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PubMed2001

Synthesis and characterization of ruthenium(II) molecular assemblies for photosensitization of nanocrystalline TiO2: utilization of hydroxyl grafting mode.

New Ru polypyridine complexes [(bpy)2Ru(L)]2+, where bpy = 2,2'-bipyridine and L = dipyrido[3,2-a:2',3'-c]-phenazine-2-carboxylic acid (dppzc), dipyrido[3,2-f:2',3'-h]quinoxaline-2,3-dicarboxylic acid (dpq(COOH)2), 3-hydroxydipyrido[3,2-f:2',3'-h]quinoxaline-2-carboxylic acid (dpq(OHCOOH)), 2,3-dihydroxydipyrido[3,2-f:2',3'-h]quinoxaline (dpq(OH)2), and [(L')Ru(dppzc)2]2+, where L' = bpy and 1,10-phenanthroline (phen), have been synthesized, characterized, and anchored to nanocrystalline TiO2 electrodes for light to electrical energy conversion in regenerative photoelectrochemical cells with I-/I2 acetonitrile electrolyte. These sensitizers have intense metal-to-ligand charge-transfer (MLCT) bands centered at approximately 450 nm. The effect of pH on the absorption and emission spectra of these complexes consisting of protonatable ligands has been investigated in water by spectrophotometric titration. The excited-state pKa values are more basic than the ground-state ones, except the pKa2 and pKa2* in [(bpy)2Ru(dpq(OH)2)]2+, which are equal, suggesting the localization of the lowest-energy MLCT on heteroaromatic bridging ligands, dppzc and dpq. Incident photon-to-current conversion efficiency (IPCE) is sensitive to the structural changes that resulted from introducing different functional groups, used for grafting.

Journal Article↗

PubMed2002

Di- and tetranuclear ruthenium(II) and/or osmium(II) complexes of polypyridyl ligands bridged by a fully conjugated aromatic spacer: synthesis, characterization, and electrochemical and photophysical studies.

A series of mono-, di-, and tetranuclear homo/heterometallic complexes of Ru(II) and Os(II) based on the bridging ligand dppz(11-11')dppz (where dppz = dipyrido[3,2-a:2',3'-c]phenazine) (BL) have been synthesized and characterized. This bridging ligand is a long rigid rod with only one rotational degree of freedom and provides complete conjugation between the chromophores. The complexes synthesized are of general formula [(bpy)(2)Ru-BL](2+), [(phen)(2)/(bpy)(2)M-BL-M(bpy)(2)/(phen)(2)](4+) (M = Ru(II) and Os(II)), [(bpy)(2)Ru-BL-Os(bpy)(2)](4+), and [((bpy)(2)Ru-BL)(3)M](8+). Detailed (1)H NMR studies of these complexes revealed that each chiral center does not influence its neighbor because of the long distance between the metal centers and the superimposed resonances of the diastereoisomers, which allowed the unambiguous assignment of the signals, particularly for homonuclear complexes. Concentration-dependent (1)H NMR studies show molecular aggregation of the mono- and dinuclear complexes in solution by pi-pi stacking. Electrospray mass spectrometry data are consistent with dimerization of mono- and dinuclear complexes in solution. Electrochemical studies show oxidations of Ru(II) and Os(II) in the potential ranges +1.38 to +1.40 and +0.92 to +1.01 V, respectively. The bridging ligand exhibits two one-electron reductions, and it appears that the added electrons are localized on the phenazene moieties of the spacer. All of these complexes show strong metal-to-ligand charge-transfer (MLCT) absorption and (3)MLCT luminescence at room temperature. Quantum yields have been calculated, and the emission lifetimes of all complexes have been measured by laser flash photolysis experiments. The luminescence intensity and lifetime data suggest that the emission due to the Ru center of the heteronuclear complexes is strongly quenched (>90%) compared to that of the corresponding model complexes. This quenching is attributed to intramolecular energy transfer from the Ru(II) center to the Os(II) center (k = (3-5) x 10(7) s(-1)) across the bridging ligand.

Journal Article↗

PubMed2002

Trans ruthenium(II) complexes with NH-bridged tetradentate symmetric and asymmetric polypyridyl ligands.

