RuII Polypyridyl Complexes Research Articles

Synthesis and Characterisation of RuII Polypyridyl Complexes: DNA-Binding, Photocleavage, and Topoisomerase I and II Inhibitory Activity

Two mixed-ligand ruthenium(ii) complexes [Ru(phen)2(cptcp)]2+ (Ru1; phen = 1,10-phenanthroline, cptcp = 2-(4-carbazol-9-yl-phenyl)-1H-1,3,7,8-tetraaza-cyclopenta-[l]-phenanthrene) and [Ru(phen)2(btcpc)]2+ (Ru2; btcpc = 9-butyl-6-(1H-1,3,7,8-tetraaza-cyclo-cyclopenta-[l]-phenanthren-2-yl)-9H-carbazole-3-carbaldehyde) have been synthesised and characterised. The DNA-binding behaviours of the two complexes have been investigated by using spectroscopic and viscosity measurements. Results suggest that the two complexes bind to DNA by intercalation. The photocleavage of plasmid pBR322 DNA indicates that Ru1 exhibits more effective DNA cleavage activity in comparison to that exhibited by Ru2 under the same conditions, and different cleavage mechanisms are determined. Topoisomerase inhibition and DNA strand passage assay confirm that Ru1 may act as an efficient dual inhibitor of topoisomerases I and II, whereas Ru2 may only act as a single inhibitor of topoisomerases II.

Cover Picture: Polypyridyl Complexes of Ruthenium(II): Stabilization of G‐quadruplex DNA and Inhibition of Telomerase Activity (ChemPlusChem 7/2012)

The cover picture shows a RuII polypyridyl complex with 1,10-phenanthroline as an ancillary ligand, which can target the telomeric DNA sequence at the ends of chromosomes and stabilize the telomeric G-quadruplex through multiple interactions (mainly intercalating) with the G-tetrad by the 3′-terminal face, and thus exhibit considerable inhibitory activity for telomerase and cancer cells. In their Full Paper on page 551 ff, J. Liu and co-workers report on how the design of RuII complexes that target and stabilize the telomeric G-quadruplex is a rational and promising approach to interfere with telomerase activity in tumor cells and to act as potential anticancer agents.

The Radiative Decay Rates Tune the Emissive Properties of Ruthenium(II) Polypyridyl Complexes: A Computational Study

Stay tuned: Tuning the excited state lifetimes of RuII polypyridyl complexes is the key to their potential applicabilities, for example, as photosensitizers. This work demonstrates that the different emissive properties of two similar RuII polypyridyl complexes bearing peripheral ligand substitution are governed by the radiative decay rates and not the energy gap law. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

“Off‐on‐off” Fluorescence pH Switch of Three Trinuclear RuII Complexes Containing Imidazole Rings

AbstractThree tripodal ligands H3L1–3 containing imidazole rings were synthesized by the reaction of 1,10‐phenanthroline‐5,6‐dione with 1,3,5‐tris[(3‐formylphenoxy)methyl]benzene, 1,3,5‐tris[(3‐formylphenoxy)methyl]‐2,4,6‐trimethylbenzene, and 2,2′,2"‐tris[(3‐formylphenoxy)ethyl]amine, respectively. Trinuclear RuII polypyridyl complexes [(bpy)6Ru3H3L1–3](PF6)6 were prepared by the condensation of Ru(bpy)2Cl2·2H2O with ligands H3L1–3. The pH effects on the UV/Vis absorption and fluorescence spectra of the three complexes were studied, and ground‐ and excited‐state ionization constants of the three complexes were derived. The three complexes act as “off‐on‐off” fluorescence pH switch through protonation and deprotonation of imidazole ring with a maximum on‐off ratio of 5 in buffer solution at room temperature.

Inside Cover: Photoactive RuII-Polypyridyl Complexes that Display Sequence Selectivity and High-Affinity Binding to Duplex DNA through Groove Binding (Chem. Eur. J. 7/2011)

Inside Cover: Photoactive RuII-Polypyridyl Complexes that Display Sequence Selectivity and High-Affinity Binding to Duplex DNA through Groove Binding (Chem. Eur. J. 7/2011)

(Polypyridyl)ruthenium(II) Complexes Based on a Back‐to‐Back Bis(pyrazolylpyridine) Bridging Ligand

