Synthesis, characterization and the effect of ligand planarity of [Ru(bpy)2L]2+ on DNA binding affinity

Binding properties of a molecular "light switch" ruthenium(II) polypyridyl complex toward double- and triple-helical forms of RNA

To further develop new luminescent probes for RNA, a new ruthenium(II) polypyridyl complex [Ru(dmb)₂dppz-idzo]²⁺ (dmb = 4,4'-dimethyl-2,2'-bipyridine, dppz-idzo = dppz-imidazolone) has been synthesized and characterized in this study. Binding properties of [Ru(dmb)₂dppz-idzo]²⁺ to RNA duplex poly(A) · poly(U) and triplex poly(U) · poly(A) ∗ poly(U) have been explored by spectroscopic techniques and viscometry experiments. The binding modes of [Ru(dmb)₂dppz-idzo]²⁺ to RNA duplex and triplex are intercalation as revealed from spectral titrations and viscosity experiments, while the binding strength of this complex to duplex structure is significantly greater than that of triplex structure. Fluorescence titrations indicate that [Ru(dmb)₂dppz-idzo]²⁺ can act as a molecular "light switch" for both duplex poly(A) · poly(U) and triplex poly(U) · poly(A) ∗ poly(U), while [Ru(dmb)₂dppz-idzo]²⁺ is more sensitive to poly(A) · poly(U) compared to poly(U) · poly(A) ∗ poly(U) and poly(U). Therefore, this complex can distinguish between RNA duplex, triplex and poly(U), and can as luminescent probes for the three RNAs used in this study. In addition, thermal denaturation studies show that [Ru(dmb)₂dppz-idzo]²⁺ is able to significantly increase the Stabilization of RNA duplex and triplex. The results obtained in this study may contribute to further understanding of the binding of Ru(II) complexes with different structural RNAs.

Insight into achirality and chirality effects in interactions of an racemic ruthenium(II) polypyridyl complex and its Δ- and Λ-enantiomers with an RNA triplex

RNA triplexes have a variety of potential applications in molecular biology, diagnostics and therapeutics, while low stabilization of the third strand hinders their practical utilities under physiological conditions. In this regard, achieving the third-strand stabilization by binding small molecules is a promising strategy. Chirality is one of the basic properties of nature. To clarify achirality and chirality effects on the binding and stabilizing effects of RNA triplexes by small molecules, we report for the first time the RNA interactions of an racemic ruthenium(II) polypyridyl complex [Ru(bpy)₂(11-CN-dppz)]²⁺ (rac-Ru1) and its two enantiomers Δ/Λ-[Ru(bpy)₂(11-CN-dppz)]²⁺ (Δ/Λ-Ru1) with an RNA triplex poly(U-A*U) (where "-" represents Watson-Crick base pairing, and "*" denotes Hoogsteen base pairing, respectively) in this work. Research shows that although rac-Ru1 and its two enantiomers Δ/Λ-Ru1 bind to the RNA triplex through the same mode of intercalation, the binding affinity for enantiomer Δ-Ru1 is much higher than that for rac-Ru1 and enantiomer Λ-Ru1. However, compared to enantiomer Λ-Ru1, the binding affinity for rac-Ru1 does not show much of an advantage, which is slightly greater than that for the former. Thermal denaturation measurements reveal both rac-Ru1 and Δ-Ru1 to have a preference for stabilizing the third strand rather than the template duplex of the RNA triplex, while Λ-Ru1 stabilizes the RNA triplex without significant selectivity. Besides, the third-strand stabilizing effects by rac-Ru1 and Δ-Ru1 are not markedly different from each other, but more marked than that by Λ-Ru1. This work shows that the binding properties of the racemic Ru(II) polypyridyl complex with the RNA triplex are not simply an average of its two enantiomers, indicating potentially complicated binding events.

