Oxidation Wave Research Articles

Analysis of Facilitated Ion Transfer across Liquid-Liquid Interfaces Using Collision Electrochemisty

Abstract An electrochemical method was developed to analyze the alkali metal ion transfer across the water/1,2-dichloroethane interfaces facilitated by dibenzo-18-crown-6 ether (DB18C6) by observing the collisions of single emulsion droplets on an ultramicroelectrode (UME). The water-in-oil emulsion droplets were stabilized by an ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides, in which a highly hydrophilic redox probe of potassium ferrocyanide/ferricyanide (K3Fe(CN)6/ K4Fe(CN)6) was used. When the droplets collided with the UME that was biased at a potential to drive the oxidation reaction of [Fe(CN)6]4− (0.05 mol/L), the current spikes could be observed only with the addition of DB18C6. It was suggested that the DB18C6 as K+ ionophore facilitated the K+ transfer from the water to the oil to maintain charge balance during the electrolysis. As more K+ ionophores were added, the integrated charge of the current spikes showed a rising trend in general because of the ionophore to lower the Gibbs energy of ion transfer. Further collision experiments were conducted to investigate the transfer of Na+ and K+ cations facilitated by the DB18C6. The order in which the “voltammetric” oxidation waves appeared indicated that the ionophore of DB18C6 was more efficient in carrying K+ across the water/1,2-Dichloroethane interface. Thereby, the collision electrochemistry is a convenient and effective mean to study the ion selectivity of ionophore.

Targeted Synthesis of NIR Luminescent Rhenium Diimine cis,trans-[Re( )(CO)2 (L)2 ]n+ Complexes Containing N-Donor Axial Ligands: Photophysical, Electrochemical, and Theoretical Studies.

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re( )(CO)3 (NCMe)]OTf ( =phenantroline and neocuproine) afforded cis,trans-Re( )(CO)2 (NCMe)2 ]+ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N-donor ligands (pyridine, pyrazine, 4,4'-bipyridine, N-methyl-4,4'-bipyridine) gave a novel family of the diimine cis,trans-[Re( )(CO)2 (L)2 ]+ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from 711 to 805 nm. The nature of emissive excited states was studied using DFT calculations to show dominant contribution of 3 MLCT (dπ(Re)→π*( )) character. Electrochemical (CV and DPV) studies of the monocationic diimine complexes revealed one reduction and one oxidation wave assigned to reduction of the diimine moiety and oxidation of the rhenium center, respectively.

Synthesis, molecular structure, spectroscopic characterization and antibacterial activity of the pyrazine magnesium porphyrin coordination polymer

A new material of magnesium(II) polymer compound with the formula {[MgII(TPP)(pz)]• 0.5[MgII(TPP)]•CH2Cl2}n (I), (TPP) = meso‑tetraphenylporphyrinato and pz = pyrazine) was synthetized and characterized by IR, UV-visible, PL photoluminescence and 1H NMR spectroscopy studies, single-crystal XRD analyses and cyclic voltammetry. The crystal structure of (I) is made by the 1D {[Mg(TPP)(pz)]} polymeric chains (molecules I(A)) where the tetracoordinated magnesium(II) complexes [Mg(TPP)] (molecules I(B)) are located as well as the dichloromethane solvent molecules. The crystal packing of (I) is stabilized by intermolecular CH⋯Cg π interactions where Cg is the centroid of phenyl and pyrrole rings. Additionally, the photophysical properties have been evaluated by UV-visible absorption and fluorescence emission spectroscopies. The UV-visible spectrum of (I) shows a redshift Soret band value (428 nm) compared to that of the free base H2TPP porphyrin while the λmax values of the Q bands are in the range 560 – 610 nm. The optical gap of (I) was estimated at 1.99 eV. The cyclic voltammogram of the title compound presents two reversible oxidation waves and one reversible reduction wave. The HOMO and LUMO energy values were deduced from the voltammogram which are -4.96 and -2.85 eV respectively. Furthermore, bioactivity investigations revealed that the free porphyrin, the starting material [MgII(TPP)] and complex (I) could be used as potential antibacterial agents.

