Trinuclear Ru(II) polypyridyl complexes as human telomeric quadruplex DNA stabilizers

Two new trinuclear ruthenium(II) complexes [(bpy)₆Ru₃(tpbip)]⁶⁺ (1) and [(bpy)₆Ru₃(tptaip)]⁶⁺ (2) (bpy = 2,2′-bipyridine, tpbip = 1,3,5-tris(1,10-phenanthroline-[5,6-d]imidazol-2-yl)-benzene, tptaip = 2,4,6-tri(1,10-phenanthroline-[5,6-d]imidazol-2-yl)-1,3,5-triazine) have been synthesized and characterized. The interaction of human telomeric DNA with Ru(II) complexes was explored by means of CD spectroscopy, fluorescence titration, ITC and FRET melting. Results indicated that two complexes not only induce a remarkable conformational change of human telomeric DNA, but also have the ability to stabilize the G-quadruplex.     

Preparation,spectroscopic, and electrochemical properties of four novel trinuclear Ru(II) polypyridyl complexes containing diazafluorene

Four tripodal ligands 2,2′,2″-tris[4-(4,5-diazafluoren-9-ylhydrazinyl)methylenephenoxyethyl]amine (L¹), 1,1,1-tris[4-(4,5-diazafluoren-9-ylhydrazinyl)methylenephenoxymethyl]propane (L²), 1,3,5-tris[4-(4,5-diazafluoren-9-ylhydrazinyl)methylenephenoxymethyl]-2,4,6-trimethylbenzene (L³), 1,3,5-tris[4-(4,5-diazafluoren-9-ylhydrazinyl)methylenephenoxymethyl]benzene (L⁴), and corresponding Ru(II) complexes [(bpy)₆L^1–4(Ru^II)₃](PF₆)₆ (Ru-L^1–4) have been synthesized. Cyclic voltammetry of these complexes comprise one Ru(II)-centered reversible oxidation and three ligand-centered reductions. Photophysical behaviors are investigated by UV–Vis absorption and luminescence spectrometry. These complexes display metal-to-ligand charge transfer absorption at around 410 nm and emission at around 582 nm.     

Preparation,photophysical, and electrochemical properties of three novel trinuclear Ru(II) polypyridyl complexes based on diazafluorenes

Three tripodal ligands 2,2′,2″-tris[(4,5-diazafluoren-9-ylimino)phenoxyethyl]amine (L¹), 1,3,5-tris[(4,5-diazafluoren-9-ylimino)phenoxymethyl]-2,4,6-trimethylbenzene (L²), 1,1′,1″-tris[(4,5-diazafluoren-9-ylimino)phenoxymethyl]-1″′-(p-tosyloxymethyl)-methane (L³), and corresponding Ru(II) complexes [(bpy)₆L^1–3(Ru^II)₃](PF₆)₆ (Ru-L^1–3) have been prepared. Cyclic voltammetry of the three complexes are consistent with one Ru(II)-centered quasi-reversible oxidation and three ligand-centered reductions. Photophysical behaviors are investigated by UV–Vis absorption and fluorescence spectrometry. The three complexes display metal-to-ligand charge transfer absorption at 445 nm and emission at 578 nm.     

Antimicrobial and nuclease activity of mixed polypyridyl ruthenium(II) complexes

The ruthenium(II) complexes with 2,9-dimethyl-1,10-phenanthroline (dmphen) and terpyridine derivatives have been synthesized and screened for their antimicrobial potency. The interaction of these complexes with Herring Sperm DNA was investigated by thermal denaturation, viscosity measurements, gel electrophoresis and spectrophotometric methods. The results indicate that the complexes bound to DNA via partial intercalative mode. The salt-dependent binding of these complexes has been determined by UV–Vis spectrophotometric titration. The contribution of the non-electrostatic binding free energy (ΔG_t^o) to the total binding free energy change (ΔG^o) is found to be ~ 88% at [Na⁺] = 0.075 M. The large value suggests that the stabilization of the DNA binding is mostly due to the contribution of non-electrostatic process.     

Aggregation-induced emission of ruthenium(II) polypyridyl complex [Ru(bpy)2(pzta)]2+

A new ruthenium(II) complex [Ru(bpy)₂(pzta)]²⁺ (1) [bpy = 2,2′-bipyridine; pzta = 6-(pyrzin2-yl)-1,3,5-triazine-2,4-diamine] has been synthesized and characterized. This complex exhibits a typical aggregation-induced emission (AIE) behavior that it is faint in solution but intense in the aggregate state.     