Comparative Studies on DNA-Binding Mechanisms between Enantiomers of a Polypyridyl Ruthenium(II) Complex

A pair of ruthenium(II) complex enantiomers, Δ- and Λ-[Ru(bpy)₂MBIP]²⁺ (bpy = 2,2'-bipyridine, MBIP = 2-(3-bromophenyl)imidazo[5,6-f]phenanthroline), were designed, synthesized, and characterized. Comparative studies between the enantiomers on their binding behaviors to calf thymus DNA (CT-DNA) were conducted using UV-visible, fluorescence, and circular dichroism spectroscopies, viscosity measurements, isothermal titration calorimetry, a photocleavage experiment, and molecular simulation. The experimental results indicated that both the enantiomers spontaneously bound to CT-DNA through intercalation stabilized by the van der Waals force or the hydrogen bond and driven by enthalpy and that Δ-[Ru(bpy)₂MBIP]²⁺ intercalated into DNA more deeply than Λ-[Ru(bpy)₂MBIP]²⁺ did and exhibited a better DNA photocleavage ability. Molecular simulation further indicated that Δ-[Ru(bpy)₂MBIP]²⁺ more preferentially intercalated between the base pairs of CT-DNA to the major groove, and Λ-[Ru(bpy)₂MBIP]²⁺ more favorably intercalated to the minor groove. These research findings should be very helpful to the understanding of the stereoselectivity mechanism of DNA-bindings of metal complexes, and be useful for the design of novel metal-complex-based antitumor drugs with higher efficacy and lower toxicity.

Organometallic ruthenium (η6-p-cymene) complexes interfering with quorum sensing and biofilm formation: an anti-infective approach to combat multidrug-resistance in bacteria

Organometallic ruthenium complexes of flavonoids as antiquorum sensing agents against pathogens likeChromobacterium violaceumATCC 12472,Pseudomonas aeruginosaPAO1 and methicillin-resistantS. aureus(MRSA).

Mitochondria-Targeting Click-Derived Pyridinyltriazolylmethylquinoxaline-Based Y-Shaped Binuclear Luminescent Ruthenium(II) and Iridium(III) Complexes as Cancer Theranostic Agents

Due to several negative issues, market available drugs have been gradually losing their importance in the treatment of cancer. With a view to discover suitable drugs capable of diagnosing as well as inhibiting the growth of cancer cells, we have aspired to develop a group of theranostic metal complexes which will be (i) target specific, (ii) cytoselective, thus rendering the normal cell unaffected, (iii) water-soluble, (iv) cancer cell permeable, and (v) luminescent, being beneficial for healing the cancer eternally. Therefore, to reach our goal, we have prepared novel Ru(II)- and Ir(III)-based bimetallic and hetero bimetallic scaffolds using click-derived pyridinyltriazolylmethylquinoxaline ligands followed by metal coordination. Most of the compounds have displayed significant cytoselectivity against colorectal adenocarcinoma (Caco-2) and epithiloid cervical carcinoma (HeLa) cells with respect to normal human embryonic kidney cells (HEK-293) compared to cisplatin [cis-diamminedichloroplatinum(II)] along with excellent binding efficacy with DNA as well as serum albumin. Complex [(η⁶-p-cymene)(η⁵-Cp*)Ru^IIIr^IIICl₂(K²-N,N-L)](PF₆)₂ [RuIrL] exhibited the best cytoselectivity against all the human cancer cells and was identified as the most significant cancer theranostic agent in terms of potency, selectivity, and fluorescence quantum yield. Investigation of the localization of complex [Ir₂L] and [RuIrL] in the more aggressive colorectal adenocarcinoma cell HT-29 indicates that mitochondria are the key cellular target for destroying cancer cells. Mitochondrial dysfunction and G2/M phase cell cycle arrest in HT-29 cell were found to be involved in the apoptotic cell death pathway induced by the test complexes [Ir₂L] and [RuIrL]. These results validate the concept that these types of complexes will be reasonably able to exert great potential for tumor diagnosis as well as therapy in the near future.

