Mixed ligand ruthenium(II) complexes of 5,6-dimethyl-1,10-phenanthroline: The role of ligand hydrophobicity on DNA binding of the complexes

Novel Octahedral Nickel (II) Complex with Flexible Piperazinyl Moiety Exhibits Potent Cytotoxic Effect Along with Anti-Migratory and Anti-Metastatic Effect on Human Cancer Cells

Synthesis of non-platinum transition metal complexes with N,O donor chelating ligand for application against pathogenesis of cancer with higher efficacy and selectivity is currently an important field of research. We assessed the anti-cancer effect of a mixed ligand Ni(II) complex on human breast and lung cancer cell lines in this investigation. Mononuclear mixed ligand octahedral Ni(II) complex [NiIIL(NO3)(MeOH)] complex (1), with tri-dentate phenol-based ligand 2,4-dichloro-6-((4-methylpiperazin-1-yl) methyl) phenol (HL) along with methanol and nitrate as ancillary ligand was prepared. Piperazine moiety of the ligand exists as boat conformation in this complex as revealed from single crystal X-ray study. UV-visible spectrum of complex (1) exhibits three distinct d-d bands due to spin-allowed 3 A2 g→3T1 g (P), 3 A2 g→3T1 g(F) and 3 A2 g→3T2 g(F) transitions as expected in an octahedral d8 system. Our study revealed that Complex (1) induces apoptotic cell death in mouse and human cancer cells such as mcf-7, A549 and MDA-MB-231 through transactivation of p53 and its pro-apoptotic downstream targets in a dose dependent manner. Furthermore, complex (1) was able to slow the migratory rate of MDA-MB-231 cells' in vitro as well as epithelia -mesenchymal transition (EMT), the key step for metastatic transition and malignancy. Over all our results suggest complex (1) as a potential agent in anti-tumor treatment regimen showing both cytotoxic and anti-metastatic activity against malignant neoplasia.

Discovery of mitochondrion-targeting copper(II)-plumbagin and -bipyridine complexes as chemodynamic therapy agents with enhanced antitumor activity

Four copper(II)-plumbagin and -bipyridine complexes (Cu1-Cu4) were synthesized as chemodynamic therapy agents with enhanced antitumor activity. As lipophilic and positively charged compounds, Cu1-Cu4 were preferentially accumulated in mitochondria and activated the mitochondrial apoptosis pathway. Mechanistic studies showed that Cu1-Cu4 reacted with GSH to reduce Cu2+ ions to Cu+ ions, catalyzed the formation of toxic hydroxyl radicals (˙OH) from hydrogen peroxide (H2O2) through a Fenton-like reaction, induced mitochondrial dysfunction, and activated caspase-9/3, which eventually led to apoptosis. Cu1-Cu4 arrested HeLa cells in the S phase and eventually killed cancer cells. Cu2 showed a favorable pharmacokinetic profile in mice. Moreover, Cu2 effectively inhibited the growth of HeLa xenografts in nude mice and showed low toxicity in vivo.

Copper(II) complexes with plumbagin and bipyridines target mitochondria for enhanced chemodynamic cancer therapy

The combination of mitochondrial targeting and chemodynamic therapy is a promising anti-cancer strategy. Three mitochondria targeting copper(II) complexes (Cu1-Cu3) with plumbagin and bipyridine ligands for enhanced chemodynamic therapy were synthesized and characterized. Their anti-proliferative activity to HeLa cells was higher than that of cisplatin, and their toxicity to normal cells was low. Cellular uptake and distribution studies indicated that Cu1 and Cu3 were mainly accumulated in mitochondria. The mechanism studies showed that Cu1 and Cu3 converted intracellular H2O2 into toxic hydroxyl radicals by consuming glutathione, leading to mitochondrial dysfunction. Treatment with the copper complex caused ER stress and cell arrest in the S phase which resulted in apoptosis. In vivo, Cu1 and Cu3 effectively inhibited the growth of HeLa xenograft tumors without obvious toxic and side effects.

Mononuclear Co(II) polypyridyl complexes: synthesis, molecular structure, DNA binding/cleavage, radical scavenging, docking studies and anticancer activities

Mononuclear Co(II) complexes [CoII(L)Cl2]; 1, [CoII(L)(bpy)Cl]PF6; 2, [CoII(L)(phen)Cl]PF6; 3 and [CoII(L)(pic)Cl]; 4, (where L = N,N-bis(pyridin-2-ylmethyl)aniline, bpy = 2,2/-bipyridine, phen = 1,10-phenanthroline, pic = picolinic acid) were systematically synthesized and...

