Variation of DNA photocleavage efficiency for [(TL)2Ru(dpp)]Cl2 complexes where TL = 2,2′-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

The complexes [(bpy)₂Ru(dpp)]Cl₂, [(phen)₂Ru(dpp)]Cl₂, and [(Ph₂phen)₂Ru(dpp)]Cl₂ (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Ph₂phen = 4,7-diphenyl-1,10-phenanthroline) have been investigated and found to photocleave DNA via an oxygen-mediated pathway. These light absorbing complexes possess intense metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum. The [(TL)₂Ru(dpp)]²⁺ systems populate ³MLCT states after visible light excitation, giving rise to emissions in aqueous solution centered at 692, 690, and 698 nm for TL = bpy, phen, and Ph₂phen respectively. The ³MLCT states and emissions are quenched by O₂, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph₂phen)₂Ru(dpp)]²⁺ > [(phen)₂Ru(dpp)]²⁺ > [(bpy)₂Ru(dpp)]²⁺. The presence of the polyazine bridging ligand will allow these chromophores to be incorporated into larger supramolecular assemblies.     

The X-ray structure analysis of bis-2,2′,N,N′-bipyridyl ketone cobalt(III) nitrate dihydrate

An X-ray structural analysis of bis-2,2′,N,N′-bipyridyl ketone cobalt(III) nitrate dihydrate, CoC₂₂H₂₀N₄O₄⁺· NO₃⁻·2H₂O,M_r=559.38 g/mol, P , a=8.862(2), b=16.195(3), c=8.772(2) Å, α=103.54(2), β=95.74(3), γ=105.07°, V=1164.4(4) ų, Z=2, D_x=1.595 g/cm³, Mo Kα radiation (λ=0.71073 Å), μ=7.8 cm⁻¹ and R=0.079, revealed a Co(III) cation in a slightly distorted octahedral environment. The structure reveals that the ligand di-2-pyridyl ketone (dpk) has undergone a hydration reaction across the ketone double bond and one of the hydrate oxygen atoms coordinated to the metal forming a tridentate chelate. This new Co(dpk-hydrate)₂⁺ complex displays the least distorted geometry yet reported for either 1:1 or 1:2 (metal:ligand) complexes. A geometry optimization using the INDO model Hamiltonian as implemented in the program ZINDO was performed on the title complex with the Co³⁺ modeled as a singlet. The result of the computation corroborates the geometry of the title complex as that expected for Co³⁺.     

Synthesis and magnetic properties of bis(μ-hydroxo)bis[(2,2 ′-bipyridyl)copper(II)] squarate. Crystal structure of bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] squarate tetrahydrate

The compound [Cu₂(bipy)₂(OH)₂](C₄O₄)·5.5H₂O, where bipy and C₄O₄²⁻ correspond to 2,2′-bipyridyl and squarate (dianion of 3,4-dihydroxy-3-cyclo- butene-1,3-dione) respectively, has been synthesized. Its magnetic properties have been investigated in the 2–300 K temperature range. The ground state is a spin-triplet state, with a singlet-triplet separation of 145 cm⁻¹. The EPR powder spectrum confirms the nature of the ground state.Well-formed single crystals of the tetrahydrate, [Cu₂(bipy)₂(OH)₂](C₄O₄)·4H₂O, were grown from aqueous solutions and characterized by X-ray diffraction. The system is triclinic, space group P , with a = 9.022(2), b = 9.040(2), c = 8.409(2) Å, α = 103.51(2), β = 103.42(3), γ = 103.37(2)°, V = 642.9(3) ų, Z = 1, D_x = 1.699 g cm⁻³, μ(Mo Kα) = 17.208 cm⁻¹, F(000) = 336 and T= 295 K. A total of 2251 data were collected over the range 1θ25°; of these, 1993 (independent and with I3σ(I)) were used in the structural analysis. The final R and R_w residuals were 0.034 and 0.038 respectively. The structure contains squarato-O¹, O³-bridged bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] units forming zigzag one-dimensional chains. Each copper atom is in a square-pyramidal environment with the two nitrogen atoms of 2,2′-bipyridyl and the two oxygen atoms of the hydroxo groups building the basal plane and another oxygen atom of the squarate lying in the apical position.The magnetic properties are discussed in the light of spectral and structural data and compared with the reported ones for other bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] complexes.     

