Bipyridyl Complexes Research Articles

9‐Borabicyclononane Bipyridyl Complexes: Synthesis, Luminescence, and Electronic Characterization

This work presents the use of organoboron compounds as anolytes in redox flow batteries. Through the study of their structural, electrochemical, and photophysical properties, four bipyridyl boronium salts show potential for application in such batteries. The compounds were synthesized in moderate to high yields by previously published methods. We find when using chelating bipyridyl‐based substituents, the complexes undergo two reversible reductions; however, when switching to phenanthroline‐based substituents, the reduction events are no longer reversible. Density‐functional theory calculations indicate that the chelating nitrogen heterocycle is the locus of reduction and fluorescence.

Fe(III) bipyridyl or phenanthroline complexes with oxidase-like activity for sensitive colorimetric detection of glutathione.

In this study, three types of Fe(III) bipyridyl or phenanthroline (Fe(III)-L3 ) complex could directly catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to induce blue chromogenic changes without H2 O2 . Fe(III)-L3 complex could induce a colour change in TMB directly after a short incubation time. Due to the high oxidase-like activity of the Fe(III)-L3 complexes, superoxide anion radicals (O2 •- ) were formed in solution. Intermediates radical involving oxo-iron species were then produced that oxidized TMB to its oxidation products (oxTMB), which had an absorbance maximum at 652 nm. Glutathione (GSH) could inhibit the oxidation reaction of the Fe(III)-L3 complex-TMB system, a rapidly colorimetric method was established for the specific detection of GSH that had a detection limit of 0.1 μM. Furthermore, Fe(III)-L3 complexes could catalyze TMB to oxTMB directly without H2 O2 . This fast and simple colorimetric method may open a new avenue for application in the point-of-care diagnosis field using the TMB chromogenic system.

Phenanthrene‐Fused‐Quinoxaline as a Key Building Block for Highly Efficient and Stable Sensitizers in Copper‐Electrolyte‐Based Dye‐Sensitized Solar Cells

AbstractDye‐sensitized solar cells (DSSCs) based on CuII/I bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open‐circuit voltages (VOC, more than 1 V). However, their short‐circuit photocurrent density (JSC) has remained modest. Increasing the JSC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO2 film and fast regeneration by the CuI complex. Herein, we report two new D‐A‐π‐A‐featured sensitizers termed HY63 and HY64, which employ benzothiadiazole (BT) or phenanthrene‐fused‐quinoxaline (PFQ), respectively, as the auxiliary electron‐withdrawing acceptor moiety. Despite their very similar energy levels and absorption onsets, HY64‐based DSSCs outperform their HY63 counterparts, achieving a power conversion efficiency (PCE) of 12.5 %. PFQ is superior to BT in reducing charge recombination resulting in the near‐quantitative collection of photogenerated charge carriers.

Phenanthrene‐Fused‐Quinoxaline as a Key Building Block for Highly Efficient and Stable Sensitizers in Copper‐Electrolyte‐Based Dye‐Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) based on Cu(II/I) bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open-circuit voltages ( V OC , > 1 V). However, their short-circuit photocurrent density ( J SC ) has remained modest. The challenge for increasing the J SC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO 2 film and fast regeneration by the Cu(I) complex. Here, we report two new D-A-π-A featured sensitizers coded HY63 and HY64 , which employ either benzothiadiazole (BT) or phenanthrene-fused-quinoxaline (PFQ) as the auxiliary electron-withdrawing acceptor moiety. In spite of very similar energy levels and absorption onsets, HY64 -based DSSCs outperform largely their HY63 counterpart, achieving an outstanding power conversion efficiency (PCE) of 12.5% with superior stability. In depth studies of interfacial charge carrier dynamics show that PFQ is superior to BT in retarding charge recombination resulting in near quantitative collection of photogenerated charge carriers.

Robust Binding of Disulfide-Substituted Rhenium Bipyridyl Complexes for CO2 Reduction on Gold Electrodes.