Synthesis and cytotoxicity against tumor cells of pincer N-heterocyclic ligands and their transition metal complexes

The complexes: [CoL₂](ClO₄)₂ (1), [FeL₂](ClO₄)₂ (2), [NiL₂](ClO₄)₂ (3) and [MnLCl₂] (4), with L = diethyl-1,1′-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazole-3-carboxylate), were synthesized and fully characterized. Structural analysis revealed two distinct patterns influenced by the counter ions where L acts as a tridentate chelating ligand. The in vitro antitumor activity of L and L′ (diethyl 2,2′-(pyridine-2,6-diylbis(5-methyl-1H-pyrazole-3,1-diyl)) diacetate) as well as their metal complexes, was tested by the measurement of their cytostatic and cytotoxic properties towards the blood cancer mastocytoma cell line P815. We have also investigated their interactions with the antioxidant enzyme system. As a result, [MnL′Cl₂] (1′) exhibited the strongest activity compared to reference cis-platin with no cytotoxicity towards normal cells PBMCs (Peripheral Blood Mononuclear Cells). On the other hand, the antioxidant enzyme activity showed that the efficiency of metal complex 1′ against P815 tumor cells was via the rise in the SOD activity and inhibition of CAT enzyme activity. This proof of concept study allows disclosure of a new class of molecules in cancer therapeutics.

The complexes: [CoL₂](ClO₄)₂ (1), [FeL₂](ClO₄)₂ (2), [NiL₂](ClO₄)₂ (3) and [MnLCl₂] (4), with L = diethyl-1,1′-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazole-3-carboxylate), were synthesized and fully characterized.

Hydrophobic interactions control the self-assembly of DNA and cellulose

Desoxyribosenucleic acid, DNA, and cellulose molecules self-assemble in aqueous systems. This aggregation is the basis of the important functions of these biological macromolecules. Both DNA and cellulose have significant polar and nonpolar parts and there is a delicate balance between hydrophilic and hydrophobic interactions. The hydrophilic interactions related to net charges have been thoroughly studied and are well understood. On the other hand, the detailed roles of hydrogen bonding and hydrophobic interactions have remained controversial. It is found that the contributions of hydrophobic interactions in driving important processes, like the double-helix formation of DNA and the aqueous dissolution of cellulose, are dominating whereas the net contribution from hydrogen bonding is small. In reviewing the roles of different interactions for DNA and cellulose it is useful to compare with the self-assembly features of surfactants, the simplest case of amphiphilic molecules. Pertinent information on the amphiphilic character of cellulose and DNA can be obtained from the association with surfactants, as well as on modifying the hydrophobic interactions by additives.

Open-tubular nanoelectrochromatography (OT-NEC): gel-free separation of single stranded DNAs (ssDNAs) in thermoplastic nanochannels

Electrophoresis or electrochromatography carried out in nanometer columns (width and depth) offers some attractive benefits compared to microscale columns. These advantages include unique separation mechanisms that are scale dependent, fast separation times, and simpler workflow due to the lack of a need for column packing and/or wall coatings to create a stationary phase. We report the use of thermoplastics, in this case PMMA, as the substrate for separating single-stranded DNAs (ssDNAs). Electrophoresis nanochannels were created in PMMA using nanoimprint lithography (NIL), which can produce devices at lower cost and in a higher production mode compared to the fabrication techniques required for glass devices. The nanochannel column in PMMA was successful in separating ssDNAs in free solution that was not possible using microchip electrophoresis in PMMA. The separation could be performed in <1 s with resolution >1.5 when carried out using at an electric field strength of 280 V/cm and an effective column length of 60 μm (100 nm × 100 nm, depth and width). The ssDNAs transport through the PMMA column was driven electrokinetically under the influence of an EOF. The results indicated that the separation was dominated by chromatographic effects using an open tubular nano-electrochromatography (OT-NEC) mode of separation. Interesting to these separations was that no column packing was required nor a wall coating to create the stationary phase; the separation was affected using the native polymer that was UV/O₃ activated and an aqueous buffer mobile phase.

