Tris Bipyridine Ruthenium Research Articles

Au Nanoparticles-Trisbipyridine Ruthenium(II) Nanoaggregates as Signal-Amplifying SERS Tags for Immunoassay of cTnI.

Acute myocardial infarction (AMI) is one of the leading causes of human mortality worldwide. In the early stages of AMI, the patient's electrocardiogram (ECG) may not change, so the fast, sensitive, and accurate detection of the specific biomarker of cardiac troponin I (cTnI) is of great importance in the early diagnosis of AMI. In this work, for the first time, electrostatic nanoaggregates of negatively charged Au nanoparticles and positively charged trisbipyridine ruthenium(II) ions (i.e., (-)AuNPs|[Ru(bpy)3]2+ ENAs) as novel and signal-amplifying surface-enhanced Raman scattering (SERS) tags were synthesized in an easy and rapid (<3 min) way and applied in the highly sensitive, rapid detection of cTnI in human serum by being combined with an immunochromatographic test strip (ICTS). The synthesized (-)AuNPs|[Ru(bpy)3]2+ ENAs exhibited strong SERS activity due to the multiple Raman-active units (three bpy ligands) carried by each [Ru(bpy)3]2+ complex ion and abundant hotspots in each SERS tag. The developed (-)AuNPs|[Ru(bpy)3]2+ ENAs-based SERS-ICTS has been validated to be applicable in detection of cTnI in human serum with excellent sensing performances, such as fast testing (5 min) and a low detection limit (60 pg/mL). It is envisioned that the developed (-)AuNPs|[Ru(bpy)3]2+ ENAs-based SERS-ICTS sensor may have promising applications in point of care testing of various biomarkers in clinic. Additionally, this work may inspire the finding and the application of new types of Raman reporter molecules based on high valent metal-multi ligand coordination compounds like [Ru(bpy)3]2+.

Test of the orbital-based LI3 index as a predictor of the height of the [formula omitted]MLCT [formula omitted][formula omitted]MC transition-state barrier for gas-phase [Ru(N[formula omitted]N)[formula omitted]][formula omitted] polypyridine complexes

Ruthenium(II) polypyridine compounds often luminesce, with ligand-dependant lifetimes. This is the third in a series of papers devoted to finding orbital-based luminescence indices (LI) for predicting luminescence lifetimes. The third attempt (LI3) was based upon a frontier molecular orbital (FMO) like estimate of the height of the barrier to conversion from an initial phosophorescent triplet metal-ligand charge transfer (3MLCT) state to a nonluminescent triplet metal-centered (3MC) state which decays nonradiatively. A linear correlation was found between LI3 and extracted empirical average 3MLCT →3MC transition state (TS) barrier heights (Eaves) which were not believed to be quantitative but which were believed to capture the trends in the true barrier heights correctly. As it is known that Eave is a large underestimate of the true 3MLCT →3MC TS barrier height in the case of the trisbipyridine ruthenium(II) cation { [Ru(bpy)3]2+ }, but accurate TS barrier heights are difficult to obtain experimentally, it was judged useful to verify the ideas used to derive the LI3 index in the present work by calculating the energetics of the gas-phase 3MLCT →3MC reaction for a series of ruthenium(II) tris bipyridine complexes using the same density functional and basis sets used in calculating LI3. Specifically, four closely-related bipyridine complexes { [Ru(N∧N)3]2+ with N∧N = bpy (6), 4,4’-dm-bpy (70), 4,4’-dph-bpy (73), and 4,4’-DTB-bpy (74) } were used for these calculations. In the process, we examined the gas-phase trans dissociation mechanism in greater detail than has been previously done and uncovered a two part mechanism. In the first part, the electron is transferred to a single ligand rather than symmetrically to all three ligands. It is the two Ru-N bonds to this ligand which are equally elongated in the transition state. The intrinsic reaction coordinate then continues down a ridge in hyperspace and bifurcates into one of two symmetry-equivalent 3MC structures with elongated trans bonds. Interestingly, no significant difference is found for the TS barriers for the four complexes treated here. Instead, LI3 is linearly correlated with the energy difference ΔE=E(3MLCT)−E(3MC), different from what was originally intended but still consistent with the FMO arguments underlying the derivation of LI3.

Initial Quenching Efficiency Determines Light-Driven H2 Evolution of [Mo3 S13 ]2- in Lipid Bilayers.