Biophysical insights into the interaction of two enantiomers of Ru(II) complex [Ru(bpy)2(7-CH3-dppz)]2+ with the RNA poly(U-A⁎U) triplex

To determine the factors affecting the stabilization of RNA triple-stranded structure by chiral Ru(II) polypyridyl complexes, a new pair of enantiomers, ∆-[Ru(bpy)₂(7-CH₃-dppz)]²⁺ (∆-1; bpy = 2,2'-bipyridine, 7-CH₃-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) and Λ-[Ru(bpy)₂(7-CH₃-dppz)]²⁺ (Λ-1), have been synthesized and characterized in this work. Binding properties of the two enantiomers with the RNA poly(U-A⁎U) triplex (where "-" denotes the Watson - Crick base pairing and "⁎" denotes the Hoogsteen base pairing) have been studied by spectroscopy and hydrodynamics methods. Under the conditions used in this study, changes in absorption spectra of the two enantiomers are not very different from each other when bound to the triplex, although the binding affinity of ∆-1 is higher than that of Λ-1. Fluorescence titrations and viscosity experiments give convincing evidence for a true intercalative binding of enantiomers with the triplex. However, melting experiments indicated that the two enantiomers selectively stabilized the triplex. The enantiomer ∆-1 stabilize the template duplex and third-strand of the triplex, while it's more effective for stabilization of the template duplex. In stark contrast to ∆-1, Λ-1 stabilizes the triplex without any effect on the third-strand stabilization, suggesting this one extremely prefers to stabilize the template duplex rather than third-strand. Besides, the triplex stabilization effect of ∆-1 is more marked in comparison with that of Λ-1. The obtained results suggest that substituent effects and chiralities of Ru(II) polypyridyl complexes play important roles in the triplex stabilization. Complexes Λ/Δ-[Ru(bpy)₂(7-CH₃-dppz)]²⁺ (Λ/Δ-1; bpy = 2,2'-bipyridine, 7-CH₃-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) were prepared as stabilizers for poly(U-A ∗ U) triplex. Results suggest the triplex stabilization depends the chiral structures of Λ/Δ-1, indicating that [Ru(bpy)₂(7-CH₃-dppz)]²⁺ is a non-specific intercalator for poly(U-A ∗ U) investigated in this work.

Synthesis and characterization of chiral Ru(II) polypyridyl complexes and their binding and stabilizing effects toward triple-helical RNA

Two novel chiral Ru(II) complexes, Λ- and Δ-[Ru(bpy)₂(7-CF₃-dppz)]²⁺ (Λ-1 and Δ-1; bpy = 2,2'-bipyridine, 7-CF₃-dppz = 7-trifluoromethyl-dipyrido[3,2-a:2',3'-c]phenazine), were synthesized and characterized in this work. The binding and stabilizing effects of Λ-1 and Δ-1 toward the RNA poly(U)•poly(A)*poly(U) triplex were studied by various biophysical techniques. Absorption spectra and fluorescence quenching indicates that the binding affinity of Δ-1 is slightly higher than that Λ-1. Both enantiomers induce significant positive viscosity changes that are indicative of intercalative binding, whereas changes in the relative viscosities of the triplex are found to be more pronounced with Δ-1. Melting experiments indicate that the triplex stabilization effects of both enantiomers are significantly different from each other. With Λ-1, the stabilization of the Watson-Crick base-paired duplex (the template duplex) of the triplex shows a moderate increase, whereas the stabilization of the Hoogsteen base-paired strand (third-strand) exhibits slight decrease under the same conditions, suggesting Λ-1 prefers to stabilize the template duplex rather than third-strand. In stark contrast to Λ-1, Δ-1 can not only strongly stabilize the template duplex, but also moderately increase the third-strand stabilization, even so, which imply that Δ-1 also prefer to stabilize the template duplex instead of the third-strand. These suggest that the [Ru(bpy)₂(7-CF₃-dppz)]²⁺ is similar as a non-specific metallointercalator the triplex studied in this work. Combined with our recent research, the obtained results further indicate that Δ- enantiomers rather than Λ-ones of Ru(II) polypyridyl complexes usually exhibit stronger binding and stabilizing effects toward the triplex.

