Spectroelectrochemical characterization and controlled potential chronocoulometric demetallation of tetra- and octa-substituted lead phthalocyanines

The solution redox properties and spectroelectrochemical investigation of the novel lead phthalocyanines carrying chloro alkylthio and alkylmalonyl at periphery were studied using various electrochemical techniques in DCM on a platinum electrode. Cyclic voltammetry and differential pulse voltammetry studies show that all of the complexes give up to five ligand-based diffusion controlled one-electron reversible redox couples. Assignments of the redox couples were confirmed by spectroelectrochemical measurements. Spectroelectrochemical studies reveal that lead phthalocyanine complexes are demetallated during the controlled potential chronocoulometry measurement before the first reduction couple of the complexes.     

Electrochemical and spectroelectrochemical characterization of the phthalocyanines with pentafluorobenzyloxy substituents

The solution redox properties and spectroelectrochemical investigation of the novel metal-free, zinc, nickel and cobalt phthalocyanines with tetra-pentafluorobenzyloxy substituents at the periphery were studied using various electrochemical and spectroelectrochemical measurements. Cyclic voltammetry and differential pulse voltammetry studies show that while Ni(II), Zn(II) and free-phthalocyanines give up to two reduction and two oxidation processes having ligand-based diffusion controlled reversible one-electron electron transfer characters, Co(II) phthalocyanine represents one ligand-based oxidation, one metal-based reduction and one ligand-based reduction processes having diffusion controlled reversible one-electron transfer characters. Assignments of the redox couples are also confirmed by spectroelectrochemical measurements. Reduction potentials of all complexes shift to positive potentials due to the electron withdrawing tetra-pentafluorobenzyloxy substituents compared with those of the phthalocyanines bearing phenoxy derivatives. A linear variation of the first reduction and oxidation potentials versus ze/r has been obtained for zinc and nickel phthalocyanines.     

1,4-Dithiaheterocycle-fused porphyrazines: Synthesis,characterization, voltammetric and spectroelectrochemical properties

Porphyrazines (M = H, Mg, Zn and Co) with a 2,3-dicyano-5-phenyl-5,6-dihydro-1,4-dithiin group fused to each pyrrole unit were synthesized and characterized starting with the corresponding unsaturated dicarbonitrile derivative. The voltammetric and spectroelectrochemical characterizations of the metallo-porphyrazines (M = 2H⁺, Mg²⁺, Zn²⁺ and Co²⁺) substituted with 2,3-dicyano-5-phenyl-5,6-dihydro-1,4-dithiin groups on peripheral positions are described. Cyclic voltammetry and differential pulse voltammetry studies showed that while metal-free, magnesium, and zinc porphyrazines represented well-defined one-electron ligand-based reductions and ligand-based one-electron oxidation couples, cobalt porphyrazine gave both metal-based and ligand-based reduction and oxidation couples. Assignments of the redox couples were confirmed by spectroelectrochemical measurements.     

Synthesis, electrochemistry and in situ spectroelectrochemistry of soluble lead phthalocyanines

The synthesis, characterization and voltammetric and spectroelectrochemical properties of newly synthesized lead phthalocyanines bearing tetra-(1,1-(dicarbpenthoxy)-2-(4-biphenyl)-ethyl), tetra-(1,1-(dicarbpenthoxy)-2-(1-naphthyl)-ethyl and tetra-((1,1,2-(tricarbopentoxyethyl)) substituents have been presented in this work for the first time. The characterization of the complexes was made by elemental analysis, ¹H NMR, FT-IR, UV-vis and Maldi-TOF. The solution redox properties and spectroelectrochemical investigation of the complexes are studied using various electrochemical techniques in DCM on a platinum electrode. Cyclic voltammetry and differential pulse voltammetry studies show that the complexes give three one-electron ligand-based reductions and two one-electron oxidation couples having diffusion-controlled mass transfer character. Assignments of the redox couples were confirmed by spectroelectrochemical measurements. Spectroelectrochemical studies reveal that all complexes are demetallized during the spectroelectrochemical measurement under the applied potentials at the first reduction and oxidation potentials of the complexes. Different ring substituents of the complexes affect the easy demetallization processes of the complexes.     

