Mixed ligand ruthenium(II) complexes of 5,6-dimethyl-1,10-phenanthroline: The role of ligand hydrophobicity on DNA binding of the complexes

A series of mixed ligand Ru(II) complexes of 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) as primary ligand and 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), pyridine (py) and NH₃ as co-ligands have been prepared and characterized by X-ray crystallography, elemental analysis and ¹H NMR and electronic absorption spectroscopy. The X-ray crystal structure of the complex [Ru(phen)₂(bpy)]Cl₂ reveals a distorted octahedral coordination geometry for the RuN₆ coordination sphere. The DNA binding constants obtained from the absorption spectral titrations decrease in the order, tris(5,6-dmp)Ru(II) > bis(5,6-dmp)Ru(II) > mono(5,6-dmp)Ru(II), which is consistent with the trend in apparent emission enhancement of the complexes on binding to DNA. These observations reveal that the DNA binding affinity of the complexes depend upon the number of 5,6-dmp ligands and hence the hydrophobic interaction of 5,6-dimethyl groups on the DNA surface, which is critical in determining the DNA binding affinity and the solvent accessibility of the exciplex. Among the bis(5,6-dmp)Ru(II) complexes, those with monodentate py (4) or NH₃ (5) co-ligands show DNA binding affinities slightly higher than the bpy and phen analogues. This reveals that they interact with DNA through the co-ligands while both the 5,6-dmp ligands interact with the exterior of the DNA surface. All these observations are supported by thermal denaturation and viscosity measurements. Two DNA binding modes - surface/electrostatic and strong hydrophobic/partial intercalative DNA interaction - are suggested for the mixed ligand complexes on the basis of time-resolved emission measurements. Interestingly, the 5,6-dmp ligands promote aggregation of the complexes on the DNA helix as a helical nanotemplate, as evidenced by induced CD signals in the UV region. The ionic strength variation experiments and competitive DNA binding studies on bis(5,6-dmp)Ru(II) complexes reveal that EthBr and the partially intercalated and kinetically inert [Ru(phen)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) complexes revert the CD signals induced by exciton coupling of the DNA-bound complexes with the free complexes in solution.     

Synthesis, characterization and electrode adsorption studies of porphyrins coordinated to ruthenium(II) polypyridyl complexes

Two new porphyrins, meso-tris-3,4-dimethoxyphenyl-mono-(4-pyridyl)porphyrin (H₂MPy3,4DMPP) and meso-tris-3-methoxy-4-hydroxyphenyl-mono-(4-pyridyl)porphyrin (H₂MPy3M4HPP), and their ruthenium analogs obtained by coordination of [Ru(bpy)₂Cl]⁺ groups (where bpy = 2,2′-bipyridine) to the pyridyl nitrogens have been synthesized and studied by electronic absorption spectroscopy, cyclic voltammetry and spectroelectrochemistry. These ruthenated porphyrins couple Ru chromophores to porphyrins containing electroactive meso-substituents. The highest energy electronic absorption for the ruthenated complexes is assigned as a bpy(π) → bpy(π*) intraligand charge transfer while the next lowest energy electronic absorption is assigned as Ru(dπ) → bpy(π*) metal-to-ligand charge transfer (MLCT) transition. The Ru^III/II couples occur at approximately 0.95 V versus the SHE reference electrode in acetonitrile solutions. The first oxidation of the porphyrin is localized on the 3,4-dimethoxyphenyl and 3-methoxy-4-hydroxyphenyl substituents, respectively. Electroactive surfaces result from adsorption of these compounds onto glassy carbon electrodes followed by anodic cycling in acidic media.     

Novel [Ru(polypyridine)(CO)2Cl2] and [Ru(polypyridine)2(CO)Cl]-type complexes: Characterizing the effects of introducing azopyridyl ligands by electrochemical, spectroscopic and crystallographic measurements

