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.     

Sequence dependence of charge transport through DNA domains

Here we examine the photooxidation of two kinetically fast electron hole traps, N4-cyclopropylcytosine (CPC) and N2-cyclopropylamine-guanosine (CPG), incorporated in DNA duplexes of various sequence using different photooxidants. DNA oxidation studies are carried out either with noncovalently bound [Ru(phen)(dppz)(bpy')]3+ (dppz = dipyridophenazine) and [Rh(phi)2(bpy)]3+ (phi = phenanthrenequinone diimine) or with anthraquinone tethered to DNA. Because the cyclopropylamine-substituted bases decompose rapidly upon oxidation, their efficiency of decomposition provides a measure of relative hole localization. Consistent with a higher oxidation potential for CPC versus CPG in DNA, CPC decomposes with photooxidation by [Rh(phi)2(bpy)]3+, while CPG undergoes ring-opening both with photoexcited [Rh(phi)2(bpy)]3+ and with [Ru(phen)(dppz)(bpy')]3+. Anthraquinone-modified DNA assemblies of identical base composition but different base sequence are also probed. Single and double base substitutions within adenine tracts modulate CPC decomposition. In fact, the entire sequence within the DNA assembly is seen to govern CPC oxidation, not simply the bases intervening between CPC and the tethered photooxidant. These data are reconciled in the context of a mechanistic model of conformationally gated charge transport through delocalized DNA domains. Photooxidations of anthraquinone-modified DNA assemblies containing both CPC and CPG, but with varied distances separating the modified bases, point to a domain size of at least three bases. Our model for DNA charge transport is distinguished from polaron models. In our model, delocalized domains within the base pair stack form transiently based upon sequence-dependent DNA structure and dynamics. Given these results, DNA charge transport is indeed remarkably sensitive to DNA sequence and structure.     

The flash-quench technique in protein-DNA electron transfer: reduction of the guanine radical by ferrocytochrome c

Electron transfer from a protein to oxidatively damaged DNA, specifically from ferrocytochrome c to the guanine radical, was examined using the flash-quench technique. Ru(phen)2dppz2+ (dppz = dipyridophenazine) was employed as the photosensitive intercalator, and ferricytochrome c (Fe3+ cyt c), as the oxidative quencher. Using transient absorption and time-resolved luminescence spectroscopies, we examined the electron-transfer reactions following photoexcitation of the ruthenium complex in the presence of poly(dA-dT) or poly(dG-dC). The luminescence-quenching titrations of excited Ru(phen)2dppz2+ by Fe3+ cyt c are nearly identical for the two DNA polymers. However, the spectral characteristics of the long-lived transient produced by the quenching depend strongly upon the DNA. For poly(dA-dT), the transient has a spectrum consistent with formation of a [Ru(phen)2dppz3+, Fe2+ cyt c] intermediate, indicating that the system regenerates itself via electron transfer from the protein to the Ru(III) metallointercalator for this polymer. For poly(dG-dC), however, the transient has the characteristics expected for an intermediate of Fe2+ cyt c and the neutral guanine radical. The characteristics of the transient formed with the GC polymer are consistent with rapid oxidation of guanine by the Ru(III) complex, followed by slow electron transfer from Fe2+ cyt c to the guanine radical. These experiments show that electron holes on DNA can be repaired by protein and demonstrate how the flash-quench technique can be used generally in studying electron transfer from proteins to guanine radicals in duplex DNA.     

