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While used in minor proportion respect to other components in cathode formulations, binders play a crucial role in lithium batteries cathode. This is particularly true in Li-O2 batteries which represent a very harsh environment mainly because of the formation, upon cycling, of very aggressive superoxide radicals. In such batteries, the use of catalyst in the cathode formulation is quite usual to help oxygen reduction reaction and oxygen evolution reaction (ORR and OER) to proceed rapidly and reversibly. However, the slightest binder degradation upon cycling can hinder the catalyst effects dramatically, modifying them to act on other reactions associated with the generated side-products, thus deteriorating cell performances and preventing researchers from drawing the right conclusions about catalytic properties of new materials. In this work, the influence of different catalysts in the degradation of the PVDF binder, on the performance of Li-O2 batteries, was investigated. The results obtained were compared with the ones of cathodes prepared with the same catalysts but Li-Nafion binder instead (already reported as stable), to further demonstrate that the choice of binder must be strongly linked to the nature of the catalyst. The catalysts employed for this study were α-MnO2, and commercial Co3O4, and Co phthalocyanines (CoPc).

Antimony(III) is a rare electroactive specie present on Earth, whose concentration is not typically determined. The presence of high concentrations of antimony is responsible for a variety of diseases, which makes it desirable to find convenient and reliable methods for its determination. We have developed a convenient glassy carbon modified electrode with electroreduced graphene oxide GC/rGO for the first time determination of Sb(III) in commercial lettuce, celery, and beverages. The surface of the electrode was characterized by scanning electron microscopy (SEM) and cyclic voltammetry, indicating a heterogeneous and rough surface with a real area of 0.28 cm2, which is ~2.5 times the area of GC. The optimal chemical and electrochemical parameters used were: sodium acetate buffer (pH = 4.3), an accumulation potential of −1.0 V and an accumulation time of 150 s. The analytical validation was developed evaluating the linear range (10–60 µg L−1), limit of detection (2.5 µg L−1), accuracy, repetibility and reproducibility with satisfactory results (relative standard deviation (RSD) values lower than 10%). All the analyzes performed in real samples by stripping voltammetry were compared with GF-AAS, showing statistically similar values, demonstrating that GC/rGO could be effectively applied in the analysis of food samples.

The use of light in metallic complexes has been widely studied in the photoelectrocatalytic performance of the hydrogen evolution reaction (HER). This reaction produces gaseous hydrogen with potential use as a fuel in clean energy conversion systems, such as fuel cells. In this context, metalloporphyrins have shown remarkable activity in the catalysis of HER, which directly depends on the metallic center of the complex. In order to analyze the electrocatalytic effect of materials composed by a mixture of cobalt and iron octaethylporphyrins over graphite paste electrodes in the study of HER, in the absence and in the presence of light, we use voltammetric techniques to analyze the potential shift. In addition, a characterization of the electrodes by electrochemical impedance spectroscopy is carried out, showing a decrease in the charge transfer resistance of the modified electrodes when they are exposed to light. A determination of gaseous hydrogen produced through the use of this material was carried out by gas chromatography. In this research, the mixture of metalloporphyrins over the graphite paste electrode is more active than the independent complexes and it also improves the electric properties in the presence of light, obtaining gaseous hydrogen in an energy-efficient way. The TON found in this research (8100) is higher than in works performed with other systems, having as advantages stability and easy preparation.

The water-soluble porphyrin, known as 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP), was successfully stabilized onto a carbon paste electrode (CP) by covering up the TMPyP-modified surface with a layer of ionic liquid (IL), particularly 1-butyl-3-methyl imidazolium hexafluorophosphate (BMim PF6) or 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide (BMim NTf2). Noncovalent interactions established between TMPyP and ILs combined with the hydrophobicity of the latter yielded a new class of modified electrodes, denoted as CP/TMPyP/IL. These new systems exhibited higher electroactive areas as compared to those of CP and CP/IL electrodes, as well as a stable and reproducible electrochemical behavior in aqueous solutions. The obtained CP/TMPyP/BMim PF6 and CP/TMPyP/BMim NTf2 electrodes were used as electrochemical sensors for nitrite oxidation. The positive results showed that these electrodes can be considered as an alternative for nitrite detection in the concentration range under investigation.

In this work, the design and manufacture of graphite paste (Gr) electrodes is carried out, including N-octylpyridinium hexafluorophosphate (OPyPF6) ionic liquid (IL) as binder and modification with Co-octaethylporphyrin (Co), in order to study the hydrogen evolution reaction (HER) in the absence and presence of light. The system is characterized by XRD and FESEM-EDX (Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy), confirming the presence of all the components of the system in the electrode surface. The studies carried out in this investigation confirm that a photoelectrocatalytic system towards HER is obtained. The system is stable, efficient and easy to prepare. Through cyclic voltammetry and electrochemical impedance spectroscopy, was determined that these electrodes improve their electrochemical and electrical properties upon the addition of OPyPF6. These effects improve even more when the systems are modified with Co porphyrin. It is also observed that when the systems are irradiated at 395 nm, the redox process is favored in energy terms, as well as in its electrical properties. Through gas chromatography, it was determined that the graphite paste electrode in the presence of ionic liquid and porphyrin (Gr/IL/Co) presents a high turnover number (TON) value (6342 and 6827 in presence of light) in comparison to similar systems reported.