Binuclear and tetranuclear Zn(ii) complexes with thiosemicarbazones: synthesis, X-ray crystal structures, ATP-sensing, DNA-binding, phosphatase activity and theoretical calculations

Two Zinc(ii) complexes [Zn₄(L¹)₄]·2H₂O (1) and [Zn₂(L²)₂]·2H₂O (2) of pyruvaldehydethiosemicarbazone ligands are reported. The complexes were characterized by elemental analysis, IR, NMR, UV-vis spectroscopy and by single-crystal X-ray crystallography. X-ray crystal structure determinations of the complexes show that though Zn : ligand stoichiometry is 1 : 1 in both the complexes, the molecular unit is tetranuclear for 1 and binuclear for 2. Both the complexes show selective sensing of ATP at pH 7.4 (0.01 M HEPES) in CH₃CN–H₂O (9 : 1) medium in the presence of other anions like AcO⁻, NO₃⁻, F⁻, Cl⁻, H₂PO₄⁻, HPO₄²⁻ and P₂O₇²⁻. The UV-titration experiments of complexes 1 and 2 with ATP results in binding constants of 2.0(±0.07) × 10⁴ M⁻¹ and 7.1(±0.05) × 10³ M⁻¹ respectively. The calculated detection limits of 6.7 μM and 1.7 μM for 1 and 2 respectively suggest that the complexes are sensitive detectors of ATP. High selectivity of the complexes is confirmed by the addition of ATP in presence of an excess of other anions. DFT studies confirm that the ATP complexes are more favorable than those with the other inorganic phosphate anions, in agreement with the experimental results. Phosphatase like activity of both complexes is investigated spectrophotometrically using 4-nitrophenylphosphate (NPP) as a substrate, indicating the complexes possess significant phosphate ester hydrolytic efficiency. The kinetics for the hydrolysis of the substrate NPP was studied by the initial rate method at 25 °C. Michaelis–Menten derived kinetic parameters indicate that rate of hydrolysis of the P–O bond by complex 1 is much greater than that of complex 2, the k_cat values being 212(±5) and 38(±2) h⁻¹ respectively. The DNA binding studies of the complexes were investigated using electronic absorption spectroscopy and fluorescence quenching. The absorption spectral titrations of the complexes with DNA indicate that the CT-DNA binding affinity (K_b) of complex 1 (2.10(±0.07) × 10⁶ M⁻¹) is slightly greater than that of 2 (1.11(±0.04) × 10⁶ M⁻¹). From fluorescence spectra the apparent binding constant (K_app) values were calculated and they are found to be 5.41(±0.01) × 10⁵ M⁻¹ for 1 and 3.93(±0.02) × 10⁵ M⁻¹ for 2. The molecular dynamics simulation demonstrates that the Zn(ii) complex 1 is a good intercalator of DNA.

A binuclear and a tetranuclear zinc(ii) of pyruvaldehyde thiosemicarbazone show selective sensing of ATP at pH 7.4 (0.01 M HEPES) in CH₃CN–H₂O (9 : 1) medium. The DNA binding and phosphatase activities of the complexes are also reported.

Synthesis, structural characterization, in vitro DNA binding, and antitumor activity properties of Ru(II) compounds containing 2(2,6-dimethoxypyridine-3-yl)-1H-imidazo(4,5-f)[1, 10]phenanthroline

