Mechanistic Investigation into DNA Modification by a RuII ,RhIII Bimetallic Complex.

Despite significant progress in the treatment of cancer, there remains an urgent need for more effective therapies that also have less impact on patient wellbeing. Photodynamic therapy employs targeted light activation of a photosensitizer in selected tissues, thereby reducing off-target toxicity. Our group previously reported a RuII ,RhIII bimetallic architecture that displays multifunctional covalent photomodification of DNA in the therapeutic window in an oxygen-independent manner, features that are essential for treating deep and hypoxic tumors. Herein, we explore the mechanism by which a new analogue, [(phen)2 Ru(dpp)Rh(phen)Cl2 ]3+ , or RuII -RhIII , interacts with DNA. We established that RuII -RhIII exhibits "light switch" behavior in the presence of DNA, undergoing strong electrostatic interactions that might involve groove binding. Furthermore, these noncovalent interactions play a major role in the covalent photobinding and photocleavage of DNA, which occur according to an oxygen-independent mechanism. Polymerase chain reaction (PCR) revealed that covalent modification of DNA by RuII -RhIII , especially photobinding, is critical to inhibiting amplification, thus suggesting that the complex could exert its toxic activity by interfering with DNA replication in cells. This new structural motif, with phenanthroline at all three terminal ligand positions, has a number of properties that are promising for the continued refinement of photodynamic-therapy strategies.

Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts.

Supramolecular mixed metal complexes combining the trimetallic chromophore [{(bpy)2Ru(dpp)}2Ru(dpp)]6+ (Ru3) with [Rh(bpy)Cl2]+ or [RhCl2]+ catalytic fragments to form [{(bpy)2Ru(dpp)}2Ru(dpp)RhCl2(bpy)](PF6)7 (Ru3Rh) or [{(bpy)2Ru(dpp)}2Ru(dpp)]2RhCl2(PF6)13 (Ru3RhRu3) (bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) catalyze the photochemical reduction of protons to H2. This first example of a heptametallic Ru,Rh photocatalyst produces over 300 turnovers of H2 upon photolysis of a solution of acetonitrile, water, triflic acid, and N,N-dimethylaniline as an electron donor. In contrast, the tetrametallic Ru3Rh produces only 40 turnovers of H2 due to differences in the excited state properties and nature of the catalysts upon reduction as ascertained from electrochemical data, transient absorption spectroscopy, and flash-quench experiments. While the lowest unoccupied molecular orbital of Ru3Rh is localized on a bridging ligand, it is Rh-centered in Ru3RhRu3 facilitating electron collection at Rh in the excited state and reductively quenched state. The Ru → Rh charge separated state of Ru3RhRu3 is endergonic with respect to the emissive Ru → dpp 3MLCT excited and cannot be formed by static electron transfer quenching of the 3MLCT state. Instead, a mechanism of subnanosecond charge separation from high lying states is proposed. Multiple reductions of Ru3 and Ru3Rh using sodium amalgam were carried out to compare UV-vis absorption spectra of reduced species and to evaluate the stability of highly reduced complexes. The Ru3 and Ru3Rh can be reduced by 10 and 13 electrons, respectively, to final states with all bridging ligands doubly reduced and all bpy ligands singly reduced.

Enhancement of Solar Fuel Production Schemes by Using a Ru,Rh,Ru Supramolecular Photocatalyst Containing Hydroxide Labile Ligands.

Polyazine-bridged Ru(II)Rh(III)Ru(II) complexes with two halide ligands, Cl(-) or Br(-), bound to the catalytically active Rh center are efficient single-component photocatalysts for H2O reduction to H2 fuel, with the coordination environment on Rh impacting photocatalysis. Herein reported is a new, halide-free Ru(II)Rh(III)Ru(II) photocatalyst with OH(-) ligands bound to Rh, further enhancing the photocatalytic reactivity of the structural motif. H2 production experiments using the photocatalyst bearing OH(-) ligands at Rh relative to the analogues bearing halides at Rh in solvents of varying polarity (DMF, CH3CN, and H2O) suggest that ion pairing with halides deactivates photocatalyst function, representing an exciting phenomenon to exploit in the development of catalysts for solar H2 production schemes.

Electrocatalytic H2 Evolution by Supramolecular Ru(II)-Rh(III)-Ru(II) Complexes: Importance of Ligands as Electron Reservoirs and Speciation upon Reduction.