Nature uses reactive components embedded in biological membranes to perform light-driven photosynthesis. Here, a model artificial photosynthetic system for light-driven hydrogen (H2 ) evolution is reported. The system is based on liposomes where amphiphilic ruthenium trisbipyridine based photosensitizer (RuC9 ) and the H2 evolution reaction (HER) catalyst [Mo3 S13 ]2- are embedded in biomimetic phospholipid membranes. When DMPC was used as the main lipid of these light-active liposomes, increased catalytic activity (TONCAT ~200) was observed compared to purely aqueous conditions. Although all tested lipid matrixes, including DMPC, DOPG, DPPC and DOPG liposomes provided similar liposomal structures according to TEM analysis, only DMPC yielded high H2 amounts. In situ scanning electrochemical microscopy (SECM) measurements using Pd microsensors revealed an induction period of around 26 minutes prior to H2 evolution, indicating an activation mechanism which might be induced by the fluid-gel phase transition of DMPC at room temperature. Stern-Volmer-type quenching studies revealed that electron transfer dynamics from the excited state photosensitizer are most efficient in the DMPC lipid environment giving insight for design of artificial photosynthetic systems using lipid bilayer membranes.

Synthesis of Ruthenium (II) trisbipyridine complex containing ionic liquids immobilized on fibrous CoMn2O4 for isolation of asphaltene from petroleum

The formation of a durable nanoadsorbent, known as DFCoMn2O4/IL@Ru(II), was achieved by binding a complex of Ru (II) trisbipyridine with ionic liquids (IL) to a dendritic fibrous CoMn2O4 (DFCoMn2O4). The resulting DFCoMn2O4/IL@Ru(II) was characterized using various techniques such as X-ray diffraction analysis (XRD), fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and scanning electron microscopy (SEM). DFCoMn2O4/IL@Ru(II) was then employed as an environmentally friendly adsorbent for the removal and adsorption of asphaltene from petroleum. The presence of fibrous CoMn2O4 categories enhanced the adsorption capacity and facilitated the recovery of the adsorbent without significantly reducing the efficiency. The results demonstrated a clear synergistic effect between dendritic fibrous CoMn2O4 and the IL@Ru(II) categories, exhibiting a strong correlation.The utilization of the DFCoMn2O4/IL@Ru(II) system resulted in quasi-second-order adsorption kinetics. The experiment was conducted using the Taguchi method to minimize costs and time. Various amounts of asphaltene, temperatures, and adsorbent quantities were examined. Minitab software was deployed to evaluate the impact of these variables on asphaltene adsorption. The presence of ionic liquid groups enhanced the solubility of the heterogeneous adsorbent in environmentally friendly solvents, thereby enhancing function and reducing the time.

Interfacial Characterization of Ruthenium-Based Amphiphilic Photosensitizers.

Nonreactive surfactant molecules have long been used and characterized for a wide range of applications in industries, life science, and everyday life. Recently, new types of functional amphiphilic molecules have emerged that bear another function, for example, a light-absorbing action, or catalytic properties. However, the surfactant properties of these molecules remain to date essentially unknown. In this context, we investigated here the interfacial activity of photocatalytic surfactants based on a ruthenium(II) tris-bipyridine core, functionalized with two alkyl tails. We realized a systematic characterization of the surfactant properties of these molecules at a water–air interface and studied the effect of the alkyl chain length and of the counterions (hexafluorophosphate or chloride) on these properties. Our data demonstrate that ruthenium surfactants with chloride counteranions form a denser layer at the interface, but their surfactant properties can dramatically deteriorate when the chain length of the alkyl tail increases, leading to simple hydrophobic molecules with poor surfactant properties for the longest chains (C17). These findings pave the way for a better use and understanding of photocatalytic soft interfaces.

Imbroglio at a photoredox-iron-porphyrin catalyst dyad for the photocatalytic CO 2 reduction

We have covalently connected the ruthenium trisbipyridine complex (bpyRu) as a photoredox module to an iron porphyrin catalyst (porFe) through an amido function for investigating the synergistic action to power the photocatalytic CO2 reduction. The electrochemical studies of the porFe-bpyRu dyad did not show any marked effect on the redox properties of the constitutive units. However, the photophysical properties of the porFe-bpyRu dyad point to the complete extinction of the photoredox module that undergoes ultrafast quenching processes with the porFe acolyte, the unavoidable dilemma in this type of molecular assemblies. Nevertheless, when exogenous bpyRu and a sacrificial electron donor were added to this dyad, we found that it exhibits much higher turnover number and selectivity towards CO2 photocatalytic reduction to CO than with the iron porphyrin analogue (porFe). Comprehensive analyses of the data suggest that this catalytic enhancement displayed by the dyad can be attributed to an interesting electron relay role played by the appended bpyRu moiety.

