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The possibility of the electrochemical execution of hydrogen peroxide sensing on CoSn(OH)6 has been evaluated from the mechanistic theoretical point of view. The correspondent model has been developed and analyzed by means of linear stability theory and bifurcation analysis. It was shown that this material may be an excellent electrode modifier for H2O2 electrochemical detection, and the electrochemical analysis is realized in a plausible way. The electroanalytical process is diffusion-controlled. The oscillatory and the monotonic instabilities in this system are possible, being caused not only by electrochemical factors, but also by those of autocatalytic behavior during H2O2 reduction, Applied Journal of Environmental Engineering Science, Vol 9, No 1 (2023)

Introduction: Omeprazole is one of the most used proton-blocking molecules applied in the gastric ulcer treatment. Its blocking effect is achieved by the presence of both acidic and basic nitrogen heteroatoms in its composition. Nevertheless, due to its collateral effects, which may be moderate to severe, the development of its electrochemical determination is really actual. Methods: In this work, we describe theoretically the possibility of omeprazole electrochemical determination, assisted by the composite, containing the silver (I, III) oxide as an active substance and the polymer of 1,2,4-triazolic derivative as a mediator. In this case, the omeprazole molecule is gradually oxidized yielding firstly phenolic and then quinonic derivative. The pyridinic nitrogen is oxidized later. Results: The electroanalytical process is described by a trivariant equation-set, analysis of which confirms the efficiency of the composite of poly(1,2,4-triazole) with Ag2O2. The electrochemical oscillations are also possible, being realized beyond the detection limit. Conclusion: The composite of poly(1,2,4-triazole) with Ag2O is suitable for omeprazole electrochemical determination both in vivo and in vitro.

Introdução: perilartina é um adoçante natural potente, considerado 2000 vezes mais doce que o açúcar comum. Ela pode ser alérgica para algumas pessoas. Além disso, ela se usa apenas no Japão, o que pressupõe a possibilidade de adulterar produtos japoneses sem o seu uso. Assim, o desenvolvimento de um método eficiente da sua determinação qualificativa e quantificação é realmente atual. Metodologia: um modelo matemático de um processo anódico foi desenvolvido e analisado mediante a teoria de estabilidade linear e análise de bifurcações. O modelo inclui os cenários mais prováveis do andamento do processo eletroanalítico. Resultados: a perilartina é oxidada no meio básico, formando o poliol e o sal do “pseudoácido” correspondente, o que contribui fortemente para a força iônica da dupla camada elétrica. Isto pode ser responsável pela aparição das instabilidades oscilatória e monotônica no processo eletroanalítico. Conclusão: malgrado o supracitado, o compósito é um modificador eficiente para a determinação eletroquímica da perilartina no meio básico.

The sucralose electrochemical determination, assisted by cobalt (III) oxyhydroxide, has been theoretically evaluated. The mathematical model, describing the electroanalytical process, has been developed. The analysis of the model by linear stability theory and bifurcation analysis has shown that CoO(OH) may be applied as an efficient electrode modifier in the sucralose determination in neutral and lightly alkaline media. The electrochemical response has to be clear and easy to interpret. The oscillatory and monotonic instabilities may occur due to double electric layer influences of the electrochemical process., Applied Journal of Environmental Engineering Science, Vol. 8, No 3 (2022): Vol8(3)2022

A novel electroanalytical process for sucralose determination has been theoretically suggested. Sucralose is immobilized over an acridine derivative 9-9´-diacridyl, yielding a quaternary salt, which is thereby gradually electrochemically reduced to an N-N´-disubstituted acridone derivative. The correspondent mathematical model has been developed and analyzed by means of linear stability theory and bifurcation analysis, and this analysis has shown the high probability of the oscillatory and monotonic instabilities, due to the double electric layer structure changes during all of the stages of the process. Nevertheless, it also confirms the efficiency of 9-9´-diacridyl-modified electrode for sucralose determination in an electroanalytical system, which may be coupled with a fluorescent indicator. DOI: http://dx.doi.org/10.17807/orbital.v13i3.1584

En este trabajo, por la primera vez se ha descrito el proceso de polimerización electroquímica de los compuestos hidroquinónicos, obtenidos electroquímicamente. El análisis del modelo matemático correspondiente mediante la teoría de estabilidad lineal y análisis de bifurcaciones ha mostrado que el comportamiento de este sistema se hace bastante semejante al ya observado durante la “paradoja de politiofeno”. Así, hay una mayor probabilidad del acaecer las inestabilidades oscilatoria y monotónica. El polímero, por su vez, se obtendrá con una conductividad reducida y morfología menos uniforme.

Introducción: en este trabajo se evalúa desde el punto de vista mecanístico teórico el comportamiento electroanalítico del compuesto oxihidróxido de vanadio colorante escuárico en la detección de la carfedona. El proceso electroanalítico incluye la formación de dos formas de vanadio tetravalente, incluyendo el dióxido de vanadio e ion vanadilo. Método: un mecanismo, capaz de describir el comportamiento del sensor, ha sido sugerido y un modelo matemático fue desarrollado y analizado mediante la teoría de estabilidad lineal y análisis de bifurcaciones. Resultados: el análisis del modelo ha probado que la dependencia lineal entre la concentración del fármaco y el parámetro electroquímico se mantiene firme en la ancha región topológica de parámetros. Las inestabilidades oscilatoria y monotónica suelen realizarse cuando son causadas por influencias fuertes de las etapas química y electroquímica en la capacitancia de la doble capa eléctrica. Conclusiones: el compuesto de nanopartículas de oxihidróxido de vanadio (estabilizadas con el colorante escuárico) puede servir como un modificador eficiente de electrodo para la detección de lacarfedona. El oxihidróxido de vanadio desempeña funciones de sustancia activa y el colorante, de la mediadora.

