Electrochemical behavior of N-nitrosothiazolidine carboxilic acid on gold and mercury electrodes

The electrochemical behavior of N-nitrosothiazolidine carboxylic acid (NTAC) on gold and hanging mercury electrodes, using the cyclic and square wave voltammetries, was studied. Whereas NTAC suffer reduction in a single step on the mercury electrode, two peaks appears on the cyclic voltammograms on the gold electrode, one anodic peak overlaying the gold oxide process at 1.2 V and one cathodic peak at -0.41 V vs Ag/AgCl, KCl 3.0 mol L-1. The cathodic peak depends on the previous oxidation of NTAC at the electrode surface, presents irreversible and adsorption controlled characteristics and it is suitable for quantitative purposes.10671072Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Electrochemical study of simple coumarin and its determination in aqueous infusion of Mikania glomerata

The present study aims the development and application of an electrochemical method for simple coumarin determination in aqueous media by using a boron-doped diamond electrode (BDDE). The studies were carried out at pH 8.0 by cyclic voltammetry (CV) and registered an irreversible reduction process controlled by diffusion with the peak potential recorded around -1.6 V. The square wave voltammetry analysis (SWV) showed the reversible behavior of the electrochemical reduction of coumarin at the same pH. Additionally, the reversibility of the process was improved by increasing the solution pH. The chronoamperometry study showed that the coumarin reduction process involves two electrons. From the optimized SWV parameters, the analytical curve was constructed in a linear range between 0.5 × 10-5 and 10.0 × 10-5 mol L-1. The limits of detection and quantification were 1.5 × 10-6 mol L-1 and 4.5 × 10-6 mol L-1, respectively. The coumarin was determined in an aqueous infusion of Mikania glomerata, showing recovery values between 92 and 104%.O presente estudo teve por objetivos o desenvolvimento e a aplicação de um método eletroquímico para a determinação da cumarina simples em meio aquoso utilizando o eletrodo de diamante dopado com boro (BDDE). Os estudos foram realizados em pH 8,0 utilizando a voltametria cíclica (CV) e observou-se um processo de redução irreversível controlado por difusão com um pico de redução em torno de -1,6 V. Entretanto, foi possível observar por voltametria de onda quadrada (SWV) que no mesmo pH a redução da cumarina possui um caráter reversível. Além disso, esta reversibilidade se tornou mais evidente com o aumento do pH da solução. Um estudo cronoamperométrico mostrou que o processo de redução da cumarina envolve dois elétrons. A partir dos parâmetros otimizados da SWV uma curva analítica foi construída no intervalo linear de 0,5 × 10-5 a 10,0 × 10-5 mol L-1. Os limites de detecção e de quantificação foram 1,5 × 10-6 mol L-1 e 4,5 × 10-6 mol L-1, respectivamente. A cumarina foi determinada em amostras de Mikania glomerata (infusão aquosa) com valores de recuperação entre 92 e 104%.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Universidade Federal de São Paulo (UNIFESP) Instituto de Ciências Ambientais, Químicas e Farmacêuticas Departamento de Ciências Exatas e da TerraUniversidade Federal do ABC Centro de Ciências Naturais e HumanasUNIFESP, Instituto de Ciências Ambientais, Químicas e Farmacêuticas Depto. de Ciências Exatas e da Terra2008/50588-6SciEL

The Methylene Blue Self-aggregation in Water/Organic Solvent Mixtures: Relationship Between Solvatochromic Properties and Singlet Oxygen Production