Heterogenization of homogenous catalysts on electrode surfaces provides a valuable approach for characterization of catalytic processes in operando conditions using surface selective spectroelectrochemistry methods. Ligand design plays a central role in the attachment mode and the resulting functionality of the heterogenized catalyst as determined by the orientation of the catalyst relative to the surface and the nature of specific interactions that modulate the redox properties under the heterogeneous electrode conditions. Here, we introduce new [Re(L)(CO)3Cl] catalysts for CO2 reduction with sulfur-based anchoring groups on a bipyridyl ligand, where L = 3,3′-disulfide-2,2′-bipyridine (SSbpy) and 3,3′-thio-2,2′-bipyridine (Sbpy). Spectroscopic and electrochemical analysis complemented by computational modeling at the density functional theory level identify the complex [Re(SSbpy)(CO)3Cl] as a multi-electron acceptor that combines the redox properties of both the rhenium tricarbonyl core and the disulfide functional group on the bipyridyl ligand. The first reduction at −0.85 V (vs. SCE) involves a two-electron process that breaks the disulfide bond, activating it for surface attachment. The heterogenized complex exhibits robust anchoring on gold surfaces, as probed by vibrational sum-frequency generation (SFG) spectroscopy. The binding configuration is normal to the surface, exposing the active site to the CO2 substrate in solution. The attachment mode is thus particularly suitable for electrocatalytic CO2 reduction.

Photoinactivation of Salmonella enterica (serovar Typhimurium) by tetra-cationic porphyrins containing peripheral [Ru(bpy)2Cl]+ units

In the last years, antimicrobial photodynamic therapy (aPDT) has been considered as one important alternative to be used in antimicrobial treatments. In the present work we report the first photoinactivation of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) by cationic free-base meso-tetra-(phenyl)porphyrin and its Zn(II) complex containing peripheral Ru(II)-bipyridyl complexes. Bacterial inoculum (107 CFU mL-1) was incubated with the porphyrins (25 μM) with an irradiation system containing a halogen lamp with fluence values of 0, 180, 360, 720 and 1080 J cm-2. Both porphyrins demonstrate phototoxicity against bacteria, but higher efficiency was observed by Zn(II) complex. It was demonstrated that RuTPyP and ZnRuTPyP phototoxicity is due to their photodynamic activity associated with the formation of singlet oxygen, anion superoxide and hydroxyl radical at their irradiation by visible light. The formation of these reactive species was confirmed using flash-photolysis technique and spin-trap electron paramagnetic resonance (EPR) spectroscopy. The singlet oxygen quantum yield was determined by indirect method using the uric acid as singlet oxygen scavenger. Besides the characterization of optical absorption and fluorescence RuTPyP and ZnRuTPyP properties were realized using optical absorption and fluorescence spectroscopies. It was observed that complexation with Zn(II) ion increases the quantum yields of porphyrin fluorescence and singlet oxygen formation.

Effect of peripheral platinum(II) bipyridyl complexes on the interaction of tetra-cationic porphyrins with human serum albumin

The interaction between human serum albumin (HSA) and two porphyrin-based tetra-cationic photosensitizers were investigated via spectroscopic techniques (steady-state, time-resolved fluorescence and circular dichroism) combined to theoretical calculations (molecular docking). Similarities and differences in the binding behavior of a porphyrin bearing peripheral chloro(2,2′bipyridine)platinum(II) complexes (4-PtTPyP) versus methyl groups (4-MeTPyP) attached in the N-pyridyl atoms were evaluated. There is a ground state association between HSA-porphyrins (static fluorescence quenching mechanism), with Ka values for 4-PtTPyP slightly higher than 4-MeTPyP. While the binding 4-MeTPyP is primarily enthalpically driven, 4-PtTPyP binds mainly due to hydrophobic forces in an entropically driven association. Far-UV CD showed that 4-PtTPyP perturbs the thermal stability of the protein, probably due to high volume of the porphyrin. Molecular docking suggested that 4-PtTPyP stablish a larger number of interactions with the neighboring amino acid residues. The likely location for the binding pocket is in subdomain IB, located in an external region of the protein structure. The bulky peripheral platinum(II)-complexes does not have a deleterious effect upon serum albumin binding spontaneity and extension, although modifies the nature of the complex formed.