In this work, the electrochemical description for metformin electrochemical determination, assisted by Ag2O2 composite with squaraine dye, is evaluated from the theoretical point of view. Metformin oxidation is realized via assisted electrochemical 1,2,4-triazole formation, followed by its polymerization and N-oxidation. The correspondent mathematical model has been developed and analyzed by means of linear stability theory and bifurcation analysis. It has shown that the neutral and basic media are more efficient for metformin electrochemical determination than acidic media, due to the absence of the influences of non-protonated aminogroupsand, furtherly, pyridinic nitrogen atoms to double electric layer (DEL) ionic force, conductivity and impedance. In these conditions, the electrochemical instabilities are less capable to realize and, therefore, the linear dependence between the analyte concentration and the current of the system will be easier to obtain and maintain, as no side reaction or additional process, capable to compromise the monomer and (or) modifier stability is realized. DOI: http://dx.doi.org/10.17807/orbital.v12i4.1537

The electrooxidation of dopamine is accompanied by its chemical and electrochemical polymerization, and in which either the monomer or the polymer may be oxidized to the respective quinonic form, was investigated from the theoretical point of view. Dopamine is one of the important neurotransmitters in human and mammal organisms. It is a precursor to epinephrine, which influences the cardiovascular, hormonal and renal functions. Its lack causes diseases like Parkinson, therefore, dopamine has been used as a drug for their treatment. On the other hand, its excess stimulates the sympatic nervous system yielding the metabolic disorders and even schizophrenia. Thus, the development of the rapid and accurate method for its concentration measurement is very important. Dopamine is very popular analyte in electroanalytical systems. The modified electrodes for its determinations have been developed by many researchers. Dopamine is widely used as a monomer for synthesis of a conducting polymer – polydopamine, whis is used as electrodes’ modifier in capacitors and in anticorrosive coatings. The electropolymerization of dopamine into polydopamine proceeds along with its traditional quinone-hydroquinonic oxidation. Both processes give their impact to the electrochemical behavior of dopamine during its electropolymerization. The mechanism’s complexity is also responsible for the electrochemical instabilities during electro-oxidation. In order to understand these instabilities it’s necessary to develop the mathematical model that is capable to describe the behavior of the system. It also helps us to esteem the influence of the electrochemical instabilities, by which it may be accompanied. The goal of this work is to describe an electrochemical oxidation and polymerization of dopamine that will provide an important connection between the electrochemical detection of biologically active compounds and their electropolymerization for electrode modification.

Introdução: a olanzapina é um dos fármacos antipsicóticos benzodiazepínicos mais usados no mundo. Apesar da sua eficiência, em concentrações excessivas, ela sói ser tóxica, como quaisquer outros fármacos desta classe. Assim, neste trabalho, se avaliou, pela primeira vez, a possibilidade da detecção eletroquímica do fármaco olanzapina, assistida pelo compósito do oxihidróxido de cobalto (III), emparelhado com o dióxido, com um corante esquaraínico. Método: o modelo matemático trivariante correspon-dente inclui dois cenários de oxidação do fármaco, possíveis para o caso, incluindo a eletropolimerização indireta da molécula da benzodiazepina condensada, bem como a oxidação do fármaco pelo átomo do enxofre. Este modelo tem sido desenvolvido e analisado mediante a teoria de estabilidade linear e análise de bifurcações. Resul-tados e discussão: a análise do modelo há mostrado que a hibridez do mecanismo do processo eletroanalítico, aliada à composição e descomposição dos compostos iônicos aquando da sua realização, aumenta a probabilidade da ocorrência do compor-tamento oscilatório, em relação ao caso mais simples e mais comum. No entretanto, a instabilidade oscilatória se realiza nos valores dos parâmetros, que estão além do limite de detecção. Por sua vez, o estado estacionário se obtém e se mantém facilmente, indicando um processo eletroanalítico eficiente, controlado pela difusão do analito. Conclusões: trata-se de um processo eletroanalítico eficiente, em que o composto de cobalto funciona como substância ativa, e o corante desempenha o papel de mediador

Por meio de uma análise teórica, foi avaliado o desempenho do compósito do oxihidróxido do vanádio trivalente com o polímero do corante alaranjado da acridina, na detecção eletroquímica do fármaco antiparquinsônico entacapona. O processo eletroanalítico é baseado na eletrorredução do fármaco mencionado. Do desenvolvimento e da análise do modelo matemático correspondente, mediante a teoria de estabilidade linear e anáise de bifurcações, foi possível concluir que o compósito pode ser um modificador eficiente para a determinação da entacapona. Os comportamentos oscilatórios e monotônico, neste sistema, também são passíveis de realizar.

The theoretical description for the chlorantraniliprole electrochemical determination, assisted by the hybrid composite of squaraine dye with CuS nanoparticles has been described. The correspondent reaction mechanism has been proposed, and the correspondent mathematical model has been developed and analyzed by means of linear stability theory and bifurcation analysis. It has been shown that the chlorantraniprole electrochemical anodical determination on high potential may be efficiently provided by cupper sulfide nanoparticles, stabilized by the squaraine dye. On the other hand, the oscillatory and monotonic instability is also possible, being caused by DEL influences of the electrochemical stage. DOI: http://dx.doi.org/10.17807/orbital.v13i3.1518