Heteroleptic NiII complexes: Synthesis, structural characterization, computational studies and amoebicidal activity evaluation

In this work, we present the synthesis, characterization, electrochemical studies, DFT calculations, and in vitro amoebicidal effect of seven new heteroleptic Ni^II coordination compounds. The crystal structures of [H₂(pdto)](NO₃)₂ and [Ni(pdto)(NO₃)]PF₆ are presented, pdto = 2,2'-[1,2-ethanediylbis-(sulfanediyl-2,1-ethanediyl)]dipyridine. The rest of the compounds have general formulae: [Ni(pdto)(NN)](PF₆) where N-N = 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (44dmbpy), 5,5'-dimethyl-2,2'-bipyridine (55dmbpy), 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (47dmphen) and 5,6-dimethyl-1,10-phenanthroline (56dmphen). The size of NN ligand and its substituents modulate the compound electronic features and influence their antiproliferative efficiency against Entamoeba histolytica. 56dmphen derivative, shows the biggest molar volume and presents a powerful amoebicidal activity (IC₅₀ = 1.2 μM), being seven times more effective than the first-line drug for human amoebiasis metronidazole. Also, increases the reactive oxygen species concentration within the trophozoites. This could be the trigger of the E. histolytica growth inhibition. The antiparasitic effect is described using Ni^II electron density, molar volume, estimated by DFT, as well as the experimental redox potential and diffusion coefficients. In general, amoebicidal efficiency is directly proportional to the increment of the molar volume and decreases when the redox potential becomes more positive.

Intercalation of manganese-mefenamic acid complex into double stranded of calf thymus DNA

The interaction of the [Mn(mef)₂(phen)H₂O] complex in which mef is mefenamic acid drug and phen is 1,10 phenanthrolin ligand with calf thymus DNA (ct-DNA) was studied by using different spectroscopic methods, molecular docking and viscometery. The competitive fluorescence and UV-Vis absorption spectroscopy indicated that the complex interacted with ctDNA via intercalating binding mode with the binding constant of 1.16 × 10⁴ Lmol^-1. The thermodynamic studies showed that the reaction between the complex and ctDNA is exothermic. Furthermore, the complex induced changes in DNA viscosity. Circular dichroism spectroscopy (CD) was employed to measure the conformational changes of ctDNA in the presence of the complex and verified intercalation binding mode. The molecular modeling results illustrated that the complex interacted via intercalation by relative binding energy of -28.45 kJ mol^-1.

Temperature-Driven Precise Control of Biological Droplet's Adhesion on a Slippery Surface

Precise control of a biological droplet's adhesive force on a liquid-repellent surface for smart antifouling systems is critical and fundamental to scientific research and industrial applications. Although slippery surfaces with stimuli-responsive wetting behaviors have been reported, challenge still remains in designing responsive biological droplets to achieve controllable adhesion and antifouling property. Here, we developed a thermoresponsive biological droplet adhesion system to precisely control its adhesion on the lubricant-infused slippery surface. Single-stranded DNA (ssDNA) in the biological droplet displays molecular configuration reversible deformation under external thermal stimuli. This property ascribes to the changing amount of exposed hydrophobic moieties of ssDNA, which strongly affects the interfacial hydrophobic interaction with the lubricant. This work may improve the understanding of the principles underlying liquid-lubricant interfacial adhesion, open up opportunities for a new class of antifouling systems, and provide a promising system for controllable manipulation of liquids' motion in biochips and microreactor devices.

Organoruthenium(II) complexes attenuate stress in Caenorhabditis elegans through regulating antioxidant machinery