Rapid quantification of ruthenium(ii) polypyridyl anti-cancer drugs using a selective ligand dissociation LC-MS/MS method.

Research on Ru anti-cancer drugs is on the rise with many complexes in clinical trials. Inductively coupled plasma-mass spectrometry (ICP-MS) has been the standard technique for bioanalytical studies on Ru and Pt complexes in biological media. Tedious ICP-MS methods rely on detecting and quantifying the element while lacking important structural information of the original complexes. Despite being equally sensitive, more accessible, and highly selective to the target species, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has not been validated for the analysis of Ru drugs. Using USFDA guidelines, we report here the optimization and validation of a facile LC-MS/MS method for the detection and quantification of three Ru(ii) polypyridyl complexes in cells, plasma, and urine matrices. Importantly, a fast (10 min), single-step procedure was efficient for both extraction and sample purification, and analytes were rapidly eluted over a 3 min simple isocratic run. Specific parent ions were differentially fragmented by tandem MS, thus forming a unique and rational ligand dissociation chemistry that exhibits high selectivity to the target species with no measurable interferences or matrix effects. The developed LC-MS/MS method was advantageous vis-à-vis the prototypical ICP-MS based techniques both in vitro and in vivo, paving the way for its utilization in elaborate cellular uptake, pharmacokinetics, and pharmacodynamics studies.

Insights into the Chemistry and Structural Features of the Copper(II) 2,2′-Bipyridyl–Thiosulfate System

In this paper, we present our findings on a series of copper(ii) 2,2′-bipyridyl (bipy) complexes that inhibit the oxidation of thiosulfate, a current problem in the gold leaching process. The formation of six complexes, five of which have been structurally characterized by X-ray crystallography, illustrate a thermally induced, controllable switching between oxidation states, which in turn inhibits the oxidation of thiosulfate. These findings give further insight and understanding into the rich chemistry of the coinage metals and the hydrolytic processes involved with gold leaching.

A mononuclear copper(II) complex containing benzimidazole and pyridyl ligands: Synthesis, characterization, and antiproliferative activity against human cancer cells

Metal complexes are recently being hybridized with different moieties to discover new drugs due to their advantageous attributes. Among the metals, copper is a good one to synthesize a metal complex due to its being endogenous, redox and DNA cleavage potential, reported anti-cancer efficacies and selective permeability for cancer cells. In this study, first we synthesized a new copper (II) complex and determined its toxic doses on NIH/3T3 normal fibroblast cells, SPC212 mesothelioma and DU145 prostate cancer cells. Then, we ascertained anti-proliferative, apoptotic, morphological, oxidative and endoplasmic reticulum (ER) stress inducing effects of these newly synthesized compounds on DU145 prostate cancer cells. A novel Copper(II)/1-(4-(trifluoromethyl)benzyl)-1H-benzimidazole/2,2′-bipyridyl complex was synthesized and mainly characterized by single crystal X-ray diffraction analysis. Anti-proliferative effect of copper(II) complex was gauged by MTT. Oxidative and ER stress were evaluated by ELISA and Western blot. The morphological effect was examined by microscope analysis. Besides, immunocytochemistry of Bax, a pro-apoptotic protein and PCNA, a proliferation marker protein was performed. As a result, the inhibitory effect of newly synthesized substance was superior to the chemicals from which it was synthesized. Its IC50s against DU145 were 37.0, 21.1 and 10.0 µM for 24, 48 and 72 h-treatments, respectively. Oxidative and ER stress increased after treatment. In microscopy, we observed apoptotic hallmarks like nuclear condensation, cellular shrinkage and membrane blebbings. In immunochemistry, increased Bax and decreased PCNA were apparent. Copper(II) complex with its relatively low IC50 can also be tested on other cancer and normal cell lines.