The supramolecular water reduction photocatalysts [{(Ph2phen)2Ru(dpp)}2RhX2](PF6)5 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline, dpp =2,3-bis(2-pyridyl)pyrazine X = Cl, Br) are efficient electrocatalysts for the reduction of CF3SO3H, CF3CO2H, and CH3CO2H to H2 in DMF or DMF/H2O mixtures. The onset of catalytic current occurs at -0.82 V versus Ag/AgCl for CF3SO3H, -0.90 V for CF3CO2H, and -1.1 V for CH3CO2H with overpotentials of 0.61, 0.45, and 0.10 V, respectively. In each case, catalysis is triggered by the first dpp ligand reduction implicating the dpp as an electron reservoir in catalysis. A new species with Epc ∼ -0.75 V was observed in the presence of stoichiometric amounts of strong acid, and its identity is proposed as the Rh(H)(III/II) redox couple. H2 was produced in 72-85% Faradaic yields and 95-116 turnovers after 2 h and 435 turnovers after 10 h of bulk electrolysis. The identities of Rh(I) species upon reduction have been studied. In contrast to the expected dissociation of halides in the Rh(I) state, the halide loss depends on solvent and water content. In dry CH3CN, in which Cl(-) is poorly solvated, a [Ru] complex dissociates and [(Ph2phen)2Ru(dpp)Rh(I)Cl2](+) and [(Ph2phen)2Ru(dpp)](2+) are formed. In contrast, for X = Br(-), the major product of reduction is the intact trimetallic Rh(I) complex [{(Ph2phen)2Ru(dpp)}2Rh(I)](5+). Chloride loss in CH3CN is facilitated by addition of 3 M H2O. In DMF, the reduced species is [{(Ph2phen)2Ru(dpp)}2Rh(I)](5+) regardless of X = Cl(-) or Br(-).

Nonchromophoric halide ligand variation in polyazine-bridged Ru(II),Rh(III) bimetallic supramolecules offering new insight into photocatalytic hydrogen production from water.

The new bimetallic complex [(Ph2phen)2Ru(dpp)RhBr2(Ph2phen)](PF6)3 (1) (Ph2phen = 4,7-diphenyl-1,10-phenanthroline; dpp = 2,3-bis(2-pyridyl)pyrazine) was synthesized and characterized to compare with the Cl(-) analogue [(Ph2phen)2Ru(dpp)RhCl2(Ph2phen)](PF6)3 (2) in an effort to better understand the role of halide coordination at the Rh metal center in solar H2 production schemes. Electrochemical properties of complex 1 display a reversible Ru(II/III) oxidation, and cathodic scans indicate multiple electrochemical mechanisms exist to reduce Rh(III) by two electrons to Rh(I) followed by a quasi-reversible dpp(0/-) ligand reduction. The weaker σ-donating ability of Br(-) vs Cl(-) impacts the cathodic electrochemistry and provides insight into photocatalytic function by these bimetallic supramolecules. Complexes 1 and 2 exhibit identical light-absorbing properties with UV absorption dominated by intraligand (IL) π → π* transitions and visible absorption by metal-to-ligand charge transfer (MLCT) transitions to include a lowest energy Ru(dπ) → dpp(π*) (1)MLCT transition (λ(abs) = 514 nm; ε = 16 000 M(-1) cm(-1)). The relatively short-lived, weakly emissive Ru(dπ) → dpp(π*) (3)MLCT excited state (τ = 46 ns) for both bimetallic complexes is attributed to intramolecular electron transfer from the (3)MLCT excited state to populate a low-energy Ru(dπ) → Rh(dσ*) triplet metal-to-metal charge transfer ((3)MMCT) excited state that allows photoinitiated electron collection. Complex 1 outperforms the related Cl(-) bimetallic analogue 2 as a H2 photocatalyst despite identical light-absorbing and excited-state properties. Additional H2 experiments with added halide suggest ion pairing plays a role in catalyst deactivation and provides new insight into observed differences in H2 production upon halide variation in Ru(II),Rh(III) supramolecular architectures.

Tuning the Photophysical Properties of Ru(II) Monometallic and Ru(II),Rh(III) Bimetallic Supramolecular Complexes by Selective Ligand Deuteration.