In this work is presented a spectrophotometric investigation focused on the solvatochromic effects upon Methylene Blue (MB). Measurements were carried out in four different water/organic solvent mixtures: low polarity protic solvent (ethanol), polar non-protic solvent (acetonitrile), highly polar protic solvent (glycerol), and non-polar solvent (dioxane). The results showed that the photophysical behavior of MB is highly affected by self-aggregates formation at 80% of water/organic solvent blends. Besides polarity, the protic character and the coordinating properties of the solvent molecules are the key parameters for its photophysical behavior, since the sulfur atom of the cationic structure can act as a coordination center due to its Lewis acid character. In fact, water and acetonitrile coordinating properties have proved to be important to determine MB interactions intensity and its spectroscopic properties as singlet oxygen emission. It was observed that an increase of the amount of the organic solvent resulted in an enhancement of the singlet oxygen emission intensity. The presence of the water increases the dielectric constant of the medium and favors the self-aggregation process. Besides, the water molecules can act as a quencher and it decreases the quantum yield of the fluorescence of MB.FAPESPCNPqFarma Service BioExtract LtdaUniv Fed Sao Joao del Rei, Dept Zootecnia DEZOO, Campus Dom Bosco, BR-36301160 Sao Joao Del Rei, MG, BrazilUniv Vale Paraiba, Ave Shishima Hifumi 2911, BR-12244000 Sao Paulo, BrazilUniv Fed Sao Paulo, Dept Quim, Rua Prof Arthur Riedel 275, BR-09972270 Sao Paulo, BrazilUniv Sao Paulo, Dept Bioquim, Inst Quim, Ave Prof Lineu Prestes 748, BR-05508900 Sao Paulo, SP, BrazilUniv Tecnol Fed Parana, Campus Apucarana,Rua Marcilio Dias 635, BR-86812460 Apucarana, Parana, BrazilUniv Fed Santa Catarina, BR-88040900 Florianopolis, SC, BrazilUniv Estadual Maringa, Dept Quim, Av Colombo 5790,Zona 07, BR-87020900 Maringa, Parana, BrazilUniv Fed Rio de Janeiro, Campus Macae,Rua Aloisio da Silva Gomes 50, BR-27930560 Rio De Janeiro, BrazilUniv Estadual Campinas, Inst Quim, BR-13083970 Sao Paulo, BrazilUniv Fed Rio Grande, Escola Quim & Alimentos, Campus Carreiros Pavilhao Quim, BR-96201900 Rio Grande, RS, BrazilUniv Fed ABC, Ctr Engn Modelagem & Ciencias Sociais Aplicadas, Ave Estados 5001, BR-09210580 Sao Paulo, BrazilUniv Fed ABC, Ctr Ciencias Nat & Humanas, Ave Estados 5001, BR-09210580 Sao Paulo, BrazilUniv Fed Sao Paulo, Dept Quim, Rua Prof Arthur Riedel 275, BR-09972270 Sao Paulo, BrazilFAPESP: JP 04/02193-1FAPESP: 02/00272-6FAPESP: 06/56701-3FAPESP: 2005/51597-8CNPq: 474019/2012-8]CNPqFarma Service BioExtract LtdaWeb of Scienc

