Kinetics and mechanism of the axial substitution reactions of (ligand)bis(4,5-dichloro-1,2-benzo semiquinonediiminato)cobalt(III) complexes

Square-pyramidal (Ph₃X)bis(4,5-dichloro-1,2-benzosemiquinonediiminato)cobalt(III) complexes (X = As, Sb or P) have been synthesized. The kinetics of axial substitution for the triphenylantimony complex have been studied for 10 entering ligands (L*). The reaction is of reversible second-order in both directions for all complexes. Labile behavior is indicated by the rate constants in the range from 6.33 × 10³ (for L* = Ph₃P in MeOH) to 5.4 (L* = py in CH₂Cl₂) M⁻¹ s⁻¹. The kinetics is consistent with an I_a mechanism. The log of the second-order rate constant for axial substitution is a linear function of nucleophilic reactivity n_Pt°, which is due to the trans-labilizing effect of the entering ligand in the six-coordinate transition state.     

Differences in structure, physiological stability, electrochemistry, cytotoxicity, DNA and protein binding properties between two Ru(III) complexes

A novel Ru(III) complex, mer-[RuCl(3)(CH(3)CN)(dpq)] (1), has been synthesized and characterized by X-ray diffraction, where dpq=dipyrido[3,2-d:2',3'-f]quinoxaline. Its chemical and biological properties have been intensively compared with those of mer-[RuCl(3)(DMSO)(dpq)] (DMSO=dimethyl sulfoxide) (2). It has been found that the stability in buffered solutions and the reduction potential for the Ru(III)/Ru(II) couple can be modulated by changing the small molecule bonded to the Ru(III) center. Interactions of 1 with DNA have been investigated by DNA melting experiments, DNA competitive binding with EB (ethidium bromide), plasmid DNA cleavage experiments and viscosity measurements. The interaction of 1 and 2 with BSA (bovine serum albumin) has also been studied using fluorescent quenching method. The experimental results show that 1 exerts higher affinity towards DNA and BSA than 2 does. The cytotoxicity of 1 has been evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method, and 2 shows slightly higher anticancer potency than 1 does against all the cell lines screened. Attempts are made to clarify the possible antitumor mechanisms of these two complexes by analyzing the experimental results presented.     

Cobalt complexes of terpyridine ligand: crystal structure and photocleavage of DNA

Two new cobalt complexes, [Co(pytpy)(2)](ClO(4))(2), 1, and [Co(pytpy)(2)](ClO(4))(3), 2 where pytpy=pyridine terpyridine, have been synthesized and characterized. Single-crystal X-ray structure of both the complexes has been resolved. The structure shows the complexes to be a monomeric cobalt(II) and cobalt(III) species with two pytpy ligands coordinated to the metal ion to give a six coordinate complex. Both cobalt(II) and cobalt(III) complexes crystallize in meridional configuration. The interaction of these complexes with calf thymus DNA has been explored by using absorption, emission spectral, electrochemical studies and viscosity measurements. From the experimental results the DNA binding constants of 1 and 2 are found to be (1.97+/-0.15)x10(4)M(-1) and (2.7+/-0.20)x10(4)M(-1) respectively. The ratio of DNA binding constants of 1 and 2 have been estimated to be 0.82 from electrochemical studies, which is in close agreement with the value of 0.73 obtained from spectral studies. The observed changes in viscosity of DNA in the presence of increasing amount of complexes 1 and 2 suggest intercalating binding of these complexes to DNA. Results of DNA cleaving experiments reveal that complex 2 efficiently cleaves DNA under photolytic conditions while complex 1 does not cleave DNA under similar conditions.     

Synthesis,spectral studies,DNA binding,photocleavage, antimicrobial and anticancer activities of isoindol Ru(II) polypyridyl complexes

Abstract

Three new Ru(II) polypyridyl complexes [Ru(phen)₂CIIP]²⁺ (1) {CIIP = 2-(5-Chloro-3a H-Isoindol-3-yl)-1H-Imidazo[4,5-f][1, 10]phenantholine} (phen = 1, 10 phenanthroline), [Ru(bpy)₂CIIP]²⁺ (2) (bpy = 2, 2′ bipyridine) and [Ru(dmb)₂CIIP]²⁺ (3) (dmb = 4, 4′-dimethyl 2, 2′ bipyridine) were synthesized and characterized by different spectral methods. The DNA-binding behavior of these complexes was investigated by absorption, emission spectroscopic titration and viscosity measurements, indicating that these three complexes bind to CT-DNA in an intercalative mode, but binding affinities of these complexes were different. The DNA-binding constants K_b of complexes 1, 2 and 3 were calculated in the order of 10⁶. All three complexes cleave pBR322 DNA in photoactivated cleavage studies and exhibit good antimicrobial activity. Anticancer activity of these Ru(II) complexes was evaluated in MCF7 cells. Cytotoxicity by MTT assay showed growth inhibition in a dose dependent manner. Cell cycle analysis by flow cytometry data showed an increase in Sub G1 population. Annexin V FITC/PI staining confirms that these complexes cause cell death by the induction of apoptosis.     