The 1:1 stoichiometric reactions of 3-methoxy salicylaldehyde-4(N)-substituted thiosemicarbazones (H₂L^1-4) with [RuCpCl(PPh₃)₂] was carried out in methanol. The obtained complexes (1-4) were characterized by analytical, IR, absorption and ¹H NMR spectroscopic studies. The structures of ligand [H₂-3MSal-etsc] (H₂L³) and complex [RuCp(Msal-etsc) (PPh₃)] (3), were characterized by single crystal X-ray diffraction studies. The interaction of the ruthenium(II) complexes (1-4) with calfthymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an intercalative binding mode of DNA has been proposed. The protein binding abilities of the new complexes were monitored by quenching the tryptophan and tyrosine residues of BSA, as model protein. From the studies, it was found that the new ruthenium metallacycles exhibited better affinity than their precursors. The free radical scavenging assay suggests that all complexes effectively scavenged the DPPH radicals as compared to that of standard control ascorbic acid and scavenging activities of complexes are in the order of 4 > 2 > 3 > 1. In addition, ruthenium(II) complexes (2-4) also exhibited an excellent in vivo antioxidant activity as it was able to increase the survival of worms exposed to lethal oxidative and thermal stresses possibly through reducing the intracellular ROS levels. It was interesting to note that complexes 2-4 failed to increase the lifespan of mev-1 mutant worms having shortened lifespan due to the over production of free radicals. This data confirmed that complexes 2-4 conferred stress resistance in C. elegans, but they also require an endogenous detoxification mechanism for doing so. The genetic and reporter gene expression analysis revealed that complexes 2-4 maintained the intracellular redox status and offered stress protection through transactivation of antioxidant defence machinery genes gst-4 and sod-3 which are directly regulated by SKN-1 and DAF-16 transcription factors, respectively. Altogether, our results suggested that complexes 2-4 might play a crucial role in stress modulation and they perhaps exert almost similar effects in higher models, which is an important issue to be validated in future.

The Anticancer Activities of Some Nitrogen Donor Ligands Containing bis-Pyrazole, Bipyridine, and Phenanthroline Moiety Using Docking Methods

The anticancer study of nitrogen-chelating ligands can be of tremendous help in choosing ligands for the anticancer metal complexes design especially with ruthenium(II). The inhibitory anticancer activities of some nitrogen-chelating ligands containing bis-pyrazole, bipyridine, and phenanthroline were studied using experimental screening against cancer cell and theoretical docking methods. In vitro anticancer activities showed compound 11 as the most promising inhibitor, and the computational docking further indicates its strong inhibitory activities towards some cancer-related receptors. Among the twenty-one modelled ligands, pyrazole-based compounds 7, 11, and 15 are the most promising inhibitors against the selected receptors followed by 18 and 21 which are derivatives of pyridine and phenanthroline, respectively. The presence of the carboxylic unit in the top five ligands that displayed stronger inhibitory activities against the selected receptors is an indication that the formation of noncovalent interactions such as hydrogen bonding and a strong electron-withdrawing group in these compounds are very important for their receptor interactions. The thermodynamic properties, the polarizabilities, and the LUMO energy of the compounds are in the same patterns as the observed inhibitory activities.

Non-enolisable Knoevenagel condensate appended Schiff bases-metal (II) complexes: Spectral characteristics, DNA-binding and nuclease activities

New Schiff base complexes [Cu(L¹)Cl] (1), [Ni(L¹)Cl] (2), [Zn(L¹)Cl] (3), and [Fe(L²)H₂OCl] (4) {L¹=(4E)-3-(2-hydroxybenzylidene)-4-(2-hydroxyphenylimino)pentan-2-one, L²=2,2'-(1E,1'E)-(3-(2-hydroxybenzylidene)-pentane-2,4-diylidene)bis(azan-1-yl-1 idene)diphenol} have been synthesized and characterized by elemental analysis, UV-Vis, IR, FAB-mass, EPR, spectral studies and electrochemical studies, the ligands L¹ &L² were characterized by ¹H and ¹³C NMR spectra. Complex 1 show a visible spectral d-d band near 600nm and display cyclic voltammetric quasireversible response for the Cu(II)/Cu(I) couple vs Ag/AgCl in DMSO. The EPR spectrum of 1 show g_‖>g_⊥ suggesting a square planar geometry around copper with d_x²_-y² as the ground state. The mass spectral results have confirmed the proposed structure for complexes 1-4. DNA binding properties of these complexes 1-4 have been investigated by absorption titrations, cyclic voltammetric studies and circular dichroism studies. On titration with DNA, the complexes 1-4 show hypochromism at the MLCT band (13-31%) with a red shift of 1-8nm in the electronic spectrum and positive shift of voltammetric E_1/2 in the CV studies are in favour of intercalative binding. CD spectra of 1 showed an increase in molar ellipticity (θ₂₇₈) of the positive band with a minor red shift indicating the transition of B-form of DNA to A like form. DNA cleavage studies of complexes 1 and 4 with pUC18 DNA were studied by gel electrophoresis and complex 4 cleaves supercoiled pUC18 DNA in an oxidative manner in the presence of H₂O₂ and on photo irradiation at 312nm.

