DNA-enhanced assembly of [Ru(bpy)2ITATP] on an ITO electrode

A novel technique for controllable assembly of [Ru(bpy)₂ITATP]^3+/2+ (where bpy = 2,2′-bipyridine, ITATP = isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) on an ITO electrode in the absence and presence of calf thymus DNA is proposed. The [Ru(bpy)₂ITATP]^3+/2+ and double stranded DNA is assembled onto the ITO electrode using repetitive voltammetric sweeping. The assembly is confirmed by ex situ cyclic voltammetry and the fluorescence microscopy. A pair of diffusion-controlled waves and prewaves for [Ru(bpy)₂ITATP]^3+/2+ is observed in the voltammetric sweeping process. The formal potential of the prewaves is found to be much negative than that of the diffusion-controlled waves. The controllable assembly of [Ru(bpy)₂ITATP]^3+/2+ on the ITO surface is accelerated by DNA and affected by ionic strength. With this DNA-prompted electrochemical technique, a multifunctional biomolecular film containing surface-confined redox center of controllable thickness is fabricated.     

DNA-promoted electrochemical assembly of [Ru(bpy)2dpp] on the ITO electrode by introducing copper(II) ion

The electrochemical assembly of [Ru(bpy)₂dpp]^3+/2+ (where bpy = 2,2′-bipyridine, dpp = 2,3-bis (2-pyridyl) pyrazine) promoted by calf thymus DNA on an ITO electrode based on the introduction of copper(II) ion has been investigated. There exists a diffusion-controlled wave and two prewaves for the complex in the differential pulse voltammetric sweeping process. The formal potential of the high prewave shift ca. 0.530 V negatively compared with that of the diffusion-controlled wave. Dpp ligand with two vacant chelating N sites in the complex can bite Cu²⁺ and the resultant heterometallic complex shows a weakened assembly in contrast to that of [Ru(bpy)₂dpp]^3+/2+ alone. Furthermore, double stranded DNA is able to accelerate the assembly of the ruthenium complex and heterometallic complex generated by chelating with Cu²⁺ by using the ITO surface, the prompted strength of the latter is far stronger than the former. Their assembled mechanism enhanced by DNA is proposed.     

Mediated oxidation of guanine by [Ru(bpy)2dpp] and their electrochemical assembly on the ITO electrode

Electrochemical oxidation of guanine mediated by [Ru(bpy)₂dpp]²⁺ (where bpy = 2,2′-bipyridine, dpp = 2,3-bis (2-pyridyl) pyrazine) and their electrochemical assembly at an ITO electrode prompted by guanine have been investigated with cyclic voltammetry and differential pulse voltammetry. It is found that [Ru(bpy)₂dpp]²⁺ can serve as an excellent mediator to induce the oxidation of guanine, and the mediated peak currents increase linearly with the rise of guanine concentration in the range from 0.01 to 0.20 mmol L⁻¹. Interestingly, with the increase of repetitive voltammetric sweeping numbers, [Ru(bpy)₂dpp]^3+/2+ can be assembled onto the ITO electrode and guanine has the ability to enhance the peak currents of prewaves. Also, with the rise of guanine concentration from 0.01 to 0.15 mmol L⁻¹, the peak currents of prewaves increase gradually. Meanwhile, the mediated mechanism of guanine oxidation by [Ru(bpy)₂dpp]²⁺ and the assembled process of [Ru(bpy)₂dpp]^3+/2+ on the ITO surface in the presence of guanine are discussed in detail.     

