Aryl substituted ruthenium bis-terpyridine complexes: intercalation and groove binding with DNA

Equilibria in the aqueous system of cobalt(II) based on 2-picolinehydroxamic acid and N-(2-hydroxybenzyl)phenylalanine and its ability to inhibit the propagation of cancer cells

Mixed-ligand complexes of cobalt(II) with two bioligands, viz. 2-picolinehydroxamic acid and the reduced Schiff base N-(2-hydroxybenzyl)phenylalanine, were studied in aqueous solution by potentiometry and UV-Vis spectroscopic analysis. The coordination mode of the complexes and their stability were determined and compared to their parent species. Stacking interactions between the rings present in the ligands influence the stability of the complexes. Also, UV-Vis spectroscopy revealed that the stacking interactions affected the intercalation of DNA and mixed-ligand complexes. The in vitro anticancer activity of the free ligand 2-picolinehydroxamic acid and the complexes was tested against cervical and gastric human adenocarcinoma epithelial cell lines. At concentrations of 0.06 and 0.11 mM, the mixed-ligand structures showed the ability to reduce gastric cancer cells with no inhibitory effect on mouse fibroblasts. The cytotoxic effect was accompanied by damage to the cell nuclei, which may confirm that the complexes demonstrate effective binding to DNA. No determination of minimal inhibitory and bactericidal/fungicidal concentrations against the test organisms was possible at higher complex concentrations due to precipitation.

Organic-Ru2+ Cluster Initiated Dendritic-faced Metallo-Octahedron and Its Unpredictable Photoactivity

Herein, a novel 3D metal-organic ligand consists of a folded Ru(II) connected tetrameric cycle and two sets of 60° juxtaposed bisterpyridine arms was synthesized and its complexation with Zn2+ gave...

Synthesis, Anticancer Evaluation, Computer-Aided Docking Studies, and ADMET Prediction of 1,2,3-Triazolyl-Pyridine Hybrids as Human Aurora B Kinase Inhibitors

A novel series of 1,2,3-triazolyl-pyridine hybrids were prepared through the reaction of the triazole derivative (1) with the appropriate aldehyde (2a-g) and malononitrile or ethyl cyanoacetate in the presence of ammonium acetate in refluxed acetic acid. The chemical composition of the products was established on the basis of spectral and elemental analyses. Aurora B kinase is a protein with diverse biological actions in controlling tumorigenesis by inhibiting apoptosis and promoting proliferation and metastasis, making it an emerging target for diseases such as hepatocellular carcinoma (HCC). Alteration in the target protein expression causes unequal distribution of genetic information, causing HCC. The new compounds were tested for their antihepatic cancer activity, and some of them had strong efficacy against human hepatoblastoma (HepG2) cell lines.

Synthesis, characterization, ADMET, in vitro and in vivo studies of mixed ligand metal complexes from a curcumin Schiff base and lawsone

Complexes are currently synthesized from plant origin because of their therapeutic effect against certain diseases with toxicity. Hence, in this work, four new transition metal(II) mixed ligand complexes have been synthesized using a curcumin Schiff base (primary ligand) and lawsone (as co-ligand). The geometry of these complexes was explored by elemental analyses, molar conductance, thermal analysis, magnetic moment values, IR, NMR, Mass, electronic and EPR spectral studies. Electronic absorption titrations, viscosity measurements and molecular docking studies reveal that all the metal complexes interact with the CT DNA by groove binding. Among all the complexes, the copper(II) complex (complex 1) exhibits a higher K_b value (3.5 × 10^-4 M) which reveals that it has a strong binding efficiency toward the CT DNA. The complexes also possess strong DNA cleavage efficiency. Cytotoxicity investigations on Artemia salina show that all the complexes possess higher cytotoxic effect than the ligand. Moreover, all the metal complexes have better antimicrobial efficacy than the ligand. Swiss ADME, PASS and pkCSM online softwares are helpful to predict the pharmacokinetic and biological actions of the curcumin Schiff base. Theoretical results obtained from the in silico study are experimentally corroborated by in vivo anti-inflammatory screening study. All the above studies demonstrate that the copper complex possesses biological activity similar to that of the drug like molecules. Research Highlights Synthesis and characterization of four novel transition mixed ligand complexes using plant moieties Promising in vivo anti-inflammatory agents and in vitro DNA metallonucleases Cytotoxicity investigation on Artemia salina Higher cytotoxic effect for the complexes than the ligand Identification of copper(II) complex as lead like molecule among all.

