Environmental effects on the photophysics of transition metal complexes with dipyrido[2,3-a:3′,2′-c]phenazine (dppz) and related ligands

Towards mismatched DNA photoprobes and photoreagents: “elbow-shaped” Ru(ii) complexes

Due to their potentially harmful consequences, the detection of mismatched DNA is a subject of high interest. In order to probe these DNA mismatches, we report new Ru(ii) complexes, bearing “elbow-shaped” extended planar ligands based on an acridine or a phenazine core.

Diiridium(iii) complexes: luminescent probes and sensors for G-quadruplex DNA and endoplasmic reticulum imaging

Two new dinuclear iridium (Ir) complexes bridged by a conjugated aromatic tppz ligand, (bhq)₂Ir(tppz)Ir(bhq)₂(1) and (ppy)₂Ir(tppz)Ir(ppy)₂(2) (bhq = benzo(h)quinolone, ppy = phenyl-pyridine, tppz = tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine), were prepared.

Photochemistry of ruthenium(ii) complexes based on 1,4,5,8-tetraazaphenanthrene and 2,2′-bipyrazine: a comprehensive experimental and theoretical study

Comprehensive study of ruthenium complexes based on 2,2′-bipyrazine and 1,4,5,8-tetraazaphenanthrene, which can be used as photoreactive materials for biomedical applications.

A ratiometric sensor for DNA based on a dual emission Ru(dppz) light-switch complex

Herein we describe the DNA binding properties of two new water-soluble ruthenium complexes; experimental and computational data reveal that both complexes display dual emission from MLCT and LLCT excited states.

Ultrafast in cellulo photoinduced dynamics processes of the paradigm molecular light switch [Ru(bpy)2dppz](2.)

An in cellulo study of the ultrafast excited state processes in the paradigm molecular light switch [Ru(bpy)₂dppz]²⁺ by localized pump-probe spectroscopy is reported for the first time. The localization of [Ru(bpy)₂dppz]²⁺ in HepG2 cells is verified by emission microscopy and the characteristic photoinduced picosecond dynamics of the molecular light switch is observed in cellulo. The observation of the typical phosphorescence stemming from a ³MLCT state suggests that the [Ru(bpy)₂dppz]²⁺ complex intercalates with the DNA in the nucleus. The results presented for this benchmark coordination compound reveal the necessity to study the photoinduced processes in coordination compounds for intracellular use, e.g. as sensors or as photodrugs, in the actual biological target environment in order to derive a detailed molecular mechanistic understanding of the excited-state properties of the systems in the actual biological target environment.

Monitoring guanine photo-oxidation by enantiomerically resolved Ru(II) dipyridophenazine complexes using inosine-substituted oligonucleotides

The intercalating [Ru(TAP)2(dppz)](2+) complex can photo-oxidise guanine in DNA, although in mixed-sequence DNA it can be difficult to understand the precise mechanism due to uncertainties in where and how the complex is bound. Replacement of guanine with the less oxidisable inosine (I) base can be used to understand the mechanism of electron transfer (ET). Here the ET has been compared for both Λ- and Δ-enantiomers of [Ru(TAP)2(dppz)](2+) in a set of sequences where guanines in the readily oxidisable GG step in {TCGGCGCCGA}2 have been replaced with I. The ET has been monitored using picosecond and nanosecond transient absorption and picosecond time-resolved IR spectroscopy. In both cases inosine replacement leads to a diminished yield, but the trends are strikingly different for Λ- and Δ-complexes.

Direct observation by time-resolved infrared spectroscopy of the bright and the dark excited states of the [Ru(phen)2(dppz)]2+ light-switch compound in solution and when bound to DNA

The [Ru(phen)2(dppz)]2+ complex (1) is non-emissive in water but is highly luminescent in organic solvents or when bound to DNA, making it a useful probe for DNA binding. To date, a complete mechanistic explanation for this "light-switch" effect is still lacking. With this in mind we have undertaken an ultrafast time resolved infrared (TRIR) study of 1 and directly observe marker bands between 1280-1450 cm-1, which characterise both the emissive "bright" and the non-emissive "dark" excited states of the complex, in CD3CN and D2O respectively. These characteristic spectral features are present in the [Ru(dppz)3]2+ solvent light-switch complex but absent in [Ru(phen)3]2+, which is luminescent in both solvents. DFT calculations show that the vibrational modes responsible for these characteristic bands are predominantly localised on the dppz ligand. Moreover, they reveal that certain vibrational modes of the "dark" excited state couple with vibrational modes of two coordinating water molecules, and through these to the bulk solvent, thus providing a new insight into the mechanism of the light-switch effect. We also demonstrate that the marker bands for the "bright" state are observed for both Λ- and Δ-enantiomers of 1 when bound to DNA and that photo-excitation of the complex induces perturbation of the guanine and cytosine carbonyl bands. This perturbation is shown to be stronger for the Λ-enantiomer, demonstrating the different binding site properties of the two enantiomers and the ability of this technique to determine the identity and nature of the binding site of such intercalators.

