Electrochemical behavior of [ReI(DMPE)3]+, where DMPE = 1,2-bis(dimethylphosphino)ethane, at perfluorosulfonated ionomer-modified electrodes

A new era of LMCT: leveraging ligand-to-metal charge transfer excited states for photochemical reactions

Ligand-to-metal charge transfer (LMCT) excited states are capable of undergoing a wide array of photochemical reactions, yet receive minimal attention compared to other charge transfer excited states. This work provides general criteria for designing transition metal complexes that exhibit low energy LMCT excited states and routes to drive photochemistry from these excited states. General design principles regarding metal identity, oxidation state, geometry, and ligand sets are summarized. Fundamental photoreactions from these states including visible light-induced homolysis, excited state electron transfer, and other photoinduced chemical transformations are discussed and key design principles for enabling these photochemical reactions are further highlighted. Guided by these fundamentals, this review outlines critical considerations for the future design and application of coordination complexes with LMCT excited states.

Highly sensitive detection of Pb2+ and Cu2+ based on ZIF-67/MWCNT/Nafion-modified glassy carbon electrode

A series of different facile modification layers (MLs) was designed to gradually increase the electrochemical sensing performance of glassy carbon electrode (GCE) for simultaneously detecting Pb²⁺ and Cu²⁺. ML designs were mainly a different combination of ZIF-67, MWCNT and Nafion, and their different electrochemical sensing performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave stripping voltammetry (SWSV) and chronocoulometry. The fabricated sensor, which modified with ZIF-67/MWCNT and Nafion layer, exhibited the biggest response peak current to Pb²⁺ and Cu²⁺. In addition, it displayed a wide linear detection range of 1.38 nM-5 μM for Pb²⁺ and 1.26 nM-5 μM for Cu²⁺, a detection accuracy of about 1 nM for both Pb²⁺ and Cu²⁺, and an excellent stability for both Pb²⁺ and Cu²⁺. We also analyzed the real water sample taken from Changchun's Sanjia Lake and Yan Lake. We believe this ML design provides instruction for building high-performance electrochemical sensing systems.

Electrogenerated Chemiluminescence from Ru(Bpy)32+ Ion-Exchanged in Carbon Nanotube/Perfluorosulfonated Ionomer Composite Films

The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)(3)(2+)) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)(3)(2+) could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)(3)(2+) and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb Ru(bpy)(3)(2+) and also acted as conducting pathways to connect Ru(bpy)(3)(2+) sites to the electrode. In the present work, the sensitivity of the ECL system at the CNT/Nafion film-modified electrodes was more than 2 orders of magnitude higher than that observed at a silica/Nafion composite film-modified electrode and 3 orders of magnitude higher than that at pure Nafion films. The CNT/Nafion composite film-modified GC electrodes also exhibited long-term stability.

Electrogenerated Chemiluminescence from Tris(2,2‘-bipyridyl)ruthenium(II) Immobilized in Titania−Perfluorosulfonated Ionomer Composite Films

Electrochemical behavior and electrogenerated chemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) immobilized in sol-gel-derived titania TiO2)-Nafion composite films coated on a glassy carbon electrode have been investigated. The electroactivity of Ru(bpy)3(2+) ion exchanged into the composite films and its ECL behavior were strongly dependent upon the amount of Nafion incorporated into the TiO2-Nafion composite films. The ECL sensor of Ru(bpy)32+ immobilized in a TiO2-Nafion composite with 50% Nafion content showed the maximum ECL intensities for both tripropylamine (TPA) and sodium oxalate in 0.05 M phosphate buffer solution at pH 7. Detection limits were 0.1 microM for TPA and 1.0 microM for oxalate (S/N = 3) with a linear range of 3 orders of magnitude in concentration. The present ECL sensor showed improved ECL sensitivity and long-term stability, as compared to the ECL sensors based on pure Nafion films. The present Ru(bpy)3(2+) ECL sensor based on TiO2-Nafion (50%) composite films was applied as an HPLC detector for the determination of erythromycin in human urine samples. The present Ru(bpy)3(2+) ECL sensor was stable in the mobile phase containing a high content of organic solvent (30%, v/v), in contrast to a pure Nafion-based Ru(bpy)3(2+) ECL sensor. The detection limit for erythromycin was 1.0 microM, with a linear range of 3 orders of magnitude in concentration.

