Search

Hydrogen (H2) has emerged as a sustainable energy carrier capable of replacing/complementing the global carbon-based energy matrix. Although studies in this area have often focused on the fundamental understanding of catalytic processes and the demonstration of their activities towards different strategies, much effort is still needed to develop high-performance technologies and advanced materials to accomplish widespread utilization. The main goal of this review is to discuss the recent contributions in the H2 production field by employing nanomaterials with well-defined and controllable physicochemical features. Nanoengineering approaches at the sub-nano or atomic scale are especially interesting, as they allow us to unravel how activity varies as a function of these parameters (shape, size, composition, structure, electronic, and support interaction) and obtain insights into structure–performance relationships in the field of H2 production, allowing not only the optimization of performances but also enabling the rational design of nanocatalysts with desired activities and selectivity for H2 production. Herein, we start with a brief description of preparing such materials, emphasizing the importance of accomplishing the physicochemical control of nanostructures. The review finally culminates in the leading technologies for H2 production, identifying the promising applications of controlled nanomaterials.

Water disinfection processes may generate several dangerous substances that can affect both human beings and the environment. As a known contaminant in drinking water, the compound 2,6-dichloro-1,4-benzoquinone (DCBQ) and its degradation products in aqueous solution are of continuing concern regarding environmental, biomedical, and technical applications. There is great interest in the development of analytical methods capable of elucidating the mechanisms of the interactions of DCBQ and its degradation products with the nucleic acids of living organisms. Here, a systematic voltammetric study employing a glassy carbon electrode was performed, for the first time, to investigate the redox properties of DCBQ and its interactions with double-stranded DNA (dsDNA). The DCBQ has a reversible process at pH range from 3.70 to 12.60 and pH-dependent until pH 9.20, resulting in the formation of a reversible oxidation product in a pH-dependent system to pH 6.00 at a glassy carbon electrode. By varying incubation time and pH of electrolyte solutions, DCBQ showed spontaneous degradation which was presented by the change of its electrochemical behavior in solution. The spontaneously degraded DCBQ underwent a reversible and pH-dependent process for 3.70 ≤ pH ≤ 6.00. By spectrophotometry experiments, the spontaneous decomposition of DCBQ in aqueous solution was verified. DCBQ interacted indirectly with dsDNA and its degradation product(s) interacted with the deoxyguanosine homopolynucleotide with release of guanine and adenine from the double helix, but no oxidative damage to the dsDNA by DCBQ or its product(s) was detected.

Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO

Rapid methods using batch injection analysis (BIA) with amperometric detection were developed for the determination of quercetin extracted from the Brazilian plants Brunfelsia uniflora (BU), Vismia guianensis (VG), and Arrabidaea brachypoda (AB). One method was based on a glassy carbon electrode (GCE) and pulsed amperometry (BIA-PA), while the other employed a screen-printed carbon electrode (SPCE) and conventional amperometry (BIA-CA). Both proposed methods required minimal sample manipulation (only dilution in the carrier electrolyte), and the determination was performed with a single injection of 100 μL of sample solution. The BIA-PA method was highly accurate (RSD = 0.7%, n = 30), fast (120 injections h−1), and presented low limits of detection (0.004 μmol L−1) and quantification (0.015 μmol L−1). The BIA-CA method was also accurate (RSD = 1.1%, n = 30), fast (120 injections h−1), and presented low limits of detection (0.027 μmol L−1) and quantification (0.091 μmol L−1). The application of the proposed methods for the determination of quercetin in the plant extracts provided results similar to those obtained by high-performance liquid chromatography (HPLC) at a confidence level of 95%.

Made available in DSpace on 2022-04-28T19:40:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-10-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The present work aims to develop electroanalytical strategies for separating and quantifying one of the most important biothiols, the reduced glutathione (GSH), based on developing and applying a new and selective magnetic molecular imprinted polymer (mag-MIP). This magnetic-supported polymer was synthesized by precipitation, using GSH as a template, having acrylamide as the functional monomer and trimethylolpropane trimethacrylate as a cross-linking agent. These materials' morphological and physical characteristics were investigated by scanning electron microscope, Fourier transform infrared, and vibrating sample magnetometry. Physicochemical parameters, such as adsorption capacity, were obtained and compared with the respective mag-NIP, which are control polymers without the selective cavity. After all characterizations, mag-MIP and mag-NIP were evaluated on magnetic graphite-epoxy composite (m-GEC) electrodes. The characteristics of the obtained sensors were investigated by cyclic voltammetry and differential pulse voltammetry. After optimizing experimental and operational conditions, a linear response for the concentration of GSH, in the range of 1–1400 μmol/L, with low detection and quantification limits of 7 and 20 nmol/L, respectively, were obtained. The GSH levels in mice liver samples were measured by electrochemical and spectrophotometric techniques to compare the method's effectiveness. A high correlation between them and a low relative error of 1.06 % were obtained, indicating the good functionality of the proposed sensor. Instituto de Química e Biotecnologia Universidade Federal de Alagoas Instituto de Química Universidade Estadual Paulista and INCT-DATREM, Rua Prof. Francisco Degni, 55 Departamento de Química Universidade Federal do Maranhão Avenida dos Portugueses, 1966 Campus de Engenharias e Ciências Agrárias Universidade Federal de Alagoas Universitat Autònoma de Barcelona, Bellaterra Instituto de Química Universidade Estadual Paulista and INCT-DATREM, Rua Prof. Francisco Degni, 55 FAPESP: 2014/50945-4 FAPESP: 2019/00677-7