NH-Bridged tetradentate ligands were synthesized to achieve stable trans Ru(II) bis(polypyridyl) complexes. The polypyridyl part of the ligand was either symmetric, as in N,N-bis(1,10-phenanthroline-2-yl)amine (phen-NH-phen), or asymmetric, as in N-(1,10-phenanthroline-2-yl)-N-(6-yl-dipyridyl[2,3-a:2',3'-c]phenazine)amine (dppz-NH-phen). Protonation of phen-NH-phen with trifluoroacetic acid and the subsequent reaction with RuCl3 yield trans-[Ru(phen-NH-phen)Cl2]. The chloro ligands in this compound can easily be replaced by stronger ligands, such as CH3CN and DMSO. In this way, complexes trans-[Ru(phen-NH-phen)(CH3CN)(DMSO)](PF6)2 (1), trans-[Ru(phen-NH-phen)(DMSO)2](PF6)2 (2), and trans-[Ru(phen-NH-phen)(CH3CN)2](PF6)2 (3) were obtained. X-ray structures were determined for 1 and 3. Following a procedure similar to that used with phen-NH-phen, the complex trans-[Ru(dppz-NH-phen)(CH3CN)2](PF6)2 (4) was obtained. To our knowledge, this is the first reported trans ruthenium(II) bis(polypyridyl) complex with two different polypyridyl ligands in the equatorial plane.

Journal Article↗

PubMed2003

Adjacent- versus remote-site electron injection in TiO2 surfaces modified with binuclear ruthenium complexes.

Nanocrystalline thin films of TiO2 cast on an optically transparent indium tin oxide glass were sensitized with ruthenium homo- and heterobinuclear complexes, [LL'Ru(BL)RuLL']n+ (n = 2, 3), where L and L' are 4,4'-dicarboxy-2,2'-bipyridine (dcb) and/or 2,2'-bipyridine (bpy) and BL is a rigid and linear heteroaromatic entity (tetrapyrido[3,2-a:2',3'-c:3",2"-h:2'",3'"-j]phenazine (tpphz) or 1,4-bis([1,10]phenanthroline[5,6-d]imidazol-2-yl)benzene (bfimbz)). The photophysical behavior of the RuII-RuII diads in solution indicated the occurrence of intercomponent energy transfer from the upper-lying Ru --> bpy charge-transfer (CT) excited state of the Ru(bpy)(2) moiety to the lower-lying Ru --> dcb CT excited state of the Ru(bpy)(dcb) (or Ru(dcb)(2)) subunit in the heterobinuclear complexes. These sensitizer diads adsorbed on nanostructured TiO2 surfaces in a perpendicular or parallel attachment mode. Adsorption was through the dcb ligands on one or both chromophoric subunits. The behavior of the adsorbed species was studied by nanosecond time-resolved transient absorption and emission spectroscopy, as well as by photocurrent measurements. In the TiO2-adsorbed samples where BL was bfimbz, the electron injection kinetics was very fast and could not be resolved because an electron is promoted from the metal center to the dcb ligand directly linked to the semiconductor. In the TiO2-adsorbed samples where BL was tpphz, for which, in the excited state, a BL localization of the lowest-lying metal-to-ligand charge transfer (MLCT) is observed, slower injection rates (9.5 x 10(7) s(-1) in [(bpy)(2)Ru(tpphz)Ru(bpy)(dcb(-))](3+)/TiO2 and 5.5 x 10(7) s(-1) in [(bpy)(dcb)Ru(tpphz)Ru(bpy)(dcb(-))](3+)/TiO2) were obtained. Among the systems, the heterotriad assembly [(bpy)(2)Ru(bfimbz)Ru(bpy)(dcb(2-))](2+)/TiO2 gave the best photovoltaic performance. In the first case, this was attributed to a fast electron injection initiated from a dcb-localized MLCT; in the second case, this is attributed to improved molecular orientation on the surface, which was due to rigidity and, at the same time, linearity of the heterotriad system, resulting in a slower charge recombination between the injected electron and the hole.

Journal Article↗

PubMed2004

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.

Antineoplastic Agents↗

PubMed2004

DNA binding and photocleavage in vitro by new dirhodium(II) dppz complexes: correlation to cytotoxicity and photocytotoxicity.

