Marked differences in light-switch behavior of Ru(II) complexes possessing a tridentate DNA intercalating ligand

The tridentate ligand 3-(pyrid-2'-yl)dipyrido[3,2-a:2',3'-c]phenazine (pydppz) has been prepared in two steps by elaboration of 2-(pyrid-2'-yl)-1,10-phenanthroline. Both homoleptic [Ru(pydppz)(2)](2+) and heteroleptic [Ru(tpy)(pydppz)](2+) (tpy = 2,2';6',2' '-terpyridine) complexes have been prepared and characterized by (1)H NMR. The absorption and emission spectra are consistent with low-lying MLCT excited states, which are typical of Ru(II) complexes. Femtosecond transient absorption measurements show that that the (3)MLCT excited state of the heteroleptic complex [Ru(tpy)(pydppz)](2+) (tau approximately 5 ns) is longer-lived than that of the homoleptic complex [Ru(pydppz)(2)](2+) (tau = 2.4 ns) and that these lifetimes are significantly longer than that of the (3)MLCT state of the parent complex [Ru(tpy)(2)](2+) (tau = 120 ps). These differences are explained by the lower-energy (3)MLCT excited state present in [Ru(tpy)(pydppz)](2+) and [Ru(pydppz)(2)](2+) compared to [Ru(tpy)(2)](2+), resulting in less deactivation of the former through the ligand-field state(s). DFT and TDDFT calculations are consistent with this explanation. [Ru(tpy)(pydppz)](2+) and [Ru(pydppz)(2)](2+) bind to DNA through the intercalation of the pydppz ligand; however, only the heteroleptic complex exhibits luminescence enhancement in the presence of DNA. The difference in the photophysical behavior of the complexes is explained by the inability of [Ru(pydppz)(2)](2+) to intercalate both pydppz ligands, such that one pydppz always remains exposed to the solvent. DNA photocleavage is observed for [Ru(tpy)(pydppz)](2+) in air, but not for [Ru(pydppz)(2)](2+). The DNA damage likely proceeds through the production of small amounts of (1)O(2) by the longer-lived complex. Although both complexes possess the intercalating pydppz ligand, they exhibit different photophysical properties in the presence of DNA.     

Stabilization of G-quadruplex DNA, inhibition of telomerase activity and live cell imaging studies of chiral ruthenium(II) complexes

Telomerase inhibition is an attractive strategy for cancer chemotherapy. In the current study, we have synthesized and characterized two chiral ruthenium(II) complexes, namely, Λ-[Ru(phen)(2)(p-MOPIP)](2+) and Δ-[Ru(phen)(2)(p-MOPIP)](2+), where phen is 1,10-phenanthroline and p-MOPIP is 2-(4-methoxyphenyl)-imidazo[4,5f][1,10]phenanthroline. The chiral selectivity of the compounds and their ability to discriminate quadruplex DNA were investigated by using UV/Vis, fluorescence spectroscopy, circular dichroism spectroscopy, fluorescence resonance energy transfer melting assay, polymerase chain reaction stop assay and telomerase repeat amplification protocol. The results indicate that the two chiral compounds could induce and stabilize the formation of antiparallel G-quadruplexes of telomeric DNA in the presence or absence of metal cations. We report the remarkable ability of the two complexes Λ-[Ru(phen)(2)(p-MOPIP)](2+) and Δ-[Ru(phen)(2)(p-MOPIP)](2+) to stabilize selectively G-quadruplex DNA; the former is a better G-quadruplex binder than the latter. The anticancer activities of these complexes were evaluated by using the MTT assay. Interestingly, the antiproliferative activity of Λ-[Ru(phen)(2)(p-MOPIP)](2+) was higher than that of Δ-[Ru(phen)(2)(p-MOPIP)](2+), and Λ-[Ru(phen)(2)(p-MOPIP)](2+) showed a significant antitumor activity in HepG2 cells. The status of the nuclei in Λ/Δ-[Ru(phen)(2) (p-MOPIP)](2+)-treated HepG2 cells was investigated by using real-time living cell microscopy to determine the effects of Λ/Δ-[Ru(phen)(2)(p-MOPIP)](2+) on intracellular accumulation. The results show that Λ/Δ-[Ru(phen)(2)(p-MOPIP)](2+) can be taken up by HepG2 cells and can enter into the cytoplasm as well as accumulate in the nuclei; this suggests that the nuclei were the cellular targets of Λ/Δ-[Ru(phen)(2)(p-MOPIP)](2+).     