Ruthenium Complex "Light Switches" that are Selective for Different G-Quadruplex Structures

Recognition and regulation of G-quadruplex nucleic acid structures is an important goal for the development of chemical tools and medicinal agents. The addition of a bromo-substituent to the dipyridylphenazine (dppz) ligands in the photophysical "light switch", [Ru(bpy)2 dppz](2+) , and the photochemical "light switch", [Ru(bpy)2 dmdppz](2+) , creates compounds with increased selectivity for an intermolecular parallel G-quadruplex and the mixed-hybrid G-quadruplex, respectively. When [Ru(bpy)2 dppz-Br](2+) and [Ru(bpy)2 dmdppz-Br](2+) are incubated with the G-quadruplexes, they have a stabilizing effect on the DNA structures. Activation of [Ru(bpy)2 dmdppz-Br](2+) with light results in covalent adduct formation with the DNA. These complexes demonstrate that subtle chemical modifications of Ru(II) complexes can alter G-quadruplex selectivity, and could be useful for the rational design of in vivo G-quadruplex probes.

[Ru(phen)2dppz]2+ luminescence reveals nanoscale variation of polarity in the cyclodextrin cavity

Insertion of dppz with phosphorylated β-cyclodextrin results in multi-exponential [Ru(phen)₂dppz]²⁺ emission; binding is weaker than [Ru(phen)₃]²⁺, but shows stereoselectivity.

Contrasting photophysical properties of rhenium(i) tricarbonyl complexes having carbazole groups attached to the polypyridine ligand

The fac-[Re(CO)₃(cbz₂phen)(L)]^0/+1 complexes showed a remarkable presence of the ILCT_cbz2phen fluorescence in addition to the usually observed ³MLCT_{Re→cbz2phen}. In PMMA films the emission is completely turned into a triplet excited state manifold.

Synthesis of three series of ruthenium tris-diimine complexes containing acridine-based π-extended ligands using an efficient “chemistry on the complex” approach

Novel multi-step chemistry on the complex strategy.

Luminescent ruthenium polypyridyl complexes with extended ‘dppz’ like ligands as DNA targeting binders and cellular agents

DNA-binding and phototoxicity of Ru(ii) complexes with ligands derived from pyrazinodipyridophenazine and either phen or TAP as ancillary ligands are reported.

Ruthenium(ii) complexes with dppz: from molecular photoswitch to biological applications

The present article describes the recent advances in biological applications of the Ru-dppz systems in DNA binding, cellular imaging, anticancer drugs, phototherapy, protein aggregation detecting and chemosensors.

Binding Behaviors for Different Types of DNA G-Quadruplexes: Enantiomers of [Ru(bpy)2(L)](2+) (L=dppz, dppz-idzo)

Polymorphic DNA G-quadruplex recognition has attracted great interest in recent years. The strong binding affinity and potential enantioselectivity of chiral [Ru(bpy)2 (L)](2+) (L=dipyrido[3,2-a:2',3'-c]phenazine, dppz-10,11-imidazolone; bpy=2,2'-bipyridine) prompted this investigation as to whether the two enantiomers, Δ and Λ, can show different effects on diverse structures with a range of parallel, antiparallel and mixed parallel/antiparallel G-quadruplexes. These studies provide a striking example of chiral-selective recognition of DNA G-quadruplexes. As for antiparallel (tel-Na(+)) basket G-quadruplex, the Λ enantiomers bind stronger than the Δ enantiomers. Moreover, the behavior reported here for both enantiomers stands in sharp contrast to B-DNA binding. The chiral selectivity toward mixed parallel/antiparallel (tel-K(+)) G-quadruplex of both compounds is weak. Different loop arrangements can change chiral complex selectivity for both antiparallel and mixed parallel/antiparallel G-quadruplex. Whereas both Δ and Λ isomers bind to parallel G-quadruplexes with comparable affinity, no appreciable stereoselective G-quadruplex binding of the isomers was observed. In addition, different binding stoichiometries and binding modes for Δ and Λ enantiomers were confirmed. The results presented here indicate that chiral selective G-quadruplex binding is not only related to G-quadruplex topology, but also to the sequence and the loop constitution.

Toward white electroluminescence by ruthenium quinoxaline light emitting diodes

Exciplex transfer as a new approach to produce white electroluminescence in ruthenium quinoxaline light emitting diodes.