Two new dirhodium(II) complexes possessing the intercalating dppz ligand (dppz = dipyrido[3,2-a:2',3'-c]phenazine), cis-[Rh(2)(mu-O(2)CCH(3))(2)(dppz)(eta(1)-O(2)CCH(3))(CH(3)OH)](+) (1) and cis-[Rh(2)(mu-O(2)CCH(3))(2)(dppz)(2)](2+) (2), were synthesized and characterized as potential agents for photochemotherapy. Various techniques show that 1 binds to DNA through intercalation, although some aggregation of the complex on the DNA surface is also present. In contrast, 2 does not intercalate between the DNA bases; however, strong hypochromic behavior is observed in the presence of DNA, which can be attributed to intermolecular pi-stacking of 2 enhanced by the polyanion. The apparent DNA binding constants determined using optical titrations are compared to those from dialysis experiments. Both complexes photocleave pUC18 plasmid in vitro under irradiation with visible light (lambda(irr) >or= 395 nm, 15 min), resulting in the nicked, circular form. Greater photocleavage is observed for 1 relative to 2, which may be due to the ability of 1 to intercalate between the DNA bases. The cytotoxicity toward human skin cells (Hs-27) measured as the concentration at which 50% cell death is recorded, LC(50), was found to be 135 +/- 8 microM for 2 in the dark (30 min), which is significantly lower than those of 1 (LC(50) = 27 +/- 2 microM) and Rh(2)(O(2)CCH(3))(4) (LC(50) = 15 +/- 2 microM). Irradiation of cell cultures containing 1 and Rh(2)(O(2)CCH(3))(4) with visible light (400-700 nm, 30 min) has little effect on their cytotoxicity, with LC(50) values of 21 +/- 3 and 13 +/- 2 microM, respectively. Interestingly, a 3.4-fold increase in the toxicity of 2 is observed when the cell cultures are irradiated (400-700 nm, 30 min), resulting in LC(50) = 39 +/- 1 microM. The greater toxicity of 1 compared to 2 in the dark may be related to the ability of the former compound to intercalate between the DNA bases. The lower cytotoxicity of 2, together with its significantly greater photocytotoxicity, makes this complex a potential agent for photodynamic therapy (PDT). These results suggest that intercalation or strong DNA binding may not be a desirable property of a potential PDT agent.

Antineoplastic Agents↗

PubMed2004

Phototoxicity against tumor cells and Sindbis virus by an octahedral rhodium bisbipyridyl complex and evidence for the genome as a target in viral photoinactivation.

An octahedral rhodium complex (cis-dichloro(dipyrido[3,2a-2',3'c]phenazine)(1,10-phenanthroline)rhodium(III) chloride; DPPZPHEN) has been prepared that can penetrate tumor cell membranes and the Sindbis viral capsid. The compound is phototoxic to these entities when irradiated with UVA light. Model studies with calf thymus and supercoiled plasmid DNA indicate that the complex can both bind with, and nick, nucleic acid. Analysis of Sindbis virus, following irradiation with the metal complex, confirmed that the viral genome was rendered noninfectious by this treatment.

Animals↗

PubMed2005

Synthesis, structure, and ligand-based reduction reactivity of trivalent organosamarium benzene chalcogenolate complexes (C(5)Me(5))(2)Sm(EPh)(THF) and [(C(5)Me(5))(2)Sm(mu-EPh)](2).

To compare the ligand-based reduction chemistry of (EPh)(-) ligands in a metallocene environment to the sterically induced reduction chemistry of the (C(5)Me(5))(-) ligands in (C(5)Me(5))(3)Sm, (C(5)Me(5))(2)Sm(EPh) (E = S, Se, Te) complexes were synthesized and treated with substrates reduced by (C(5)Me(5))(3)Sm: cyclooctatetraene; azobenzene; phenazine. Reactions of PhEEPh with (C(5)Me(5))(2)Sm(THF)(2) and (C(5)Me(5))(2)Sm produced THF-solvated monometallic complexes, (C(5)Me(5))(2)Sm(EPh)(THF), and their unsolvated dimeric analogues, [(C(5)Me(5))(2)Sm(mu-EPh)](2), respectively. Both sets of the paramagnetic benzene chalcogenolate complexes were definitively identified by X-crystallography and form homologous series. Only the (TePh)(-) complexes show reduction reactivity and only upon heating to 65 degrees C.

Journal Article↗

PubMed2006

DNA cleavage on photoexposure at the d-d band in ternary copper(II) complexes using red-light laser.