Water splitting with polyoxometalate-treated photoanodes: enhancing performance through sensitizer design

Visible light driven water oxidation has been demonstrated at near-neutral pH using photoanodes based on nanoporous films of TiO₂, polyoxometalate (POM) water oxidation catalyst [{Ru₄O₄(OH)₂(H₂O)₄}(γ-SiW₁₀O₃₆)₂]^10- (1), and both known photosensitizer [Ru(bpy)₂(H₄dpbpy)]²⁺ (P2) and the novel crown ether functionalized dye [Ru(5-crownphen)₂(H₂dpbpy)](H₂2). Both triads, containing catalyst 1, and catalyst-free dyads, produce O₂ with high faradaic efficiencies (80 to 94%), but presence of catalyst enhances quantum yield by up to 190% (maximum 0.39%). New sensitizer H₂2 absorbs light more strongly than P2, and increases O₂ quantum yields by up to 270%. TiO₂-2 based photoelectrodes are also more stable to desorption of active species than TiO₂-P2: losses of catalyst 1 are halved when pH > TiO₂ point-of-zero charge (pzc), and losses of sensitizer reduced below the pzc (no catalyst is lost when pH < pzc). For the triads, quantum yields of O₂ are higher at pH 5.8 than at pH 7.2, opposing the trend observed for 1 under homogeneous conditions. This is ascribed to lower stability of the dye oxidized states at higher pH, and less efficient electron transfer to TiO₂, and is also consistent with the 4^th1-to-dye electron transfer limiting performance rather than catalyst TOF_max. Transient absorption reveals that TiO₂-2-1 has similar 1^st electron transfer dynamics to TiO₂-P2-1, with rapid (ps timescale) formation of long-lived TiO₂(e^-)-2-1(h⁺) charge separated states, and demonstrates that metallation of the crown ether groups (Na⁺/Mg²⁺) has little or no effect on electron transfer from 1 to 2. The most widely relevant findings of this study are therefore: (i) increased dye extinction coefficients and binding stability significantly improve performance in dye-sensitized water splitting systems; (ii) binding of POMs to electrode surfaces can be stabilized through use of recognition groups; (iii) the optimal homogeneous and TiO₂-bound operating pHs of a catalyst may not be the same; and (iv) dye-sensitized TiO₂ can oxidize water without a catalyst.

New water-soluble copper (II) complexes including 4,7-dimethyl-1,10-phenanthroline and L-tyrosine: synthesis, characterization, DNA interactions and cytotoxicities

Two new water-soluble copper(II) complexes, [Cu(dmphen)2(NO3)]NO3 (1), [Cu(dmphen)(tyr)(H2O)]NO3·H2O (2) and the diquarternary salt of dmphen (dmphen = 4,7-dimethyl-1,10-phenanthroline and tyr = L-tyrosine), have been synthesized and characterized by elemental analysis, (1)H NMR, (13)C NMR and IR spectroscopy, thermal analysis and single crystal X-ray diffraction techniques. The CT-DNA binding properties of these compounds have been investigated by absorption, emission spectroscopy and thermal denaturation measurements. The supercoiled pBR322 plasmid DNA cleavage activity of these compounds has been explored by agarose gel electrophoresis. The cytotoxicity of these compounds against MCF-7, Caco-2, A549 cancer cells and BEAS-2B healthy cells was also studied by the XTT method. Complexes 1 and 2 exhibit significant cytotoxicity, with lower IC50 values than those of cisplatin.

Design and synthesis of enantiomeric (R)- and (S)-copper(II) and diorganotin(IV)-based antitumor agents: their in vitro DNA binding profile, cleavage efficiency and cytotoxicity studies