Oxidation-state speciation of

The analytical utility of chemically modified microelectrodes for oxidation-state speciation of redox couples by cyclic voltammetry has been explored. [Re(I)(DMPE)3]+/[Re(II)(DMPE)3]2+, where DMPE = 1,2-bis(dimethylphosphino)ethane, was studied at carbon-fiber microelectrodes of approximately 5 microm in radius coated with Nafion-entrapped solgel-derived silica (Nafion-silica) composite. The results are compared with cyclic voltammetry of [Fe(CN)6]3-/[Fe(CN)6]4- at bare carbon-fiber microelectrodes. At both microelectrodes, the cathodic and anodic limiting currents are linearly proportional to the concentrations of the reducible and oxidizable species of a redox couple, respectively. The shape of the cyclic voltammogram and the magnitude of the steady-state limiting current are not affected by the potential at which the scan starts. Speciation of both forms of a redox couple could be achieved voltammetrically at the microelectrodes. However, a considerably slower scan rate was required to achieve steady state at the modified electrode because of the smaller diffusion coefficients of [Re(I)(DMPE)3]+ and [Re(II)(DMPE)3]2+ in the Nafion-silica composite. The detection limit at the modified electrode was considerably lower (5 x 10(-9) M for [Re(I)(DMPE)3]+) than at the bare electrode (6 x 10(-5) M for [Fe(CN)6]3- and [Fe(CN)6]4-) because of the substantial preconcentration of [Re(I)(DMPE)3]+ by the Nafion-silica composite.

Spectroscopic and electrochemical evaluation of a perfluorosulfonated ionomer and its gel as preconcentrating media for [ReI(DMPE)3]+, where DMPE = 1,2-bis(dimethylphosphino)ethane

The interaction of [ReI(DMPE)3]+, where DMPE = 1,2-bis(dimethylphosphino)ethane, a nonradioactive analogue of a heart imaging agent, with Nafion gel, which is Nafion plasticized with tri-n-butyl phosphate, has been evaluated spectroscopically and electrochemically. Thin-layer spectroelectrochemistry on the rhenium compound yields a linear Nernst plot with an n value of 0.99 and E degree' of 0.049 V vs Ag/AgCl. The electrochemistry is consistent with a reversible one-electron transfer between the mono- and dicationic forms of the complex. The UV-visible spectrum of electrogenerated [ReII(DMPE)3]2+ is identical to that obtained by air oxidation of [ReI(DMPE)3]+. Thin, free-standing films of Nafion gel and Nafion that were sufficiently clear to record visible spectra were cast. Spectroscopic measurement of the partitioning of [ReI-(DMPE)3]+ from aqueous solution into these films shows a more rapid uptake of the complex by the Nafion gel. Preconcentration factors into Nafion gel and Nafion were 350 and 50, respectively, after 4 h of soaking. Cyclic voltammetry of 1.0 x 10(-4)-1.0 x 10(-7) M (ReI(DMPE)3]+ in 0.15 M supporting electrolyte aqueous solution at bare gold and spectroscopic graphite electrodes suggests that the complex adsorbs to these electrodes. By comparison, the well-defined cyclic voltammograms at Nafion gel-modified electrodes exhibit diffusion-controlled behavior. The formal reduction potential at Nafion gel-modified electrodes is shifted positively compared to bare electrodes. A current enhancement of approximately 4 was observed at Nafion gel-modified spectroscopic graphite over a bare electrode. A calibration plot of peak current for differential pulse voltammetry vs concentration at Nafion gel-modified spectroscopic graphite was linear in the 10(-7)-10(-5) M concentration range, with a detectable signal down into the 10(-9) M range.