Comparing the spectroscopic and electrochemical properties of ruthenium and osmium complexes of the tridentate polyazine ligands 2,2′:6′,2″-terpyridine and 2,3,5,6-tetrakis(2-pyridyl)pyrazine

A number of osmium and ruthenium complexes of the tridentate ligands 2,2′:6′,2″-terpyridine (tpy) and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tpp) have been prepared and characterized by our laboratory. All these complexes possess metal based oxidations and ligand based reductions localized on each polyazine ligand. Polymetallic complexes bridged by the tpp ligand exhibit two sequential tpp based reductions prior to the reduction of other polyazine ligands in these complexes. The spectroscopy of these complexes is dominated by ligand based π-π^* transitions in the ultraviolet and MLCT (metal-to-ligand charge transfer) bands terminating on each polyzine ligand in the visible. For the complexes reported herein the lowest lying optical transitionis a M → BL CT band. For most of the complexes reported, occupation of this excited state gives rise to an observable emission at room temperature. For ruthenium complexes of these tridentate ligands, the presence of a low-lying LF state shortens the excited state lifetimes of these chromophores. This gives rise to ruthenium complexes that display shorter excited state lifetimes than the analogous osmium based systems. Incorporation of tpp based chromophores into polymetallic frameworks leads to the production of bimetallic species with long-lived excited states, 100 ns at room temperature. This makes these chromophores good candidates for the development of stereochemically defined supramolecular complexes. It is possible to measure an electrochemical HOMO-LUMO energy gap and a correlation between this electrochemically measured energy gap and the spectroscopic energy associated with this HOMO→LUMO transition are reported herein (HOMO== highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital).     

Monomeric and dimeric mixed-ligand copper(II) complexes of 2,2′-bipyridine/1,10-phenanthroline and 1-methylimidazole with imidazoles as catalysts for superoxide dismutation

Monomeric complexes [Cu(LL)(L′)(NO₃)₂] (where LL is 2,2′-bipyridine or 1,10-phenanthroline and L′ is 1-methylimidazole) and dimeric complexes [Cu₂(LL)₂(L″)]NO₃ (where L″ is an anion of imidazole or 2-methylimidazole) have been synthesized. These complexes show a d-d transition in the range of 600 to 710 nm. The infrared spectra of monomeric complexes show that the NO₃⁻ is coordinated to copper as a monodentate ligand through an oxygen atom. The ESR spectra of monomeric complexes indicate that the ligands are bonded in axial environment around copper (square pyramidal geometry) with three nitrogen donors occupying an equatorial plane. The ESR spectra of dimeric complexes show a broad signal at about G = 2 with an additional weak signal at about G = 4. This suggests that two copper atoms are in close proximity of < 7 Å. The ESR studies reveal that the formation of imidazolate-bridged binuclear copper(II) complexes from [Cu(LL)(L′)(NO₃)₂] and imidazole is pH dependent with apparent pK_a values of 8.25 to 8.30. The superoxide dismutase activity of ICu(phen)(L′)(NO₃)₂], [Cu(bipy)(L′)(NO₃)₂], and [Cu₂(bipy)₂(L′)₂(L″)]NO₃ has been measured and the latter two complexes show better activity than the former complex.     