Ternary copper(II) complexes [Cu(L1)B](ClO4) (1, 2) and [Cu(L2)B](ClO4) (3, 4), where HL1 and HL2 are tridentate NSO- and ONO-donor Schiff bases and B is a heterocyclic base, viz. dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 1 and 3) or dipyrido[3,2-a:2',3'-c]phenazine (dppz, 2 and 4), were prepared and their DNA binding and photoinduced DNA cleavage activity studied. Complex 1, structurally characterized by single-crystal X-ray crystallography, shows an axially elongated square-pyramidal (4 + 1) coordination geometry in which the monoanionic L1 binds at the equatorial plane. The NN-donor dpq ligand exhibits an axial-equatorial binding mode. The complexes display good binding propensity to calf thymus DNA, giving a relative order 2 (NSO-dppz) > 4 (ONO-dppz) > 1 (NSO-dpq) > 3 (ONO-dpq). They cleave supercoiled pUC19 DNA to its nicked circular form when treated with 3-mercaptopropionic acid (MPA) by formation of hydroxyl radicals as the cleavage active species under dark reaction conditions. The photoinduced DNA cleavage activity of the complexes was investigated using UV radiation of 365 nm and red light of 633, 647.1, and 676.4 nm (CW He-Ne and Ar-Kr mixed gas ion laser sources) in the absence of MPA. Complexes 1 and 2, having photoactive NSO-donor Schiff base and dpq/dppz ligands, show dual photosensitizing effects involving both the photoactive ligands in the ternary structure with significantly better cleavage properties when compared to those of 3 and 4, having only photoactive dpq/dppz ligands. Involvement of singlet oxygen in the light-induced DNA cleavage reactions is proposed. A significant enhancement of the red-light-induced DNA cleavage activity is observed for the dpq and dppz complexes containing the sulfur ligand when compared to their earlier reported phen (1,10-phenanthroline) analogue. Enhancement of the cleavage activity on photoexposure at the d-d band indicates the occurrence of metal-assisted photosensitization processes involving the LMCT and d-d band in the ternary structure.

Copper↗

PubMed2006

Interfacial charge-transfer switch: ruthenium-dppz compounds anchored to nanocrystalline TiO2.

The compound Ru(bpy)2(dppz-R)(PF6)2, where bpy is 2,2'-bipyridine and dppz-R is 11-(diethoxyphosphorylmethyl)dipyrido[3,2-a:2',3'-c]phenazine, was prepared and anchored to mesoporous nanocrystalline (anatase) TiO2 thin films as a probe of the effects of interfacial water on excited-state charge transfer processes at semiconductor interfaces. In nitrogen-saturated fluid acetonitrile, the Ru(bpy)2(dppz-R)(PF6)2 compound was found to be highly photoluminescent. Water was found to quench the excited state by a mechanism adequately described by the Perrin model, from which the radius of quenching was abstracted, 75 +/- 2 A. The Ru(bpy)2(dppz-R)(PF6)2 compounds were found to bind to the TiO2 thin films in high surface coverages, 5 x 10(-8) mol cm(-2). When these films were immersed in acetonitrile, long-lived excited states (tau = 825 ns) that were quenched by the addition of water were observed. About 30% of the excited states could not be quenched by water. Efficient electron injection, phi(inj) = 0.8, was observed after light excitation of Ru(bpy)2(dppz-R)/TiO2 in a 0.1 M LiClO4/acetonitrile solution. The addition of large concentrations of water, >0.5 M, was found to decrease the injection yield to phi(inj) = 0.3.

Journal Article↗

PubMed1998

Tetranuclear Tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-j]phenazineruthenium Complex: Synthesis, Wide-Angle X-ray Scattering, and Photophysical Studies.

The tetranuclear ruthenium complex {Ru[(tpphz)Ru(bpy)(2)](3)}(8+), where tpphz is tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-j]phenazine, has been synthesized by reaction of [Ru(tpphz)(3)](2+) with [Ru(bpy)(2)Cl(2)] and by reaction of [Ru(bpy)(2)(tpphz)](2+) with [Ru(DMSO)(4)Cl(2)]. The large distance between the chiral centers allows full (1)H NMR interpretation despite the mixture of eight stereoisomers. The tetranuclear complex was further characterized by electrospray mass spectrometry and by the wide-angle X-ray scattering technique, which confirmed the starburst geometry. The photophysical properties of the tetranuclear complex in acetonitrile were studied and compared with those of [Ru(tpphz)(3)](2+) (1 x 10(-)(4) M acidic solution) and [(bpy)(2)Ru(tpphz)Ru(bpy)(2)](4+) model molecules. The tetranuclear complex gives rise to a single emission, attributed to metal-to-ligand charge-transfer states involving peripheral Ru centers and tpphz bridging ligands.