Facile synthesis and antiproliferative activity of new 3-cyanopyridines

Background

Pyridines have been reported to possess various pharmacological activities.

Results

Sodium 3-oxo-3-(2-oxo-2H-chromen-3-yl)prop-1-en-1-olate (2) and sodium 3-oxo-3-(3-oxo-3H-benzo[f]chromen-2-yl)prop-1-en-1-olate (7) were prepared and reacted with 2-cyano-N'-(1-aryl(heteryl)ethylidene)acetohydrazides 3a-d to produce 2-oxo-1,2-dihydropyridine-3-carbonitrile derivatives 5a-d and 9a-d, respectively, in good yields. Also, 3a-d reacted with sodium (2-oxocyclopentylidene)methanolate (11a) or sodium (2-oxocyclohexylidene) methanolate (11b) to yield 2-oxo-tetrahydro-1H-cyclopenta[b]pyridine-3-carbonitriles 13a-d and 2-oxo-hexahydroquinoline-3-carbonitriles 13e-h, respectively. The mechanisms that account for the formation of the products are discussed. Additionally, the structures of all the newly synthesized products are confirmed, based on elemental analysis and spectral data. Several of the newly synthesized compounds are evaluated for their antitumor activity against HEPG2 and their structure activity relationship (SAR) was studied.

Conclusions

The results revealed that the pyridine derivatives 5c and 5d (IC₅₀ = 1.46, 7.08 µM, respectively) have promising antitumor activity against liver carcinoma cell line (HEPG2), compared to the reference drug, doxorubicin.

Systematic investigation of the antiproliferative activity of a series of ruthenium terpyridine complexes

Due to acquired resistance or limitations of the currently approved drugs against cancer, there is an urgent need for the development of new classes of compounds. Among others, there is an increasing attention towards the use of Ru(II) polypyridyl complexes. Most studies in the literature were made on complexes based on the coordination of N-donating bidentate ligands to the ruthenium core whereas studies on 2,2':6', 2″-terpyridine (terpy) coordinating ligands are relatively scare. However, several studies have shown that [Ru(terpy)2]²⁺ derivatives are able bind to DNA through various binding modes making these compounds potentially suitable as chemotherapeutic agents. Additionally, light irradiation of these compounds was shown to enable DNA cleavage, highlighting their potential use as photosensitizers (PSs) for photodynamic therapy (PDT). In this work, we present the systematic investigation of the potential of 7 complexes of the type [Ru(terpy)(terpy-X)]2+ (X = H (1), Cl (2), Br (3), OMe (4), COOH (5), COOMe (6), NMe2 (7)) as potential chemotherapeutic agents and PDT PSs. Importantly, six of the seven complexes were found to be stable in human plasma as well as photostable in acetonitrile upon continuous light irradiation (480 nm). The determination of the distribution coefficient logP values for the 7 complexes revealed their good water solubility. Complex 7 was found to be cytotoxic in the micromolar range in the dark as well as to have some phototoxicity upon light exposure at 480 nm in non-cancerous retinal pigment epithelium (RPE-1) and cancerous human cervical carcinoma (HeLa) cells. SYNOPSIS: The systematic investigation of the potential of 7 complexes of the type [Ru(terpy)(terpy-X)]²⁺ (terpy: 2,2':6', 2″-terpyridine; X = H (1), Cl (2), Br (3), OMe (4), COOH (5), COOMe (6), NMe2 (7)) as potential chemotherapeutic agents and photosensitizers for photodynamic therapy is presented.