Ruthenium complexes containing tertiary phosphines and imidazole or 2,2′-bipyridine ligands

Complexes RuCl₃(PPh₃)L₂ (L = MeIm (1a, Im (1b)) and [RuCl₂(PPh₃)₂(bipy)]Cl·4H₂O (2) have been synthesized via the ruthenium(III) precursor RuCl₃(PPh₃)₂ (DMA), and characterized, including an X-ray structural analysis for 1a (MeIm = N-methylimidazole, Im = imidazole, bipy = 2,2′-bipyridyl, and DMA = N, N′-dimethylacetamide). Crystals of 1a are monoclinic, space group P2₁/n, A = 10.5491(5), B = 20.4934(9), C = 12.8285(4) Å, β = 90.166(4)°, Z = 4. The structure, which reveals a mer configuration for the chlorides, and cis-methylimidazoles, was solved by conventional heavy atom methods and was refined by full-matrix least-square procedures to R = 0.041 and R_w = 0.042 for 3328 reflections with I 3σ(I). From the RuCl₂(PPh₃)₃ precursor, the ruthenium(II) complexes RuCl₂(PPh₃)₂L₂ and [RuCl(PPh₃)L₄]Cl have been made (L = Im or MeIm), while [RuCl(dppb)Im₃]Cl has been made from [RuCl₂(dppb)]₂(μ-dppb) (dppb = Ph₂P(CH₂)₄PPh₂).     

Saccharinate-metal complexes with 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) as co-ligands; the synthesis, crystal and molecular structures of five new compounds of divalent metals

Five new saccharinate complexes of divalent metals with either phen or bipy as co-ligands have been synthesised, and fully characterised by single crystal X-ray diffraction at low temperature. The complexes [M(phen)₂(H₂O)₂](sac)₂·H₂O (M = Co or Zn) are isostructural, while [Hg(bipy)₂(sac)₂] is isostructural with the analogous cadmium(II) compound, which has been described previously in the literature. Cadmium(II) complex [Cd(phen)₂(sac)(H₂O)](sac).H₂O has an octahedral cation with the unidentate ligands in cis-positions, while [Hg(phen)₂(sac)](sac)·2.5 H₂O provides a rare example of a distorted tbp structure for the cation, with five nitrogen donors. The structures are compared with those of related saccharinate complexes. In general, the more sterically demanding phen, when compared with bipy, forces more of the saccharinate anions to be uncoordinated, and for smaller ligands such as H₂O to be coordinated to the metal, despite the electrostatic attraction between the positively charged metal and the anion. Intramolecular hydrogen bonding involving saccharinate groups plays an important role in all the hydrated complexes.     

Synthesis and structural studies of gallium(III) and indium(III) complexes of 2-acetylpyridine thiosemicarbazones

Four 2-acetylpyridine ⁴N-alkyl thiosemicarbazones, and their Ga(III) and In(III) complexes have been prepared and characterised by fluorescence, UV-Vis, IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry and X-ray crystallographic analysis. Comparison of the crystal structures gave an insight into the nature of the complexes formed, demonstrating a preference for [ML₂]⁺ type complexes with gallium and [MLX₃] species with indium. Stability studies on two candidates indicated that complex [InL³Cl₂MeOH] was stable to chemical degradation for prolonged periods in human serum, giving this complex potential for further biological evaluation.     

Origin of electronic absorption spectra of MLCT-excited and one-electron reduced 2,2′-bipyridine and 1,10-phenanthroline complexes

UV-Vis absorption spectra of one-electron reduction products and ³MLCT excited states of [Re^ICl(CO)₃(N,N)] (N,N = 2,2′-bipyridine, bpy; 1,10-phenanthroline, phen) have been measured by low-temperature spectroelectrochemistry and UV-Vis transient absorption spectroscopy, respectively, and assigned by open-shell TD-DFT calculations. The characters of the electronic transitions are visualized and analyzed using electron density redistribution maps. It follows that reduced and excited states can be approximately formulated as [Re^ICl(CO)₃(N,N⁻)]⁻ and ^∗[Re^IICl(CO)₃(N,N⁻)], respectively. UV-Vis spectra of the reduced complexes are dominated by IL transitions, plus weaker MLCT contributions. Excited-state spectra show an intense band in the UV region of ∼50% IL origin mixed with LMCT (bpy, 373 nm) or MLCT (phen, 307 nm) excitations. Because of the significant IL contribution, this spectral feature is akin to the principal IL band of the anions. In contrast, the excited-state visible spectral pattern arises from predominantly LMCT transitions, any resemblance with the reduced-state visible spectra being coincidental. The Re complexes studied herein are representatives of a broad class of metal α-diimines, for which similar spectroscopic behavior can be expected.     