Journal Article↗

PubMed1999

Excited-State Electron Transfer in a Chromophore-Quencher Complex. Spectroscopic Identification of a Redox-Separated State.

In the chromophore-quencher complex fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (Aqphen is 12,17-dihydronaphtho[2,3-h]dipyrido[3,2-a:2',3'-c]-phenazine-12,17-dione; py-PTZ is 10-(4-picolyl)phenothiazine), Aqphen is a dppz derivative, containing a pendant quinone acceptor at the terminus of a rigid ligand framework. This introduces a third, low-lying, ligand-based pi acceptor level localized largely on the quinone fragment. Laser flash excitation of fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (354.7 nm; in 1,2-dichloroethane) results in the appearance of a relatively long-lived transient that decays with tau(298K) = 300 ns (k = 3.3 x 10(6) s(-)(1)). Application of transient absorption, time-resolved resonance Raman, and time-resolved infrared spectroscopies proves that this transient is the redox-separated state fac-[Re(I)(Aqphen(*)(-)())(CO)(3)(py-PTZ(*)(+)())](+) in which the excited electron is localized largely on the quinone portion of the Aqphen ligand.

Journal Article↗

PubMed1999

Absorption Spectra, Photophysical Properties, and Redox Behavior of Stereochemically Pure Dendritic Ruthenium(II) Tetramers and Related Dinuclear and Mononuclear Complexes.

The absorption spectra, luminescence properties, and redox behavior of stereochemically pure, dendritic Ru(II) tetramers have been studied. Furthermore, the investigation has also been performed on stereochemically resolved dinuclear complexes of the same family and on racemic forms of their mononuclear precursors and models. The complexes studied are the racemic species [(phen)(2)Ru(1,10-phenanthroline-5,6-dione)](PF(6))(2) (A, phen = 1,10-phenanthroline), [(phen)(2)Ru(1,10-phenanthroline-5,6-diamine)](PF(6))(2) (B), [Ru(1,10-phenanthroline-5,6-dione)(3)](PF(6))(2) (C), [(phen)(2)Ru(tpphz)](PF(6))(2) (1, tpphz = tetrapyrido[3,2-a:2',3'-c:3' ',2' '-h:2' ',3' '-j]phenazine), [(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (2), and [{(phen)(2)Ru(&mgr;-tpphz)}(3)Ru](PF(6))(8) (4), the stereochemically pure dinuclear species DeltaDelta-[(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (DeltaDelta-2), LambdaLambda-[(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (LambdaLambda-2), and DeltaLambda-[(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (DeltaLambda-2), and the stereochemically pure dendritic tetranuclear complexes [(Delta-(phen)(2)Ru(&mgr;-tpphz))(3)-Delta-Ru](PF(6))(8) (Delta(3)Delta-4), [(Delta-(phen)(2)Ru(&mgr;-tpphz))(3)-Lambda-Ru](PF(6))(8) (Delta(3)Lambda-4), and [(Lambda-(phen)(2)Ru(&mgr;-tpphz))(3)-Lambda-Ru](PF(6))(8) (Lambda(3)Lambda-4). All the complexes exhibit reversible metal-centered oxidation processes: the mononuclear complexes undergo a one-electron oxidation within the potential range +1.30 to +1.70 V vs SCE, whereas the dinuclear complexes undergo a two-electron oxidation at about +1.35 V and the tetranuclear compounds undergo a three-electron process at about +1.35 V followed by a one-electron process at +1.46 V. On reduction, each compound undergoes several reversible or quasireversible ligand-centered reductions within the potential window investigated (+2.00/-1.80 V vs SCE). The absorption spectra of the complexes exhibit intense ligand-centered (LC) bands in the UV region (epsilon up to 10(6) M(-)(1) cm(-)(1)) and moderately intense metal-to-ligand charge-transfer (MLCT) bands in the visible region (epsilon in the range 10(4)-10(5) M(-)(1) cm(-)(1)). All the complexes are luminescent both in fluid acetonitrile solution at room temperature (lambda(max) in the range 600-720 nm) and in MeOH/EtOH 4:1 (v/v) rigid matrix at 77 K (lambda(max) in the range 560-620 nm), except C which is luminescent only at 77 K. In all the cases, luminescence decays are monoexponential with lifetimes in the range 10(-)(5)-10(-)(8) s. Energy transfer occurs in the dendritic tetranuclear complexes from the central chromophore to the peripheral ones. For the oligonuclear tpphz-containing complexes, luminescence at room temperature and at 77 K originates from different MLCT states. When the experimental uncertainties are taken into account, the absorption spectra, luminescence properties, and redox behavior of the various stereoisomers studied here are practically undistinguishable one another. Comparison of our results with the photophysical results reported for other stereochemically pure luminescent multimetallic arrays is attempted.