Building-up novel coordination polymer with magnesium porphyrin: Synthesis, molecular structure, photophysical properties and spectroscopic characterization. Potential application as antibacterial agent

The new meso-tetraphenylporphyrin magnesium(II) polymer compound with the formula {[MgII(TPP)(4,4′-bpy)]}n.n[MgII(TPP)(4,4′-bpy)2] (I), (TPP) = meso-tetraphenylporphyrinato and 4,4′-bipy = 4,4′-bipyridine) was synthetized and characterized by IR, UV–visible, photoluminescence and 1H NMR spectroscopy studies, single-crystal XRD analyses and cyclic voltammetry. From the X-ray data, it was established that the central metal Mg2+ is located on an inversion center, being octahedrally coordinated to four pyrrole nitrogen atoms of the porphyrin ring and the nitrogen atoms of the two 4,4′-bipyridine axial ligand situated in trans positions with respect to the metal center. The crystal of (I) is made by [MgII(TPP)(4,4′-bipy)2] monomer complexes and {[MgII(TPP)(4,4′-bpy)]}n polymers linked together via CH…π type intermolecular interactions leading to a three-dimensional network. The UV–visible spectrum of (I) shows that the Soret band value (432 nm) is redshifted compared to the free base H2TPP while the λmax values of the Q bands are in the range 570–610 nm. The optical gap of (I) was estimated at 2.00 eV and the cyclic voltammogram of the title compound presents two reversible oxidation waves and one reversible reduction wave. The HOMO and LUMO energy values were deduced from the voltammogram which are −4.94 and −3.06 eV respectively. The use of [MgII(TPP)(DMF)] starting material compound, {[MgII(TPP)(4,4′-bpy)]}n.n[MgII(TPP)(4,4′-bpy)2] (I) and the [MgII(TPP)(HTMA)2] (HTMA = hexamethylenetetramine) (II) as novel significant antibacterial agents was also tested.

Preparation, absorption spectra, and electrochemsitry of the trigermanes R3GeGePh2GeR3 (R3 = ButMe2, PhMe2, Bun3) and tetragermanes R3Ge(GePh2)2GeR3 (R3 = Et3, Bun3)

The trigermanes ButMe2GeGePh2GeMe2But and PhMe2GeGePh2GeMe2Ph and the tetragermanes Et3Ge(GePh2)2GeEt3 and Bun3Ge(GePh2)2GeBun3 were synthesized via the hydrogermolysis reaction. These species were characterized by UV/visible spectroscopy, cyclic voltammetry, and differential pulse voltammetry. The properties of the two trigermanes were also compared with those of Bun3GeGePh2GeBun3, and the UV/visible absorption maxima of these three trigermanes fall in the narrow range of 246 – 249 nm while their oxidation potentials differ by 233 mV. Both ButMe2GeGePh2GeMe2But and Bun3GeGePh2GeBun3 exhibit two irreversible oxidation waves in their CVs and DPVs. The absorption maxima for the two tetragermanes are similar and their oxidation potentials differ by only 58 mV. The CV and DPV of Et3Ge(GePh2)2GeEt3 exhibits three irreversible oxidation waves while that of Bun3Ge(GePh2)2GeBun3 contains only one. The X-ray crystal structure of Et3Ge(GePh2)2GeEt3 was determined and this represents a rare example of a tetragermane with alkyl substituents at the terminal germanium atoms.