Investigations into the DNA-binding mode of doxorubicinone

Cancer treatment is one of the major challenges facing the modern biomedical profession. Development of new small-molecule chemotherapeutics requires an understanding of the mechanism of action for these treatments, as well as the structure-activity relationship. Study of the well-known DNA-intercalating agent, doxorubicin, and its aglycone, doxorubicinone, was undertaken using a variety of spectroscopic and calorimetric techniques. It was found that, despite conservation of the planar, aromatic portion of doxorubicin, the agylcone does not intercalate; it instead likely binds to the DNA minor-groove.

4-Acetamidophenol Binding Mechanism with DNA by UV-Vis and FTIR Techniques Based on Binding Energy, LUMO and HOMO Orbitals and Geometry of Molecule

Present study was conducted to appraise the interaction mechanism of 4-acetamidophenol (4-AP) with DNA based on UV-Vis and FTIR techniques based on binding energy, isolated atomic energy, LUMO and HOMO orbitals gap and geometry of molecule. Analysis revealed the groove binding and intercalation mode of interaction between 4-AP and DNA since hyperchromic and bathochromic shifts were observed in response of interaction of DNA. The planar part of interacting molecule intercalated with DNA and non-planar part of 4-acetamidophenol bounded with DNA (groove binding). The constants for binding between 4-AP and DNA were calculated and 20.12 × 103 mol−1 dm3 binding constant was recorded at pH 4.7, whereas this value was 5.32 × 103 mol−1 dm3 for the pH 7.4. The binding constant value for interaction of 4-AP with DNA revealed the possibility of oral administration of 4-AP. The 4-AP binding with DNA is spontaneous process, which was confirmed from negative value of free energy at room temperature. FTIR study revealed that C–H and C=C (aromatic) functional groups were involved in binding at pH 4.7 and C=O (amide) was involved in groove binding, whereas C–H (aromatic) was responsible for intercalation at pH 7.4 and C–H (alkaline) and C=O (amide) were responsible for groove binding at pH 4.7.

Synthesis, characterization and biological evaluation of six highly cytotoxic ruthenium(ii) complexes with 4'-substituted-2,2':6',2''-terpyridine

Herein, six ruthenium(ii) terpyridine complexes, i.e. [RuCl2(4-EtN-Phtpy)(DMSO)] (Ru1), [RuCl2(4-MeO-Phtpy)(DMSO)] (Ru2), [RuCl2(2-MeO-Phtpy)(DMSO)] (Ru3), [RuCl2(3-MeO-Phtpy)(DMSO)] (Ru4), [RuCl2(1-Bip-Phtpy)(DMSO)] (Ru5), and [RuCl2(1-Pyr-Phtpy)(DMSO)] (Ru6) with 4'-(4-diethylaminophenyl)-2,2':6',2''-terpyridine (4-EtN-Phtpy), 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (4-MeO-Phtpy), 4'-(2-methoxyphenyl)-2,2':6',2''-terpyridine (2-MeO-Phtpy), 4'-(3-methoxyphenyl)-2,2':6',2''-terpyridine (3-MeO-Phtpy), 4'-(1-biphenylene)-2,2':6',2''-terpyridine (1-Bip-Phtpy), and 4'-(1-pyrene)-2,2':6',2''-terpyridine (1-Pyr-Phtpy), respectively, were synthesized and fully characterized. The MTT assay demonstrates that the in vitro anticancer activity of Ru1 is higher than that of Ru2-Ru6 and more selective for Hep-G2 cells than for normal HL-7702 cells. In addition, various biological assays show that Ru1 and Ru6, especially the Ru1 complex, are telomerase inhibitors targeting c-myc G4 DNA and also cause apoptosis of Hep-G2 cells. With the same Ru center, the in vitro antitumor activity and cellular uptake ability of the 4-EtN-Phtpy and 1-Bip-Phtpy ligands follow the order 4-EtN-Phtpy > 1-Bip-Phtpy.

