁₂)]²⁺ complex into live P. aeruginosa was confirmed by using fluorescence microscopy. The water/octanol partition coefficients (log P) were determined to gain understanding of the relative cellular uptake. The cis‐α‐ and cis‐β‐[Ru(phen)(bb_n)]²⁺ complexes exhibited relatively strong binding to DNA (K_b≈10⁶ M ^?1), but no significant difference between the geometric isomers was observed.     

Synthesis,DNA‐Binding and Photocleavage Studies of the Ruthenium(II) Complexes [Ru(phen)2(ppd)]2+ and [Ru(phen)(ppd)2]2+ (ppd=Pteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione,phen=1,10‐Phenanthroline)

Two new complexes, [Ru(phen)₂(ppd)]²⁺ ( 1 ) and [Ru(phen)(ppd)₂]²⁺ ( 2 ) (ppd=pteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione, phen=1,10‐phenanthroline) were synthesized and characterized by ES‐MS, ¹H‐NMR spectroscopy, and elemental analysis. The intercalative DNA‐binding properties of 1 and 2 were investigated by absorption‐spectroscopy titration, luminescence‐spectroscopy studies, thermal denaturation, and viscosity measurements. The theoretical aspects were further discussed by comparative studies of 1 and 2 by means of DFT calculations and molecular‐orbital theory. Photoactivated cleavage of pBR322 DNA by the two complexes were also studied, and 2 was found to be a much better photocleavage reagent than 1 . The mechanism studies revealed that singlet oxygen and the excited‐states redox potentials of the complex may play an important role in the DNA photocleavage.     

Synthesis,Characterization, and DNA Interaction Studies of the Ruthenium(II) Complexes [Ru(bpy)2(ipbp)]2+ and [Ru(ipbp)(phen)2]2+ (ipbp=3‐(1H‐Imidazo[4,5‐f][1,10]phenanthrolin‐2‐yl)‐4H‐1‐benzopyran‐2‐one; bpy=2,2′‐Bipyridine; phen=1,10‐Phenanthroline)

A novel ligand 3‐(1H‐imidazo[4,5‐f][1,10]phenanthrolin‐2‐yl)‐4H‐1‐benzopyran‐4‐one (ipbp) and its ruthenium(II) complexes [Ru(bpy)₂(ipbp)]²⁺ ( 1 ) and [Ru(ipbp)(phen)₂]²⁺ ( 2 ) (bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline) were synthesized and characterized by elemental analysis and mass, ¹H‐NMR, and electronic‐absorption spectroscopy. The electrochemical behavior of the complexes was studied by cyclic voltammetry. The DNA‐binding behavior of the complexes was investigated by spectroscopic methods and viscosity measurements. The results indicate that complexes 1 and 2 bind with calf‐thymus DNA in an intercalative mode. In addition, 1 and 2 promote cleavage of plasmid pBR 322 DNA from the supercoil form I to the open circular form II upon irradiation.     

Ruthenium(II) complexes of 6,7-dicyanodipyridoquinoxaline: synthesis, luminescence studies, and DNA interaction

The hexaflurophosphate and chloride salts of a series of ruthenium(II) complexes incorporating a new dipyridophenazine-based ligand, dicnq (6,7-dicyanodipyrido[2,2-d:2',3'-f]quinoxaline), are synthesized in good-to-moderate yields. These mono ([Ru(phen)2(dicnq)]2+; phen = 1,10-phenanthroline), bis ([Ru(phen)(dicnq)2]2+), and tris ([Ru(dicnq)3]2+) complexes are fully characterized by elemental analysis, infrared, FAB-MS, 1H NMR, and cyclic voltammetric methods. Results of absorption titration and thermal denaturation studies reveal that these complexes are moderately strong binders of calf-thymus (CT) DNA, with their binding constants spanning the range (1-3) x 10(4) M-1. On the other hand, under the identical set of experimental conditions of light and drug dose, the DNA (pBR 322)-photocleavage abilities of these ruthenium(II) complexes follow the order [Ru(phen)2(dicnq)]2+ > [Ru(phen)(dicnq)2]2+ > [Ru(dicnq)3]2+, an order which is the same as that observed for their MLCT emission quantum yields. Steady-state emission studies carried out in nonaqueous solvents and in aqueous media with or without DNA reveal that while [Ru(dicnq)3]2+ is totally nonemissive under these solution conditions, both [Ru(phen)2(dicnq)]2+ and [Ru(phen)(dicnq)2]2+ are luminescent and function as "molecular light switches" for DNA. Successive addition of CT DNA to buffered aqueous solutions containing the latter two complexes results in an enhancement of the emission in each case, with the enhancement factors at saturation being approximately 16 and 8 for [Ru(phen)2(dicnq)]2+ and [Ru(phen)(dicnq)2]2+, respectively. These results are discussed in light of the relationship between the structure-specific deactivations of the MLCT excited states of these metallointercalators and the characteristic features of their DNA interactions, and attempts are made to compare and contrast their properties with those of analogous dipyridophenazine-based complexes, including the ones reported in the preceding paper.     