DNA mismatch detection by resonance energy transfer between ruthenium(II) and osmium(II) tris(2,2'-bipyridyl) chromophores

Octahedral tris-chelate complexes [M(II)(bpy)(3)](2+) (M = Ru or Os, bpy = 2,2'-bipyridyl), covalently attached to the 3'- and 5'-phosphates of two oligonucleotides, are juxtaposed when hybridized contiguously to a fully complementary DNA target. Visible metal-to-ligand charge-transfer (MLCT) excitation of the [Ru(II)(bpy)(3)](2+) unit leads to resonance energy transfer to the MLCT state of the [Os(II)(bpy)(3)](2+) moiety, with the energy transfer efficiency depending on the degree of hybridization. The extent of attenuation of the intense red luminescence from the Ru(II) chromophore hence allows highly sensitive structural probing of the assembly and constitutes a novel approach to DNA sensing which is capable of detecting mutations.     

Preparation of a [Ru(bpy)2(dppz)]2+-intercalated DNA cast film using a self-standing method and its luminescence tuning by Cu2+ ions and EDTA

In this correspondence, we report on the first preparation of [Ru(bpy)(2)(dppz)](2+)-intercalated (bpy = 2,2'-bipyridine; dppz = dipyrido[3,2-a:2',3'-c]phenazine) DNA films on an indium-tin oxide surface via a solution-based self-standing strategy, carried out by the direct mixing of aqueous solutions of both anionic DNA and cationic metallointercalator at a molar ratio of 5:6. The luminescence of a [Ru(bpy)(2)(dppz)](2+)-intercalated DNA cast film is studied and found to show excellent tunable characteristics by Cu(2+) ions and ethylenediaminetetraacetic acid addition.     

Preparation and multicolor electrochromic performance of a WO3/tris(2,2'-bipyridine)ruthenium(II)/polymer hybrid film

A tungsten trioxide (WO(3))/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+); bpy=2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) hybrid film was prepared by electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and PSS. A binary solution of [Ru(bpy)(3)](2+) and PTA (30 vol % ethanol in water) gradually gave an orange precipitate, possibly caused by the electrostatic interaction between the cationic [Ru(bpy)(3)](2+) and the anionic PTA. The addition of PSS to the binary PTA/[Ru(bpy)(3)](2+) solution remarkably suppressed this precipitation and caused a stable, colloidal triad solution to form. The spectrophotometric measurements and lifetime analyses of the photoluminescence from the excited [Ru(bpy)(3)](2+) ion in the colloidal triad solution suggested that the [Ru(bpy)(3)](2+) ion is partially shielded from electrostatic interaction with anionic PTA by the anionic PSS polymer chain. The formation of the colloidal triad made the ternary [Ru(bpy)(3)](2+)/PTA/PSS solution much more redox active. Consequently, the rate of electrodeposition of WO(3) from PTA increased appreciably by the formation of the colloidal triad, and fast electrodeposition is required for the unique preparation of this hybrid film. The absorption spectrum of the [Ru(bpy)(3)](2+) ion in the film was close to its spectrum in water, but the photoexcited state of the [Ru(bpy)(3)](2+) ion was found to be quenched completely by the presence of WO(3) in the hybrid film. The cyclic voltammogram (CV) of the hybrid film suggested that the [Ru(bpy)(3)](2+) ion performs as it is adsorbed onto WO(3) during the electrochemical oxidation. An ohmic contact between the [Ru(bpy)(3)](2+) ion and the WO(3) surface could allow the electrochemical reaction of adsorbed [Ru(bpy)(3)](2+). The composition of the hybrid film, analyzed by electron probe microanalysis (EPMA), suggested that the positive charge of the [Ru(bpy)(3)](2+) ion could be neutralized by partially reduced WO(3)(-) ions, in addition to Cl(-) and PSS units, based on the charge balance in the film. The electrostatic interaction between the WO(3)(-) ion and the [Ru(bpy)(3)](2+) ion might be responsible for forming the electron transfer channel that causes the complete quenching of the photoexcited [Ru(bpy)(3)](2+) ion, as well as the formation of the ohmic contact between the [Ru(bpy)(3)](2+) ion and WO(3). A multicolor electrochromic performance of the WO(3)/[Ru(bpy)(3)](2+)/PSS hybrid film was observed, in which transmittances at 459 and 800 nm could be changed, either individually or at once, by the selection of a potential switch. Fast responses, of within a few seconds, to these potential switches were exhibited by the electrochromic hybrid film.     