In the field of catalysis on solid surfaces, discrimination of the site-specific chemistry taking place on surfaces consisting of multiple types of sites is challenging, especially at electrified solid/liquid interfaces. In this study, site-specific chemical labeling on Pt stepped surfaces was achieved by attaching the 13CO species exclusively on the top side of the (110) steps, while making all of the (111) sites available. The catalysts were then employed in a spectro-electrochemical study of the electro-oxidation of methanol and ethanol. The onset potentials for the formation of 13CO2 and 12CO2 revealed the existence of two channels of carbon dioxide formation, separated by about 0.22 V, on the same Pt surface. The active sites with lower overpotential requirement (or lower energy input) for activation of the reaction pathway of CO2 formation resided on the (111) terraces. On the other hand, the active sites with higher overpotential requirement (or higher energy input) for activation of the reaction pathway for electro-oxidation of 13COads species to 13CO2 were at the top of the (110) steps. The findings revealed the identities of the most active sites and least active sites involved in the formation of CO2 during the electro-oxidation of alcohols. On Pt surfaces, the complex interplay involving the steps on the surface favors activation of the pathways for COads oxidation on the (111) terraces, rather than promoting reaction steps directly on the steps themselves. M.J.S.F. is grateful to PNPD/CAPES (Brazil). A.A.T acknowledges CAPES (PROCAD-2013) and CNPq (309066/2013-1). J.M.F. thanks the MINECO (Spain) project CTQ2016-762213-P.

This work presents an analytical study of the determination of catechin, extracted from the Brazilian plants Rhizophora mangle, Arrabidaea brachypoda, and Lippia origanoides, using disposable screen-printed carbon electrodes (C-SPE) coupled to a batch injection analysis (BIA) system. Preliminary cyclic voltammetry experiments in acetate buffer solution (pH 4.5) containing catechin revealed reversible redox processes, with anodic and cathodic peak potentials located at ~0.16 V and ~0.10 V vs. Ag/AgCl, respectively, and an irreversible peak at ~0.49 V. Under optimized conditions, the repeatability for direct amperometric determination of catechin, performed at +0.3 V with the C-SPE in the BIA system, using successive injections of 50 μmol L−1 of catechin, was RSD = 1.03% (n = 30). The sampling throughput was 120 injections per hour. The amperometric response showed a linear range from 1 to 150 μmol L−1 (R = 0.999), with detection and quantification limits of 0.021 and 0.070 μmol L−1, respectively. Application of the proposed methodology for the determination of catechin in extracts of the medicinal plants provided quantitative results similar to those obtained by high performance liquid chromatography (HPLC), at a confidence level of ~95%.

Made available in DSpace on 2021-06-25T11:57:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-06-01. Added 1 bitstream(s) on 2021-07-15T15:06:12Z : No. of bitstreams: 1 S0103-50532021000601286.pdf: 927767 bytes, checksum: 84f8c76db461c524a73422eb1e4babd4 (MD5) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) FAPEMA Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Brazil has the greatest plant diversity on the planet, distributed in different types of biomes. These plants are important sources of biologically active natural products, which are derived from various drugs marketed worldwide. This paper presents an electrochemical study of three unusual dimeric flavonoids, pharmacologically active, isolated and identified for the first time by our research group, in a Brazilian plant (Fridericia platyphylla). The results showed that oxidation processes are favored at higher pH, and mass transport was controlled by diffusion. Brachydins derivatives, Bra-A was oxidized at the lowest potential value (0.48 V vs. Ag/AgCl, KCl(sat)) and Bra-B and Bra-C, presented the highest oxidation potentials (ca. 0.71 and ca. 0.57 V vs. Ag/AgCl, KCl(sat), respectively). This study shows that electrochemistry is one more tool that would help us focus on future bio-pharmacological investigations of these unusual compounds. Univ Fed Maranhao, Ctr Ciencias Exatas & Tecnol, Dept Quim, BR-65080805 Sao Luis, MA, Brazil Univ Estadual Paulista, Dept Quim, BR-14800060 Araraquara, SP, Brazil Univ Sao Paulo, Dept Quim Fundamental, Inst Quim, BR-05508000 Sao Paulo, SP, Brazil Inst Nacl Ciencia & Tecnol Bioanalit, CP 6154, BR-13083970 Campinas, SP, Brazil Univ Fed Maranhao, Dept Tecnol Quim, Ctr Ciencias Exatas & Tecnol, BR-65080805 Sao Luis, MA, Brazil Univ Estadual Paulista, Dept Quim, BR-14800060 Araraquara, SP, Brazil CNPq: 205220/2018-5 CNPq: 307172-2017-0 CNPq: 465389/2014-7 FAPEMA: 00849/18-Universal CAPES: 88887.472618/2019-00-PROCADAM

