Nucleic acid intercalators and avidin probes derived from luminescent cyclometalated iridium(III)-dipyridoquinoxaline and -dipyridophenazine complexes

Six luminescent cyclometalated iridium(III)-dipyridoquinoxaline and -dipyridophenazine complexes [Ir(ppy)2(N-N)](PF6) (Hppy = 2-phenylpyridine; N-N = dipyrido[3,2-f:2',3'-h]quinoxaline, dpq (1); 2-n-butylamidodipyrido[3,2-f:2',3'-h]quinoxaline, dpqa (2); 2-((2-biotinamido)ethyl)amidodipyrido[3,2-f:2',3'-h]quinoxaline, dpqB (3); dipyrido[3,2-a:2',3'-c]phenazine, dppz (4); benzo[i]dipyrido[3,2-a:2',3'-c]phenazine, dppn (5); 11-((2-biotinamido)ethyl)amidodipyrido[3,2-a:2',3'-c]phenazine, dppzB (6)) have been designed as luminescent intercalators for DNA and probes for avidin. The structure of complex 4 has been studied by X-ray crystallography. The photophysical and electrochemical properties of the complexes have also been investigated. The binding of these complexes to double-stranded calf thymus DNA and synthetic double-stranded oligonucleotides poly(dA) x poly(dT) and poly(dG) x poly(dC) has been investigated by spectroscopic titrations. The interactions between the two biotin-containing complexes and avidin have been studied by 4'-hydroxyazobenzene-2-carboxylic acid (HABA) assays and emission titrations.     

Structure of the Complex of [Ru(tpm)(dppz)py]2+ with a B‐DNA Oligonucleotide—A Single‐Substituent Binding Switch for a Metallo‐Intercalator

We report the synthesis of three new complexes related to the achiral [Ru(tpm)(dppz)py]²⁺ cation (tpm=tripyridazole methane, dppz=dipyrido[3,2‐a:2′,3′‐c]phenazine, py=pyridine) that contain an additional single functional group on the monodentate ancillary pyridyl ligand. Computational calculations indicate that the coordinated pyridyl rings are in a fixed orientation parallel to the dppz axis, and that the electrostatic properties of the complexes are very similar. DNA binding studies on the new complexes reveal that the nature and positioning of the functional group has a profound effect on the binding mode and affinity of these complexes. To explore the molecular and structural basis of these effects, circular dichroism and NMR studies on [Ru(tpm)(dppz)py]Cl₂ with the octanucleotides d(AGAGCTCT)₂ and d(CGAGCTCG)₂, were carried out. These studies demonstrate that the dppz ligand intercalates into the G²–A³ step, with {Ru(tpm)py} in the minor groove. They also reveal that the complex intercalates into the binding site in two possible orientations with the pyridyl ligand of the major conformer making close contact with terminal base pairs. We conclude that substitution at the 2‐ or 3‐position of the pyridine ring has little effect on binding, but that substitution at the 4‐position drastically disrupts intercalative binding, particularly with a 4‐amino substituent, because of steric and electronic interactions with the DNA. These results indicate that complexes derived from these systems have the potential to function as sequence‐specific light‐switch systems.     

A convenient synthetic route to half-sandwich rhodium(III) complexes of the tripodal ligand tris(3,5-dimethylpyrazolyl)methane

The synthesis of the complex [RhCl3tpm*], (1), (tpm*= tris(3,5-dimethylpyrazolyl)methane) is reported. This complex is a suitable starting material for the synthesis of heteroleptic half-sandwich complexes: it has been used to synthesise the complexes; [RhCl(bpy)tpm*][(PF6)2][2][(PF6)2](bpy = 2,2'-bipyridyl), [RhCl(phen)tpm*][(PF6)2][3][(PF6)2]. (phen = 1,10-phenanthroline), [RhCl2(py)tpm*][(PF6)], [4][(PF6)2], (py = pyridine), and[RhCl(py)2tpm*][(PF6)2], [5][(PF6)2]. The structures of [2][(PF6)2], [33][(PF6)2], [4][(PF6)2], and [5][(PF6)2] have been determined by X-ray crystallography. The electrochemical and photophysical properties of these new compounds have also been investigated.     