RuII tris-bipyridine-modified electrode as a sensor for battery electrolyte

Functionalization of a carbon electrode through the electrochemical reduction of ruthenium tris-bipyridine diazonium salts prepared in situ allows determination of the nature of the anions often present in commonly used lithium and sodium battery electrolyte (i.e. PF6− and ClO4−) and also the presence of fluoride anions arising from PF6− degradation. Surprisingly, although these “battery” anions are supposed to exhibit poor coordination ability, their interaction with the electrogenerated RuIII complex is sufficiently strong and reversible to selectively discriminate between the anions ClO4− and PF6− through the observed shift in E°. This study examined the impact of any fluoride present and found a linear relationship between the current response and the F− concentration. This has been applied to ageing LP30 battery electrolyte, confirming the low solubility of LiF in battery electrolyte. This overall behavior could help in the analysis of electrolytes from the recycling sector.

Time-Resolved Resonant Raman Spectroscopy of the Photoinduced Electron Transfer from Ruthenium(II) Trisbipyridine to Methyl Viologen.

We report the first time-resolved resonant Raman (TR3) spectra of photoinduced charge transfer from [Ru(bpy)3]2+ to methyl viologen, with observations of vibrational structure. The presence of singly charged methyl viologen in solution is noted by the appearance of several spectroscopic lines, which are visible in the spectra following subtraction of reagent molecules. Assignments are confirmed using both density functional theory (DFT) calculations and literature values and are shown to be consistent with transient absorption spectroscopy data. This presents proof-of-concept for the application of TR3 in mechanistic studies of photocatalytic systems.

Vibrational Spectra of the Ruthenium–Tris-Bipyridine Dication and Its Reduced Form in Vacuo

Experimental IR spectra in the 500–1850 cm–1 fingerprint frequency range are presented for the isolated, gaseous redox pair ions [Ru(bpy)3]2+, and [Ru(bpy)3]+, where bpy = 2,2′-bipyridine. Spectra are obtained using the FELIX free-electron laser and a quadrupole ion trap mass spectrometer. The 2+ complex is generated by electrospray ionization and the charge-reduced radical cation is produced by gas-phase one-electron reduction in an ion–ion reaction with the fluoranthene radical anion. Experimental spectra are compared against computed spectra predicted by density functional theory (DFT) using different levels of theory. For the closed-shell [Ru(bpy)3]2+ ion, the match between experimental and computed IR spectra is very good; however, this is not the case for the charge-reduced [Ru(bpy)3]+ ion, which demands additional theoretical investigation. When using the hybrid B3LYP functional, we observe that better agreement with experiment is obtained upon reduction of the Hartree–Fock exact-exchange contribution from 20% to about 14%. Additionally, calculations using the M06 functional appear to be promising in terms of the prediction of IR spectra; however, it is unclear if the correct electronic structure is obtained. The M06 and B3LYP functionals indicate that the added electron in [Ru(bpy)3]+ is delocalized over the three bpy ligands, while the long-range corrected LC-BLYP and the CAM-B3LYP functionals show it to be more localized on a single bpy ligand. Although these latter levels of theory fail to reproduce the experimentally observed IR frequencies, one may argue that the unusually large bandwidths observed in the spectrum are due to the fluxional character of a complex with the added electron not symmetrically distributed over the ligands. The experimental IR spectra presented here can serve as benchmark for further theoretical investigations.

Voltammetric behaviour of cationic redox probes at mesoporous silica film electrodes

The effect of vertically aligned silica nanochannels on the electrochemical response of various cationic redox probes has been investigated. To this end, an oriented mesoporous silica thin film has been generated by electro-assisted self-assembly onto a fluorine-doped tin oxide (FTO) electrode, which was then used to characterize the voltammetric behaviour of redox cations of different nature, size and charge. Methylene Blue (MB+), paraquat (PQ2+), diquat (DQ2+), ruthenium trisbipyridine (Ru(bpy)32+) and ruthenium hexamine (Ru(NH3)63+) were selected for that purpose. Multisweep cyclic voltammetry experiments showed significant accumulation of these cations thanks to favourable electrostatic interactions with the negatively-charge silica surface, but the enhancement of the votammetric signals compared to the bare FTO electrode was strongly dependent on the probe type, according the following trend: MB+ > PQ2+ > DQ2+ > Ru(bpy)32+ > Ru(NH3)63+. The accumulation processes were very fast owing to the vertical orientation of the mesopore channels ensuring fast diffusion from the solution to the electrode surface. Operating at various potential scan rates and different probe concentrations enabled to quantify the relative ratio between surface-confined and diffusion-controlled processes, the adsorption phenomena being clearly more prominent in diluted media and also accentuated at high potential scan rates. The mesoporous silica film electrodes exhibited higher sensitivities at lower concentrations, which can give benefits for sensor applications at trace levels.