Overcoming cisplatin resistance using gold(III) mimics: anticancer activity of novel gold(III) polypyridyl complexes

Gold(III) compounds have been recognized as anticancer agents due to their structural and electronic similarities with currently employed platinum(II) species. An added benefit to gold(III) agents is the ability to overcome cisplatin resistance. This work identified four gold(III) compounds, [Au(Phen)Cl₂]PF₆, [Au(DPQ)Cl₂]PF₆, [Au(DPPZ)Cl₂]PF₆, and [Au(DPQC)Cl₂]PF₆, (Phen = 1,10-phenanthroline, DPQ = dipyrido[3,2-d:2′,3′-f]quinoxaline, DPPZ = dipyrido[3,2-a:2′,3′-c] phenazine, DPQC = dipyrido[3,2-d:2′,3′-f] cyclohexyl quinoxaline) that exhibited anticancer activity in both cisplatin sensitive and cisplatin resistant ovarian cancer cells. Two of these compounds, [Au(DPQ)Cl₂]PF₆ (AQ) and [Au(DPPZ)Cl₂]PF₆ (AZ), displayed exceptional anticancer activity and were the focus of more intensive mechanistic study. At the molecular level, AQ and AZ formed DNA adducts, generated free radicals, and upregulated pro-apoptotic signaling molecules (p53, caspases, PARP, death effectors). Taken together, these two novel gold(III) polypyridyl complexes exhibit potent antitumor activity in cisplatin resistant cancer cells. These activities may be mediated, in part, by the activation of apoptotic signaling.     

Binding and photocleavage of DNA by mixed ligand Co(III) and Ni(II) complexes of thiophene[2, 3-b] quinoline and phenanthrolie/bipyridine

In order to systematically perform an experimental and theoretical study on DNA binding and photocleavage properties of transition metal complexes of the type [M(L)₂(L₁)](PF₆)_n · xH₂O (where M = Co(III) or Ni(II), L = 1,10-phenanthroline or 2.2′ bipryidine, L₁ = Thiophene [2,3-b] quinoline (qt), n = 3 or 2 and x = 5 or 2) have been synthesized and characterized by elemental analysis, IR, ¹H NMR, UV and magnetic susceptibility data. The DNA-binding properties of these complexes have been investigated with UV-Vis, viscosity measurements, thermal denaturation and cyclic voltametric studies. It is experimentally found that all the complexes are bound to DNA via intercalation in the order [Co(bpy)₂(qt)](PF₆)₃ > [Co(phen)₂(qt)](PF₆)₃ > [Ni(phen)₂(qt)](PF₆)₂ > [Ni(bpy)₂(qt)](PF₆)₂. The photocleavage studies with pUC19 DNA shows that all these complexes promoted the conversion of SC form to NC form in absence of ‘inhibitors’.     

Synthesis, structural characteristics, DNA binding properties and cytotoxicity studies of a series of Ru(III) complexes

Four related ruthenium(III) complexes, with the formula mer-[RuCl₃(dmso)(N−N)] (dmso = dimethyl sulfoxide; N−N = 2,2′-bipyridine (1), 1,10-phenantroline (2), dipyrido[3,2-f:2′,3′-h]quinoxaline (3) and dipyrido[3,2-a:2′,3′-c]phenazine (4)), have been reported. Complexes 3 and 4 are newly synthesized and characterized by X-ray diffraction. The hydrolysis process of 1-4 has been studied by UV-vis measurement, and it has been found that the extension of the N−N ligands can increase the stability of the complexes. The binding of these complexes with DNA has been investigated by plasmid cleavage assay, competitive binding with ethidium bromide (EB), DNA melting experiments and viscosity measurements. The DNA binding affinity is increased with the extension of the planar area of the N−N ligands, and complex 4 shows an intercalative mode of interaction with DNA. The in vitro anticancer activities of these compounds are moderate on the five human cancer cell lines screened.     