Synthesis, spectroscopic, and electrochemical properties of one novel hexanuclear Ru(II) polypyridyl complex

One novel hexapodal ligand 1,2,3,4,5,6-hexakis[(4,5-diazafluoren-9-yliminoxy)methyl]benzene (L) and corresponding Ru(II) polypyridyl complex [(bpy)₁₂(Ru^II)₆L](PF₆)₁₂ have been synthesized. Spectroscopic properties of the complex are investigated by UV–Vis absorption and fluorescence spectrometry. The complex shows metal-to-ligand charge transfer absorption at 438 nm and emission at 579 nm. Cyclic voltammetry of the complex comprises one Ru(II)-centered quasi-reversible oxidation at 1.31 V and three ligand-centered reductions.     

Linear trinuclear manganese(II) complexes: crystal structures and magnetic properties

Two new trinuclear manganese(II) complexes, [Mn₃(O₂CCH(CH₃)₂)₆(N–N)₂] (N–N is 1,10′-phenanthroline (1) and 2,2′-bipyridine (2)) have been prepared and fully characterized. Single crystal X-ray diffraction analysis confirmed a linear arrangement of three Mn(II) centers bridged by six isobutyric carboxylate groups. The magnetic measurements showed that both complexes exhibit an S_T = 5/2 spin ground state induced by antiferromagnetic interactions between the Mn(II) sites: J/k_B = −2.31(2) and −2.67(2) K for 1 and 2, respectively.     

Ru(II) and Zn(II) complexes of multicomponent ligands incorporating triazine-based tridentate ligands

Ru(II) and Zn(II) complexes of multicomponent ligands have been synthesised and characterised incorporating triazine-based coordinating motifs with pendant phenanthryl and phenyl–phenanthryl groups. At room temperature the ligands emit from intra-ligand charge-transfer (ILCT) states, the energy of which may be lowered significantly by metal–ion coordination (e.g. Zn(II)). The ILCT state is efficiently quenched in the Ru(II) complexes by energy transfer to a low-lying metal–ligand charge-transfer ³MLCT state.     

Zeolite encapsulated Ru(III), Cu(II) and Zn(II) complexes as effective catalysts for the oxidation of ethylbenzene

Ru(III), Cu(II) and Zn(II) complexes of imidazole (ImzlH) have been synthesized in the supercages of zeolite-Y by flexible ligand method and characterized by spectroscopic (IR and UV?CVis) studies, XRD and thermogravimetric analysis, surface area, and pore volume measurements. These complexes were screened for their catalytic study towards the oxidation of ethylbenzene to a mixture of acetophenone, benzaldehyde and styrene using tert-butylhydroperoxide (TBHP) as an oxidant. A best-suited reaction condition has been optimized for these catalysts by varying the amount of the oxidant and catalyst, reaction time and volume of solvent for maximum transformation of ethylbenzene. Under the optimized reaction conditions, [Cu(ImzlH)]-Y gave 79.3% conversion after 1?h of reaction time. All these catalysts were more selective towards acetophenone formation. Among the prepared catalysts, zeolite encapsulated Cu(II) complex was found to be more active than the corresponding Ru(III) and Zn(II) complexes and all the complexes were stable enough to be reused. The catalytic activities of the neat complexes and metal exchanged zeolites were also compared with the zeolite encapsulated metal complexes.     

Reversible electrochemical and chemical addressing of optical properties of ternary Os(II) polypyridyl complexes

Electrochemical- and chemical-induced variation of the metal oxidation state of ternary Os(II) polypyridyl complexes triggers reversible changes in optical properties. This read/write process can be carried out conveniently and monitored with optical (UV/Vis or luminescence) spectrophotometers. An excellent sensitivity and reversibility may make it a suitable candidate for integration of molecular sensors and logic gate system.     

Intraligand fluorescence of Zn(II) and Pt(II) complexes of pyridoxal thiosemicarbazone

Pyridoxal (vitamin B₆ aldehyde) thiosemicarbazone (B₆TSC) is deprotonated to its anion (B₆TSC – H⁺) in basic solution at pH = 9. It shows an intense green fluorescence with λ_max = 500 nm and a quantum yield of unity. Zn(II)(B₆TSC – H⁺)(acetate) displays an blue-green intraligand (B₆TSC) fluorescence of moderate intensity. The complex cation [Pt(II)(B₆TSC)Cl]⁺ is isolated as tetraphenylborate. In basic solution (pH = 9) this cation is deprotonated to the neutral complex [Pt(II)(B₆TSC – H⁺)Cl] which exhibits the same green intraligand fluorescence as the free anion (B₆TSC – H⁺)⁻. However, in the platinum complex this emission is much less intense. It is reduced to φ = 10^− 2.     