A series of three new complexes of the design [(TL)2Ru(BL)](2+), two new complexes of the design [(TL)2Ru(BL)Ru(TL)2](4+), and three new complexes of the design [(TL)2Ru(BL)RhCl2(TL)](3+) (TL = bpy or d8-bpy; BL = dpp or d10-dpp; TL = terminal ligand; BL = bridging ligand; bpy = 2,2'-bipyridine; dpp = 2,3-bis(2-pyridyl)pyrazine) were synthesized and the (1)H NMR spectroscopy, electrochemistry, electronic absorbance spectroscopy, and photophysical properties studied. Incorporation of deuterated ligands into the molecular architecture simplifies the (1)H NMR spectra, allowing for complete (1)H assignment of [(d8-bpy)2Ru(dpp)](PF6)2 and partial assignment of [(bpy)2Ru(d10-dpp)](PF6)2. The electrochemistry for the deuterated and nondeuterated species showed nearly identical redox properties. Electronic absorption spectroscopy of the deuterated and nondeuterated complexes are superimposable with the lowest energy transition being Ru(dπ) → BL(π*) charge transfer in nature (BL = dpp or d10-dpp). Ligand deuteration impacts the excited-state properties with an observed increase in the quantum yield of emission (Φ(em)) and excited-state lifetime (τ) of the Ru(dπ) → d10-dpp(π*) triplet metal-to-ligand charge transfer ((3)MLCT) excited state when dpp is deuterated, and a decrease in the rate constant for nonradiative decay (knr). Choice of ligand deuteration between bpy and dpp strongly impacts the observed photophysical properties with BL = d10-dpp complexes showing an enhanced Φ(em) and τ, providing further support that the lowest electronic excited state populated via UV or visible excitation is the photoactive Ru(dπ) → dpp(π*) CT excited state. The Ru(II),Rh(III) complex incorporating the deuterated BL shows increased hydrogen production compared to the variants incorporating the protiated BL, while demonstrating identical dynamic quenching behaviors in the presence of sacrificial electron donor.

Increased Water Reduction Efficiency of Polyelectrolyte-Bound Trimetallic [Ru,Rh,Ru] Photocatalysts in Air-Saturated Aqueous Solutions.

The groundbreaking use of polyelectrolytes to increase the efficiency of supramolecular photocatalysts in solar H2 production schemes under aqueous aerobic conditions is reported. Supramolecular photocatalysts of the architecture [{(TL)2 Ru(BL)}2 RhX2 ](5+) (BL=bridging ligand, TL=terminal ligand, X=halide) demonstrate high efficiencies in deoxygenated organic solvents but do not function in air-saturated aqueous solution because of the quenching of the metal-to-ligand charge-transfer (MLCT) excited state under these conditions. The new photocatalytic system incorporates poly(4-styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)2 Ru(dpp)}2 RhCl2 ](5+) (bpy=2,2'-bipyridine, dpp=2,3-bis(2-pyridyl)pyrazine). PSS has a profound impact on the photocatalyst efficiency, increasing H2 production over three times that of deoxygenated aqueous solutions alone. H2 photocatalysis proceeds even under aerobic conditions for PSS-containing solutions, an exciting consequence for solar hydrogen-production research.

Mechanistic insight into the electronic influences imposed by substituent variation in polyazine-bridged ruthenium(II)/rhodium(III) supramolecules.

Unusual and unprecedented multipathway electrochemical mechanisms for a new class of supramolecular Ru/Rh bimetallic photocatalysts have been uncovered. The near isoenergetic Rh(dσ*) and bridging ligand(π*) molecular orbitals and a rate of halide loss that occurs on the cyclic voltammetry timescale provide a series of closely related complexes which display four different electrochemical mechanisms. A single complex displays two concurrent electrochemical pathways in marked contrast to all previously studied cis-[Rh(NN)(2)X(2)] motifs.

New supramolecular structural motif coupling a ruthenium(II) polyazine light absorber to a rhodium(I) center.