RESUMO Introdução: Pela primeira vez, o processo eletroanalítico da detecção da ergina (LSA) sobre um elétrodo, modificado por um derivado triazólico, dopado pelo íon amavadina, tem sido descrito teoricamente. Métodos: O modelo matemático, correspondente ao desempenho do sensor, tem sido desenvolvido e analisado do ponto de vista da teoria de estabilidade linear. Foi mostrado que a amavadina pode servir de modificador eficiente para a detecção eletroanalítica da ergina. Outrossim, a presença de um material orgânico no modificador reforça a capacidade da ergina de polimerizar-se, formando um compósito polimérico. Resultados: Os comportamentos oscilatório e monotô-nico são mais prováveis que no caso mais comum, haja vista a formação-deformação de compostos iônicos aquando da detecção eletroanalítica. SUMMARY Introduction: For the first time, the electroanalytical process of ergin (LSA) determination over an electrode, modified by triazolic derivative, doped by an amavadin-ion, has been theoretically described. Methods: The mathematical model, correspondent to the sensor function, has been developed and analyzed by means of linear stability theory. It has been shown that the amavadin may serve as an efficient electrode modifier for the electroanalytical detection of ergin. Moreover, the presence of an organic material as electrode modifier reinforces the possibility of ergin polymerization, yielding a polymer composite. Results: The oscillatory and monotonic behavior is more probable than in the common case, considering the formation and destruction of the ionic compounds during the electroanalytical detection. RESUMEN Introducción: Por primera vez se ha descrito teóricamente el proceso eletroanalítico de detección de ergina (LSA) en un electrodo, modificado por un derivado triazólico, dopado por el ión amavadina. Métodos: El modelo matemático, correspondiente al rendimiento del sensor, ha sido desarrollado y analizado desde el punto de vista de la teoría de la estabilidad lineal. Se ha demostrado que la amavadina puede servir como un modificador eficaz para la detección eletroanalítica de ergina. Además, la presencia de un material orgánico en el modificador refuerza la capacidad de la ergina para polimerizar, formando un compuesto polimérico. Resultados: Los comportamientos oscilatorios y monótonos son más probables que en el caso más común, dada la formación-deformación de compuestos iónicos durante la detección eletroanalítica.

Objetivo: neste trabalho, a avaliação teórica da detecção eletroanalítica do antissifilíticosalvarsan é feita pela primeira vez. O oxihidróxido de cobalto em um compostocom o corante esquaraína é usado como modificador de eletrodo. Metodologia:por meio da análise de estabilidade é confirmada a eficiência da determinação desalvarsan. A linearidade da dependência entre o parâmetro eletroquímico e a concentraçãodo fármaco é facilmente obtida e mantida. Conclusão: as instabilidades oscilatóriase monotônicas são percebidas neste sistema, sendo causadas pelas influênciasdos estágios eletroquímicos sobre a dupla camada elétrica (DEL).

In this study, we investigated the effectiveness of photocatalysis using TiO2 as catalyst on the removal of ametryn. The evaluation of photocatalytic activity under simulated sunlight was discussed as evidence by numerous controlled trials and several operational parameters such as ametryn concentration, total organic carbon, chemical oxygen demand, specific UV absorbance, biochemical oxygen demand, toxicity and formed intermediates. Moreover, the roles of reactive species involved in the degradation of ametryn were examined by using different specific scavengers. Ametryn removed by photocatalysis using 0.4 g L−1 of TiO2 was 100% within 60 min, while only 30% was achieved by photolysis at the same time. Biodegradability index improved from 0.3 (raw solution) up to 0.8 while the acute toxicity measured by the inhibition percentage of bioluminescence from Vibro fischeri indicates that the photocatalytic treatment promotes 97% of toxicity reduction. The scavenger study shows different percentages of inhibition in ametryn degradation, which allowed to conclude that HO•, valence-band holes and O2•− could intervene in the degradation of ametryn, with predominance of HO•. Thirty-eight intermediates were identified from the photocatalytic degradation of ametryn. The comparison of the generation of those intermediates with and without the addition of scavengers showed that different by-products are generated depending on the predominance of the active species. For example, the presence of azide resulted in intermediates formed by condensation reactions. Based on the identified intermediates, reaction pathways and a degradation mechanism were proposed, including HO• radicals, O2•−, holes, and 1O2.

Um processo eletroanalítico da detecção quantitativa dos íons de zinco bivalente sobre as novas bases de Schiff no modo galvanostático tem sido simulado teoricamente. O respectivo modelo matemático tem sido desenvolvido e analisado mediante a teoria de estabilidade linear e da análise de bifurcações. Foi estabelecido que o sistema é eficiente tanto do ponto de vista eletroanalítico, como do ponto de vista eletrossintético, por ser facilmente estabilizado o estado estacionário. Todavia, o comportamento oscilatório, neste sistema é mais provável que no caso clássico do desempenho de sensores, baseados em polímeros condutores e outros materiais orgânicos, por haver influências na dupla camada elétrica, causadas pela reação química da formação de complexo.

RESUMO O desempenho dos polímeros condutores dos corantes azoicos durante a detecção eletroquímica de indigo-carmim foi investigado do ponto de vista teórico, sendo o modelo, correspondente ao caso, descrito e analisado mediante a teoria de estabilidade lineal e da análise de bifiircações. Foi mostrado que o sistema eletroanalítico depende fortemente do pH, pois as concentrações excessivas dos prótons levam à ineficiência eletroanalítica, haja vista o bloqueio dos centros ativos da reação. No entretanto, malgrado o supracitado, os polímeros dos corantes azoicos são modificadores eficientes para determinação do indigo-carmim. A possibilidade das instabilidades oscilatória e monotônica também foi verificada. SUMMARY The function of the conducting polymers of azo-dyes during the indigo-carmine electrochemical detection has been investigated from the theoretical point of view. The correspondent model has been described and analyzed by means of linear stability theory and bifurcation analysis. It has been shown that the electroanalytical system depends strongly on pH, as the excessive protons concentrations drive the system to the electroanalytical inefficiency, as they block the reaction active sites. Nevertheless, despite of the mentioned, the azo-dyes conducting polymers are efficient modifiers for indigo-carmine electrochemical determination. The possibility of oscillatory and monotonic instabilities has also been verified.