Photophysical, electrochemical, and DFT studies of the novel azacrown-bridged dinuclear ruthenium dye sensitizers for solar cells

A dinuclear ruthenium bipyridyl complex with 1,10-diaza-18-crown-6 bridging ligand was synthesized and characterized. Its photophysical and electrochemical properties were also studied. DFT computations were performed to complement the experimental investigations. Analysis of the results indicates that the path in which charges move from one metal center to the other is significant for effective electronic coupling. However, electron transfer between the two ruthenium centers is hindered by the azacrown bridging ligand, compared to the smooth electronic transfer reported for a related dye involving an azo bridging ligand.

Ru(II) Bipyridyl Complex and TiO2 Nanocomposite Based Biomolecule-free Photoelectrochemical Sensor for Highly Selective Determination of Ultra-trace Hg2+ in Aqueous Systems

A biomolecule-free photoelectrochemical(PEC) probe(denoted as Ru-1) was designed, synthesized and coupled with TiO2 nanoparticles(NPs) for the highly sensitive and selective PEC detection of Hg2+, a model analyte with hypertoxicity to both human health and ecosystem. The probe Ru-1 was designed with Ru(II) bipyridyl complex as the chromophore, thiocyanate ligand as the recognition unit, and carboxylate group as the linkage site to connect Ru-1 to TiO2 nanoparticles. Under irradiation, Ru-1 shows strong affinity to TiO2 and good photophysical properties of strong visible light absorption, slow electron-hole(e-h+) recombination, and fast photoelectron injection to TiO2 nanoparticles via the π-bridge of 4-(2,2′-bipyridin)-4-yl-thiophene moiety. However, the specific coordination of Hg2+ with Ru-1 via the thiol moiety in the thiocyanate enlarges the band gap of the complex and reduces the photocurrent significantly. The synergistic interaction between TiO2 nanoparticles and the Ru-1 complex led to a selective PEC sensing strategy for Hg2+ detection. Detectable linear ranges from 10−12 g/mL to 10−7 g/mL and from 10−7 g/mL to 10−3 g/mL were obtained without the interference from possibly co-existed metal ions. The good analytical performances indicate the chemical probe based biomolecule-free PEC platform may offer a new route for the detection of biologically and environmentally important small molecules.

Bio Active Bipyridyl Complexes: Synthesis, Structure and Antimicrobial Activities

Bio Active Bipyridyl Complexes: Synthesis, Structure and Antimicrobial Activities

Abundant Manganese Complex-Anchored BiOI Hybrid Photocatalyst for Visible Light-Driven CO2 Reduction

An abundant manganese complex-anchored BiOI hybrid system for CO2 photocatalytic conversion was constructed. Layered BiOI and tricarbonyl Mn bipyridyl complex with carboxyl acid groups were connected with covalent bonds and used as visible light antenna and CO2 reduction reaction centers, respectively. The covalent connection of this hybrid system benefits the transfer of electrons from the semiconductor to the Mn complex. The anchoring group (carboxyl) is the key to CO2 reduction for the direct coupling of the two units, facilitating the transfer of electrons from BiOI to the manganese complexes. The photocatalytic properties and stability of the tricarbonyl Mn–bipyridyl complex were significantly enhanced with the aid of anchored BiOI. A high turnover number ([Formula: see text]) of HCOO− formation from CO2 could be achieved using this hybrid system under visible light irradiation.

Insights into the Mechanisms of Aquaporin-3 Inhibition by Gold(III) Complexes: the Importance of Non-Coordinative Adduct Formation.