Electrochemical assembly of [Ru(bpy)<Subscript>2</Subscript>tatp]<Superscript>2+</Superscript> associated with surfactants on the MWNTs/GC electrode

The electrochemical assembly of [Ru(bpy)₂tatp]²⁺ (where bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene) on the multi-walled carbon nanotubes-modified glassy carbon electrode (MWNTs/GC) in the presence of anionic and cationic surfactants has been investigated. A diffusion-controlled wave and three prewaves are exhibited on the differential pulse voltammogram of [Ru(bpy)₂tatp]²⁺. The formal potential of the prewaves is found to be much negative than that of the diffusion-controlled wave. An appropriate amount of anionic surfactants including dihexadecyl phosphate (DHP) and deoxyribonucleic acid (DNA) can prompt the assembly of [Ru(bpy)₂tatp]²⁺ on the MWNTs/GC electrode by using the method of repetitive voltammetric sweeping. In contrast, cationic surfactant such as hexadecyl trismethyl ammonium chrolide (HTAC) dispersed on the MWNTs surface is found to inhibit the assembly of [Ru(bpy)₂tatp]²⁺. Meanwhile, the assembled principle of [Ru(bpy)₂tatp]²⁺ on the MWNTs/GC electrode with the participation of surfactants is discussed in detail.     

Electrochemical fabrication and potential-enhanced luminescence of [Ru(bpy)2tatp] incorporating DNA-stabilized single-wall carbon nanotubes on an indium tin oxide electrode

A simple method was developed for the preparation of [Ru(bpy)₂tatp]²⁺-based aggregates (where bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene) on an indium tin oxide (ITO) electrode in the presence of DNA-stabilized single-walled carbon nanotubes (DNA–SWCNTs). The presence of SWCNTs in the concentration range from 0.02 to 0.125 g L⁻¹ dispersed with 0.25 mmol L⁻¹ DNA was found to promote the immobilization of [Ru(bpy)₂tatp]²⁺ on the ITO electrode by the method of repetitive voltammetric sweeping. The photoluminescence of [Ru(bpy)₂tatp]²⁺ incorporating DNA–SWCNTs both in solution and on the ITO electrode was systematically investigated by emission spectra and fluorescence microscopic imaging. An excess amount of SWCNTs can quench the photoluminescence of [Ru(bpy)₂tatp]²⁺ enhanced by DNA. The anodic potentials combined with CW green laser via an optical microscope was found to significantly increase the emission intensity of [Ru(bpy)₂tatp]²⁺–DNA–SWCNTs aggregates on the ITO electrode. In addition, the electrochemical fabrication and photoluminescence principles of [Ru(bpy)₂tatp]²⁺–DNA–SWCNTs aggregates on the ITO electrode tuned by the external electric fields were discussed in detail.     

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”.     

Preparation and characterization of thin films of amine functionalised mesoporous silica having cubic pore structures and their use for electrode surface modifications

Thin films of amine functionalised mesoporous silica were deposited on tin-doped indium oxide (ITO) slides by dip-coating mixtures of TEOS (tetraethyl orthosilicate), APTES ((3-aminopropyl)triethoxysilane), and the non-ionic surfactant Brij56. The pore structure of the films was found to depend on the temperature use during calcination to remove the templates. Films calcined at 350 °C had highly ordered mesostructures with face-centred cubic pore arrangements, while films calcined at 275 °C had primitive cubic pore structures. The as-prepared films, or films extracted with acidic ethanol solutions had very poorly ordered mesopores. Calcination at 275 °C was sufficient to remove the Brij56 templates, without damaging the organic amine chains. Calcination at 350 °C however, also resulted in the lost of the organic groups. The use of ITO substrates allowed the dip-coated films to be used directly as working electrodes. At pH 4.7, the voltammetric response of [Ru(bpy)₃]²⁺ was completely suppressed by the amine functionalised films. This was attributed to protonation of the amine groups that gave the films positive charges. At higher pH, the amine groups were no longer protonated and the voltammetric response of [Ru(bpy)₃]²⁺ was restored. Conversely, [Ru(bpy)₃]²⁺ was adsorbed by the unmodified films that carried negative charges at pH 4.7, resulting in a 4-fold increase in the peak currents compared to uncoated ITO. For [Fe(CN)₆]^3? at low pH the unmodified films blocked the response of the ions, while the functionalised films gave small but distinct voltammetric peaks.     