This work describes the electrochemical, spectroscopic and electrochemiluminescent (ECL) characterization of graphite screen-printed electrodes (SPE) modified with a multilayer electrostatic assembly between 3-aminopropyltriethoxysilane (APTES) and CdTe quantum dots stabilized with glutathione (GSH) as the cationic and the negative layers, respectively. The characterization of the obtained system was performed by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy and Raman spectroscopy, which confirm the homogeneous presence of CdTe quantum dots on the multilayer assembly. The electrochemiluminescent properties were measured in a potentiostat coupled with a photodiode detector, showing stable and repetitive electrochemiluminescent signals. The ECL response was studied using potassium persulfate and hydrogen peroxide as co-reactants, and the measurements were carried out at different scan rates, pH values and concentrations. The ECL properties of the studied system at specific experimental conditions demonstrated different mechanisms by changing the co-reactants associated with the electrochemical step to generate the radical species and its interaction with the SPE/APTES/CdTe (GSH) reduced system, obtaining a more intense ECL signal with H2O2 than with S2O82−. Some analytical parameters, such as the linear range and the limit of detection for SPE/APTES/CdTe (GSH) in ECL H2O2 detection, were obtained.

Carbon paste electrodes modified with a family of ionic liquids (as binders) derived from N-octyl-pyridinium hexafluorophosphate, (composite-ionic liquid electrodes (CILEs)) were studied toward the oxidation of sulfite as an inner-sphere probe reaction and compared to a conventional carbon paste electrode (CPE) in which the binder was mineral oil. The ionic liquids were modified at para -position with substituents that are electron withdrawing: -CN (CILE/CN) and –CF3 (CILE/CF3) and substituents that are electron donating: -CH3 (CILE/CH3) and –OCH3 (CILE/OCH3), and compared with the ionic liquid without substituents (CILE/OPy). The results showed that CILEs are capable of catalyzing the sulfite oxidation, shifting the oxidation potential to more negative values compared to CPE. Also, they showed linear correlations between increasing sulfite concentration and increasing current density. The best system in terms of sensitivity was the electrode modified with the 4-methyl-N-octylpyridiniumhexafluorophosphate CILE/CH3 and, then, that modified with the non-substituted ionic liquid CILE/OPy measured by amperometry. In terms of potential, the best systems are the CILEs modified with ILs with inductive-substituents, -CH3 and –CF3 and OPy, indicating that the delocalization of the charge of the cation produced by the mesomeric-substituent (-OCH3, -CN) diminishes the electrocatalytic behavior of these binders for that oxidation. On the other hand, the analytical parameters of all the amperometric sensors studied here (all CILEs excepts CILE/OCH3) are good enough to be applied in food industry for samples without polyphenols at concentrations higher than ca. 1mM of sulfite. Their stability is very high (at least 100 cycles after obtaining a stable response without changing its current, exposed to air and humidity) and they can be used to remove sulfite from wastewaters. Finally, to our knowledge, there are not comparative studies about the effect of changing the substituent of the cation in electrocatalysis of modified IL-electrodes.

A series of N-octylpyridinium hexafluorophosphate ionic liquids (ILs), ascribed as ROpyPF6, where Opy = N-octylpyridinium and R are the substituents OCH3, CH3, CF3 and CN at the para position of the cation, were characterized and employed as binders in carbon paste electrodes (CILEs) to evaluate the electron donating or withdrawing effects of the substituent of the cation in physical and electrochemical properties of these CILEs. Substituents strongly affect the melting point of the ILs, the electric properties of the CILEs measured by electrochemical impedance spectroscopy, and the electrochemical behavior measured by the response for an outer-sphere reaction (ferro/ferricyanide redox couple) and for an inner-sphere irreversible reaction (oxidation of sulfite). Results show that ILs can be separated in two different groups: those that have withdrawing electron substituents and those that have donating-electron substituents. OpyPF6 has a behavior similar to those that have withdrawing electron substituents. Carbon paste electrode prepared with mineral oil as binder (CPE) has a very different behavior and is described for comparison purposes only. Results show that the ILs with withdrawing electron substituents have more polarized cations (a more localized positive charge) acquiring a slight ionic character in comparison to the ILs with donating substituents. The electron withdrawing effect modifies the hydrogen-fluorine interactions and also the electrostatic interactions between anion and cation, modifying the electric and electrochemical response of the CILEs, resulting in more conductive and homogeneous surfaces.

An inexpensive and environmental friendly electrochemical sensor based on a glassy carbon electrode (GC) modified with graphene quantum dots (GQDs) and Nafion (NF) has been developed for the determination of Cd(II) and Pb(II) in bivalve mollusks using square wave anodic stripping voltammetry (SWASV). GQDs were characterized by UV–Vis spectroscopy, fluorescence and transmission electronic microscopy (TEM). The modified electrode was evaluated by cyclic voltammetry, scanning electronic microscopy (SEM) and electrochemical impedance spectroscopy (EIS). A linearity of 20–200 μg L−1 was found, with a limit of detection (LOD) of 11.30 μg L−1 for Cd(II) and 8.49 μg L−1 for Pb(II). The proposed methodology was validated with a certified reference material TMDA-64.2. The reproducibility of GC/GQDs-NF for both species had an RSD of less than 10%. The results were compared with ICP-OES. The method was applied in the determination of Cd(II) and Pb(II) in bivalve mollusks samples with excellent results.

A mixed electrocatalyst that consists of multi walled carbon nanotubes (MWCNTs) and the ionic liquid (IL) N-octylpyridinum hexafluorophosphate (OPyPF6) as binder (MWCNT/IL system) was used in the study of hydrogen evolution reaction. This electrocatalyst was compared to graphite/mineral oil (Gr), graphite/OPyPF6 (Gr/IL), MWCNT/mineral oil (MWCNT) systems. All systems were characterized by cyclic voltammetry determining that MWCNT/IL system is highly electrocatalytic (E onset = -0.3 V vs Ag/AgCl) in relation to the other systems studied containing MWCNT or IL separately. The presence of each of the components that form the electrodic surface is corroborated by XRD, Raman, and FESEM-EDX, and it is demonstrated by chronoamperometric analysis that MWCNT/IL system is highly stable. The efficiency of the electrode, determined by its electrocatalytic activity, is confirmed by the quantification by gas chromatography of the hydrogen produced. Moreover, an elevated TON value (16274) and faradaic efficiency close to 60% are calculated, in comparison to other electrocatalysts found in literature. All these attractive properties are complemented by the fact that the MWCNT/IL system is simple, novel and easy to prepare.