Triclosan (TCS) is an antiseptic agent widely used mainly in personal care products and an important contaminant, which degrades in the environment causing toxicity on health, including negative effects on DNA. In this context, an electrochemical investigation of TCS in aqueous solution was studied by voltammetric techniques. The TCS underwent irreversible oxidation in a pH-dependent process, leading to the formation of two reversibly oxidized and pH-dependent oxidation products. An oxidation mechanism for TCS and its oxidation products in neutral aqueous medium was proposed. Besides that, the TCS spontaneously degraded into supporting eletrolytes with 3.4 ≤ pH ≤ 12.04 over the incubation time and the degraded TCS in solution was detected by electrochemical and spectrophotometric techniques. A higher degradation of TCS was observed in alkaline medium. In addition, the interaction in situ of this anti-microbial with DNA was investigated using dsDNA incubated solutions and dsDNA electrochemical bisosensor, by voltammetry. TCS and degraded TCS interacted with dsDNA causing the condensation of the double helix structure, release of guanine (by TCS and dedraded TCS) and adenine (by degraded TCS) bases from dsDNA and a possible intercalation of degraded TCS in the polynucleotide chain. No dsDNA oxidative damage was detected.

In this work, several PGM-free materials supported on three types of carbon blacks (Vulcan XC-72, Monarch-1000, and Ketjenblack EC-600JD) and pyrolysed on N2 and NH3 atmosphere are investigated as catalysts for the oxygen reduction reaction (ORR) in acid and alkaline electrolytes. The synthesized materials are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The electrochemical characterization shows that for all N2- and NH3-treated catalysts, the ORR activity is higher in alkaline than acidic conditions, though in both cases, the main reaction product is water, thus evidencing a predominant occurrence of a 4-electron oxygen reduction mechanism. Further, a reasonable relationship is established between Fe-Nx coordination (pyridinic-N) and pyrrolic-N contents and the ORR activity of catalysts in acid media (FeNx supported on Monarch-1000). In alkaline conditions, the iron coordination with pyridinic-N, coupled to a high carbon surface area (Ketjenblack), enhances the ORR activity regardless of the pyrolysis atmosphere. Finally, the ORR performance in alkaline medium of the FeNx/Ketjenblack catalyst pyrolysed under N2 atmosphere is essentially the same as that achieved for the benchmark catalyst (Pt/C), while the durability of the best catalysts evidence to be quite promising in both acidic and alkaline media, as shown by a standard accelerated stability test.

Antibiotics in water bodies have raised global concerns due to the risk of developing drug-resistant bacteria stains. Thus, the occurrence of macrolide antibiotic residues in environmental waters has attracted significant attention lately. Herein, a composite material comprised of Super P carbon black particles and chitosan was developed as an electrochemical sensor to determine macrolide antibiotics, including erythromycin, azithromycin, clarithromycin, and roxithromycin. The electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, and Raman spectroscopy. The proposed sensor coupled to a batch injection analysis system proved to be rapid (125 injections h−1), reproducible (RSD = 2.60%), and present a wide linear range (1.0–190.0 µmol L−1). Also, it was successfully applied for the direct determination of the four macrolide antibiotics in water and pharmaceutical samples. Recovery tests were performed on both samples, in which recovery values between 96.0% and 104.7% were achieved for tests performed on environmental samples, and between 95.6% and 105.1% for tests performed on pharmaceutical samples, proving the excellent accuracy of the system. Based on electrochemical/physicochemical characterizations and sensing performance, the applicability of this material was demonstrated as an attractive alternative for use in routine analysis from economic and portability points of view.

This study evaluated the incorporation of niobophosphate bioactive glass (NbG) fillers into a commercial adhesive resin.The silanized (NbGs) or non-silanized (NbG) NbG was added to the commercial adhesive system One Step (OS) at 30% by weight; unfilled adhesive served as control. The bioactivity of adhesives was analyzed by SEM and FTIR/ATR after 28 days in PBS. The adhesives were evaluated as regards microtensile bond strength immediately and after six months (n = 6); degree of conversion (n = 3), microhardness (n = 5); and radiopacity (n = 3). Data from each test were submitted to ANOVA and Tukey tests (P0.05).FTIR/ATR analysis showed phosphate and carbonate precipitates on the NbG adhesive specimen surface. Statistical analysis of microtensile bond strength values showed that material x time interaction was not significant, but NbG group values were similar to those of unfilled adhesive (p0.05). Addition of NbG did not alter the degree of conversion, but did increase microhardness and radiopacity values of the adhesive systems compared with those of the control group (OS). Incorporation of NbG into the adhesive system did not compromise the properties of the adhesive.A smart adhesive system with bioactive properties, high radiopacity, microhardness, and similar bond strength and degree of conversion was obtained by incorporating 30% by weight of NbG.