Synthesis and characterization of partially crosslinked poly(N-vinylcarbazole-vinylalcohol) copolymers with polypyridyl Ru(II) luminophores: Potential materials for electroluminescence

Summary A novel difunctionalized 5,5'-dibromomethylene-2,2' bipyridine ligand was prepared and covalently bound with concurrent crosslinking by a post-polymer modification method to (N-vinylcarbazole-vinylalcohol) copolymer. The electrochemistry and UV-vis spectroscopy results both confirm the covalent attachment of ruthenium transition metal complex to the polymer backbone. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicate high thermal stability of the copolymer. The copolymer is also highly phosphorescent making it a potential polymeric material for transition metal based electroluminescent devices. Received: 1 November 1998/Revised version: 18 August 1999/Accepted: 18 August 1999     

A novel DNA light switch [Ru(bpy)2pzip]2+ activated by cobalt(II) ion

A novel ruthenium(II) complex, [Ru(bpy)₂pzip]²⁺ has been synthesized and characterized. The DNA-binding properties of this complex have been studied by spectroscopic and viscosity measurements. The results indicated that the complex [Ru(bpy)₂pzip]²⁺ bound to double-stranded DNA in an intercalation mode. In the presence of Co²⁺, the emission of DNA–[Ru(bpy)₂pzip]²⁺ can be quenched. And when EDTA was added, the emission was recovered. The experiment results show that [Ru(bpy)₂pzip]²⁺ exhibited the “on–off–on” properties of molecular “light switch”.     

Anticancer activity studies of ruthenium(II) polypyridyl complexes against human gastric carcinoma SGC-7901 cell

A new ligand TCPI and its three ruthenium(II) polypyridyl complexes [Ru(N-N)₂(TCPI)](PF₆)₂ (N-N = bpy: 2,2′-bipyridine 1; phen: phenanthroline 2; dmp: 2,9-dimethyl-1,10-phenanthroline 3) were synthesized and characterized by elemental analysis, ESI-MS, ¹H NMR, IR, absorption and emission spectra. The cytotoxic activity in vitro of the ligand and complexes against cancer cells SGC-7901, PC-12, HepG-2, SiHa, Eca-109, HeLa and normal cell LO2 was evaluated by MTT method. Complex 3 shows the highest cytotoxic activity toward SGC-7901 cell among the complexes. Interestingly, the complexes show low or no cytotoxic activity against normal cell LO2. The apoptosis in SGC-7901 cell was investigated with AO/EB staining method. The ROS levels and the changes of mitochondrial membrane potential were studied under fluorescent microscope and flow cytometry. The cell invasion, cell cycle arrest and the expression of Bcl-2 family proteins were studied in detail. The results demonstrate that the complexes induce apoptosis in SGC-7901 cell through a ROS-mediated mitochondrial dysfunction pathway, which was accompanied by the regulation of Bcl-2 family proteins.     

Zeolite encapsulated Ru(III), Cu(II) and Zn(II) complexes of benzimidazole as reusable catalysts for the oxidation of organic substrates

Ru(III), Cu(II) and Zn(II) complexes of benzimidazole (BzlH) have been synthesized in the supercages of zeolite-Y by the flexible ligand method and were characterized by spectroscopic (IR, UV–Vis and ESR) studies, XRD and thermogravimetric analysis, surface area, and pore volume measurements. The zeolite encapsulated complexes catalyzed the oxidation of ethylbenzene, benzoin, and cyclohexanol. Various parameters, such as concentration of oxidant and catalyst, reaction time, temperature of the reaction and type of solvents have been optimized to obtain the maximum transformation of ethylbenzene to a mixture of acetophenone, benzaldehyde and styrene. Under the optimized reaction conditions, [Ru(BzlH)]-Y gave 80.4 % conversion of ethylbenzene in 1 h. All these zeolite encapsulated complexes were more selective towards acetophenone formation. Oxidation of benzoin catalyzed by [Cu(BzlH)]-Y, [Ru(BzlH)]-Y and [Zn(BzlH)]-Y encapsulated complexes resulted in 75.5, 78.7 and 59.9 % conversion respectively to give benzaldehyde as exclusive product. A maximum conversion of 39.1 % cyclohexanol with [Cu(BzlH)]-Y was achieved to give cyclohexanone. The activity of neat complexes towards these reactions was also carried out. The encapsulated catalysts were significantly more active than neat complexes and recyclable without much loss in catalytic activity.     