In this work, a cationic porphyrin, ascribed as [Ttolyl(P-(C6H5)3)4]4+, where Ttolyl = 5,10,15,20 tetrakistolylporphyrin, was electrostatically assembled with CdTe quantum dots capped with glutathione (GSH) of diameter ~3.28 nm via a layer-by-layer methodology. This multilayer assembly was evaluated as a biocompatible interface with synergic effects for calf thymus double-stranded DNA (CT DNA) immobilization, considering that the hybrid assembly contains a cationic porphyrin with a high binding constant for CT DNA, and quantum dots with polypeptide as a capping agent. The multilayer assembly, ascribed as ITO/{[Ttolyl(P-(C6H5)3)4]4+/CdTe} n (n = 1–5), was characterized by UV-Vis spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The last technique was explored in order to check the adsorption of CT DNA onto the multilayer porphyrin/quantum dot assembly. The difference in electron transfer resistance (ΔR ct) obtained after CT DNA incubations showed the best result for a specific multilayer assembly, n = 3. {[Ttolyl(P-(C6H5)3)4]4+/CdTe}3 showed a good correlation of ΔR ct with the logarithmic concentration of CT DNA, in the range 1.0 × 10−10 to 1.0 × 10−6 M with a limit of detection (LOD) of 1.5 × 10−12 M. Conversely, when the {[Ttolyl(P-(C6H5)3)4]4+/CdTe}3 system was incubated with calf thymus single-stranded DNA and salmon testes DNA, no significant difference in ΔR ct was observed. We conclude that the newly described {[Ttolyl(P-(C6H5)3)4]4+/CdTe} n system is a choice method for the impedimetric determination of CT DNA.

The oxygen reduction reaction (ORR) is the most important reaction in life processes and in energy transformation. The following work presents the design of a new electrode which is composed by deposited cobalt octaethylporphyrin onto glassy carbon and graphene, where both carbonaceous materials have been electrochemically oxidized prior to the porphyrin deposition. The novel generated system is stable and has an electrocatalytic effect towards the oxygen reduction reaction, as a result of the significant overpotential shift in comparison to the unmodified electrode and to the electrodes used as target. Kinetic studies corroborate that the system is capable of reducing molecular oxygen via four electrons, with a Tafel slope value of 60 mV per decade. The systems were morphologically characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) Electrochemical impedance spectroscopy studies showed that the electrode previously oxidized and modified with cobalt porphyrin is the system that possesses lower resistance to charge transfer and higher capacitance.

Hydrogen peroxide (H2O2) plays an important role as an intermediary in different biological, chemical and environmental systems. It has been widely used as an oxidizing and antimicrobial agent, in germicides production and textile and paper bleaching. However, it is well known, that H2O2 is a possible responsible in many diseases and is a chemical agent that threatens the environment, so it becomes important to detect peroxide with high accuracy. In this study, carbon paste electrode (CPE), modified with Co2SnO4 was synthesized and tested. It was successfully obtained a non-enzymatic H2O2 detection type sensor, based on Co2SnO4/ CPE composite, showing good linear response in concentration of H2O2 in the range of 88 - 605.9 μM.

In this work, we present a comparison among three glassy carbon electrodes modified by Co-porphyrin, ortho-phenylenediamine, or both simultaneously. This comparison shows the differences among the electrochemical behavior, morphological characteristics and electrocatalytic behavior toward the sulfite oxidation of these electrodes. The electrode modified by Co-porphyrin, ortho-phenylenediamine and copolymer has been investigated in detail for the comparision of electrocatalytic activity towards the sulfite oxidation. In the case of the glassy carbon-modified electrodes, the presence of the copolymer enhances the electrocatalytic performance of the modified electrodes in spite of the non-catalytic response (compared to the bare glassy carbon) of both homopolymer-modified electrodes toward the oxidation of sulfite. Additionally, the oxidation of sulfite extracted from red wine is shown. The copolymer-modified electrode is capable of oxidizing the extracted free sulfite in a 0.02 M NaOH solution. Through the addition of standards method, a concentration of free sulfite in a Chilean red wine sample was determined to be 44 ppm.

The sulfite is commonly used antiseptic wine and food. You can find free or bound to phenols , aldehydes and other organic compounds. Its concentration at high levels produces toxic effects, such as pain when breathing in asthmatic patients , hypotension and gastrointestinal problems. Therefore it is useful to determine the electrochemically concentration , and with this, to separate , by absorbing membrane system , the other impurities present in food. Sulfite (SO3 -2) in aqueous solution is in equilibrium with bisulfite ( HSO3 - ) and sulfur dioxide ( SO2) , where their concentrations depend mainly on the pH. As to the electrochemical method , the cyclic voltammetry was used. This technique is widely used and is of considerable use in the study of oxide / reduction , detection of reaction intermediates and observing reactions monitoring electrode products formed in reactions . In conjunction with the cyclic voltammetry method of calibration curve is applied and thus determine how feasible it is to implement in an electrochemical analysis. The method of calibration curve represents the response of an analytical method to known concentrations of analyte . Previous studies done in the laboratory show that it is possible to find a potential range where the SO3 -2 shows an increasing response in current and potential displacement , and in addition, all the parameters are optimized for system performance membrane absorber .