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+).     

Iron(III) Schiff base complexes of arginine and lysine as netropsin mimics showing AT-selective DNA binding and photonuclease activity

Iron(III) complexes [Fe(L)₂]Cl (1-3), where L is monoanionic N-salicylidene-arginine (sal-argH for 1), hydroxynaphthylidene-arginine (nap-argH for 2) and N-salicylidene-lysine (sal-lysH for 3), were prepared and their DNA binding and photo-induced DNA cleavage activity studied. Complex 3 as its hexafluorophosphate salt [Fe(sal-lysH)₂](PF₆)·6H₂O (3a) was structurally characterized by single crystal X-ray crystallography. The crystals belonged to the triclinic space group P-1. The complex has two tridentate ligands in FeN₂O₄ coordination geometry with two pendant cationic amine moieties. Complexes 1 and 2 with two pendant cationic guanidinium moieties are the structural models for the antitumor antibiotics netropsin. The complexes are stable and soluble in water. They showed quasi-reversible Fe(III)/Fe(II) redox couple near 0.6 V in H₂O-0.1 M KCl. The high-spin 3d⁵-iron(III) complexes with μ_eff value of ∼5.9 μ_B displayed ligand-to-metal charge transfer electronic band near 500 nm in Tris-HCl buffer. The complexes show binding to Calf Thymus (CT) DNA. Complex 2 showed better binding propensity to the synthetic oligomer poly(dA)·poly(dT) than to CT-DNA or poly(dG)·poly(dC). All the complexes displayed chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent and cleaved supercoiled pUC19 DNA to its nicked circular form. They exhibited photo-induced DNA cleavage activity in UV-A light and visible light via a mechanistic pathway that involves the formation of reactive hydroxyl radical species.     

Synthesis, structure, DNA binding and DNA cleavage activity of oxovanadium(IV) N-salicylidene-S-methyldithiocarbazate complexes of phenanthroline bases

Ternary oxovanadium(IV) complexes [VO(salmdtc)(B)] (1-3), where salmdtc is dianionic N-salicylidene-S-methyldithiocarbazate and B is N,N-donor phenanthroline bases like 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3), are prepared, characterized and their DNA binding and DNA cleavage activity studied. Complex 3 is structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in six-coordinate VN₃O₂S coordination geometry. The S-methyldithiocarbazate Schiff base acts as a tridentate NSO-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo-group. The complexes show a d-d band in the range of 675-707 nm in DMF. They exhibit an irreversible oxidative cyclic voltammetric response near 0.9 V due to the V(V)/V(IV) couple and a quasi-reversible reductive V(IV)/V(III) redox couple near −1.0 V vs. SCE in DMF-0.1 M TBAP. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range of 7.4 × 10⁴-2.3 × 10⁵ M⁻¹. The thermal denaturation and viscosity binding data suggest DNA surface and/or groove binding nature of the complexes. The complexes show poor chemical nuclease activity in dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide. The dpq and dppz complexes show efficient DNA cleavage activity in UV-A light of 365 nm via a type-II mechanistic pathway involving formation of singlet oxygen (¹O₂) as the reactive species.     

Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions

Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2′-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields. Complexes [Ru(bpy)₂(mppne)]²⁺ (bpy is 2, 2′–bipyridyl), [Ru(bpy)₂(mppae)]²⁺, [Ru(bpy)₂(mpppe)]²⁺, [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ (phen is 1,10-phenanthroline) were fully characterized by elemental analysis, IR, ¹H NMR, fast-atom bombardment or electron-impact mass, UV–vis and cyclic voltammetric methods. In the latter three complexes, the ligands catpy, catphen and cat are actually bound to the metal center as the corresponding semiquinone species, viz., 4-(4-pyridyl)-1,2-benzenedioleto(+I) (sq-py), 1,10-phenanthroline-5,6-dioleto(+I) (sq-phen) and 1,2-benzenedioleto(+I) (bsq), thus making the overall charge of the complexes formally equal to + 1 in each case. These three complexes are electron paramagnetic resonance active and exhibit an intense absorption band between 941 and 958 nm owing to metal-to-ligand charge transfer (MLCT, d _Ru→π*_sq) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d _Ru→π*_bpy ) bands in the 454–461-nm region and are diamagnetic. These can be characterized by the ¹H NMR method. [Ru(bpy)₂(mppne)]²⁺, [Ru(bpy)₂(mppae)]²⁺ and [Ru(bpy)₂(mpppe)]²⁺ exhibit redox waves corresponding to the Ru^III/Ru^II couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH₃CN, 0.1 M tetrabutylammonium hexafluorophosphate)—corresponding voltammograms of [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ are mainly characterized by waves corresponding to the quinone/semiquinone (q/sq) and semiquinone/1,2-diol (sq/cat) redox processes. The results of absorption and fluorescence titration as well as thermal denaturation studies reveal that [Ru(bpy)₂(mppne)]²⁺ and [Ru(bpy)₂(mppae)]²⁺ are moderate-to-strong binders of calf thymus DNA with binding constants ranging from 10⁵ to 10⁶ M⁻¹. Under the identical conditions of drug and light dose, the DNA (supercoiled pBR 322) photocleavage activities of these two complexes follow the order:[Ru(bpy)₂(mppne)]²⁺>[Ru(bpy)₂(mppae)]²⁺, although the emission quantum yields follow the reverse order. The other ruthenium(II) complexes containing the semiquinone-based ligands are found to be nonluminescent and inefficient photocleavage agents of DNA. However, experiments shows that [Ru(bpy)₂(sq)]⁺-based complexes oxidize the sugar unit and could be used as mild oxidants for the sugar moiety of DNA. Possible explanations for these observations are presented.Electronic Supplementary Material Supplementary material is available for this article at .     

