Synthesis and electrochemiluminescence studies of tricarbonylrhenium(I) complexes with a cationic 2,2′-bipyridyl ligand

A sensitive photoluminescent sensor based on highly charged monoruthenium(II) complexes for dopamine detection

A sensitive and selective photoluminescent sensor based on the highly charged monoruthenium(II) complex was designed to detect dopamine (DA) in aqueous samples. Two novel highly charged cationic ruthenium(II) complexes [Ru(bpy)₂(bpy-N)]X₄ (bpy = 2,2'-bipyridine, bpy-N = 4,4'-bis[N,N,N-triethyl-(methylamino)]-2,2'-bipyridine, X^- = [PF₆]^- (1a) or Cl^- (1b) and [Ru(bpy)(bpy-N)₂]X₆ (X^- = [PF₆]^- (2a) or Cl^-(2b)) can be assembled with anionic surfactant sodium dodecylbenzene sulfonate (SDBS), leading to an enhancement of photoluminescence intensity. Upon addition of DA to the system, the photoluminescence intensity of the assembled system was quenched due to the energy transfer effect. It exhibited a wide linear range (0.1-50 μM) and low detection limit (10 nM). The sensor demonstrated a high selectivity toward DA, especially in the presence of adrenaline (Adr) and norepinephrine (NE), whose structures are similar to DA in biological systems. With the merits of simple operation, obvious phenomenon and fast response speed, the sensor had a potential application prospect in human urine sample.

Resolving Halide Ion Stabilization through Kinetically Competitive Electron Transfers

Stabilization of ions and radicals often determines reaction kinetics and thermodynamics, but experimental determination of the stabilization magnitude remains difficult, especially when the species is short-lived. Herein, a competitive kinetic approach to quantify the stabilization of a halide ion toward oxidation imparted by specific stabilizing groups relative to a solvated halide ion is reported. This approach provides the increase in the formal reduction potential, ΔE°'(Χ^•/-), where X = Br and I, that results from the noncovalent interaction with stabilizing groups. The [Ir(dF-(CF₃)-ppy)₂(tmam)]³⁺ photocatalyst features a dicationic ligand tmam [4,4'-bis[(trimethylamino)methyl]-2,2'-bipyridine]²⁺ that is shown by ¹H NMR spectroscopy to associate a single halide ion, K _eq = 7 × 10⁴ M^-1 (Br^-) and K _eq = 1 × 10⁴ M^-1 (I^-). Light excitation of the photocatalyst in halide-containing acetonitrile solutions results in competitive quenching by the stabilized halide and the more easily oxidized diffusing halide ion. Marcus theory is used to relate the rate constants to the electron-transfer driving forces for oxidation of the stabilized and unstabilized halide, the difference of which provides the increase in reduction potentials of ΔE°'(Br^•/-) = 150 ± 24 meV and ΔE°'(I^•/-) = 67 ± 13 meV. The data reveal that K _eq is a poor indicator of these reduction potential shifts. Furthermore, the historic and widely used assumption that Coulombic interactions alone are responsible for stabilization must be reconsidered, at least for polarizable halogens.

Amino group-driven distinguishing homocysteine from cysteine and glutathione in photoluminesecent signal of the iridium(III) complexes

In this work, six iridium(III) complexes have been designed, synthesized and characterized. The molecular structures of complex 1 ([(pba)₂Ir(bpy-2N(CH₃)₂)]PF₆), 2 ([(pba)₂Ir(bpy-2NH₂)]PF₆) and 3 ([(pba)₂Ir(bpy-2CH₃)]PF₆) were determined by single crystal X-ray diffraction. Upon addition of Hcy (homocysteine) to the solution of complex 1, a luminescent variation from orange red to green was observed by the naked eye, corresponding to a large blue shift from 604 nm to 498 nm (~106 nm). While the emission intensity of complex 1 was almost no change after addition of other common amino acids including Cys (cysteine) and GSH (glutathione). The aldehyde group of complex 1 formed a new thiazinane/thiazolidine ring with Hcy/Cys confirmed by ¹H NMR and high-resolution mass spectrometry. And the new product 1-Hcy had a higher quantum yield than 1-Cys. Theoretical calculations showed that the HOMO (highest occupied molecular orbital) of 1-Hcy was located on the newly formed six-membered thiazinane ring, which was different from the HOMO of 1-Cys. Compared with the other iridium(III) complexes, we can speculate that the large blue shift and enhancement of the emission intensity of the complex 1 were related to the strong electron donating ability of the modified amino groups on bipyridine ligand. This will provide an idea for the design of ratio-based luminescence probes for Hcy in future.