Bioactive compounds have several biological activities, promoting health. Among these compounds, those, such as vitamins and phenolic compounds, with antioxidant properties have attracted significant interest due to their proven effects in protection against oxidative stress. Most of the bioactive phenolic compounds are highly difficult to be determined by voltammetric techniques at bare electrodes since polymerization process occurs on the electrode surface during phenol oxidation. In this study, we described the determination of a bioactive compound, catechin, by electrochemical oxidation via batch injection analysis (BIA) with multiple amperometric detection (MPA) using an unmodified glassy carbon (GC) electrode in an acetate buffer solution (pH 4.5). The proposed BIA method is based on the application of multiple pulse potentials of 0.4 V (oxidation potential), 1.4 V (cleaning potential), and 0.0 V (conditioning potential) vs. Ag/AgCl (KCl 3 M), hence avoiding passivation by oxidation products and enabling the quantification of catechin. Under these conditions, the repeatability of the method for successive injections of catechin at a concentration of 50 μmol L−1 (n = 30) was 0.85%, and the sampling rate was 120 injections per hour. The amperometric response presented a linear range for solutions containing catechin at concentrations ranging from 20 to 100 μmol L−1 (R = 0.999), with a detection limit of 0.03 μmol L−1 and a quantification limit of 0.10 μmol L−1. In addition, the proposed method was shown to be fast and sensitive for the determination of catechin in real samples, and the results were comparable to those obtained via high-performance liquid chromatography (HPLC), at a 95% confidence level.

Carbon-supported Pd, Pt, Pt1Pd1, and Pt3Pd1 electrocatalysts were prepared by metal ion chemical reduction with borohydride. The electrocatalysts were analyzed by EDS, HRTEM, and XRD techniques. The EDS spectra showed that the actual compositions of the materials were close to the nominal compositions. The XRD measurements revealed that the materials were crystalline, and no oxide peaks were observed. The HRTEM micrographs showed homogeneous particle distributions on the carbon, with Gaussian particle size distributions. The mean particle sizes were taken as the maxima of the Gaussian distributions. All the materials presented electrochemical activities for the ethanol oxidation reaction, with the exception of Pd in acid media. Pt showed poor performance in alkaline media. The poisoning rate was determined by cyclic voltammetry (i forward/i backward ratios), as well as by chronoamperometry experiments, both of which indicated a low poisoning rate for Pd in alkaline medium and higher poisoning rates as the Pt content increased in the PtPd electrocatalyst

The electrochemical behaviour of the antitumor drug mitomycin C (MMC) was investigated on carbon paste electrode over a wide pH range and using voltammetric techniques. The MMC undergoes diffusion-controlled irreversible oxidation in two different processes, one pH-independent for 2.2 ˂ pH ˂ 4.5 and one pH-dependent for 4.5 ˂ pH ˂ 12.0, and does not involve the formation of any electroactive oxidation product. Upon incubation in different pH electrolytes, chemical degradation of MMC was electrochemically detected by the appearance of a new oxidation peak at a lower potential. The chemically degraded MMC undergoes an irreversible, pH-dependent oxidation for 3.4 ˂ pH ˂ 5.4, and its redox products are reversibly oxidised. The spontaneous degradation of MMC in aqueous solution was confirmed by UV–Vis spectrophotometry. Moreover, a multilayer dsDNA-electrochemical biosensor was used to evaluate the interaction between MMC and DNA. The results have clearly proven that MMC interacts and binds to dsDNA strands immobilized onto a glassy carbon electrode surface and its metabolite(s) cause oxidative damage to DNA.

Carbon-supported Pd and PdNi electrocatalysts with different Ni contents were prepared by metal ion chemical reduction with borohydride. XRF analyses showed that the actual compositions of the materials were close to the nominal compositions. XRD measurements revealed that the materials were crystalline, with small peak displacements when Ni and Pd ions were reduced on carbon support, and suggested a segregated phase and not a Ni incorporation into the Pd lattice. HRTEM micrographs showed homogeneous particle distributions on the carbon, with a narrow particle size distribution and few agglomerations of nanoparticles. All the materials presented electrochemical activity for the oxidation of methanol, ethanol, and glycerol in KOH, and the oxidation current peak increased as a function of the Ni content in the catalyst.