The reaction of ruthenium carbonyl polymer ([Ru(CO)₂Cl₂]_n) with azopyridyl compounds (2,2′-azobispyridine; apy or 2-phenylazopyridine; pap) generated new complexes, [Ru(azo)(CO)₂Cl₂] (azo = apy, pap). [Ru(apy)(CO)₂Cl₂] underwent photodecarbonylation to give a chloro-bridged dimer complex, whereas the corresponding pap complex ([Ru(pap)(CO)₂Cl₂]) was not converted to a dimer. The reactions of the chloro-bridged dimer containing the bpy ligand (bpy = 2,2′-bipyridine) with either apy or pap resulted in the formation of mixed polypyridyl complexes, [Ru(azo)(bpy)(CO)Cl]⁺. The novel complexes containing azo ligands were characterized by various spectroscopic measurements including the determination of X-ray crystallographic structures. Both [Ru(azo)(CO)₂Cl₂] complexes have two CO groups in a cis position to each other and two chlorides in a trans position. The azo groups are situated cis to the CO ligand in [Ru(azo)(bpy)(CO)Cl]⁺. All complexes have azo N-N bond lengths of 1.26-1.29 Å. The complexes exhibited azo-based two-electron reduction processes in electrochemical measurements. The effects of introducing azopyridyl ligands to the ruthenium carbonyl complexes were examined by ligand-based redox potentials, stretching frequencies and force constants of CO groups and bond parameters around Ru-CO moieties.     

Electrogenerated chemiluminescence properties of bisalicylideneethylenediamino (salen) metal complexes

The spectroscopy, electrochemistry and electrogenerated chemiluminescence (ECL) of eight bisalicylideneethylenediamino (salen) metal complexes are reported. Two of the complexes contain an unsubstituted salen ligand and either cobalt(II) or nickel(II). The others have 1,2-cyclohexanediamonio-N,N′-bis(3,5-di-t-butylsalicylidene) as the ligand, and chromium(III), aluminum(III), cobalt(II), cobalt(III) or manganese(II) as the metal center. The complexes have lowest energy absorption maxima between 350 and 430 nm. When excited at these wavelengths, the complexes emit between 417 and 594 nm in acetonitrile. Photoluminescence efficiencies (?_em) were between 0.0310 and 23.8 compared to Ru(bpy)₃²⁺ (bpy = 2,2′-bipyridine; ?_em = 1), with the aluminum complexes displaying the most intense photoluminescence. Both reversible and irreversible oxidative electrochemistry is displayed by the metal–salen complexes with oxidation potentials ranging between +0.152 and +1.661 V versus Ag/AgCl. The ECL intensity peaks at a potential corresponding to oxidation of both TPrA and the salen systems, indicating that both are involved in the ECL reaction sequence. ECL efficiencies (?_ecl) were between 0.0018 and 0.0086 when compared to Ru(bpy)₃²⁺ (?_ecl = 1) in acetonitrile (0.05 M tri-n-propylamine (TPrA) as an oxidative–reductive ECL coreactant). Also, qualitative studies using transmission filters suggest that the complexes emit ECL in approximately the same region as their photoluminescence, indicating that the same excited state is formed in both experiments.     

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.     

Cobalt(II), nickel(II), copper(II) and zinc(II) complexes with an open-chain pentadentate nitrogen ligand

The open-chain, potentially, pentadentate, ligan 1,11-bis(dimethylamino)-3,6,9-trimethyl-3,6,9,-triazaundecane (Me₇tetren) forms a series of metal complexes having the general formula [M(Me₇tetren)]Y₂ (Y = 1, M = Co, Ni; Y = ClO₄, M = Co, Ni, Cu, Zn). On the basis of their physical properties, it is suggested that all these compounds contains isostructural five-coordinate [M(Me₇tetren)]²⁺ cations, the ligand acting as pentadentate. These complexes react in solution with thiocyanate ion to give mono- and, with exception of copper(II), di-thiocyanato five- and six-co-ordinate derivatives. Mono-thiocyanato derivatives of cobalt(II), nickel(II) and zinc(II) have been isolated as tetraphenylborate salts. Cobalt(II) and nickel (II) di-thiocyanato derivatives have been also isolated. Results are discussed in terms of the steric requirements of the ligand and electronic properties of the metal ions.     

DNA-Binding and Photocleavage Properties of Ru(II) Polypyridyl Complexes with DNA and Their Toxicity Studies on Eukaryotic Microorganisms

Four Ru(II) polypyridyl complexes, [Ru(bpy)₂(7-NO₂-dppz)]²⁺, [Ru(bpy)₂(7-CH₃-dppz)]²⁺, [Ru(phen)₂(7-NO₂-dppz)]²⁺, and [Ru(phen)₂(7-CH₃-dppz)]²⁺ (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), (7-Nitro-dppz = 7-Nitro dipyrido[3,2-a:2′-3′-c]phenazine, 7-CH₃-dppz = 7-Methyl dipyrido[3,2-a:2′-3′-c]phenazine), have been synthesized and characterized by IR, UV, elemental analysis, ¹H NMR, ¹³C-NMR, and mass spectroscopy. The DNA-binding properties of the four complexes were investigated by spectroscopic and viscosity measurements. The results suggest that all four complexes bind to DNA via an intercalative mode. Under irradiation at 365 nm, all four complexes were found to promote the photocleavage of plasmid pBR 322 DNA. Toxicological effects of the selected complexes were performed on industrially important yeasts (eukaryotic microorganisms).     