Two new complexes, [(bpy)2Ru(dpp)Rh(I)(COD)](PF6)3 and [(Me2bpy)2Ru(dpp)Rh(I)(COD)](PF6)2(BF4) (bpy = 2,2'-bipyridine, Me2bpy = 4,4'-dimethyl-2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, and COD = 1,5-cyclooctadiene), representing a new Ru(II),Rh(I) structural motif, have been prepared and characterized by mass spectrometry, (1)H NMR spectroscopy, electrochemistry, electronic absorption spectroscopy, and emission spectroscopy. These two complexes represent a new type of supramolecular complex with a [(TL)2Ru(dpp)](2+) (TL = terminal ligand) light absorber (LA) coupled to a Rh(I) center and are models for Ru(II),Rh(I) intermediates in the photochemical reduction of water using dpp-bridged Ru(II),Rh(III) photocatalysts. Electrochemical study reveals overlapping reversible Ru(II/III) and irreversible Rh(I/II/III) oxidations and a quasi-reversible dpp(0/-) reduction, demonstrating that the lowest unoccupied molecular orbital (LUMO) is dpp(π*) based. The COD ligand is sterically bulky, displaying steric repulsions between hydrogen atoms on the alkene of COD and dpp about the square planar Rh(I) center. An interesting reactivity occurs in coordinating solvents such as CH3CN, where Rh(I) substitution leads to an equilibrium between the Ru(II),Rh(I) bimetallic and [(TL)2Ru(dpp)](2+) and [Rh(I)(COD)(solvent)2](+) monometallic species. The electronic absorption spectra of both complexes feature transitions at ca. 500 nm attributed to a Ru(dπ) → dpp(π*) metal-to-ligand charge transfer (MLCT) transition that is slightly red-shifted from the Ru synthon upon Rh(I) complexation. The methylation of TL on the Ru impacts the electrochemical and optical properties in a minor but predictable manner. The photophysical studies, by comparison with the model complex [{Ru(bpy)2}2(dpp)](PF6)4 and related Rh(III) complex [(bpy)2Ru(dpp)Rh(III)Cl2(phen)](PF6)3, reveal the expected absence of a Ru(dπ) → Rh(dσ*) (3)MMCT state (metal-to-metal charge transfer) in the title complexes, which is present in Rh(III) systems. The absence of this (3)MMCT state in Ru(II),Rh(I) complexes results in a longer lifetime and higher emission quantum yield for the Ru(dπ) → dpp(π*) (3)MLCT state than [(bpy)2Ru(dpp)Rh(III)Cl2(phen)](PF6)3. Both complexes display photocatalytic hydrogen production activity in the presence of water and a sacrificial electron donor, with the [(bpy)2Ru(dpp)Rh(I)(COD)](PF6)3 possessing a higher catalytic activity than the methyl analogue. Both display low activities, hypothesized to occur due to steric crowding about the Rh(I) site.

Subunit variation to uncover properties of polyazine-bridged Ru(II), Pt(II) supramolecules with low lying charge separated states providing insight into the functioning as H2O reduction photocatalysts to produce H2.

Two new structurally diverse polyazine-bridged Ru(II),Pt(II) tetrametallic complexes, [{(Ph2phen)2Ru(dpp)}2Ru(dpp)PtCl2](PF6)6 (1a) and [{(Ph2phen)2Ru(dpp)}2Ru(dpq)PtCl2](PF6)6 (2a) (Ph2phen = 4,7-diphenyl-1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline), as well as their trimetallic precursors have been synthesized to provide a comparison for detailed analysis to elucidate component effects in the previously reported photocatalyst [{(phen)2Ru(dpp)}2Ru(dpq)PtCl2](PF6)6 (4a) (phen = 1,10-phenanthroline). Electrochemistry shows terminal Ru based highest occupied molecular orbitals (HOMOs) with remote BL' (BL' = bridging ligand coupling central Ru and cis-PtCl2 moiety) based lowest unoccupied molecular orbitals (LUMOs). Population of a lowest-lying charge separated ((3)CS) excited state with oxidized terminal Ru and reduced remote BL' via intramolecular electron transfer is predicted by electrochemical analysis and is observed through steady-state and time-resolved emission studies as well as emission excitation profiles which display unusual nonunity population of the lowest lying emissive Ru→dpp (3)MLCT (metal-to-ligand charge transfer) state. Each tetrametallic complex is an active photocatalyst for H2 production from H2O with 2a showing the highest activity (94 TON (turnover number) in 10 h, where TON = mol H2/mol catalyst). The nature of the bridging ligand coupling the trimetallic light absorber to the cis-PtCl2 moiety has a significant impact on the catalyst activity, correlated to the degree of population of the (3)CS excited state. The choice of terminal ligand affects visible light absorption and has a minor influence on photocatalytic H2 production from H2O. Evidence that an intact supramolecule functions as the photocatalyst includes a strong dependence of the photocatalysis on the identity of BL', an insensitivity to Hg(l), no detectable H2 production from the systems with the trimetallic synthons and cis-[PtCl2(DMSO)2] as well as spectroscopic analysis of the photocatalytic system.