Characterization of electrochemiluminescence of tris(2,2′-bipyridine)ruthenium(II) with glyphosate as coreactant in aqueous solution

Glyphosate, a phosphorus-containing amino acid type herbicide was used as a coreactant for studying of electrochemiluminescence (ECL) reaction of tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺] in an aqueous solution. In a phosphate buffer solution of pH 8, glyphosate itself was known to be electrochemically inactive at glassy carbon electrode, however, it participated in a homogeneous chemical reaction with the electrogenerated Ru(bpy)₃³⁺, and resulted in producing Ru(bpy)₃²⁺ species at the electrode surface. Kinetic and mechanistic information for the catalysis of glyphosate oxidation were evaluated by the steady-state voltammetric measurement with an ultramicroelectrode. The simulated cyclic voltammogram based on this mechanism was in good agreement with that obtained experimentally. ECL reaction of Ru(bpy)₃²⁺/glyphosate system was found to be strongly dependent on the media pH. In a pH region of 5-9, an ECL wave appeared at ca. +1.1 V vs. Ag/AgCl, which was caused by the generation of *Ru(bpy)₃²⁺ via a Ru(bpy)₃³⁺-mediated oxidation of glyphosate. When pH >10, a second ECL wave was observed at ca. +1.35 V vs. Ag/AgCl, which was believed to be associated with a reaction between Ru(bpy)₃³⁺ and the species from direct oxidation of GLYP at a GC electrode surface.     

Ru(bpy)3-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy)₃²⁺-doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy)₃²⁺-doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bpy)₃²⁺ molecules inside SNPs, the assay allows detection at levels as low as 1.0 × 10⁻¹³ mol l⁻¹ of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 × 10⁻¹³ to 2.0 × 10⁻⁹ mol l⁻¹.     

Influencing factors on electrochromic hysteresis performance of ruthenium purple produced by a WO3/Tris(2,2′-bipyridine)ruthenium(II)/polymer hybrid film

A [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine)/WO₃ hybrid (denoted as Ru-WO₃) film was prepared as a base layer on an indium tin oxide electrode by electrodeposition from a colloidal solution containing peroxotungstic acid, [Ru(bpy)₃]²⁺ and poly(sodium 4-styrenesulfonate). A ruthenium purple (RP, Fe^III₄[Ru^II(CN)₆]₃, denoted as Fe^III-Ru^II) layer was electrodeposited on a neat WO₃ film or a Ru-WO₃ film from an aqueous RP colloid solution to yield a WO₃/RP bilayer film or a Ru-WO₃/RP bilayer film, respectively. The spectrocyclic voltammetry measurement reveals that Fe^II-Ru^II is oxidized to Fe^III-Ru^II by a geared reaction of [Ru(bpy)₃]^2+/3+ and Fe^III-Ru^II is reduced by a geared reaction of H_xWO₃/WO₃ in the Ru-WO₃/RP film. These geared reactions produced electrochromic hysteresis of the RP layer. However, the absorbance change in the hysteresis was smaller than that for the Ru-WO₃/Prussian blue bilayer film reported previously, resulting from the lower electroactivities of any redox component for the Ru-WO₃/RP film. The lower electroactivities could be explained by the specific interface between the Ru-WO₃ and RP layers. It might contribute to either an increase of the interfacial resistance between the Ru-WO₃ and RP layers, or formation of the physically precise interface between the layers to make it difficult for counter ions to be transported in the interfacial liquid phase involved in the redox reactions in the film. The specific interface at the Ru-WO₃ and RP layers could be formed possibly by the electrostatic interaction between [Ru(bpy)₃]²⁺ and terminal [Ru(CN)₆]⁴⁻ moieties of RP. It could be suggested by the decreased redox potential of [Ru(bpy)₃]²⁺ in the Ru-WO₃ layer from 1.03 to 0.61 V by formation of the RP layer.     