This work investigates the mechanisms by which Sn and Ru can improve or inhibit the site-specific catalytic activity of Pt (neighboring or distant from foreign atoms) at bimetallic surfaces. For this purpose, we decorated Pt stepped surfaces (nonequivalent sites) by site-selective electrodeposition of different coverages of either Sn or Ru on (110) Pt steps, forming Snsteps/Pt(hkl) and Rusteps/Pt(hkl) bimetallic surfaces, and we used CO adlayer electro-oxidation as a surface probe reaction, monitored by in situ FTIR and cyclic voltammetry techniques. The results showed that both Sn and Ru selectively accelerated the reaction pathway of CO electro-oxidation only at the (111) Pt terrace sites but importantly played different underlying roles in favoring activity at these active sites. In the case of Snsteps/Pt(hkl) catalysts, the CO adlayer oxidation started at potentials lower than those on Rusteps/Pt(hkl), but Sn only improved the activity at sites on atoms of the first rows of (111) Pt terraces, while the catalytic benefit of Ru seemed to extend further along the (111) Pt terraces. In comparison to unmodified Pt surfaces, Ru did not influence the activity at the line of the (110) Pt steps, while Sn slightly inhibited the activity there, which characterized a slight contrasting effect in catalytic activity at the (111) terraces in comparison to the (110) step sites. In this regard, the chemical modification by irreversible deposition of either Sn or Ru at lines of Pt steps on a stepped Pt surface interestingly resulted in a nonuniform synergistic effect or balancing of energies involving different site-specific catalytic activities at nonequivalent Pt surface sites. Since the electro-oxidation of CO takes place at the (111) Pt terrace sites away from Sn or Ru, and because COads behaves as an immobile species during its oxidation, it is reasonable to assume that the classical bifunctional mechanism completely fails as a model to interpret the enhancement of catalytic activity toward CO electro-oxidation at Snsteps/Pt(hkl) or Rusteps/Pt(hkl) catalysts. The selective alteration in site-specific catalytic activity of Pt was related to (i) the type and coverage of foreign atoms (Sn or Ru) at the lines of Pt steps, (ii) the crystallographic orientation of Pt sites, whether (111) terraces or steps, and (iii) the width of the (111) Pt terraces. M.J.S.F. acknowledges financial support from PNPD/CAPES (Brazil). A.A.T. acknowledges support from CAPES (PROCAD 2013) and CNPq (grant #309066/2013-1). J.M.F. thanks MINECO (Project CTQ2016-76221-P) and GV (Project PROMETEOII/2014/013) for financial support. W.C. is grateful for the award of an F.P.I. grant associated with project CTQ2009-13142.

Electrochemical techniques were used to investigate the behavior of lomustine (CCNU) and its degradation in aqueous solution at a glassy carbon electrode (GCE). The in situ interaction of CCNU and chemically degraded CCNU (cdCCNU) with dsDNA was then investigated in dsDNA incubated solutions, using dsDNA electrochemical biosensors and comet assays. CCNU undergoes electrochemical reduction in two irreversible, diffusion-controlled, and pH-dependent redox processes, each with transfer of two electrons and one proton. At pH ≥ 10.1, the peak potential for the two processes was essentially pH-independent and involved only one electron. A mechanism was proposed for the reduction of CCNU in a neutral medium. In addition, it was found that CCNU underwent spontaneous degradation during incubation in aqueous solution, without the formation of electroactive degradation products. The degradation process was faster in basic media. Moreover, this pro-drug interacted with the DNA. Its metabolite(s) initially caused condensation of the double helix chains, followed by the unwinding of these chains. In addition, free guanine (Gua) was released from the dsDNA and oxidative damage to the DNA by the CCNU metabolite(s) was evidenced from the detection of 8-oxoGua and 2,8-oxoAde. These results were confirmed by the poly(dA)- and poly(dG)-polyhomonucleotide biosensors, which revealed the oxidative damage caused to both bases (guanine and adenine) of the dsDNA by the CCNU metabolite(s). The comet assay indicated breaks in the single strand DNA, complementing the results of the studies using differential pulse voltammetry. Conformational changes of dsDNA caused by CCNU and cdCCNU were confirmed using comet assays.

A simple and sensitive electrochemical method was developed for the determination of N-Acetylcysteine (NAC) and Glutathione (GSH), on glassy carbon electrode. The results indicate that α-lipoic acid (LipS2) is oxidized at the electrode, but is regenerated by thiols, suggesting a redox catalytic effect. Under optimized conditions, the analytical curves for NAC and GSH were obtained in the range of 1 up to 10 µM and 1 up to 60 µM, respectively. The quantification can be performed in a single assay with high sensitivity, reproducibility and low detection limit of 0.27 and 0.67 µM for NAC and GSH, respectively. This method was successfully applied to the determination of NAC and GSH in artificial saliva and human urine samples, with excellent recovery results.