Dinuclear ruthenium(ii) complexes with flexible bridges as non-duplex DNA binding agents

The stereoisomers of a series of dinuclear ruthenium(ii) complexes [{Ru(phen)(2)}(2)(micro-BL)](4+) (phen = 1,10-phenanthroline) with flexible bridging ligands (BL) bb2 {1,2-bis[4(4'-methyl-2,2'-bipyridyl)]ethane}, bb5 {1,5-bis[4(4'-methyl-2,2'-bipyridyl)]pentane}, bb7 {1,7-bis[4(4'-methyl-2,2'-bipyridyl)]heptane}, and bb10 {1,10-bis[4(4'-methyl-2,2'-bipyridyl)]decane} have been synthesised. Their binding to a control dodecanucleotide, d(CCGGAATTCCGG)(2), and a tridecanucleotide, d(CCGAGAATTCCGG)(2), which contains a single adenine bulge have been studied using fluorescence displacement assays involving intercalating and groove-binding dyes, equilibrium dialysis and binding affinity chromatography. The fluorescence intercalator displacement (FID) assay indicated that LambdaLambda-[{Ru(phen)(2)}(2)(micro-bb7)](4+) had the greatest binding affinity with all the oligonucleotides, whereas an analogous fluorescence technique using a minor-groove binding dye, equilibrium dialysis and affinity binding chromatography showed that DeltaDelta-[{Ru(phen)(2)}(2)(micro-bb7)](4+) had the strongest binding. An (1)H NMR study of the binding of the DeltaDelta-enantiomer of [{Ru(phen)(2)}(2)(micro-bb7)](4+) to d(CCGAGAATTCCGG)(2) confirmed the selectivity of the metal complex for the bulge site and provided the basis for an energy-minimised binding model of the dinuclear ruthenium complex with the single adenine bulge containing trinucleotide. The binding model demonstrated the ability of the flexibly-linked complex to follow the curvature of the DNA minor groove.     

多吡啶钌(Ⅱ)配合物化学发光性质研究

详细研究了Ru(bpy)3^2+,Ru(bpy)2(dppx)^2+,Ru(bpy)2(dppz)^2+,Ru(phen)3^2+,Ru(phen)2(dppx)^2+和Ru(phen)2(dppz)^2+六个多吡啶钌(Ⅱ)配合物的化学发光性质,筛选出Ru(bpy)3^2+和Ru(phen)3^2+两种性能优良的化学发光试剂;并探讨了它们发光的可能机理和影响因素,为钌(Ⅱ)配合物在化学发光分析中的应用提供了可供参考的理论依据。     

Structural Studies Reveal Enantiospecific Recognition of a DNA G‐Quadruplex by a Ruthenium Polypyridyl Complex

By using X‐ray crystallography, we show that the complexes Λ/Δ‐[Ru(TAP)₂(11‐CN‐dppz)]²⁺ (TAP=1,4,5,8‐tetraazaphenanthrene, dppz=dipyridophenazine) bind DNA G‐quadruplex in an enantiospecific manner that parallels the specificity of these complexes with duplex DNA. The Λ complex crystallises with the normally parallel stranded d(TAGGGTTA) tetraplex to give the first such antiparallel strand assembly in which syn‐guanosine is adjacent to the complex at the 5′ end of the quadruplex core. SRCD measurements confirm that the same conformational switch occurs in solution. The Δ enantiomer, by contrast, is present in the structure but stacked at the ends of the assembly. In addition, we report the structure of Λ‐[Ru(phen)₂(11‐CN‐dppz)]²⁺ bound to d(TCGGCGCCGA), a duplex‐forming sequence, and use both structural models to provide insight into the motif‐specific luminescence response of the isostructural phen analogue enantiomers.     