For the first time, the perillaldehyde aldoxime electrochemical determination has been evaluated from the theoretical point of view. The correspondent mathematical model, including different scenarios of the electroanalytical process, has been developed and analyzed by means of linear stability theory and bifurcation analysis. The model analysis clearly shows that the composite of a squaraine dye in organic phase and vanadium oxyhydroxide in the inorganic phase may be an efficient electrode modifier for perillaldehyde aldoxime electrochemical determination. On the other hand, both oscillatory and monotonic instabilities may be realized in the electroanalytical process, and their probability will strongly depend on the direction of the electroanalytical scenario in the concrete conditions. DOI: http://dx.doi.org/10.17807/orbital.v12i3.1498

RESUMO Pela primeira vez, foi feita uma abordagem teórica do desempenho dos novos derivados triazólicos durante a determinação química dos alcaloides acridínicos do grupo insubosina, na presença de uma concentração pequena de um composto de ligação. A detecção eletroanalítica é realizada mediante um mecanismo híbrido, envolvendo ou não a formação de novos compostos iónicos. É possível mostrar que o estado estacionário é estabilzado, apesar de a região topológica, que lhe é correspondente, ser mais estreita que no caso da detecção mais comum. O comportamento oscilatório, neste caso, é mais provável que nos casos mais comuns, mas o fator adicional é relacionado apenas com a introdução de um composto de ligação. SUMMARY For the first time, a theoretical investigation of novel triazolic derivatives during the chemical determination of acridinic alkaloids of insubosin group in the presence of the presence of the small quantity of the link compound has been realized. The electrochemical determination is realized by a hybrid mechanism, involving or not the formation of novel ionic compounds. It is possible to show that the steady-state is stabilized, despite ofthe narrower correspondent topological region, while compared to the more common detection case. The oscillatory behavior is more probable than in more common cases, due to the introduction of the link compound.

EnglishThe function of the conducting polymer, doped by triiodide ion in the electrochemical determination of the ascorbic acid has been mathematically evaluated. The mathematical model, correspondent to the system, was developed and analyzed by linear stability theory and bifurcation analysis. It was confirmed that the conducting polymer might be an excellent electrode modifier for ascorbic acid determination. The triiodide ion acts as the active substance, and the conducting polymer, as a mediator. The stable steady-state is easy maintain, which is correspondent to the vast zone of the linear dependence between the drug concentration and electrochemical parameter The possibility of oscillatory and monotonic instabilities has also been verified. portuguesO desempenho do polimero condutor, dopado pelo ion triiodeto, na deteccao eletroquimica do acido ascorbico foi avaliado matematicamente. O modelo matematico, correspondente ao sistema, foi desenvolvido e analisado mediante a teoria de estabilidade linear e de bifurcacoes. Verificou-se que o polimero condutor pode servir de excelente modificador de eletrodo para a deteccao do acido ascorbico, sendo o triiodeto a substância ativa, e o polimero condutor o mediador. O estado estacionario mantem-se estavel facilmente, o que corresponde a vasta zona da linearidade da dependencia entre a concentracao do farmaco e o parâmetro eletroquimico. A possibilidade das instabilidades oscilatoria e monotonica tambem foi verificada.

RESUMEN Mediante el análisis mecanístico teórico, ha sido evaluada la posibilidad del empleo del oxihidróxido de vanadio como modificador de electrodo para la detección electroquímica de sacarina. El proceso electroanalítico se realiza a través de un proceso catódico. El modelo matemático correspondiente ha sido analizado mediante la teoría de estabilidad lineal y análisis de bifurcaciones. El análisis del modelo ha mostrado que el oxihidróxido de vanadio puede ser un modificador eficiente para la detección electroquímica de la sacarina en las condiciones del pH suficientemente ácido para mover el proceso, pero insuficiente para disolver el oxihidróxido. Las causas de los comportamientos oscilatorio y monotónico también fueron estipuladas. SUMMARY By means of the theoretical mechanistic analysis, the possibility of the use of vanadium oxyhydroxide as electrode modifier for saccharin electrochemical determination has been evaluated. The electroanalytical process is realizing by a cathodic route. The correspondent mathematical model has been analyzed by means of the linear stability theory and bifurcation analysis. The analysis of the model has shown that the vanadium oxyhydroxide is an efficient electrode modifier for saccharin electrochemical detection in pH sufficiently low to maintain the process, but insufficiently acidic to dissolve the oxyhydroxide. The causes for the oscillatory and monotonic instabilities have also been derived.

RESUMEN La posibilidad de usar el oxihidróxido del cobalto en la detección electroquímica de la gabapentina ha sido evaluada, y se sugirió un mecanismo del desempeño del analito y del modificador. Este fue desarrollado y analizado (mediante la teoría de estabilidad lineal y análisis de bifurcaciones) un modelo matemático basado en este mecanismo. La evaluación teórica confirma que el oxihidróxido de cobalto puede ser un modificador eficiente para la detección de la gabapentina, a pesar de la hibridez de su mecanismo de oxidación. La posibilidad y las causas de los comportamientos oscilatorio y monotónico también han sido investigadas. SUMMARY The possibility for the use of cobalt (III) oxyhydroxide in gabapentine electrochemical determination has been evaluated. A mechanism for analyte and modifier function has been suggested. A mathematical model based in this mechanism has been developed and analyzed (by means of linear stability theory and bifurcation analysis). The theoretical evaluation confirms that the cobalt (III) oxyhydroxide may be an efficient modifier for gabapentine electrochemical determination, despite of the hybridity of its oxidation mechanism. The possibility and the causes for oscillatory and monotonic instabilities have also been investigated.