In this work, we studied carbon paste electrodes (CPEs) with two kinds of binders: mineral oil or ionic liquids (IL) derived from N-substituted octyl pyridinium bis(trifluoromethylsulfonyl)imide with the substituents H-, CH3-, CN- and CF3-. The work aims to study this series of IL and determine a possible effect of the substituent of the cation in the behavior of the IL as a binder of graphite for obtaining IL-CPEs. The electrochemical response and the electrical behavior were measured by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Surprisingly, the substituent does not affect the cyclic voltammetry response because in all the cases, high resistance and high capacitive currents were obtained. The best response in terms of conductivity is obtained by CPE. In the case of impedance measurements, the substituent does not cause differences, and in all the cases, the IL-CPEs show nearly the same responses. CPE shows lower capacitance and higher resistance for diffusion compared to the IL-CPEs due to his lower porosity. The high resistance showed by the IL-CPEs by cyclic voltammetry can be attributed to poorly intermolecular forces among graphite, water, electrolyte, and ILs as demonstrated by theoretical calculations.

Sulfites [Formula: see text] or sulfur dioxide (SO2) is a preservative widely used in fruits and fruit-derived products. This study aims to propose a membrane contactor process for the selective removal and recovery of SO2 from wines in order to obtain its reliable quantification. Currently, the aspiration and Ripper methods offer a difficult quantification of the sulfite content in red wines because they involve evaporation steps of diluted compounds and a colorimetric assay, respectively. Therefore, an inexpensive and accurate methodology is not currently available for continuous monitoring of SO2 in the liquids food industry. Red wine initially acidified at pH 2, which is evaporated through the membrane pores filled with gas. Thus, SO2 is trapped in a colorless solution and the membrane contactor controls its transfer, decreasing experimental error induced in classical methods. Experimental results using model solutions with known concentration values of [Formula: see text] show an average extraction percentage of 98.91 after 4 min. On the other hand, two types of Chilean Cabernet Sauvignon wines were analyzed with the same system to quantify the content of free and total sulfites. Results show a good agreement between these methods and the proposed technique, which shows a lower experimental variability.

This research demonstrates how the sulfite content can be measured by cyclic voltammetry using a previously reported membrane absorber system, which separates efficiently sulfite present in wine. Results obtained show notably similar values to those obtained for the same wine samples using modified Monier- Williams method (aspiration method) and Ripper method. The membrane absorber system allows the release of the free SO2, and can be used to determine the sulfur dioxide present in juices and other foods that contain high concentrations of phenols, polyphenols and other structurally related compounds that act as interferers in the electrochemical oxidation of sulfite. The absorber solution allows a direct measurement without change in pH or added electrolyte, facilitating the determination of great amounts of samples from diverse wines using only one calibration curve. In this way, a system that allows the detection of sulfite and that can be used in vineyards is obtained. Finally, the method was assessed on linearity, sensitivity, accuracy, reproducibility and repeatability, obtaining values that account for the applicability of the method.

In the present work, known concentration of sulfite aqueous solutions in the presence and absence of gallic acid was measured to corroborate the validity of modified Monier-Williams method. Free and bound-sulfite was estimated by differential pulse voltammetry. To our surprise, the modified Monier-Williams method (also known as aspiration method) showed to be very inaccurate for free-sulfite, although suitable for bound-sulfite determination. The differential pulse approach, using the standard addition method and a correction coefficient, proved to be swift, cheap, and very precise and accurate.

This paper describes the electrochemical reduction of nitrite ion in neutral aqueous solution mediated by tetraruthenated metalloporphyrins (Co(II), Ni(II) and Zn(II)) electrostatically assembled onto a Nafion film previously adsorbed on glassy carbon or ITO electrodes. Scanning electron microscope (SEM-EDX) and transmission electron microscopy (TEM) results have shown that on ITO electrodes the macrocycles forms multiple layers with a disordered stacking orientation over the Nafion film occupying hydrophobic and hydrophilic sites in the polyelectrolyte. Atomic force microscopy (AFM) results demonstrated that the Nafion film is 35 nm thick and tetraruthenated metalloporphyrins layers 190 nm thick presenting a thin but compacted morphology. Scanning electrochemical microscopy (SECM) images shows that the Co(II) tetraruthenated porphyrins/Nf/GC modified electrode is more electrochemically active than their Ni and Zn analogues. These modified electrodes are able to reduce nitrite at −660 mV showing enhanced reduction current and a decrease in the required overpotential compared to bare glassy carbon electrode. Controlled potential electrolysis experiments verify the production of ammonia, hydrazine and hydroxylamine at potentials where reduction of solvent is plausible demonstrating some selectivity toward the nitrite ion. Rotating disc electrode voltammetry shows that the factor that governs the kinetics of nitrite reduction is the charge propagation in the film.

Summary: This paper describes the electrochemical reduction of nitrite ion in 0.1MNaClO 4 , on glassy carbon or ITO electrodes modified with mixtures PVC- tetraruthe-nated metalloporphyrins. This electrode is able to keep the extraordinary electro-catalytic properties of the macrocycle allowing multielectronic transfers and a greatstability as a consequence of the inclusion of the macrocycles into a polymericsupport such as PVC. On the other hand, the electrochemical reduction of nitrite ionon these modified electrodes studied by cyclic voltammetry shows an enhancementin the current values and lower overpotential compared with the activity of the bareglassy carbon electrode. Controlled potential electrolysis experiments verify theproduction of ammonia, hydrazine and hydroxylamine, showing the electrocatalyticcharacter and the stability of this modified electrode. Keywords: electrocatalysis; modified electrodes; nitrite; PVC; tetraruthenated porphyrins Introduction Nitrite ions are produced by photolysis ofnitrate ions and by photodegradation ofaquatic humic substances present in theaquatic environment. Nitrite is a keyspecies in global nitrogen cycle. Nitritesshow environmental and biological impor-tance. Moreover, they have an importantrole as additive in the alimentary industryas preservative, antimicrobial and colorfixative agent.