The authors describe a platform for the electrochemical reduction of oxygen. It is based on the use of a glassy carbon electrode (GCE) that was modified in a single-step microwave assisted reaction with a N4-macrocycle containing iron(III) (FeN4) and with reduced graphene oxide. The FeN4/rGO composite was characterized by cyclic voltammetry, differential pulse voltammetry, and scanning electrochemical microscopy (SECM). Cyclic voltammetry showed the composite to enable efficient reduction of O2 at a very low overpotential (−0.05 V vs. Ag/AgCl). SECM measurements were carried out to map (in the redox competition mode) the activity of a GCE microelectrode modified with FeN4/rGO. Under optimized conditions, the response to dissolved O2 ranges from 0.8 up to 25 mg⋅L‾1, and the limit of detection is 0.2 mg⋅L‾1.

Pt-based cathodes in direct methanol fuel cells are promising materials for a wide range of applications. However, such materials suffer significant performance loss due to severe methanol crossover from anode to cathode, resulting in mixed potentials from methanol oxidation and oxygen reduction reaction. Herein, we proposed some facile synthesis procedures to avoid Pt active sites contamination from methanol. The strategy was to associate controlled ultrasmall Pt nanoparticles (NPs), Vulcan XC-72, and MnOx species prepared from Mn(NO3)2.4H2O. Interestingly, we have observed that depending on the synthetic pathway chosen, the methanol-tolerance ability of the material increased, suggesting different interactions among the components of the catalyst. The results indicated an improved selectivity of the system due to a synergy between Pt and MnOx. The best strategy was the immobilization of ultrasmall Pt NPs (~2 nm) on carbon black, before impregnation and thermal decomposition of MnOx, which almost wholly suppressed the methanol oxidation interference on the system. Also, the optimized cathode presented a comparable performance for ORR to the traditional Pt/C without methanol addition. To further rationalize such findings, physical and electrochemical characterizations were successfully performed, which allowed us to better understand the proposed catalysts and their different methanol-tolerance abilities.

This works shows the combination of batch-injection analysis with multiple-pulse amperometric detection (BIA-MPA) for the determination of the diuretics furosemide (FRD) and hydrochlorothiazide (HCT) in urine and pharmaceutical samples. Under optimized electrolyte conditions (0.04 mol L−1 Britton-Robinson buffer solution at pH 4.0) FRD was oxidized at + 1.10 V and both compounds were oxidized at + 1.30 V. The MPA detection involves the continuous application of two potential pulses as a function of time to determine FRD at the first potential and HCT at the second after subtracting the FRD current obtained at the second potential. A correction factor was needed because the current of FRD at both potentials was different. A boron-doped diamond working electrode was selected for the simultaneous determination as its surface is less susceptive to fouling. The compounds exhibited a linear response range of 2 to 100 μmol L−1 for HCT (r = 0.9990) and 2 to 300 μmol L−1 for FRD (r = 0.9993), satisfactory repeatability (RSD lower than 5% for n = 30), detection limits of 0.65 μmol L−1 for FRD and 0.63 μmol L−1 for HCT, and analytical frequency of 130 injections per hour. The proposed method was applied for the analysis of synthetic urine samples spiked with both compounds and proper recovery values were obtained (95–110%), confirming the potential application for anti-doping analyses. Moreover, the proposed method was compared to UV–Vis spectrophotometry for the analysis of pharmaceutical formulations and they were found to be statistically similar at the 95% confidence level.

This paper presents, for the first time, an amperometric electroanalytical method for ampicillin determination using a copper electrode in a batch injection analysis (BIA) system. Initial voltammetric measurements were performed to establish the working potential in the amperometric assays and to optimize parameters such as the supporting electrolyte and the pH of the medium. The method was shown to be precise (RSD = 3.5%, n = 18), reliable (confirmed by an application using a drug sample), sensitive (LOD = 7.11 μmol L−1; LOQ = 23.7 μmol L−1), and fast (86 injections h−1). The proposed method was successfully applied for the determination of ampicillin in commercial drug samples. The results were compared with those obtained using HPLC-UV/Vis and UV–Vis spectrophotometry. There were no significant differences, indicating that the new technique could be used in routine analyses.

This works deals with the identification of preferential site-specific activation at a model Pt surface during a multiproduct reaction. The (110)-type steps of a Pt(332) surface were selectively marked by attaching isotope-labeled

This paper presents a theoretical study of the effects of substituents (F, Cl, Br, CH3, and CN) on the aromaticity of borazine (B3N3H6), using density functional theory (DFT) and the Hartree-Fock (HF) method. The calculations to optimize the geometries, structural properties, and vibrational frequencies were performed using the same 6–311G(d,p) and 6–311++G(d,p) basis sets, comparing the methods with experimental results. In the analysis of the NICSZZ values, it was found that that replacing the hydrogen atoms by halogen atoms (F, Cl, and Br) and CH3 reduced the aromaticity of the borazine molecule, while use of the CN group resulted in NICSZZ values (0.9–2.0 A) very close to those of borazine, presenting the following order of increasing aromaticity: B3N3H3-(Br)3