Following our recent reports on the inhibition of the water and glycerol channel aquaglyceroporin-3 (AQP3) by the coordination complex [AuIII(1,10-phenanthroline)Cl2] (Auphen), a series of six new Au(III) complexes featuring substituted 1,10-phenanthroline ligands (1-6) have been synthesized and characterized. The speciation of the compounds studied in buffered solution by UV-visible spectrophotometry showed that most of the complexes remain stable for several hours. Quantum mechanics (QM) studies of the hydrolysis processes of the compounds suggest that they are thermodynamically less prone to exchange the chlorido ligands with H2O or OH- in comparison to Au(III) bipyridyl complexes. Preliminary data on the antiproliferative activity against A549 human lung cancer cells indicate that the compounds are able to inhibit cell proliferation in vitro. Stopped-flow spectroscopy showed that these complexes potently inhibit glycerol permeation in human red blood cells (hRBC) through AQP3 blockage. The QM investigation of the ligand exchange with methanethiol, used as a model of Cys40 of AQP3, was carried out for some derivatives and showed that the affinity of the compounds' binding for thiols is higher in comparison to the Aubipy complex ([AuIII(bipy)Cl2]PF6, bipy = 2,2'-bipyridine). In addition, both noncovalent and coordinative binding of complex 3( [AuIII(5-chloro-1,10-phenanthroline)Cl2]PF6) to the protein channel has been investigated in comparison to the benchmark Auphen and Aubipy using a computational workflow, including QM, molecular dynamics (MD), and quantum mechanics/molecular mechanics (QM/MM) approaches. Finally, atoms in molecules (AIM) and natural bond orbital (NBO) analyses corroborate the MD predictions, providing quantification of the noncoordinative interactions between the compounds and AQP3. AQP3 inhibition is the result of protein conformational changes, upon coordinative gold binding, which induce pore closure. The importance of noncoordinative adducts in modulating the AQP3 inhibition properties of the investigated Au(III) compounds has been elucidated, and these interactions should be further considered in the future design of isoform-selective AQP inhibitors.

New π-extended catecholato complexes of Pt(ii) and Pd(ii) containing a benzothienobenzothiophene (BTBT) moiety: synthesis, electrochemical behavior and charge transfer properties.

Benzothienobenzothiophene (BTBT) and derivatives have received increasing attention as organic field-effect transistor materials and molecular conductors. This report presents the first synthesis of metal complexes involving a BTBT moiety, which was achieved by complexation of 2,2'-bipyridyl complexes of Pt(ii) and Pd(ii) with dihydroxy-substituted BTBT (1) as a new π-extended catecholato ligand (tBu2Bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl). The resulting complexes M(tBu2Bpy)(O2BTBT) (M = Pt (3Pt) and Pd (3Pd)) were characterized by UV-vis spectroscopy, density functional theory (DFT) calculations, and cyclic voltammetry. The electron donating ability of BTBT was substantially enhanced upon including two oxygen substituents followed by metal coordination. This enabled chemical oxidation of 3Pt and 3Pd with a mild chemical oxidant (ferrocenium hexafluorophosphate) and formation of the one-electron-oxidized state. While 3Pt and 3Pd exhibited an absorption band originating from a catecholate → Bpy ligand-to-ligand charge transfer transition typical of this class of catecholato complexes, the radical cations exhibited a unique π-π* intramolecular charge transfer (ICT) transition absorption in which the π and π* orbitals were the newly incorporated benzothienothiophene-based donor and semiquinonato-based acceptor, respectively. The BTBT+ skeleton was electronically divided into two sites by the present chemical modification. The ICT properties of the complexes were found to be modulated by varying the metal ions. These findings offer a new approach to molecular design for (semi)conducting materials using optical properties.

Synthesis and Characterization of Cobalt(II) N,N'-Diphenylazodioxide Complexes.