Unexpected DNA binding properties with correlated downstream biological applications in mono vs. bis-1,8-naphthalimide Ru(ii)-polypyridyl conjugates

The development of two 1,8-napthalimide-conjugated Ru(ii)-polypyridyl complexes which exhibit different DNA binding and photocleavage behavior is presented.

Photophysical properties of ruthenium(II) polypyridyl DNA intercalators: effects of the molecular surroundings investigated by theory

The environmental effects on the structural and photophysical properties of [Ru(L)2 (dppz)](2+) complexes (L=bpy=2,2'-bipyridine, phen=1,10-phenanthroline, tap=1,4,5,8-tetraazaphenanthrene; dppz=dipyrido[3,3-a:2',3'-c]phenazine), used as DNA intercalators, have been studied by means of DFT, time-dependent DFT, and quantum mechanics/molecular mechanics calculations. The electronic characteristics of the low-lying triplet excited states in water, acetonitrile, and DNA have been investigated to decipher the influence of the environment on the luminescent behavior of this class of molecules. The lowest triplet intra-ligand (IL) excited state calculated at λ≈800 nm for the three complexes and localized on the dppz ligand is not very sensitive to the environment and is available for electron transfer from a guanine nucleobase. Whereas the lowest triplet metal-to-ligand charge-transfer ((3)MLCT) states remain localized on the ancillary ligand (tap) in [Ru(tap)2 (dppz)](2+), regardless of the environment, their character is drastically modified in the other complexes [Ru(phen)2 (dppz)](2+) and [Ru(bpy)2 (dppz)](2+) upon going from acetonitrile (MLCTdppz/phen or MLCTdppz/bpy) to water (MLCTdppz) and DNA (MLCTphen and MLCTbpy). The change in the character of the low-lying (3) MLCT states accompanying nuclear relaxation in the excited state controls the emissive properties of the complexes in water, acetonitrile, and DNA. The light-switching effect has been rationalized on the basis of environment-induced control of the electronic density distributed in the lowest triplet excited states.

RutheniumII complexes bearing fused polycyclic ligands: from fundamental aspects to potential applications

In this review, we first discuss the photophysics reported in the literature for mononuclear ruthenium complexes bearing ligands with extended aromaticity such as dipyrido[3,2-a:2',3'-c]phenazine (DPPZ), tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]-phenazine (TPPHZ),  tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]acridine (TPAC), 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene (PHEHAT) 9,11,20,22-tetraaza- tetrapyrido[3,2-a:2',3'-c:3'',2''-l:2''',3'''-n]pentacene (TATPP), etc. Photophysical properties of binuclear and polynuclear complexes based on these extended ligands are then reported. We finally develop the use of binuclear complexes with extended π-systems for applications such as photocatalysis.

Dinuclear ruthenium(II) complexes as two-photon, time-resolved emission microscopy probes for cellular DNA

The first transition-metal complex-based two-photon absorbing luminescence lifetime probes for cellular DNA are presented. This allows cell imaging of DNA free from endogenous fluorophores and potentially facilitates deep tissue imaging. In this initial study, ruthenium(II) luminophores are used as phosphorescent lifetime imaging microscopy (PLIM) probes for nuclear DNA in both live and fixed cells. The DNA-bound probes display characteristic emission lifetimes of more than 160 ns, while shorter-lived cytoplasmic emission is also observed. These timescales are orders of magnitude longer than conventional FLIM, leading to previously unattainable levels of sensitivity, and autofluorescence-free imaging.

Selective DNA purine base photooxidation by bis-terdentate iridium(III) polypyridyl and cyclometalated complexes

Two bis-terdentate iridium(III) complexes with polypyridyl and cyclometalated ligands have been prepared and characterized. Their spectroscopic and electrochemical properties have been studied, and a photophysical scheme addressing their properties is proposed. Different types of excited states have been considered to account for the deactivation processes in each complex. Interestingly, in the presence of mono- or polynucleotides, a photoinduced electron-transfer process from a DNA purine base (i.e., guanine or adenine) to the excited complex is shown through luminescence quenching experiments. For the first time, this work reports evidence for selective DNA purine bases oxidation by excited iridium(III) bis-terdentate complexes.

The photophysics of fac-[Re(CO)3(NN)(bpa)]+ complexes: a theoretical/experimental study

The influence of the polypyridyl ligand on the photophysics of Re(i) tricarbonyl complexes was investigated by steady-state and time resolved spectroscopy as well as by theoretical calculations.