Discovering the balance of steric and electronic factors needed to provide a new structural motif for photocatalytic hydrogen production from water.

Ru,Rh,Ru supramolecules are known to undergo multielectron photoreduction and reduce H(2)O to H(2). Ru,Rh bimetallics were recently shown to photoreduce but not catalyze H(2)O reduction. Careful tuning of sterics and electronics for [(TL)(2)Ru(dpp)RhCl(2)(TL')](3+) produce active bimetallic photocatalysts (TL = terminal ligand). The system with TL,TL' = Ph(2)phen photocatalytically reduces H(2)O to H(2) while TL,TL' = phen,bpy or bpy,(t)Bu(2)bpy do not.

Redox, spectroscopic, and photophysical properties of Ru-Pt mixed-metal complexes incorporating 4,7-diphenyl-1,10-phenanthroline as efficient DNA binding and photocleaving agents.

The redox, spectroscopic, and photophysical properties as well as DNA interactions of the new bimetallic complexes [(Ph2phen)2Ru(BL)PtCl2](2+) (Ph2phen = 4,7-diphenyl-1,10-phenanthroline, and BL (bridging ligand) = dpp = 2,3-bis(2-pyridyl)pyrazine, or dpq = 2,3-bis(2-pyridyl)quinoxaline) were investigated. These Ru-polyazine chromophores with Ph2phen TLs (terminal ligands) and polyazine BLs are efficient light absorbers. The [(Ph2phen)2Ru(BL)PtCl2](2+) complexes display reversible Ru(II/III) oxidations at 1.57 (dpp) and 1.58 (dpq) V vs SCE (saturated calomel electrode) with an irreversible Pt(II/IV) oxidation occurring prior at 1.47 V vs SCE. Four, reversible ligand reductions occur at -0.50 dpp(0/-), -1.06 dpp(-/2-), -1.37 Ph2phen(0/-), and -1.56 V vs SCE Ph2phen(0/-). For the [(Ph2phen)2Ru(dpq)PtCl2](2+) complex, the first two reductions shift to more positive potentials at -0.23 and -0.96 V vs SCE. The electronic absorption spectroscopy is dominated in the UV region by π → π* ligand transitions and in the visible region by metal-to-ligand charge transfer (MLCT) transitions at 517 nm for [(Ph2phen)2Ru(dpp)PtCl2](2+) and 600 nm for [(Ph2phen)2Ru(dpq)PtCl2](2+). Emission spectroscopy shows that upon attaching Pt to the Ru monometallic precursor the λmax(em) shifts from 664 nm for [(Ph2phen)2Ru(dpp)](2+) to 740 nm for [(Ph2phen)2Ru(dpp)PtCl2](2+). The cis-Pt(II)Cl2 bioactive site offers the potential of targeting DNA by covalently binding the mixed-metal complex to DNA bases. The multifunctional interactions with DNA were assayed using both linear and circular plasmid pUC18 DNA gel shift assays. Both title complexes can bind to and photocleave DNA with dramatically enhanced efficiency relative to previously reported systems. The impact of the Ph2phen TL on photophysics and bioreactivity is somewhat surprising given the Ru → BL charge transfer (CT) nature of the photoreactive state in the complexes.

Electrochemical, spectroscopic, and photophysical properties of structurally diverse polyazine-bridged Ru(II),Pt(II) and Os(II),Ru(II),Pt(II) supramolecular motifs.