AbstractTwo (polypyridyl)ruthenium(II) complexes, [(tpy)RuII(L)](PF6)2 (1) and [(tpy)RuII(L)RuII(tpy)](PF6)4 (2) {tpy is 2,2′:6′,2″‐terpyridine and L is 1,4‐bis[(2,6‐dipyrazol‐1‐yl)pyrid‐4‐yl]benzene}, were synthesised and studied in view of their electrochemical and photophysical properties. The structural characterisation of 1 and 2 was carried out by 1H and 13C NMR spectroscopy, MALDI‐TOF/ESI mass spectrometry and single‐crystal X‐ray analysis. The spectro‐ and electrochemical consequences of the introduction of 2,6‐dipyrazol‐1‐ylpyridine coordinating units into RuII polypyridyl complexes were investigated by UV/Vis, low‐temperature emission spectroscopy and square‐wave voltammetry. It was shown that ligand L can be used as a back‐to‐back bridging ligand in the construction of multinuclear ruthenium(II) ion arrays. In comparison to the widely used 2,2′:6′,2″‐terpyridyl system, the 2,6‐dipyrazol‐1‐ylpyrid‐4‐yl unit was found to act as a relatively strong σ‐donor and weak π‐acceptor ligand which allows its use as a structural and electronic alternative in multinuclear architectures.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Distinguishing between Dexter and Rapid Sequential Electron Transfer in Covalently Linked Donor−Acceptor Assemblies

The syntheses, physical, and photophysical properties of a family of complexes having the general formula [M2(L)(mcb)(Ru(4,4'-(X)2-bpy)2)](PF6)3 (where M = Mn(II) or Zn(II), X = CH3 or CF3, mcb is 4'-methyl-4-carboxy-2,2'-bipyridine, and L is a Schiff base macrocycle derived from 2,6-diformyl-4-methylphenol and bis(2-aminoethyl)-N-methylamine) are described. The isostructural molecules all consist of dinuclear metal cores covalently linked to a Ru(II) polypyridyl complex. Photoexcitation of [Mn2(L)(mcb)(Ru((CF3)2-bpy)2)](PF6)3 (4) in deoxygenated CH2Cl2 solution results in emission characteristic of the 3MLCT excited state of the Ru(II) chromophore but with a lifetime (tau(obs) = 5.0 +/- 0.1 ns) and radiative quantum yield (Phi(r) approximately 7 x 10(-4)) that are significantly attenuated relative to the Zn(II) model complex [Zn2(L)(mcb)(Ru((CF3)2-bpy)2)](PF6)3 (6) (tau(obs) = 730 +/- 30 ns and Phi(r) = 0.024, respectively). Quenching of the 3MLCT excited state is even more extensive in the case of [Mn2(L)(mcb)(Ru((CH3)2-bpy)2)](PF6)3 (3), whose measured lifetime (tau(obs) = 45 +/- 5 ps) is >10(4) shorter than the corresponding model complex [Zn2(L)(mcb)(Ru((CH3)2-bpy)2)](PF6)3 (5) (tau(obs) = 1.31 +/- 0.05 micros). Time-resolved absorption measurements on both Mn-containing complexes at room-temperature revealed kinetics that were independent of probe wavelength; no spectroscopic signatures for electron-transfer photoproducts were observed. Time-resolved emission data for complex 4 acquired in CH2Cl2 solution over a range of 200-300 K could be fit to an expression of the form k(nr) = k0 + A x exp{-DeltaE/kB T} with k0 = 1.065 +/- 0.05 x 10(7) s(-1), A = 3.7 +/- 0.5 x 10(10) s(-1), and DeltaE = 1230 +/- 30 cm(-1). Assuming an electron-transfer mechanism, the variable-temperature data on complex 4 would require a reorganization energy of lambda approximately 0.4-0.5 eV which is too small to be associated with charge separation in this system. This result coupled with the lack of enhanced emission at temperatures below the glass-to-fluid transition of the solvent and the absence of visible absorption features associated with the Mn(II)2 core allows for a definitive assignment of Dexter transfer as the dominant excited-state reaction pathway. A similar conclusion was reached for complex 3 based in part on the smaller driving force for electron transfer (DeltaG0(ET) = -0.1 eV), the increase in probability of Dexter transfer due to the closer proximity of the donor excited state to the dimanganese acceptor, and a lack of emission from the compound upon formation of an optical glass at 80 K. Electronic coupling constants for Dexter transfer were determined to be approximately 10 cm(-1) and approximately 0.15 cm(-1) in complexes 3 and 4, respectively, indicating that the change in spatial localization of the excited state from the bridge (complex 3) to the periphery of the chromophore (complex 4) results in a decrease in electronic coupling to the dimanganese core of nearly 2 orders of magnitude. In addition to providing insight into the influence of donor/acceptor proximity on exchange energy transfer, this study underscores the utility of variable-temperature measurements in cases where Dexter and electron-transfer mechanisms can lead to indistinguishable spectroscopic observables.

A 3.0 μs Room Temperature Excited State Lifetime of a Bistridentate RuII−Polypyridine Complex for Rod-like Molecular Arrays

A bistridentate RuII-polypyridine complex [Ru(bqp)2]2+ (bqp = 2,6-bis(8'-quinolinyl)pyridine) has been prepared, which has a coordination geometry much closer to a perfect octahedron than the typical Ru(terpyridine)2-type complex. Thus, the complex displays a 3.0 mus lifetime of the lowest excited metal-to-ligand charge transfer (3MLCT) state at room temperature. This is, to the best of our knowledge, the longest MLCT state lifetime reported for a RuII-polypyridyl complex at room temperature. The structure allows for the future construction of rod-like, isomer-free molecular arrays by substitution of donor and acceptor moieties on the central pyridine units. This makes it a promising photosensitizer for applications in molecular devices for artificial photosynthesis and molecular electronics.