Electrochemical characterisation of tetra- and octa-substituted oxo(phthalocyaninato)titanium(IV) complexes

The synthesis and electrochemical characterisation of the following oxotitanium tetra-substituted phthalocyanines are reported: 1,(4)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (5a); 1,(4)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (5b); 2,(3)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (6a) and 2,(3)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (6b). The electrochemical characterisation of complexes octa-substituted with 4-(benzyloxy)phenoxy (9b), phenoxy (9c) and tert-butylphenoxy (9d) groups is also reported. The cyclic voltammograms of the complexes exhibit reversible couples I-III and couple IV is quasi-reversible for complexes 5a, 5b, 6a and 6b. The first two reductions are metal-based processes, confirmed by spectroelectrochemistry to be due to Ti^IVPc²⁻/Ti^IIIPc²⁻ and Ti^IIIPc²⁻/Ti^IIPc²⁻ redox processes and the last two reductions are ring-based processes due to Ti^IIPc²⁻/Ti^IIPc³⁻ and Ti^IIPc³⁻/Ti^IIPc⁴⁻. Chronocoulometry confirmed a one-electron transfer at each reduction step. The electrochemistry of the above complexes is also compared to the previously reported 5c, 5d, 6c and 6d.     

Theory of differential normal pulse voltammetry

An analytical solution is presented for the case of double potential step chronoamperometry at a stationary planar electrode for the case of heterogeneous charge transfer control. Extension of the result to multiple potential steps gives the current—potential response for differential normal pulse voltammetry. The dependence of the response on the experimental parameters is examined. The dependence on duration of the first pulse is especially significant, for the case of long duration of the first pulse corresponds to the widely-used technique of differential pulse voltammetry. The advantage of using shorter durations for the first pulse (ie using differential normal pulse voltammetry) when examining irreversible reactions is shown.     

Mechanism of the electroreduction of 1,1-dicyanoethylene derivatives

The electroreduction behaviour of some substituted 1,1-dicyanoethylene derivatives in acetonitrile was investigated. The mechanism for the electroreduction of different substituted compounds was proposed using the results of cyclic voltammetry, rotating disc voltammetry, dc and differential pulse polarography and controlled potential electrolysis experiments. The effect of the presence of protons on the mechanism was also elucidated. The products of large scale electrolysis experiments were identified by the aid of electroanalytical and chromatographic methods.     

Electrochemical study of cerium(IV) in the presence of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetate (DTPA) ligands

The electrochemical behaviour of the complexation of cerium(IV) with EDTA and DTPA was studied using both cyclic voltammetry (CV) and rotating disc electrode (RDE). The Ce(IV)–DTPA complex at various scan rates gave a linear correlation between the peak potential (E _p ) and square root of scan rate, showing that the kinetics of the overall process was controlled by mass transport. However, when the EDTA ligand was added to the Ce(IV) there was no specific change to the potential peak, i.e. the Ce(IV)–EDTA complex has the same redox potential as the Ce(IV)/(III) couple. Kinetic parameters such as potential, limiting current, diffusion coefficients, transfer coefficient and rate constants were studied. The results from RDE experiments confirmed that the parameters measured by CV are similar under hydrodynamic conditions and can be used to determine the kinetic parameters of the redox couples. The use of DTPA as a ligand for complexation of Ce(IV) gaves more favourable results compared to the Ce–(EDTA) complex reported previously. The results of kinetic studies of Ce(IV)–DTPA complex shows promise as an electrolyte for redox flow battery.     

The electroreduction mechanism of Di- and tricyanobenzenes

The electroreduction behaviour of 1,2-, 1,4-, 1,3-dicyano- and 1,3,5-tricyanobenzenes in acetonitrile was investigated. The mechanism for the electroreduction of these compounds was proposed using the results of cyclic voltammetry, rotating disc voltammetry, dc and differential pulse polarography and controlled potential electrolysis experiments. The effect of the presence of protons on the mechanism was also elucitated. The products of large scale electrolysis experiments were identified by the aid of electroanalytical and chromatographic methods.     

Synthesis and solution properties of phthalocyanines substituted with four crown ethers

Metal-free and metal phthalocyanines (M = Ni, Zn, Co) substituted with four benzo-15-crown-5 units through oxy-bridges have been synthesized from a new phthalonitrile derivative, 1-{[(benzo-15-crown-5)-4′-yl]oxy}phthalonitrile (3). The newly prepared compounds have been characterized by elemental analyses, IR, ¹H NMR, MS and UV–Vis spectroscopy. Alkali metal interactions of the crown ethers on the zinc phthalocyaninato (6) are shown to form intermolecular adduct. The electrochemical properties of ZnPc were investigated by using cyclic voltammetry and controlled potential coulometry.     