A new conducting film derived from the complex [Fe (diaphen)3]2+, (diaphen=5,6-diamino-1,10-phenanthroline) was electropolymerized by cyclic voltammetry onto a glassy carbon electrode. Poly-[FeII (diaphen)3] was studied by cyclic voltammetry, SEM, UV-vis and micro-Raman spectroscopy. Poly-[FeII (diaphen)3] shows electrocatalytic activity in HSO3− reduction in an ethanol/water solution. Electrocatalysis is centered at the π ring of phenanthroline. Rotating disk electrode studies showed a 0.117 V/dec Tafel slope, suggesting an EC process where the electrochemical process is the determining step. The chemical step was studied by UV-vis spectroelectrochemistry. Amperometric behavior showed a linear range between 47.5 µM to 417 µM and the LOD was 19.5 µM.

This work describes the preparation of modified electrodes with Poly-tetraruthenated porphyrin. Also, a detailed Raman and electrochemical characterization of these surfaces is shown. Glassy carbon electrodes were modified with Ni (II), Zn (II) and metal free polymeric film of tetrapyridylporphyrin coordinated to four [Ru(5-NO2-phen)2Cl]+ moieties. These modified electrodes are very stable in aqueous solutions, and were evaluated for the electrochemical reduction of nitrite ion at pH = 5.9 in 0.1 M NaClO4. When the solution contains 0.01 M nitrite, linear sweep voltammetry results, show an enhancement in the current from −0,3 V with the conducting polymers, compared to the bare electrode behavior. Analyses after controlled potential electrolysis experiments verify the production of hydrazine, hydroxylamine and ammonia. Hydroxylamine was the product of higher production among the three studied catalysts. The behavior of the modified electrodes allows predicting that the reduction process of nitrite takes place through reduced macrocycle ring. The electrocatalytic activity of the modified electrodes, measured as turn over frequency is dependent on the potential and the central ion in the cavity of the macrocycle. Finally, the modified electrode containing Ni2+ in the cavity of the macrocycle was used as an amperometric sensor toward nitrite detection. The results show a limit of detection of 9.37 × 10−6 M and a linear rage of concentration of 1.49 × 10−5 to 1.24 × 10−4 M.

The fungotoxicity against Botrytis cinerea of a flavonoid isolated from Pseudognaphalium robustum was analyzed. Two absorption column chromatographies and one semipreparative thin layer chromatography were used to purify the active flavonoid. It was determined, by 1H-NMR spectroscopy and co-elution with standards in HPLC, that this compound was 5,7-dihydroxy-3,8-dimethoxyflavone (gnaphaliin A). To determine the fungitoxicity of the purified compound, the effect on in vitro mycelial growth and conidial germination was studied. The compound concentration that reduced mycelial growth by 50% was 45.5 mg/mL. This compound also partially affected conidial germination of B. cinerea, reduced oxygen consumption by germinating conidia and affected the integrity of plasma membrane. Finally, using cyclic voltammetry, it was shown that the purified flavone had a pro-oxidant effect.

In contrast to the UV-photoinduced ligand photoionization of the flavonoid complexes of FeIII, redox reactions initiated in ligand-to-metal charge-transfer excited states were observed on irradiation of the quercetin (1) and rutin (2) complexes of CuII. Solutions of complexes with stoichiometries [CuIIL2] (L=quercetin, rutin) and [CuII2Ln] (n=1, L=quercetin; n=3, L=rutin) were flash-irradiated at 351 nm. Transient spectra observed in these experiments showed the formation of radical ligands corresponding to the one-electron oxidation of L and the reduction of CuII to CuI. The radical ligands remained coordinated to the CuI centers, and the substitution reactions replacing them by solvent occurred with lifetimes τ 1 ms) of the quercetin and rutin radical's decay.

Oenologists and wine exporters know that a serious problem is to determine the quality of wine after it travels to final market. In fact the last quality controls are made after the bottling and before the trip. Chile is an important exporter of wine and Asiatic markets are a common destination for this exportation, taking long times of traveling. If wine changes it quality due to different stressing situations during the trip, the final costumer will receive a low-quality beverage in spite of the high quality of the original wine. This fact can reduce the interest of the costumer to consume Chilean wine and diminishes the importations of this product.

This work describes the preparation of a new tetraruthenated porphyrin and the corresponding polymeric film. This macromolecule consists of a Ni(II) tetrapyridylporphyrin coordinated to four [Ru(5-NO 2 -phen) 2 Cl] + moieties. The 5-NO 2 -phen ligands are reduced at −0.90 V, generating a radical anion that is able to generate polymeric coatings onto glassy carbon (GC) electrodes. These polymeric films are very stable in aqueous solutions. The polymeric films are characterized by electrochemistry, infrared spectroelectrochemistry (IR-SEC) and atomic force microscopy (AFM).