Nimesulide (Nim) degradation in ultrapure water (UW) and municipal sewage (MS) via UV-ABC/H2O2 was investigated. The variables included in the experimental design were time, initial Nim, and initial H2O2 concentrations. Resulting decreases in Nim concentration (monitored by high performance liquid chromatography (HPLC) using a photodiode array detector operating at a maximum UV absorbance of 300 nm), mineralization (from total organic carbon (TOC) measurements), and ecotoxicity (assays employing the bioindicators Daphnia similis, Artemia salina, and Allium cepa) were also studied. Degradation rates of 90% or higher were found for 15–20 min reaction times, employing combinations of [H2O2] = 50–150 mg L−1 and [Nim] = 8.5–15 mg L−1 prepared with MS. Mineralization rates of 70% and higher were attained within 60 min of reaction for [Nim] = 15 mg L−1 prepared in MS with [H2O2] = 100 mg L−1. Nim by-products were detected and possible degradation pathways proposed. Ecotoxicity evaluation using A. salina, D. similis, and A. cepa revealed that the treated samples had significantly lower toxicity. Exposure to treated samples resulted in survival rates of 79% for A. salina and over 90% for D. similis. No root growth inhibition was observed in A. cepa exposed to treated samples, whereas exposure to untreated samples inhibited root growth by 60%. Statistical analysis revealed elimination of cytotoxicity and reduction of genotoxicity against A. cepa. The results showed that the UV-ABC/H2O2 process can be employed as a pre- or post-treatment method to remove Nim from contaminated wastewater.

RESUMO Pela primeira vez foi descrito um caso interessante de uso do oxihidróxido de vanádio trivalente (VO(OH)) como modificador de elétrodo na detecção eletroquímica de nandrolona. Foi mostrado que o oxihidróxido de vanádio pode ser um modificador eficiente para a detecção de nandrolona, mas, ao contrário da maioria dos casos de uso de oxihidróxido de cobalto, composto parecido, o processo é catódico e dá-se em meio moderadamente ácido a neutro. O comportamento oscilatório, no sistema, é possível apenas por causa das influências do processo da eletrorredução de vanádio tetravalente em trivalente na dupla camada elétrica. SUMMARY An interesting case of the use of trivalent vanadium oxyhydroxide (VO(OH)) as an electrode modifier for nandrolone electrochemical determination has been described for the first time. It was shown that vanadium (III) oxyhydroxide may be an efficient electrode modifier for nandrolone determination, but, contrarily to the majority of the cases of the use of cobalt (III) oxyhydroxide, which is a relative compound, the process is cathodic and it is realized in moderately acid solutions, tending to neutral. The oscillatory behavior in the system is possible, due to the influence of the electrochemical reduction of tetravalent vanadium to trivalent in double electric layer.

The degradation and mineralization ability of electrochemical processes like electro-oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA-assisted photoelectro-Fenton (PEF) has been comparatively studied for solutions of the herbicide S-metolachlor. Solutions of 100 mL have been treated using an undivided cell equipped with an air-diffusion cathode and a boron-doped diamond (BDD) anode. The effect of pH, current density, and Fe2+ and S-metolachlor concentrations has been thoroughly studied. The total organic carbon removal profiles have demonstrated the feasibility of almost overall mineralization by EF and PEF after 9 h at 300 mA. The herbicide decays in both treatments informed about the complexation of Fe(III) ions formed from Fenton’s reaction, which decelerated S-metolachlor removal. However, the high oxidation power of BDD anode allowed the gradual mineralization of such complexes. The identification of chlorinated and non-chlorinated degradation byproducts by GC–MS has allowed the proposal of main degradation routes.

EnglishAn interesting case of the application of the functionalized conducting polymer in the analysis of hydroxyzine drug in acid solutions is described from the theoreticalpoint of view. A mathematical model, correspondent to the case, is developed and analyzed by means of linear stability theory and bifurcation analysis. It was detected that the use of an acid conducting polymer may permit the use of less acid solutionwithout mischief of the electroanalytical efficiency. Moreover, the influence of the aminogroups´ behavior to the process was also evaluated. The possibility of the oscillatory and monotonic instabilities has also been verified. portuguesUm caso interessante da aplicacao dos polimeros condutores funcionalizados na analise do farmaco hidroxizina em solucoes acidas vem sendo descrito do ponto de vista teorico. Um modelo matematico, correspondente ao caso, e desenvolvidoe analisado mediante a teoria de estabilidade linear e da analise de bifurcacoes. Foi detectado que o uso de um polimero condutor de natureza acida no processo podedeixar o uso das solucoes menos acidas do farmaco sem prejuizo para a eficiencia eletroanalitica. Outrossim, foi avaliada a influencia para o processo do comportamentodos grupos amina. A possibilidade das instabilidades oscilatoria e monotonica tambem foi verificada.

The possibility of use of cobalt oxyhydroxide as an electrode modifier in the uric acid determination has been investigated from the theoretical point of view. The mechanism of the use of the inorganic compound in the process has been suggested, and the model, correspondent to the process, has been analyzed by means of linear stability theory and bifurcation analysis. It has been concluded that the cobalt oxyhydroxide may serve as an efficient modifier, making easier the analyte oxidation in neutral media in galvanostatic mode. The monotonic instability for this case isn’t capable to realize, and the oscillatory behavior is caused by the unique factor.