Interaction of rac-[Ru(5,6-dmp)3]2+ with DNA: enantiospecific DNA binding and ligand-promoted exciton coupling

The X-ray crystal structure of the complex rac-[Ru(5,6-dmp)(3)]Cl(2) (5,6-dmp = 5,6-dimethyl-1,10-phenanthroline) reveals a distorted octahedral coordination geometry with the Ru-N bond distances shorter than in its phen analogue. Absorption spectral titrations with CT DNA reveal that rac-[Ru(5,6-dmp)(3)](2+) interacts (K(b), (8.0 +/- 0.2) x 10(4) M(-1)) much more strongly than its phen analogue. The emission intensity of the 5,6-dmp complex is dramatically enhanced on binding to DNA, which is higher than that of the phen analogue. Also, interestingly, time-resolved emission measurements on the DNA-bound complex shows biexponential decay of the excited states with the lifetimes of short- and long-lived components being higher than those for the phen analogue. The CD spectral studies of rac-[Ru(5,6-dmp)(3)](2+) bound to CT DNA provide a definite and elegant evidence for the enantiospecific interaction of the complex with B-form DNA. Competitive DNA binding studies using rac-[Ru(phen)(3)](2+) provide support for the strong binding of the complex with DNA. The Delta-enantiomer of rac-[Ru(5,6-dmp)(3)](2+) binds specifically to the right-handed B-form of poly d(GC)(12) at lower ionic strength (0.05 M NaCl), and the Lambda-enantiomer binds specifically to the left-handed Z-form of poly d(GC)(12) generated by treating the B-form with 5 M NaCl. The strong electronic coupling of the DNA-bound complex with the unbound complex facilitates the change in its enantiospecificity upon changing the conformation of DNA. The (1)H NMR spectra of rac-[Ru(5,6-dmp)(3)](2+) bound to poly d(GC)(12) reveal that the complex closely interacts most possibly in the major grooves of DNA. Electrochemical studies using ITO electrode show that the 5,6-dmp complex stabilizes CT DNA from electrocatalytic oxidation of its guanine base more than the phen analogue does.     

Entrapment of [Ru(bpy)3]2+ in the anionic metal-organic framework: novel photoluminescence behavior exhibiting dual emission at room temperature

[Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) ions were entrapped into the cavities of two-dimensional anionic sheet-like coordination polymeric networks of [M(dca)(3)](-) (dca = dicyanamide; M = Mn(II) and Fe(II)). The prepared compounds, {[Ru(bpy)(3)][Mn(dca)(3)](2)}(n) (1) and {[Ru(bpy)(3)][Fe(dca)(3)](2)}(n) (2), were structurally characterized by X-ray single crystal analysis. The spectroscopic properties of the [Ru(bpy)(3)](2+) ion dramatically changed on its entrapment in [M(dca)(3)](-). The [Ru(bpy)(3)](2+) moiety present in 1 and 2 exhibits novel dual photo-emission at room temperature.     