Non-covalent ruthenium polypyridyl complexes-carbon nanotubes composites: an alternative for functional dissolution of carbon nanotubes in solution

The dispersion of single-walled carbon nanotubes (SWCNTs) in the presence of water soluble polypyridyl complexes of the general formula [Ru(x)(bpy)(y)L](2+) (L = dppz, dppn, tpphz) is reported. These ligands have extended planar π systems, which aid in the solubilization of SWCNTs via π-π interactions.     

Structure-activity relationship of photocytotoxic iron(III) complexes of modified dipyridophenazine ligands

Iron(III) complexes [FeL(B)] (1-5) of a tetradentate trianionic phenolate-based ligand (L) and modified dipyridophenazine bases (B), namely, dipyrido-6,7,8,9-tetrahydrophenazine (dpqC in 1), dipyrido[3,2-a:2',3'-c]phenazine-2-carboxylic acid (dppzc in 2), dipyrido[3,2-a:2',3'-c]phenazine-11-sulfonic acid (dppzs in 3), 7-aminodipyrido[3,2-a:2',3'-c]phenazine (dppza in 4) and benzo[i]dipyrido[3,2-a:2',3'-c]phenazine (dppn in 5), have been synthesized and their photocytotoxic properties studied along with their dipyridophenazine analogue (6). The complexes have a five electron paramagnetic iron(III) center, and the Fe(III)/Fe(II) redox couple appears at about -0.69 V versus SCE in DMF-0.1 M TBAP. The physicochemical data also suggest that the complexes possess similar structural features as that of its parent complex [FeL(dppz)] with FeO3N3 coordination in a distorted octahedral geometry. The DNA-complex and protein-complex interaction studies have revealed that the complexes interact favorably with the biomolecules, the degree of which depends on the nature of the substituents present on the dipyridophenazine ring. Photocleavage of pUC19 DNA by the complexes has been studied using visible light of 476, 530, and 647 nm wavelengths. Mechanistic investigations with inhibitors show formation of HO(?) radicals via a photoredox pathway. Photocytotoxicity study of the complexes in HeLa cells has shown that the dppn complex (5) is highly active in causing cell death in visible light with sub micromolar IC(50) value. The effect of substitutions and the planarity of the phenazine moiety on the cellular uptake are quantified by determining the total cellular iron content using the inductively coupled plasma-optical emission spectrometry (ICP-OES) technique. The cellular uptake increases marginally with an increase in the hydrophobicity of the dipyridophenazine ligands whereas complex 3 with dppzs shows very high uptake. Insights into the cell death mechanism by the dppn complex 5, obtained through DAPI nuclear staining in HeLa cells, reveal a rapid programmed cell death mechanism following photoactivation of complex 5 with visible light. The effect of substituent on the DNA photocleavage activity of the complexes has been rationalized from the theoretical studies.     

Fused donor-acceptor ligands in RuII chemistry: synthesis, electrochemistry and spectroscopy of [Ru(bpy)3-n(TTF-dppz)n](PF6)2.

Three ruthenium(II) polypyridine complexes of general formula [Ru(bpy)(3-n)(TTF-dppz)n](PF6)2 (n=1-3, bpy=2,2'-bipyridine), with one, two or three redox-active TTF-dppz (4',5'-bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2',3'-c]phenazine) ligands, were synthesised and fully characterised. Their electrochemical and photophysical properties are reported together with those of the reference compounds [Ru(bpy)3](PF6)2, [Ru(dppz)3](PF6)2 and [Ru(bpy)2(dppz)](PF6)2 and the free TTF-dppz ligand. All three complexes show intraligand charge-transfer (ILCT) fluorescence of the TTF-dppz ligand. Remarkably, the complex with n=1 exhibits luminescence from the Ru(2+)-->dppz metal-to-ligand charge-transfer ((3)MLCT) state, whereas for the other two complexes, a radiationless pathway via electron transfer from a second TTF-dppz ligand quenches the (3)MLCT luminescence. The TTF fragments as electron donors thus induce a ligand-to-ligand charge-separated (LLCS) state of the form TTF-dppz- -Ru(2+)-dppz-TTF(+). The lifetime of this LLCS state is approximately 2.3 micros, which is four orders of magnitude longer than that of 0.4 ns for the ILCT state, because recombination of charges on two different ligands is substantially slower.     