Electric-Field-Induced Connectivity Switching in Single-Molecule Junctions.

SummaryThe manipulation of molecule-electrode interaction is essential for the fabrication of molecular devices and determines the connectivity from electrodes to molecular components. Although the connectivity of molecular devices could be controlled by molecular design to place anchor groups in different positions of molecule backbones, the reversible switching of such connectivities remains challenging. Here, we develop an electric-field-induced strategy to switch the connectivity of single-molecule junctions reversibly, leading to the manipulation of different connectivities in the same molecular backbone. Our results offer a new concept of single-molecule manipulation and provide a feasible strategy to regulate molecule-electrode interaction.

Definition of the Interaction Domain and Electron Transfer Route between Cytochrome c and Cytochrome Oxidase.

The reaction between cytochrome c (Cc) and cytochrome c oxidase (CcO) was studied using horse cytochrome c derivatives labeled with ruthenium trisbipyridine at Cys 39 (Ru-39-Cc). Flash photolysis of a 1:1 complex between Ru-39-Cc and bovine CcO at a low ionic strength resulted in the electron transfer from photoreduced heme c to CuA with an intracomplex rate constant of k3 = 6 × 104 s-1. The K13A, K72A, K86A, and K87A Ru-39-Cc mutants had nearly the same k3 value but bound much more weakly to bovine CcO than wild-type Ru-39-Cc, indicating that lysines 13, 72, 86, and 87 were involved in electrostatic binding to CcO, but were not involved in the electron transfer pathway. The Rhodobacter sphaeroides (Rs) W143F mutant (bovine W104) caused a 450-fold decrease in k3 but did not affect the binding strength with CcO or the redox potential of CuA. These results are consistent with a computational model for Cc-CcO (Roberts and Pique ( 1999 ) J. Biol. Chem. 274 , 38051 - 38060 ) with the following electron transfer pathway: heme c → CcO-W104 → CcO-M207 → CuA. A crystal structure for the Cc-CcO complex with the proposed electron transfer pathway heme c → Cc-C14 → Cc-K13 → CcO-Y105 → CcO-M207 → CuA ( S. Shimada ( 2017 ) EMBO J. 36 , 291 - 300 ) is not consistent with the kinetic results because the K13A mutation had no effect on k3. Addition of 40% ethylene glycol (as present during the crystal preparation) decreased k3 significantly, indicating that it affected the conformation of the complex. This may explain the discrepancy between the current results and the crystallographic structure.

Synthesis and characterization of a novel ruthenium(ii) trisbipyridine complex magnetic nanocomposite for the selective oxidation of phenols.

Anchoring ruthenium(ii) trisbipyridine complex [Ru(Bpy)3]2+ into a magnetic dendritic fibrous silica nanostructure produces an unprecedented strong nanocatalyst, FeNi3/DFNS/[Ru(Bpy)3]2+. Impressive oxidation of phenols to 1,4-benzoquinones catalyzed by FeNi3/DFNS/[Ru(Bpy)3]2+ is obtained in acetonitrile and water solution with molecular dioxygen as oxidant. Exclusively, apparently inert phenols such as phenol itself and mono-alkyl-substituted phenols are impressively oxidized to produce 1,4-benzoquinones through activation of the C–H bond in the position para to the carbon–oxygen bond under mild conditions. In addition, the production of industrially significant quinones that are known intermediates for vitamin combinations is investigated and studied FeNi3/DFNS/[Ru(Bpy)3]2+ magnetic nanoparticles were produced, and their properties were investigated by AFM, FTIR, XRD, TGA, SEM, TEM, and VSM.