Photodriven electron and energy transfer from a light-harvesting metallodendrimer

Intermolecular electron and energy transfer from a light-harvesting metallodendrimer [Ru[bpy(C-450)(4)](3)](2+), where bpy(C-450)(4) is a 2,2'-bipyridine derivative containing 4 coumarin-450 units connected together through aryl ether linkages, is observed in acetonitrile solutions at room temperature. The model complex [Ru(dmb)(3)](2+), where dmb is 4,4'-dimethyl-2,2'-bipyridine, is included for quantitative comparison. The excited states of both compounds are metal-to-ligand charge transfer in nature and participate in excited-state electron and triplet energy transfer processes. Quenching constants were determined from luminescence and time-resolved absorption experiments at constant ionic strength. [Ru[bpy(C-450)(4)](3)](2+) displays significantly slower quenching rates to molecular oxygen and methyl viologen relative to the other processes investigated. Triplet energy transfer from [Ru[bpy(C-450)(4)](3)](2+) to 9-methylanthracene is quantitatively indistinguishable from [Ru(dmb)(3)](2+) while reductive electron transfer from phenothiazine was slightly faster in the former. With the exception of dioxygen quenching, our results indicate that the current dendritic structure is ineffective in shielding the core from bimolecular electron and triplet energy transfer reactions. Electrochemical measurements of [Ru[bpy(C-450)(4)](3)](2+) reveal irreversible oxidative processes at potentials slightly negative to the Ru(III/II) potential that are assigned to oxidations in the dendritic structure. Excited-state oxidative electron-transfer reactions facilitate this process resulting in the reduction of ground-state Ru(III) to Ru(II) and the trapping of the methyl viologen radical cation (MV(*+)) when methyl viologen serves as the quencher. This process generates a minimum of 9 MV(*+)'s for every [Ru[bpy(C-450)(4)](3)](2+) molecule and disassembles the metallodendrimer, resulting in the production of a [Ru(dmb)(3)](2+)-like species and "free" C-450-like dyes.     

Photoinitiated DNA Binding by cis-[Ru(bpy)2(NH3)2]2+

The ligand-loss photochemistry of cis-[Ru(bpy)(2)(NH(3))(2)](2+) (bpy = 2,2'-bipyridine) was investigated in water and in the presence of added ligands such as bipyridine and chloride. Irradiation of the complex results in the covalent binding to 9-methyl- and 9-ethylguanine, as well as to single-stranded and double-stranded DNA. This photoinduced DNA binding is not observed for the control complex [Ru(bpy)(2)(en)](2+) (en = ethylenediamine) under similar irradiation conditions. The results presented here show that octahedral Ru(II) complexes with photolabile ligands may prove useful as photoactivated cisplatin analogs.     

A ruthenium(II) complex based turn-on electrochemiluminescence probe for the detection of nitric oxide

Electrochemiluminescence (ECL) detection technique using bipyridine-ruthenium(II) complexes as probes is a highly sensitive and widely used method for the detection of various biological and bioactive molecules. In this work, the spectral, electrochemical and ECL properties of a chemically modified bipyridine-ruthenium(II) complex, [Ru(bpy)(2)(dabpy)](2+) (bpy: 2,2'-bipyridine; dabpy: 4-(3,4-diaminophenoxy)-2,2'-bipyridine), were investigated and compared with those of its nitric oxide (NO)-reaction derivative [Ru(bpy)(2)(T-bpy)](2+) (T-bpy: 4-triazolephenoxy-2,2'-bipyridine) and [Ru(bpy)(3)](2+). It was found that the ECL intensity of [Ru(bpy)(2)(dabpy)](2+) could be selectively and sensitively enhanced by NO due to the formation of [Ru(bpy)(2)(T-bpy)](2+) in the presence of tri-n-propylamine. By using [Ru(bpy)(2)(dabpy)](2+) as a probe, a sensitive and selective ECL method with a wide linear range (0.55 to 220.0 μM) and a low detection limit (0.28 μM) was established for the detection of NO in aqueous solutions and living cells. The results demonstrated the utility and advantages of the new ECL probe for the detection of NO in complicated biological samples.     