Targeting the endoplasmic reticulum with a membrane-interactive luminescent ruthenium(ii) polypyridyl complex†Electronic supplementary information (ESI) available: Experimental details, characterization of and Fig. S1-S6. See DOI: 10.1039/c3sc51725jClick here for additional data file

The characterization and bioactivity of the dinuclear ruthenium(ii) complex [(Ru(DIP)2)2(tpphz)]4+ (DIP = 4,7-diphenyl-1,10-phenanthroline and tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) is reported. This new complex is found to be luminescent in acetonitrile, where excitation into MLCT (metal-to-ligand charge-transfer) bands in the visible area of the spectrum (λex = 450 nm, ε = 45 000 M-1 cm-1) result in red emission (λem,max = 620 nm, ΦMLCT = 0.017). Aqueous in vitro binding studies indicate that this complex binds to duplex DNA with an affinity of 1.8 × 106 M-1 through a non-classical groove-binding interaction, however, unlike the parent complex [(Ru(phen)2)2(tpphz)]4+ (phen = 1,10-phenanthroline), it also displays an increase in MLCT luminescence on addition of liposomes. Confocal microscopy and TEM studies show that this lipophilic complex targets the endoplasmic reticulum of eukaryotic cells, where it functions as an imaging agent for this organelle, and cytotoxicity studies in human cancer cell lines indicate a comparable potency to the anti-cancer drug cisplatin.

Peptide directed transmembrane transport and nuclear localization of Ru(II) polypyridyl complexes in mammalian cells

The targeted delivery of luminescent Ru(II) polypyridyl complexes to the nucleus of live mammalian cells by a Nuclear Localisation Signal (NLS) peptide; NF-κB is demonstrated.

X-ray crystal structure of rac-[Ru(phen)2dppz]2+ with d(ATGCAT)2 shows enantiomer orientations and water ordering

We report an atomic resolution X-ray crystal structure containing both enantiomers of rac-[Ru(phen)2dppz](2+) with the d(ATGCAT)2 DNA duplex (phen = phenanthroline; dppz = dipyridophenazine). The first example of any enantiomeric pair crystallized with a DNA duplex shows different orientations of the Λ and Δ binding sites, separated by a clearly defined structured water monolayer. Job plots show that the same species is present in solution. Each enantiomer is bound at a TG/CA step and shows intercalation from the minor groove. One water molecule is directly located on one phenazine N atom in the Δ-enantiomer only.

Photoexpulsion of surface-grafted ruthenium complexes and subsequent release of cytotoxic cargos to cancer cells from mesoporous silica nanoparticles

Ruthenium(II) polypyridyl complexes have emerged both as promising probes of DNA structure and as anticancer agents because of their unique photophysical and cytotoxic properties. A key consideration in the administration of those therapeutic agents is the optimization of their chemical reactivities to allow facile attack on the target sites, yet avoid unwanted side effects. Here, we present a drug delivery platform technology, obtained by grafting the surface of mesoporous silica nanoparticles (MSNPs) with ruthenium(II) dipyridophenazine (dppz) complexes. This hybrid nanomaterial displays enhanced luminescent properties relative to that of the ruthenium(II) dppz complex in a homogeneous phase. Since the coordination between the ruthenium(II) complex and a monodentate ligand linked covalently to the nanoparticles can be cleaved under irradiation with visible light, the ruthenium complex can be released from the surface of the nanoparticles by selective substitution of this ligand with a water molecule. Indeed, the modified MSNPs undergo rapid cellular uptake, and after activation with light, the release of an aqua ruthenium(II) complex is observed. We have delivered, in combination, the ruthenium(II) complex and paclitaxel, loaded in the mesoporous structure, to breast cancer cells. This hybrid material represents a promising candidate as one of the so-called theranostic agents that possess both diagnostic and therapeutic functions.

Preferred orientation in an angled intercalation site of a chloro-substituted Λ-[Ru(TAP)2(dppz)]2+ complex bound to d(TCGGCGCCGA)2

The crystal structure of the ruthenium DNA 'light-switch' complex Λ-[Ru(TAP)2(11-Cl-dppz)](2+) (TAP=tetraazaphenanthrene, dppz=dipyrido[3,2-a':2',3'-c]phenazine) bound to the oligonucleotide duplex d(TCGGCGCCGA)2 is reported. The synthesis of the racemic ruthenium complex is described for the first time, and the racemate was used in this study. The crystal structure, at atomic resolution (1.0 Å), shows one ligand as a wedge in the minor groove, resulting in the 51(°) kinking of the double helix, as with the parent Λ-[Ru(TAP)2(dppz)](2+). Each complex binds to one duplex by intercalation of the dppz ligand and also by semi-intercalation of one of the orthogonal TAP ligands into a second symmetrically equivalent duplex. The 11-chloro substituent binds with the major component (66%) oriented with the 11-chloro substituent on the purine side of the terminal step of the duplex.