(Invited) Anisotropic Self-Oscillating Reaction in Liquid Crystalline Nanosheets Hydrogels

Soft and wet structures with anisotropy and hierarchy are regarded as key for various intriguing functions and properties of living organisms. Liquid crystal (LC) materials are often utilized to artificially fabricate such sophisticated structures likeliving organisms. For this purpose, lyotropic LC phases of inorganic nanosheets are emerging as new type LC materialsdue to many fascinating characteristics. Actually, inorganic nanosheet LCs have been utilized as unusual anisotropic reaction media,the materials to fabricate tough fibers and inorganic-polymer composites. The most distinctive feature of inorganic nanosheet LCs is that they can effectively barrier the diffusion of molecules. Since the nanosheets are two dimensional objects with huge aspect ratio (the lateral dimension of several micrometer and the thickness of ~1 nm), aligned nanosheets can effectively retard molecular diffusion compared to the materials made with conventional LC molecules. We recently communicated that dye ions anisotropically diffuse into the polymer gel embedded with macroscopically aligned LC nanosheets.1 Meanwhile, combining artificial soft and wet structures with particular chemical reactions that have characteristic features of biological systems is fascinating because such combinations will lead us to fabrication of artificial living organisms or molecular robots. Yoshida et al. reported the hydrogel of poly(N-isopropylacrylamide) (pNIPA) copolymerized with ruthenium trisbipyridine (Ru(bpy)3) units, which is a catalyst of self-oscillating Belouzov-Zhabozinsky reaction (BZ-reaction)2. Not only BZ reaction proceeded in this gel, but also the gel showed self-oscillating motion. After this pioneering work, many kinds of self-oscillating gels with improved properties such as faster and larger oscillation, were reported in view of applications for micro-robotics and micro electro mechanical systems (MEMS). The concentric circlesor rotating spiral waves that appear during BZ reaction is also interesting phenomena as a model of chemical waves in biological systemssuch as embryo, neural networks, and heart muscles. In this context, controlling and modifying the wave patterns in anisotropic, heterogeneous, or patterned media are interested. The BZ-reactions under electric field, in the lamellar phase of surfactant solution and in a porous glass were investigated to control the reaction. However, anisotropic BZ reaction has not been investigated so far. In this study3, anisotropic chemical wave propagation of self-oscillating Belouzov-Zhabozinsky (BZ) reaction was demonstrated in the poly(N-isopropylacrylamide gel films embedded with macroscopically aligned liquid crystalline inorganic nanosheets. While the average propagation rate of chemical wave was 3.56 mm min-1in the gels without nanosheets, the propagation was retarded in the gels with 1 wt% of nanosheets: v//= 1.89 mm min-1and v⊥= 1.33 mm min-1along the direction parallel and perpendicular to the nanosheet planes, respectively. Thus, the wave propagation is anisotropic with the anisotropy ratio v// / v⊥= 1.42 in these gels and the periodic patterns formed by the BZ-reaction were concentric ellipses, different from circles seen in isotropic gels. Furthermore, the propagation rate and degree of anisotropy were controllable by nanosheet concentration. These phenomena can be explained that the diffusion of molecules inside the gel is effectively hindered along the direction perpendicular to the nanosheet planes due to very large aspect ratio of the aligned nanosheets.The present systems will be applicable for anisotropic self-oscillating soft actuators with one-dimensional motions as well as for ideal model system of BZ reactions. Acknowledgement This research was supported by: Research Center for Materials and Energy Devices of Fukuoka Institute of Technology (FIT-ME) (Strategic Research Foundation Grant-Aided Project for Private University from MEXT; #S1511036L); KAKENHI (#24104005, #15K05657, and #17H03209); Canon Foundation; Network Joint Research Center for Materials and Devices (#201507 and #20166009); and Electronics Research Laboratory of Fukuoka Institute of Technology.

Visible‐Light‐Driven Reduction of CO2 to CO and Its Subsequent Valorization in Carbonylation Chemistry and 13C Isotope Labeling

AbstractA convenient and safe approach in valorizing carbon monoxide (CO) produced from the photocatalytic reduction of carbon dioxide (CO2) has been investigated. Visible light was used to drive an optimized photocatalytic reduction using a ruthenium trisbipyridine complex as a sensitizer and a rhenium bipyridyl carbonyl complex as a catalyst to perform an efficient reduction of CO2 to CO, which was then simultaneously utilized in a palladium‐catalyzed aminocarbonylation reaction at room temperature. This approach provides safe handling of the produced CO which also opens the way for a more efficient application of 13C‐isotope and 14C‐radioisotope‐labeled CO2 in pharmaceutically relevant drug labeling.

Covalent and Non-covalent Conjugation of Few-Layered Graphene Oxide and Ruthenium(II) Complex Hybrids and Their Energy Transfer Modulation via Enzymatic Hydrolysis.