The anthocyanin fractions were extracted from Cabernet Sauvignon red wine, skins of Vitis vinifera grapesand raspberry fruits (Rubus idaeus). In red wine extract, 16 anthocyanins were identified, malvidin-3-O-glucoside being the main anthocyanin, which comprised 53.6% of the total anthocyanin in grape extract.Raspberry extract contained mainly delphinidin-3-O-glucoside and cyanidin-3-O-glucoside. The antiox-idant capacity of the extracts was assayed by electrochemical methods. Best resolution of the oxidationpeaks for the extracts and diluted wine was obtained by pulse differential voltammetry. The wine diluted20 presented values of P1 (443 mV) and P2 (676 mV) similar to those corresponding to wine extract,and to the anthocyanin malvidin-3-O-glucoside. The antioxidant capacity of anthocyanins in extractsof wine, grape skin and raspberry fruit was also determined by the Trolox equivalent antioxidant capacity(TEAC) method. 2009 Elsevier Ltd. All rights reserved. 1. IntroductionRed wine is a complex system which contains a large variety ofphenolic compounds, such as flavonols, flavan-3-ols, anthocyaninsand phenolic acids. Anthocyanins are extracted from red grapesand are largely responsible for the colour exhibited by red wine;they play an important role in the antioxidant activity of red wine(Zoecklein, Fugelsang, Gump, & Nury, 2001). In red wine, anthocya-ninsinteractwithphenolicscompounds,pyruvicacidandacetalde-hyde to give new pigments (Francia-Aricha, Guerra, Rivas-Gonzalo,SFulcrand,Bernabdeljalil,Rigaud,Cheynier,M Mateus, Silva, Vercauteren, & De Feitas, 2001).The antioxidative capacity of anthocyanin was studied by differentchemical methods. The Folin–Ciocalteu method, the oxygen radicalabsorbancecapacity(ORAC)assayandtheTroloxequivalentantiox-idantcapacity(TEAC)assayarethemostconsideredmethods(Prior,Wu, & Schaich, 2005). Kilmartin and Hsu (2001) developed anelectrochemical method for the characterization of the antioxidantproperties of wine and wine phenolics. Recently, Janeiro andOliveira Brett (2007) studied the redox behaviour of anthocyaninsby voltammetric techniques, they found that all the phenolichydroxylgroupscanbeelectrochemicallyoxidized.DaSilva,RamosStradiotto,andOliveira(2008)developedamethodforthedetermi-nation of caffeic acid in red wine by differential pulse voltammetry.Zienlin´ska, Nagels, and Piskula (2008) determined the antioxidantcapacity of quercetin and its glycosides of onion by cyclic voltam-metry. Ghiselli, Nardini, Baldi, and Scaccini (1998) reported thatamong the red wine components, anthocyanins were the mosteffectiveinscavengingreactiveoxygenspecies(ROS)andinhibitinglipoprotein oxidation. Anthocyanins comprise around 70% of thetotalphenolsofItalianredwine.Inthisworkweevaluatedtheelec-trochemical behaviour of Chilean Cabernet Sauvignon red wine,Vitis vinifera grape and raspberry anthocyanin extracts in a modelwine solution at pH 3.6, and in acetate buffer.2. Materials and methods2.1. MaterialsCabernet Sauvignon red wine vintage 2005 and V. viniferagrapes were supplied by a local producer. Mature raspberry fruits(Rubus idaeus) were purchased in the local market. All the solventswere reagent grade and/or HPLC grade (Merck, Darmstadt,Germany), all the chemicals were reagent grade (Sigma, St. Louis,MO, USA).2.2. HPLC analysisFor the high performance liquid chromatography (HPLC) analy-sis a Waters 600 HPLC chromatograph (Waters, Mildford, MA, USA)equipped with a Waters 2990 diode array detector, and a

This work describes electrocatalytic detection of S(IV) compounds in water-ethanol solutions under acidic conditions, on a glassy carbon electrode modified with Co(II) tetraruthenated porphyrin electrostatically assembled onto a Nafion film. The Ipc current shows a linear relationship with the concentration of S(IV) oxo-anions. Controlled potential electrolysis shows that thiosulfate was detected as reaction product. Rotating disk electrode and UV-visible spectroelectrochemistry experiments showed a kinetic limitation to the electron transfer controlled by charge propagation in the film and the formation of an intermediary between Co center and S(IV) species. The reproducibility of the modification methodology presents a RSD of 4.1%.

In this work, the modification of a glassy carbon electrode with tetraruthenated porphyrins electrostatically assembled onto a Nafion film, previously adsorbed on the electrode surface, is reported. This modified electrode was characterized by scanning electron microscopy–energy-dispersive X-ray, Raman spectroscopy, UV-Vis spectroelectrochemistry, and cyclic voltammetry. The Nafion film onto the glassy carbon electrode shows a smooth disposition; when the tetraruthenated porphyrin is incorporated on the Nafion film, the complex is adsorbed in a homogeneous way. The modified electrode catalyzes HSO 3 − oxidation in water–ethanol solutions and shows an enhanced stability compared with the electrode modified with the dip coating method. Rotating disk electrode experiments showed a kinetic limitation to the electron transfer controlled by charge propagation in the film. I/E curves show a Tafel slope of 120 mV/decade corresponding to a first electron-transfer reaction, depending on the potential, as the determining step. Spectroelectrochemical experiments demonstrated that Ru(II) is the active site for the electrocatalysis.

The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the...

A neutral fraction (PS-SI) (0.3 g/L) with MW of 74 kDa, which contained galactose, arabinose, mannose, and glucose in the molar ratio of 1.0:0.6:0.4:0.2 was obtained by treatment of the whole polysaccharide extracted from red wine with cetrimide, followed by gel permeation chromatography. Spectroscopic and methylation analyses indicated that PS-SI is a mixture of neutral polysaccharides, consisting mainly of β (1→3)-linked galactopyranosyl residues, with side chains of galactopyranosyl residues at positions O- 6. Arabinofuranosyl residues linked α (1→5), α-mannopyranosyl and glucosyl residues appear to be components of different polysaccharides. The in vitro antioxidant capacity of fractions of wine polysaccharide was studied by hydroxyl radical scavenging and ORAC assays. Fraction PS-SI presented the strongest effect on hydroxyl radicals (IC 50 = 0.21).