Variation of DNA photocleavage efficiency for [(TL)2Ru(dpp)]Cl2 complexes where TL=2,2'-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

The complexes [(bpy)₂Ru(dpp)]Cl₂, [(phen)₂Ru(dpp)]Cl₂, and [(Ph₂phen)₂Ru(dpp)]Cl₂ (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Ph₂phen = 4,7-diphenyl-1,10-phenanthroline) have been investigated and found to photocleave DNA via an oxygen-mediated pathway. These light absorbing complexes possess intense metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum. The [(TL)₂Ru(dpp)]²⁺ systems populate ³MLCT states after visible light excitation, giving rise to emissions in aqueous solution centered at 692, 690, and 698 nm for TL = bpy, phen, and Ph₂phen respectively. The ³MLCT states and emissions are quenched by O₂, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph₂phen)₂Ru(dpp)]²⁺ > [(phen)₂Ru(dpp)]²⁺ > [(bpy)₂Ru(dpp)]²⁺. The presence of the polyazine bridging ligand will allow these chromophores to be incorporated into larger supramolecular assemblies.     

A new polymorph of dichlorido(1,10-phenanthroline)platinum(II)

A yet unreported polymorph of [PtCl₂(1,10-phenanthroline)] was obtained by slow decomposition, in CH₂Cl₂ solution, of [Pt{CH₂CH₂N(CH₂CH₃)₂-κC,κN}(1,10-phenanthroline)](ClO₄). The structure of the new orthorhombic form, III, (space group Pna2₁), is described and compared to those of the two already reported forms, I and II, which are monoclinic (space group P2₁/c) and orthorhombic (space group Pca2₁), respectively [21]. Polymorph III appears to be the least stable of the three.     

Structure and properties of a novel OH bridged dimetal helical complex with 6,6-dimethyl-2,2′:6′,2″:6″,2:6,2-quinquepyridine ligand

A new monohelical OH⁻ bridged dinuclear complex [Zn₂(dmqpy)(OOCCH₃)₂(μ-OH)][ClO₄] · 0.5EtOH, where dmqpy is 6,6-dimethyl-2,2′:6′,2″:6″,2:6,2-quinquepyridine, has been synthesized and characterized by X-ray crystallography: monoclinic, space group P2₁/c, a=13.670(1), b=14.751(1), c=16.782(1) Å, β=96.59(1)°, U=3361.7(4) ų, Z=4, R=0.0601. Two Zn(II) ions are in different coordination modes, one is five-coordinate with a N₃O₂ donor set and the other is N₂O₂ four-coordinate with a distorted tetrahedral geometry, and the zinc ions are bridged by a hydroxyl group. The presence of the OH⁻ bridge is further confirmed by electrospray mass and infrared spectroscopies. The solution properties of the complex were investigated by ¹H NMR spectroscopy. The results of NMR indicate that the complex has higher symmetry in solution than in the solid state.     

Syntheses and molecular structures of ruthenium(II) complexes of the atropisomeric ligands 1,1′-biphenyl-2,2′-diamine and 3,3′-diamino-2,2′-bipyridine

The unique ligands of [Ru(bipy)₂(bpda)](PF₆)₂ (1, BPDA=1,1′-biphenyl-2,2′-diamine) and [Ru(bipy)₂(dabipy)](PF₆)₂ (2, DABIPY=3,3′-diamino-2,2′-bipyridine) are atropisomeric (exhibit hindered rotation about the sigma bonds that connect the two aromatic groups), so the complexes are diasteromeric with conformation isomers possible for the atropisomeric ligands and configurational isomers possible at the metal centers. Only one diastereomer is observed in the solid-state in both cases. The seven- (1) and five-membered (2) chelate ring of dabipy and bpda (the ligand is bound through its pyridyl groups) ligands are δ when the configuration at the metal is Δ. No evidence for atropisomerization is found in solution. For 1, we conclude bpda binds stereospecifically; however, the atropisomerization barrier of dabipy may be sufficiently low for 2 to preclude the observation of diastereomers by low-temperature NMR spectroscopy.     