The octahedral Ru(II) complexes containing the 2(2,6-dimethoxypyridine-3-yl)-1H-imidazo(4,5-f)[1, 10]phenanthroline ligand of type [Ru(N-N)₂(L)]²⁺, where N-N = phen (1,10-phenanthroline) (1), bpy (2,2^'-bipyridine) (2), and dmb (4,4^'-dimethyl-2,2^'-bipyridine) (3); L(dmpip) = (2(2,6-dimethoxypyridine-3-yl)1Himidazo(4,5-f)[1, 10]phenanthroline), have been synthesized and characterized by UV-visible absorption, molar conductivity, elemental analysis, mass, IR, and NMR spectroscopic techniques. The physicochemical properties of the Ru(II) complexes were determined by UV-Vis absorption spectroscopy. The DNA binding studies have been explored by UV-visible absorption, fluorescence titrations, and viscosity measurements. The supercoiled pBR322 DNA cleavage efficiency of Ru(II) complexes 1-3 was investigated. The antimicrobial activity of Ru(II) complexes was done against Gram-positive and Gram-negative microorganisms. The in vitro anticancer activities of all the complexes were investigated by cell viability assay, apoptosis, cellular uptake, mitochondrial membrane potential detection, and semi-quantitative PCR on HeLa cells. The result indicates that the synthesized Ru(II) complexes probably interact with DNA through an intercalation mode of binding with complex 1 having slightly stronger DNA binding affinity and anticancer activity than 2 and 3.

VR, Mallepally RR, Chintakuntla N, Ch R, Thakur SS, Rao CM, S. S. Studies on the DNA binding and anticancer activity of Ru(ii) polypyridyl complexes by using a (2-(4-(diethoxymethyl)-1H-imidazo[4,5-f][1,10] phenanthroline)) intercalative ligand

Graphical representation of Ru(ii) complexes causing cell death.

Ultrasonic effect on RuO2 nanostructures prepared by direct calcination of two new Ru(II)-organic supramolecular polymers

Two novel Ru(II) complexes [(η⁶-p-cymene)RuCl(L1)]PF₆ (R1) and [(η⁶-C₆H₆)RuCl(L1)]PF₆ (R3) with ligand (E)-4-(methylthio)-N-((quinolin-2-yl)methylene)benzenamine (L1), were synthesized and investigated using elemental analysis, IR, ¹H NMR, ¹³C NMR spectroscopy and X-ray crystallography. Complexes R1 and R3 have coordination environments with formulated (η⁶-p-cymene)Ru(N₂Cl) and (η⁶-C₆H₆)Ru(N₂Cl) respectively. The thermal stabilities of compounds R1 and R3 were studied by thermal gravimetric (TG) and differential scanning calorimetry (DSC). The binding of the complexes R1 and R3 to calf thymus DNA (CT DNA) was investigated by using electronic absorption spectra, fluorescence and redox behavior studies. Such experimental data showed that there are interactions between complexes and CT-DNA and the nature of this binding is electrostatic interaction type. Calcination of ultrasonic treated R1 and R3 results in the formation of nanoparticles of RuO₂. The nanoparticles were characterized by IR spectroscopy and X-ray diffraction (XRD). Also size and morphology of nanoparticles were investigated by scanning electron microscopy (SEM).

Effects of TiO2 crystal structure on the luminescence quenching of [Ru(bpy)2(dppz)]2+-intercalated into DNA

The intercalation of [Ru(bpy)₂(dppz)]²⁺ labeled as Ru(II) (bpy=2,2'-bipyridine and dppz=dipyrido[3,2,-a:2',3'-c]phenazine) into herring sperm DNA leads to the formation of emissive Ru(II)-DNA dyads, which can be quenched by TiO₂ nanoparticles (NPs) and sol-gel silica matrices at heterogeneous interfaces. The calcinations temperature exhibits a remarkable influence on the luminescence quenching of the Ru(II)-DNA dyads by TiO₂ NPs. With increasing calcinations temperature in the range from 200 to 850°C, the anatase-to-rutile TiO₂ crystal structure transformation increases the average particle size and hydrodynamic diameter of TiO₂ and DNA@TiO₂. The anatase TiO₂ has the stronger ability to unbind the Ru(II)-DNA dyads than the rutile TiO₂ at room temperature. The TiO₂ NPs and sol-gel silica matrices can quench the luminescence of the Ru(II) complex intercalated into DNA by selectively capturing the negatively DNA and positively charged Ru(II) complex to unbind the dyads, respectively. This present results provide new insights into the luminescence quenching and competitive binding of dye-labeled DNA dyads by inorganic NPs.