Sugar interaction with metal ions: synthesis,spectroscopic, and structural analysis of Zn(II), Cd(II), and Hg(II) complexes,containing d-glucuronate anion

Interaction between D-glucuronic acid and Zn(II), Cd(II), and Hg(II) metal ion salts has been studied in solution and solid complexes of the type M(D-glucuronate)X · nH₂O and M(D-glucuronate)₂·nH₂O, where M = Zn(II), Cd(II), and Hg(II), X = Cl⁻ or Br⁻, and n = 0–2 were isolated and characterized. Spectroscopic and other evidence indicated that in the metal-halide-sugar complexes the Zn(II) and Cd(II) ions bind to two D-glucuronate moieties via 06, 05 of the carboxyl oxygen atoms of the first and 04, 06' of hydroxyl and carbonyl groups of the second as well as to two H₂O molecules, whereas in the corresponding M(D-glucuronate)₂ · nH₂O salts, the metal ions are bonded to two sugar anions through 06 and 06' of the ionized carboxyl groups and two water molecules, resulting in a six-coordination around each metal cation. The Hg(II) ion binds to 06 and 05 oxygen atoms of a sugar anion and to a halide anion or water molecule, in the Hg(D-glucuronate)X·nH₂O compounds, while in the corresponding metal-glucuronate salt mercury is bonded to 06 and 06' of the two glucuronate anions with four-coordination around the Hg(II) ion. The β-anomer sugar conformation is predominant in the free acid and in these series of metal-sugar complexes.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Sugar complexes with alkaline earth metal ions. Synthesis,structure, and spectroscopic studies of Mg(II), Sr(II), and Ba(II) complexes of d-glucur

Interaction between D-glucuronic acid and alkaline earth metal ions leads to the formation of the complexes such as M(D-glucuronate)X· nH₂O and M(D-glucuronate)₂ · nH₂O, where M = Mg(II), Sr(II), and Ba(II), X = Cl^? or Br^?, and n = 2–4. Owing to the distinct spectral similarities with the structurally known Ca(D-gluguronate)Br · 3H₂O compound, the metal cations bind to three sugar moieties (through O₆, O₅ of the first, O₆', O₄ of the second, and O₁, O₂ of the third residue) and to two H₂O molecules, forming an eight-coordination geometry around each metal ion, in M(D-glucuronate)X · nH₂O (except for Mg(II) ion, which is six-coordination). The metal ions in M(D-glucuronate)₂-nH₂O show six-coordination in different structural environments. The strong hydrogen bonding network of the free acid is weakened upon metalation and the sugar moiety crystallizes as α-anomer, in these series of metal-sugar complexes.     

Sugar-metal ion interaction. Synthesis,spectroscopic and structural analysis of Zn(II), Cd(II), and Hg(II) sugar complexes containing l-arabinose

Interaction between l-arabinose and the zinc group metal-ion salts has been studied in aqueous solution and solid complexes of the type M(l-arabinose)X₂·nH₂O, where M = Zn(II), Cd(II), and Hg(II) ions, X = Cl⁻ or Br⁻, and n = 0–2 have been isolated and characterized. On comparison with the structurally known Ca(l-arabinose) Cl₂·4H₂O and the corresponding magnesium compounds, it is concluded that the Zn(II) and Cd(II) ions are six-coordinated, binding to two arabinose moieties via 03, 04 of the first and 01, 05 of the second sugar molecule as well as to two H₂O molecules. The Hg(II) ion binds only to two sugar molecules in a similar fashion to zinc and cadmium ions, resulting in a four coordination around the mercury ion. The strong intermolecular hydrogen bonding network of the free arabinose is rearranged to that of the sugar OH...H₂O...halide system upon metalation. The β-anomer sugar conformation is predominant in the free sugar, while the α-anomer conformation is preferred by the alkaline earth and Zn(II), Cd(II), and Hg(II) cations.     