Effects of the photooxidant on DNA-mediated charge transport

A direct comparison of DNA charge transport (CT) with different photooxidants has been made. Photooxidants tested include the two metallointercalators, Rh(phi)(2)(bpy')(3+) and Ru(phen)(bpy')(dppz)(2+), and three organic intercalators, ethidium (Et), thionine (Th), and anthraquinone (AQ). CT has been examined through a DNA duplex containing an A(6)-tract intervening between two 5'-CGGC-3' sites with each of the photooxidants covalently tethered to one end of the DNA duplex. CT is assayed both through determination of the yield of oxidative guanine damage and, in derivative DNA assemblies, by analysis of the yield of a faster oxidative trapping reaction, ring opening of N(2)-cyclopropylguanine (d(CP)G) within the DNA duplex. We find clear differences in oxidative damage ratios at the distal versus proximal 5'-CGGC-3' sites depending upon the photooxidant employed. Importantly, nondenaturing gel electrophoresis data demonstrate the absence of any DNA aggregation by the DNA-bound intercalators. Hence, differences seen with assemblies containing various photooxidants cannot be attributed to differential aggregation. Comparisons in assemblies using different photooxidants thus reveal characteristics of the photooxidant as well as characteristics of the DNA assembly. In the series examined, the lowest distal/proximal DNA damage ratios are obtained with Ru and AQ, while, for both Rh and Et, high distal/proximal damage ratios are found. The oxidative damage yields vary in the order Ru > AQ > Rh > Et, and photooxidants that produce higher distal/proximal damage ratios have lower yields. While no oxidative DNA damage is detected using thionine as a photooxidant, oxidation is evident using the faster cyclopropylguanosine trap; here, a complex distance dependence is found. Differences observed among photooxidants as well as the complex distance dependence are attributed to differences in rates of back electron transfer (BET). Such differences are important to consider in developing mechanistic models for DNA CT.     

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.     

meso-[{Ru(phen)2}2(mu-HAT)]4+: a high-affinity DNA hairpin probe {HAT = 1,4,5,8,9,12-hexaazatriphenylene; phen = 1,10-phenanthroline}

1H NMR spectroscopy and fluorescent intercalator displacement (FID) assays have been used to investigate the DNA-binding abilities of two series of dinuclear polypyridyl ruthenium(II) complexes of the form [{Ru(L)2}2(mu-BL)]4+ {L = 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), or 4,7-dimethyl-1,10-phenanthroline (Me2phen); BL = 2,2'-bipyrimidine (bpm) or 1,4,5,8,9,12-hexaazatriphenylene (HAT)}. Preliminary FID surveys of these metal complexes against a variety of different oligonucleotides revealed that those complexes based upon the HAT bridging ligand induced greater fluorescence decreases in dye-bound DNA than did their bpm-bridged counterparts, suggesting a higher binding affinity by the HAT-bridged species. Furthermore, the greatest fluorescence decreases were typically observed in an oligonucleotide featuring a six-base hairpin loop. The apparent binding affinity of the metal complexes was also found to be a function of the stereochemistry and identity of the terminal ligands of the complex. The meso (DeltaLambda) stereoisomer generally induced greater fluorescence decreases than did either enantiomer (DeltaDelta or LambdaLambda), phen-based terminal ligands performed better than bpy-based terminal ligands, and those terminal ligands with methyl substituents demonstrated stronger apparent binding than did their non-methylated analogues. NMR experiments on meso-[{Ru(phen)2}2(mu-HAT)]4+ and meso-[{Ru(Me2phen)2}2(mu-HAT)]4+ demonstrated that both complexes bound with high affinity to the six-base hairpin oligonucleotide at the stem-loop interface and provided evidence to support stronger binding by the methylated species. meso-[{Ru(phen)2}2(mu-HAT)]4+ was found to bind poorly to duplex DNA and smaller four-base hairpin loops in FID and NMR experiments, whereas FID data suggest that the methylated analogue binds relatively strongly to most oligonucleotide sequences (the four- and six-base hairpins in particular). These results demonstrate that binding affinity can come at the expense of selectivity, with meso-[{Ru(phen)2}2(mu-HAT)]4+ proving to be an efficient compromise between the two as a high-affinity DNA hairpin probe.     