A study on the electrooxidation of vitamin B6 compounds on glassy carbon and polycrystalline gold electrodes

Abstract An electrochemical analysis of B6 vitamins has been presented. The electrooxidation of vitamin B6 group and related compounds has been performed at neutral pH using glassy carbon and gold electrodes. Irreversible electrochemical processes are observed for these substances by cyclic voltammetry. The rate of the first or second electron transfer (E) and/or the presence of chemical steps (C) determinate the electrode process (with schemes classified as EC, CE, ECE, ECEC, mostly). In numerous cases the values of Ep-Ep/2 suggest the first electron transfer (apparent αna The compounds of the series showed oxidation waves in a glassy carbon electrode at potentials that are relatively low compared to the oxidation potential of the same electroactive groups on this electrode. This behavior suggests an activation of the oxidation of the vitamin B-6 derivatives. In the same way the compounds of the series showed oxidation waves in a polycrystalline gold electrode. In some cases, an oxidation process at a less anodic potential is also observed showing efficient electrocatalytic behavior.

Synthesis and Characterization of Push‐Pull Aza‐BODIPY Dyes Towards Application in NIR‐II Photothermal Therapy

AbstractA new series of aza‐BODIPYs (CN−X) with significantly red‐shifted absorbances were designed and synthesized by installation of various electron‐donating groups on the para‐positions of 3,5‐phenyl groups while strong electron‐withdrawing groups (nitrile groups) were fixed on the para‐positions of 1,7‐phenyl moieties. Interestingly, strong electron‐donating groups such as N'N‐dimethylaniline (CN−NMe2) could provide strong NIR absorption up to 857 nm and weak fluorescence emission up to 967 nm, whereas strong evidence supported heat production via non‐radiative decay after excitation. Electrochemical studies revealed that the substituents on the dyes showed strong effects on the oxidation potentials where the oxidation wave of CN−NMe2 occurred at the lowest overpotential, followed by CN−OMe, CN−Me, CN−Br and CN−H, respectively. Calculations were also performed to understand the push‐pull effect of the substituents on the aza‐BODIPY systems. Finally, applications of dyes in NIR cancer cell imaging and the NIR‐II photothermal effect were also investigated.

Trialkylphosphines Having a Bulky Phosphacyclopentane Backbone: Structural and Redox Properties Depending on the Exocyclic Alkyl Groups and EPR Observation of a Persistent Trialkylphosphine Radical Cation.

Bulky phosphines and their redox properties have received increased attention in the view of useful auxiliary ligands for transition metal catalysts and Lewis-base components of frustrated Lewis pairs for chemical transformations. Herein we report the synthesis, structure, and properties of a series of trialkylphosphines 2R (R = methyl, ethyl, isopropyl, tert-butyl, 1-adamantyl) that possess the bulky 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane as a structural backbone. Among these phosphines, 2Ad, which contains an adamantyl moiety, has a very large buried volume (%Vbur) for a trialkylphosphine (62.0) and shows a quasi-reversible oxidative wave at a lower oxidation potential (-0.12 V in CH2Cl2, vs ferrocene/ferrocenium couple) by cyclic voltammetry. The reaction of 2Ad with AgPF6 afforded a cationic silver aquo complex [Ag(2Ad)(H2O)]+[PF6]-, whereas the reaction with NOSbF6 gave a persistent phosphine radical cation [2Ad]•+. Based on the EPR spectra and DFT studies, the spin and positive charge of [2Ad]•+ are localized on the phosphorus atom.

Targeted DNA oxidation by LSD1-SMAD2/3 primes TGF-β1/ EMT genes for activation or repression.