Five new tetrametallic supramolecules of the motif [{(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2)](6+) and three new trimetallic light absorbers [{(TL)(2)M(dpp)}(2)Ru(BL)](6+) (TL = bpy = 2,2'-bipyridine or phen = 1,10-phenanthroline; M = Ru(II) or Os(II); BL = dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline, or bpm = 2,2'-bipyrimidine) were synthesized and their redox, spectroscopic, and photophysical properties investigated. The tetrametallic complexes couple a Pt(II)-based reactive metal center to Ru and/or Os light absorbers through two different polyazine BL to provide structural diversity and interesting resultant properties. The redox potential of the M(II/III) couple is modulated by M variation, with the terminal Ru(II/III) occurring at 1.58-1.61 V and terminal Os(II/III) couples at 1.07-1.18 V versus Ag/AgCl. [{(TL)(2)M(dpp)}(2)Ru(BL)](PF(6))(6) display terminal M(dπ)-based highest occupied molecular orbitals (HOMOs) with the dpp(π*)-based lowest unoccupied molecular orbital (LUMO) energy relatively unaffected by the nature of BL. The coupling of Pt to the BL results in orbital inversion with localization of the LUMO on the remote BL in the tetrametallic complexes, providing a lowest energy charge separated (CS) state with an oxidized terminal Ru or Os and spatially separated reduced BL. The complexes [{(TL)(2)M(dpp)}(2)Ru(BL)](6+) and [{(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2)](6+) efficiently absorb light throughout the UV and visible regions with intense metal-to-ligand charge transfer (MLCT) transitions in the visible at about 540 nm (M = Ru) and 560 nm (M = Os) (ε ≈ 33,000-42,000 M(-1) cm(-1)) and direct excitation to the spin-forbidden (3)MLCT excited state in the Os complexes about 720 nm. All the trimetallic and tetrametallic Ru-based supramolecular systems emit from the terminal Ru(dπ)→dpp(π*) (3)MLCT state, λ(max)(em) ≈ 750 nm. The tetrametallic systems display complex excited state dynamics with quenching of the (3)MLCT emission at room temperature to populate the lowest-lying (3)CS state population of the emissive (3)MLCT state.

Multifunctional DNA interactions of Ru-Pt mixed metal supramolecular complexes with substituted terpyridine ligands.

The coupling of a light absorbing unit to a bioactive site allows for the development of supramolecules with multifunctional interactions with DNA. A series of mixed metal supramolecular complexes that couple a DNA-binding cis-Pt(II)Cl(2) center to a ruthenium chromophore via a polyazine bridging ligand have been prepared, and their DNA interactions have been studied, [(TL)RuCl(dpp)PtCl(2)](PF(6)) (TL = tpy (2,2':6',2''-terpyridine), MePhtpy (4'-(4-methylphenyl)-2,2':6',2''-terpyridine), or (t)Bu(3)tpy (4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine). This series provides for unique tridentate coordinated Ru(II) systems to photocleave DNA with preassociation with the DNA target via coordination of the Pt(II) center. Electronic absorption spectroscopy of the complexes displays intense ligand-based pi-->pi* transitions in the UV region and metal to ligand charge transfer (MLCT) transitions in the visible region. The Ru(dpi)-->dpp(pi*) MLCT transitions occur at 545 nm, red-shifted relative to the 520 nm maxima for the monometallic synthons, [(TL)RuCl(dpp)](PF(6)). The title RuPt complexes display reversible Ru(II/III) oxidative couples at 1.10, 1.10, and 1.01 V vs Ag/AgCl for TL = tpy, MePhtpy, and (t)Bu(3)tpy, respectively. The TL(0/-) reduction occurred at -1.43, -1.44, and -1.59 V vs Ag/AgCl for TL = tpy, MePhtpy, and (t)Bu(3)tpy, respectively. These complexes display a dpp(0/-) couple (-0.50 -0.55, and -0.59 V) significantly shifted to positive potential relative to their monometallic synthons (-1.15, -1.16, and -1.22 V), consistent with the bridging coordination of the dpp ligand. Coupling of (TL)Ru(II)Cl(BL) subunit to a cis-Pt(II)Cl(2) site provides for the application of photochemically inactive Ru(II)(tpy)-based chromophores in DNA photocleavage applications. The [(TL)RuCl(dpp)PtCl(2)](+) complexes display covalent binding to DNA and photocleavage upon irradiation with visible light modulated by TL identity. The redox, spectroscopic, DNA-binding, and photocleavage properties of a series of supramolecular complexes are presented.

Design considerations for a system for photocatalytic hydrogen production from water employing mixed-metal photochemical molecular devices for photoinitiated electron collection.