Polarization spectroscopy methods in the determination of interactions of small molecules with nucleic acids - tutorial

The structural characterization of non-covalent complexes between nucleic acids and small molecules (ligands) is of a paramount significance to bioorganic research. Highly informative methods about nucleic acid/ligand complexes such as single crystal X-ray diffraction or NMR spectroscopy cannot be performed under biologically compatible conditions and are extensively time consuming. Therefore, in search for faster methods which can be applied to conditions that are at least similar to the naturally occurring ones, a set of polarization spectroscopy methods has shown highly promising results. Electronic circular dichroism (ECD) is the most commonly used method for the characterization of the helical structure of DNA and RNA and their complexes with ligands. Less common but complementary to ECD, is flow-oriented linear dichroism (LD). Other methods such as vibrational CD (VCD) and emission-based methods (FDCD, CPL), can also be used for suitable samples. Despite the popularity of polarization spectroscopy in biophysics, aside several highly focused reviews on the application of these methods to DNA/RNA research, there is no systematic tutorial covering all mentioned methods as a tool for the characterization of adducts between nucleic acids and small ligands. This tutorial aims to help researchers entering the research field to organize experiments accurately and to interpret the obtained data reliably.

Fluorescence detected linear dichroism spectroscopy: A selective and sensitive probe for fluorophores in flow-oriented systems

Fluorescence detection typically enhances sensitivity and selectivity for fluorescent analytes. The potential for combining fluorescence detection with flow orientation of the sample in the normal configuration of linear dichroism experiments is explored in this work by measuring the fluorescence emitted from flow-orientated DNA-bound ligands and M13 bacteriophage. Data for ethidium bromide, Hoechst 33258, and 4,6-diamidino-2-phenyindole are presented. The theoretical basis of the technique is also presented for instruments running in both the fixed direct-current mode, which is the normal operation mode of circular dichroism spectropolarimeters, and also in fixed high-tension voltage mode. The role of the stray light reaching the detector that results in a spectral shape in fixed direct current mode that resembles the shape of a linear dichroism spectrum, rather than the expected reduced linear dichroism, is also explored.

Excited State Dynamics of a Photobiologically Active Ru(II) Dyad Are Altered in Biologically Relevant Environments

In this study femtosecond and nanosecond time-resolved transient absorption spectroscopy was used to investigate the influence of ionic strength and complexity on the excited state dynamics of a Ru(II)-based metal-organic dyad. The bis-heteroleptic complex [Ru(bpy)₂(ippy)]²⁺ (1), where bpy = 2,2'-bipyridine and ippy = 2-(1-pyrenyl-1H-imidazo[4,5-f][1,10]phenanthroline, is a potent photosensitizer for in vitro photodynamic therapy (PDT) and photodynamic inactivation (PDI) of microorganisms owing to a long-lived triplet excited state derived from a metal-to-ligand charge-transfer (³MLCT) state that is equilibrium with an intraligand (³IL) state. The prolonged lifetime provides ample opportunity for bimolecular quenching of this state by oxygen; thus singlet oxygen (¹O₂) sensitization is very efficient. In simple aqueous solution, fast cooling within the ³MLCT manifold is followed by energy transfer to an ³IL state, which is facilitated by rotation of a pyrenyl unit about the imidazo-pyrenyl (ip) coannular bond. For solutions of 1 in high ionic strength simulated biological fluid (SBF), a more physiologically relevant solvent that contains a complex mixture of ions at pH 7.4, femtosecond studies revealed an additional excited state, possibly based on an ion-ligand interaction. This new state appearing in high ionic strength SBF was not observable in water, simple buffers, or low ionic strength SBF. These photoinduced dynamics were also affected by the presence of biomolecules such as DNA in simple buffer, whereby relaxation on the picosecond time scale was accelerated from 39 to 18 ps with DNA intercalation by 1. The increased rate of coplanarization of the pyrene and the imidazole units was attributed to DNA-induced conformational restriction of the pyrenyl unit relative to the ip bond. Quantitative changes to excited state decay rates of 1 in solutions of high ionic strength were also observed when probed on the microsecond time scale. Notably, the thermalized excited state decay pathways were altered substantially with DNA intercalation, with access to some states being completely blocked. Experimentally, this manifested in the absence of the slowest microsecond decay channel, which is normally observed for 1 in solution. The quantitative and qualitative observations from this study highlight the importance of employing biologically relevant solvents and potential biomolecule targets when the excited state dynamics and photophysical properties (under cell-free conditions) responsible for the potent photobiological effects are assessed in the context of photodynamic therapy and photodynamic inactivation.