Complexation, luminescence and energy transfer in the Ce(III)– 2,2′-bipyridine complexes

Fluorescence characteristics and energy transfer to a cerium complex with 2,2′-bipyridine (bpy) in methanol are described. Stoichiometries and the stability constant of the Ce(III)–bpy complex in methanol were determined by use of the molar ratio method. A fluorescence lifetime and a quantum yield have been measured for the 2:1 complex. Decay times and time-resolved (T---S) emission spectra for Ce(III)–bpy and CeCl₃ were measured in methanol at room temperature. An energy transfer rate constant was determined from the luminescence lifetime and the quantum yield. The mechanism of energy transfer from the lowest excited singlet S₁ to the 5d level of the Ce(III) in the Ce(III)–bpy complex system is discussed in some detail.     

Praseodymium (III) complexes with 1,10-phenanthroline and cyanamide derivatives as N-donor ligands

The molecular structure of praseodymium (III) complex with 1,10-phenanthroline (phen), [Pr(phen)₂Cl₃·OH₂] (1) was determined by single-crystal X-ray diffraction. Crystal data: crystal system, triclinic, space group P and Z = 2, a = 7.1110(7) ?, b = 10.1716(10) ?, c = 17.2367(18) ?, α = 80.922(5)°, β = 78.759(5)°, γ = 70.151(5)°, R₁ = 0.036; wR₂ = 0.076 for all data. Treatment of aqueous solution of [Pr(phen)₂Cl₃·OH₂] (1) with thallium phenylcyanamide salts yield [Pr(phen)₂(L)₃] (L = pcyd (2), 2-Clpcyd (3), 2,3,5-Cl₃pcyd (4), 2,3,4,5-Cl₄pcyd (5)). Four new praseodymium (III) complexes have been characterized by IR, UV-Vis and ¹H NMR spectroscopy as well as elemental analysis. The ¹H NMR spectra of these complexes show broadening of ligand protons attributed to coordination of paramagnetic center.     

Complexes of copper(II) dihalide with 2,2′-dipyridylamine. X-ray diffraction structures of the [dibromo-bis(dipyam)copper(II)]–water (1:2) and di[chloro-bis(dipyam)copper(II)]diiodide–acetonitrile (1:2) complexes

The formation of complexes between copper(II) halides and 2,2′-dipyridylamine (dipyam) has been studied systematically. Only complexes with a 1:1 and 1:2 metal-to-ligand ratio are formed. Some mixed chloro–iodide and halide–PF₆ compounds have also been isolated. The X-ray diffraction structures of the [Cu(dipyam)₂Br₂] · 2H₂O (I) and the [Cu(dipyam)₂Cl]₂I₂ · 2CH₃CN (II) complexes are reported. I is a rare example of an octahedral coordination among the copper(II) halide complexes of dipyam. The two bromo atoms, which occupy the apical positions, are H-bonded to the water molecules of crystallization. II is a dimer, where each copper forms a cationic chloro-complex of approximately trigonal bipyramidal geometry, the dimerization being due to hydrogen bonds formed by the NH group of one of the two dipyams coordinated to each metal atom with the chlorine atom of the centrosymmetric cationic complex. The iodide anions are hydrogen-bonded to the NH groups of the dipyams not involved in the dimerization.     