Composite Luminescent Material for Dual Sensing of Oxygen and Temperature

AbstractA novel kind of composite material is presented that contains two indicators incorporated into a single polymer matrix, thus allowing simultaneous determination of oxygen partial pressure and temperature. The temperature‐sensitive dye (ruthenium tris‐1,10‐phenanthroline) was chosen for its highly temperature‐dependent luminescence which is the highest among the RuII polypyridyl complexes. A fluorinated palladium(II) tetraphenylporphyrin served as the oxygen probe. The indicators were incorporated into either poly(styrene‐co‐acrylonitrile) microparticles (to sense oxygen) or into poly(acrylonitrile) (for temperature sensing, since this polymer is virtually impermeable to oxygen). The luminescence of both dyes can be separated either spectrally (due to different absorption and emission spectra of the indicators) or via luminescence decay time. The material is suitable for temperature‐compensated oxygen sensing, for example, in high‐resolution oxygen profiling, and for imaging temperature in the range between 0 and 60 °C. This enables one to “see” (rather than to “feel”) temperature in this important range. Simultaneous imaging of pressure and temperature also has been achieved. It enables contactless imaging of the two parameters, for example, in wind tunnels. Due to the use of a biocompatible hydrogel matrix, the material conceivably is suited for biomedical applications.

Energy Transfer between Ru(II) and Os(II) Polypyridyl Complexes Linked to Polystyrene

Energy transfer between RuII and OsII polypyridyl complexes covalently attached to polystyrene has been in studied in CH3CN. The polymer is a 1:1 styrene-p-aminomethylstyrene copolymer derivatized by amide coupling with the acid-functionalized metal complexes [MII(bpy)2(bpy-COOH)](PF6)2 (MII = RuII, OsII; bpy is 2,2‘-bipyridine and bpy-COOH is 4‘-methyl-2,2‘-bipyridine-4-carboxylic acid). In the resulting polymer [co-PS−CH2NHCO−(RuII11OsII5)](PF6)32, 11 of, on the average, 16 polymer sites are derivatized by RuII and five by OsII. Photophysical properties compared to the homopolymers [co-PS−CH2NHCO−(RuII16)](PF6)32 and [co-PS−CH2NHCO−(OsII16)](PF6)32 reveal that excitation at RuII is followed by efficient energy transfer to the lower energy OsII sites with near unit efficiency (95%). Time-correlated single photon counting measurements with picosecond time resolution reveal that quenching of RuII* produced adjacent to an OsII trap site is quenched with an average rate constant 〈ken〉 = 4.2 × 108 s-1. RuII* decay and OsII* sensitization kinetics are complex because the polymer sample consists of a distribution of individual strands varying in chain length, loading pattern, and number of styryl spacers. The kinetics are further complicated by a contribution from random walk energy migration. An average energy transfer matrix element of 〈Ven〉 ∼ 2 cm-1 for RuII* → OsII energy transfer has been estimated by using emission spectral fitting parameters to calculate the energy transfer barrier.

Static and Time-Resolved Spectroscopic Studies of Low-Symmetry Ru(II) Polypyridyl Complexes

The spectroscopic and electrochemical properties of a series of four RuII polypyridyl complexes are reported. Compounds of the form [Ru(dmb)x(dea)3-x]2+ (x = 0−3), where dmb is 4,4‘-dimethyl-2,2‘-bipyridine and dea is 4,4‘-bis(diethylamino)-2,2‘-bipyridine, have been prepared and studied using static and time-resolved electronic and vibrational spectroscopies as a prelude to femtosecond spectroscopic studies of excited-state dynamics. Static electronic spectra in CH3CN solution reveal a systematic shift of the MLCT absorption envelope from a maximum of 458 nm in the case of [Ru(dmb)3]2+ to 518 nm for [Ru(dea)3]2+ with successive substitutions of dea for dmb, suggesting a dea-based chromophore as the lowest-energy species. However, analysis of static and time-resolved emission data indicates an energy gap ordering of [Ru(dmb)3]2+ > [Ru(dmb)2(dea)]2+ > [Ru(dea)3]2+ > [Ru(dmb)(dea)2]2+, at variance with the electronic structures inferred from the absorption spectra. Nanosecond time-resolved electronic absorp...

Application of deuteriation to determine the location of the emitting state in mixed-ligand RuIIpolypyridyl complexes

The location of the emitting triplet state in heteroleptic RuII polypyridyl complexes has been determined by a new method using deuteriated ligands and emission-lifetime measurements, and a new single-step, high yield synthesis of perdeuteriated 2,2′-bipyridyl has been developed.