The epithelial-to-mesenchymal transition (EMT) is a complex transcriptional program induced by transforming growth factor β1 (TGF-β1). Histone lysine-specific demethylase 1 (LSD1) has been recognized as a key mediator of EMT in cancer cells, but the precise mechanism that underlies the activation and repression of EMT genes still remains elusive. Here, we characterized the early events induced by TGF-β1 during EMT initiation and establishment. TGF-β1 triggered, 30–90 min post-treatment, a nuclear oxidative wave throughout the genome, documented by confocal microscopy and mass spectrometry, mediated by LSD1. LSD1 was recruited with phosphorylated SMAD2/3 to the promoters of prototypic genes activated and repressed by TGF-β1. After 90 min, phospho-SMAD2/3 downregulation reduced the complex and LSD1 was then recruited with the newly synthesized SNAI1 and repressors, NCoR1 and HDAC3, to the promoters of TGF-β1-repressed genes such as the Wnt soluble inhibitor factor 1 gene (WIF1), a change that induced a late oxidative burst. However, TGF-β1 early (90 min) repression of transcription also required synchronous signaling by reactive oxygen species and the stress-activated kinase c-Jun N-terminal kinase. These data elucidate the early events elicited by TGF-β1 and the priming role of DNA oxidation that marks TGF-β1-induced and -repressed genes involved in the EMT.

Polymorphous Indium Metal-Organic Frameworks Based on a Ferrocene Linker: Redox Activity, Porosity, and Structural Diversity.

The metallocene-based linker molecule 1,1'-ferrocenedicarboxylic acid (H2FcDC) was used to synthesize four different polymorphs of composition [In(OH)(FeC12H8O4)]. Using conventional solvent-based synthesis methods and varying the synthetic parameters such as metal source, reaction temperature, and solvent, two different MOFs and one 1D-coordination polymer denoted as CAU-43 (1), In-MIL-53-FcDC_a (2), and In-FcDC (3) were obtained. Furthermore, thermal treatment of CAU-43 (1) at 190 °C under vacuum yielded a new polymorph of 2, In-MIL-53-FcDC_b (4). Both MOFs 2 and 4 crystallize in a MIL-53 type structure, but in different space groups C2/m for 2 and P1̅ for 4. The structures of the four title compounds were determined by single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), or a combination of three-dimensional electron diffraction measurements (3D ED) and PXRD. N2 sorption experiments of 1, 2, and 4 showed specific surface areas of 355 m2 g-1, 110 m2 g-1, and 140 m2 g-1, respectively. Furthermore, the electronic properties of the title compounds were characterized via Mössbauer and EPR spectroscopy. All Mössbauer spectra showed the characteristic doublet, proving the persistence of the ferrocene moiety. In the cases of 1, 3, and 4, appreciable impurities of ferrocenium ions could be detected by electron paramagnetic resonance spectroscopy. Cyclovoltammetric experiments were performed to demonstrate the accessible redox activity of the linker molecule of the title compounds. A redox process of FcDC2- with oxidation (between 0.86 and 0.97 V) and reduction wave (between 0.69 and 0.80 V) was observed.

Inspection of electrochemical behavior of tolnaftate a topical antifungal agent and its active hydrolysis products by disposable screen-printed carbon electrode

Inspection of the electrochemical behavior tolnaftate (TNF), of a topical antifungal agent and its active hydrolysis products, was carried out by utilizing a disposable screen-printed carbon electrode (SPCE) for the first time. The voltammetric behavior of TNF was studied in various pH values using cyclic voltammetry and differential pulse voltammetry. A well-defined irreversible oxidation wave of TNF was observed at 1.20 V (vs. pseudo Ag/AgCl) and did not shift with different pH of solutions. The electro-analytical performance of the disposable SPCE was investigated in wide concentration ranges with limits of detection (LOD) of 0.24 μM and 3.76 μM in 0.1 M H2SO4 and B.R. buffer pH 7, respectively. Thus, the disposable SPCEs offer a sensitive and reproducible electrochemical platform for TNF in dosage forms. Further, the TNF was hydrolyzed in an alkaline medium to release its possible lethal products i.e. 2- Naphthol which can be analyzed voltammetrically without any interference so it is considered as a first selective stability-indicating assay for TNF.