Synthesis, characterization and application of Ru(BINAP) (Acac) (MNAA) (MeOH), a highly effective catalyst for the asymmetric hydrogenation of 2-(6′-methoxynaphth-2′-yl)acrylic acid

Ru(S-BINAP) (Acac) (MNAA) (MeOH) (1) (where MNAA (2) = 2-(6′-methoxynaphth-2′-yl)acrylate anion), a highly effective catalyst for the asymmetric hydrogenation of 2-(6′-methoxynaphth-2′-yl) acrylic acid (3), was isolated from a dichloromethane/methanol (vol./vol. = 1/4) solution of Ru(S-BINAP) (Acac)₂ and excess of 2-(6′-methoxynaphth-2′-yl)acrylic acid after the solution was exposed to visible light for 2 weeks. On side by side comparison studies, the rate of the hydrogenation of 3 catalyzed by 1 was found to be substantially faster than the same reaction catalyzed by Ru(S-BINAP) (OAc)₂. The molecular structure of 1 was unambiguously characterized by single crystal X-ray diffraction.     

Synthesis, characterization, and DNA binding and cleavage properties of copper(II)-tryptophanphenyl-alanine-1,10-phenanthroline/2,2'-bipyridine complexes

The mononuclear dipeptide‐based Cu^II complexes [Cu^II(trp‐phe)(phen)(H₂O)] ⋅ ClO₄ ( 1 ) and [Cu^II(trp‐phe)(bpy)(H₂O)] ⋅ ClO₄ ( 2 ) (trp‐phe=tryptophanphenylalanine, phen=1,10‐phenanthroline, bpy=2,2′‐bipyridine) were isolated, and their interaction with DNA was studied. They exhibit intercalative mode of interaction with DNA. The intercalative interaction was quantified by Stern Volmer quenching constant (K_sq=0.14 for 1 and 0.08 for 2 ). The Cu^II complexes convert supercoiled plasmid DNA into its nicked circular form hydrolytically at physiological conditions at a concentration as low as 5 μM (for 1 ) and 10 μM (for 2 ). The DNA hydrolysis rates at a complex concentration of 50 μM were determined as 1.74 h⁻¹ (R=0.985) for 1 and 0.65 h⁻¹ (R=0.965) for 2 . The rate enhancement in the range of 2.40–4.10×10⁷‐fold compared to non‐catalyzed double‐stranded DNA is significant. This was attributed to the presence of a H₂O molecule in the axial position of the Cu complexes.     

Solvent effect on the synergic extraction of thulium(III) with acetylacetone and 1,10-phenanthroline

The synergic extraction equilibrium of Tm(III) with acetylacetone (Hacac) and 1,10-phenanthroline (phen) in various organic solvents has been studied. The adduct formation constants, β_s, for Tm(acac)₃^? phen, were determined in heptane, cyclohexane, carbon tetrachloride, benzene and chloroform. The solvent effect on β_s is explained in connection with the activity coefficients of the neutral ligand, the chelate, and the adduct in the organic solvent. The activity coefficients can be calculated from the corresponding solubility parameters on the basis of the regular solution theory, and the solubility parameters of the solutes were estimated from their two-phase partition coefficients. It is demonstrated that β_s in different organic solvents except those having a specific interaction with the solute, such as chloroform, can be calculated by the present approach.     

Tricarbonyl(1,10-phenanthroline) (imidazole) rhenium(I): a powerful photooxidant for investigations of electron tunneling in proteins

The structure of [Re(CO)₃(phen)(im)]₂SO₄·4H₂O has been determined by X-ray crystallography. The yellow crystals are orthorhombic, space group Pccn (No. 56), with a=17.456(6), B=18.194(5), C=12.646(4) Å, R=0.063 for F_o²>0, R=0.032 for F_o²>3σ. The compound, which also has been characterized by IR, ¹H NMR, and UV---Vis spectroscopies, exhibits room temperature luminescence in aqueous solution (τ=120 ns) as well as reversible oxidation and reduction in acetonitrile solution (1.85 and −1.30 V versus SCE). The redox properties of the excited state of the complex (E⁰(Re^+*/0 = 1.2; E⁰(Re^2+/+*) = −0.7 V) are being exploited in studies of laser-induced electron tunneling in Re(CO)₃(phen)(histidine)-modified proteins.