Surface confinement and its effects on the luminescence quenching of a ruthenium-containing metallopolymer

Luminescence quenching of the metallopolymers [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(PVP)(10)Os(bpy)(2)](4+), both in solution and as thin films, is reported, where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine). When the metallopolymer is dissolved in ethanol, quenching of the ruthenium excited state, Ru(2+*), within [Ru(bpy)(2)(PVP)(10)](2+) by [Os(bpy)(3)](2+) proceeds by a dynamic quenching mechanism and the rate constant is (1.1 +/- 0.1) x 10(11) M(-1) s(-1). This quenching rate is nearly two orders of magnitude larger than that found for quenching of monomeric [Ru(bpy)(3)](2+) under the same conditions. This observation is interpreted in terms of an energy transfer quenching mechanism in which the high local concentration of ruthenium luminophores leads to a single [Os(bpy)(3)](2+) centre quenching the emission of several ruthenium luminophores. Amplifications of this kind will lead to the development of more sensitive sensors based on emission quenching. Quenching by both [Os(bpy)(3)](2+) and molecular oxygen is significantly reduced within a thin film of the metallopolymer. Significantly, in both optically driven emission and electrogenerated chemiluminescence, emission is observed from both ruthenium and osmium centres within [Ru(bpy)(2)(PVP)(10)Os(bpy)(2)](4+) films, i.e. the ruthenium emission is not quenched by the coordinated [Os(bpy)(2)](2+) units. This observation opens up new possibilities in multi-analyte sensing since each luminophore can be used to detect separate analytes, e.g. guanine and oxoguanine.     

Water oxidation by mononuclear ruthenium complexes with TPA-based ligands

The synthesis, characterization, and water oxidation activity of mononuclear ruthenium complexes with tris(2-pyridylmethyl)amine (TPA), tris(6-methyl-2-pyridylmethyl)amine (Me(3)TPA), and a new pentadentate ligand N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy) have been described. The electrochemical properties of these mononuclear Ru complexes have been investigated by both experimental and computational methods. Using Ce(IV) as oxidant, stoichiometric oxidation of water by [Ru(TPA)(H(2)O)(2)](2+) was observed, while Ru(Me(3)TPA)(H(2)O)(2)](2+) has much less activity for water oxidation. Compared to [Ru(TPA)(H(2)O)(2)](2+) and [Ru(Me(3)TPA)(H(2)O)(2)](2+), [Ru(DPA-Bpy)(H(2)O)](2+) exhibited 20 times higher activity for water oxidation. This study demonstrates a new type of ligand scaffold to support water oxidation by mononuclear Ru complexes.     

Photocatalytic generation of a non-heme oxoiron(IV) complex with water as an oxygen source

The photocatalytic formation of a non-heme oxoiron(IV) complex, [(N4Py)Fe(IV)(O)](2+) [N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine], efficiently proceeds via electron transfer from the excited state of a ruthenium complex, [Ru(II)(bpy)(3)](2+)* (bpy = 2,2'-bipyridine) to [Co(III)(NH(3))(5)Cl](2+) and stepwise electron-transfer oxidation of [(N4Py)Fe(II)](2+) with 2 equiv of [Ru(III)(bpy)(3)](3+) and H(2)O as an oxygen source. The oxoiron(IV) complex was independently generated by both chemical oxidation of [(N4Py)Fe(II)](2+) with [Ru(III)(bpy)(3)](3+) and electrochemical oxidation of [(N4Py)Fe(II)](2+).     

Photophysical and novel charge-transfer properties of adducts between [RuII(bpy)3]2+ and [S2Mo18O62]4-

The photophysical properties of acetonitrile solutions of [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) are described. We discuss evidence for ion cluster formation in solution and the observation that despite the strong donor ability of the excited state of [Ru(bpy)(3)](2+) and its inherent photolability, adducts with [S(2)Mo(18)O(62)](4-) were photostable. Photophysical studies suggest that the quenching of the [Ru(bpy)(3)](2+) excited state by [S(2)Mo(18)O(62)](4-) occurs via a static mechanism and that binding is largely electrostatic in nature. Evidence is provided from difference spectroscopy and luminescence excitation spectroscopy for good electronic communication between [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) with the presence of a novel, luminescent, inter-ion charge-transfer transition. The identity of the transition is confirmed by resonance Raman spectroscopy.     