Heteroleptic Cu(ii)–polypyridyl complexes as photonucleases

Four new copper(ii)–polypyridyl complexes having tail groups with increasing aromaticity, hydrophobicity and planarity are synthesized. These complexes are found to be avid DNA binders and show efficient nuclease activity under either chemical stimulus or UV-A light irradiation.

Metal complex interactions with DNA

Increasing numbers of DNA structures are being revealed using a diverse range of transition metal complexes and biophysical spectroscopic techniques. Here we present a review of metal complex-DNA interactions in which several binding modes and DNA structural forms are explored.

Binding of Ru(terpyridine)(pyridine)dipyridophenazine to DNA studied with polarized spectroscopy and calorimetry

Achiral Ru(tpy)(py)dppz²⁺ intercalated into DNA has similar intermolecular interactions as opposite enantiomers of its structural isomer, the “light-switch” complex Ru(bpy)₂dppz²⁺.

Interaction of doxorubicin with polynucleotides. A spectroscopic study

The interaction of doxorubicin (DX) with model polynucleotides poly(dG-dC)·poly(dG-dC) (polyGC), poly(dA-dT)·poly(dA-dT) (polyAT), and calf thymus DNA has been studied by several spectroscopic techniques in phosphate buffer aqueous solutions. UV-vis, circular dichroism, and fluorescence spectroscopic data confirm that intercalation is the prevailing mode of interaction, and also reveal that the interaction with AT-rich regions leads to the transfer of excitation energy to DX not previously documented in the literature. Moreover, the DX affinity for AT sites has been found to be on the same order of magnitude as that reported for GC sites.

Synthesis, characterization, and anticancer activity of ruthenium(II)-β-carboline complex

Four [Ru(tpy)(N-N)(L)] type complexes: [Ru(tpy)(bpy)(Nh)](2+) (Ru1, tpy = 2,2';6',2″-terpyridine, bpy = 2'2-bipyridine, Nh = Norharman), [Ru(tpy)(phen)(Nh)](2+) (Ru2, phen = 1,10-phenanthroline), [Ru(tpy)(dpa)(Nh)](2+) (Ru3, dpa = 2,2'-dipyridylamine) and [Ru(tpy)(dip)(Nh)](2+) (Ru4, dip = 4,7-diphenyl-1,10-phenanthroline) were presented as anticancer drugs. In vitro cytotoxicity assays indicated that these complexes showed anticancer activity against various cancer cells. Flow cytometry and signaling pathways analysis demonstrated that these complexes induced apoptosis via the mitochondrial pathway, as evidenced by the loss of mitochondrial membrane potential and the release of cytochrome c. The resulting accumulation of p53 proteins from phosphorylation at serine-15 and serine-392 was correlated with an increase in p21 and caspase activation. Taken together, these findings suggested that Ru1-Ru4 may contribute to the future development of improved chemotherapeutics against human cancers.

Does cytotoxicity of metallointercalators correlate with cellular uptake or DNA affinity?