Supramolecular complexes coupling Ru(II) or Os(II) polyazine light absorbers through bridging ligands to Rh(III) or Ir(III) allow the study of factors impacting photoinitiated electron collection and multielectron water reduction to produce hydrogen. The [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) system represents the first photoinitiated electron collector in a molecular system (bpy = 2,2'-bipyridine, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline). The [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) system represents the first photoinitiated electron collector that affords photochemical hydrogen production from water in the presence of an electron donor, N,N-dimethylaniline (dpp = 2,3-bis(2-pyridyl)pyrazine). The complexes [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5), [{(bpy)(2)Ru(dpp)}(2)RhBr(2)](PF(6))(5), [{(phen)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5), [{(bpy)(2)Os(dpp)}(2)RhCl(2)](PF(6))(5), [{(tpy)RuCl(dpp)}(2)RhCl(2)](PF(6))(3), [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3), and [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) are herein evaluated with respect to their functioning as hydrogen photocatalysts (tpy = 2,2':6',2''-terpyridine, phen = 1,10-phenanthroline). With the exceptions of [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) and [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3), all other complexes demonstrate photocatalytic activity. The functioning systems possess a rhodium localized lowest unoccupied molecular orbital that serves as the site of electron collection and a metal-to-ligand charge-transfer ((3)MLCT) and/or metal-to-metal charge-transfer ((3)MMCT) excited-state with sufficient driving force for excited-state reduction by the electron donor. The lack of photocatalytic activity by [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5), although photoinitiated electron collection occurs, establishes the significance of the rhodium center in the photocatalytic system. The lack of photocatalytic activity of [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3) is attributed to the lower-energy (3)MLCT state that does not possess sufficient driving force for excited-state reduction by the electron donor. The variation of electron donor showed the photocatalysis efficiency to decrease in the order N,N-dimethylaniline > triethylamine > triethanolamine. The general design considerations for development of supramolecular assemblies that function as water reduction photocatalysts are discussed.

Ruthenium(II)-polyazine light absorbers bridged to reactive cis-dichlororhodium(III) centers in a bimetallic molecular architecture.

Bimetallic complexes of the form [(bpy)(2)Ru(BL)RhCl(2)(phen)](PF(6))(3), where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and BL = 2,3-bis(2-pyridyl)pyrazine (dpp) or 2,2'-bipyrimidine (bpm), were synthesized, characterized, and compared to the [{(bpy)(2)Ru(BL)}(2)RhCl(2)](PF(6))(5) trimetallic analogues. The new complexes were synthesized via the building block method, exploiting the known coordination chemistry of Rh(III) polyazine complexes. In contrast to [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) and [{(bpy)(2)Ru(bpm)}(2)RhCl(2)](PF(6))(5), [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) have a single visible light absorber subunit coupled to the cis-Rh(III)Cl(2) moiety, an unexplored molecular architecture. The electrochemistry of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) showed a reversible oxidation at 1.61 V (vs Ag/AgCl) (Ru(III/II)), quasi-reversible reductions at -0.39 V, -0.74, and -0.98 V. The first two reductive couples corresponded to two electrons, consistent with Rh reduction. The electrochemistry of [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) exhibited a reversible oxidation at 1.76 V (Ru(III/II)). A reversible reduction at -0.14 V (bpm(0/-)), and quasi-reversible reductions at -0.77 and -0.91 V each corresponded to a one electron process, bpm(0/-), Rh(III/II), and Rh(II/I). The dpp bridged bimetallic and trimetallic display Ru(dpi)-->dpp(pi*) metal-to-ligand charge transfer (MLCT) transitions at 509 nm (14,700 M(-1) cm(-1)) and 518 nm (26,100 M(-1) cm(-1)), respectively. The bpm bridged bimetallic and trimetallic display Ru(dpi)-->bpm(pi*) charge transfer (CT) transitions at 581 nm (4,000 M(-1) cm(-1)) and 594 nm (9,900 M(-1) cm(-1)), respectively. The heteronuclear complexes [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) had (3)MLCT emissions that are Ru(dpi)-->dpp(pi*) CT in nature but were red-shifted and lower intensity than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4). The lifetimes of the (3)MLCT state of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) at room temperature (30 ns) was shorter than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4), consistent with favorable electron transfer to Rh(III) to generate a metal-to-metal charge-transfer ((3)MMCT) state. The reported synthetic methods provide means to a new molecular architecture coupling a single Ru light absorber to the Rh(III) center while retaining the interesting cis-Rh(III)Cl(2) moiety.