Direct DNA photocleavage by a new intercalating dirhodium(II/II) complex: comparison to Rh2(mu-O2CCH3)4

Transition metal complexes possessing the intercalating dppz ligand (dppz = dipyrido[3,2-a:2',3'-c]phenazine) typically bind ds-DNA through intercalation (K(b) approximately 10(5)-10(6) M(-1)), and DNA photocleavage by these complexes with visible light proceeds through the generation of a reactive oxygen species. The DNA binding and photocleavage by [Rh(2)(mu-O(2)CCH(3))(2)(eta(1)-O(2)CCH(3))(CH(3)OH)(dppz)](+) (2) is reported and compared to that of Rh(2)(mu-O(2)CCH(3))(4) (1). Spectral changes and an increase in viscosity provide evidence for the intercalation of 2 to double stranded DNA with K(b) = 1.8 x 10(5) M(-1). DNA photocleavage by 2 is observed upon irradiation with lambda(irr) > 395 nm both in air and deoxygenated solution. DNA photocleavage is not observed for 1 or free dppz ligand under these irradiation conditions. The coupling of a single dppz ligand to a dirhodium(II/II) bimetallic core in 2 provides a means to access oxygen-independent DNA photocleavage with visible light.     

Ferrocene-conjugated L-tryptophan copper(II) complexes of phenanthroline bases showing DNA photocleavage activity and cytotoxicity

Ferrocene-conjugated L-tryptophan (L-Trp) reduced Schiff base (Fc-TrpH) copper(II) complexes [Cu(Fc-Trp)(L)](ClO(4)) of phenanthroline bases (L), viz. 2,2'-bipyridine (bpy in 1), 1,10-phenanthroline (phen in 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 4), were prepared and characterized and their photocytotoxicity studied. Cationic reduced Schiff base (Ph-TrpH) complexes [Cu(Ph-Trp)(L)(H(2)O)](ClO(4)) (L = phen in 5; dppz in 6) having the ferrocenyl moiety replaced by a phenyl group and the Zn(II) analogue (7) of complex 4 were prepared and used as control species. The crystal structures of 1 and 5 with respective square-planar CuN(3)O and square-pyramidal CuN(3)O(2) coordination geometry show significantly different core structures. Complexes 1-4 exhibit a Cu(II)-Cu(I) redox couple near -0.1 V and the Fc(+)-Fc couple at ~0.5 V vs SCE in DMF-0.1 M [Bu(n)(4)N](ClO(4)) (Fc = ferrocenyl moiety). The complexes display a copper(II)-based d-d band near 600 nm and a Fc-centered band at ~450 nm in DMF-Tris-HCl buffer. The complexes are efficient binders to calf thymus DNA. They are synthetic chemical nucleases in the presence of thiol or H(2)O(2), forming hydroxyl radicals. The photoactive complexes are cleavers of pUC19 DNA in visible light, forming hydroxyl radicals. Complexes 2-6 show photocytotoxicity in HeLa cancer cells, giving IC(50) values of 4.7, 10.2, 1.3, 4.8, and 4.3 μM, respectively, in visible light with the appearance of apoptotic bodies. The complexes also show photocytotoxicity in MCF-7 cancer cells. Nuclear chromatin cleavage has been observed with acridine orange/ethidium bromide (AO/EB) dual staining with complex 4 in visible light. The complexes induce caspase-independent apoptosis in the HeLa cells.     

Intercalation of fac-[(4,4'-bpy)ReI(CO)3(dppz)]+, dppz = dipyridyl[3,2-a:2'3'-c]phenazine, in polynucleotides. On the UV-vis photophysics of the Re(I) intercalator and the redox reactions with pulse radiolysis-generated radicals