新型多吡啶配体的设计及其对配合物与DNA作用机制的影响

近年来 ,以钌 ( )多吡啶配合物为探针研究 DNA的结构已成为生物无机化学领域中的一个热点[1,2 ] .这些配合物由于热力学稳定性好 ,光化学和光物理信息丰富 ,在研究 DNA内部的电子转移和Fig.1　 Structures of the ligandsDNA的结构识别等方面均有重要的作用[3～ 7] .在配合物与 DNA的相互作用中 ,配合物的形状、大小以及中心离子电荷等都有一定的影响[8] ,其中 ,配合物的形状起着至关重要的作用 ,与 DNA的形状匹配的配合物与DNA的结合较强 .这些配合物中通常含有平面性较大的芳香环配体 ,可插入到 DNA的碱基对之间 ,并与 DNA具有…     

Oxidative damage by ruthenium complexes containing the dipyridophenazine ligand or its derivatives: a focus on intercalation

Interactions with DNA by a family of ruthenium(II) complexes bearing the dppz (dppz = dipyridophenazine) ligand or its derivatives have been examined. The complexes include Ru(bpy)(2)(dppx)(2+) (dppx = 7,8-dimethyldipyridophenazine), Ru(bpy)(2)(dpq)(2+) (dpq = dipyridoquinoxaline), and Ru(bpy)(2)(dpqC)(2+) (dpqC = dipyrido-6,7,8,9-tetrahydrophenazine). Their ground and excited state oxidation/reduction potentials have been determined using cyclic voltammetry and fluorescence spectroscopy. An intercalative binding mode has been established on the basis of luminescence enhancements in the presence of DNA, excited state quenching, fluorescence polarization values, and enantioselectivity. Oxidative damage to DNA by these complexes using the flash/quench method has been examined. A direct correlation between the amount of guanine oxidation obtained via DNA charge transport and the strength of intercalative binding was observed. Oxidative damage to DNA through DNA-mediated charge transport was also compared directly for two DNA-tethered ruthenium complexes. One contains the dppz ligand that binds avidly by intercalation, and the other contains only bpy ligands, that, while bound covalently, can only associate with the base pairs through groove binding. Long range oxidative damage was observed only with the tethered, intercalating complex. These results, taken together, all support the importance of close association and intercalation for DNA-mediated charge transport. Electronic access to the DNA base pairs, provided by intercalation of the oxidant, is a prerequisite for efficient charge transport through the DNA pi-stack.     

Ruthenium(II) complexes of redox-related, modified dipyridophenazine ligands: synthesis, characterization, and DNA interaction

The synthesis, spectral characterization, and electrochemical properties of [Ru(phen)2(qdppz)]2+, which incorporates a quinone-fused dipyridophenazine ligand (naphtho[2,3-a]dipyrido[3,2-h:2',3'-f]phenazine-5,18-dione, qdppz), are described in detail. Chemical or electrochemical reduction of [Ru(phen)2(qdppz)]2+ leads to the generation of [Ru(phen)2(hqdppz)](2+)--a complex containing the hydroquinone form (hqdppz = 5,18-dihydroxynaphtho[2,3-a]-dipyrido[3,2-h:2',3'-f]phenazine) of qdppz. Absorption and viscometric titration, thermal denaturation, topoisomerase assay, and differential-pulse voltammetric studies reveal that [Ru(phen)2(qdppz)]2+ is an avid binder of calf-thymus DNA due to a strong intercalation by the ruthenium-bound qdppz, while [Ru(phen)2(hqdppz)]2+ binds to DNA less strongly than the parent "quinone"-containing complex. DNA-photocleavage efficiencies of these complexes also follow a similar trend in that the MLCT-excited state of [Ru(phen)2(qdppz)]2+ is more effective than that of [Ru(phen)2(hqdppz)]2+ in cleaving the supercoiled plasmid pBR 322 DNA (lambda exc = 440 +/- 5 nm), as revealed by the results of agarose gel electrophoresis experiments. The photochemical behaviors of both the quinone- and hydroquinone-appended ruthenium(II) complexes in the presence of DNA not only provide valuable insights into their modes of binding with the duplex but also lead to detailed investigations of their luminescence properties in nonaqueous, aqueous, and aqueous micellar media. On the basis of the results obtained, (i) a photoinduced electron transfer from the MLCT state to the quinone acceptor in Ru(phen)2(qdppz)]2+ and (ii) quenching of the excited states due to proton transfer from water to the dipyridophenazine ligand in both complexes are invoked to rationalize the apparent lack of emission of these redox-related complexes in the DNA medium.     