First proton-induced near-infrared fluorescent switch at room temperature of a novel Ru(II) complex

A novel Ru(II) complex, Ru(bpy)₂(L)(ClO₄)₂ (bpy=2,2^′-bipyridine and L=2-pyridin-2-yl-1H -phenanthro[9,10-d]imidazole) acts as a pH-induced “off/on” near-infrared luminescent switch through protonation and deprotonation in aqueous solution at room temperature.     

Cu(II) complexes as receptor molecules for development of new chloride sensors

Highly sensitive and selective chloride polymeric membrane sensors are developed that employ Cu(II) complexes as anion carriers. Optimized membrane sensors showed a near-Nernstian response towards chloride anion over a wide concentration range of 2.5 × 10⁻⁵ to 1.0 × 10⁻¹ M and have micromolar level detection limits. These sensors have fast response time and work well in the pH range of 4.2-9.6. They exhibited enhanced potentiometric selectivity for chloride over other anions, including more lipophilic anions such as perchlorate, thiocyanate, nitrate, etc. Response characteristics (e.g. detection limit, linear range, response slope and selectivity) of these sensors remain essentially the same over a period of ∼5 months, reflecting remarkable stability.     

Syntheses and magnetic properties of trinuclear trithiocyanurato-bridged manganese(II) complexes involving bidentate aromatic N-donor heterocycles

Trinuclear manganese(II) complexes of the compositions [Mn₃(phen)₆(ttc)](ClO₄)₃ (1), [Mn₃(dmbpy)₆(ttc)](ClO₄)₃? 2H₂O (2) and [Mn₃(bpy)₆(ttc)](ClO₄)₃? 3H₂O (3), where phen = 1,10-phenanthroline, dmbpy = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine and H₃ttc = trithiocyanuric acid (2,4,6-trimercapto-1,3,5-triazine), were prepared and characterized by elemental analysis, FTIR and Raman spectroscopies, MALDI-TOF mass spectrometry, magnetic and conductivity measurements. The magnetic analysis incorporating simultaneous fitting of the temperature dependence and the field dependence of the magnetization using the isosceles triangle spin Hamiltonian model revealed a weak antiferromagnetic exchange within the trinuclear units.     

DNA and copper (II) governed fluorescence tuning of phenanthroline possessing Ru(II) complex. Interplay of electrostatic interactions

Tuning of the fluorescence properties of [Ru (bpy) ₂ (L₁)] ^2 + (1) [L₁ = 2-(2-methoxyphenyl)-1H–imidazo [4, 5-f] Kumar et al. (2010), Rawle et al. (1992) phenanthroline] by DNA and/or Cu^2 + ion have been investigated. Fluorescence of 1 gets enhanced upon binding to DNA owing to electrostatic interactions. The binding constant of 8.4 × 10⁴ has been evaluated. Cu^2 + ions though unable to alter the fluorescence intensity of free 1 but successfully sequestrate the DNA bound 1, evidently decreasing its fluorescence intensity. The reversibility of the sequestration process was ascertained by the recovery of the quenched fluorescence intensity via introduction of equimolar EDTA to the buffer system of DNA bound 1 and Cu^2 +.     

Studies on interaction of Cr(III) polypyridyl complexes with DNA

Two chromium(III) complexes containing derivatives of 1,10-phenanthroline were synthesized and characterized using different spectroscopic methods. The interaction of the synthesized complexes with DNA was performed. From the absorption titration data, the binding constant for the complexes [Cr(imiphen)₂Cl₂]⁺ (1) and [Cr(furphen)₂Cl₂]⁺ (2) with DNA were found to be 5.69 ± 0.3 × 10⁴ M^− 1 for 1 and 3.7 ± 0.2 × 10⁴ M^− 1 for 2, respectively. The viscosity studies show that both the complexes bind to DNA in a partial intercalative mode. The results of competitive binding assay reveal that both complexes displace EB from DNA marginally. Gel electrophoresis data show that both the complexes 1 and 2 requires co-reagent to induce DNA cleavage but complex 2 exhibit better nuclease activity compared to complex 1. The results from this study describe the role of ligand structure in the binding and cleavage of DNA as furan based ligand exhibit better cleaving ability compared to imidazole moiety.