This study describes the performance of electro-Fenton (EF) and photoelectro-Fenton (PEF) processes to degrade the herbicide tebuthiuron (TBH) in 0.050 M Na2SO4 at pH = 3.0. Experiments were performed in an undivided cell equipped with a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode that produces H2O2. Physisorbed hydroxyl radicals (M( OH)) generated from water oxidation at the anode and/or free OH formed from Fenton’s reaction acted as main oxidants. All processes became much more effective using a BDD anode because of the higher oxidation power of BDD( OH). Sulfate and nitrate were the predominant ions released during TBH destruction. In both, EF and PEF treatments, two distinct kinetic regimes were observed, the first one corresponding to the oxidation of free TBH by OH and the second one to that of the Fe(III)-TBH complex by M( OH). The effect of Fe2+ and TBH concentrations on the kinetics of both regions has been examined. Moreover, a poor mineralization was reached with Pt anode, whereas almost total mineralization was attained by EF and PEF with BDD. Both processes showed analogous mineralization rates because the intermediates produced could not be photodegraded by UVA light. Gas chromatography-mass spectrometry analysis of electrolyzed solutions revealed the generation of eight heteroaromatics along with 1,3-dimethylurea, which have been included in a reaction pathway proposed for the initial degradation of TBH.

Solutions with 0.65 mM of the antituberculosis drug isoniazid (INH) in 0.050 M Na2SO4 at pH 3.0 were treated by electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) processes using a cell with a BDD anode and a carbon-PTFE air-diffusion cathode. The influence of current density on degradation, mineralization rate, and current efficiency has been thoroughly evaluated in EF. The effect of the metallic catalyst (Fe2+ or Fe3+) and the formation of products like short-chain linear aliphatic carboxylic acids were assessed in PEF. Two consecutive pseudo-first-order kinetic regions were found using Fe2+ as catalyst. In the first region, at short time, the drug was rapidly oxidized by ●OH, whereas in the second region, at longer time, a resulting Fe(III)-INH complex was much more slowly removed by oxidants. INH disappeared completely at 300 min by EF, attaining 88 and 94% mineralization at 66.6 and 100 mA cm-2, respectively. Isonicotinamide and its hydroxylated derivative were identified as aromatic products of INH by GC-MS and oxalic, oxamic, and formic acids were quantified by ion-exclusion HPLC. The PEF treatment of a real wastewater polluted with the drug led to slower INH and TOC abatements because of the parallel destruction of its natural organic matter content.

This paper reports the degradation of 10 mg L−1 Ametryn solution with different advanced oxidation processes and by ultraviolet (UV254) irradiation alone with the main objective of reducing acute toxicity and increase biodegradability. The investigated factors included Fe2+ and H2O2 concentrations. The effectiveness of the UV254 and UV254/H2O2 processes were investigated using a low-pressure mercury UV lamp (254 nm). Photo-Fenton process was explored using a blacklight blue lamp (BLB, λ = 365 nm). The UV254 irradiation process achieved complete degradation of Ametryn solution after 60 min. The degradation time of Ametryn was greatly improved by the addition of H2O2. It is worth pointing out that a high rate of Ametryn removal was attained even at low concentrations of H2O2. The kinetic constant of the reaction between Ametryn and HO● for UV254/H2O2 was 3.53 × 108 L mol−1 s−1. The complete Ametryn degradation by the Fenton and photo-Fenton processes was observed following 10 min of reaction for various combinations of Fe2+ and H2O2 under investigation. Working with the highest concentration (150 mg L−1 H2O2 and 10 mg L−1 Fe2+), around 30 and 70% of TOC removal were reached within 120 min of treatment by Fenton and photo-Fenton processes, respectively. Although it did not obtain complete mineralization, the intermediates formed in the degradation processes were hydroxylated and did not promote acute toxicity of Vibrio fischeri. Furthermore, a substantial improvement of biodegradability was obtained for all studied processes.

O comportamento eletroquímico da lidocaína durante a sua eletrooxidação sobre o oxihidróxido de cobalto trivalente em meio levemente básico, realizada para fins eletroanalíticos, foi avaliado do ponto de vista mecanístico matemático. Da análise foi feita uma conclusão acerca do desempenho do CoO(OH) como modificador de elétrodo na eletrooxidação da lidocaína in vivo e in vitro. Foi, outrossim, verificadaa possibilidade da realização das instabilidades oscilatória e monotônica no sistema. The electrochemical behavior of lidocaine during its electrooxidation over trivalent cobalt oxyhydroxide in lightly alkaline medium, realized for electroanalytical purposes, was evaluated from the mechanistic mathematical point of view. From analysis a conclusion has been made of the electroanalytical function of CoO(OH)as an electrode modifier for lidocaine electrooxidation in vivo and in vitro. Also, the possibility of oscillatory and monotonic instabilities has been verified in the system.

Bu calismada, kobalt (III) oksihidroksit kullanilarak fipronil pestisidinin elektrokimyasal tespit olasiligi belirlenmistir. Bu islemde redoks cifti CoO(OH)/CoO 2 kullanilmistir. Karsilik gelen matematiksel model, dogrusal kararlilik teorisi ve bifurkasyon analizi vasitasiyla gelistirilmis ve analiz edilmistir. Oksihidroksidin, notr ve hafif alkali ortamda fipronilin saptanmasinda etkili bir elektrot degistirici olarak uygulanabilecegi gosterilmistir. Elektrokimyasal cevabin acik ve kolay anlasilir oldugu belirlenmistir. Titresimli ve monotonik istikrarsizlik olasiligi da calismada dogrulanmistir.