Catalyst Support Based on Oxygen-Deficient Titanium Suboxide Nanosheets with Pt Nanoparticles for Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cell Application

Developing stable nanocatalysts with high activity for oxygen reduction reaction (ORR) remains a great challenge in the field of clean energy. As one of the most important means of electrochemical energy conversion, proton-exchange membrane fuel cells (PEMFCs) have attracted much attention in the scientific and industrial communities [1]. There has been increasing interest in the development of advanced electrode materials for the next generation of high-performance, durable PEMFCs. Importantly, the practical use of conventional carbon supported platinum (Pt) catalyst (i.e., Pt/C) materials is limited by their low electrochemical oxidation resistance and the consequent structural collapse of the carbon-based support material in electrodes, especially under dynamic operating conditions [2,3]. As such, there are still some limitations to the performance of PEMFCs with these carbon-based hybrid electrodes, and further improvement or optimization of their electrochemical performance remains challenging. Additionally, the electronic paths in these surfaces functionalized carbon supports are not effectively shortened, because electrons move less freely between them, via direct contact or by jumping from one particle to another as the conductive carbon particles are passivated [4]. Therefore, the development of conductive and corrosion-resistant non-carbon nanostructured support materials for catalysis, to replace carbon black particle aggregates, is the ultimate route to eliminating electrochemical instability [5]. Herein, we developed two-dimensional oxygen-deficient Titania nanosheets (TiO2-x NSs) as electrocatalyst support by simple hydrothermal reaction followed by NaBH4 reduction in ambient atmosphere. Electrochemical accelerated degradation tests (ADTs) and post-test elemental analysis revealed that the higher surface area and oxygen deficiency play a key role in the high-performance corrosion-resistant TiO2-x NSs electrocatalyst supports, as they serve as a means for improving electrical conductivity. The density of states of the valence band (VB) for TiO2-x NSs was measured by X-ray photoelectron spectroscopy (XPS), and exhibited a remarkable band gap narrowing (~ 2.7 eV) based on the introduced surface defect (oxygen vacancy). After the deposition of Pt nanoparticles (NPs), the TiO2-x NS catalysts exhibited both higher electrocatalytic activity and outstanding electrochemical stability compared to commercial Pt/C. From the cyclic voltammogramms, it was observed that the Pt-TiO2-x NSs displayed positive shift of an oxidation wave assigned to the adsorption of oxygenated species (e.g., OHad, at 0.7 - 0.9 V) compared to Pt/C. These observations suggest that the surface of catalyst is less oxophilic and has weaker binding to the oxygenated species than the surface of pure Pt, which is desired for lowering the kinetic barrier of the ORR. The calculated Tafel slope was 68 mVs-1 at low current density region, indicating that the transfer of the first electron on the catalyst is the rate determining step for the adsorption of intermediates. The mass activity (MA) of the catalyst is 314 Agpt -1, which is 1.5 times higher than that of Pt/C. The enhanced activity for ORR of Pt-TiO2-x NSs was attributable to the strong metal-support interaction (SMSI) effect. Due to the spillover effect, charge transfer occurred from the TiO2-x NSs to the Pt NPs and caused the electron density of the Pt NPs to increase. Accordingly, the obtained catalyst delivers a high power density of 958 mWcm-2 in H2-O2 PEMFC at 80 °C in ambient pressure as cathode. Moreover, no decay was observed during continuous operation at 1.5 Acm-2 for 100 h from the projected catalyst support based fuel cell. Benefiting from the unique structural functionality, interaction and electronic effects, the Pt-TiO2-x NSs displayed a negligible performance deterioration overlong-term cycling, demonstrating cell performance comparable to that of state-of-the-art commercial Pt/C during practical PEMFC operation. This strategy offers a new concept for designing an ultra-low Pt loading yet highly active and durable catalytic support for fuel cell applications and beyond. ACKNOWLEDGMENTS We acknowledge the financial support from the (Grants in Aid for scientific research (KAKENHI)) Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) under the ‘Multifunctional durable nanostructured redox electrocatalysts on conducting titanium oxide support’ project (Project Number: 18F18372). Keerti M. Naik is thankful to the Japan Society for the Promotion of Sciences for a JSPS Postdoctoral Fellowship (Standard).