This works deals with the identification of preferential site-specific activation at a model Pt surface during a multiproduct reaction. The (110)-type steps of a Pt(332) surface were selectively marked by attaching isotope-labeled 13CO molecules to them, and ethanol oxidation was probed by in situ Foureir transfrom infrared spectroscopy in order to precisely determine the specific sites at which CO2, acetic acid, and acetaldehyde were preferentially formed. The (110) steps were active for splitting the C–C bond, but unexpectedly, we provide evidence that the pathway of CO2 formation was preferentially activated at (111) terraces, rather than at (110) steps. Acetaldehyde was formed at (111) terraces at potentials comparable to those for CO2 formation also at (111) terraces, while the acetic acid formation pathway became active only when the (110) steps were released by the oxidation of adsorbed 13CO, at potentials higher than for the formation of CO2 at (111) terraces of the stepped surface. M.J.S.F. is grateful to PNPD/CAPES (Brazil). A.A.T. acknowledges CAPES (PROCAD-2013) and CNPq (309066/2013-1). J.M.F. thanks the MINECO (Spain) project-CTQ2013-44083-P.

The activation pathway of CO electro-oxidation at low potentials is frequently favored on a catalyst with surface defects. Here, we report a discovery in which an initial long-range substrate structure is required for the activation of an unusual CO pre-oxidation reaction pathway on Pt(111) surfaces which have been flame annealed and then cooled in a CO atmosphere. Different to current understanding about the oxidation of CO on Pt, the activation of this reaction pathway is inhibited as the (111) planes become defect-rich. M.J.S.F and A.A.T. thanks the CAPES (Brazil) Finance Code 001. J.M.F. thanks the MINECO (Spain) CTQ2013-44083-P project.

This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0–150.0 µmol/L (r = 0.997), a limit of detection (3σ) of 2.0 µmol/L, a sample throughput of 164 determinations per hour, reagent consumption of 9 µg luminol and 42 µg hypochlorite per determination and generation of 0.63 mL of waste. A relative standard deviation of 1% (n = 6) for a standard solution containing 80 µmol/L captopril was also obtained. Copyright © 2015 John Wiley & Sons, Ltd.

The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with first row transition metals (M II (DBTAA)), employing calculations made using the B3LYP hybrid functional with the Lanl2DZ/6-31G ∗ basis set. The parameters considered were bond distances and angles, electron configurations, interaction energies, vibrational frequencies, and frontier molecular orbitals (HOMO and LUMO). The calculations indicated that the key to complexes of the metals Ti, and Cr was the high spin state, while for Mn and Fe it was the intermediate spin state and for Co, Ni, Cu, and Zn it was the low spin state. The M–N distance (d(M–N)) and vibrational frequency showed inversely proportional behavior as a function of the atomic number of the metal. The Ni(DBTAA) complex showed the smallest d(M–N) and highest vibrational frequency, indicating greater compaction of the ligand on nickel. The interaction energy and the gap (HOMO–LUMO) were also calculated in order to estimate the stability and reactivity of the complexes. The stability increased with the atomic number of the central metal, in agreement with the Irving–Williams series, with Ni(DBTAA) being the most stable, and Ti(DBTAA) and Mn(DBTAA) being the most reactive of the complexes investigated.

This paper presents a theoretical study of the effects of substituents (F, Cl, Br, CH

This work describes a DFT level theoretical quantum study using the B3LYP functional with the Lanl2TZ(f)/6-31G* basis set to calculate parameters including the bond distances and angles, electronic configurations, interaction energies, and vibrational frequencies of FeTClTAA (iron-tetrachloro-tetraaza[14]annulene), FeTOHTAA (iron-tetrahydroxy-tetraaza[14]annulene), FeTOCH3TAA (iron- tetramethoxy-tetraaza[14]annulene), FeTNH2TAA (iron-tetraamino-tetraaza[14]annulene), and FeTNO2TAA (iron-tetranitro-tetraaza[14]annulene) complexes, as well as their different spin multiplicities. The calculations showed that the complexes were most stable in the triplet spin state (S = 1), while, after interaction with carbon monoxide, the singlet state was most stable. The reactivity of the complexes was evaluated using HOMO–LUMO gap calculations. Parameter correlations were performed in order to identify the best complex for back bonding (3d xzFe → 2p xC and 3d yzFe → 2p zC) with carbon monoxide, and the degree of back bonding increased in the order: FeTNO2TAA