Comparison of Physical and Photophysical Properties of Monometallic and Bimetallic Ruthenium(II) Complexes Containing Structurally Altered Diimine Ligands

The physical and photophysical properties of a series of monometallic, [Ru(bpy)(2)(dmb)](2+), [Ru(bpy)(2)(BPY)](2+), [Ru(bpy)(Obpy)](2+) and [Ru(bpy)(2)(Obpy)](2+), and bimetallic, [{Ru(bpy)(2)}(2)(BPY)](4+) and [{Ru(bpy)(2)}(2)(Obpy)](4+), complexes are examined, where bpy is 2,2'-bipyridine, dmb is 4,4'-dimethyl-2,2'-bipyridine, BPY is 1,2-bis(4-methyl-2,2'-bipyridin-4'-yl)ethane, and Obpy is 1,2-bis(2,2'-bipyridin-6-yl)ethane. The complexes display metal-to-ligand charge transfer transitions in the 450 nm region, intraligand pi --> pi transitions at energies greater than 300 nm, a reversible oxidation of the ruthenium(II) center in the 1.25-1.40 V vs SSCE region, a series of three reductions associated with each coordinated ligand commencing at -1.3 V and ending at approximately -1.9 V, and emission from a (3)MLCT state having energy maxima between 598 and 610 nm. The Ru(III)/Ru(II) oxidation of the two bimetallic complexes is a single, two one-electron process. Relative to [Ru(bpy)(2)(BPY)](2+), the Ru(III)/Ru(II) potential for [Ru(bpy)(2)(Obpy)](2+) increases from 1.24 to 1.35 V, the room temperature emission lifetime decreases from 740 to 3 ns, and the emission quantum yield decreases from 0.078 to 0.000 23. Similarly, relative to [{Ru(bpy)(2)}(2)(BPY)](4+), the Ru(III)/Ru(II) potential for [{Ru(bpy)(2)}(2)(Obpy)](4+) increases from 1.28 to 1.32 V, the room temperature emission lifetime decreases from 770 to 3 ns, and the room temperature emission quantum yield decreases from 0.079 to 0.000 26. Emission lifetimes measured in 4:1 ethanol:methanol were temperature dependent over 90-360 K. In the fluid environment, emission lifetimes display a biexponential energy dependence ranging from 100 to 241 cm(-)(1) for the first energy of activation and 2300-4300 cm(-)(1) for the second one. The smaller energy is attributed to changes in the local matrix of the chromophores and the larger energy of activation to population of a higher energy dd state. Explanations for the variations in physical properties are based on molecular mechanics calculations which reveal that the Ru-N bond distance increases from 2.05 ? (from Ru(II) to bpy and BPY) to 2.08 ? (from Ru(II) to Obpy) and that the metal-to-metal distance increases from approximately 7.5 ? for [{Ru(bpy)(2)}(2)(Obpy)](4+) to approximately 14 ? for [{Ru(bpy)(2)}(2)(BPY)](4+).     

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.     

Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [Ru(II)(2)Fe(II)(2)(mu-CN)(4)(bpy)(8)](PF6)(4).CHCl(3).H(2)O

A cyanide-bridged molecular square of [Ru(II) (2)Fe(II) (2)(mu-CN)(4)(bpy)(8)](PF(6))(4).CHCl(3).H(2)O, abbreviated as [Ru(II) (2)Fe(II) (2)](PF(6))(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [Ru(II) (2)Fe(II) (2)](4+) is nearly a square and is composed of alternate Ru(II) and Fe(II) ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [Ru(II) (2)Fe(II) (2)](PF(6))(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70 V (vs. SSCE), which correspond to the four one-electron redox processes of [Ru(II) (2)Fe(II) (2)](4+) right arrow over left arrow [Ru(II) (2)Fe(II)Fe(III)] (5+) right arrow over left arrow [Ru(II) (2)Fe(III) (2)](6+) right arrow over left arrow [Ru(II)Ru(III)Fe(III) (2)](7+) right arrow over left arrow [Ru(III) (2)Fe(III) (2)](8+). Electrochemically generated [Ru(II) (2)Fe(II)Fe(III)](5+) and [Ru(II) (2)Fe(III) (2)](6+) showed new absorption bands at 2350 nm (epsilon =5500 M(-1) cm(-1)) and 1560 nm (epsilon =10 500 M(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fe(II) to Fe(III) and from Ru(II) to Fe(III) ions, respectively. The electronic interaction matrix elements (H(AB)) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [Ru(II) (2)Fe(II)Fe(III) (2)](5+) state and 1990 cm(-1) and 0.065 for the [Ru(II) (2)Fe(III) (2)](6+) states.     