DNA-binding of semirigid binuclear ruthenium complex delta,delta-[mu-(11,11'-bidppz)(phen)(4)ru(2)](4+): extremely slow intercalation kinetics

We here report a remarkably slow rearrangement of binding modes for a binuclear ruthenium(II) complex upon interaction with DNA. It has been previously shown that Delta,Delta-[mu-(11,11'-bidppz)(phen)4Ru2]4+ binds to DNA in one of the grooves. However, we find that this is only an initial, metastable, binding mode, which is extremely slowly reorganized into an intercalative binding geometry. The slow rearrangement and dissociation, revealed by flow linear dichroism and fluorescence spectroscopy, are concluded to be a result from the complex being threaded through the DNA, with one of the bridging aromatic dppz ligands intercalated between the base pairs of the DNA, placing one metal center in the minor groove and one in the major groove. A negative LD, a high luminescence quantum yield, and long luminescence lifetimes, similar to the intercalating complex Delta-[Ru(phen)2dppz]2+, indicate intercalation of the bidppz moiety. The unique slow dissociation of the complex in its final DNA-binding mode suggests that this class of threading, partially intercalated binuclear complexes may be interesting in the context of cancer therapy. Also, their unique optical and photophysical properties could make such complexes, either alone or scaffolded by DNA structures, of interest for the development of nanometer-sized molecular optoelectronic devices.     

Enantioselective luminescence quenching of DNA light-switch [Ru(phen)2dppz]2+ by electron transfer to structural homologue [Ru(phendione)2dppz]2+

The quenching of the luminescence of [Ru(phen)(2)dppz](2+) by structural homologue [Ru(phendione)(2)dppz](2+), when both complexes are bound to DNA, has been studied for all four combinations of Delta and Lambda enantiomers. Flow linear dichroism spectroscopy (LD) indicates similar binding geometries for all the four compounds, with the dppz ligand fully intercalated between the DNA base pairs. A difference in the LD spectrum observed for the lowest-energy MLCT transition suggests that a transition, potentially related to the final localization of the excited electron to the dppz ligand in [Ru(phen)(2)dppz](2+), is overlaid by an orthogonally polarized transition in [Ru(phendione)(2)dppz](2+). This would be consistent with a low-lying LUMO of the phendione moiety of [Ru(phendione)(2)dppz](2+) that can accept the excited electron from [Ru(phen)(2)dppz](2+), thereby quenching the emission of the latter. The lifetime of excited Delta-[Ru(phen)(2)dppz](2+) is decreased moderately, from 664 to 427 ns, when bound simultaneously with the phendione complex to DNA. The 108 ns lifetime of opposite enantiomer, Lambda-[Ru(phen)(2)dppz](2+), is only shortened to 94 ns. These results are consistent with an average rate constant for electron transfer of approximately 1.10(6) s(-1) between the phenanthroline- and phendione-ruthenium complexes. At binding ratios close to saturation of DNA, the total emission of the two enantiomers is lowered equally much, but for the Lambda enantiomer, this is not paralleled by a decrease in luminescence lifetime. A binding isotherm simulation based on a generalized McGhee-von Hippel approach shows that the Delta enantiomer binds approximately 3 times stronger to DNA both for [Ru(phendione)(2)dppz](2+) and [Ru(phen)(2)dppz](2+). This explains the similar decrease in total emission, without the parallel decrease in lifetime for the Lambda enantiomer. The simulation also does not indicate any significant binding cooperativity, in contrast to the case when Delta-[Rh(phi)(2)bipy](3+) is used as quencher. The very slow electron transfer from [Ru(phen)(2)dppz](2+) to [Ru(phendione)(2)dppz](2+), compared to the case when [Rh(phi)(2)phen](3+) is the acceptor, can be explained by a much smaller driving free-energy difference.     