Electrocatalytic activity of [Ru(bpy)<Subscript>3</Subscript>]<Superscript>2+</Superscript> toward guanine oxidation upon incorporation of surfactants and SWCNTs

The homogeneous and mediated oxidation of guanine by [Ru(bpy)₃]²⁺ (2,2′-bipypyridine) in the presence of surfactants and single-walled carbon nanotubes (SWCNTs) has been investigated using cyclic voltammetry, repetitive differential pulse voltammetry and rotating electrode method. In acidic medium, the oxidation of guanine was controlled by mass transport process of [Ru(bpy)₃]²⁺ in solution, leading to a homogeneous electrocatalysis. In neutral medium, the result from emission spectroscopy suggested the formation of the aggregates containing [Ru(bpy)₃]²⁺, dihexadecyl phosphate (DHP) and guanine. The electrocatalysis of [Ru(bpy)₃]²⁺ toward guanine oxidation was promoted by anionic surfactant DHP and, however, hindered by an excess amount of hexadecyl trismethyl ammonium chloride (HTAC) or SWCNTs added to solutions. The electrocatalytic mechanism of [Ru(bpy)₃]²⁺ for guanine oxidation becomes evident, strongly depending on the presence of anionic or cationic surfactants and SWCNTs.     

Electrochemiluminescent determination of nicotine based on tri(2,2′-bipyridyl) ruthenium (II) complex through flow injection analysis

This paper describes the electrogenerated chemiluminescence (ECL) processes of Ru(bpy)₃²⁺/nicotine system at ITO working electrode. An ECL-based method for rapid and sensitive detection of nicotine in phosphate buffer solution at pH 8.0 is established. Strong ECL emission was observed at a positive potential of 1.4 V vs. Ag/AgCl. A possible ECL mechanism is proposed for the Ru(bpy)₃²⁺/nicotine system, the oxidation product of nicotine at the electrode surface reacts with the 3+ state of ruthenium bipyridyl (2+) complex and form ruthenium complex exited state ions and thus releases photons. Effect of pH (medium/electrolyte), working potential, buffer composition, buffer concentration, reactant and co-reactant (nicotine) concentration, flow rate and loop size on the ECL spectrum of the Ru(bpy)₃²⁺/nicotine were studied. At the optimized experimental conditions, lower detection limit for nicotine was observed as 1.2 nmol L⁻¹ (S/N = 3). Linear relationship between ECL current and concentration of nicotine was observed (up to 100 μmol L⁻¹) with R-value of 0.997. The relative standard deviation with 5 μmol L⁻¹ concentration of nicotine for 20 analyses was only 1.4%. A 94% recovery rate was observed in a real sample analysis without any complications/disturbance in measurement. Interferences of humid acid, camphor and SDS were not observed in their presence in the sample solution. The established procedure for nicotine quantification manifests fascinating results and can be suggested for further applications.     

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.     

A new family of trinuclear Ru(II) polypyridyl complexes acting as pH-induced fluorescence switch

Tripodal ligands 1,3,5-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2-yl)phenoxy)methyl}-2,4,6-trimethylbenzene (L¹), 1,1,1-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2-yl)phenoxy)methyl}propane (L²), 2,2′,2′′-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2-yl)phenoxy)ethyl}amine (L³), and corresponding Ru(II) complexes [(bpy)₆L^1–3(Ru^II)₃](PF₆)₆, shortly called (Ru–L^1–3), have been synthesized. UV–vis absorption and fluorescence spectra of these complexes are both strongly dependent on the pH of the buffer solution. These complexes act as pH-induced off–on–off fluorescence switch through protonation and deprotonation of the imidazole-containing ligands.     

Supramolecular Photochemistry and Photophysics. Adducts of Metal Complexes with the Natural Ionophore Lasalocid A Anion

The formation of adducts of Cr(bpy)₃³⁺, Cr (phen)₃³⁺, Ru(bpy)₃²⁺, and Pt(bpy)(NH₃)₂²⁺ (bpy = 2, 2′-bipyridine; phen = 1, 10-phenanthroline) with the lasalocid A anion (LAS-⁾ in CH₂Cl₂ solution has been investigated by means of electronic absorption and emission spectroscopy. Cr(bpy)₃³⁺ forms a 1:1 adduct with LAS⁻. In this adduct, the fluorescence of LAS⁻ is quenched, whereas the phosphorescence intensity and lifetime of Cr(bpy)₃³⁺ increase. In the case of Cr(phen)₃³⁺, only a dynamic quenching of the Cr(phen)₃³⁺ phosphorescence by LAS⁻ is observed. For Ru(bpy)₃²⁺, either no adduct is formed or the interaction is too weak to cause changes in the absorption and emission properties. For Pt(bpy)(NH₃)₂²⁺, evidence has been obtained for formation of a 1:2 Pt(bpy)(NH₃)₂²⁺ / LAS⁻ adduct, where the LAS⁻ fluorescence is statically quenched.     