Reduced amino acid Schiff base containing ruthenium(III) complexes: Synthesis,characterization, DNA interaction,and in vitro cytotoxicity

A number of reduced amino Schiff base ligands and corresponding ruthenium(III) complexes were designed and prepared based on the fact that amino acids not only possess multiple coordinate atoms but also improve the solubility of drugs in the body. The interaction of the complexes with calf thymus DNA was analyzed with spectroscopic methods of ultraviolet‐visible absorption spectra, DNA competitive binding with ethidium bromide, circular dichroism spectra, and DNA melting experiments, and DNA viscosity measurements, indicating that the complexes bind to DNA primarily in the grooving mode. With respect to the ligands, the cytotoxicity in vitro of the complexes against Hela, A549, and MCF‐7 cells was much enhanced, with most of the IC₅₀ values less than 50 μM or even comparable with those of cisplatin.     

Study of the interaction of Co(III) polypyridyl complexes with DNA: an experimental and computational approach

Three new cobalt(III) polypyridyl complexes, [Co(L - L)₂IIP]³⁺ where IIP = 2-(2H-isoindol-1-yl)-2H-imidazo[4,5-f][1, 10]phenanthroline, L?=?1) phen (1,10-phenanthroline), 2) bpy (2,2’bipyridyl), 3) dmb (4, 4-dimethyl 2, 2’-bipyridine) have been synthesized, characterized (UV –VIS, IR, ¹HNMR and ¹³C NMR spectroscopy) and screened for their in vitro antibacterial activity against E.coli, Staphylococcus aureus and Bacillus subtilis. The binding of these complexes with calf-thymus DNA (CT-DNA) has been investigated by absorption and fluorescence spectroscopy, viscosity measurements. The experimental studies indicate that complexes bind to CT-DNA by means of intercalation, but with different binding affinities due to differences in the planarity of the ancillary ligand. The complexes promote photocleavage of plasmid DNA from super coiled form I to the open circular form II. The antibacterial activities suggest that the metal complexes are more active as compared to the prepared un-complexed IIP ligand.

In addition, a conformational search was carried out by Molecular Dynamics Simulations, and docking revealed that complexes intercalate between base pairs of DNA. The experimental and computational approaches reveal that the length of the intercalator and the nature of ancillary ligand are highly important factors for DNA binding.     

DNA binding and bending by dinuclear complexes comprising ruthenium polypyridyl centres linked by a bis(pyridylimine) ligand

The interaction of enantiomerically pure dinuclear complexes of the form [Ru₂(L-L)₄L¹]⁴⁺ (where L-L = 2,2^′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L¹ = bis(pyridylimine) ligand ((C₅H₄N)CN(C₆H₄))₂CH₂)) with ct-DNA have been investigated by absorbance, circular dichroism, fluorescence displacement assays, thermal analysis, linear dichroism and gel electrophoresis. The complexes all bind more strongly to DNA than ethidium bromide, stabilise DNA and have a significant bending effect on DNA. The data for Δ,Δ-[Ru₂(bpy)₄L¹]⁴⁺ are consistent with it binding to DNA outside the grooves wrapping the DNA about it. By way of contrast the other complexes are groove-binders. The phen complexes provide a chemically and enantiomerically stable alternative to the DNA-coiling di-iron triple-helical cylinder previously studied. In contrast to the di-iron helicates, the phen complexes show DNA sequence effects with Δ,Δ-[Ru₂(phen)₄L¹]⁴⁺ binding preferentially to GC and Λ,Λ-[Ru₂(phen)₄L¹]⁴⁺ to AT.     