Synthesis, Structures, and Photoluminescent Properties of Tricyanidonitridorhenium(V) Complexes with Bipyridine-Type Ligands.

Tricyanidonitridorhenium(V) complexes with 2,2'-bipyridine (bpy) derivatives in which the 4 and 4' positions were substituted by X, [ReN(CN)3(X2bpy)]- (X = NMe2, NH2, OMe, Me, Cl, and Br), were newly synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. UV-vis spectra of the complexes in dimethyl sulfoxide (DMSO) showed that the peak maximum wavelengths of rhenium-to-π* bpy-type-ligand charge transfer were in the range of 474-542 nm. Cyclic voltammograms in n-(C4H9)4NPF6-DMSO showed one-electron oxidation and reduction waves corresponding to the Re(VI/V) and X2bpy0/- processes, respectively. The new complexes and [ReN(CN)3bpy]- showed photoluminescence in the crystalline phase at 295 and 80 K and in DMSO at 295 K. The origin of the emission in DMSO was attributed to the triplet nature of the rhenium-to-π* bpy-type-ligand charge-transfer transition. Density functional theory calculations showed that the highest occupied and lowest unoccupied molecular orbitals were primarily localized on the dxy orbital of the rhenium and π* orbitals of the bpy-type ligand, respectively.

Effect of Distortions on the Geometric and Electronic Structures of One-Electron Oxidized Vanadium(IV), Copper(II), and Cobalt(II)/(III) Salen Complexes.

The ligands N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,2-ethanediamine and N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,3-propanediamine were chelated to V(IV)═O (1, 2), Cu(II) (3, 4), Co(II) (5), and Co(III) (6). The X-ray crystal structures of 1-6 were solved. The vanadium center in 1-2 resides in square pyramidal geometry, with an axially bound oxo ligand, whereas the metal ion displays a tetrahedrally distorted square planar geometry in 3-5. The extent of distortion is correlated to the length of the diamine spacer: The longer the linker, the larger the tetrahedral distortions. Complex 6 is octahedral with a bidentate acetate molecule that completes the coordination sphere. All the complexes were characterized by UV-vis and EPR spectroscopies, as well as DFT calculations and electrochemistry. Complexes 1-6 exhibit a reversible one-electron oxidation wave in the range -0.11-0.26 V vs Fc+/Fc. The cations 1+ and 2+ were structurally characterized, showing an octahedral V(V) ion with one oxo and one water molecule coordinated in axial positions. Their vis-NIR spectra are dominated by a band at 727 and 815 nm, respectively, which is assigned to a phenolate-to-vanadium(V) charge transfer (CT) transition. The crystal structures of 3+ and 4+ are congruent with Cu(II)-radical species, wherein the metal center remains four-coordinated. Both feature a Class II (Robin-Day classification scale) IVCT transition at around 1200 nm (ε > 1 mM cm-1), indicative of partial localization of the radical. The structure of 5+ displays a square pyramidal cobalt ion, where the fifth (axial) coordination is occupied by a water molecule. It displays a NIR feature at 1244 nm and is described as intermediate between high spin Co(III) and Co(II) radical. In the presence of acetate the dimer [(5)2(μ-OAc)]+ forms, which was structurally characterized and shows a blue shift and lowering in intensity of the NIR absorption band in comparison to 5+. Complex 6+ is a genuine Co(III) radical complex, wherein the phenoxyl moiety is localized on one side of the molecule.

A Ru-bda Complex with a Dangling Carboxylate Group: Synthesis and Electrochemical Properties.