Study of the interaction between ruthenium(II) complexes and CT-DNA: synthesis,characterisation, photocleavage and antimicrobial activity studies

Two polypyridyl ligands 6-fluro-3-(1H-imidazo [4,5-f] [1,10]-phenanthroline-2-yl)-4H-chromen-4-one (FIPC), 6-chloro-3-(1H-imidazo [4,5-f] [1,10]-phenanthroline-2-yl)-4H-chromen-4-one (ClIPC) polypyridyl ligands and their Ru(II) complexes [Ru(bipy)₂FIPC]²⁺(1), [Ru(dmb)₂FIPC]²⁺(2), [Ru(phen)₂FIPC]²⁺(3), [Ru(bipy)₂ClIPC]²⁺(4), [Ru(dmb)₂ClIPC]²⁺(5) and [Ru(phen)₂ClIPC]²⁺(6) ((bipy = 2,2′-bipyridine, dmb = 4,4′-dimethyl-2,2′-bipyridine and phen = 1,10-phenanthroline) have been synthesised and characterised by elemental analysis, Mass spectra, IR, ¹H and ¹³C-NMR. The DNA-binding of the six complexes to calf-thymus DNA (CT-DNA) has been investigated by different spectrophotometric, fluorescence and viscosity measurements. The results suggest that 1–6 complexes bind to CT-DNA through intercalation. The variation in binding affinities of these complexes is rationalised by a consideration of electrostatic, steric factors and nature of ancillary ligands. Under irradiation at 365 nm, the three complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA. Inhibitor studies suggest that singlet oxygen (¹O₂) plays a significant role in the cleavage mechanism of Ru(II) complexes. Thereby, under comparable experimental conditions [Ru(phen)₂FIPC]²⁺(3), [Ru(phen)₂ClIPC]²⁺(6) cleaves DNA more effectively than 1, 2, 4 and 5 complexes do. The Ru(II) polypyridyl complexes (1–6) have been screened for antimicrobial activities.     

Equilibria in complexes ofN-heterocycles. Part 49(1). Additions of cyanide and hydroxide to ruthenium(II) complexes in aqueous solution

Summary The complex ions [Ru(5-NO₂phen)₂(bipy)]²⁺ and [Ru(5-NO₂phen)(bipy)₂]²⁺ form adducts in aqueous solution with OH^– and CN^– via attack at the ligand, as shown by spectrophotometry. The rates of these additions have been measured and compared to those of similar reactions.     

Synthesis,DNA-binding,and photocleavage properties of Ru(II) complexes containing dppz-based ligand

A ligand ipdp (ipdp?=?indeno[1′,2′?:?5,6]pyrazino[2,3-i]dipyrido[3,2-a?:?2′,3′-c]phenazine-8-one) and its ruthenium complexes, [Ru(L)₂(ipdp)]²⁺ (L?=?bpy (2,2′-bipyridine), phen (1,10-phenanthroline)), have been synthesized and characterized by elemental analysis, electrospray mass spectra, and ¹H NMR. The interaction between the complexes and calf thymus DNA (CT-DNA) has been investigated by spectroscopic methods and viscosity measurements. The results indicate that the complexes can bind to CT-DNA in an intercalative mode. In addition, both complexes promote the photocleavage of plasmid pBR322 DNA under irradiation. The mechanistic studies reveal that singlet oxygen ¹O₂ plays a significant role in DNA photocleavage.     