Removal of chloride from CoCl2 with TlPF6 in acetonitrile, followed by addition of excess nitrosobenzene, yielded the eight-coordinate cobalt(II) complex salt [Co{Ph(O)NN(O)Ph}4](PF6)2, shown by single-crystal X-ray analysis to have a distorted tetragonal geometry. The analogous treatment of the bipyridyl complex Co(bpy)Cl2 yielded the mixed-ligand cobalt(II) complex salt [Co(bpy){Ph(O)NN(O)Ph}2](PF6)2, whose single-crystal X-ray structure displays a trigonal prismatic geometry, similar to that of the iron(II) cation in the previously known complex salt [Fe{Ph(O)NN(O)Ph}3](FeCl4)2. The use of TlPF6 to generate solvated metal complex cations from chloride salts or chlorido complexes, followed by the addition of nitrosobenzene, is shown to be a useful synthetic strategy for the preparation of azodioxide complex cations with the noncoordinating, diamagnetic PF6– counteranion. Coordination number appears to be more important than d electron count in determining the geometry and metal–ligand bond distances of diphenylazodioxide complexes.

Ruthenium(II) Tris(2,2′-bipyridyl) Complex Incorporated in UiO-67 as Photoredox Catalyst

Ruthenium(II) bis(2,2′-bipyridine) (2,2′-bipyridyl-5,5′-dicarboxylic acid), Rudcbpy, attached to the UiO-67(Zr) metal organic framework (MOF), generates upon visible light excitation the localized triplet excited state of the ruthenium(II) bipyridyl complex that decays partly to a very long-lived (millisecond time scale) photoinduced charge-separated state following a similar behavior as that of analogous ruthenium(II) tris(bipyridyl) complex dissolved in water, except that the lifetime of the soluble complex excited state is orders of magnitude shorter. The occurrence of photoinduced charge separation on the Rudcbpy-UiO-67(Zr) MOF has been proven visually by using methyl viologen as electron acceptor. Rudcbpy-UiO-67(Zr) behaves as a heterogeneous, reusable, photoredox catalyst promoting debromination of α-bromoketones with excellent selectivity at high conversions. Characterization data show that Rudcbpy-UiO-67(Zr) is stable under the photocatalytic reaction conditions.

Ruthenium(II) Bipyridyl Complexes with C∧C* Cyclometalated Mesoionic Carbene Ligands

The synthesis of four 2,2′-bipyridyl ruthenium(II) complexes with cyclometalating mesoionic 1,2,3-triazolylidene ligands via their respective p-cymene ruthenium(II) precursors is presented. Solid-state structures confirm the formation of the proposed complexes, which were characterized by UV/vis and electrochemical experiments as well as time-dependent DFT calculations including NTO analysis. The title motif shows improved photophysical properties compared to structurally related ruthenium(II) complexes with C∧C* cyclometalating imidazole-based N-heterocyclic carbene ligands. Due to their electronic properties, the presented dyes are promising candidates for an application in dye-sensitized solar cells.

Highly Selective and Sensitive Luminescent Turn‐On Probe for Pyrophosphate Detection in Aqueous Solution

AbstractIn this work, a luminescent probe (RuE, the abbreviation of Ru(bpy)2(E)Cl2, where bpy=2,2′‐bipyridine, E=N,N′‐5,6‐(1,10‐phenanthroline)‐bis(2‐hydroxy benzaldehyde)diamine) based on the ruthenium(II) bipyridyl complex conjugated with functionalized Schiff bases, which revealed a highly selective luminescence quenching by Cu2+ in aqueous solution was prepared. Because of the quenching effect of copper ions, the luminescence of RuE−Cu(II) solution was weak. However, in the presence of pyrophosphate (P 2O4‐ 7, PPi), the strong binding ability of PPi to Cu2+ can promote the break up of RuE−Cu(II) complex and then recover the luminescence. Most of other potential interfering anions, including strong interfering substance, like phosphate, ATP, ADP and AMP can not enhance the luminescence apparently. Therefore, the RuE−Cu(II) ensemble can act as an excellently selective and sensitive turn‐on probe for the sequential determination of PPi in aqueous solution. The detection limit of the probe for PPi was 0.58 nM and the linear concentration range was 0−16 μM. In addition, the potential applicability of this probe has been demonstrated by the successful detection of PPi in human urine samples.