Al proceso de la electrooxidación de procarbacina fue atribuido el mecanismo, incluyendo dos etapas electroquímicas y las dos químicas. También, ha sido desarrollado y analizado un modelo matemático, capaz de describir el comportamiento del sistema.Por su intermedio, se dio la posibilidad de comparar el comportamiento de este sistema con el de los semejantes y análogos, como con el sistema de la electrosíntesis de monómeros. A mechanism, including two electrochemical and two chemical stages, has been attributed to the procarbazine electrooxidation. Also, a mathematical model, capable to describe the system’s behavior, has been developed. My its means, it was possible to compare the behavior of this system with that of the monomers’ electrosynthesis.

This work describes the synthesis, structural characterization and emissive behavior of a new copper (I) complex based on 1-thiocarbamoyl-5-(4-methoxiphenyl)-3-phenyl-4,5-dihydro-1H-pyrazole ligand. A dimeric self-assembling via hydrogen bonding was determined by analyzing the short contacts present in the solid-state structure by means of X-ray crystallography. The spectroscopic properties were determined using UV-Vis and fluorescence experiments and an interesting behavior as bluish luminescence was assigned mainly to the mixed (MLCT + IL) electronic transitions of the Cu(I)d10 ® (S=C–Nligand) type. The complete characterization of the new copper (I) complex also included elemental analyses and IR spectroscopy. DOI: http://dx.doi.org/10.17807/orbital.v9i1.952

RESUMO O processo da determinação eletroanalítica do fármaco letrozol, assistida pelo compósito VO(OH)-polipirrol, obtido mediante um processo catódico, foi descrito teoricamente. Tanto para a síntese do compósito, como para o processo eletroana-lítico foi sugerido e analisado, mediante a teoria de estabilidade linear e análise de bifurcações, um modelo matemático. Foi mostrado que, ao contrário da eletrossín-tese de polipirrol catódica, iniciada por um composto na solução, o polipirrol resultante tem uma morfologia mais "centrada" aos centros ativos da matriz, dopados pelos cátions VO2+. No entretanto, tanto a síntese do compósito, como o seu desempenho eletroanalítico com o letrozol podem ser considerados eficientes. SUMMARY The process of the electroanalytical determination of letrozol drug, assisted by the cathodically obtained VO(OH)-Polypyrrole, has been theoretically described. For both the composite synthesis and electroanalytical function a mathematical model has been suggested and analyzed by means of linear stability theory and bifurcation analysis. It was shown that, contrarily to the cathodic polypyrrole electrosynthesis, initiated by a compound in a solution, the resulting cathodic polypyrrole has more "centred" morphology, in the relation to the matrix active centers, doped by VO2+ cations. Nevertheless, either the synthesis of the composite, or its electroanalytical function with letrozole may be considered efficient.

ZnO nanorods were grown on silicon (Si) substrates by two techniques: (i) Chemical Bath Deposition (CBD) and (ii) a CBD seed layer combined with Carbothermal Reduction Vapor Phase Transport (CTR-VPT). The structured ZnO nanorods were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and contact angle measurments. The photoelectrochemical property of ZnO nanorods were analyzed by linear voltammetry under UV-ABC light excitation. Using the ZnO nanorod samples as photoanodes, the removal of methylene blue (MB) as a representative organic compound was studied by the photoelectrocatalytic (PEC) technique applying a potential (E) of 0.6 V. For comparison purposes, experiments were performed under the same conditions using photocatalysis (PC), direct photolysis and using samples of pure Si (support material) as working electrodes in PEC. XRD analyses of ZnO prepared by both methods showed the expected ZnO wurtzite phase and a preferred c-axial orientation in the growth of the nanorods. The presence of ZnO was further confirmed by XPS and contact angle measurements showed that ZnO grown by CBD (ZnO/CBD) had a slightly hydrophobic behavior while ZnO grown by CTR-VPT (ZnO/CTR-VPT) is hydrophilic. Both ZnO sample types were shown to be photoactive, with ZnO/CBD showing higher resultant photocurrent compared to ZnO/CTR-VPT. For the degradation of MB 53% of the compound was removed using ZnO/CBD as a working electrode, while using the ZnO/CTR-VPT electrode led to a removal of 43% of MB. However, direct photolysis alone removed 39% of the MB. The lower removal of MB using ZnO/CTR-VPT samples was related to surface dissociation during the degradation process. The results show that ZnO nanorods prepared by the CBD techique are a promising photoelectrode for PEC applications. Our data also indicate that CTR-VPT-grown nanorods produce uniform nanorod arrays, but this uniform nanostructure deposit does not lead to any increase in PEC activity.

This study reports the use of advanced oxidation processes (AOPs), specifically O3, O3/H2O2 and UV/H2O2, in combination with granular activated carbon (GAC) to polish secondary effluents. For this purpose, three configurations were tested: O3-GAC-O3, O3/H2O2-GAC-O3/H2O2 and UV/H2O2-GAC-UV/H2O2. The efficiency evaluation was based on the ability of the systems to remove aromaticity (UV254), organic matter (chemical oxygen demand - COD), Escherichia coli and total coliforms content as well as toxicity (Artemia salina and Allium cepa). The methods were optimized using central composite design to investigate the influence of O3 and H2O2 concentration in the efficiency of the system and the optimal conditions were subsequently applied to treat urban secondary effluents. High organic matter removal rates were obtained by all the tested configurations, of which O3-GAC-O3 proved to be the most efficient. The systems were also efficient to disinfect the samples, promoting nearby 5-log reduction of E. coli and total coliforms. Acute toxicity, cytotoxicity, and genotoxicity were observed in samples subjected to the UV/H2O2-GAC-UV/H2O2 method. When used alone, GAC removed around 80% of organic matter, nevertheless failed to disinfect the samples, which furthermore exhibited acute toxicity and genotoxicity toward A. cepa. Samples subjected to direct photolysis proved more toxic than untreated samples while uncombined H2O2, O3, GAC, and UV, as well as O3/H2O2 and UV/H2O2 failed to degrade organic matter or to mitigate the toxicity of the samples.