Cobalt(III), nickel(II) and ruthenium(II) complexes of 1,10-phenanthroline family of ligands: DNA binding and photocleavage studies

DNA binding and photocleavage characteristics of a series of mixed-ligand complexes of the type [M(phen)₂LL]ⁿ⁺ (where M = Co(III), Ni(II) or Ru(II), LL = 1,10-phenanthroline (phen), phenanthroline-dione (phen-dione) or dipyridophenazine (dppz) andn = 3 or 2) have been investigated in detail. Various physico-chemical and biochemical techniques including UV/Visible, fluorescence and viscometric titration, thermal denaturation, and differential pulse voltammetry have been employed to probe the details of DNA binding by these complexes; intrinsic binding constants (K _b) have been estimated under a similar set of experimental conditions. Analysis of the results suggests that intercalative ability of the coordinated ligands varies as dppz>phen>phen-dione in this series of complexes. While the Co(II) and Ru(II) complexes investigated in this study effect photocleavage of the supercoiled pBR 322 DNA, the corresponding Ni(II) complexes are found to be inactive under similar experimental conditions. Results of detailed investigations carried out inquiring into the mechanistic aspects of DNA photocleavage by [Co(phen)₂(dppz)]³⁺ have also been reported.     

Evidence for symmetry reduction in excited states of [Ru(bpy)3]+ and related compounds

Photoselection and other spectroscopic data for [Ru(bpy)₃]²⁺, [Ru(phen)₃]²⁺, [Ru(bpy)(py)₄]²⁺ and [Os(bpy)₃]²⁺ suggest that the emitting state for the tris compounds may be localized on a single ring.     

1-(2′-Pyridylazo)-2-naphtholate complexes of ruthenium: Synthesis,characterization, and DNA binding properties

Reaction of 1-(2′-pyridylazo)-2-naphthol (Hpan) with [Ru(dmso)₄Cl₂] (dmso = dimethylsulfoxide), [Ru(trpy)Cl₃] (trpy = 2,2′,2″-terpyridine), [Ru(bpy)Cl₃] (bpy = 2,2′-bipyridine) and [Ru(PPh₃)₃Cl₂] in refluxing ethanol in the presence of a base (NEt₃) affords, respectively, the [Ru(pan)₂], [Ru(trpy)(pan)]⁺ (isolated as perchlorate salt), [Ru(bpy)(pan)Cl] and [Ru(PPh₃)₂(pan)Cl] complexes. Structures of these four complexes have been determined by X-ray crystallography. In each of these complexes, the pan ligand is coordinated to the metal center as a monoanionic tridentate N,N,O-donor. Reaction of the [Ru(bpy)(pan)Cl] complex with pyridine (py) and 4-picoline (pic) in the presence of silver ion has yielded the [Ru(bpy)(pan)(py)]⁺ and [Ru(bpy)(pan)(pic)]⁺ complexes (isolated as perchlorate salts), respectively. All the complexes are diamagnetic (low-spin d⁶, S = 0) and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru(II)–Ru(III) oxidation on the positive side of SCE. Except in the [Ru(pan)₂] complex, a second oxidative response has been observed in the other five complexes. Reductions of the coordinated ligands have also been observed on the negative side of SCE. The [Ru(trpy)(pan)]ClO₄, [Ru(bpy)(pan)(py)]ClO₄ and [Ru(bpy)(pan)(pic)]ClO₄ complexes have been observed to bind to DNA, but they have not been able to cleave super-coiled DNA on UV irradiation.     

Equilibria in complexes ofN-heterocyclic molecules,Part XXIV. The reaction of nucleophiles with tris-(2,2′-bipyrimidine)iron(II) ion and its ruthenium(II) analogue

Summary The reactions of [Fe(bipym)₃]²⁺ and [Ru(bipym)₃]²⁺ with hydroxide ion in aqueous solution have been followed. The [Ru(bipym)₃]²⁺ species undergoes nucleophilic attack at the ligand to yield [Ru(bipym)₂(pyrimidine)(OH)]⁺ and [HCO₂]^– ion, involving cleavage of one pyrimidyl ring. Intermediates can be observed in the reaction of [Fe(bipym)₃]²⁺ with HO^–, N₃ ^– and SCN^–. The kinetics of the first reaction have been followed and the results are compared with those known for the reactions of [Fe(bipy)₃]²⁺, [Fe(phen)₃]²⁺ and similar compounds.Part XXIII: P. A. Williams,Transition Met. Chem., 78/84.     