The intercalation of fac-[(4,4'-bpy)Re(I)(CO)3(dppz)]+ (dppz = dipyridyl[3,2-a:2'3'-c]phenazine) in polynucleotides, poly[dAdT]2 and poly[dGdC]2, where A = adenine, G = guanine, C = cytosine and T = thymine, is a major cause of changes in the absorption and emission spectra of the complex. A strong complex-poly[dAdT]2 interaction drives the intercalation process, which has a binding constant, Kb approximately 1.8 x 10(5) M(-1). Pulse radiolysis was used for a study of the redox reactions of e(-)(aq), C*H(2)OH and N3* radicals with the intercalated complex. These radicals exhibited more affinity for the intercalated complex than for the bases. Ligand-radical complexes, fac-[(4,4'-bpy*)Re(I)(CO)3(dppz)] and fac-[(4,4'-bpy)Re(I)(CO)3(dppz *)], were produced by e(-)(aq) and C*H(2)OH, respectively. A Re(II) species, fac-[(4,4'-bpy)Re(II)(CO)3(dppz)](2+), was produced by N3* radicals. The rate of annihilation of the ligand-radical species was second order on the concentration of ligand-radical while the disappearance of the Re(II) complex induced the oxidative cleavage of the polynucleotide strand.     

Mixed ligand cobalt(II) picolinate complexes: synthesis, characterization, DNA binding and photocleavage

Complexes of the type [Co(pic)(2)(NN)], where pic = picolinate, NN = dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (4) and 4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f][1,10]-phenanthroline-6,13-dione (bipyridyl-glycoluril) (bpg) (6) have been synthesized and characterized by elemental analysis, IR, UV-vis, NMR and ESI-MS spectroscopy and thermogravimetic analysis (TGA). Their physicochemical properties are compared with previously synthesized complexes, where NN = (H(2)O)(2) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (5). The crystal structures of the complexes 4-6 were solved by single-crystal X-ray diffraction. The complexes 4 and 5 crystallize from a mixture of chloroform and methanol in monoclinic and orthorhombic crystal systems, respectively, whereas complex 6 crystallizes from dimethyl sulfoxide (DMSO) in a tetragonal crystal system. The coordination sphere consists of two oxygen atoms and two nitrogen atoms from the two picolinates and two nitrogen atoms from the dpq, dppz or bpg ligand, respectively. Co(ii)/Co(iii) oxidation potentials have been determined by cyclic voltammetry. The DNA binding of complexes 1-5 has been investigated using thermal melting, fluorescence quenching and viscosity measurements, which indicate the partial intercalation of complex 5 with an apparent binding constant (k(app)) of 8.3 × 10(5) M(-1). DNA cleavage studies of complexes 1-5 have been investigated using gel electrophoresis in the presence of H(2)O(2) as an oxidizing agent and also by photoirradiation at 365 nm. The mechanistic investigations suggest that singlet oxygen ((1)O(2)) is the major species involved in the DNA cleavage by these complexes. The structures of complexes 2-6 were optimized with density functional theory (DFT) method (B3LYP/6-31G(d,p)). The low vertical ionization potential values indicate photoredox pathways for the DNA cleavage activity by complexes 4 and 5, which is corroborated by DNA cleavage experiments.     

Mixed ligand ruthenium(II) complexes of bis(pyrid-2-yl)-/bis(benzimidazol-2-yl)-dithioether and diimines: study of non-covalent DNA binding and cytotoxicity

A series of mixed ligand ruthenium(II) complexes [Ru(pdto)(diimine)](ClO4)2/(PF6)2 1-3 and [Ru(bbdo)(diimine)](ClO4), 4-6, where pdto is 1,8-bis(pyrid-2-yl)-3,6-dithiooctane, bbdo is 1,8-bis(benzimidazol-2-yl)-3,6-dithiooctane and diimine is 1,10-phenanthroline (phen), dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz), have been isolated and characterised by analytical and spectral methods. The complexes [Ru(pdto)(phen)](PF6)2 la, [Ru(pdto)(dpq)(Cl](PF6) 2a, [Ru(bbdo)(phen)](PF6)2 4a and [Ru(bbdo)(dpq)](ClO4)2 5 have been structurally characterized and their coordination geometries around ruthenium(II) are described as distorted octahedral. In la, 4a and 5 the two thioether sulfur and two py/bzim nitrogen atoms of the tetradentate pdto/bbdo ligand are folded around Ru(II) to give predominantly a "cis-alpha" configuration. (I)H NMR spectral data of the complexes support this configuration in solution. In [Ru(pdto)(dpq)Cl](PF6) 2a with a distorted octahedral coordination geometry, one of the two py nitrogens of pdto is not coordinated. The DNA binding constants (Kb: 2, 2.00 +/- 0.02 x 10(4) M(-1), s = 1.0; 3, 3.00 +/- 0.01 x 10(6) M(-1), s = 1.3) determined by absorption spectral titrations of the complexes with CT DNA reveal that 3 interacts with DNA more tightly than 2 through partial intercalation of the extended planar ring of coordinated dppz with the DNA base stack. The DNA binding affinities of the complexes increase with increase in the number of planar aromatic rings in the co-ligand, and on replacing both the py moieties in pdto complexes (1-3) by bzim moieties to give bbdo complexes (4-6). Upon interaction with CT DNA the complexes 1, 2, 5 and 6 show a decrease in anodic current in the cyclic voltammograms. On the other hand, interestingly, 3 and 4 show an increase in anodic current suggesting their involvement in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 6 alters the superhelicity of DNA upon binding with supercoiled pBR322 DNA. The cytotoxicities of the dppz complexes 3 and 6, which avidly bind to DNA, have been examined by screening them against cell lines of different cancer origins. It is noteworthy that 6 exhibits selectivity with higher cytotoxicity against the melanoma cancer cell line (A375) than other cell lines, potency approximately twice that of cisplatin and toxicity to normal cells 3 and 90 times less than cisplatin and adriamycin respectively.     