Quinquangulin and Rubrofusarin: A Spectroscopy Study

In this work, excitation and emission spectra were evaluated in order to elucidate the properties of quinguangulin and rubrofusarin in water/ethanol mixture. The study demonstrates that the maximum excitation wavelength can be significantly modulated changing the proportion of organic solvent in the water/organic solvent system. Quinquangulin presented the higher wavelength of maximum excitation in an ethanol-water mixture containing 70% of water. Probably, the organization between ethanol and water molecules in this condition favors the formation of strong polar interactions with the pi* orbitals of naphthopyrones. It is interesting to register that the additional methyl group in quinquangulin seems to develop a decisive function related to the ability to formation of hydrogen bonds, altering significantly the mechanism of solute-solvent interaction. This work, which involves both theoretical and experimental analyses, demonstrates the relevance of the studies focused on solvent mixtures as well as emphasizes the potential of quinguangulin and rubrofusarin as photosensitizers.FAPESPFundacao AraucariaFAPEMIGCNPqCAPESUniv Fed Sao Joao Del Rei, Dept Zootecnia DEZOO, Campus Dom Bosco, BR-36301160 Sao Joao Del Rei, MG, BrazilUniv Vale Paraiba, Ave Shishima Hifumi 2911, BR-12244000 Sao Paulo, BrazilUniv Fed Sao Paulo, Dept Quim, Rua Prof Arthur Riedel 275, BR-09972270 Sao Paulo, BrazilUniv Fed Uberlandia, Inst Quim, Lab Fotoquim & Ciencia Mat, Uberlandia, MG, BrazilUniv Fed Goias, Dept Quim, Campus Catalao, Catalao, Go, BrazilUniv Estadual Maringa, Dept Quim, Av Colombo 5790,Zona 07, BR-87020900 Maringa, Parana, BrazilUniv Fed Rio de Janeiro, Campus Macae,Rua Aloisio da Silva Gomes 50, BR-27930560 Rio De Janeiro, BrazilUniv Estadual Campinas, Inst Quim, BR-13083970 Sao Paulo, BrazilUniv Fed Rio Grande, Escola Quim & Alimentos, Campus Carreiros Pavilhao Quim, BR-96201900 Rio Grande, RS, BrazilUniv Fed ABC, Ctr Engn Modelagem & Ciencias Sociais Aplicadas, Ave Estados 500, BR-09210580 Sao Paulo, BrazilUniv Fed ABC, Ctr Ciencias Nat & Humanas, Ave Estados 5001, BR-09210580 Sao Paulo, BrazilUniv Fed Sao Paulo, Dept Quim, Rua Prof Arthur Riedel 275, BR-09972270 Sao Paulo, BrazilFAPESP: 06/56701-3Fundacao AraucariaFAPEMIGCNPq: 474019/2012-8CNPq: 303872/2009-8CAPESWeb of Scienc

Simultaneous voltammetric determination of carbendazim and carbaryl in medicinal plant infusions with a boron-doped diamond electrode

This study is aimed to develop an electroanalytical methodology using a boron-doped diamond electrode to determine simultaneously and selectively carbendazim (CBZ) and carbaryl (CAR). In previous studies using cyclic voltammetry oxidation, peaks were observed at 1.03V (CBZ) and 1.44V (CAR), with characteristics of an irreversible process controlled by diffusion of species, with a supporting electrolyte of BR buffer (0.1mol L-1) and pH adjusted to 6.0. The differences between the potentials for both pesticides, about 400mV, indicate the possibility of selective determination of CBZ and CAR. The square-wave voltammetric parameters were optimised. The best separation conditions were pH 6.0, square-wave frequency of 100s(-1), pulse amplitude of 50mV and scan increment of 2.0mV. These parameters were used to obtain the calibration curves of CBZ and CAR. An analytical curve was constructed in the range concentration of CBZ of 1.3mg L-1 to 15.3mg L-1 and CAR of 1.0mg L-1 to 11.4mg L-1, respectively. The limits of detection (LOD) and limits of quantification (LOQ) for CBZ were 0.40mg L-1 and 1.30mg L-1, respectively. For CAR, the LOD and LOQ were 0.30mg L-1 and 1.00mg L-1, respectively. Sensitivity values were 0.78 and 2.60 mu A/mg L-1 for CBZ and CAR, respectively. The electroanalytical method was applied in Mikania glomerata infusions. The recovery values were 106.2% and 116.5% for CBZ and CAR, respectively. The results show that the developed method is suitable for application in medicinal plant samples.FAPESPCAPESFundacao de Amparo a Pesquisa do Estado de Sao PauloUniv Fed Sao Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Dept Ciencias Exatas & Terra, Diadema, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, BrazilUniv Fed Sao Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Dept Ciencias Exatas & Terra, Diadema, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, BrazilFAPESP: 2014/23858-3FAPESP: 2014/23858-3FAPESP: 2008/50588-6Web of Scienc

Comportamento eletroquímico da N-nitrosotiazolidina ácido carboxílico sobre eletrodos de ouro e mercúrio