Reactions of [Ru(H(2)O)(6)](2+) with water-soluble tertiary phosphines

In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction.     

Self assembled composites of luminescent Ru(II) metallopolymers and the Dawson polyoxometalate α-[Mo18O54(SO4)2]4-

The interaction of two luminescent metallopolymers; [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP)co-poly(7)](+), where bpy is 2,2'-bipyridyl, PVP is polyvinylpyridine, and (CAIP)co-poly(7) is poly(styrene(6)-co-p-(aminomethyl)styrene) amide linked to 2-(4-carboxyphenyl)imidazo[4,5-f] [1,10]phenanthroline, with the Dawson polyoxomolybdate α-[Mo(18)O(54)(SO(4))(2)](4-) is described. Both metallopolymers undergo electrostatic association with the polyoxometalate. From both electronic and luminescence spectroscopy the thermodynamic products were determined to be {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) and {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+), i.e. in both instances, the number of ruthenium centres in the cluster exceeds the number required for charge neutralization of the molybdate centre. Association quenches the luminescence of the metallopolymer although, consistent with the excess of Ru(ii) present in the associated composites, emission is not completely extinguished even when a large excess of [Mo(18)O(54)(SO(4))(2)](4-) is present. The observed emission lifetime was not affected by [Mo(18)O(54)(SO(4))(2)](4-) therefore quenching was deemed static. The luminescent intensity data was found to fit best to a (sphere of action) Perrin model from which the radii of the quenching were calculated as 4.6 ? and 5.8 ? for [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP co-poly)(7)](+) respectively. Both UV/Vis and resonance Raman data indicate the presence of a new optical transition centered around 490 nm for the composite, {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). This indicates strong electronic interaction between the metal centres in the former composite, which despite good thermodynamic analogy, is not observed for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). These results are consistent with photoelectrochemical studies of layer by layer assemblies of these films which indicate that the ruthenium centre sensitizes polyoxometalate photo-oxidation of benzyl alcohol in {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not in {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+).     

Linear-type S-bridged triruthenium complexes with aliphatic aminothiolate ligands: synthesis, characterization, and properties

Treatment of [RuCl(2)(DMSO)(4)] with 2-aminoethanethiol (Haet) in ethanol gave a dicationic triruthenium complex, [Ru[Ru(aet)(3)](2)]Cl(2) ([1]Cl(2)). Complex [1]Cl(2) was also obtained by treatment of RuCl(3).nH(2)O with excess Haet in water. When [1](2+) was chromatographed on a cation-exchange column of SP-Sephadex C-25, meso (DeltaLambda) and racemic (DeltaDelta/LambdaLambda) isomers of the corresponding tricationic complex, [Ru[Ru(aet)(3)](2)](3+) ([2](3+)), were eluted with aqueous NaNO(3). The racemic isomer of [2](3+) was optically resolved into DeltaDelta and LambdaLambda isomers by using [Sb(2)(R,R-tartrato)(2)](2-) as a resolving agent. The molecular structures of DeltaLambda- and DeltaDelta/LambdaLambda-[2](NO(3))(3) were determined by X-ray crystallography. In these complexes, the central Ru atom is coordinated by six thiolato groups from two terminal fac-(S)-[Ru(aet)(3)] units in an octahedral geometry, forming a linear-type S-bridged triruthenium structure. The spectroelectrochemical studies on the electronic absorption and CD spectra, together with the electrochemical studies, demonstrated that [1](2+) and [2](3+) are interconvertible with each other through a one-electron redox process, retaining the chirality of the triruthenium structure. Their electronic structures were investigated on the basis of EPR and magnetic susceptibility measurements, which indicated that [1](2+) and [2](3+) have spin ground states of S(t) = 0 and S(t) = 1/2, respectively. The corresponding L-cysteinato complex, [Ru[Ru(L-cys-N,S)(3)](2)](3-), which was formed from RuCl(3).nH(2)O and excess L-cysteine (L-H(2)cys) in water followed by air oxidation, is also presented.