Water-soluble, luminescent iridium(iii)-ytterbium(iii) complexes using dipyrido[3,2-a:2',3'-c]phenazine derivatives as bridging units

Amino-substituted dipyrido[3,2-a:2',3'-c]phenazine (L(1)) and dimethyl-dipyrido[3,2-a:2',3'-c]phenazine (L(2)) have been investigated as: (i) chromophores in cyclen-based ligands for lanthanide(iii) ions; (ii) ancillary co-ligands in cyclometalated iridium(iii) complexes; (iii) bridging, linker units in covalently linked, water-soluble bimetallic lanthanide(iii) iridium(iii) hybrid complexes. The dipyrido[3,2-a:2',3'-c]phenazine (dppz) derivatives can act as sensitising chromophores (λ(ex) 400 nm) for Yb(iii), resulting in characteristic near-IR emission at 950-1050 nm. The incorporation of dppz-type ligands into cyclometalated Ir(III) complexes of the general type [Ir(epqc)(2)(L(n))](PF(6)) (where epqc = ethylphenylquinoline carboxylate) gave luminescent species with solvent-sensitive emission properties. Steady state and time-resolved luminescence measurements on the water-soluble d-f hybrid species showed that Yb(III) can be sensitised using visible light.     

Complexes of functionalized dipyrido[3,2-a:2',3'-c]-phenazine: a synthetic, spectroscopic, structural, and density functional theory study

The ligands 11-bromodipyrido[3,2-a:2',3'-c]phenazine and ethyl dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylate have been prepared and coordinated to ruthenium(II), rhenium(I), and copper(I) metal centers. The electronic effects of substitution of dipyrido[2,3-a:3',2'-c]phenazine (dppz) have been investigated by spectroscopy and electrochemistry, and some photophysical properties have been studied. The crystal structures of [Re(L)(CO)(3)Cl] (L = ethyl dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylate or 11-bromodipyrido[3,2-a:2',3'-c]phenazine) are presented. Density functional theory calculations on the complexes show only small deviations in bond lengths and angles (most bonds within 0.02 Angstroms, most angles within 2 degrees) from the crystallographic data. Furthermore, the vibrational spectra of the strongest Raman and IR bands are predicted to within an average 6 cm(-1) for the complexes [Re(L)(CO)(3)Cl] and [Cu(L)(triphenylphosphine)(2)]BF(4) (in the 1000-1700 cm(-1) region). Spectroscopic and electrochemical evidence suggest that reduction of the complex causes structural changes across the entire dppz ligand. This is unusual as dppz-based ligands typically have electrochemical properties that suggest charge localization with reduction on the phenazine portion of the ligand. The excited-state lifetimes of the complexes have been measured, and they range from ca. 200 ns for the [Ru(L)(2,2'-bipyridine)(2)](PF(6))(2) complexes to over 2 mus for [Cu(11-bromodipyrido[3,2-a:2',3'-c]phenazine)(PPh(3))(2)](BF(4)) at room temperature. The emission spectra suggest that the unusually long-lived excited states of the copper complexes result from metal-to-ligand charge transfer (MLCT) transitions as they are completely quenched in methanol. Electroluminescent films may be fabricated from these compounds; they show MLCT state emission even at low doping levels [<0.1% by weight in poly(vinylcarbazole) polymer matrix].     