New chiral reduced Schiff base ligands (R)/(S)-2-(2-hydroxy-1-phenylethylaminomethyl)phenol (L), (R)/(S)-2-(benzylamino)-2-phenylethanol (L') and their Cu(II)/organotin(IV) complexes (1-4) were synthesized and thoroughly characterized. Preliminary in vitro DNA binding studies of (R)- and (S)-enantiomeric pairs of ligands L, L' and complexes 1-4 were carried out employing UV-vis, fluorescence and circular dichroic techniques to evaluate their enantioselective DNA binding potential, thereby to act as antitumor chemotherapeutic drug entities. The observations demonstrated that S-enantiomer of Cu(II) complex, 1 binds more avidly to DNA in comparison to its R-enantiomeric form and organotin(IV) complex 2. This was further established by Kb and Ksv values of ligands L and L' and (S)-/(R)-1-4 complexes, which demonstrated multifold increase in case of S-enantiomer of copper complex 1 in comparison to its R-enantiomeric form. This clearly demonstrates the chiral preference of S-enantiomer over R-enantiomer and its potency to act as a chemotherapeutic agent. Cleavage studies of 1-4 with pBR322 plasmid DNA were carried out, noticeably, S-enantiomer of complex 1 exhibited effective DNA cleavage efficiency in absence of external agents. The cytotoxicity of ligands L and L' and (S)-/(R)-1-4 complexes was examined on a panel of 19 human tumor cell lines of different histological origins by SRB assay. In the both the cases, the S-enantiomer of complex 1 and 3 revealed remarkably good cytotoxic activity (GI50 values <10) against T24 (Urinary Bladder), DU145 (Prostate), U373MG (Astrocytoma) and HCT15, SW620 (Colon) clearly underlining the influence of enantiomeric discrimination. Interestingly, ligands L, L' and rest of the complexes demonstrated moderate cytotoxic activity (GI50 values <40).

2-Nitroimidazole-ruthenium polypyridyl complex as a new conjugate for cancer treatment and visualization

A novel long-lifetime highly luminescent ruthenium polypyridyl complex containing 2-nitroimidazole moiety [Ru(dip)2(bpy-2-nitroIm)]Cl2 (dip=4,7-diphenyl-1,10-phenanthroline, bpy-2-nitroIm=4-[3-(2-nitro-1H-imidazol-1-yl)propyl]-2,2'-bipyridine) has been designed cancer treatment and imaging. The luminescence properties of the synthesized compound strongly depend on the oxygen concentration. Under oxygen-free conditions quantum yield of luminescence and the average lifetime of emission were found to be 0.034 and 1.9 μs, respectively, which is ca. three times higher in comparison to values obtained in air-equilibrated solution. The binding properties of the investigated ruthenium complex to human serum albumin have been studied and the apparent binding constant for the formation of the protein-ruthenium adduct was determined to be 1.1×10(5)M(-1). The quantum yield and the average lifetime of emission are greatly enhanced upon binding of ruthenium compound to the protein. The DNA binding studies revealed two distinguished binding modes which lead to a decrease in luminescence intensity of ruthenium complex up to 60% for [DNA]/[Ru]<2, and enhancement of emission for [DNA]/[Ru]>80. Preliminary biological studies confirmed fast and efficient accumulation of the ruthenium complex inside cells. Furthermore, the ruthenium complex was found to be relatively cytotoxic with LD50 of 12 and 13 μM for A549 and CT26 cell lines, respectively, under normoxic conditions. The retention and cellular uptake of ruthenium complex is enhanced under hypoxic conditions and its LD50 decreases to 8 μM for A549 cell line.

Effects of molecular size and surface hydrophobicity on oligonucleotide interfacial dynamics

Single-molecule total internal reflection fluorescence microscopy was used to observe the dynamic behavior of polycytosine single-stranded DNA (ssDNA) (1-50 nucleotides long) at the interface between aqueous solution and hydrophilic (oligoethylene glycol-modified fused silica, OEG) and hydrophobic (octadecyltriethoxysilane-modified fused silica, OTES) solid surfaces. High throughput molecular tracking was used to determine >75,000 molecular trajectories for each molecular length, which were then used to calculate surface residence time and squared displacement (i.e., "step-size") distributions. On hydrophilic OEG surfaces, the surface residence time increased systematically with ssDNA chain length, as expected due to increasing molecule-surface interactions. Interestingly, the residence time decreased with increasing ssDNA length on the hydrophobic OTES surface, particularly for longer chains. Similarly, the interfacial mobility of polynucleotides slowed with increasing chain length on OEG, but became faster on OTES. On OTES surfaces, the rates associated with desorption and surface diffusion exhibited the distinctive anomalous temperature dependence that is characteristic of hydrophobic interactions for short-chain species but not for longer chains. These combined observations suggest that long oligonucleotides adopt conformations minimizing hydrophobic interactions, e.g., by internal sequestration of hydrophobic nucleobases.