DNA-binding, molecular docking studies and biological activity studies of ruthenium(ii) polypyridyl complexes

Three new Ru(ii) complexes [Ru(N–N)₂(PTCP)]²⁺ were synthesized and characterized. The DNA-binding, in vitro cytotoxicity, apoptosis, autophagy and western blot analysis were investigated.

Homo- and Heterobimetallic Ruthenium(II) and Osmium(II) Complexes Based on a Pyrene-Biimidazolate Spacer as Efficient DNA-Binding Probes in the Near-Infrared Domain

We report in this work a new family of homo- and heterobimetallic complexes of the type [(bpy)2M(Py-Biimz)M'(II)(bpy)2](2+) (M = M' = Ru(II) or Os(II); M = Ru(II) and M' = Os(II)) derived from a pyrenyl-biimidazole-based bridge, 2-imidazolylpyreno[4,5-d]imidazole (Py-BiimzH2). The homobimetallic Ru(II) and Os(II) complexes were found to crystallize in monoclinic form with space group P21/n. All the complexes exhibit strong absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. For osmium-containing complexes (2 and 3) both the absorption and emission band stretched up to the NIR region and thus afford more biofriendly conditions for probable applications in infrared imaging and phototherapeutic studies. Detailed luminescence studies indicate that the emission originates from the respective (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes and is only slightly affected by the pyrene moiety. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations in the positive potential window and several reduction processes in the negative potential window. An efficient intramolecular electronic energy transfer is found to occur from the Ru center to the Os-based component in the heterometallic dyad. The binding studies of the complexes with DNA were thoroughly studied through different spectroscopic techniques such as UV-vis absorption, steady-state and time-resolved emission, circular dichroism, and relative DNA binding study using ethidium bromide. The intercalative mode of binding was suggested to be operative in all cases. Finally, computational studies employing DFT and TD-DFT were also carried out to interpret the experimentally observed absorption and emission bands of the complexes.

Modulating the Bond Strength of DNA-Nanoparticle Superlattices

A method is introduced for modulating the bond strength in DNA-programmable nanoparticle (NP) superlattice crystals. This method utilizes noncovalent interactions between a family of [Ru(dipyrido[2,3-a:3',2'-c]phenazine)(N-N)2](2+)-based small molecule intercalators and DNA duplexes to postsynthetically modify DNA-NP superlattices. This dramatically increases the strength of the DNA bonds that hold the nanoparticles together, thereby making the superlattices more resistant to thermal degradation. In this work, we systematically investigate the relationship between the structure of the intercalator and its binding affinity for DNA duplexes and determine how this translates to the increased thermal stability of the intercalated superlattices. We find that intercalator charge and steric profile serve as handles that give us a wide range of tunability and control over DNA-NP bond strength, with the resulting crystal lattices retaining their structure at temperatures more than 50 °C above what nonintercalated structures can withstand. This allows us to subject DNA-NP superlattice crystals to conditions under which they would normally melt, enabling the construction of a core-shell (gold NP-quantum dot NP) superlattice crystal.

An investigation on new ruthenium(II) hydrazone complexes as anticancer agents and their interaction with biomolecules