Ru(phen)2(PHEHAT)]2+ and [Ru(phen)2(HATPHE)]2+: two ruthenium(II) complexes with the same ligands but different photophysics and spectroelectrochemistry

The properties of two mononuclear Ru(II) complexes formed with the extended planar ligand PHEHAT depend drastically on the chelation site by the metallic ion. When the chelation takes place on the HAT site of the ligand (case of the novel complex [Ru(phen)2(HATPHE)]2+), the emission behavior is quite similar to that of [Ru(phen)2(HAT)]2+. In contrast, when the chelation is on the phen motif of the ligand (case of [Ru(phen)2(PHEHAT)]2+), the spectroscopic (absorption and emission) and electrochemical data for the complex do not obey the linear spectroelectrochemical correlation and the emission behavior is comparable to that of the extensively studied dppz complex ([Ru(phen/bpy)2(dppz)]2+). Thus, for [Ru(phen)2(PHEHAT)]2+, the emission lifetimes and intensities as a function of temperature exhibit a maximum for nitrile solvents. However, in contrast to the dppz case, at least three different states (two emitting and one dark) participate in the deactivation with different contributions depending on the temperature. These different contributions explain the observed maximum. Moreover, the fact that the solvent is liquid or frozen also influences the nature of the luminescent species.     

Exploring the interaction of ruthenium(II) polypyridyl complexes with DNA using single-molecule techniques

Here we explore DNA binding by a family of ruthenium(II) polypyridyl complexes using an atomic force microscope (AFM) and optical tweezers. We demonstrate using AFM that Ru(bpy)2dppz2+ intercalates into DNA (K(b) = 1.5 x 10(5) M(-1)), as does its close relative Ru(bpy)2dppx2+ (K(b) = 1.5 x 10(5) M(-1)). However, intercalation by Ru(phen)3(2+) and other Ru(II) complexes with K(b) values lower than that of Ru(bpy)2dppz2+ is difficult to determine using AFM because of competing aggregation and surface-binding phenomena. At the high Ru(II) concentrations required to evaluate intercalation, most of the DNA strands acquire a twisted, curled conformation that is impossible to measure accurately. The condensation of DNA on mica in the presence of polycations is well known, but it clearly precludes the accurate assessment by AFM of DNA intercalation by most Ru(II) complexes, though not by ethidium bromide and other monovalent intercalators. When stretching individual DNA molecules using optical tweezers, the same limitation on high metal concentration does not exist. Using optical tweezers, we show that Ru(phen)2dppz2+ intercalates avidly (K(b) = 3.2 x 10(6) M(-1)) whereas Ru(bpy)3(2+) does not intercalate, even at micromolar ruthenium concentrations. Ru(phen)3(2+) is shown to intercalate weakly (i.e., at micromolar concentrations (K(b) = 8.8 x 10(3) M(-1))). The distinct differences in DNA stretching behavior between Ru(phen)3(2+) and Ru(bpy)3(2+) clearly illustrate that intercalation can be distinguished from groove binding by pulling the DNA with optical tweezers. Our results demonstrate both the benefits and challenges of two single-molecule methods of exploring DNA binding and help to elucidate the mode of binding of Ru(phen)3(2+).     