Ruthenium(II) complexes containing asymmetric 2-(pyrazin-2-yl)naphthoimidazole: syntheses, characterization, DNA-binding and photocleavage studies

A novel asymmetric bidentate ligand, 2-(pyrazin-2-yl)naphthoimidazole (PZNI), and its Ru(II) complexes [Ru(bpy)₂(PZNI)]²⁺ (1) and [Ru(phen)₂(PZNI)]²⁺ (2) have been synthesized and characterized by elemental analysis, mass spectra, ¹H NMR, and electronic spectroscopy. The electrochemical behaviors of the novel complexes were studied by cyclic voltammetry. The DNA-binding properties of the complexes were investigated by spectroscopic methods and viscosity measurements. The experimental results indicate that the complexes 1 and 2 interact with calf thymus DNA by intercalative mode via the terminal naphthyl ring into the base pairs of DNA. The two Ru(II) complexes have also been found to promote the cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation.     

Electronic absorption and MCD spectra for octacyanometallate complexes M(CN)8, M=Mo(IV), W(IV), n=4 and Mo(V), W(V), n=3

Electronic absorption and 8.0 T magnetic circular dichroism (MCD) spectra are reported for M(CN)₈ ⁴⁻, M=Mo(IV) and W(IV), in aqueous solution and M(CN)₈ ³⁻, M=Mo(V) and W(V), in acetonitrile solutions. In addition some absorption and MCD spectra are reported for the M(CN)₈ ³⁻ ions embedded in thin poly methyl methacrylate (PMMA) plastic films at temperatures from 295 to 10 K. The temperature dependence of the MCD spectra confirms the presence of C terms. The solution and PMMA spectra for the both Mo and W complexes in either the IV or V oxidation states are remarkably similar to each other for the same oxidation state and are interpreted within a D_2d structural framework for the isotropic environment. The weak bands below 3.0 μm⁻¹ (1 μm⁻¹=10⁴ cm⁻¹) for the M(IV) complexes are assigned as metal-localized ligand field (LF) transitions. LF transitions are also suggested for weaker unresolved absorption between 3.0 and 3.6 μm⁻¹ for the M(V) ions. The intense bands above 3.6 μm⁻¹ for M(IV) and 4.6 μm⁻¹ for M(V) complexes are interpreted as metal to ligand charge transfer (MLCT) from the metal b₁(x²−y²) HOMO to CN⁻-based π * orbitals. The prominent intense bands observed below 4.5 μm⁻¹for the M(V) complexes are assigned as ligand to metal charge transfer (LMCT) from occupied non-bonding or weakly π bonding CN⁻ orbitals to the half-filled b₁(x²−y²) HOMO.     

Mixed ligand complexes of osmium(II)-2,2-bipyridine: synthesis, spectral characterization and electrochemical properties of bis-chelated-arylazoimidazole-bipyridine-osmium(II) and X-ray crystal structure of [(2,2-bipyridine)-bis-{1-methyl-2-(p-tolylazo)imidazole}osmium(II) hexafluorophosphate

Reaction of ctc-OsBr₂(RaaiR^′)₂ [RaaiR^′=1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-NN-C₃H₂-NN-1-R^′, where R=H (a), Me (b), Cl (c) and R^′=Me (2), Et (3) and CH₂Ph (4)] with 2,2^′-bipyridine (bpy) in presence of AgNO₃ in EtOH followed by the addition of NH₄PF₆ afforded a mixed ligand complex [Os(bpy)(RaaiR^′)₂](PF₆)₂. The structure of the complex, in one case [Os(bpy)(MeaaiMe)₂](PF₆)₂ · 4H₂O, has been confirmed by X-ray crystallography. The complexes are diamagnetic (low spin d⁶, s=0) and they show intense MLCT transition in the visible region (480-525 nm) and a weak transition at longer wavelength (>850 nm) in CH₃CN solution. Cyclic voltammetry of the complexes show two metal oxidation, Os(II)/Os(III) at 0.72-0.76 V and Os(III)/Os(IV) at 1.34-1.42 V and three successive ligand reductions.     