Ruthenium complexes containing the tetradentate 2,2'-bipyridine-6,6'-dicarboxylato (bda2-) equatorial ligand and ortho-subsituted pyridines in the axial position have been prepared and characterized using spectroscopic, crystallographic and electrochemical techniques. Complexes [Ru(Hbda)(DMSO)(pyC)] (1) and [Ru(bda)(DMSO)(pyA)] (2) (where pyC is 2-pyridinecarboxylate, pyA is pyridine-2-ylmethanol and DMSO is dimethyl sulfoxide) have been isolated in moderate to high yields. The solid state structures of (1-H)- and 2 reveal the strong chelate effect of the axial pyridine ligand that coordinates in a bidentate fashion leaving the bda2- equatorial ligand coordinating in a tridentate mode. In solution, compound 2 shows a dynamic equilibrium between different coordination modes of the bda2- and pyA ligands. This phenomenon does not occur for 1 because the carboxylate binds stronger than the labile alcohol in 2. Cyclic voltammetry analysis of 1 reveals a complex behavior with a pH-independent wave at E1/2 = 1.12 V that is tentatively associated with the two-electron RuIV/II couple. In sharp contrast, complex 2 shows a pH-dependent one-electron wave at E1/2 = 0.83 V (pH 1), assigned to the proton-coupled electron transfer process of the RuIII/II couple and a pH-independent wave at E1/2 = 1.06 V assigned to the RuIV/III couple. Compound 2 is used to prepare complex [Ru(bda)(pic)(pyA)] (4). This complex is air sensitive and converts to complex [Ru(bda)(pic)(pyE)] (5) (where pyE is methyl 2-pyridine carboxylate) in the presence of methanol. This oxidation also occurs by applying a positive potential to an aqueous solution of 4, producing the derivative [Ru(bda)(pic)(pyC)] (3). Cyclic voltammetry of 3 shows two pH-independent one-electron oxidation waves at E1/2 = 0.64 V and E1/2 = 1.0 V, corresponding to the RuIII/II and RuIV/III couples, respectively. In addition, a water oxidation catalytic wave appears at Eonset ≈ 1.4 V. Foot-of-the-wave analysis of this catalytic wave based on a water nucleophilic attack accounts for a TOFmax = 0.63-0.74 s-1.

A simple adsorptive chronopotentiometric stripping method for determination of vitamin B1 in pharmaceutical products

A new electroanalytical method for vitamin B1 determination, based on adsorptive chronopotentiometric stripping analysis and non-specific adsorption onto mercury film electrode, was developed and validated. Stripping chronopotentiograms showed a single well-defined oxidation wave corresponding to vitamin B1 at about − 0.43 V in citrate buffer pH 6.0. The most important experimental factors affecting the monitored electroanalytical response of vitamin B1 were investigated and optimised. Under the optimal experimental conditions, linear response of vitamin B1 was obtained in the concentration range of 5–50 mg dm−3, with the achieved limit of detection of 1.64 mg dm−3, and the limit of quantitation of 4.97 mg dm−3. A mean recovery of 97.1% and relative standard deviations of 3.75% were achieved. The developed electrochemical procedure was successfully applied for the determination of vitamin B1 in pharmaceutical products. The results of the proposed method were in good agreement with those obtained by parallel HPLC analyses, confirming an accuracy of the developed method.

Syntheses, crystal structures and electrochemical properties of a series of ruthenium(II) bipyridine complexes with ferrocene carboxylate ligands

The reaction of Ru(bpy)2(PPh3)(CF3SO3), Ru(bpy)(PPh3)2(CF3SO3)2 or Ru(bpy)2(CF3SO3)2 with mono- or di-carboxylate ligands in the presence of triethylamine afforded the heterometallic Ru(II) and Fe(II) complexes [Ru(bpy)(PPh3)2(η2-O2CFc)](CF3SO3) (1), [Ru(bpy)2(PPh3)(O2CFc)](CF3SO3) (2), [Ru(bpy)2(η2-O2CFc)](CF3SO3) (3) and [{Ru(bpy)2(PPh3)}2{O2CFcCO2}](CF3SO3)2 (4). The molecular structures of complexes 1 and 2 have been determined by single-crystal X-ray diffraction analysis and show that the ruthenium units are coordinated by the ferrocene carboxylate ligand in a monodentate mode or a bidentate-chelating mode. Electrochemical studies reveal that complexes 1, 2, 3 and 4 contain reversible or quasi-reversible Ru and Fe oxidation waves. The redox potentials have been well ascribed. By comparing the coordination environment of the central ruthenium atoms, we found that the RuII/RuIII redox potential shifted to the negative direction along with the increase of electron-deficient bpy ligands. The redox potentials for the ferrocenecarboxylate ligand ranged from +0.5 to +0.6 V.