Journal Article↗

PubMed2001

Synthesis of [Ru(phen)(2)dppz](2+)-tethered oligo-DNA and studies on the metallointercalation mode into the DNA duplex.

To explore the binding properties of [Ru(phen)(2)dppz](2+) complex (phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine) in a sequence-specific manner in DNA duplex, it was tethered through the dppz ligand to a central position as well as both at the 3'- and 5'-ends of oligodeoxyribonucleotide (ODN). The middle [Ru(phen)(2)dppz](2+)-ODN tethered was resolved and isolated as four pure diastereomers, while the 3'- or 5'-[Ru(phen)(2)dppz](2+)-ODNs were inseparable on RP-HPLC. Thermal stability of the (Ru(2+)-ODN).DNA duplexes is found to increase considerably (DeltaT(m) = 12.8-23.4 degrees C), depending upon the site of the covalent attachment of the tethered [Ru(phen)(2)dppz](2+) complex, or the chirality of the [Ru(phen)(2)dppz](2+)-linker tethered at the middle of the ODN, compared to the unlabeled counterpart. Gross differences in CD between the [Ru(phen)(2)dppz](2+)-tethered and the native DNA duplexes showed that the global duplex conformation of the former has considerably altered from the B-type, but is still recognized by DNase I. The thermal melting studies, CD measurements, as well as DNase I digestion data, are interpreted as a result of intercalation of the dppz moiety, which is realized by threading of the Ru(phen)(2) complex part through the DNA duplex core. DNase I footprinting with four diastereomerically pure middle ([Ru(phen)(2)dppz](2+)-ODN).DNA duplexes furthermore showed that the tethered [Ru(phen)(2)dppz](2+)-linker chirality dictates the stereochemical accessibility of various phosphodiester moieties (around the intercalation site) toward the cleavage reaction by the enzyme. The diastereomerically pure ruthenium-modified duplexes, with the well-defined pi-stack, will be useful to explore stereochemistry-dependent energy- and electron-transfer chemistry to understand oxidative damage to the DNA double helix as well as the long-range energy- and electron-transfer processes with DNA as a reactant.

Circular Dichroism↗

PubMed2002

Synthesis of the DNA-[Ru(tpy)(dppz)(CH(3)CN)](2+) conjugates and their photo cross-linking studies with the complementary DNA strand.