The complex [FeII(Imz-phen)3](PF6)2, (Imz-phen = imidazolidine-[4,5-f]-1,10-phenanthroline) has been prepared and characterized using X-ray diffraction, UV–vis and IR spectroscopy, elemental analysis, fast atomic bombardment (FAB) mass spectrometry, and cyclic voltammetry. Its crystal lattice includes acetonitrile (π–π bound to phenanthroline), methanol, and water molecules. Scanning continuously between 1000 mV and 1650 mV in CH3CN, a modified electrode that includes the iron (II) complex is obtained; after the 25th continuous cycle a stable film is formed that is electrocatalytically active in the reduction of sulfur oxoanions. When the electrocatalytic properties are evaluated in ethanol/water solution, the current achieved from the electroreduction of these sulfur species is linearly dependent on the respective concentrations, suggesting potential application in sulfite determination.

A modified synthetic route for the complexes [Cu(II)5,7,12,14-tetramethyldinaphtho [b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)tmdnTAA], and [Cu(II) 5,7,12,14-tetramethyl-6,13-dichloro-dinaphtho[b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)dCltmdnTAA], is presented in this work. The electrochemical characterization of both complexes and their precursors, [bis(2,4-pentanedionato)copper(II)], [Cu(II)(acac)2] and [bis(3-chloro-2,4-pentanedionato)copper(II)], [Cu(II)(3-Cl-acac)2], respectively, under nitrogen and carbon dioxide is also presented. The voltammetric response of [Cu(II)(acac)2] and [Cu(II)(3-Cl-acac)2] are different compared to [Cu(II)tmdnTAA] and [Cu(II)dCltmdnTAA] under nitrogen. Precursors show the reduction of Cu(I) to Cu(0) and the tetraazadinaphtho[14]annulene complexes do not. The chlorine substituted complex has a lower reduction potential than the unsubstituted homologue under nitrogen atmosphere. However, the contrary response is obtained in the presence of carbon dioxide: the unsubstit...

Electro and photoelectrochemical reduction of nitrite in aqueous solution was studied using a multielectrocatalysts modified ITO electrode. ITO modification was carried out using the layer-by-layer (LBL) method, where sequential electrostatic assemblies were formed using a μ-(meso-5,10,15,20-tetra(pirydil)porphyrin)tetrakis{bis(bipyridine)chloride ruthenium (II)} [MTRP] n+ , coordinated in its central cavity with Mn(III), Zn(II) or Ni(II) as a cationic layer, and polyoxotungstate [SiW 12 O 40 ] 4− as the anionic layer. Electrochemical measurements and UV–vis spectroscopy were used to monitor the modification process. Optimal results were obtained when three layers were deposited onto the ITO surface and were stable in aqueous solution. The order of the multilayer formation was explored by comparing a modified electrode where [Zn(II)TRP] 4+ was the outermost layer with an electrode where [SiW 12 O 40 ] 4− was the outer layer. Results show that the best performing electrode is one with [SiW 12 O 40 ] 4− as the outer layer. Nitrite reduction on these electrode surfaces was studied in dark conditions and under light irradiation. Potential controlled electrolysis experiments were also performed, finding hydroxylamine, hydrazine and ammonia as the reduction products in dark conditions. Under light irradiation, only hydrazine and ammonia were found and, we observed an increase in the amount of obtained product. In this case, the electrolysis was carried out 150 mV less and half of time than in dark conditions. These results show that the combination of light and potential give rise to an improvement in the electrocatalytic properties of the modified electrodes. Continuous photolysis and IR spectroelectrochemical experiments were carried out to determinate the nature of this phenomena, evidencing the formation of an intermediary species between nitrite and [Mn(III)TRP] 5+.

Three glass electrodes covered with Co-cobaltite/SnO2:F (to obtain conducting glass electrodes) modified with p-Ni-tetraaminophenylporphyrin are described. In one electrode the porphyrin was absorbed on the electrode surface at room temperature, in another the porphyrin was electropolymerized on the electrode surface by cyclic voltammetry, and in the third the bare electrode was immersed in DMF containing the porphyrin and refluxed 6 h at 150°C. The three electrodes were tested as electrocatalysts for the oxidation of hydrazine and as potentiometric sensors of this chemical. The electrode modified by refluxing showed good electrocatalytic behavior as well as a linear relationship between its open circuit potential and the concentration of hydrazine in a concentration range from 0.16 to 12 µM, with fast response. These characteristics indicate that the conducting glass electrode of Co-cobaltite/SnO2:F covered with p-Ni-tetraaminophenylporphyrin by the reflux method is a good potentiometric sensor of hydraz...

5,15‐Bis(veratryl)porphyrin (1), 5,10,15‐tris(veratryl)porphyrin (2), and 5,10,15,20‐tetrakis(veratryl)porphyrin (3), C36H30N4O4, C44H38N4O6, and C52H46N4O8 were synthesized by an acid‐catalyzed, one‐pot reaction of meso‐dipyrromethane, 3,4‐di‐OCH3‐benzaldehyde (veratraldehyde), and trifluoroacetic acid (TFA). These three different products were obtained as a result of scrambling reactions. The molecular structures have been characterized by elemental analysis, ESI mass spectra, 1D and 2D NMR techniques (1H and 13C), and UV‐visible spectroscopy.

Reactions of photochemically or radiolytically generated radicals with tetrakis(x-aminophenyl)porphyrin, tapp2−, initiate the polymerization of the porphyrin complexes Mtapp, where M = Ni or Zn. In the photochemical process, the porphyrin-centered excited state of Mtapp reacts with the ground state to generate oxidized and reduced radical species. The cationic radical, M(tapp +), appears to be the initiator of the porphyrin polymerization. An electron transfer reaction between the excited state of Mtapp and a Co(III) complex generates also the cation radical and initiates the polymerization process. Pulse radiolytically generated Cl 2 - and OH radicals were also able to initiate the polymerization of the porphyrin complexes.