Solutions of single real formulations of herbicides tebuthiuron and ametryn have been degraded by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and solar photoelectro-Fenton (SPEF). The assays were made in a flow plant of 2.5 L equipped with a boron-doped diamond (BDD)/air-diffusion cell and a solar planar photoreactor. Main oxidants were hydroxyl radicals formed from water discharge at the BDD anode and in the bulk from Fenton's reaction between added Fe2+ and cathodically generated H2O2. Partial mineralization was achieved for all the treatments, with the relative oxidation ability growing in the sequence: AO-H2O2 < EF < SPEF. The superiority of SPEF over EF was related to the contribution of photo-oxidation of intermediates and/or their Fe(III) complexes upon sunlight irradiation. No short-linear carboxylic acids were identified, whereas heteroatoms were mainly released as NO3- and SO42- ions. For herbicide contents < 0.18 mM in EF and SPEF, a very rapid pseudo-first-order decay kinetics was related to the oxidation of the Fe(II) complexes of each herbicide at short time, whereupon a much slower pseudo-first-order kinetics associated with the decay of their Fe(III) complexes was observed. Ametryn disappeared more quickly than tebuthiuron, but its solutions were more poorly mineralized. The effect of j and substrate concentration on the performance of SPEF was examined. Mixtures of both formulations were efficiently treated by SPEF, showing similar but slower decays than single solutions. Four primary heteroaromatic products were detected by GC-MS upon prolonged electrolysis of an equimolar mixture. Our results indicate that SPEF is viable for the treatment of water contaminated with tebuthiuron and ametryn herbicides, either single or mixed.

This study employed direct UV-ABC photolysis and the UV-ABC/H2O2 process to investigate the degradation of tolfenamic acid (TA), a common anti-inflammatory drug used in both human and veterinary medicine. A 23 factorial design with added center point was used to evaluate the effect of three independent variables-namely, H2O2 concentration ([H2O2]), TA concentration ([TA]), and experiment time (time)-on TA degradation and H2O2 photolysis during UV-ABC/H2O2 treatment using a high-pressure mercury vapor lamp (photon flux of 2.6307 × 104 J s-1) as the UV irradiation source. The responses yielded similar values, revealing a linear behavior, with correlation coefficients R = 0.9968 and Radj = 0.9921 for TA degradation and R = 0.9828 and Radj = 0.9570 for H2O2 photolysis. The most efficient combination of variables was [H2O2] = 255 mg L-1 and [TA] = 25 mg L-1, resulting in 100% TA degradation and 98.87% H2O2 photolysis by 90 min of treatment. Additionally, the second-order kinetic constant of the reaction between TA and HO● was determined using a competitive kinetic model, employing 2,4-dichlorophenoxyacetic acid (2,4D) as the reference compound. The kinetic constant was 1.9 × 1010 M-1 s-1 in alkaline medium. TA degradation by direct photolysis generated quinone imines as by-products, responsible for the formation of a dark red "internal filter" that increased the value of acute toxicity to Artemia salina. The UV-ABC/H2O2 process did not promote formation of quinone imines by 90 min of treatment and therefore did not increase acute toxicity values. Several by-products generated during TA degradation were identified and possible degradation pathways for the UV-ABC and UV-ABC/H2O2 processes were proposed.

O processo da eletrorredução de benzodiazepinas, uma ferramenta, capaz de usar-se em pesquisa eletroanalítica, foi analisado dos pontos de vista mecanístico e matemático.O modelo correspondente veio sendo investigado por meio de teoria de estabilidade linear e análise de bifurcações e, por meio da sua análise, pôde-se obter o requisito da melhor eficiência do processo, investigar a pH-dependência do seu desempenho, bem como as condições das instabilidades oscilatória e monotónica.Faz-se uma tentativa de uma análise mecanística sistemática do desempenho de sensores eletroquímicos de benzodiazepinas. The benzodiazepines' electrochemical reduction process, a tool, capable to be used in electroanalytic investigation, was anaylzed by mechanistic and mathematical means. The correspondent model was analyzed by means of linear stability theory and bifurcation analysis, and by its mean it was possible to get the requisite for the best process efficiency, the pH-dependence of its function, like also of oscillatory and monotonic instability. An effort is made fot the systematic mechanistic analysis of the work of benzodiazepine electrochemical sensors.

The theoretical description for 4-4´-dihydroxyazobenzene CoO(OH) – assisted electrochemical determination in the mushroom pulp, food, and biological liquids has been described. In this system, a squaraine dye is used as a Cobalt(III)oxyhydroxide stabilizer and electron transfer mediator. It is shown that, contrary to the large part of the systems with cobalt (III) oxyhydroxide, this system will behave more stably, providing an efficient diffusion-controlled process. On the other hand, the oscillatory and monotonic instabilities, although possible, are caused by the double electric layer influences of either chemical or electrochemical stage.

Por primera vez, ha sido dada una evaluación teórica de la posibilidad de la detección de los compuestos hidroquinónicos sobre el electrodo, modificado por la melanina. La melanina, formada durante el proceso electroanalítico suele oxidarse regenerándose o formando su polímero, también sensible a la presencia de las hidroquinonas. El modelo matemático, correspondiente al proceso, ha sido desarrollado y analizado mediante la teoría de estabilidad lineal y análisis de bifurcaciones. El análisis del modelo ha confirmado la eficiencia del proceso para fines electroanalíticos. Y a el comportamiento oscilatorio se observa con más probabilidad que en los sistemas semejantes, por la presencia de dos etapas electroquímicas, en lugar de solamente una en los sistemas análogos.