The cytotoxicity of the metallointercalators, [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1R,2R-diaminocyclohexane)](2+) ([56MERR]) and [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1S,2S-diaminocyclohexane)](2+) ([56MESS]), towards A549 human lung cancer cells was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC(50) value obtained following exposure of A549 cells to [56MESS] for 4 h was approximately three times smaller than that obtained when [56MERR] was administered under the same conditions, indicating that the former complex displayed greater cytotoxicity. Both IC(50) values were greater than that obtained after exposure of A549 cells to cisplatin, demonstrating that the latter compound was the most cytotoxic of the three examined. Microprobe synchrotron radiation X-ray fluorescence (SR-XRF) analyses of metallointercalator-treated A549 cells showed that platinum became localised in DNA-rich regions of the nucleus. In contrast, when the same cells were treated with cisplatin the metal became distributed throughout the cell. Determination of the maximum concentration of platinum present inside the cells using graphite furnace atomic absorption spectrophotometry (GFAAS) of platinum-treated cells suggested that there was greater uptake of [56MERR] compared to [56MESS] by the A549 cells, and that platinum uptake did not account for the greater toxicity of [56MESS], as assessed by the MTT assay. Electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic studies of solutions containing either [56MERR] or [56MESS], and a duplex hexadecamer molecule, showed the two metallointercalators displayed very similar affinity towards the nucleic acid. Overall these results indicate that the difference in cytotoxicity of the two platinum metallointercalators is probably the result of variations in their interactions with other cellular components.

Synthesis, DNA binding, and cleavage studies of Co(III) complexes with fused aromatic NO/NN-containing ligands

Four new Co(III) complexes, namely [Co(cq)(3)](PF(6))(3), [Co(phen)(2)(cq)](PF(6))(3), [Co(bnp)(3)] (PF(6))(3), and [Co(phen)(2)(bnp)](PF(6))(3) (where cq = chromeno[2,3-b]quinoline, phen = 1,10-phenanthroline and bnp = dibenzo[b,g][1,8]naphthyridine), were synthesized and structurally characterized. Spectroscopic data suggested an octahedral geometry for all the complexes. Binding studies of these complexes with double-stranded (ds)DNA were analyzed by absorption spectra, viscosity, and thermal denaturation studies. The results revealed that the metal complex intercalates into the DNA base stack as intercalator. The oxidative cleavage activities of the complexes were studied with supercoiled pUC19 DNA using gel electrophoresis and the results show that the complexes have potent nuclease activity.

Experimental and theoretical polarized Raman linear difference spectroscopy of small molecules with a new alignment method using stretched polyethylene film

This paper reports the development of the new technique of Raman linear difference (RLD) spectroscopy and its application to small molecules: anthracene and nucleotides adenosine-5'-monophosphate, thymidine-5'-monophosphate, guanosine-5'-monophosphate, and cytidine-5'-monophosphate. In this work we also present a new alignment method for Raman spectroscopy where stretched polyethylene films are used as the matrix. Raman spectra using light polarized along the orientation direction and perpendicular to it are reported. The polyethylene (PE) film spectra are consistent with powder samples and films deposited on quartz. RLD spectra determined from the difference of the parallel and perpendicular polarized light Raman spectra are also reported. The equations describing RLD are derived, and RLD spectra of anthracene and thymidine are calculated from these equations using Density Functional Theory and assuming perfect orientation of the samples. Because of the wealth of spectroscopic information in the vibrational spectra of biomolecules together with our ability to calculate spectra as a function of orientation, we conclude that RLD has the potential to provide structural information for biological samples that currently cannot be extracted from any other method.

DNA Interaction and DNA Cleavage Studies of a New Platinum(II) Complex Containing Aliphatic and Aromatic Dinitrogen Ligands

A new Pt(II) complex, [Pt(DIP)(LL)](NO₃)₂ (in which DIP is 4,7-diphenyl-1,10-phenanthroline and LL is the aliphatic dinitrogen ligand, N,N-dimethyl-trimethylenediamine), was synthesized and characterized using different physico-chemical methods. The interaction of this complex with calf thymus DNA (CT-DNA) was investigated by absorption, emission, circular dichroism (CD), and viscosity measurements. The complex binds to CT-DNA in an intercalative mode. The calculated binding constant, K_b, was 6.6 × 10⁴ M⁻¹. The enthalpy and entropy changes of the reaction between the complex and CT-DNA showed that the van der Waals interactions and hydrogen bonds are the main forces in the interaction with CT-DNA. In addition, CD study showed that phenanthroline ligand insert between the base pair stack of double helical structure of DNA. It is remarkable that this complex has the ability to cleave the supercoiled plasmid.