The electro-oxidation of sulfite was studied by using a glassy carbon electrode coated with a polymeric film of Fe-tetra-4-aminophenylporphyrin, in a wide pH range. The polymeric complex-modified electrode catalyses the electro-oxidation of sulfite to sulfate in acid and basic media, but it is more active at pH higher than 8.5. The polymer film coating is obtained by cycling the electrode in a solution containing the complex (monomer). The polymerization process takes place after the oxidation of the amino groups via a radical mechanism. When the modified electrode is obtained, the polymeric system needs to be over-oxidized in order to avoid the further oxidation of the remaining amino groups in the potential range where the oxidation of the sulfite takes place. The over-oxidation process destroys the monomer-modified electrode. Then, the electropolymerization of the iron complex is the only way to obtain a catalyst for this reaction with this porphyrin. The specie postulated for the oxidation is Fe(IV). The polymer-modified electrode is very stable and its activity remains almost constant for more than 500 consecutive cycles. Also, its activity remains unchanged during more than 30 days of exposure to air and light. The oxidation process occurs during the anodic and the cathodic potentiodynamic scans, showing that it is only necessary the recovery of the active sites; the formation of Fe(IV) is probably needed to promote the oxidation. However, this regeneration is low and becomes the slow step of the reaction.

In this study, six polymer-modified electrodes were used to electrocatalyze the reduction of nitrate in two aqueous media: 0.5 M HClO 4 and 0.1 M NaClO 4 . These six polymers were prepared from the electropolymerization of tetrakis( x -aminophenyl)porphyrin (where x = o , p ), and their Cu(II) and Ni(II) complexes in HCl solution on the surface of a conducting glass electrode. The results indicate that the catalytic response depends on the position of the amino group, the metal and the pH of the solution. In HClO 4 , the modified electrodes show two reduction processes. The voltammetric responses of the modified electrodes show a reduction process that takes place during the negative scan and another reduction process occurring during the return potential sweep. Indeed, there is a change in the number of reduction processes depending on the direction of the scan at low scan rate (5 mV s −1 ). In HClO 4 , the products of electrolysis are nitrite and nitrous oxide for Cu and Ni- ortho -polymers and nitrite for the others polymers. In NaClO 4 , only one reduction process takes place, independently of the direction of the scan, giving nitrite and nitrous oxide for the Ni and Cu- ortho systems and only nitrite for the other systems. In both cases, HClO 4 and NaClO 4 , the best polymers are poly Cu(II) and Ni(II)tetrakis( o -aminophenyl)porphyrin as electrocatalysts.

The electro-reduction of carbon dioxide was studied by using a glassy carbon electrode modified with Co(II)-tetrabenzoporphyrin as adsorbed layers or as a supramolecular system. In order to obtain the supramolecular electrode, 4-aminopyridine was chemically bonded to the electrodic surface. On this surface, a first layer of porphyrins was anchored by the pyridine as a fifth ligand. Packed on the first layer of porphyrins, a supramolecular system is formed. The electrode modified with physically adsorbed layers of porphyrins does not show catalytic response toward the electroreduction of CO2. However, the supramolecular electrode is very stable and shows a high catalytic response.

The electrochemical reduction of carbon dioxide using hexa-aza-macrocycles derived from the condensation of 1,10-phenanthroline and its Co(II) complex as an electrocatalyst dissolved in dimethylformamide has been studied by cyclic voltammetry and UV-visible spectroscopy. The ligand does not show catalytic activity and only generates hydrogen when it is reduced under carbon dioxide. The cobalt complex shows electrocatalytic activity toward the reduction of carbon dioxide, generating carbon monoxide and formic acid. Cyclic voltammetry and UV-visible spectroscopy show that the active site for the reduction is the metal center in oxidation state (I), although the reduced cobalt center alone is not enough to promote reduction of the carbon dioxide. Electrolysis at controlled potential shows that only at potentials corresponding to reduction of the ligand (second reduction) does carbon dioxide reduction occur. Cobalt(I) probably reacts with CO2 forming a non-isolated intermediate which, when reduced, gives CO a...

The electrocatalyzed reduction of carbon dioxide was investigated with cobalt(II), nickel(II) and copper(II) complexes of hexaaza-macrocycle ligands. The macrocyclic ligands were obtained via the condensation of phenanthroline or bipyridine. The X-ray structure of a triflate derivative was determined and it showed the less common “CuN4O2” centrosymmetric octahedral configuration with apically elongated CuO bonds. A preference for a neutral, mononuclear, octahedral configuration is exhibited by the planar macrocycle with an extended π-electron system. Its structure is characterized by shorter CuN bonds than those of Cu complexes with saturated macrocycles. The reduction of the complexes has been studied by cyclic voltammetry and UV–Vis spectroscopy. The results show that the metal center in its lower oxidation state, i.e. M(I), is the active site. The metal center is oxidized to M(II) in the presence of CO2 with the concomitant formation of an adduct between the metal center and CO2. A further one electron reduction regenerates the catalyst and produces carbon monoxide and/or formic acid. A theoretical model is proposed for a simple mechanism that involves initial coordination of CO2 to the metal center.

In this work we have investigated the electrocatalytic activity for O2 reduction of monomeric (FePcTA) and polymeric (poly-FePcTA) iron tetraaaminophthalocyanine, deposited on glassy carbon. The activity of the electropolymerized ligand (poly-H2PcTA) was also investigated. Its activity is much lower than the activity of both monomeric and polymeric FePcTA. The electropolymerized FePcTA is more active and stable for O2 reduction than the monomeric species. In contrast to other Fe-phthalocyanines, poly-FePcTA only catalyzes the two-electron reduction of O2 to peroxide. Both monomeric and polymeric Fe species seem to form an adduct with oxygen and this causes a gradual deactivation, However at pH 5.85, using sodium perchlorate as electrolyte, the polymer does not lose its activity for O2 reduction.