Spectroscopic and photoelectrochemical differences between racemic and enantiomeric [Ru(phen)3] ions intercalated into layered niobate K4Nb6O17

Chirality effects have been observed in the intercalation, spectroscopic and photoelectrochemical behavior when enantiomeric and racemic [Ru(phen)₃]²⁺ complexes were intercalated in the interlayer spaces of K₄Nb₆O₁₇. The results were interpreted in terms of a [Nb₆O₁₇]⁴⁻-chelate and chelate–chelate interactions. The faster luminescence decay and higher photocurrent of the enantiomeric [Ru(phen)₃]²⁺–K₄Nb₆O₁₇ compounds than the racemic ones suggest that the emission of adsorbed [Ru(phen)₃]²⁺ ions was not only quenched by adsorbed complexes (or concentration quenching) but also by the semiconductive host lattices.     

Synthesis,characterization and DNA binding and photocleavage studies of [Ru(bpy)2BDPPZ]2+, [Ru(dmb)2BDPPZ]2+ and [Ru(phen)2BDPPZ]2+ complexes and their antimicrobial activity

Polypyridyl ligand 9a,13a‐dihydro‐4,5,9,14‐tetraaza‐benzo[b]triphenylene‐11‐yl)‐phenyl‐methanone (BDPPZ) and its complexes [Ru(bpy)₂BDPPZ]²⁺, [Ru(dmb)₂BDPPZ]²⁺ and [Ru(phen)₂BDPPZ]²⁺ (where bpy = 2,2′‐bipyridine, dmb = 4,4′‐dimethyl‐2,2′‐bipyridine, phen = 1,10‐phenanthroline) have been synthesized and characterized by elemental analysis, IR, UV–vis, ¹H‐NMR, ¹³C‐NMR and mass spectra. The DNA‐binding properties of the complexes were investigated by absorption, emission, melting temperature and viscosity measurements. Experimental results indicate that the three complexes can intercalate into DNA base pairs. Photo activated cleavage of pBR‐322 DNA by the three complexes was also studied. Further, all three Ru(II) complexes synthesized were screened for their antimicrobial activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,DNA interaction and photocleavage studies of ruthenium(II) complexes with 2-(pyrrole) imidazo[4,5-f]-1,10-phenanthroline as an intercalative ligand

Three Ru(II) complexes, namely [Ru(bipy)₂PRIP]²⁺ (1), [Ru(dmb)₂PRIP]²⁺ (2), and [Ru(phen)₂PRIP]²⁺ (3) (dmb = 4,4′-dimethyl-2,2′-bipyridine; PRIP = 2-(pyrrole) imidazo [4,5-f]-1,10-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra, IR, ¹H NMR and ¹³C NMR. The DNA-binding properties of the three complexes with calf-thymus DNA (CT-DNA) were investigated by spectrophotometry, fluorescence methods and viscosity measurements. The results suggest that all three complexes bind to CT-DNA through intercalation. Also, when irradiated at 365 nm, the three complexes promote the photocleavage of plasmid pBR-322 DNA. Under comparable experimental conditions, complex 3 cleaves DNA more effectively than complexes 1 and 2.     

Cationic carbonyl complexes of ruthenium(II) and osmium(II) containing 2,2′-bipyridyl and 1,10-phenanthroline

Summary Reactions of ruthenium carbonyl complexes of the type [RuX₂(CO)(Ph₂RAs)₃] (X=Cl or Br; R=Me or Et) with 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) in alcohol produce orange red cationic products of the formula [RuX(CO)(N-N)(Ph₂RAs)₂]ClO₄ (N-N=bipy or phen). Likewise, the hydridocarbonyls of ruthenium and osmium of the type [MHX(CO)(Ph₂RAs)₃] (M=Ru or Os) react with bipy and phen to yield yellow cationic complexes of the composition [(MH(CO)(N-N)(Ph₂RAs)₂]ClO₄. Structures have been assigned to all the complexes on the basis of i.r. and¹ H n.m.r. spectral data.     