DNA interaction studies of a platinum(II) complex, PtCl(2)(NN) (NN=4,7-dimethyl-1,10-phenanthroline), using different instrumental methods

The Pt(II) complex, PtCl(2)(4,7-Me(2)phen) (4,7-Me(2)phen=chelating dinitrogen ligand: 4,7-dimethyl-1,10-phenanthroline) was synthesized and characterized by spectroscopic ((1)H, (13)C NMR) and elemental analysis techniques. Binding interaction of this complex with calf thymus (CT) DNA has been investigated by emission, absorption, circular dichroism, viscosity and DNA thermal denaturation studies. The complex displays significant binding properties to the CT DNA. In fluorimeteric studies, the binding mode of complex with CT DNA was studied by using methylene blue as a fluoresce probe. As evidenced by the increasing fluorescence of methylene blue-DNA solutions in presence of increasing amount of complex, PtCl(2)(NN) complex is able to displace the methylene blue intercalated into DNA completely as to indicate intercalation. Furthermore, mentioned complex induces detectable changes in the CD spectrum of CT-DNA, an increase in T(m) value, and an increase in its viscosity. The experimental results showed that Pt(II) complex bound to DNA by an intercalative mode of binding.

Synthesis and photophysical properties of naphthyl-, phenanthryl-, and pyrenyl-appended bis(pyridyl)triazine ligands and their Zn(II) and Ru(II) complexes1

A family made of four bis(pyridyl)triazine ligands with appended aryl rings, including three fused aromatic rings, have been synthesized, and their corresponding homoleptic Ru(II) and Zn(II) complexes have been prepared and characterized by several means. The free ligands 2,4-di(2-pyridyl)-6-phenyl-1,3,5-triazine (L1); 2,4-di(2-pyridyl)-6-(1-naphthyl)-1,3,5-triazine (L2); 2,4-di(2-pyridyl)-6-(9-phenanthryl)-1,3,5-triazine (L3); and 2,4-di(2-pyridyl)-6-(1-pyrenyl)-1,3,5-triazine (L4) were formed in triazine ring-forming reactions from the reactions of the cyano-functionalized aromatic rings with LiNMe2 followed by the addition of 2 equiv. of 2-cyanopyridine. The metal complexes examined in this study are the homoleptic Ru(II) complexes Ru(L1)22+ (2a), Ru(L2)22+ (2b), Ru(L3)22+ (2c), and Ru(L4)22+ (2d) and Zn(II) complexes Zn(L1)22+ (3a), Zn(L2)22+ (3b), Zn(L3)22+ (3c), and Zn(L4)22+ (3d). Also, crystallographic data for the free ligands and Zn(II) and Ru(II) complexes have been obtained in some cases. The redox behaviour and absorption spectra of all the species have been investigated, together with the luminescence properties of the free ligands at room temperature in fluid solution and of the Ru(II) complexes both at room temperature in fluid solution and at 77 K in rigid matrix. The redox data indicate that the free ligands are reduced twice at relatively mild potentials (< –2.30 V vs. SCE), with the first reduction almost independent of the nature of the substituted aryl group. The UV absorption spectra of all the compounds are dominated by intense spin-allowed π–π* transitions mainly centered on the bis(pyridyl)triazine moiety; however, in L2–L4, moderately intense intraligand charge-transfer (ILCT) bands are also present. Such bands are red-shifted in the Zn(II) compounds, while they are obscured in the Ru(II) species by the more intense spin-allowed metal-to-ligand charge-transfer (MLCT) bands. The free ligands exhibit interesting emission properties, ranging from fluorescence from π–π* states to excimeric (in L4) and ILCT (in L2 and L3) emission. In the Ru(II) complexes, strong emission is found at 77 K from triplet MLCT states. For 2c and 2d, the emissive MLCT states are mixed with low-lying triplet ligand-centered states.Key words: triazine ligands, ruthenium complexes, zinc complexes, ILCT emission.