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

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

DNA-binding and photocleavage studies of cobalt(III) polypyridyl complexes:

Two complexes of [Co(phen)2IP]3+ (IP=imidazo[4,5-f][l,10]phenanthroline) and [Co(phen)2PIP]3+ (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline) have been synthesized and characterized by UV/VIS, IR, EA and mass spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectroscopy, cyclic voltammetry, viscosity measurements and DNA cleavage assay. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both of the complexes bind to CT DNA by intercalation via IP or PIP into the base pairs of DNA. [Co(phen)2PIP]3+ binds more avidly to CT DNA than [Co(phen)2IP]3+, which is consistent with the extended planar and pi system of PIP. Noticeably, the two complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.     

Probing the antibacterial and anticancer potential of tryptamine based mixed ligand Schiff base Ruthenium(III) complexes

Development of new chemotherapeutic agents to treat microbial infections and recurrent cancers is of pivotal importance. Metal based drugs particularly ruthenium complexes have the uniqueness and desired properties that make them suitable candidates for the search of potential chemotherapeutic agents. In this study, two mixed ligand Ru(III) complexes [Ru(Cl)₂(SB)(Phen] (RC-1) and [Ru(Cl)₂(SB)(Bipy)] (RC-2) were synthesised and characterized by elemental analysis, IR, UV–Vis, ¹H, ¹³C NMR spectroscopic techniques and their molecular structure was confirmed by X-ray crystallography. Antibacterial activity evaluation against two Gram-positive (S. pneumonia and E. faecalis) and four Gram-negative strains (P. aurogenosa, K. pneumoniae, S. enterica, and E. coli) revealed their moderate antibacterial activity with MIC value of ≥250 μg/mL. Anticancer activity evaluation against a non-small lung cancer cell line (H1299) revealed the tremendous anticancer activity of these complexes which was further validated by DNA binding and docking results. DNA binding profile of the complexes studied by UV–Visible and fluorescence spectroscopy showed an intercalative binding mode with CT-DNA and an intrinsic binding constant in the range of 3.481–1.015× 10⁵ M⁻¹. Both the complexes were also found to exert weak toxicity to human erythrocytes by haemolytic assay compared to cisplatin. Potential of these complexes as anticancer agents will be further delineated by in vivo studies.     

Synthesis of cobalt(III) complexes with novel open chain oxime ligands and metal-ligand coordination in aqueous solution

Cobalt(III) complexes with new open chain oxime ligands: N,N′-bis(2-hydroxyiminopropionyl)-1,2-aminoethane (H₂pen) and N,N′-bis(2-hydroxyiminopropionyl)-1,3-diaminopropane (H₂pap) have been investigated. Single crystals of Co(papH₋₁)(Im₂)·CH₃OH (1) and Co(papH₋₁)(MEA)₂·1.5H₂O (2) (where Im = imidazole, MEA = monoethanolamine) suitable for X-ray crystallography were grown by slow evaporation of methanol/water solutions at room temperature. The molecular structures have been determined using single-crystal X-ray diffraction methods. The potentiometric and spectrophotometric results in aqueous solution reveal that both of the open chain ligands show a very high efficacy in the coordination of Co(II) ions. As it has been indicated, differences between the two oxime ligands in complexing ability may be attributed to the longer -CH₂- chain in H₂pap and by that a better fit of the relatively large Co(II) ion to the accessible binding site. One of the complex species confirmed under inert atmosphere, namely of type Co(LH₋₁)⁻ (where L = pap or pen), has been shown as the “active” form, capable of dioxygen uptake followed by irreversible oxidation to Co(III).     

Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties

The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (1) [Cr₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (2) and [Co(C₄O₄)(H₂O)₄]_n (3) [H₂C₄O₄ = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1. The iron-iron distance with the dinuclear unit is 3.0722(6) Å and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 Å and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato-O¹,O³-bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt-cobalt separation across the squarate bridge is 8.0595(4) Å. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2, the exchange pathway being the same [J = −14.4 (1) and −0.07 cm⁻¹ (2), the spin Hamiltonian being defined as ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 (J = −0.30 cm⁻¹). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.     

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.