Synthesis, structure, spectroscopic properties, and electrochemical oxidation of ruthenium(II) complexes Incorporating monocarboxylate bipyridine ligands

[Ru(bpy)(2)(Mebpy-COOH)](PF(6))(2).3H(2)O (1), [Ru(phen)(2)(Mebpy-COOH)](ClO(4))(2).5H(2)O (2), [Ru(dppz)(2)(Mebpy-COOH)]Cl(2).9H(2)O (3), and [Ru(bpy)(dppz)(Mebpy-COOH)](PF(6))(2).5H(2)O (4) (bpy = 2,2'-bipyridine, Mebpy-COOH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid, phen = 1,10-phenanthroline, dppz = dipyrido[3,2,-a;2',3-c]phenazine) have been synthesized and characterized spectroscopically and by microanalysis. The [Ru(Mebpy-COOH)(CO)(2)Cl(2)].H(2)O intermediate was prepared by reaction of the monocarboxylic acid ligand, Mebpy-COOH, with [Ru(CO)(2)Cl(2)](n), and the product was then reacted with either bpy, phen, or dppz in the presence of an excess of trimethylamine-N-oxide (Me(3)NO), as the decarbonylation agent, to generate 1, 2, and 3, respectively. For compound 4, [Ru(bpy)(CO)Cl(2)](2) was reacted with Mebpy-COOH to yield [Ru(bpy)(Mebpy-COOH)(CO)Cl](PF(6)).H(2)O as a mixture of two main geometric isomers. Chemical decarbonylation in the presence of dppz gave 4 also as a mixture of two isomers. Electrochemical and spectrophotometric studies indicated that complexes 1 and 2 were present as a mixture of protonated and deprotonated forms in acetonitrile solution because of water of solvation in the isolated solid products. The X-ray crystal structure determination on crystals of [Ru(bpy)2(MebpyCOO)][Ru(bpy)(2)(MebpyCOOH)](3)(PF(6))(7), 1a, and [Ru(phen)(2)(MebpyCOO)](ClO(4)).6H(2)O, 2a, obtained from solutions of 1 and 2, respectively, revealed that 1a consisted of a mixture of protonated and deprotonated forms of the complex in a 1:3 ratio and that 2a consisted of the deprotonated derivative of 2. A distorted octahedral geometry for the Ru(II) centers was found for both complexes. Upon excitation at 450 nm, MeCN solutions of the protonated complexes 1-4 were found to exhibit emission bands in the 635-655 nm range, whereas the corresponding emission maxima of their deprotonated forms were observed at lower wavelengths. Protonation/deprotonation effects were also observed in the luminescence and electrochemical behavior of complexes 1-4. Comprehensive electrochemical studies in acetonitrile show that the ruthenium centers on 1, 2, 3, and 4 are oxidized from Ru(II) to Ru(III) with reversible potentials at 917, 929, 1052, and 1005 mV vs Fc(0/+) (Fc = ferrocene), respectively. Complexes 1 and 2 also exhibit an irreversible oxidation process in acetonitrile, and all compounds undergo ligand-based reduction processes.     

Synthesis,crystal structures,DNA/bovine serum albumin binding,DNA cleavage and cytotoxicity of five mononuclear zinc(II) complexes

Five new mononuclear zinc(II) complexes containing ligands with extended planar phenanthroline moieties (dipyrido‐[3,2‐a:2′,3′‐c]phenazine (dppz) or dipyrido[3,2‐d:2′,3′‐f] quinoxaline (dpq)), namely [Zn(dppz)(acac)₂]⋅CH₃OH ( 1 ), [Zn(dppz)(dbm)(OAc)] ( 2 ), [Zn(dpq)(dbm) (OAc)] 1.5H₂O ( 3 ), [Zn(dpq)(tfnb)(OAc)] ( 4 ) and [Zn(dpq)(tfnb)₂] ( 5 ), where acac = acetylacetonate, tfnb = benzoyltrifluoroacetone and dbm = dibenzoylmethane, were synthesized and structurally characterized. The binding ability of complexes 1 – 5 with calf thymus DNA was investigated by spectroscopic titration methods and viscosity measurements. Results indicate that all complexes bind to calf thymus DNA via intercalative mode, and the DNA binding affinities of dppz complexes 1 and 2 are apparently stronger than those of dpq complexes 3 – 5 . DNA photocleavage experiments reveal that these complexes are efficient DNA cleaving agents and they are more active in UV‐A (365 nm) than in visible light. In particular, the in vitro cytotoxicity of the complexes for human cancer cell line A549 demonstrates that the five compounds have anticancer activity with low IC₅₀ values. Meanwhile, interaction of the complexes with bovine serum albumin investigated using UV–visible and fluorescence methods indicates that all complexes can quench the intrinsic fluorescence of bovine serum albumin in a static quenching process.     