A new set of ruthenium(II) hydrazone complexes [Ru(H)(CO)(PPh3)2(L)] (1) and [RuCl2(DMSO)2(HL)] (2), with triphenyl phosphine or DMSO as co-ligands was synthesized by reacting benzoyl pyridine furoic acid hydrazone (HL) with [Ru(H)(Cl)(CO)(PPh3)3] and [RuCl2(DMSO)4]. The single crystal X-ray data of complexes 1 and 2 revealed an octahedral geometry around the ruthenium ion in which the hydrazone is coordinated through ON and NN atoms in complexes 1 and 2 respectively. The interaction of the compounds with calf thymus DNA (CT-DNA) has been estimated by absorption and emission titration methods which indicated that the ligand and the complexes interacted with CT-DNA through intercalation. In addition, the DNA cleavage ability of these newly synthesized ruthenium complexes assessed by an agarose gel electrophoresis method demonstrated that complex 2 has a higher DNA cleavage activity than that of complex 1. The binding properties of the free ligand and its complexes with bovine serum albumin (BSA) protein have been investigated using UV-visible, fluorescence and synchronous fluorescence spectroscopic methods which indicated the stronger binding nature of the ruthenium complexes to BSA than the free hydrazone ligand. Furthermore, the cytotoxicity of the compounds examined in vitro on a human cervical cancer cell line (HeLa) and a normal mouse embryonic fibroblasts cell line (NIH 3T3) revealed that complex 2 exhibited a superior cytotoxicity than complex 1 to the cancer cells but was less toxic to the normal mouse embryonic fibroblasts under identical conditions.

Ru(II) dyads derived from 2-(1-pyrenyl)-1H-imidazo[4,5-f][1,10]phenanthroline: versatile photosensitizers for photodynamic applications

Combining the best attributes of organic photosensitizers with those of coordination complexes is an elegant way to achieve prolonged excited state lifetimes in Ru(II) dyads. Not only do their reduced radiative and nonradiative rates provide ample time for photosensitization of reactive oxygen species at low oxygen tension but they also harness the unique properties of (3)IL states that can act as discrete units or in concert with (3)MLCT states. The imidazo[4,5-f][1,10]phenanthroline framework provides a convenient tether for linking π-expansive ligands such as pyrene to a Ru(II) scaffold, and the stabilizing coligands can fine-tune the chemical and biological properties of these bichromophoric systems. The resulting dyads described in this study exhibited nanomolar light cytotoxicities against cancer cells with photocytotoxicity indices exceeding 400 for some coligands employed. This potency extended to bacteria, where concentrations as low as 10 nM destroyed 75% of a bacterial population. Notably, these dyads remained extremely active against biofilm with light photocytotoxicities against these more resistant bacterial populations in the 10-100 nM regime. The results from this study demonstrate the versatility of these highly potent photosensitizers in destroying both cancer and bacterial cells and expand the scope of compounds that utilize low-lying (3)IL states for photobiological applications.

Bis-amide transition metal complexes: isomerism and DNA interaction study

A quatridentate bis-amide ligand, N,N'-propylenebis(salicylamide) H2pbs, and its transition metal complexes [M(pbs)(H2O)2], where M=Co(II), Ni(II), Cu(II), and Zn(II) have been synthesized and characterized by elemental analysis, UV-Vis, IR, NMR, Mass, EPR, molar conductivity, magnetic moment values and thermal analysis. The NMR spectrum of ligand evidences the E/Z isomerism. All the evidences reveal that the metal ions adopt octahedral geometry with metal:ligand:solvent ratio 1:1:2. The conductivity measurements exhibit that the complexes are non-electrolytes. DNA binding properties of these complexes have been explored by UV-Vis and cyclic voltammetry. The results indicate that these complexes are good intercalators.

DNA-binding and photocleavage properties of Ru(II) polypyridyl complexes with DNA and their toxicity studies on eukaryotic microorganisms

Four Ru(II) polypyridyl complexes, [Ru(bpy)(2)(7-NO(2)-dppz)](2+), [Ru(bpy)(2)(7-CH(3)-dppz)](2+), [Ru(phen)(2)(7-NO(2)-dppz)](2+), and [Ru(phen)(2)(7-CH(3)-dppz)](2+) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline), (7-Nitro-dppz = 7-Nitro dipyrido[3,2-a:2'-3'-c]phenazine, 7-CH(3)-dppz = 7-Methyl dipyrido[3,2-a:2'-3'-c]phenazine), have been synthesized and characterized by IR, UV, elemental analysis, (1)H NMR, (13)C-NMR, and mass spectroscopy. The DNA-binding properties of the four complexes were investigated by spectroscopic and viscosity measurements. The results suggest that all four complexes bind to DNA via an intercalative mode. Under irradiation at 365 nm, all four complexes were found to promote the photocleavage of plasmid pBR 322 DNA. Toxicological effects of the selected complexes were performed on industrially important yeasts (eukaryotic microorganisms).