Electrochemical study of the activating solution for electroless plating of polymers

This paper presents an electrochemical study about the activating solutions of the electroless plating of polymers, containing Pd(II), Sn(II) and Sn(IV) mixtures in HCl as main components. The objective of the study is the voltammetric characterization of these solutions by cyclic and linear voltammetry in order to study the recovery of tin and palladium from these solutions. The effect of concentration and rotation rate on the current−potential curves was studied using the RDE technique. The electrochemical behaviour of solutions prepared in the laboratory was performed as a prior step to the further study of real activating rinsing solutions. The electrochemical reduction of Pd(II) takes place in two one-electron transfer steps which are mass transport controlled. The electrochemical reduction of Sn(II) and Sn(IV) is also mass transport controlled and takes place with direct formation of metallic tin, although the electrochemical reduction of Sn(IV) only takes place in solutions with HCl concentrations higher than 1 M. The presence of additives in the real solutions prevent the chemical reduction of Pd(II) and the formation of Sn(IV) hydroxylated complexes. This causes the appearance of well defined diffusion waves attributable to the electrochemical reduction of Pd(II) and Sn(IV). Hence, the recovery of both species simultaneously as well as separately could be carried out, if appropriate conditions are selected.     

Electrochemical investigations into host-guest interactions of a natural antioxidant compound with β-cyclodextrin

The electrochemical behavior of mangiferin (MGN), a natural antioxidant compound, is examined using cyclic and differential pulse voltammetry in a protic medium on a glassy carbon electrode. The voltammograms exhibit a single irreversible pH-dependent anodic wave with current controlled by adsorption.Complexes of MGN with β-cyclodextrin (β-CD) were prepared and their formation was confirmed by UV-vis spectroscopy and electrochemical experiments, using a self-assembled monolayer of cyclodextrin on a gold electrode. The association constant of MGN:β-CD complexes was estimated by the Benesi-Hildebrand method, based on the spectrophotometric quantification of free β-CD and by the direct method using cyclic voltammetry and the Langmuir isotherm.PM IRRAS experiments corroborated the inclusion process based on the observation of the corresponding peaks in the spectra of the samples.MGN was quantified using a simple electrochemical method based on a β-CD incorporated carbon nanotube (CNT)-modified electrode (β-CDCNT). The presence of β-CD led to a 10-fold lower detection limit than that obtained with a CNT-modified electrode.     

Electrochemical characterization of two different framework Ti(IV) species in Ti/Beta zeolites in contact with solvents

Five Ti/Beta zeolites prepared by the conventional hydroxide procedure or by using fluoride as mineralizer have been studied by cyclic voltammetry and pulse voltammetry. Three peak couples (AA′, BB′ and CC′) were recorded. The AA′ peak was due to Ti atoms leached to the solution. Peak BB′ is relatively insensitive to the electrolyte salt, while the reduction potential of CC′ decreases progressively from perchlorate or nitrate to chloride and bromide. This suggests the presence of two framework Ti populations, one less prone to expand its coordination number (proposed to be Ti(OSi≡)₄) and other Ti atoms that coordinate with ligands within the short timescales of the electrochemical measurements (either (≡SiO)₃TiOH or (≡SiO)₂Ti(OH)₂ titanols). This revised version was published online in August 2006 with corrections to the Cover Date.     

一系列硫代双烯镍近红外染料的合成及性能

该文分别通过安息香路线和二酮路线合成了4种具有不同取代基的硫代双烯镍近红外染料,并考察了染料的物理、光电化学及热稳定性等性质。紫外-可见-近红外(UV-Vis-NIR)吸收光谱测试结果表明,配合物在700～1 100 nm都具有较强的吸收。对化合物的取代基效应及溶剂效应的研究发现:供电子基团导致λmax红移,而吸电子基团导致λmax蓝移,且λmax随着溶剂极性增大而增大。利用循环伏安法和差分脉冲伏安法(CV/DPV)测试了化合物的电化学性质。此外,该文还通过密度泛函理论(DFT)对化合物的HOMO和LUMO能级进行了计算。热失重测试研究表明,合成的化合物具有较好的热稳定性。     

A biosensor platform based on amine functionalized conjugated benzenediamine-benzodithiophene polymer for testosterone analysis

A novel benzenediamine-benzodithiophene polymer is synthesized for use in biosensor fabrication for the detection of testosterone. The sensory platform is constructed via drop coating on a screen-printed carbon electrode, using poly(benzenediamine-Bis[(2-ethylhexyl)oxy]benzodithiophene) (pBDBT) as the polymer layer. Testosterone antibodies are immobilized on the polymer-coated electrode surface via glutaraldehyde, which binds to the surface through the amino functional groups on the polymer backbone. The changes in the surface features due to testosterone binding are investigated via electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectrometry as well as contact angle measurements. Surface morphology of the modified electrodes is characterized by atomic force microscopy. The linear range and limit of detection of the sensor are calculated. Impact of possible interfering compounds is investigated. Furthermore, the sensory platform is utilized for testosterone analysis in synthetic biological fluids.     