Rich spectroscopic and molecular dynamic studies on the interaction of cytotoxic Pt(II) and Pd(II) complexes of glycine derivatives with calf thymus DNA

Some amino acid derivatives, such as R-glycine, have been synthesized together with their full spectroscopic characterization. The sodium salts of these bidentate amino acid ligands have been interacted with [M(bpy)(H₂O)₂](NO₃)₂ giving the corresponding some new complexes with formula [M(bpy)(R-gly)]NO₃ (where M is Pt(II) or Pd(II), bpy is 2,2′-bipyridine and R-gly is butyl-, hexyl- and octyl-glycine). Due to less solubility of octyl derivatives, the biological activities of butyl and hexyl derivatives have been tested against chronic myelogenous leukemia cell line, K562. The interaction of these complexes with highly polymerized calf thymus DNA has been extensively studied by means of electronic absorption, fluorescence and other measurements. The experimental results suggest that these complexes positive cooperatively bind to DNA presumably via groove binding. Molecular dynamic results show that the DNA structure is largely maintained its native structure in hexylglycine derivative–water mixtures and at lower temperatures. The simulation data indicates that the more destabilizing effect of butylglycine is induced by preferential accumulation of these molecules around the DNA and due to their more negative free energy of binding via groove binding.     

Synthesis and characterization of Mg(II), Mn(II), Zn(II) and Cd(II) complexes with a new heptaaza Schiff base pendant-armed macrocycle: X-ray crystal structure, NMR and computational study

New 2-aminoethyl pendant-armed Schiff base macrocyclic complexes, [ML⁷]²⁺ (M = Mn(II), Mg(II), Zn(II) and Cd(II)), have been prepared via M(II) templated [1 + 1] cyclocondensation of 2,6-diacetylpyridine with a new branched hexamine, N,N,N′,N′-tetrakis(2-aminoethyl)-2,2-dimethylpropane-1,3-diamine. The ligand is a 16-membered pentaaza macrocycle having two 2-aminoethyl pendant arms [L⁷ is 2,14-dimethyl-6,10-bis(2-aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]8,8-dimethylnonadeca-1(19),2,13,15,17-pentaene]. The crystal structures of [MnL⁷]²⁺ and [MgL⁷]²⁺ were determined from X-ray diffraction data. The geometry of the coordination sphere of complexes is a slightly distorted pentagonal bipyramid with the metal ion located within a pentaaza macrocycle and two pendant amines coordinating on opposite sides. All complexes were characterized by IR, microanalysis and except of [MnL⁷]²⁺ by ¹H NMR, ¹³C NMR, DEPT135, COSY(H, H) and HMQC spectroscopy. The data indicate that the structure is pentagonal bipyramidal in each case. The structure of all complexes has also been theoretically studied by ab initio Hartree-Fock and density functional theory methods.     

Speciation, stability constants and structures of complexes of copper(II), nickel(II), silver(I) and mercury(II) with PAMAM dendrimer and related tetraamide ligands

The acid-base properties and Cu(II), Ni(II), Ag(I) and Hg(II) binding abilities of PAMAM dendrimer, L, and of the simple model compounds, the tetraamides of EDTA and PDTA, L¹, were studied in solution by pH-metric methods and by ¹H NMR and UV-Vis spectroscopy. PAMAM is hexabasic and six pK_a values have been determined and assigned. PAMAM forms five identifiable complexes with copper(II), [CuLH₄]⁶⁺, [CuLH₂]⁴⁺, [CuLH]³⁺, [CuL]²⁺ and [CuLH_-1]⁺ in the pH range 2-11 and three with nickel(II), [NiLH]³⁺, [NiL]²⁺ and [NiLH_-1]⁺ in the pH range 7-11. The complex [CuLH₄]⁶⁺, which contains two tertiary nitrogen and three amide oxygen atoms coordinated to the metal ion, is less stable than the analogous EDTA and PDTA tetraamide complexes [CuL¹]²⁺, which contain two tertiary nitrogen and four amide oxygen atoms, due to ring size and charge effects. With increasing pH, [CuLH₄]⁶⁺ undergoes deprotonation of two coordinated amide groups to give [CuLH₂]⁴⁺ with a concomitant change from O-amide to N-amidate coordination. Surprisingly and in contrast to the tetraamide complexes [CuL¹]²⁺, these two deprotonation steps could not be separated. As expected the nickel(II) complexes are less stable than their copper(II) analogues. The tetra-N-methylamides of EDTA, L¹(b), and PDTA form mononuclear and binuclear complexes with Hg(II). In the case of L¹(b) these have stoichiometries HgL¹(b)Cl₂, [HgL¹(b)H₋₂Cl₂]²⁻, [Hg₂L¹(b)Cl₂]²⁺, Hg₂L¹(b)H₋₂Cl₂ and [Hg₂L¹(b)H₋₅Cl₂]³⁻. Based on ¹H NMR and pH-metric data the proposed structure for HgL¹(b)Cl₂, the main tetraamide ligand containing species in the pH range <3-6.5, contains L¹(b) coordinated to the metal ion through the two tertiary nitrogens and two amide oxygens while the structure of [HgL¹(b)H₋₂Cl₂]²⁻, the main tetraamide ligand species at pH 7.5-9.0, contains the ligand similarly coordinated but through two amidate nitrogen atoms instead of amide oxygens. The proposed structure of [Hg₂L¹(b)Cl₂]²⁺, a minor species at pH 3-6.5, also based on ¹H NMR and pH-metric data, contains each Hg(II) coordinated to a tertiary amino nitrogen, two amide oxygens and a chloride ligand while that of [Hg₂L¹(b)H₋₅Cl₂]³⁻, contains each Hg(II) coordinated to a tertiary amino nitrogen, two amidate nitrogens, a chloride and a hydroxo ligand in the case of one of the Hg(II) ions. The parent EDTA and PDTA amides only form mononuclear complexes. PAMAM also forms dinuclear as well as mononuclear complexes with mercury(II) and silver(I). In the pH range 3-11 six complexes with Hg(II) i.e. [HgLH₄Cl₂]⁴⁺, [HgLH₃Cl₂]³⁺, [Hg₂LCl₂]²⁺, [Hg₂LH₋₁Cl₂]⁺, [HgLH₋₁Cl₂]⁻ and [HgLH₋₂Cl₂]²⁻ were identified and only two with Ag(I), [AgLH₃]⁴⁺ and [Ag₂L]²⁺. Based on stoichiometries, stability constant comparisons and ¹H NMR data, structures are proposed for these species. Hence [HgLH₄Cl₂]⁴⁺ is proposed to have a similar structure to [CuLH₄]⁶⁺ while [Hg₂LCl₂]²⁺has a similar structure to [Hg₂L¹(b)H₋₅Cl₂]³⁻.     