Pyrene-containing ruthenium(II) tris-bipyridine complexes have been prepared. These complexes have been non-covalently attached onto the few-layered graphene oxide (GO) sheets through their high binding affinity for flat π-surfaces. Alternatively, the reduced graphene oxide (rGO) sheets have also been covalently functionalized with the ruthenium(II) tris-bipyridine complex. The prepared conjugates have been characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, thermogravimetric analysis (TGA), and UV-visible absorption spectroscopy. The energy transfer properties of the resulted conjugates between the graphene and transition metal complexes have been studied via esterase hydrolysis. The energy transfer efficiencies were found to vary with the separation between the donor and the acceptor units.

Layer-by-Layer Molecular Assemblies for Dye-Sensitized Photoelectrosynthesis Cells Prepared by Atomic Layer Deposition.

In a dye sensitized photoelectrosynthesis cell (DSPEC), the relative orientation of the catalyst and chromophore plays an important role in determining the device efficiency. Here we introduce a new, robust atomic layer deposition (ALD) procedure for the preparation of molecular chromophore-catalyst assemblies on wide bandgap semiconductors. In this procedure, solution deposited, phosphonate derivatized metal complexes on metal oxide surfaces are treated with reactive metal reagents in the gas phase by ALD to form an outer metal ion bridging group, which can bind a second phosphonate containing species from solution to establish a R1-PO2-O-M-O-PO2-R2 type surface assembly. With the ALD procedure, assemblies bridged by Al(III), Sn(IV), Ti(IV), or Zr(IV) metal oxide units have been prepared. To evaluate the performance of this new type of surface assembly, intra-assembly electron transfer was investigated by transient absorption spectroscopy, and light-driven water splitting experiments under steady-state illumination were conducted. A SnO2 bridged assembly on SnO2/TiO2 core/shell electrodes undergoes light-driven water oxidation with an incident photon to current efficiency (IPCE) of 17.1% at 440 nm. Light-driven water reduction with a ruthenium trisbipyridine chromophore and molecular Ni(II) catalyst on NiO films was also used to produce H2. Compared to conventional solution-based procedures, the ALD approach offers significant advantages in scope and flexibility for the preparation of stable surface structures.

Multivalent Azide‐Functionalized Polypyridyl Ruthenium Complexes and Their DNA Conjugates through Click Chemistry

A new series of azide‐functionalized ruthenium complexes were synthesized. Six trisbipyridine ruthenium complexes bearing one to six azide functions were developed from the corresponding carboxy derivatives. By using four alkyne‐functionalized DNA sequences and performing copper‐catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry reactions, the formation of symmetric and unsymmetric multivalent DNA–ruthenium conjugates was realized. They are composed of one to six oligonucleotides.

Ruthenium tris bipyridine derivatives and their photocatalytic activity in [4 + 2] cycloadditions. An experimental and DFT study

We report the study of a series of Ru-bipyridine (Ru-Bpy) complexes to correlate their photophysical and electrochemical properties to their performance in [4+2] cycloadditions, as a model reaction for electron transfer catalysis. Redox potentials, absorption and emission spectra, quantum yields and DFT calculations are presented to understand the catalytic transformation. The study shows that complex [Ru(Bpy)3](PF6)2 is the more active photocatalyst, giving complete conversion to the product after 2h reaction under white light. Any substitution in the para position of the Bpy ring decreases the reaction conversion. The [4+2] cycloaddition can be performed with different substrates and dienes, using either acetonitrile or nitromethane as solvents. Mechanistic studies suggest that the active catalyst for the transformation is [Ru(Bpy)3]3+ and that the rate determining step is the oxidation of [Ru(Bpy)3]2+ to generate the corresponding Ru3+ species.

Silica-Based Nanoparticles as Bifunctional and Bimodal Imaging Contrast Agents.

New bifunctional and bimodal nanoparticles (NPs) have been elaborated and characterised. They are based on silica NPs that incorporate a silylated ruthenium tris-bipyridine complex. The resulting suspension of amine-modified NPs with diameters of 20 nm was post-functionalised with a stable gadolinium ion complex. Interest in these NPs lies mainly in the confinement of optical and magnetic imaging agents (Ru and Gd complexes, respectively) within the NP volume. Their potential use as a bimodal probe (luminescence/magnetic resonance imaging) and theranostic agent (photodynamic therapy/imaging) is described. The biological potential of these NPs has been studied on HCT-116 cells and microscopy and cytotoxicity results are given.