We here report our studies on the conjugation of photoreactive Ru(2+) complex to oligonucleotides (ODNs), which give a stable duplex with the complementary target DNA strand. These functionalized DNA duplexes bearing photoreactive Ru(2+) complex can be specifically photolyzed to give the reactive aqua derivative, [Ru(tpy)(dppz)(H(2)O)](2+)-ODN (tpy = 2,2':6',2' '-terpyridine; dppz = dipyrido[3,2-a:2',3'-c]phenazine), in situ, which successfully cross-links to give photoproduct(s) in the duplex form with the target complementary DNA strand. Thus, the stable precursor of the aquaruthenium complex, the monofunctional polypyridyl ruthenium complex [Ru(tpy)(dppz)(CH(3)CN)](2+), has been site-specifically tethered to ODN, for the first time, by both solid-phase synthesis and postsynthetic modifications. (i) In the first approach, pure 3'-[Ru(tpy)(dppz)(CH(3)CN)](2+)-ODN conjugate has been obtained in 42% overall yield (from the monomer blocks) by the automated solid-phase synthesis on a support labeled with [Ru(tpy)(dppz)Cl](+) complex with subsequent liberation of the crude conjugate from the support under mild conditions and displacement of the Cl(-) ligand by acetonitrile in the coordination sphere of the Ru(2+) label. (ii) In the second approach, the single-modified (3'- or 5'- or middle-modified) or 3',5'-bis-modified Ru(2+)-ODN conjugates were prepared in 28-50% yield by an amide bond formation between an active ester of the metal complex and the ODNs conjugated with an amino linker. The pure conjugates were characterized unambiguously by ultraviolet-visible (UV-vis) absorption spectroscopy, enzymatic digestion followed by HPLC quantitation, polyacrylamide gel electrophoresis (PAGE), and mass spectrometry (MALDI-TOF as well as by ESI). [Ru(tpy)(dppz)(CH(3)CN)](2+)-ODNs form highly stabilized ODN.DNA duplexes compared to the unlabeled counterpart (DeltaT(m) varies from 8.4 to 23.6 degrees C) as a result of intercalation of the dppz moiety; they undergo clean and selective photodissociation of the CH(3)CN ligand to give the corresponding aqua complex, [Ru(tpy)(dppz)(H(2)O)](2+)-ODNs (in the aqueous medium), which is evidenced from the change of their UV-vis absorption properties and the detection of the naked Ru(2+)-ODN ions generated in the course of the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric analysis. Thus, when [Ru(tpy)(dppz)(CH(3)CN)](2+)-ODN conjugate was hybridized to the complementary guanine (G)-rich target strand (T), and photolyzed in a buffer (pH 6.8), the corresponding aqua complex formed in situ immediately reacted with the G residue of the opposite strand, giving the cross-linked product. The highest yield (34%) of the photo cross-linked product obtained was with the ODN carrying two reactive Ru(2+) centers at both 3'- and 5'-ends. For ODNs carrying only one Ru(2+) complex, the yield of the cross-linked adduct in the corresponding duplex is found to decrease in the following order: 3'-Ru(2+)-ODN (22%) > 5'-Ru(2+)-ODN (9%) > middle-Ru(2+)-ODN (7%). It was also found that the photo cross-coupling efficiency of the tethered Ru(2+) complex with the target T strand decreased as the stabilization of the resulting duplex increased: 3'-Ru(2+)-ODN (VI.T) (DeltaT(m)(b) = 7 degrees C) < 5'-Ru(2+)-ODN (V.T) (DeltaT(m)(b) = 16 degrees C) < middle-Ru(2+)-ODN (VII.T) (DeltaT(m)(b) = 24.3 degrees C, Table 2). This shows that, with the rigidly packed structure, as in the duplex with middle-Ru(2+)-ODN, the metal center flexibility is considerably reduced, and consequently the accessibility of target G residue by the aquaruthunium moiety becomes severely restricted, which results in a poor yield in the cross-coupling reaction. The cross-linked product was characterized by PAGE, followed by MALDI-TOF MS.

Chromatography, High Pressure Liquid↗

PubMed2003

Design of novel inorganic-organic hybrid materials based on iron-chloranilate mononuclear complexes: characteristics of hydrogen-bond-supported layers toward the intercalation of guests.

Novel intercalation compounds constructed from the common two-dimensional hydrogen-bond-supported layers and functional guests [(H(0.5)phz)(2)[Fe(CA)(2)(H(2)O)(2)].2H(2)O](n)(1), ([Fe(Cp)(2)][Fe(CA)(2)(H(2)O)(2)])(n)(2), ([Fe(Cp*)(2)][Fe(CA)(2)(H(2)O)(2)])(n)(3), and [(TTF)(2)[Fe(CA)(2)(H(2)O)(2)]](n)(4) (H(2)CA = chloranilic acid, phz = phenazine, [Fe(Cp)(2)] = ferrocene, [Fe(Cp*)(2)] = decamethylferrocene, TTF = tetrathiafulvalene) are described. The guest cations are introduced between the ([Fe(CA)(2)(H(2)O)(2)](m-))(l) layers by electrostatic (1-4) and pi-pi stacking (3, 4) interactions. [Fe(Cp*)(2)](+) cations in 3 are stacked on each other making tilted columns which are included in the channel created by the chlorine atoms of CA(2-) dianions. TTF cations in 4 are stacked face to face with two types of S...S distances (type A; 3.579(3) A, and type B; 3.618(3) A) making a columnar structure. The TTF cations in the stacked column have a head-to-tail arrangement with respect to the iron-chloranilate layer. Mössbauer spectroscopy suggests that [Fe(CA)(2)(H(2)O)(2)](m-) anion in 3 is consistent with high-spin (S = 5/2) iron(III) ions and [Fe(Cp*)(2)](+) in the low-spin (S = 1/2) iron(III) ions. In 4, Mössbauer spectroscopy shows high-spin iron(II) ions (IS = 1.10 mm.s(-1) and QS = 1.66 mm.s(-1) at 297 K) and high-spin iron(III) ions (IS = 0.42 mm.s(-1) and QS = 1.27 mm.s(-1) at 297 K), suggesting that the anionic layer of iron-chloranilate has a valence-trapped mixed-valence state. At the temperature range of 77-300 K, the compounds 1, 2, and 3 are EPR silent, whereas the EPR spectrum of 4 shows two types of signals with g = 2.008 indicating the radical form of TTF.