Highly conjugated donor-acceptor dyad based on monotetrathiafulvalene covalently attached to a magnesium norphthalocyanine unit

A novel highly conjugated donor–acceptor dyad composed of a tetrathiafulvalene (TTF) moiety covalently attached to a magnesium norphthalocyanine (NPc) unit (1) has been synthesized and full characterized. Ultraviolet–visible spectroscopy and electron paramagnetic resonance data reveal that 1 forms an electron transfer complex with 2,3,5,6-tetrafluoro-7,7,8,8-tetra-cyanoquinodimethane (F4TCNQ). Detailed electrochemical investigations show one irreversible one-electron oxidation wave, two quasi-reversible one-electron oxidation waves, and two irreversible one-electron reduction waves, indicating that 1 is a good π-electron donor. Compound 1 shows clear intramolecular charge transfer (ICT) interactions from the tetrathiafulvalene fragments to the norphthalocyanine core. This phenomenon can be explained by density functional theory (DFT).

IR spectroelectrochemistry as efficient technique for elucidation of reduction mechanism of chlorine substituted 1,10-phenanthrolines

The electrochemical behaviour of 4,7-dichloro-1,10-phenanthrolines was studied in non-aqueous solution using cyclic voltammetry, controlled potential electrolysis, in-situ UV–Vis and IR spectroelectrochemistry, and HPLC-DAD (HPLC with diode array detector) and HPLC-MS/MS techniques. The substitution of phenanthrolines at position C2 and C5 with methyl groups, chlorine and/or fluorine atoms influences the redox properties and the potential gap between the oxidation and reduction potentials. Reduction leads to the formation of a radical anion and the subsequent cleavage of halide from the molecule. Compounds containing also chlorine or fluorine atoms at position C5 were found to be the most easily reduced. The oxidation of 4,7-dichloro-1,10-phenanthrolines proceeds primarily on the conjugated aromatic rings of phenanthroline forming a short living radical cation at the first oxidation wave and a dication at the second oxidation wave. The changes of the absorption spectra during IR spectroelectrochemistry suggested the formation of an unstable species, whose dimeric structure was hypothesized. Frontier molecular orbitals calculations and theoretical calculations of IR spectra support the findings.

Elucidating the Electrochemical Mechanism of NG-Hydroxy-L-Arginine

NG-Hydroxy-L-arginine (NOHA) is a stable intermediate product in the urea cycle that can be used to monitor the consumption of L-arginine by nitrous oxide synthase (NOS) to produce nitric oxide (NO) and L-citrulline. Research has implicated the urea cycle in many diseases and NO has cultivated interest as a potential biomarker for neural health. Electrochemical detection is an established, cost-effective method that can successfully detect low levels of analyte concentrations. As one of the few electrochemically active species in the urea cycle, NOHA shows promise as a biomarker for monitoring disruptions in this biochemical process. In this study, we show that NOHA has an oxidation peak at +355 mV vs Ag/AgCl at a glassy carbon electrode. In addition, cyclic voltammetry studies with structural analogs—alanine and N-hydroxyguanidine—allowed us to approximate the oxidation wave at +355 mV vs Ag/AgCl to be a one electron process. Diffusivity of NOHA was found using linear scan voltammetry with a rotating disk electrode and approximated at 5.50 × 10−5 cm2 s−1. Ample work is still needed to make a robust biosensor, but the results here characterize the electrochemical activity and represent principle steps in making a NOHA biosensor.