Syntheses and characterization of titanium(IV) and titanium(III) complexes with (2-dimethylphosphino)ethane-1-thiolate and (3-dimethylphosphino)propane-1-thiolate as ligands

Reactions of Cp(2)TiCl(2) (Cp = eta(5)-cyclopentadienide) with 2 or 1 equiv of hybrid P-S ligands (L), (CH(3))(2)P(CH(2))(n)()S(-) (n = 2, dmpet; n = 3, dmppt), produced new dicyclopentadienyltitanium(IV) complexes with L, Cp(2)Ti(L-kappaS)(2) (1, L = dmpet; 2, L = dmppt) and [Cp(2)Ti(L-kappa(2)S,P)]BPh(4) (3, L = dmpet; 4, L = dmppt). The Ti(III) complexes, Cp(2)Ti(L-kappa(2)S,P) (5, L = dmpet; 6, L = dmppt), were prepared by the reaction of Cp(2)Ti(eta(3)-C(3)H(5)) with 1 equiv of L. The structures of complexes 1-6 were confirmed by X-ray diffraction analyses. It was found that complexes 3 and 5 were isostructural around Ti(IV) and Ti(III) centers: the Ti(IV)-S bond length in 3 (2.3498(9) A) is shorter by 0.14 A than Ti(III)-S in 5 (2.4877(7) A), while Ti(IV)-P (2.534(1) A) was merely 0.05 A shorter than Ti(III)-P (2.5844(7) A). The redox potential between 3 and 5 in acetonitrile was -1.14 V vs the ferricinium/ferrocene couple. A heterobimetallic complex that has the frame of complex 1, [Cp(2)Ti(dmpet)(2)Cu]PF(6) (7), was also isolated and structurally characterized: the Ti-Cu distance (2.95(1) A) was shorter than that in [Cp(2)Ti(SC(2)H(4)PPh(2))(2)Cu]BF(4), previously reported by White and Stephan. Structural characterization was also carried out for CpTi(dmpet-kappaS)(2)(dmpet-kappa(2)S,P) (8) and CpTiCl(2)(dmppt-kappa(2)S,P) (9), which were obtained by the reactions of Cp(or Cp)TiCl(3) (Cp = eta(5)-C(5)Me(5)(-)) with n equiv (n = 1-3) of L. The mutual site-exchange reaction between phosphorus atoms on a coordinated dmpet in the kappa(2)S,P mode and on two other coordinated dmpet's in the kappaS mode within complex 8 was analyzed by the variable-temperature (31)P[(1)H] dynamic NMR method. The kinetic parameters for this process, k(ex)(298) = 1.9 x 10(5) s(-)(1), DeltaH = 48 kJ mol(-)(1), and DeltaS = 17 J mol(-)(1) K(-)(1), as well as the rather long Ti(IV)-P distance (2.652(1) A), indicate the fluxional nature of the coordination geometry in complex 8.     