Electroanalysis of the binding and adsorption of Hg with seleno aminoacids by differential pulse and elimination voltammetry at the Au-disk electrode

The complexation of Se-aminoacids selenomethionine (SeMet) and selenocystine (SeCyst) with Hg²⁺ was investigated by differential pulsed voltammetry (DPV) on Au-disk electrode. Complexation processes are proposed from the Gaussian Peak Adjustment analysis of DPV titration data. Main complexes were both 1:1 Hg:SeMet and Hg:SeCyst, although the formation of 2:1 complexes can be also proposed for Hg:SeCyst. Elimination voltammetry with linear scan was applied to investigate the adsorption of the ligands and the complexes on the Au surface.     

Voltammetry and spectroelectrochemistry of solid indigo dispersed in carbon paste

Cyclic voltammetry, square wave voltammetry and double potential step UV-vis spectroelectrochemistry were used to study the redox processes of indigo microparticles dispersed in a solid carbon paste electrode. The spectroelectrochemical measurements were performed in a home-made long-path-length thin-layer electrolysis cell. Both the indigo/leucoindigo and indigo/dehydroindigo redox couples underwent reversible 2e⁻/2H⁺ surface-confined reactions. Alkaline electrolytes showed more negative effect on the reduction of indigo to leucoindigo than on its oxidation to dehydroindigo. A new species (probably indolone) was monitored in the re-oxidation of leucoindigo, while isatin was found in the oxidation of indigo at enough positive potential. More detailed electrochemical mechanisms were proposed for the two redox systems, respectively. The present work shows that the microparticle-dispersed carbon paste is an attractive electrode material not only for solid state voltammetry but also for stripping spectroelectrochemistry.     

微分脉冲阳极溶出伏安法测定氢溴酸右美沙芬

应用循环伏安法和微分脉冲阳极溶出伏安法在玻碳电极上对氢溴酸右美沙芬的伏安行为进行了研究。实验结果表明,在pH6.5的B-R(Britton-Robinson)缓冲底液中,氢溴酸右美沙芬在+1.01 V(vs.Ag/AgCl)处有一明显的氧化峰,在4.0×10-6~8.0×10-5mol/L范围内与峰电流呈良好的线性关系(r=0.995 1),检出限为5.6×10-7mol/L。用该方法对氢溴酸右美沙芬片进行了测定,回收率为98.6%~102.9%,结果令人满意,还对其电极反应机理进行了初步探讨。     

The synthesis,spectroscopy, electrochemistry and photophysical properties of novel,sandwich europium(III) complexes with a porphyrin ligand bearing four pyrenyl groups in meso-positions

Novel, metal free porphyrins containing four pyrenyl groups in the meso-positions were used to provide novel, sandwich-type mixed tetrapyrrole europium double- and triple-deck complexes. The sandwich-type complexes together with the metal free porphyrin were characterized using electronic absorption, IR and ¹H NMR spectroscopy in addition to elemental analysis. The electrochemical behaviour of the sandwich complexes was investigated by cyclic voltammetry and differential pulse voltammetry in CH₂Cl₂, their photophysical properties were studied in comparison to those of the metal free porphyrin ligand. Fluorescence quenching observed was tentatively attributed to efficient and rapid energy transfer from the pyrenyl groups to porphyrin followed by electron transfer from porphyrin to phthalocyanine.     

Attomole voltammetric determination of metallothionein

Number of authors have concerned with electrochemical analysis of metallothionein. Recently new electroanalytical techniques enabling determination of MT at picomole level has been suggested. The aim of the presented work was to show advantages and disadvantages of the different electrochemical procedures, which are commonly used for the detection of MT—(i) cyclic voltammetry, (ii) differential pulse voltammetry, and (iii) Brdicka reaction. Primarily we aimed on improvement of the mentioned techniques. Using of reducing agent (tris(2-carboxyethyl)phosphine) and combination of the mentioned method with adsorptive transfer stripping technique (AdTS) were the main improvements of the voltammetric method. The detection limits of metallothionein measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and DPV Brdicka reaction were 0.5 pmol, 4 fmol and 10 amol, respectively. In addition AdTS DPV Brdicka reaction was used for the determination of metallothionein in human blood serum of 11-year-old girl, which were lead poisoned.