Unusual sandwich platinum(II) complex: [Pt(phen)2]2+ cation between two Pt(phen)(OOCMe)2 molecules

New carboxylate platinum(II) complexes: syn and anti isomers of Pt(phen)(OOCMe)₂ molecular complex, [Pt(phen)(NCMe)₂](O₃SCF₃)₂, as well as unusual sandwich complex [Pt(phen)₂]²⁺ · 2syn-[Pt(phen)(OOCMe)₂] where [Pt(phen)₂]²⁺ cation is inserted between two syn-Pt(phen)(OOCMe)₂ molecules were synthesized and structurally characterized by X-ray diffraction analysis. As distinct from syn- and anti-Pt(phen)(OOCMe)₂ and [Pt(phen)(NCMe)₂](O₃SCF₃)₂ complexes with flat phenanthroline ligand, the phen ligands in [Pt(phen)₂]²⁺ cation have a curved configuration. Comparative DFT analysis of geometry of model structures phen, phen⁺, phenH⁺, and [Ptphen₂] ⁿ⁺ (n = 1, 2) showed that electron removal from phen molecule had no effect on its geometry in both free state and platinum(II) complexes.     

Studies on the nuclease activity and interactions of the mixed‐polypyridyl [Ni2(1,3‐tpbd)(diimine)2(H2O)2]4+ complexes with thioredoxin reductase

Three new nickel(II) complexes formulated as [Ni₂(1,3‐tpbd)(diimine)₂(H₂O)₂]⁴⁺ [1,3‐tpbd = N,N,N′,N′‐tetrakis(2‐pyridylmethyl)benzene‐1,3‐diamine, where diimine is an N,N‐donor heterocyclic base like 1,10‐phenanthroline (phen),2,2′‐bipyridine (bpy), 4,5‐diazafluoren‐9‐one (dafo)], have been synthesized and structurally characterized by X‐ray crystallography: [Ni₂(1,3‐tpbd)(phen)₂(H₂O)₂]⁴⁺ (1), [Ni₂(1,3‐tpbd)(bpy)₂(H₂O)₂]⁴⁺(2) and [Ni₂(1,3‐tpbd)(dafo)₂(H₂O)₂]⁴⁺ (3). Single‐crystal diffraction reveals that the metal atoms in the complexes are all in a distorted octahedral geometry and in a trans arrangement around 1,3‐tpbd ligand. The interactions of the three complexes with calf thymus DNA (CT‐DNA) have been investigated by UV absorption, fluorescence spectroscopy, circular dichroism and viscosity. The apparent binding constant (K_app) values are calculated to be 1.91 × 10⁵ m ^?1 for 1, 1.18 × 10⁵ m ^?1 for 2, and 1.35 × 10⁵ m ^?1 for 3, following the order 1 > 3 > 2. The higher DNA binding affinity of 1 is due to the involvement in partial insertion of the phen ring between the DNA base pairs. A decrease in relative viscosities of DNA upon binding to 1–3 is consistent with the DNA binding affinities. These complexes efficiently display oxidative cleavage of supercoiled DNA in the presence of H₂O₂ (250 µ m ), with 3 exhibiting the highest nuclease activity. The rate constants for the conversion of supercoiled to nicked DNA are 5.28 × 10^?5 s^?1 (for 1), 6.67 × 10^?5 s^?1 (for 2) and 1.39 × 10^?4 s^?1 (for 3), also indicating that complex 3 shows higher catalytic activity than 1 and 2. Here the nuclease activity is not readily correlated to binding affinity. The inhibitory effect of complexes 1–3 on thioredoxin reductase has also been examined. The IC₅₀ values are calculated to be 26.54 ± 0.57, 31.03 ± 3.33 and 8.69 ± 2.54 µ m , respectively, showing a more marked inhibitory effect on thioredoxin reductase by complex 3 than the other two complexes. Copyright © 2012 John Wiley & Sons, Ltd.