The electrochemical behavior of N-nitrosothiazolidine carboxylic acid (NTAC) on gold and hanging mercury electrodes, using the cyclic and square wave voltammetries, was studied. Whereas NTAC suffer reduction in a single step on the mercury electrode, two peaks appears on the cyclic voltammograms on the gold electrode, one anodic peak overlaying the gold oxide process at 1.2 V and one cathodic peak at -0.41 V vs Ag/AgCl, KCl 3.0 mol L-1. The cathodic peak depends on the previous oxidation of NTAC at the electrode surface, presents irreversible and adsorption controlled characteristics and it is suitable for quantitative purposes

Voltammetric determination of 17 alpha-ethinylestradiol hormone in supply dam using BDD electrode

In this work, a simple method for electroanalytical determination of 17 alpha-ethinylestradiol (EE2) hormone in natural waters was developed using a boron-doped diamond electrode (BDD). The analyses were performed using square wave voltammetry and the parameters were optimized. The results showed a well-defined irreversible oxidation peak (BR buffer 0.1 mol L-1, pH 8.0) at +0.65 V (vs. Ag/AgCl). The voltammetric results showed also that the oxidation process is controlled by adsorption of species and indicated that there are two electrons involved. The obtained analytical curves for 17 alpha-ethinylestradiol presented good linearity in the concentration range 9.9 x 10(-7) to 5.2 x 10(-6) mol L-1 in utlrapure water and 7.9 x 10(-7) to 5.2 x 10(-6) mol L-1 in natural water samples (supply dam). Detection limits (DL) obtained were between 2.4 x 10(-7) and 7.5 x 10(-7) mol L-1 and quantification limits (QL) between 7.9 x 10(-7) and 2.5 x 10(-6) mol L-1. The recovery experiments showed values between 86 and 114 % for spiked samples thus indicating the applicability of the electroanalytical methodology to quantify 17 alpha-ethinylestradiol directly in natural water of supply Dam (Billings Dam in Diadema-SP. Brazil), without any preconcentration or derivatization.Univ Fed Sao Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Campus Diadema,Prof Arthur Riedel St 275, BR-09972270 Sao Paulo, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Campus Baixada Santista,Ave Almirante Saldanha da, BR-11040300 Sao Paulo, BrazilUniv Fed Sao Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Campus Diadema,Prof Arthur Riedel St 275, BR-09972270 Sao Paulo, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Campus Baixada Santista,Ave Almirante Saldanha da, BR-11040300 Sao Paulo, BrazilWeb of Scienc

Electroanalytical Determination of Fenthion in Passiflora alata Tincture Samples

In this work a direct, simple, fast and sensitive method to determine Fenthion was developed using a Boron-Doped Diamond Electrode and Square Wave Voltammetry. The method was applied into Passiflora alata herbal medicinal tinctures derivate from passion fruits. None previous treatment such as derivation or pre-concentration of the analyte was done. Cyclic Voltammetry results showed well defined irreversible oxidation peaks at around 1.27 V into the pH range of 2.0 to 8.0. Square Wave Voltammetry was used to analytical determination and the analysis parameters, such as frequency, amplitude and pH from support electrolyte were optimized. A calibration curve was obtained, and it was observed a sensitivity of 0.38 A/mol L-1 and linearity of 0.995. The limits of detection and quantification were 8.0x10-8 mol L-1 (21 mg L-1) and 2.5x10-7 mol L-1 (70 mg L-1), respectively. Recovery studies were applied using Passiflora alata samples fortified with Fenthion in concentrations of 2.5 µmol L-1and 4.0 µmol L-1, followed by the standard addition of the pesticide aliquots. It was observed that the complex matrix does not interferes in the method. The recovery results were about 98.4 and 112.0%, reinforcing that the method is suitable to determine the analyte in target complexes samples, such as Herbal Medicinal Plants. DOI: http://dx.doi.org/10.17807/orbital.v10i2.1077 </p