Bis(allyl)gallium cation, tris(allyl)gallium, and tetrakis(allyl)gallate: synthesis, characterization, and reactivity

A series of cationic, neutral, and anionic allylgallium complexes has been isolated and fully characterized. It includes neutral [Ga(η(1)-C(3)H(5))(3)(L)] (1, L = THF; 2, L = OPPh(3)), cationic [Ga(η(1)-C(3)H(5))(2)(THF)(2)](+)[A](-) (3, [A](-) = [B(C(6)F(5))(4)](-); 4, [A](-) = [B(C(6)H(3)Cl(2))(4)](-)), as well as anionic [Cat](+)[Ga(η(1)-C(3)H(5))(4)](-) (5, [Cat](+) = K(+); 6, [Cat](+) = [K(dibenzo-18-c-6](+); 7, [Cat](+) = [PPh(4)](+)). Binding modes of the allyl ligand in solution and in the solid state have been studied comparatively. Single crystal X-ray analyses revealed a four-coordinate neutral gallium center in 2, a five-coordinate cationic gallium center in 4 and [4·THF], and a four-coordinate anionic gallium center with a bridging μ(2)-η(1):η(2) coordination mode of the allyl ligand in 6. The reactivity of this series of allylgallium complexes toward benzophenone and N-heteroaromatics has been investigated. Counterion effects have also been studied. Reactions of 1 and 5 with isoquinoline revealed the first examples of organogallium complexes reacting under 1,2-insertion with pyridine derivatives.     

Electronic structure of nitric oxide adducts of bis(diaryl-1,2-dithiolene)iron compounds: four-membered electron-transfer series [Fe(NO)(L)2]z (z = 1+, 0, 1-, 2-)

Four members of the electron-transfer series [Fe(NO)(S(2)C(2)R(2))2]z (z = 1+, 0, 1-, 2-) have been isolated as solid materials (R = p-tolyl): [1a](BF4), [1a]0, [Co(Cp)2][1a], and [Co(Cp)2]2[1a]. In addition, complexes [2a]0 (R = 4,4-diphenyl), [3a]0 (R = p-methoxyphenyl), [Et(4)N][4a] (R = phenyl), and [PPh(4)][5a] (R = -CN) have been synthesized and the members of each of their electron-transfer series electrochemically generated in CH(2)Cl(2) solution. All species have been characterized electro- and magnetochemically. Their electronic, M?ssbauer, and electron paramagnetic resonance spectra as well as their infrared spectra have been recorded in order to elucidate the electronic structure of each member of the electron-transfer series. It is shown that the monocationic, neutral, and monoanionic species possess an {FeNO}6 (S = 0) moiety where the redox chemistry is sulfur ligand-based, (L)2-(L*)1-: [Fe(NO)(L*)2]+ (S = 0), [Fe(NO)(L*)(L)]0 <--> [Fe(NO)(L)(L*)]0 (S = 1/2), [Fe(NO)(L)2]- (S = 0). Further one-electron reduction generates a dianion with an {FeNO}7 (S = 1/2) unit and two fully reduced, diamagnetic dianions L2-: [Fe(NO)(L)2]2- (S = 1/2).     

Synthesis of acetimino complexes of Pt(II) and Pt(IV) and the first heteronuclear mu-acetimido complexes

The reactions of [Ag(NH=CMe2)2]ClO4 with cis-[PtCl2L2] in a 1:1 molar ratio give cis-[PtCl(NH=CMe2)(PPh3)2]ClO4 (1cis) or cis-[PtCl(NH=CMe2)2(dmso)]ClO4 (2), and in 2:1 molar ratio, they produce [Pt(NH=CMe2)2L2](ClO4)2 [L = PPh3 (3), L2= tbbpy = 4,4'-di-tert-butyl-2,2'-dipyridyl (4)]. Complex 2 reacts with PPh3 (1:2) to give trans-[PtCl(NH=CMe2)(PPh3)2]ClO(4) (1trans). The two-step reaction of cis-[PtCl2(dmso)2], [Au(NH=CMe2)(PPh3)]ClO4, and PPh3 (1:1:1) gives [SP-4-3]-[PtCl(NH=CMe2)(dmso)(PPh3)]ClO4 (5). The reactions of complexes 2 and 4 with PhICl2 give the Pt(IV) derivatives [OC-6-13]-[PtCl3(NH=CMe2)(2)(dmso)]ClO4 (6) and [OC-6-13]-[PtCl2(NH=CMe2)2(dtbbpy)](ClO4)2 (7), respectively. Complexes 1cis and 1trans react with NaH and [AuCl(PPh3)] (1:10:1.2) to give cis- and trans-[PtCl{mu-N(AuPPh3)=CMe2}(PPh3)2]ClO4 (8cis and 8trans), respectively. The crystal structures of 4.0.5Et2O.0.5Me2CO and 6 have been determined; both exhibit pseudosymmetry.