Detection of N-methyladenosine in urine samples by electrochemiluminescence using a heated ITO electrode

A sensitive and rapid electrochemiluminescence (ECL) method for the detection of N⁶-Methyladenosine (m6A) in urine samples on a heated indium-tin-oxide (ITO) electrode is presented. The ECL intensity of Tris(2,2′-bipyridyl) dichlororuthenium(II)hexahydrate (Ru(bpy)₃²⁺) can be enhanced by the presence of m6A. Experimental results showed that the change of ECL intensities (ΔI) of the Ru(bpy)₃²⁺ between before and after addition of m6A was affected by the working electrode surface temperature (T_e); the highest ΔI occurred at 31 °C. Under optimum conditions, the ΔI had a linear relationship with the m6A concentration in the range of 1.9 × 10⁻⁹-3.9 × 10⁻⁶ mol/L and a detection limit of 7.7 × 10⁻¹⁰ mol/L (S/N = 3) at T_e = 31 °C. The recovery of m6A standards added to urine samples verified the accuracy of the proposed method.     

Preparation and chemical properties of π-conjugated poly(1,10-phenanthroline-3,8-diyl)s with crown ether subunits

π-Conjugated polymers consisting of 1,10-phenanthroline units and crown ether subunits (Poly-1, Poly-2, and Poly-3) were prepared by dehalogenation polycondensation of the corresponding dibromo monomers using a zero-valent nickel complex as a condensing agent. They were characterized by elemental analysis, ¹H NMR and UV–Vis spectroscopies, and cyclic voltammetry (CV). They were partly soluble in CHCl₃, and the number average molecular weight of the soluble part of Poly-2, which had 15-crown-5 subunits, was estimated to be 5300. The polymers exhibited UV–Vis peaks at approximately λ_max = 360 nm, which was reasonable. Complexation with [Ru(bpy)₂]²⁺ and alkaline metal ions made the polymer soluble in organic solvents. The complexation of [Ru(bpy)₂]²⁺ to the 1,10-phenanthroline unit proceeded quantitatively, and the [Ru(bpy)₂]²⁺ complexes exhibited CV curves characteristic of [Ru(N-N)₃]²⁺ complexes.     

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.     

Mitochondrial Fragmentation Is an Important Cellular Event Induced by Ruthenium(II) Polypyridyl Complexes in Osteosarcoma Cells

A series of ruthenium(II) polypyridyl complexes were synthesized and evaluated for their in vitro anticancer activities. The results showed that ruthenium polypyridyl complexes, especially [Ru(bpy)₂(p‐tFPIP)]²⁺ ( 2 a ; bpy=bipyridine, tFPIP=2‐(2‐trifluoromethane phenyl)imidazole[4,5‐f][1,10]phenanthroline), exhibited novel anticancer activity against human cancer cell lines, but with less toxicity to a human normal cell line. The results of flow cytometry and caspase activities analysis indicated that the 2 a ‐induced growth inhibition against MG‐63 osteosarcoma cells was mainly caused by mitochondria‐mediated apoptosis. DNA fragmentation and nuclear condensation as detected by TUNEL–DAPI co‐staining further confirmed 2 a ‐induced apoptotic cell death. Further, fluorescence imaging revealed that ruthenium(II) polypyridyl complexes could target mitochondria to induce mitochondrial fragmentation, accompanied by depletion of mitochondrial membrane potential. Taken together, these findings suggest a potential application of theses ruthenium(II) complexes in the treatment of cancers.