Cytotoxicity of the traditional chinese medicine (TCM) plumbagin in its copper chemistry

The anticancer traditional Chinese medicine (TCM), plumbagin (PLN), was isolated from Plumbago Zeylanica. Reaction of plumbagin with Cu(II) salt, afforded [Cu(PLN)(2)].2H(2)O (1). With 2,2'-bipyridine (bipy) as a co-ligand, PLN reacts with Cu(II) to give [Cu(PLN)(bipy)(H(2)O)](2)(NO(3))(2).4H(2)O (2). 1 and 2 were characterized by elemental analysis, IR, ESI-MS spectra. Their crystal structures were determined by single crystal X-ray diffraction methods. The in vitro cytotoxicity of PLN, 1 and 2 against seven human tumour cell lines was assayed. The metal-based compounds exhibit enhanced cytotoxicity vs. that of free PLN, suggesting that these compounds display synergy in the combination of metal ions with PLN. The binding properties of PLN, 1 and 2 to DNA were investigated through UV-vis, fluorescence, CD spectra, and gel mobility shift assay, which indicated that 1 and 2 were non-covalent binding and mainly intercalated the neighboring base pairs of DNA. PLN, 1 and 2 exhibit inhibition activity to topoisomerase I (TOPO I), but 1 and 2 were more effective than PLN.

Synthesis, DNA-binding and photocleavage studies of [Ru(phen)2(pbtp)]2+ and [Ru(bpy)2(pbtp)]2+ (phen=1,10-phenanthroline; bpy=2,2'-bipyridine; pbtp=4,5,9,11,14-pentaaza-benzo[b]triphenylene)

Based on the ligand dppz (dppz=dipyrido-[3,2-a:2',3'-c]phenazine), a new ligand pbtp (pbtp=4,5,9,11,14-pentaaza-benzo[b]triphenylene) and its polypyridyl ruthenium(II) complexes [Ru(phen)(2)(pbtp)](2+) (1) (phen=1,10-phenanthroline and [Ru(bpy)(2)(pbtp)](2+) (2) (bpy=2,2'-bipyridine) have been synthesized and characterized by elemental analysis, ES-MS and (1)H NMR spectroscopy. The DNA-binding of these complexes were investigated by spectroscopic methods and viscosity measurements. The experimental results indicate that both complexes 1 and 2 bind to CT-DNA in classical intercalation mode, and can enantioselectively interact with CT-DNA. It is interesting to note that the pbtp ruthenium(II) complexes, in contrast to the analogous dppz complexes, do not show fluorescent behavior when intercalated into DNA. When irradiated at 365 nm, both complexes promote the photocleavage of pBR 322 DNA.

pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

A novel Ru(II) complex, [Ru(bpy)(2)(btppz)]Cl(2), where bpy=2,2'-bipyridine and btppz=benzo[h]tripyrido[3,2-a:2',3'-c:2'',3''-j]phenazine, has been synthesized and characterized. The pH effects on UV-visible (UV-vis) absorption and emission spectra of the complex have been studied and ground- and excited-state ionization constants of the complex have been derived. The calf thymus DNA (ct-DNA) binding properties of the complex were investigated with UV-vis absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)(6)](4-), DNA competitive binding with ethidium bromide, DNA melting experiments, reverse salt titrations and viscosity measurements. The complex was demonstrated to act as dual molecular switches: pH-induced "on-off" emission switch with an on-off intensity ratio of approximately 54 which is favorably compared with those reported for structurally analogous Ru(II) complexes, and a DNA molecular light switch with a luminescence enhancement factor of 22 as it intercalatively bound to the DNA.