Journal Article↗

PubMed2003

Ultrafast processes in bimetallic dyads with extended aromatic bridges. Energy and electron transfer pathways in tetrapyridophenazine-bridged complexes.

The energy and electron transfer processes taking place in binuclear polypyridine complexes of ruthenium and osmium based on the tetrapyrido[3,2-a:2',3'-c:3' ',2' '-h:2' "-3' "-j]phenazine bridging ligand (tpphz) have been investigated by ultrafast absorption spectroscopy. In the binuclear complexes, each chromophore is characterized by two spectrally distinguishable metal-to-ligand charge transfer (MLCT) excited states: MLCT1 (with promoted electron mainly localized on the bpy-like portion of tpphz, higher energy) and MLCT0 (with promoted electron mainly localized on the pyrazine-like portion of tpphz, lower energy). In the homodinuclear complexes Ru(II)-Ru(II) and Os(II)-Os(II), MLCT1 --> MLCT0 relaxation (intraligand electron transfer) is observed, with strongly solvent-dependent kinetics (ca. 10(-10) s in CH2Cl2, ca. 10(-12) s in CH3CN). In the heterodinuclear Ru(II)-Os(II) complex, *Ru(II)-Os(II) --> Ru(II)-Os(II) energy transfer takes place by two different sequences of time-resolved processes, depending on the solvent: (a) in CH2Cl2, ruthenium-to-osmium energy transfer at the MLCT1 level followed by MLCT1 --> MLCT0 relaxation in the osmium chromophore, (b) in CH3CN, MLCT1 --> MLCT0 relaxation in the ruthenium chromophore followed by osmium-to-ruthenium metal-to-metal electron transfer. In the mixed-valence Ru(II)-Os(III) species, the *Ru(II)-Os(III) --> Ru(III)-Os(II) electron transfer quenching is found to proceed by two consecutive steps in CH3CN: intraligand electron transfer followed by ligand-to-metal electron transfer. On a longer time scale, charge recombination leads back to the ground state. Altogether, the results show that the tpphz bridge plays an active mechanistic role in these systems, efficiently mediating the transfer processes with its electronic levels.

Journal Article↗

PubMed2004

Effects of methyl substitution on radiative and solvent quenching rate constants of [Ru(phen)2dppz]2+ in polyol solvents and bound to DNA.

Methyl substituents on the distant benzene ring of the dppz ligand in the "light switch" complex [Ru(phen)(2)dppz](2+) have profound effects on the photophysics of the complexes in water as well as in the polyol solvents ethylene glycol, glycerol, and 1,2- and 1,3-propanediol. Whereas 11,12-dimethyl substitution decreases the rate of quenching by diminishing hydrogen bonding by solvent, the 10-methyl substituent in addition also decreases both the radiative and the nonradiative rate constant for decay to the ground state of the non-hydrogen-bonded excited state species. For both the 10-methyl and the 11,12-dimethyl derivatives, the effect of methyl substitution on the equilibrium of solvent hydrogen bonding to the excited state is due to changes in the entropy terms, rather than in the enthalpy, indicating that the effect is a steric perturbation of the solvent cage around the molecule. When intercalated into DNA, the effects of methyl substitution is smaller than those in polyol solvent or water, suggesting that the water molecules that quench the excited state by hydrogen bonding to the phenazine aza nitrogens mainly access them from the same groove as in which the Ru(II) ion resides. Since the Delta-enantiomer of [Ru(phen)(2)10-methyl-dppz](2+) has an absolute quantum yield of up to 0.23 when bound to DNA, a value 7000 times higher than in pure water solution, it is promising as a new luminescent DNA probe.

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