Stepped Pt surfaces having different width (1 1 1) terraces interrupted by (1 1 0) or (1 0 0) monoatomic steps were employed to evaluate the catalytic activity toward CO oxidation at Pt specific sites in HClO4, H2SO4, and H3PO4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (1 1 1) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on activity was detected at the monoatomic steps. A change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (1 1 1) terraces and the step sites, with the catalytic activity of the (1 1 1) terraces improving, while activity at the step sites deteriorated. During the CO adlayer oxidation, the release of surface sites occurred preferentially from the (1 1 1) terraces of the Pt(s) − [(n − 1)(1 1 1) × (1 1 0)] surfaces, while from Pt(s) − [(n)(1 1 1) × (1 0 0)] surfaces, (1 1 1) terrace and (1 0 0) step sites were released simultaneously. M.J.S. Farias acknowledges financial support from PNPD/CAPES (Brazil). G.A.B.M. received a post-doctorate fellowship from CNPq (grant no. PDE 233268/2014-6). A.A.T. acknowledges support from CAPES (PROCAD 2013) and CNPq (grant no. 309066/2013-1). J.M.F. thanks MICINN (Project CTQ2016-76221-P) and Generalitat Valenciana (Project PROMETEOII/2014/013) for financial support.

Objectives: The aim of this study was to evaluate the shear bond strength (SBS) of metal brackets bondedwith two self-etching adhesives using different times of air drying.Materials and methods: 120 healthy bovine incisors were divided into 6 groups (n¼20). Transbond PlusSelf Etching Primer and Adper Easy One Self-Etch Adhesive were gently dried at a distance of 20 cm for3 different times (5 s, 10 s and 15 s). Metal incisor orthodontic brackets were used. The pH of theadhesives was tested with indicator strips and the specimens were tested using a universal testingmachine (Instron 3342). Once debonded, each specimen was examined to identify the failure mode (ARI)and SEM was utilized to visualize the enamel conditions. SBS data were subjected to Two-way ANOVAand Tukey tests, while ARI data were analyzed using the Kruskal–Wallis test (p¼0.05).Results: Statistically significant differences were found between Groups Transbond 5 (11.7271.52),Transbond 10 (15.2572.27) and Transbond 15 (20.4571.93), with increases in SBS values as exposuretime to the air jet was increased. For adhesive Easy One, there was no statistically significant differencebetween Groups Easy One 5 (13.1073.46) and Easy One 10 (16.4372.56), or between Groups Easy One10 and Easy One 15 (18.4372.46). There were no differences between ARI values in the tested groups.Conclusions: The SBS of the self etching adhesive was directly influenced by the length of time air dryingwas applied. The pH did not affect the shear bond strength and SEM showed conserved enamel afterdebonding, suggesting that a smaller amount of adhesive on the enamel surface is better.& 2014 Elsevier Ltd. All rights reserved.

The present work describes the development of a selective and sensitive voltammetric sensor for simulta- neous determination of catechol (CC) and hydroquinone (HQ), based on a glassy carbon (GC) electrode modified with manganese phthalocyanine azo-macrocycle (MnPc) adsorbed on multiwalled carbon nanotubes (MWCNT). Scanning electron microscopy and scanning electrochemi- cal microscopy were used to characterize the composite material (MnPc/MWCNT) on the glassy carbon electrode surface. The modified electrode showed excellent electro- chemical activity towards the simultaneous oxidation and reduction of CC and HQ. On the MnPc/MWCNT/GC electrode, both CC and HQ can generate a pair of quasi- reversible and well-defined redox peaks. Under optimized experimental and operational conditions, the cathodic peak currents were linear over the range 1-600 mmol L � 1 for both CC and HQ, with limits of detection of 0.095 and 0.041 mmol L � 1 , respectively. The anodic peak cur- rents were also linear over the range 1-600 mmol L � 1 for both CC and HQ, with limits of detection of 0.096 and 0.048 mmol L � 1 , respectively. The proposed method was effectively applied for the simultaneous detection of hy- droquinone and catechol in water samples and the results were in agreement with those obtained by a comparative method described in the literature.

This paper presents a theoretical study using density functional theory (DFT) to investigate the bonding between carbon monoxide (CO) molecules and type FeN4 macrocycle complexes of iron to form FeN4–CO adducts. In order to understand how different macrocycle ligands affect this interaction, CO molecules were bound to the following complexes: iron–porphyrin (FeP), iron–tetraaza[14]annulene (FeTAA), iron–tetramethyl-tetraaza[14]annulene (FeTMTAA), iron–dibenzotetraaza[14]annulene (FeDBTAA), and iron–tetramethyl-dibenzotetraaza[14]annulenes (FeTMDBTAA1, FeTMDBTAA2). The best description of the systems investigated was provided by the Lanl2TZ(f)/6-31G⁎ basis set, which was therefore used throughout the work. Analysis of the factors influencing the CO bonding process showed that different macrocycle ligands produced adducts that were different in terms of CO bond length, total CO fragment charge, CO vibrational frequency, and CO bond order. The activity of the interaction between CO and the iron-complex was inversely proportional to the energy gap between the HOMO of the FeN4 complex and the LUMO of CO. Finally, a greater degree of back-bonding was characterized by increased occupancy of the px and py orbitals of the O atom of the CO fragment, confirming that the TAAs were more active than porphyrin, in the ascending order: FeP