Synthesis and study of the spectroscopic and redox properties of Ru(II),Pt(II) mixed-metal complexes bridged by 2,3,5,6-tetrakis(2-pyridyl)pyrazine.

The mixed-metal supramolecular complexes [(tpy)Ru(tppz)PtCl](PF6)3 and [ClPt(tppz)Ru(tppz)PtCl](PF6)4 (tpy = 2,2':6',2''-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) were synthesized and characterized. These complexes contain ruthenium bridged by tppz to platinum centers to form stereochemically defined linear assemblies. X-ray crystallographic determinations of the two complexes confirm the identity of the metal complexes and reveal intermolecular interactions of the Pt sites in the solid state for [(tpy)Ru(tppz)PtCl](PF6)3 with a Pt...Pt distance of 3.3218(5) A. The (1)H NMR spectra show the expected splitting patterns characteristic of stereochemically defined mixed-metal systems and are assigned with the use of (1)H-(1)H COSY and NOESY. Electronic absorption spectroscopy displays intense ligand-based pi --> pi* transitions in the UV and MLCT transitions in the visible. Electrochemically [(tpy)Ru(tppz)PtCl](PF6)3 and [ClPt(tppz)Ru(tppz)PtCl](PF6)4 display reversible Ru (II/III) couples at 1.63 and 1.83 V versus Ag/AgCl, respectively. The complexes display very low potential tppz (0/-) and tppz(-/2-) couples, relative to their monometallic synthons, [(tpy)Ru(tppz)](PF6)2 and [Ru(tppz)2](PF6)2, consistent with the bridging coordination of the tppz ligand. The Ru(dpi) --> tppz(pi*) MLCT transitions are also red-shifted relative to the monometallic synthons occurring in the visible centered at 530 and 538 nm in CH3CN for [(tpy)Ru(tppz)PtCl](PF6)3 and [ClPt(tppz)Ru(tppz)PtCl](PF6)4, respectively. The complex [(tpy)Ru(tppz)PtCl](PF6)3 displays a barely detectable emission from the Ru(dpi) --> tppz(pi*) (3)MLCT in CH 3CN solution at RT. In contrast, [ClPt(tppz)Ru(tppz)PtCl](PF6)4 displays an intense emission from the Ru(dpi) --> tppz(pi*) (3)MLCT state at RT with lambda max(em) = 754 nm and tau = 80 ns.

Photochemical methods to assay DNA photocleavage using supercoiled pUC18 DNA and LED or xenon arc lamp excitation.

Methods for the study of DNA photocleavage are illustrated using a mixed-metal supramolecular complex [{(bpy)(2)Ru(dpp)}(2)RhCl(2)]Cl(5). The methods use supercoiled pUC18 plasmid as a DNA probe and either filtered light from a xenon arc lamp source or monochromatic light from a newly designed, high-intensity light-emitting diode (LED) array. Detailed methods for performing the photochemical experiments and analysis of the DNA photoproduct are delineated. Detailed methods are also given for building an LED array to be used for DNA photolysis experiments. The Xe arc source has a broad spectral range and high light flux. The LEDs have a high-intensity, nearly monochromatic output. Arrays of LEDs have the advantage of allowing tunable, accurate output to multiple samples for high-throughput photochemistry experiments at relatively low cost.

In vivo inhibition of E. coli growth by a Ru(II)/Pt(II) supramolecule [(tpy)RuCl(dpp)PtCl2](PF6).

Supramolecular complexes consisting of ruthenium chromophores and a cisplatin unit represent an emerging class of bioactive molecules of interest as anti-cancer agents. Although the ability of Ru(II)/Pt(II) heteronuclear complexes to bind to DNA has been demonstrated, the in vivo activity of these complexes has not yet been reported. In the present work, we report the anti-bacterial activity of the complex [(tpy)RuCl(dpp)PtCl(2)](PF(6)) (where dpp=2,3-bis(2-pyridyl)pyrazine, tpy=2,2':6',2''-terpyridine). The impact on bacterial cell growth of exposure to different concentrations of [(tpy)RuCl(dpp)PtCl(2)](PF(6)) and cisplatin was studied. The bioactivity of this complex was found to be due to the presence of the cis-PtCl(2) moiety, as the monometallic synthon [(tpy)RuCl(dpp)](PF(6)) did not inhibit bacterial cell growth.