Binding Studies of a New Water-Soluble Iron(III) Schiff Base Complex to DNA Using Multispectroscopic Methods

A novel iron(III) complex [Fe(SF)](ClO₄)₃.2H₂O; in which SF = N,N₀-bis{5-[(triphenylphosphonium chloride)-methyl] salicylidene}-o-phenylenediamine) has been synthesized and characterized using different physicochemical methods. The binding of this complex with calf thymus (CT) DNA was investigated by circular dichroism, absorption studies, emission spectroscopy, voltammetric studies, and viscosity measurements. The results showed that this complex can bind to DNA via external and groove binding modes.

New modulated design and synthesis of chiral CuII/SnIV bimetallic potential anticancer drug entity: in vitro DNA binding and pBR322 DNA cleavage activity

A new chiral ligand scaffold L derived from (R)-2-amino-2-phenyl ethanol and diethyl oxalate was isolated and thoroughly characterized by various spectroscopic methods. The ligand L was allowed to react with CuCl(2)·2H(2)O and NiCl(2)·6H(2)O to achieve monometallic complexes 1 and 2, respectively. Subsequently modulation of 1 and 2 was carried out in the presence of SnCl(4)·5H(2)O to obtain heterobimetallic potential drug candidates 3 and 4 possessing (Cu(II)/Sn(IV) and Ni(II)/Sn(IV)) metallic cores, respectively and characterized by elemental analysis and spectroscopic data including (1)H, (13)C and (119)Sn NMR in case of 3 and 4. In vitro DNA binding studies revealed that complex 3 avidly binds to DNA as quantified by K(b) and K(sv) values. Complex 3 exhibits a remarkable DNA cleavage activity (concentration dependent) with pBR322 DNA and the cleavage activity of 3 was significantly enhanced in the presence of activators and follows the order H(2)O(2)>Asc>MPA>GSH. Complex 3 cleave pBR322 DNA via hydrolytic pathway and accessible to major groove of DNA.

Single photon counting fluorescence lifetime detection of pericellular oxygen concentrations

Fluorescence lifetime imaging microscopy offers a non-invasive method for quantifying local oxygen concentrations. However, existing methods are either invasive, require custom-made systems, or show limited spatial resolution. Therefore, these methods are unsuitable for investigation of pericellular oxygen concentrations. This study describes an adaptation of commercially available equipment which has been optimized for quantitative extracellular oxygen detection with high lifetime accuracy and spatial resolution while avoiding systematic photon pile-up. The oxygen sensitive fluorescent dye, tris(2,2'-bipyridyl)ruthenium(II) chloride hexahydrate [Ru(bipy)(3)](2+), was excited using a two-photon excitation laser. Lifetime was measured using a Becker & Hickl time-correlated single photon counting, which will be referred to as a TCSPC card. [Ru(bipy)(3)](2+) characterization studies quantified the influences of temperature, pH, cellular culture media and oxygen on the fluorescence lifetime measurements. This provided a precisely calibrated and accurate system for quantification of pericellular oxygen concentration based on measured lifetimes. Using this technique, quantification of oxygen concentrations around isolated viable chondrocytes, seeded in three-dimensional agarose gel, revealed a subpopulation of cells that exhibited significant spatial oxygen gradients such that oxygen concentration reduced with increasing proximity to the cell. This technique provides a powerful tool for quantifying spatial oxygen gradients within three-dimensional cellular models.

DNA interaction studies of cobalt (II) mixed-ligand complexes containing dimethyl-1, 10-phenanthroline and dipyrido[3,2-a:2',3'-c]phenazine: the role of methyl substitutions on the mode of binding

Two cobalt (II) complexes containing a dipyrido[3,2-a:2',3'-c]phenazine (dppz) base with the general formulation [Co(dppz)(dmp)(2)]Cl(2), where dmp is 4,7-dimethyl-1,10-phenanthroline ligand (4,7-dmp) (1) and 2,9-dimethyl-1,10-phenanthroline ligand (2,9-dmp) (2) were synthesized and characterized. Binding interactions of these complexes with calf thymus DNA were investigated by emission, absorption, circular dichroism, and viscosity studies, and the effects of the positions of methyl substitutions in phenanthroline coligands were investigated. The DNA binding constants obtained from the absorption spectral titrations decrease in the order of 1 > 2, which is consistent with the trend in apparent emission enhancement of the complexes on binding to calf thymus DNA. These observations were supported by circular dichroism spectroscopy and viscosity measurements and reveal that DNA binding affinity of the complexes depends on the position of methyl groups on the phenanthroline ligands.