Intervalence charge transfer in a "chain-like" ruthenium trinuclear assembly based on the bridging ligand 4,7-phenanthrolino-5,6:5',6'-pyrazine (ppz)

The IVCT characteristics of the mixed valence forms of the trinuclear complex [{Delta-Ru(bpy)2}2{Delta(t)-Ru(bpy)(mu-ppz)2}]n+ (n = 7, 8; t = trans), and the diastereoisomers (meso and rac) of the dinuclear complex [{Ru(bpy)2}2(mu-ppz)]5+, display a marked dependence on the nuclearity and extent of oxidation of the assemblies. The dinuclear species are classified as borderline localised-delocalised mixed valence species while the two mixed valence states of the trinuclear complex exhibit localised behaviour. One-electron oxidation of a terminal Ru centre in the trinuclear case gives rise to a broad, low intensity IVCT band for the +7 mixed valence species which is composed of two underlying Gaussian-shaped bands. The transitions are identified as adjacent and remote IVCT transitions, with the former dominating the intensity of the IVCT manifold. The +8 mixed valence species exhibits a single dominant IVCT band arising from the equivalent IVCT transitions from the central Ru(II) to peripheral Ru(III) centres.     

Two-photon absorption of metal-organic DNA-probes

We report remarkable multiphoton absorption properties of DNA intercalating ruthenium complexes: (1) [Ru(phen)(2)dppz](2+); (2) [(11,11'-bidppz)(phen)(4)Ru(2)](4+); (3) [11,11'-bipb(phen)(4)Ru(2)](4+). Two-photon spectra in the range from 460 to 1100 nm were measured using the Z-scan technique. In particular, complex 2 was found to exhibit very strong two- and three-photon absorption properties, which could be an effect of symmetric charge transfer from the ends towards the middle of the conjugated dimeric orbital system. We propose that these molecules could provide a new generation of DNA binding nonlinear chromophores for wide applications in biology and material science. The combination of a large two-photon cross section and strong luminescence quantum yields for the molecules when intercalated makes the compounds uniquely bright and photo-stable probes for two-photon luminescence imaging and also promising as enhanced photosensitizers in two-photon sensitizing applications.     

Ruthenium(II) complexes of 6,7-dicyanodipyridoquinoxaline: synthesis, luminescence studies, and DNA interaction

The hexaflurophosphate and chloride salts of a series of ruthenium(II) complexes incorporating a new dipyridophenazine-based ligand, dicnq (6,7-dicyanodipyrido[2,2-d:2',3'-f]quinoxaline), are synthesized in good-to-moderate yields. These mono ([Ru(phen)2(dicnq)]2+; phen = 1,10-phenanthroline), bis ([Ru(phen)(dicnq)2]2+), and tris ([Ru(dicnq)3]2+) complexes are fully characterized by elemental analysis, infrared, FAB-MS, 1H NMR, and cyclic voltammetric methods. Results of absorption titration and thermal denaturation studies reveal that these complexes are moderately strong binders of calf-thymus (CT) DNA, with their binding constants spanning the range (1-3) x 10(4) M-1. On the other hand, under the identical set of experimental conditions of light and drug dose, the DNA (pBR 322)-photocleavage abilities of these ruthenium(II) complexes follow the order [Ru(phen)2(dicnq)]2+ > [Ru(phen)(dicnq)2]2+ > [Ru(dicnq)3]2+, an order which is the same as that observed for their MLCT emission quantum yields. Steady-state emission studies carried out in nonaqueous solvents and in aqueous media with or without DNA reveal that while [Ru(dicnq)3]2+ is totally nonemissive under these solution conditions, both [Ru(phen)2(dicnq)]2+ and [Ru(phen)(dicnq)2]2+ are luminescent and function as "molecular light switches" for DNA. Successive addition of CT DNA to buffered aqueous solutions containing the latter two complexes results in an enhancement of the emission in each case, with the enhancement factors at saturation being approximately 16 and 8 for [Ru(phen)2(dicnq)]2+ and [Ru(phen)(dicnq)2]2+, respectively. These results are discussed in light of the relationship between the structure-specific deactivations of the MLCT excited states of these metallointercalators and the characteristic features of their DNA interactions, and attempts are made to compare and contrast their properties with those of analogous dipyridophenazine-based complexes, including the ones reported in the preceding paper.