Synthesis,antineoplastic and cytotoxic activities of some mononuclear Ru(II) complexes

A series of mononuclear Ru(II) complexes of the type [Ru(S)₂(K)]²⁺, where S = 1,10-phenanthroline/2,2′-bipyridine and K = 4-OH-btsz, 4-CH₃-btsz, 3,4-di-OCH₃-btsz, 4-OH-binh, 4-CH₃-binh, 3,4-di-OCH₃-binh, were prepared and characterized by elemental analysis, FTIR, ¹H-NMR, and mass spectroscopy. The complexes displayed metal–ligand charge transfer (MLCT) transitions in the visible region. These ligands formed bidentate octahedral ruthenium complexes. The title complexes were evaluated for their in vivo anticancer activity against a transplantable murine tumor cell line, Ehrlisch’s ascites carcinoma (EAC), and in vitro cytotoxic activity against human cancer cell lines Molt 4/C₈ and CEM and murine tumor cell line L1210. The ruthenium complexes showed promising biological activity especially in decreasing tumor volume and viable ascites cell counts. Treatment with these complexes prolonged the life span of mice bearing EAC tumors by 10–52%. In vitro evaluation of these ruthenium complexes revealed cytotoxic activity from 0.21 to 24 μM against Molt 4/C₈, 0.16 to 19 μM aginst CEM, and 0.75 to 32 μM against L1210.     

Strong and weak coupling in mixed-valence complexes bridged by 4,4′-azo-di(phenylcyanamido)

The complexes [{Ru(tpy^∗)(bpy)}₂(μ-adpc)][PF₆]₂ where tpy^∗ is 4,4′,4″-tri-(tert-butyl)-2,2′:6′,2″-terpyridine, bpy is 2,2′-bipyridine, and adpc²⁻ is 4,4′-azo-diphenylcyanamide dianion and trans,trans-[{Ru(tpy^∗)(pc)}₂(μ-adpc)] where pc⁻ is 2-pyrazine-carboxylato were prepared and characterized by cyclic voltammetry and spectroelectrochemical methods. Intervalence band properties and IR spectroelectrochemistry of the mixed-valence complexes [{Ru(tpy^∗)(bpy)}₂(μ-adpc)]³⁺ and trans,trans-[{Ru(tpy^∗)(pc)}₂(μ-adpc)]⁺ are consistent with delocalized and valence-trapped mixed-valence properties respectively. The reduction in mixed-valence coupling upon substituting a bipyridine ligand with 2-pyrazine carboxylato strongly suggests that hole-transfer superexchange is the dominant mechanism for metal-metal coupling in these complexes.